Seismologists estimate stress drops of small earthquakes based on specific theoretical source models. We explore the accuracy of the stress-drop estimates for several earthquake source models obtained in dynamic simulations on rate-and-state faults. We consider Madariaga-like symmetric circular sources as well as sources with directivity, elongated shapes, partial ruptures, and complex changes in the slip direction. The energy-based average stress drops computed directly on the fault for all simulated source models range from 1.5 to 5 MPa. We consider a range of focal depths and fault dips that results in 980 scenarios overall with respect to a surface network of 16 stations, where we produce synthetic waveforms assuming a known homogeneous velocity structure, and use them to obtain seismologically inferred stress drops. For the second-moment approach and spectral-fitting approach based on S waves and n = 2, the stress drops for most sources are reproduced well on average but with a significant scatter from nearly 0.01 to 100 MPa, representative of scatter for natural earthquakes, despite the actual stress-drop variation of 1.5–5 MPa. The scatter is smaller by a factor of 2 for the second-moment approach. The spectral-fitting approach based on P waves consistently underestimates the stress drops for noncircular sources. All approaches underestimate stress drops for ring-like sources, which leave part of the seismogenic patch unruptured. The spectral estimates are significantly affected by different averages of corner frequencies over the focal sphere for our sources versus typically assumed simple theoretical sources, as was already pointed out for some of the sources by Kaneko and Shearer (2015) and Lin and Lapusta (2018). For both second-moment and spectral methods, the scatter is amplified by partial coverage of the focal sphere by the assumed station geometry, which can also cause systematic depth-dependent artifacts.
", "doi": "10.1785/0120240147", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "2025-06", "series_number": "3", "volume": "115", "issue": "3", "pages": "1072-1104" }, { "id": "authors:s3d3g-sn589", "collection": "authors", "collection_id": "s3d3g-sn589", "cite_using_url": "https://authors.library.caltech.edu/records/s3d3g-sn589", "type": "article", "title": "Community-Driven Code Comparisons for Simulations of Fluid-Induced Aseismic Slip", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re R.", "orcid": "0000-0002-6174-9651" }, { "family_name": "Erickson", "given_name": "Brittany A." }, { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846" }, { "family_name": "Dunham", "given_name": "Eric M.", "orcid": "0000-0003-0804-7746" }, { "family_name": "Kim", "given_name": "Taeho", "orcid": "0000-0002-2560-7728", "clpid": "Kim-Taeho" }, { "family_name": "Ampuero Saenz", "given_name": "Jean Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Ando", "given_name": "Ryosuke", "orcid": "0000-0002-6205-3699" }, { "family_name": "Cappa", "given_name": "Fr\u00e9d\u00e9ric", "orcid": "0000-0003-4859-8024" }, { "family_name": "Dublanchet", "given_name": "Pierre", "orcid": "0000-0003-4903-0246" }, { "family_name": "Elbanna", "given_name": "Ahmed" }, { "family_name": "Fialko", "given_name": "Yuri", "orcid": "0000-0002-6161-8467" }, { "family_name": "Gabriel", "given_name": "Alice\u2010Agnes", "orcid": "0000-0003-0112-8412" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Li", "given_name": "Meng", "orcid": "0000-0001-9459-7167" }, { "family_name": "Marcum", "given_name": "Jasper", "orcid": "0009-0000-2920-3790" }, { "family_name": "May", "given_name": "David", "orcid": "0000-0003-2471-7498" }, { "family_name": "Mia", "given_name": "Md Shumon", "orcid": "0000-0002-7982-8809" }, { "family_name": "Ozawa", "given_name": "So", "orcid": "0000-0002-6507-6925" }, { "family_name": "Pranger", "given_name": "Casper", "orcid": "0000-0002-8943-896X" }, { "family_name": "Romanet", "given_name": "Pierre", "orcid": "0000-0001-6232-4906" }, { "family_name": "Scuderi", "given_name": "Marco M.", "orcid": "0000-0001-5232-0792" }, { "family_name": "van Dinther", "given_name": "Ylona" }, { "family_name": "Yang", "given_name": "Yuyun", "orcid": "0000-0001-5260-8593" }, { "family_name": "Yun", "given_name": "Jeena", "orcid": "0000-0002-2215-4647" } ], "abstract": "Numerical simulations of Sequences of Earthquakes and Aseismic Slip (SEAS) have rapidly progressed to address fundamental problems in fault mechanics and provide self\u2010consistent, physics\u2010based frameworks to interpret and predict geophysical observations across spatial and temporal scales. To advance SEAS simulations with rigor and reproducibility, we pursue community efforts to verify numerical codes in an expanding suite of benchmarks. Here we present code comparison results from a new set of quasi\u2010dynamic benchmark problems BP6\u2010QD\u2010A/S/C that consider an aseismic slip transient induced by changes in pore fluid pressure consistent with fluid injection and diffusion in fault models with different treatments of fault friction. Ten modeling groups participated in problems BP6\u2010QD\u2010A and BP6\u2010QD\u2010S considering rate\u2010and\u2010state fault models using the aging (\u2010A) and slip (\u2010S) law formulations for frictional state evolution, respectively, allowing us to better understand how various computational factors across codes affect the simulated evolution of pore pressure and aseismic slip. Comparisons of problems using the aging versus slip law, and a constant friction coefficient (\u2010C), illustrate how aseismic slip models can differ in the timing and amount of slip achieved with different treatments of fault friction given the same perturbations in pore fluid pressure. We achieve excellent quantitative agreement across participating codes, with further agreement attained by ensuring sufficiently fine time\u2010stepping and consistent treatment of boundary conditions. Our benchmark efforts offer a community\u2010based example to reveal sensitivities of numerical modeling results, which is essential for advancing multi\u2010physics SEAS models to better understand and construct reliable predictive models of fault dynamics.
", "doi": "10.1029/2024jb030601", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2025-04", "series_number": "4", "volume": "130", "issue": "4", "pages": "e2024JB030601" }, { "id": "authors:jhn9c-8er13", "collection": "authors", "collection_id": "jhn9c-8er13", "cite_using_url": "https://authors.library.caltech.edu/records/jhn9c-8er13", "type": "article", "title": "Sliding and healing of frictional interfaces that appear stationary", "author": [ { "family_name": "Sirorattanakul", "given_name": "Krittanon", "orcid": "0000-0003-2310-8447", "clpid": "Sirorattanakul-Krittanon" }, { "family_name": "Larochelle", "given_name": "Stacy", "orcid": "0000-0001-6161-5605", "clpid": "Larochelle-Stacy" }, { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Roaskis-A-J" } ], "abstract": "Frictional interfaces are found in systems ranging from biological joints to earthquake faults. When and how these interfaces slide is a fundamental problem in geosciences and engineering. It is believed that there exists a threshold shear force, called static friction, below which the interface is stationary, despite many studies suggesting that this concept is outdated. By contrast, rate-and-state friction formulations predict that interfaces are always sliding, but this feature is often considered an artefact that calls for modifications. Here we show that nominally stationary interfaces subjected to constant shear and normal loads, with a driving force that is notably below the classically defined static friction for which creep is known to occur, are sliding, but with diminishingly small rates down to 10−12 m s−1. Our precise measurements directly at the interface are enabled by digital image correlation. This behaviour contradicts classical models of friction but confirms the prediction of rate-and-state friction. The diminishing slip rates of nominally stationary interfaces reflect interface healing, which would manifest itself in higher peak friction in subsequent slip events, such as earthquakes and landslides, substantially modifying their nucleation and propagation and hence their hazard.
", "doi": "10.1038/s41586-025-08673-0", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2025-03-27", "series_number": "8056", "volume": "639", "issue": "8056", "pages": "947-953" }, { "id": "authors:xyw3y-m8j25", "collection": "authors", "collection_id": "xyw3y-m8j25", "cite_using_url": "https://authors.library.caltech.edu/records/xyw3y-m8j25", "type": "article", "title": "Dynamic Emergence of Plate Motions and Great Megathrust Earthquakes Across Length and Time Scales", "author": [ { "family_name": "Fang", "given_name": "Jiaqi", "orcid": "0000-0001-6369-4802", "clpid": "Fang-Jiaqi" }, { "family_name": "Gurnis", "given_name": "Michael", "orcid": "0000-0003-1704-597X", "clpid": "Gurnis-M" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "The slow motion of tectonic plates over thousands of kilometers is intermittently interrupted by great earthquakes with sudden slips localized near convergent plate boundaries. We developed a subduction model that self-consistently integrates buoyancy forces, diffusion and dislocation creep, and inter-plate friction. From the nonlinear dynamics emerge long-term plate motions that achieve velocities of ≈5 cm/year, effective viscosities of ≈1\u20620¹\u2079 Pa⋅s below plates, and sudden slips up to ≈10 m repeating every several hundred years. Along-strike resistance arising from long-wavelength variation of coseismic slip is naturally incorporated with a rupture length scale, L. Computations with L∼1\u20620³ km generate events with M_w≈9. When L decreases, there is a commensurate decrease in the effective moment of rupture events. Predicted long-term plate velocities, mantle viscosities, cycles of stress loading and release, and rupture event size and magnitude all show good agreement with observations.
", "doi": "10.1029/2024gl110821", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2024-11-28", "series_number": "22", "volume": "51", "issue": "22", "pages": "e2024GL110821" }, { "id": "authors:sar53-81n52", "collection": "authors", "collection_id": "sar53-81n52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230725-745742000.16", "type": "article", "title": "Absolute stress levels in models of low-heat faults: Links to geophysical observables and differences for crack-like ruptures and self-healing pulses", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Absolute levels of stress on faults have profound implications for earthquake physics and fault mechanics. A number of observations suggest that well-developed, mature faults such as the San Andreas Fault are generally \"weak,\" i.e. operate at much lower levels of shear stress compared to the higher expected shear resistance \u223c100 MPa at seismogenic depths. In particular, low heat flow measurements suggest shear stress levels of \u223c10 MPa or less on highly localized faults. Geodynamic constraints based on topography and similar considerations also support \"weak\" fault operation, and are comparable with heat-based constraints for some mature faults, but potentially higher for regions with substantial topography. Here, we investigate measures of average fault shear stress and their relationship to geophysically inferable quantities using numerical simulations of earthquake sequences on rate-and-state faults with low heat production, due to chronic fluid overpressure and/or enhanced dynamic weakening from the thermal pressurization of pore fluids. We review the earthquake energy balance, focusing on energy-based definitions of average shear stress and how the average fault prestress (a measure of fault strength plausibly relevant to geodynamic constraints) can be expressed as the sum of the dissipation-based average rupture stress (which can, in principle, be inferred from shear-heating constraints), and seismologically inferable source properties, such as the static stress drop and apparent stress. Our modeling demonstrates that rapid dynamic weakening and healing of shear resistance during ruptures, as exhibited in self-healing pulses, allows faults to maintain higher average interseismic stress levels despite low dynamic resistance and realistic static stress drops, providing a physical explanation for potential differences between topography-based and heat-based constraints on fault shear stress. In our models, the difference is related to stress undershoot and apparent stress, which can be as large as 1-3 times the static stress drop based on our simulations. Yet suitably large values of apparent stress (and hence radiated energy) are rarely inferred for natural earthquakes, either because radiated energy is underestimated, or suggesting that most large earthquakes do not propagate as sharp enough self-healing pulses with sufficiently large undershoot. Our results emphasize the distinction between dynamic versus static stress changes when relating earthquake source observations to absolute levels of fault stress and suggest that reviewing estimates of radiated energy and static stress drop from large earthquakes, with input from finite-fault numerical modeling, may improve constraints on absolute fault stress levels.", "doi": "10.1016/j.epsl.2023.118277", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "2023-09-15", "volume": "618", "pages": "Art. No. 118277" }, { "id": "authors:mypge-8d791", "collection": "authors", "collection_id": "mypge-8d791", "cite_using_url": "https://authors.library.caltech.edu/records/mypge-8d791", "type": "article", "title": "The break of earthquake asperities imaged by distributed acoustic sensing", "author": [ { "family_name": "Li", "given_name": "Jiaxuan", "orcid": "0000-0002-3766-0876", "clpid": "Li-Jiaxuan" }, { "family_name": "Kim", "given_name": "Taeho", "clpid": "Kim-Taeho" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Biondi", "given_name": "Ettore", "orcid": "0000-0002-3305-0982", "clpid": "Biondi-Ettore" }, { "family_name": "Zhan", "given_name": "Zhongwen", "orcid": "0000-0002-5586-2607", "clpid": "Zhan-Zhongwen" } ], "abstract": "Rupture imaging of megathrust earthquakes with global seismic arrays revealed frequency-dependent rupture signatures, but the role of high-frequency radiators remains unclear. Similar observations of the more abundant crustal earthquakes could provide critical constraints but are rare without ultradense local arrays. Here we use distributed acoustic sensing technology to image the high-frequency earthquake rupture radiators. By converting a 100-kilometre dark-fibre cable into a 10,000-channel seismic array, we image four high-frequency subevents for the 2021 Antelope Valley, California, moment-magnitude 6.0 earthquake. After comparing our results with long-period moment-release and dynamic rupture simulations, we suggest that the imaged subevents are due to the breaking of fault asperities\u2014stronger spots or pins on the fault\u2014that substantially modulate the overall rupture behaviour. An otherwise fading rupture propagation could be promoted by the breaking of fault asperities in a cascading sequence. This study highlights how we can use the extensive pre-existing fibre networks as high-frequency seismic antennas to systematically investigate the rupture process of regional moderate-sized earthquakes. Coupled with dynamic rupture modelling, it could improve our understanding of earthquake rupture dynamics.
", "doi": "10.1038/s41586-023-06227-w", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2023-08-24", "series_number": "7975", "volume": "620", "issue": "7975", "pages": "800-806" }, { "id": "authors:ytjw1-xqc57", "collection": "authors", "collection_id": "ytjw1-xqc57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230512-807765000.5", "type": "article", "title": "Incorporating Full Elastodynamic Effects and Dipping Fault Geometries in Community Code Verification Exercises for Simulations of Earthquake Sequences and Aseismic Slip (SEAS)", "author": [ { "family_name": "Erickson", "given_name": "Brittany A.", "orcid": "0000-0001-9457-8572", "clpid": "Erickson-Brittany-A" }, { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846" }, { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651" }, { "family_name": "Barbot", "given_name": "Sylvain D.", "orcid": "0000-0003-4257-7409" }, { "family_name": "Abdelmeguid", "given_name": "Mohamed", "orcid": "0000-0002-3985-1721" }, { "family_name": "Almquist", "given_name": "Martin", "orcid": "0000-0002-8012-5860" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987" }, { "family_name": "Ando", "given_name": "Ryosuke", "orcid": "0000-0002-6205-3699" }, { "family_name": "Cattania", "given_name": "Camilla", "orcid": "0000-0003-0031-1696" }, { "family_name": "Chen", "given_name": "Alexandre" }, { "family_name": "Dal Zilio", "given_name": "Luca", "orcid": "0000-0002-5642-0894" }, { "family_name": "Deng", "given_name": "Shuai" }, { "family_name": "Dunham", "given_name": "Eric M.", "orcid": "0000-0003-0804-7746" }, { "family_name": "Elbanna", "given_name": "Ahmed E." }, { "family_name": "Gabriel", "given_name": "Alice-Agnes", "orcid": "0000-0003-0112-8412" }, { "family_name": "Harvey", "given_name": "Tobias W." }, { "family_name": "Huang", "given_name": "Yihe", "orcid": "0000-0001-5270-9378" }, { "family_name": "Kaneko", "given_name": "Yoshihiro", "orcid": "0000-0003-2342-0131" }, { "family_name": "Kozdon", "given_name": "Jeremy E.", "orcid": "0000-0002-2493-4292" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Li", "given_name": "Duo", "orcid": "0000-0002-8641-337X" }, { "family_name": "Li", "given_name": "Meng", "orcid": "0000-0001-9459-7167" }, { "family_name": "Liang", "given_name": "Chao", "orcid": "0000-0001-5237-9655" }, { "family_name": "Liu", "given_name": "Yajing", "orcid": "0000-0002-5323-8077" }, { "family_name": "Ozawa", "given_name": "So", "orcid": "0000-0002-6507-6925" }, { "family_name": "Perez-Silva", "given_name": "Andrea", "orcid": "0000-0002-8555-5122" }, { "family_name": "Pranger", "given_name": "Casper", "orcid": "0000-0002-8943-896X" }, { "family_name": "Segall", "given_name": "Paul", "orcid": "0000-0001-5973-471X" }, { "family_name": "Sun", "given_name": "Yudong", "orcid": "0000-0003-0809-936X" }, { "family_name": "Thakur", "given_name": "Prithvi", "orcid": "0000-0001-6687-0787" }, { "family_name": "Uphoff", "given_name": "Carsten", "orcid": "0000-0002-9169-7485" }, { "family_name": "van Dinther", "given_name": "Ylona", "orcid": "0000-0002-4273-8287" }, { "family_name": "Yang", "given_name": "Yuyun", "orcid": "0000-0001-5260-8593" } ], "abstract": "Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The sequences of earthquakes and aseismic slip (SEAS) initiative has set out to facilitate community code comparisons, and verify and advance the next generation of physics-based earthquake models that reproduce all phases of the seismic cycle. With the goal of advancing SEAS models to robustly incorporate physical and geometrical complexities, here we present code comparison results from two new benchmark problems: BP1-FD considers full elastodynamic effects, and BP3-QD considers dipping fault geometries. Seven and eight modeling groups participated in BP1-FD and BP3-QD, respectively, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. With new comparison metrics, we find that numerical resolution and computational domain size are critical parameters to obtain matching results. Codes for BP1-FD implement different criteria for switching between quasi-static and dynamic solvers, which require tuning to obtain matching results. In BP3-QD, proper remote boundary conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain excellent quantitative agreements among codes in earthquake interevent times, event moments, and coseismic slip, with reasonable agreements made in peak slip rates and rupture arrival time. We find that including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi-dynamic counterpart. For BP3-QD, both dip angle and sense of motion (thrust versus normal faulting) alter ground motion on the hanging and foot walls, and influence event patterns, with some sequences exhibiting similar-size characteristic earthquakes, and others exhibiting different-size events. These findings underscore the importance of considering full elastodynamics and nonvertical dip angles in SEAS models, as both influence short- and long-term earthquake behavior and are relevant to seismic hazard.", "doi": "10.1785/0120220066", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "2023-04", "series_number": "2", "volume": "113", "issue": "2", "pages": "499-523" }, { "id": "authors:bh7ea-yp672", "collection": "authors", "collection_id": "bh7ea-yp672", "cite_using_url": "https://authors.library.caltech.edu/records/bh7ea-yp672", "type": "article", "title": "Uncertainty Analysis of Dynamic Rupture Measurements Obtained Through Ultrahigh-Speed Digital Image Correlation", "author": [ { "family_name": "Lattanzi", "given_name": "A.", "orcid": "0000-0001-7540-3136", "clpid": "Lattanzi-Attilio" }, { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rossi", "given_name": "M.", "clpid": "Rossi-M" }, { "family_name": "Donzelli", "given_name": "A.", "clpid": "Donzelli-A" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Background: The full-field behavior of dynamic shear cracks, with their highly transient features, has recently been quantified by employing Digital Image Correlation (DIC) coupled with ultrahigh-speed photography (at 1-2 million frames/sec). The use of ultrahigh-speed DIC has enabled the observation of complex structures associated with the evolution of the dynamic shear fractures under controlled laboratory conditions, providing a detailed description of their distinctive full-field kinematic features. This has allowed to identify, for instance, the spatiotemporal characteristics of sub-Rayleigh and intersonic shear ruptures, and to measure the evolution of dynamic friction during rupture propagation of frictional shear ruptures. \n\nObjective: Capturing such highly transient phenomena represents a challenging metrological process influenced by both ultra-fast imaging procedures and DIC analysis parameters. However, the effect of these parameters on the quantification of the rupture features has not been assessed yet. Here, a simulated experiment framework is presented and employed to evaluate the uncertainties associated with ultrahigh-speed DIC measurements. \n\nMethods: Finite element simulations replicate laboratory experiments of dynamic ruptures spontaneously propagating along frictional interfaces. Experimental images of the specimen acquired with an ultrahigh-speed camera are numerically deformed by the displacement fields obtained from the numerical simulations and are analyzed using the same DIC analysis procedure as in the laboratory experiments. \n\nResults: The displacement, particle velocity, and strain fields obtained from the DIC analysis are compared with the ground-truth fields of the numerical simulations, correlating the measurement resolution with the physical length scale of the propagating Mode II rupture. In addition, the full-field data are employed to estimate the capability of the ultrahigh-speed DIC setup to infer the dynamic friction evolution. \n\nConclusions: This methodology allows us to quantify the accuracy of the ultrahigh-speed DIC measurements in resolving the complex spatiotemporal structures of dynamic shear ruptures, focusing on the impact of the key correlation parameters.", "doi": "10.1007/s11340-022-00932-9", "issn": "0014-4851", "publisher": "Springer", "publication": "Experimental Mechanics", "publication_date": "2023-03", "series_number": "3", "volume": "63", "issue": "3", "pages": "529-563" }, { "id": "authors:qw52z-k2169", "collection": "authors", "collection_id": "qw52z-k2169", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220817-927590000", "type": "article", "title": "A Spectral Boundary-Integral Method for Faults and Fractures in a Poroelastic Solid: Simulations of a Rate-and-State Fault With Dilatancy, Compaction, and Fluid Injection", "author": [ { "family_name": "Heimisson", "given_name": "El\u00edas Rafn", "orcid": "0000-0001-8342-7226", "clpid": "Heimisson-El\u00edas-Rafn" }, { "family_name": "Liu", "given_name": "Shengduo", "clpid": "Liu-Shengduo" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rudnicki", "given_name": "John", "orcid": "0000-0002-4258-8506", "clpid": "Rudnicki-John-W" } ], "abstract": "Fluid-fault interactions result in many two-way coupled processes across a range of length scales, from the micron scale of the shear zone to the kilometer scale of the slip patch. The scale separation and complex coupling render fluid-fault interactions challenging to simulate, yet they are key for our understanding of experimental data and induced seismicity. Here we present spectral boundary-integral solutions for in-plane interface sliding and opening in a poroelastic solid. We solve for fault slip in the presence of rate-and-state frictional properties, inelastic dilatancy, injection, and the coupling of a shear zone and a diffusive poroelastic bulk. The shear localization zone is treated as having a finite width and non-constant pore pressure, albeit with a simplified mathematical representation. The dimension of the 2D plane strain problem is reduced to a 1D problem resulting in increased computational efficiency and incorporation of small-scale shear-zone physics into the boundary conditions. We apply the method to data from a fault injection experiment that has been previously studied with modeling. We explore the influence of bulk poroelastic response, bulk diffusivity in addition to inelastic dilatancy on fault slip during injection. Dilatancy not only alters drastically the stability of fault slip but also the nature of pore pressure evolution on the fault, causing significant deviation from the standard square-root-of-time diffusion. More surprisingly, varying the bulk's poroelastic response (by using different values of the undrained Poisson's ratio) and bulk hydraulic diffusivity can be as critical in determining rupture stability as the inelastic dilatancy.", "doi": "10.1029/2022jb024185", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2022-09", "series_number": "9", "volume": "127", "issue": "9", "pages": "Art. No. e2022JB024185" }, { "id": "authors:6gcmj-reb48", "collection": "authors", "collection_id": "6gcmj-reb48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220602-794026200", "type": "article", "title": "Intermittent lab earthquakes in dynamically weakening fault gouge", "author": [ { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" } ], "abstract": "Large and destructive earthquakes on mature faults in Earth's crust occur as slip in a layer of a fine granular material\u2014fault gouge\u2014produced by comminution during sliding. A range of insights into the frictional resistance of faults\u2014one of the main factors controlling earthquake nucleation, dynamic propagation and arrest, and hence the destructive ground shaking of earthquakes\u2014has been obtained in experiments with spatially uniform slip imposed in small samples. However, how various features of gouge friction combine to determine spontaneous progression of earthquakes is difficult to study in the lab owing to substantial challenges with sample sizes and adequate imaging. Here, using lab experiments, we show that spontaneously propagating dynamic ruptures navigate a fault region with fine rock gouge through complex, intermittent slip processes with dramatic friction evolution. These include repeated arrest of rupture propagation caused by friction strengthening at lower slip rates and dynamic earthquake re-nucleation enabled by pronounced rapid friction weakening at higher slip rates consistent with flash heating. The spontaneous repeated weakening and strengthening of friction in fine rock gouge highlights the fundamental dependence of friction on slip rate and associated processes, such as shear heating, localization and delocalization of shear, and dilation and compaction of the shear layer. Our findings expand experimental support of the concept that co-seismic weakening may enable earthquake rupture to break through stable fault regions, with substantial implications for seismic hazard.", "doi": "10.1038/s41586-022-04749-3", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2022-06-30", "volume": "606", "pages": "922-929" }, { "id": "authors:py16w-tp603", "collection": "authors", "collection_id": "py16w-tp603", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220309-676473000", "type": "article", "title": "Subduction earthquake sequences in a non-linear visco-elasto-plastic megathrust", "author": [ { "family_name": "Dal\u00a0Zilio", "given_name": "Luca", "orcid": "0000-0002-5642-0894", "clpid": "Dal-Zilio-Luca" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Gerya", "given_name": "Taras", "orcid": "0000-0002-1062-2722", "clpid": "Gerya-Taras" } ], "abstract": "We present a 2-D thermomechanical computational framework for simulating earthquake sequences in a non-linear visco-elasto-plastic compressible medium. The method is developed for a plane-strain problem and incorporates an invariant formulation of the classical rate- and state-dependent friction law and an adaptive time-stepping, which allows the time step to vary by many orders of magnitude during a simulation. Long-term tectonic convergence is imposed by displacing a boundary at a constant rate, whereas temperature-dependent viscosity is solved using a rapidly converging Newton\u2013Raphson scheme. The 2-D volume is discretized using finite differences on a fully staggered grid and marker-in-cell techniques. An adaptive free-surface approximation is used to modulate the air viscosity with the time step, which allows stresses to vanish on the free surface during the propagation of fast slipping events. We present a set of increasingly complex models in which we investigate how inertia, radiation damping, thermally activated non-linear rheology and off-megathrust splay-fault events affect sequences of seismic and aseismic slip on a simplified subduction megathrust. The new method provides a unique computational framework to analyse earthquake sequences and to connect forearc deformation with the dynamic properties of the megathrust, thus providing a physical link between observations spanning from slow interseismic strain accumulation to localized coseismic slip of individual earthquakes and post-seismic viscoelastic relaxation.", "doi": "10.1093/gji/ggab521", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2022-05", "series_number": "2", "volume": "229", "issue": "2", "pages": "1098-1121" }, { "id": "authors:t6vh7-y7011", "collection": "authors", "collection_id": "t6vh7-y7011", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211206-184347093", "type": "article", "title": "Community-Driven Code Comparisons for Three-Dimensional Dynamic Modeling of Sequences of Earthquakes and Aseismic Slip", "author": [ { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" }, { "family_name": "Erickson", "given_name": "Brittany A.", "orcid": "0000-0001-9457-8572", "clpid": "Erickson-Brittany-A" }, { "family_name": "Lambert", "given_name": "Val\u00e8re R.", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re-R" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Ando", "given_name": "Ryosuke", "orcid": "0000-0002-6205-3699", "clpid": "Ando-Ryosuke" }, { "family_name": "Barbot", "given_name": "Sylvain D.", "orcid": "0000-0003-4257-7409", "clpid": "Barbot-Sylvain-D" }, { "family_name": "Cattania", "given_name": "Camilla", "orcid": "0000-0003-0031-1696", "clpid": "Cattania-Camilla" }, { "family_name": "Dal Zilio", "given_name": "Luca", "orcid": "0000-0002-5642-0894", "clpid": "Dal-Zilio-Luca" }, { "family_name": "Duan", "given_name": "Benchun", "orcid": "0000-0003-2622-3811", "clpid": "Duan-Benchun" }, { "family_name": "Dunham", "given_name": "Eric M.", "orcid": "0000-0003-0804-7746", "clpid": "Dunham-Eric-M" }, { "family_name": "Gabriel", "given_name": "Alice-Agnes", "orcid": "0000-0003-0112-8412", "clpid": "Gabriel-Alice-Agnes" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Li", "given_name": "Duo", "orcid": "0000-0002-8641-337X", "clpid": "Li-Duo" }, { "family_name": "Li", "given_name": "Meng", "orcid": "0000-0001-9459-7167", "clpid": "Li-Meng" }, { "family_name": "Liu", "given_name": "Dunyu", "orcid": "0000-0001-6740-3080", "clpid": "Liu-Dunyu" }, { "family_name": "Liu", "given_name": "Yajing", "orcid": "0000-0002-5323-8077", "clpid": "Liu-Yajing" }, { "family_name": "Ozawa", "given_name": "So", "orcid": "0000-0002-6507-6925", "clpid": "Ozawa-So" }, { "family_name": "Pranger", "given_name": "Casper", "orcid": "0000-0002-8943-896X", "clpid": "Pranger-Casper" }, { "family_name": "van Dinther", "given_name": "Ylona", "orcid": "0000-0002-4273-8287", "clpid": "van-Dinther-Ylona" } ], "abstract": "Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self-consistent, physics-based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three-dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary-element, finite-element, and finite-difference methods, in a community initiative. Our benchmarks consider a planar vertical strike-slip fault obeying a rate- and state-dependent friction law, in a 3D homogeneous, linear elastic whole-space or half-space, where spontaneous earthquakes and slow slip arise due to tectonic-like loading. We use a suite of quasi-dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain-size-dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community-based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics.", "doi": "10.1029/2021JB023519", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2022-03", "series_number": "3", "volume": "127", "issue": "3", "pages": "Art. No. e2021JB023519" }, { "id": "authors:z2msj-wj442", "collection": "authors", "collection_id": "z2msj-wj442", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220317-377260000", "type": "article", "title": "Dynamics and Near-Field Surface Motions of Transitioned Supershear Laboratory Earthquakes in Thrust Faults", "author": [ { "family_name": "Tal", "given_name": "Yuval", "orcid": "0000-0001-7308-9294", "clpid": "Tal-Yuval" }, { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "We study how the asymmetric geometry of thrust faults affects the dynamics of supershear ruptures and their associated trailing Rayleigh ruptures as they interact with the free surface, and investigate the resulting near-field ground motions. Earthquakes are mimicked by propagating laboratory ruptures along a frictional interface with a 61\u00b0 dip angle. Using an experimental technique that combines ultrahigh-speed photography with digital image correlation, we produce sequences of full-field evolving measurements of particle displacements and velocities. Our full-field measurement capability allows us to confirm and quantify the asymmetry between the experimental motions of the hanging and footwalls, with larger velocity magnitudes occurring at the hanging wall. Interestingly, because the motion of the hanging wall is generally near-vertical, while that of the footwall is at dip direction shallower than the dip angle of the fault, the horizontal surface velocity components are found to be larger at the footwall than at the hanging wall. The attenuation in surface velocity with distance from the fault trace is generally larger at the hanging wall than at the footwall and it is more pronounced in the vertical component than in the horizontal one. Measurements of the rotations in surface motions confirm experimentally that the interaction of the rupture with the free surface can be interpreted through a torqueing mechanism that leads to reduction in normal stress near the free surface for thrust earthquakes. Nondimensional analysis shows that the experimental measurements are consistent with larger-scale numerical simulations as well as field observations from thrust earthquakes.", "doi": "10.1029/2021jb023733", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2022-03", "series_number": "3", "volume": "127", "issue": "3", "pages": "Art. No. e2021JB023733" }, { "id": "authors:wncf8-t8y24", "collection": "authors", "collection_id": "wncf8-t8y24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220223-919579000", "type": "article", "title": "A unified perspective of seismicity and fault coupling along the San Andreas Fault", "author": [ { "family_name": "Liu", "given_name": "Yuan-Kai", "orcid": "0000-0003-4032-9444", "clpid": "Liu-Yuan-Kai" }, { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Cochran", "given_name": "Elizabeth S.", "orcid": "0000-0003-2485-4484", "clpid": "Cochran-Elizabeth-S" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "The San Andreas Fault (SAF) showcases the breadth of possible earthquake sizes and occurrence behavior; in particular, the central SAF is a microcosm of such diversity. This section also exhibits the spectrum of fault coupling from locked to creeping. Here, we show that the observations of aseismic slip, temporal clustering of seismicity, and spatial variations in earthquake size distributions are tightly connected. Specifically, the creep rate along the central SAF is shown to be directly proportional to the fraction of nonclustered earthquakes for the period 1984\u20132020. This relationship provides a unified perspective of earthquake phenomenology along the SAF, where lower coupling manifests in weaker temporal clustering, with repeating earthquakes as an end-member. This new paradigm provides additional justification for characterizing the northwest \u223c75 kilometers of the creeping segment as a transition zone, with potential implications for seismic hazard.", "doi": "10.1126/sciadv.abk1167", "pmcid": "PMC8865773", "issn": "2375-2548", "publisher": "American Association for the Advancement of Science", "publication": "Science Advances", "publication_date": "2022-02-25", "series_number": "8", "volume": "8", "issue": "8", "pages": "Art. No. eabk1167" }, { "id": "authors:9hx71-mz455", "collection": "authors", "collection_id": "9hx71-mz455", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220127-621076900", "type": "article", "title": "Fault rock heterogeneity can produce fault weakness and reduce fault stability", "author": [ { "family_name": "Bedford", "given_name": "John D.", "orcid": "0000-0002-2077-4797", "clpid": "Bedford-John-D" }, { "family_name": "Faulkner", "given_name": "Daniel R.", "orcid": "0000-0002-6750-3775", "clpid": "Faulkner-Daniel-R" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Geological heterogeneity is abundant in crustal fault zones; however, its role in controlling the mechanical behaviour of faults is poorly constrained. Here, we present laboratory friction experiments on laterally heterogeneous faults, with patches of strong, rate-weakening quartz gouge and weak, rate-strengthening clay gouge. The experiments show that the heterogeneity leads to a significant reduction in strength and frictional stability in comparison to compositionally identical faults with homogeneously mixed gouges. We identify a combination of weakening effects, including smearing of the weak clay; differential compaction of the two gouges redistributing normal stress; and shear localization producing stress concentrations in the strong quartz patches. The results demonstrate that geological heterogeneity and its evolution can have pronounced effects on fault strength and stability and, by extension, on the occurrence of slow-slip transients versus earthquake ruptures and the characteristics of the resulting events, and should be further studied in lab experiments and earthquake source modelling.", "doi": "10.1038/s41467-022-27998-2", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2022-01-17", "volume": "13", "pages": "Art. No. 326" }, { "id": "authors:dv27e-2sy47", "collection": "authors", "collection_id": "dv27e-2sy47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211217-790936300", "type": "article", "title": "Dynamic rupture initiation and propagation in a fluid-injection laboratory setup with diagnostics across multiple temporal scales", "author": [ { "family_name": "Gori", "given_name": "Marcello", "orcid": "0000-0002-7380-3723", "clpid": "Gori-Marcello" }, { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Fluids are known to trigger a broad range of slip events, from slow, creeping transients to dynamic earthquake ruptures. Yet, the detailed mechanics underlying these processes and the conditions leading to different rupture behaviors are not well understood. Here, we use a laboratory earthquake setup, capable of injecting pressurized fluids, to compare the rupture behavior for different rates of fluid injection, slow (megapascals per hour) versus fast (megapascals per second). We find that for the fast injection rates, dynamic ruptures are triggered at lower pressure levels and over spatial scales much smaller than the quasistatic theoretical estimates of nucleation sizes, suggesting that such fast injection rates constitute dynamic loading. In contrast, the relatively slow injection rates result in gradual nucleation processes, with the fluid spreading along the interface and causing stress changes consistent with gradually accelerating slow slip. The resulting dynamic ruptures propagating over wetted interfaces exhibit dynamic stress drops almost twice as large as those over the dry interfaces. These results suggest the need to take into account the rate of the pore-pressure increase when considering nucleation processes and motivate further investigation on how friction properties depend on the presence of fluids.", "doi": "10.1073/pnas.2023433118", "pmcid": "PMC8713790", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2021-12-21", "series_number": "51", "volume": "118", "issue": "51", "pages": "Art. No. e2023433118" }, { "id": "authors:fb7gx-zkf44", "collection": "authors", "collection_id": "fb7gx-zkf44", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210421-092618302", "type": "article", "title": "Resolving Simulated Sequences of Earthquakes and Fault Interactions: Implications for Physics-Based Seismic Hazard Assessment", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Physics-based numerical modeling of earthquake source processes strives to predict quantities of interest for seismic hazard, such as the probability of an earthquake rupture jumping between fault segments. How to assess the predictive power of numerical models remains a topic of ongoing debate. Here, we investigate how sensitive the outcomes of numerical simulations of sequences of earthquakes and aseismic slip are to choices in numerical discretization and treatment of inertial effects, using a simplified 2-D crustal fault model with two co-planar segments separated by a creeping barrier. Our simulations demonstrate that simplifying inertial effects and using oversized cells significantly affects the resulting earthquake sequences, including the rate of two-segment ruptures. We find that fault models with different properties and modeling assumptions can produce similar frequency-magnitude statistics and static stress drops but have different rates of two-segment ruptures. For sufficiently long faults, we find that long-term sequences of events can substantially differ even among simulations that are well resolved by standard considerations. In such simulations, some outcomes, such as static stress drops, are similar among adequately resolved simulations, whereas others, such as the rate of two-segment ruptures, can be highly sensitive to numerical procedures and modeling assumptions. While it is possible that the response of models with additional ingredients -Realistic fault geometry, fluid effects, etc. -Would be less sensitive to numerical procedures, our results emphasize the need to examine the potential dependence of simulation outcomes on the modeling procedures and resolution, particularly when assessing their predictive value for seismic hazard assessment.", "doi": "10.1029/2021JB022193", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2021-10", "series_number": "10", "volume": "126", "issue": "10", "pages": "Art. No. e2021JB022193" }, { "id": "authors:n2b9p-8jf71", "collection": "authors", "collection_id": "n2b9p-8jf71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210216-124009098", "type": "article", "title": "Scale Dependence of Earthquake Rupture Prestress in Models With Enhanced Weakening: Implications for Event Statistics and Inferences of Fault Stress", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Faulkner", "given_name": "Daniel", "orcid": "0000-0002-6750-3775", "clpid": "Faulkner-Daniel-R" } ], "abstract": "Determining conditions for earthquake slip on faults is a key goal of fault mechanics highly relevant to seismic hazard. Previous studies have demonstrated that enhanced dynamic weakening (EDW) can lead to dynamic rupture of faults with much lower shear stress than required for rupture nucleation. We study the stress conditions before earthquake ruptures of different sizes that spontaneously evolve in numerical simulations of earthquake sequences on rate-and-state faults with EDW due to thermal pressurization of pore fluids. We find that average shear stress right before dynamic rupture (aka shear prestress) systematically varies with the rupture size. The smallest ruptures have prestress comparable to the local shear stress required for nucleation. Larger ruptures weaken the fault more, propagate over increasingly under-stressed areas due to dynamic stress concentration, and result in progressively lower average prestress over the entire rupture. The effect is more significant in fault models with more efficient EDW. We find that, as a result, fault models with more efficient weakening produce fewer small events and result in systematically lower b-values of the frequency-magnitude event distributions. The findings (a) illustrate that large earthquakes can occur on faults that appear not to be critically stressed compared to stresses required for slip nucleation; (b) highlight the importance of finite-fault modeling in relating the local friction behavior determined in the lab to the field scale; and (c) suggest that paucity of small events or seismic quiescence may be the observational indication of mature faults that operate under low shear stress due to EDW.", "doi": "10.1029/2021JB021886", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2021-10", "series_number": "10", "volume": "126", "issue": "10", "pages": "Art. No. e2021JB021886" }, { "id": "authors:fpwm2-c9z86", "collection": "authors", "collection_id": "fpwm2-c9z86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211006-161417119", "type": "article", "title": "Evolution of dynamic shear strength of frictional interfaces during rapid normal stress variations", "author": [ { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Tal", "given_name": "Yuval", "orcid": "0000-0001-7308-9294", "clpid": "Tal-Yuval" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Pressure shear plate impact tests have revealed that when normal stress changes rapidly enough, the frictional shear resistance is no longer proportional to the normal stress but rather evolves with slip gradually. Motivated by these findings, we focus on characterizing the dynamic shear strength of frictional interfaces subject to rapid variations in normal stress. To study this problem, we use laboratory experiments featuring dynamic shear cracks interacting with a free surface and resulting in pronounced and rapid normal stress variations. As dynamic cracks tend to propagate close to the wave speeds of the material, capturing their behavior poses the metrological challenge of resolving displacements on the order of microns over timescales microseconds. Here we present our novel approach to quantify the full-field behavior of dynamic shear ruptures and the evolution of friction during sudden variations in normal stress, based on ultrahighspeed photography (at 1-2 million frames/sec) combined with digital image correlation. Our measurements allow us to capture the evolution of dynamic shear cracks during these short transients and enable us to decode the nature of dynamic friction.", "doi": "10.1051/epjconf/202125001016", "issn": "2100-014X", "publisher": "EDP Sciences", "publication": "EPJ Web of Conferences", "publication_date": "2021-09-08", "volume": "250", "pages": "Art. No. 01016" }, { "id": "authors:5pppk-3qt52", "collection": "authors", "collection_id": "5pppk-3qt52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210701-172839842", "type": "article", "title": "Dilatancy and Compaction of a Rate-and-State Fault in a Poroelastic Medium: Linearized Stability Analysis", "author": [ { "family_name": "Heimisson", "given_name": "El\u00edas Rafn", "orcid": "0000-0001-8342-7226", "clpid": "Heimisson-El\u00edas-Rafn" }, { "family_name": "Rudnicki", "given_name": "John", "orcid": "0000-0002-4258-8506", "clpid": "Rudnicki-John" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Faults in the crust at seismogenic depths are embedded in a fluid-saturated, elastic, porous material. Slip on such faults may induce transient pore pressure changes through dilatancy or compaction of the gouge or host rock. However, the poroelastic nature of the crust and the full coupling of inelastic gouge processes and the host rock have been largely neglected in previous analyses. Here, we present a linearized stability analysis of a rate-and-state fault at steady-state sliding in a fully-coupled poroelastic solid under in-plane and anti-plane sliding. We further account for dilatancy of the shear zone and the associated pore pressure changes in an averaged sense. We derive the continuum equivalent of the analysis by Segall and Rice (1995, https://doi.org/10.1029/95jb02403), and highlight a new parameter regime where dilatancy stabilization can act in a highly diffusive solid. Such stabilization is permitted since the time scale of flux through the shear zone and diffusion into the bulk can be very different. A novel aspect of this study involves analyzing the mechanical expansion of the shear layer causing fault-normal displacements, which we describe by a mass balance of the solid constituent of the gouge. This effect gives rise to a universal stabilization mechanism in both drained and undrained limits. The importance of the mechanism scales with shear-zone thickness and it is significant for wider shear zones exceeding approximately 1 cm. We hypothesize that this stabilization mechanism may alter and delay an ongoing shear localization process.", "doi": "10.1029/2021jb022071", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2021-08", "series_number": "8", "volume": "126", "issue": "8", "pages": "Art. No. e2021JB022071" }, { "id": "authors:z9cb5-1yn82", "collection": "authors", "collection_id": "z9cb5-1yn82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201022-125153125", "type": "article", "title": "Constraining Fault Friction and Stability With Fluid-Injection Field Experiments", "author": [ { "family_name": "Larochelle", "given_name": "Stacy", "orcid": "0000-0001-6161-5605", "clpid": "Larochelle-Stacy" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Cappa", "given_name": "Fr\u00e9d\u00e9ric", "orcid": "0000-0003-4859-8024", "clpid": "Cappa-Fr\u00e9d\u00e9ric" } ], "abstract": "While the notion that injecting fluids into the subsurface can reactivate faults by reducing frictional resistance is well established, the ensuing evolution of the slip is still poorly understood. What controls whether the induced slip remains stable and confined to the fluid-affected zone or accelerates into a runaway earthquake? Are there observable indicators of the propensity to earthquakes before they happen? Here, we investigate these questions by modeling a unique fluid-injection experiment on a natural fault with laboratory-derived friction laws. We show that a range of fault models with diverging stability with sustained injection reproduce the slip measured during pressurization. Upon depressurization, however, the most unstable scenario departs from the observations, suggesting that the fault is relatively stable. The models could be further distinguished with optimized depressurization tests or spatially distributed monitoring. Our findings indicate that avoiding injection near low-residual-friction faults and depressurizing during slip acceleration could help prevent large-scale earthquakes.", "doi": "10.1029/2020GL091188", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2021-05-28", "series_number": "10", "volume": "48", "issue": "10", "pages": "Art. No. e2020GL091188" }, { "id": "authors:8pz43-q0q97", "collection": "authors", "collection_id": "8pz43-q0q97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210310-112130851", "type": "article", "title": "Propagation of large earthquakes as self-healing pulses or mild cracks", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Perry", "given_name": "Stephen", "orcid": "0000-0003-1748-1827", "clpid": "Perry-Stephen" } ], "abstract": "Observations suggest that mature faults host large earthquakes at much lower levels of stress than their expected static strength. Potential explanations are that the faults are quasi-statically strong but experience considerable weakening during earthquakes, or that the faults are persistently weak, for example, because of fluid overpressure. Here we use numerical modelling to examine these competing theories for simulated earthquake ruptures that satisfy the well known observations of 1\u201310 megapascal stress drops and limited heat production. In that regime, quasi-statically strong but dynamically weak faults mainly host relatively sharp, self-healing pulse-like ruptures, with only a small portion of the fault slipping at a given time, whereas persistently weak faults host milder ruptures with more spread-out slip, which are called crack-like ruptures. We find that the sharper self-healing pulses, which exhibit larger dynamic stress changes compared to their static stress changes, result in much larger radiated energy than that inferred teleseismically for megathrust events. By contrast, milder crack-like ruptures on persistently weak faults, which produce comparable static and dynamic stress changes, are consistent with the seismological observations. The larger radiated energy of self-healing pulses is similar to the limited regional inferences available for crustal strike-slip faults. Our findings suggest that either large earthquakes rarely propagate as self-healing pulses, with potential differences between tectonic settings, or their radiated energy is substantially underestimated, raising questions about earthquake physics and the expected shaking from large earthquakes.", "doi": "10.1038/s41586-021-03248-1", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2021-03-11", "series_number": "7849", "volume": "591", "issue": "7849", "pages": "252-258" }, { "id": "authors:zyge8-axx47", "collection": "authors", "collection_id": "zyge8-axx47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210107-102417875", "type": "article", "title": "Rupture-dependent breakdown energy in fault models with thermo-hydro-mechanical processes", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Substantial insight into earthquake source processes has resulted from considering frictional ruptures analogous to cohesive-zone shear cracks from fracture mechanics. This analogy holds for slip-weakening representations of fault friction that encapsulate the resistance to rupture propagation in the form of breakdown energy, analogous to fracture energy, prescribed in advance as if it were a material property of the fault interface. Here, we use numerical models of earthquake sequences with enhanced weakening due to thermal pressurization of pore fluids to show how accounting for thermo-hydro-mechanical processes during dynamic shear ruptures makes breakdown energy rupture-dependent. We find that local breakdown energy is neither a constant material property nor uniquely defined by the amount of slip attained during rupture, but depends on how that slip is achieved through the history of slip rate and dynamic stress changes during the rupture process. As a consequence, the frictional breakdown energy of the same location along the fault can vary significantly in different earthquake ruptures that pass through. These results suggest the need to reexamine the assumption of predetermined frictional breakdown energy common in dynamic rupture modeling and to better understand the factors that control rupture dynamics in the presence of thermo-hydro-mechanical processes.", "doi": "10.5194/se-11-2283-2020", "issn": "1869-9529", "publisher": "Copernicus GmbH", "publication": "Solid Earth", "publication_date": "2020-11-26", "series_number": "6", "volume": "11", "issue": "6", "pages": "2283-2302" }, { "id": "authors:3zw5c-60v02", "collection": "authors", "collection_id": "3zw5c-60v02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200818-083332830", "type": "article", "title": "Illuminating the physics of dynamic friction through laboratory earthquakes on thrust faults", "author": [ { "family_name": "Tal", "given_name": "Yuval", "orcid": "0000-0001-7308-9294", "clpid": "Tal-Yuval" }, { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Large, destructive earthquakes often propagate along thrust faults including megathrusts. The asymmetric interaction of thrust earthquake ruptures with the free surface leads to sudden variations in fault-normal stress, which affect fault friction. Here, we present full-field experimental measurements of displacements, particle velocities, and stresses that characterize the rupture interaction with the free surface, including the large normal stress reductions. We take advantage of these measurements to investigate the dependence of dynamic friction on transient changes in normal stress, demonstrate that the shear frictional resistance exhibits a significant lag in response to such normal stress variations, and identify a predictive frictional formulation that captures this effect. Properly accounting for this delay is important for simulations of fault slip, ground motion, and associated tsunami excitation.", "doi": "10.1073/pnas.2004590117", "pmcid": "PMC7474586", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2020-09-01", "series_number": "35", "volume": "117", "issue": "35", "pages": "21095-21100" }, { "id": "authors:hcg0j-pk874", "collection": "authors", "collection_id": "hcg0j-pk874", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200513-130033224", "type": "article", "title": "Unraveling scaling properties of slow-slip events", "author": [ { "family_name": "Dal Zilio", "given_name": "Luca", "orcid": "0000-0002-5642-0894", "clpid": "Dal-Zilio-Luca" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean\u2010Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "abstract": "A major debate in geophysics is whether earthquakes and slow\u2010slip events (SSEs) arise from similar failure mechanisms. Recent observations from different subduction zones suggest that SSEs follow the same moment\u2010duration scaling as earthquakes, unlike qualitatively different scaling proposed by earlier studies. Here, we examine the scaling properties using dynamic simulations of frictional sliding. The resulting sequences of SSEs match observations from the Cascadia subduction zone, including the earthquake\u2010like cubic moment\u2010duration scaling. In contrast to conventional and widely used assumptions of magnitude\u2010invariant rupture velocities and stress drops, both simulated and natural SSEs have rupture velocities and stress drops that increase with event magnitudes. These findings support the same frictional origin for both earthquakes and SSEs while suggesting a new explanation for the observed SSEs scaling.", "doi": "10.1029/2020gl087477", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2020-05-28", "series_number": "10", "volume": "47", "issue": "10", "pages": "Art. No. e2020GL087477" }, { "id": "authors:p5r6d-w2704", "collection": "authors", "collection_id": "p5r6d-w2704", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191223-131340451", "type": "article", "title": "Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)", "author": [ { "family_name": "Erickson", "given_name": "Brittany A.", "orcid": "0000-0001-9457-8572", "clpid": "Erickson-B-A" }, { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" }, { "family_name": "Barall", "given_name": "Michael", "clpid": "Barall-M" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Dunham", "given_name": "Eric M.", "clpid": "Dunham-E-M" }, { "family_name": "Harris", "given_name": "Ruth", "clpid": "Harris-R" }, { "family_name": "Abrahams", "given_name": "Lauren S.", "clpid": "Abrahams-L-S" }, { "family_name": "Allison", "given_name": "Kali L.", "clpid": "Allison-K-L" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Barbot", "given_name": "Sylvain", "orcid": "0000-0003-4257-7409", "clpid": "Barbot-S" }, { "family_name": "Cattania", "given_name": "Camilla", "clpid": "Cattania-C" }, { "family_name": "Elbanna", "given_name": "Ahmed", "clpid": "Elbanna-A-E" }, { "family_name": "Fialko", "given_name": "Yuri", "orcid": "0000-0002-6161-8467", "clpid": "Fialko-Y-A" }, { "family_name": "Idini", "given_name": "Benjam\u00edn", "orcid": "0000-0002-2697-3893", "clpid": "Idini-B" }, { "family_name": "Kozdon", "given_name": "Jeremy E.", "clpid": "Kozdon-J-E" }, { "family_name": "Lambert", "given_name": "Valere", "clpid": "Lambert-V" }, { "family_name": "Liu", "given_name": "Yajing", "clpid": "Liu-Yajing" }, { "family_name": "Luo", "given_name": "Yingdi", "orcid": "0000-0002-1165-6107", "clpid": "Luo-Yingdi" }, { "family_name": "Ma", "given_name": "Xiao", "orcid": "0000-0002-2125-0880", "clpid": "Ma-Xiao" }, { "family_name": "McKay", "given_name": "Maricela Best", "clpid": "McKay-M-B" }, { "family_name": "Segall", "given_name": "Paul", "clpid": "Segall-P" }, { "family_name": "Shi", "given_name": "Pengcheng", "orcid": "0000-0003-3558-458X", "clpid": "Shi-Pengcheng" }, { "family_name": "van den Ende", "given_name": "Martijn", "clpid": "van-den-Ende-M-P-A" }, { "family_name": "Wei", "given_name": "Meng", "clpid": "Wei-Meng" } ], "abstract": "Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code\u2010verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well\u2010defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike\u2010slip fault obeying rate\u2010and\u2010state friction, embedded in a 2D homogeneous, linear elastic half\u2010space. Sequences of quasi\u2010dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long\u2010term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics.", "doi": "10.1785/0220190248", "issn": "0895-0695", "publisher": "Seismological Society of America", "publication": "Seismological Research Letters", "publication_date": "2020-03-01", "series_number": "2A", "volume": "91", "issue": "2A", "pages": "874-890" }, { "id": "authors:gha4w-hxy53", "collection": "authors", "collection_id": "gha4w-hxy53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200113-161350780", "type": "article", "title": "Recent Milestones in Unraveling the Full-Field Structure of Dynamic Shear Cracks and Fault Ruptures in Real-Time: From Photoelasticity to Ultrahigh-Speed Digital Image Correlation", "author": [ { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-V" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "The last few decades have seen great achievements in dynamic fracture mechanics. Yet, it was not possible to experimentally quantify the full-field behavior of dynamic fractures, until very recently. Here, we review our recent work on the full-field quantification of the temporal evolution of dynamic shear ruptures. Our newly developed approach based on digital image correlation combined with ultrahigh-speed photography has revolutionized the capabilities of measuring highly transient phenomena and enabled addressing key ques- tions of rupture dynamics. Recent milestones include the visualization of the complete displacement, particle velocity, strain, stress and strain rate fields near growing ruptures, capturing the evolution of dynamic friction during individual rupture growth, and the detailed study of rupture speed limits. For example, dynamic friction has been the big- gest unknown controlling how frictional ruptures develop but it has been impossible, until now, to measure dynamic friction during spontaneous rupture propagation and to understand its dependence on other quantities. Our recent measurements allow, by simul- taneously tracking tractions and sliding speeds on the rupturing interface, to disentangle its complex dependence on the slip, slip velocity, and on their history. In another application, we have uncovered new phenomena that could not be detected with previous methods, such as the formation of pressure shock fronts associated with \"supersonic\" propagation of shear ruptures in viscoelastic materials where the wave speeds are shown to depend strongly on the strain rate.", "doi": "10.1115/1.4045715", "issn": "0021-8936", "publisher": "American Society Mechanical Engineers", "publication": "Journal of Applied Mechanics", "publication_date": "2020-03", "series_number": "3", "volume": "87", "issue": "3", "pages": "Art. No. 030801" }, { "id": "authors:qjzq0-71624", "collection": "authors", "collection_id": "qjzq0-71624", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200306-132842975", "type": "article", "title": "Nearly magnitude\u2010invariant stress drops in simulated crack\u2010like earthquake sequences on rate\u2010and\u2010state faults with thermal pressurization of pore fluids", "author": [ { "family_name": "Perry", "given_name": "Stephen M.", "clpid": "Perry-Stephen-M" }, { "family_name": "Lambert", "given_name": "Val\u00e8re", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Val\u00e8re" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Stress drops, inferred to be magnitude\u2010invariant, are a key characteristic used to describe natural earthquakes. Theoretical studies and laboratory experiments indicate that enhanced dynamic weakening, such as thermal pressurization of pore fluids, may be present on natural faults. At first glance, magnitude invariance of stress drops and enhanced dynamic weakening seem incompatible since larger events may experience greater weakening and should thus have lower final stresses and higher stress drops. We hypothesize that enhanced dynamic weakening can be reconciled with magnitude\u2010invariant stress drops due to larger events having lower average prestress when compared to smaller events. We conduct numerical simulations of long\u2010term earthquake sequences in fault models with rate\u2010and\u2010state friction and thermal pressurization, and in the parameter regime that results mostly in crack\u2010like ruptures, we find that such models can explain both the observationally inferred stress drop invariance and increasing breakdown energy with event magnitude. Smaller events indeed have larger average initial stresses than medium\u2010sized events, and we find nearly constant stress drops for events spanning up to two orders of magnitude in average slip, comparable to approximately six orders of magnitude in seismic moment. Segment\u2010spanning events have more complex behavior, which depends on the properties of the arresting velocity\u2010strengthening region at the edges of the faults.", "doi": "10.1029/2019jb018597", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2020-03", "series_number": "3", "volume": "125", "issue": "3", "pages": "Art. No. e2019JB018597" }, { "id": "authors:kz506-yqx70", "collection": "authors", "collection_id": "kz506-yqx70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200204-112042828", "type": "article", "title": "Spatiotemporal Properties of Sub\u2010Rayleigh and Supershear Ruptures Inferred From Full\u2010Field Dynamic Imaging of Laboratory Experiments", "author": [ { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-V" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Many earthquakes propagate at sub\u2010Rayleigh speeds. Earthquakes propagating at supershear speeds, though less common, are by far more destructive. Hence, it is important to quantify the motion characteristics associated with both types of earthquake ruptures. Here we report on the spatiotemporal properties of dynamic ruptures measured in our laboratory experiments using the dynamic digital image correlation technique. Earthquakes are mimicked by the frictional rupture propagating along the interface of two Homalite plates. Digital images of the propagating ruptures are captured by an ultrahigh\u2010speed camera and processed with digital image correlation in order to produce sequences of evolving displacement and velocity maps. Our measurements reveal the full\u2010field structure of the velocity components, bridge the gap between previous spatially sparse velocimeter measurements available only at two to three locations, and enable us to quantify the attenuation patterns away from the interface.", "doi": "10.1029/2019JB018922", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2020-02", "series_number": "2", "volume": "125", "issue": "2", "pages": "Art. No. e2019JB018922" }, { "id": "authors:3n0e4-vgt48", "collection": "authors", "collection_id": "3n0e4-vgt48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190911-151422000", "type": "article", "title": "On behaviour and scaling of small repeating earthquakes in rate and state fault models", "author": [ { "family_name": "Chen", "given_name": "Ting", "orcid": "0000-0002-9599-871X", "clpid": "Chen-Ting" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "With abundant seismic data for small repeating earthquakes, it is important to construct a dynamic model that can explain various aspects of related observations. In this work, we study small repeating earthquakes on a fault governed by rate- and state-dependent friction laws. The earthquakes occur on a velocity-weakening patch surrounded by a much larger velocity-strengthening region. The whole fault is subject to long-term tectonic loading. The model with a circular patch and the aging form of rate- and state-dependent friction laws has been shown to reproduce the scaling of recurrence time versus seismic moment for small repeating earthquakes in a previous study. Here we investigate the behaviour of small repeating earthquakes in related models under different scenarios, including several forms of the state evolution equations in rate- and state-dependent friction laws, rectangular velocity-weakening patch geometries, quasi-dynamic versus fully dynamic representation of inertial effects and 2-D versus 3-D simulations. We find that the simulated scalings between the recurrence time and seismic moment for these different scenarios is similar while differences do exist. We propose a theoretical consideration for the scaling between the recurrence time and seismic moment of small repeating earthquakes. For patch radii smaller than or comparable to the full nucleation size, the scaling is explained by the increase of seismic to aseismic slip ratio with magnitude. For patch radii larger than the full nucleation size, the scaling is explained by the model in which the recurrence time is determined by the earthquake nucleation time, which is in turn determined by the time for aseismic slip to penetrate the distance of the full nucleation size into the patch. The obtained theoretical insight is used to find the combinations of fault properties that allow the model to fit the observed scaling and range of the seismic moment and recurrence time.", "doi": "10.1093/gji/ggz270", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2019-09", "series_number": "3", "volume": "218", "issue": "3", "pages": "2001-2018" }, { "id": "authors:gq28f-7cb06", "collection": "authors", "collection_id": "gq28f-7cb06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190905-102805142", "type": "article", "title": "Full-field Ultrahigh-speed Quantification of Dynamic Shear Ruptures Using Digital Image Correlation", "author": [ { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-V" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Producing dynamic ruptures in the laboratory allows us to study fundamental characteristics of interface dynamics. Our laboratory earthquake experimental setup has been successfully used to reproduce a number of dynamic rupture phenomena, including supershear transition, bimaterial effect, and pulse-like rupture propagation. However, previous diagnostics, based on photoelasticity and laser velocimeters, were not able to quantify the full-field behavior of dynamic ruptures and, as a consequence, many key rupture features remained obscure. Here we report on our dynamic full-field measurements of displacement, velocities, strains and strain rates associated with the spontaneous propagation of shear ruptures in the laboratory earthquake setup. These measurements are obtained by combining ultrahigh-speed photography with the digital image correlation (DIC) method, enhanced to capture displacement discontinuities. Images of dynamic shear ruptures are taken at 1-2 million frames/s over several sizes of the field of view and analyzed with DIC to produce a sequence of evolving full-field maps. The imaging area size is selected to either capture the rupture features in the far field or to focus on near-field structures, at an enhanced spatial resolution. Simultaneous velocimeter measurements on selected experiments verify the accuracy of the DIC measurements. Owing to the increased ability of our measurements to resolve the characteristic field structures of shear ruptures, we have recently been able to observe rupture dynamics at an unprecedented level of detail, including the formation of pressure and shear shock fronts in viscoelastic materials and the evolution of dynamic friction.", "doi": "10.1007/s11340-019-00501-7", "issn": "0014-4851", "publisher": "Springer", "publication": "Experimental Mechanics", "publication_date": "2019-06", "series_number": "5", "volume": "59", "issue": "5", "pages": "551-582" }, { "id": "authors:xd4kt-9qm38", "collection": "authors", "collection_id": "xd4kt-9qm38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190418-111823081", "type": "article", "title": "Enhanced Digital Image Correlation Analysis of Ruptures with Enforced Traction Continuity Conditions Across Interfaces", "author": [ { "family_name": "Tal", "given_name": "Yuval", "orcid": "0000-0001-7308-9294", "clpid": "Tal-Yuval" }, { "family_name": "Rubino", "given_name": "Vito", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-V" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Accurate measurements of displacements around opening or interfacial shear cracks (shear ruptures) are challenging when digital image correlation (DIC) is used to quantify strain and stress fields around such cracks. This study presents an algorithm to locally adjust the displacements computed by DIC near frictional interfaces of shear ruptures, in order for the local stress fields to satisfy the continuity of tractions across the interface. In the algorithm, the stresses near the interface are extrapolated by local polynomials that are constructed using a constrained inversion. This inversion is such that the traction continuity (TC) conditions are satisfied at the interface while simultaneously matching the displacements produced by the DIC solution at the pixels closest to the center of the subset, where the DIC fields are more accurate. We apply the algorithm to displacement fields of experimental shear ruptures obtained using a local DIC approach and show that the algorithm produces the desired continuous traction field across the interface. The experimental data are also used to examine the sensitivity of the algorithm against different geometrical parameters related to construction of the polynomials in order to avoid artifacts in the stress field.", "doi": "10.3390/app9081625", "issn": "2076-3417", "publisher": "MDPI", "publication": "Applied Sciences", "publication_date": "2019-04-02", "series_number": "8", "volume": "9", "issue": "8", "pages": "Art. No. 1625" }, { "id": "authors:60sqw-x9n90", "collection": "authors", "collection_id": "60sqw-x9n90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190328-180954384", "type": "article", "title": "Microseismicity on Patches of Higher Compression During Larger-Scale Earthquake Nucleation in a Rate-and-State Fault Model", "author": [ { "family_name": "Schaal", "given_name": "Natalie", "orcid": "0000-0003-4825-4344", "clpid": "Schaal-N" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "While many large earthquakes are preceded by observable foreshocks, the mechanism responsible for the occurrence of these smaller\u2010scale seismic events remains uncertain. One physical explanation of foreshocks with growing support is that they are produced by the interaction of slow slip with fault heterogeneity. Inspired by the suggestion from laboratory experiments that foreshocks occur on fault asperities (bumps), we explore rate\u2010and\u2010state fault models with patches of higher normal stress embedded in a larger seismogenic region by conducting 3\u2010D numerical simulations of their behavior over long\u2010term sequences of aseismic and seismic slips. The models do produce smaller\u2010scale seismicity during the aseismic nucleation of larger\u2010scale seismic events. These smaller\u2010scale events have reasonable stress drops, despite the highly elevated compression assigned to the source patches. We find that the two main factors contributing to the reasonable stress drops are the significant extent of the rupture into the region surrounding the patches and the aseismic stress release just prior to the seismic events. The smaller\u2010scale seismicity can only occur if a sufficient separation in nucleation scales between the foreshock\u2010like events and mainshocks is achieved. Our modeling provides insight into the conditions conducive for generating foreshocks on both natural and laboratory faults.", "doi": "10.1029/2018jb016395", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2019-02", "series_number": "2", "volume": "124", "issue": "2", "pages": "1962-1990" }, { "id": "authors:4y4gx-g5m86", "collection": "authors", "collection_id": "4y4gx-g5m86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190206-134734051", "type": "article", "title": "Modeling High Stress Drops, Scaling, Interaction, and Irregularity of Repeating Earthquake Sequences Near Parkfield", "author": [ { "family_name": "Lui", "given_name": "Semechah K. Y.", "orcid": "0000-0001-7801-3635", "clpid": "Liu-Semechah-K-Y" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Repeating earthquake sequences have been actively investigated to clarify many aspects of earthquake physics. The two particularly well\u2010studied sequences, known as the Los Angeles and San Francisco repeaters, have several intriguing observations, including their long (for the seismic moment) recurrence times that would suggest stress drops of 300 MPa based on typical assumptions, near\u2010syncronized timing prior to 2004, and higher than typical inferred stress drops (of 25 to 65 MPa, up to 90 MPa locally), but not as high as the recurrence times suggest. Here we show that all these observations are self\u2010consistent, in the sense that they can be reproduced in a single fault model. The suitable models build on the standard rate\u2010and\u2010state fault models, with velocity\u2010weakening patches imbedded into a velocity\u2010strengthening region, by adding either enhanced dynamic weakening during seismic slip or elevated normal stress on the patches, or both, to allow for the higher stress drops. Such models are able to match the observed average properties of the San Francisco and Los Angeles repeaters, as well as the overall nontrivial scaling between the recurrence time and seismic moment exhibited by many repeating sequences as a whole, for reasonable parameter choices based on experiments and theoretical studies. These models are characterized by the occurrence of substantial and variable aseismic slip at the locations of the repeating sources, which explains their atypical relation between recurrence interval and seismic moment, induces variability in the repeating source properties as observed, and results in their neither slip\u2010 nor time\u2010predictable behavior.", "doi": "10.1029/2018jb016472", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2018-12", "series_number": "12", "volume": "123", "issue": "12", "pages": "10854-10879" }, { "id": "authors:59j5y-3d634", "collection": "authors", "collection_id": "59j5y-3d634", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181113-112608952", "type": "article", "title": "Pressure shock fronts formed by ultra-fast shear cracks in viscoelastic materials", "author": [ { "family_name": "Gori", "given_name": "M.", "orcid": "0000-0002-7380-3723", "clpid": "Gori-Marcello" }, { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Spontaneously propagating cracks in solids emit both pressure and shear waves. When a shear crack propagates faster than the shear wave speed of the material, the coalescence of the shear wavelets emitted by the near-crack-tip region forms a shock front that significantly concentrates particle motion. Such a shock front should not be possible for pressure waves, because cracks should not be able to exceed the pressure wave speed in isotropic linear-elastic solids. In this study, we present full-field experimental measurements of dynamic shear cracks in viscoelastic polymers that result in the formation of a pressure shock front, in addition to the shear one. The apparent violation of classic theories is explained by the strain-rate-dependent material behavior of polymers, where the crack speed remains below the highest pressure wave speed prevailing locally around the crack tip. These findings have important implications for the physics and dynamics of shear cracks such as earthquakes.", "doi": "10.1038/s41467-018-07139-4", "pmcid": "PMC6232150", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2018-11-12", "volume": "9", "pages": "Art. No. 4754" }, { "id": "authors:6kssp-afg75", "collection": "authors", "collection_id": "6kssp-afg75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181011-124535028", "type": "article", "title": "Microseismicity Simulated on Asperity-Like Fault Patches: On Scaling of Seismic Moment With Duration and Seismological Estimates of Stress Drops", "author": [ { "family_name": "Lin", "given_name": "Yen-Yu", "orcid": "0000-0002-6971-3960", "clpid": "Lin-Yen-Yu" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Observations show that microseismic events from the same location can have similar source durations but different seismic moments, violating the commonly assumed scaling. We use numerical simulations of earthquake sequences to demonstrate that strength variations over seismogenic patches provide an explanation of such behavior, with the event duration controlled by the patch size and event magnitude determined by how much of the patch area is ruptured. We find that stress drops estimated by typical seismological analyses for the simulated sources significantly increase with the event magnitude, ranging from 0.006 to 8 MPa. However, the actual stress drops determined from the on\u2010fault stress changes are magnitude\u2010independent and ~3 MPa. Our findings suggest that fault heterogeneity results in local deviations in the moment\u2010duration scaling and earthquake sources with complex shapes of the ruptured area, for some of which stress drops may be significantly (~100\u20131,000 times) underestimated by the typical seismological methods.", "doi": "10.1029/2018GL078650", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2018-08-28", "series_number": "16", "volume": "45", "issue": "16", "pages": "8145-8155" }, { "id": "authors:7afyy-zz077", "collection": "authors", "collection_id": "7afyy-zz077", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180418-152250720", "type": "article", "title": "Finite-fault source inversion using adjoint methods in 3D heterogeneous media", "author": [ { "family_name": "Somala", "given_name": "Surendra Nadh", "clpid": "Somala-S-N" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Accounting for lateral heterogeneities in the 3-D velocity structure of the crust is known to improve earthquake source inversion, compared to results based on 1-D velocity models which are routinely assumed to derive finite-fault slip models. The conventional approach to include known 3-D heterogeneity in source inversion involves pre-computing 3-D Green's functions, which requires a number of 3-D wave propagation simulations proportional to the number of stations or to the number of fault cells. The computational cost of such an approach is prohibitive for the dense data sets that could be provided by future earthquake observation systems. Here, we propose an adjoint-based optimization technique to invert for the spatio-temporal evolution of slip velocity. The approach does not require pre-computed Green's functions. The adjoint method provides the gradient of the cost function, which is used to improve the model iteratively employing an iterative gradient-based minimization method. The adjoint approach is shown to be computationally more efficient than the conventional approach based on pre-computed Green's functions in a broad range of situations. We consider data up to 1 Hz from a Haskell source scenario (a steady pulse-like rupture) on a vertical strike-slip fault embedded in an elastic 3-D heterogeneous velocity model. The velocity model comprises a uniform background and a 3-D stochastic perturbation with the von Karman correlation function. Source inversions based on the 3-D velocity model are performed for two different station configurations, a dense and a sparse network with 1 and 20\u2009km station spacing, respectively. These reference inversions show that our inversion scheme adequately retrieves the rise time when the velocity model is exactly known, and illustrates how dense coverage improves the inference of peak-slip velocities. We investigate the effects of uncertainties in the velocity model by performing source inversions based on an incorrect, homogeneous velocity model. We find that, for velocity uncertainties that have standard deviation and correlation length typical of available 3-D crustal models, the inverted sources can be severely contaminated by spurious features even if the station density is high. When data from thousand or more receivers is used in source inversions in 3-D heterogeneous media, the computational cost of the method proposed in this work is at least two orders of magnitude lower than source inversion based on pre-computed Green's functions.", "doi": "10.1093/gji/ggy148", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2018-07-01", "series_number": "1", "volume": "214", "issue": "1", "pages": "402-420" }, { "id": "authors:wxnkm-ktg86", "collection": "authors", "collection_id": "wxnkm-ktg86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180402-100646598", "type": "article", "title": "Static and sliding contact of rough surfaces: effect of asperity-scale properties and long-range elastic interactions", "author": [ { "family_name": "Hulikal", "given_name": "Srivatsan", "clpid": "Hulikal-S" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" } ], "abstract": "Friction in static and sliding contact of rough surfaces is important in numerous physical phenomena. We seek to understand macroscopically observed static and sliding contact behavior as the collective response of a large number of microscopic asperities. To that end, we build on Hulikal et al. (2015) and develop an efficient numerical framework that can be used to investigate how the macroscopic response of multiple frictional contacts depends on long-range elastic interactions, different constitutive assumptions about the deforming contacts and their local shear resistance, and surface roughness. We approximate the contact between two rough surfaces as that between a regular array of discrete deformable elements attached to a elastic block and a rigid rough surface. The deformable elements are viscoelastic or elasto/viscoplastic with a range of relaxation times, and the elastic interaction between contacts is long-range. We find that the model reproduces the main macroscopic features of evolution of contact and friction for a range of constitutive models of the elements, suggesting that macroscopic frictional response is robust with respect to the microscopic behavior. Viscoelasticity/viscoplasticity contributes to the increase of friction with contact time and leads to a subtle history dependence. Interestingly, long-range elastic interactions only change the results quantitatively compared to the meanfield response. The developed numerical framework can be used to study how specific observed macroscopic behavior depends on the microscale assumptions. For example, we find that sustained increase in the static friction coefficient during long hold times suggests viscoelastic response of the underlying material with multiple relaxation time scales. We also find that the experimentally observed proportionality of the direct effect in velocity jump experiments to the logarithm of the velocity jump points to a complex material-dependent shear resistance at the microscale.", "doi": "10.1016/j.jmps.2018.03.022", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2018-07", "volume": "116", "pages": "217-238" }, { "id": "authors:70t37-k4742", "collection": "authors", "collection_id": "70t37-k4742", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170817-075028405", "type": "article", "title": "Pulse-Like Partial Ruptures and High-Frequency Radiation at Creeping-Locked Transition during Megathrust Earthquakes", "author": [ { "family_name": "Michel", "given_name": "Sylvain", "orcid": "0000-0001-7878-6603", "clpid": "Michel-S" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" } ], "abstract": "Megathrust earthquakes tend to be confined to fault areas locked in the interseismic period and often rupture them only partially. For example, during the 2015 M7.8 Gorkha earthquake, Nepal, a slip pulse propagating along strike unzipped the bottom edge of the locked portion of the Main Himalayan Thrust (MHT). The lower edge of the rupture produced dominant high-frequency (>1 Hz) radiation of seismic waves. We show that similar partial ruptures occur spontaneously in a simple dynamic model of earthquake sequences. The fault is governed by standard laboratory-based rate-and-state friction with the aging law and contains one homogenous velocity-weakening (VW) region embedded in a velocity-strengthening (VS) area. Our simulations incorporate inertial wave-mediated effects during seismic ruptures (they are thus fully dynamic) and account for all phases of the seismic cycle in a self-consistent way. Earthquakes nucleate at the edge of the VW area and partial ruptures tend to stay confined within this zone of higher prestress, producing pulse-like ruptures that propagate along strike. The amplitude of the high-frequency sources is enhanced in the zone of higher, heterogeneous stress at the edge of the VW area.", "doi": "10.1002/2017GL074725", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2017-08-28", "series_number": "16", "volume": "44", "issue": "16", "pages": "8345-8351" }, { "id": "authors:vqwwm-zx574", "collection": "authors", "collection_id": "vqwwm-zx574", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171005-104503035", "type": "article", "title": "Connecting depth limits of interseismic locking, microseismicity, and large earthquakes in models of long-term fault slip", "author": [ { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Thickness of the seismogenic zone is commonly determined based on the depth of microseismicity or the fault locking depth inferred from geodetic observations. The relation between the two estimates and their connection to the depth limit of large earthquakes remain elusive. Here we explore the seismic and geodetic observables in models of faults governed by laboratory-based friction laws that combine quasi-static rate-and-state friction and enhanced dynamic weakening. Our models suggest that the transition between the locked and fully creeping regions can occur over a broad depth range. The effective locking depth, D_(elock), associated with concentrated loading and promoting microseismicity, is located at the top of this transition zone; the geodetic locking depth, D_(glock), inverted from surface geodetic observations, corresponds to the depth of fault creeping with approximately half of the long-term rate. Following large earthquakes, D_(elock) either stays unchanged or becomes shallower due to creep penetrating into the shallower locked areas, whereas D_(glock) deepens as the slip deficit region expands, compensating for the afterslip. As the result, the two locking depths diverge in the late interseismic period, consistent with available seismic and geodetic observations from several major fault segments in Southern California. We find that D_(glock) provides a bound on the depth limit of large earthquakes in our models. However, the assumed layered distribution of fault friction and simple depth estimates are insufficient to characterize more heterogeneous faults, e.g., ones with significant along-strike variations. Improved observations and models are needed to illuminate physical properties and seismic potential of fault zones.", "doi": "10.1002/2017JB014030", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2017-08", "series_number": "8", "volume": "122", "issue": "8", "pages": "6491-6523" }, { "id": "authors:y52z8-p2409", "collection": "authors", "collection_id": "y52z8-p2409", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170629-084215836", "type": "article", "title": "Understanding dynamic friction through spontaneously evolving laboratory earthquakes", "author": [ { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-Vito" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Friction plays a key role in how ruptures unzip faults in the Earth's crust and release waves that cause destructive shaking. Yet dynamic friction evolution is one of the biggest uncertainties in earthquake science. Here we report on novel measurements of evolving local friction during spontaneously developing mini-earthquakes in the laboratory, enabled by our ultrahigh speed full-field imaging technique. The technique captures the evolution of displacements, velocities and stresses of dynamic ruptures, whose rupture speed range from sub-Rayleigh to supershear. The observed friction has complex evolution, featuring initial velocity strengthening followed by substantial velocity weakening. Our measurements are consistent with rate-and-state friction formulations supplemented with flash heating but not with widely used slip-weakening friction laws. This study develops a new approach for measuring local evolution of dynamic friction and has important implications for understanding earthquake hazard since laws governing frictional resistance of faults are vital ingredients in physically-based predictive models of the earthquake source.", "doi": "10.1038/ncomms15991", "pmcid": "PMC5493769", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2017-06-28", "volume": "8", "pages": "Art. No. 15991" }, { "id": "authors:kbgv8-msj95", "collection": "authors", "collection_id": "kbgv8-msj95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170615-065728719", "type": "article", "title": "The relation between a microscopic threshold-force model and macroscopic models of adhesion", "author": [ { "family_name": "Hulikal", "given_name": "Srivatsan", "clpid": "Hulikal-S" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solids 76, 144\u2013161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally, while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study rough-surface adhesion.", "doi": "10.1007/s10409-016-0630-y", "issn": "0567-7718", "publisher": "Springer Verlag", "publication": "Acta Mechanica Sinica", "publication_date": "2017-06", "series_number": "3", "volume": "33", "issue": "3", "pages": "508-515" }, { "id": "authors:27jtn-xg898", "collection": "authors", "collection_id": "27jtn-xg898", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170317-102149527", "type": "article", "title": "Rate-and-state friction properties of the Longitudinal Valley Fault from kinematic and dynamic modeling of seismic and aseismic slip", "author": [ { "family_name": "Thomas", "given_name": "Marion Y.", "orcid": "0000-0002-4335-8841", "clpid": "Thomas-M-Y" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "The Longitudinal Valley Fault (LVF, Taiwan) is a fast slipping fault (\u223c5 cm/yr), which exhibits both seismic, and aseismic slip. Geodetic and seismological observations (1992-2010) were used to infer the temporal evolution of fault slip [Thomas et al., 2014a]. This kinematic model is used here to estimate spatial variations of steady-state velocity dependence of fault friction and to develop a simplified fully-dynamic rate-and-state model of the LVF. Based on the postseismic slip, we estimate that the rate-and-state parameter (a \u2013 b) \u03c3[over-bar] decreases from \u223c1.2 MPa near the surface to near velocity-neutral at 19 km depth. The inferred (a \u2212 b) values are consistent with the laboratory measurements on clay-rich fault gouges comparable to the Lichi M\u00e9lange, which borders the LVF. The dynamic model that incorporates the obtained (a \u2013 b) \u03c3[over-bar] estimates as well as a VW patch with tuned rate-and-state properties produces a sequence of earthquakes with some realistic diversity and a spatio-temporal pattern of seismic and aseismic slip similar to that inferred from the kinematic modeling. The larger events have moment magnitude (M_w\u223c6.7) similar to the 2003 Chenkung earthquake, with a range of smaller events. The model parameterization allows reproducing partial overlap of seismic and aseismic slip before the earthquake, but cannot reproduce the significant postseismic slip observed in the previously locked patch. We discuss factors that can improve the dynamic model in that regard, including the possibility of temporal variations in (a \u2212 b) due to shear heating. Such calibrated dynamic models can be used to reconcile field observations, kinematic analysis, and laboratory experiments, and assess fault behavior.", "doi": "10.1002/2016JB013615", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2017-04", "series_number": "4", "volume": "122", "issue": "4", "pages": "3115-3137" }, { "id": "authors:pdz7g-b0b04", "collection": "authors", "collection_id": "pdz7g-b0b04", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161011-133057552", "type": "article", "title": "Repeating microearthquake sequences interact predominantly through postseismic slip", "author": [ { "family_name": "Lui", "given_name": "Semechah K. Y.", "orcid": "0000-0001-7801-3635", "clpid": "Lui-Semechah-K-Y" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Studying small repeating earthquakes enables better understanding of fault physics and characterization of fault friction properties. Some of the nearby repeating sequences appear to interact, such as the 'San Francisco' and 'Los Angeles' repeaters on the creeping section of the San Andreas Fault. It is typically assumed that such interactions are induced by static stress changes due to coseismic slip. Here we present a study of the interaction of repeating earthquakes in the framework of rate-and-state fault models using state-of-the-art simulation methods that reproduce both realistic seismic events and long-term earthquake sequences. Our simulations enable comparison among several types of stress transfer that occur between the repeating events. Our major finding is that postseismic creep dominates the interaction, with earthquake triggering occurring at distances much larger than typically assumed. Our results open a possibility of using interaction of repeating sequences to constrain friction properties of creeping segments.", "doi": "10.1038/ncomms13020", "pmcid": "PMC5059473", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2016-10-05", "volume": "7", "pages": "Art. No. 13020" }, { "id": "authors:zfd6f-6q534", "collection": "authors", "collection_id": "zfd6f-6q534", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160818-075652559", "type": "article", "title": "Evidence for non-self-similarity of microearthquakes recorded at a Taiwan borehole seismometer array", "author": [ { "family_name": "Lin", "given_name": "Yen-Yu", "orcid": "0000-0002-6971-3960", "clpid": "Lin-Yen-Yu" }, { "family_name": "Ma", "given_name": "Kuo-Fong", "clpid": "Ma-Kuo-Fong" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Song", "given_name": "Teh-Ru Alex", "orcid": "0000-0003-3697-5881", "clpid": "Song-Teh-Ru-Alex" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Tsai", "given_name": "Victor C.", "orcid": "0000-0003-1809-6672", "clpid": "Tsai-V-C" } ], "abstract": "We investigate the relationship between seismic moment M_0 and source duration t_w of microearthquakes by using high-quality seismic data recorded with a vertical borehole array installed in central Taiwan. We apply a waveform cross-correlation method to the three-component records and identify several event clusters with high waveform similarity, with event magnitudes ranging from 0.3 to 2.0. Three clusters\u2014Clusters A, B and C\u2014contain 11, 8 and 6 events with similar waveforms, respectively. To determine how M_0 scales with t_w, we remove path effects by using a path-averaged Q. The results indicate a nearly constant t_w for events within each cluster, regardless of M_0, with mean values of t_w being 0.058, 0.056 and 0.034 s for Clusters A, B and C, respectively. Constant t_w, independent of M_0, violates the commonly used scaling relation t_w \u221d M^(1/3)_0. This constant duration may arise either because all events in a cluster are hosted on the same isolated seismogenic patch, or because the events are driven by external factors of constant duration, such as fluid injections into the fault zone. It may also be related to the earthquake nucleation size.", "doi": "10.1093/gji/ggw172", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2016-08", "series_number": "2", "volume": "206", "issue": "2", "pages": "757-773" }, { "id": "authors:qae8q-mny68", "collection": "authors", "collection_id": "qae8q-mny68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160613-091714645", "type": "article", "title": "Deeper penetration of large earthquakes on seismically quiescent faults", "author": [ { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Why many major strike-slip faults known to have had large earthquakes are silent in the interseismic period is a long-standing enigma. One would expect small earthquakes to occur at least at the bottom of the seismogenic zone, where deeper aseismic deformation concentrates loading. We suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes. We support this conclusion with numerical simulations of fault behavior and observations of recent major events. Our modeling implies that the 1857 Fort Tejon earthquake on the San Andreas Fault in Southern California penetrated below the seismogenic zone by at least 3 to 5 kilometers. Our findings suggest that such deeper ruptures may occur on other major fault segments, potentially increasing the associated seismic hazard.", "doi": "10.1126/science.aaf1496", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2016-06-10", "series_number": "6291", "volume": "352", "issue": "6291", "pages": "1293-1297" }, { "id": "authors:e5v37-h6325", "collection": "authors", "collection_id": "e5v37-h6325", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150416-154546979", "type": "article", "title": "Numerical modeling of long-term earthquake sequences on the NE Japan megathrust: Comparison with observations and implications for fault friction", "author": [ { "family_name": "Cubas", "given_name": "Nadaya", "clpid": "Cubas-N" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Perfettini", "given_name": "Hugo", "orcid": "0000-0001-6829-5472", "clpid": "Perfettini-H" } ], "abstract": "We use numerical modeling to investigate fault properties that explain key features of the 2011 Mw 9.0 Tohoku-Oki earthquake as well as the overall regional behavior of the NE Japan megathrust. In particular, we study the possibility that slip near the trench resulted from thermal pressurization on a shallow patch of the megathrust, and investigate whether low-velocity friction on that patch is rate-strengthening or rate-weakening. Our models also contain a deeper rate-weakening patch, not prone to efficient thermal pressurization, to account for the moderate-sized interplate seismicity. We produce earthquake sequences and aseismic slip in our models using 2D dynamic simulations that incorporate shear-induced temperature variations and the associated change in pore fluid pressure to capture thermal pressurization. We find that all our models can reproduce more frequent deeper moderate (Mw 7.5) events and less frequent larger events with substantial slip at shallow depth, as observed along the Fukushima\u2013Miyagi segment of the Japan megathrust. However, only the scenario with a sufficiently rate-strengthening patch can match the thousand-year recurrence time of Tohoku-Oki-like earthquakes suggested by the historical and geological record, due to co-existence of seismic and aseismic slip at the shallow depths. This scenario also reproduces other characteristics of the Tohoku-Oki earthquake: the trenchward-skewed distribution of slip, the backward re-rupture of the deeper patch, as well as the weaker radiation at high frequency of the shallower portion of the rupture in spite of its larger slip.", "doi": "10.1016/j.epsl.2015.03.002", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "2015-06-01", "volume": "419", "pages": "187-198" }, { "id": "authors:vep55-wns78", "collection": "authors", "collection_id": "vep55-wns78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140603-102932593", "type": "article", "title": "Collective behavior of viscoelastic asperities as a model for static and kinetic friction", "author": [ { "family_name": "Hulikal", "given_name": "Srivatsan", "clpid": "Hulikal-S" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "We propose a statistical model for static and sliding friction between rough surfaces. Approximating the contact between rough surfaces by the contact of an ensemble of one-dimensional viscoelastic elements with a rough rigid surface, we study the collective behavior of the elements. We find that collective response of the contacts can lead to macroscopic behavior very different from the microscopic behavior. Specifically, various observed features of friction emerge as collective phenomena, without postulating them directly at the microscale. We discuss how parameters in our model can be related to material and surface properties of the contacting surfaces. We compare our results to commonly used rate and state phenomenological models, and propose a new interpretation of the state variable.", "doi": "10.1016/j.jmps.2014.10.008", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2015-03", "volume": "76", "pages": "144-161" }, { "id": "authors:fcdba-ht686", "collection": "authors", "collection_id": "fcdba-ht686", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150402-135439354", "type": "article", "title": "Static Laboratory Earthquake Measurements with the Digital Image Correlation Method", "author": [ { "family_name": "Rubino", "given_name": "V.", "orcid": "0000-0002-4023-8668", "clpid": "Rubino-V" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "A. J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Leprince", "given_name": "S.", "orcid": "0000-0003-4555-8975", "clpid": "Leprince-S" }, { "family_name": "Avouac", "given_name": "J. P.", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "abstract": "Mapping full-field displacement and strain changes on the Earth's surface following an earthquake is of paramount importance to enhance our understanding of earthquake mechanics. Currently, aerial and satellite images taken pre- and post-earthquake can be processed with sub-pixel correlation algorithms to infer the co-seismic ground deformations (e.g., [1, 2]). However, the interpretation of this data is not straightforward due to the inherent complexity of natural faults and deformation fields. To gain understanding into rupture mechanics and to help interpret complex rupture features occurring in nature, we develop a laboratory earthquake setup capable of reproducing displacement and strain maps similar to those obtained in the field, while maintaining enough simplicity so that clear conclusions can be drawn. Earthquakes are mimicked in the laboratory by dynamic rupture propagating along an inclined frictional interface formed by two Homalite plates under compression (e.g., [3]). In our study, the interface is partially glued, in order to confine the rupture before it reaches the ends of the specimen. The specimens are painted with a speckle pattern to provide the surface with characteristic features for image matching. Images of the specimens are taken before and after dynamic rupture with a 4 Megapixels resolution CCD camera. The digital images are analyzed with two software packages for sub-pixel correlation: VIC-2D (Correlated Solutions Inc.) and COSI-Corr. Both VIC-2D and COSI-Corr are able to characterize the full-field static displacement of the experimentally produced dynamic shear ruptures. The correlation analysis performed with either software clearly shows (i) the relative displacement (slip) along the frictional interface, (ii) the rupture arrest on the glued boundaries, and (iii) the presence of wing cracks. The obtained displacement measurements are converted to strains, using non-local de-noising techniques; stresses are obtained by introducing Homalite's constitutive properties. This study is a first step towards using the digital image correlation method in combination with high-speed photography to capture the highly transient phenomena involved in dynamic rupture.", "doi": "10.1007/s11340-014-9893-z", "issn": "0014-4851", "publisher": "Springer", "publication": "Experimental Mechanics", "publication_date": "2015-01", "series_number": "1", "volume": "55", "issue": "1", "pages": "77-94" }, { "id": "authors:gmyy0-ff333", "collection": "authors", "collection_id": "gmyy0-ff333", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150108-082122516", "type": "article", "title": "Resolution of Rise Time in Earthquake Slip Inversions: Effect of Station Spacing and Rupture Velocity", "author": [ { "family_name": "Somala", "given_name": "Surendra Nadh", "clpid": "Somala-S-N" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Earthquake finite\u2010source inversions provide us with a window into earthquake dynamics and physics. Unfortunately, rise time, an important source parameter that describes the local slip duration, is still quite poorly resolved. This may be at least partly due to sparsity of currently available seismic networks, which have average sensor spacing of a few tens of kilometers at best. However, next generation observation systems could increase the density of sensing by orders of magnitude. Here, we explore whether such dense networks would improve the resolution of the rise time in idealized scenarios. We consider steady\u2010state pulselike ruptures with spatially uniform slip, rise time, and rupture speed and either Haskell or Yoffe slip\u2010rate function on a vertical strike\u2010slip fault. Synthetic data for various network spacings are generated by forward wave propagation simulations, and then source inversions are carried out using that data. The inversions use a nonparametric linear inversion method that does not impose any restrictions on rupture complexity, rupture velocity, or rise time. We show that rupture velocity is an important factor in determining the rise\u2010time resolution. For sub\u2010Rayleigh rupture speeds, there is a characteristic length related to the decay of the wavefield away from the fault that depends on rupture speed and rise time such that only networks with smaller station spacings can adequately resolve the rise time. For supershear ruptures, the wavefield contains homogeneous S waves the decay of which is much slower, and an adequate resolution of the rise time can be achieved for all station spacings considered in this study (up to few tens of kilometers). Finally, we find that even if dense measurements come at the expense of large noise (e.g., 1\u2009\u2009cm/s noise for space\u2010based optical systems), the conclusions on the performance of dense networks still hold.", "doi": "10.1785/0120130185", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "2014-12", "series_number": "6", "volume": "104", "issue": "6", "pages": "2717-2734" }, { "id": "authors:23djw-hrq80", "collection": "authors", "collection_id": "23djw-hrq80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140828-112246557", "type": "article", "title": "Response of rate-and-state seismogenic faults to harmonic shear-stress perturbations", "author": [ { "family_name": "Ader", "given_name": "Thomas J.", "clpid": "Ader-T-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" } ], "abstract": "Field and laboratory observations show that seismicity has non-trivial period-dependent response to periodic stress perturbations. In Nepal, seismicity shows significant variations in response to annual monsoon-induced stress variations but not to semidiurnal tidal stresses of the same magnitude. Such period dependence cannot be explained by the Coulomb failure model and spring-slider rate-and-state model (SRM). Here, we study seismicity response to periodic stress perturbations in a 2-D continuum model of a rate-and-state fault (that is, a finite rate-and-state fault). We find that the resulting seismicity indeed exhibits nearly periodic variations. Their amplitude is maximum at a certain period, T_a, and decreases with smaller and larger periods to the SRM predictions, remaining much larger than the SRM predictions for a wide range of periods around T_a. We attribute the higher sensitivity of finite faults to their finite nucleation zones which vary in space and have a different slip-velocity evolution than that of the SRM. At periods T \u226b T_a and T \u226a T_a, the seismicity-rate variations are in phase with the stress-rate and stress variations, respectively, consistent with the SRM, although a gradual phase shift appears as T increases towards T_a. Based on the similarities with the SRM and our simulations, we propose a semi-analytical expression for T_a. Plausible sets of model parameters make T_a equal to 1\u2009yr, potentially explaining Nepal observations and constraining the fault properties. Our finite-fault findings indicate that a\u03c3, where a is a rate-and-state parameter and \u03c3 is the effective normal stress, can be severely underestimated based on the SRM.", "doi": "10.1093/gji/ggu144", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2014-07", "series_number": "1", "volume": "198", "issue": "1", "pages": "385-413" }, { "id": "authors:tc3en-62n23", "collection": "authors", "collection_id": "tc3en-62n23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140703-104019674", "type": "article", "title": "Quasi-dynamic versus fully dynamic simulations of earthquakes and aseismic slip with and without enhanced coseismic weakening", "author": [ { "family_name": "Thomas", "given_name": "Marion Y.", "orcid": "0000-0002-4335-8841", "clpid": "Thomas-M-Y" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Noda", "given_name": "Hiroyuki", "clpid": "Noda-Hiroyuki" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "abstract": "Physics-based numerical simulations of earthquakes and slow slip, coupled with field observations and laboratory experiments, can, in principle, be used to determine fault properties and potential fault behaviors. Because of the computational cost of simulating inertial wave-mediated effects, their representation is often simplified. The quasi-dynamic (QD) approach approximately accounts for inertial effects through a radiation damping term. We compare QD and fully dynamic (FD) simulations by exploring the long-term behavior of rate-and-state fault models with and without additional weakening during seismic slip. The models incorporate a velocity-strengthening (VS) patch in a velocity-weakening (VW) zone, to consider rupture interaction with a slip-inhibiting heterogeneity. Without additional weakening, the QD and FD approaches generate qualitatively similar slip patterns with quantitative differences, such as slower slip velocities and rupture speeds during earthquakes and more propensity for rupture arrest at the VS patch in the QD cases. Simulations with additional coseismic weakening produce qualitatively different patterns of earthquakes, with near-periodic pulse-like events in the FD simulations and much larger crack-like events accompanied by smaller events in the QD simulations. This is because the FD simulations with additional weakening allow earthquake rupture to propagate at a much lower level of prestress than the QD simulations. The resulting much larger ruptures in the QD simulations are more likely to propagate through the VS patch, unlike for the cases with no additional weakening. Overall, the QD approach should be used with caution, as the QD simulation results could drastically differ from the true response of the physical model considered.", "doi": "10.1002/2013JB010615", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2014-03", "series_number": "3", "volume": "119", "issue": "3", "pages": "1986-2004" }, { "id": "authors:nnzw3-15242", "collection": "authors", "collection_id": "nnzw3-15242", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140613-101245398", "type": "article", "title": "Experimental investigation of strong ground motion due to thrust fault earthquakes", "author": [ { "family_name": "Gabuchian", "given_name": "Vahe", "clpid": "Gabuchian-V" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Oglesby", "given_name": "David D.", "clpid": "Oglesby-D-D" } ], "abstract": "Thrust fault earthquakes are studied in a laboratory earthquake setup previously used to investigate analog strike-slip seismic events. Dynamic mode II ruptures are generated along preexisting faults in an analog material, Homalite H-100, and their interaction with the free surface is studied for both sub-Rayleigh and supershear rupture speeds. High-speed digital photography and laser velocimeter diagnostics are used synergistically to identify and study the ground velocity signatures caused by the various features of the generated ruptures. The obtained surface-normal motions of both sub-Rayleigh and supershear ruptures show substantial asymmetry between the hanging and footwall, with the hanging wall experiencing much larger velocity amplitudes. The main features of the surface velocity traces at various stations can be explained by the calculated arrivals of various waves and fronts\u2014Mach cones, Pand S waves, and sub-Rayleigh features. In both the sub-Rayleigh and supershear cases, the arrival of the rupture tip generates a prominent Rayleigh wave traveling along the simulated Earth's surface. Supershear events feature larger amplitudes of ground shaking profiles. All signatures in the surface motion records attenuate and broaden with increasing distance from the fault trace. The signatures corresponding to the arrival of the Mach fronts attenuate with distance at a slower rate than those from sub-Rayleigh ruptures. The arrival of the updip supershear rupture at the free surface creates a downdip propagating slip feature with its own Mach cone. These additional Mach fronts further amplify ground shaking on the hanging and footwalls.", "doi": "10.1002/2013JB010409", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Solid Earth", "publication_date": "2014-02", "series_number": "2", "volume": "119", "issue": "2", "pages": "1316-1336" }, { "id": "authors:qevbf-c0w60", "collection": "authors", "collection_id": "qevbf-c0w60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131101-103258519", "type": "article", "title": "Kinematic Inversion of Physically Plausible Earthquake Source Models Obtained from Dynamic Rupture Simulations", "author": [ { "family_name": "Konca", "given_name": "Ali Ozgun", "clpid": "Konca-A-G" }, { "family_name": "Kaneko", "given_name": "Yoshihiro", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "abstract": "One approach to investigate earthquake source processes is to produce kinematic source models from inversion of seismic records and geodetic data. The setup of the inversion requires a variety of assumptions and constraints to restrict the range of possible models. Here, we evaluate to what extent physically plausible earthquake scenarios are reliably restituted in spite of these restrictions. We study which characteristics of ruptures, such as rupture velocity, slip distribution, stress drop, rise time, and slip function, can be reliably determined from the inversion of near\u2010field seismic and geodetic data. Using spontaneous dynamic rupture simulations, we generate five earthquake scenarios, each of which has different characteristics of the source process. Then we conduct a blind test by modeling the synthetic near\u2010source data using a standard inversion scheme that optimizes the fit to the observations while searching for solutions with minimum roughness. The inversion procedure assumes a rupture front propagating away from the hypocenter with variable rupture velocity and a simple cosine slip\u2010time function. Our results show that, overall, slip distribution and stress drop are reasonably well determined even for input models with relatively complex histories (such as a subshear rupture transitioning to supershear speeds). Depth\u2010averaged rupture velocities are also reasonably well resolved although their estimate progressively deteriorates away from the hypocenter. The local rise time and slip function are not well resolved, but there is some sensitivity to the rupture pulse width, which can be used to differentiate between pulse\u2010like and crack\u2010like ruptures. Our test for understanding the inaccuracies in Green's functions shows that random 3D perturbations of 5% standard deviation do not lead to significant degradation of the estimation of earthquake source parameters. As remedies to the current limitations, we propose smoothing slip function parameters and using more complicated inversion schemes only if data necessitates them.", "doi": "10.1785/0120120358", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "2013-10", "series_number": "5", "volume": "103", "issue": "5", "pages": "2621-2644" }, { "id": "authors:43a9t-nh566", "collection": "authors", "collection_id": "43a9t-nh566", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130718-112434964", "type": "article", "title": "Comparison of average stress drop measures for ruptures with\n heterogeneous stress change and implications for earthquake physics", "author": [ { "family_name": "Noda", "given_name": "Hiroyuki", "clpid": "Noda-Hiroyuki" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "abstract": "Stress drop, a measure of static stress change in earthquakes, is the subject of numerous investigations. Stress drop in an earthquake is likely to be spatially varying over the fault, creating a stress drop distribution. Representing this spatial distribution by a single number, as commonly done, implies averaging in space. In this study, we investigate similarities and differences between three different averages of the stress drop distribution used in earthquake studies. The first one, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM, is the commonly estimated stress drop based on the seismic moment and fault geometry/dimensions. It is known that \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM corresponds to averaging the stress drop distribution with the slip distribution due to uniform stress drop as the weighting function. The second one, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afA, is the simplest (unweighted) average of the stress drop distribution over the fault, equal to the difference between the average stress levels on the fault before and after an earthquake. The third one, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE, enters discussions of energy partitioning and radiation efficiency; we show that it corresponds to averaging the stress drop distribution with the actual final slip at each point as the weighting function. The three averages, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afA, and \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE, are often used interchangeably in earthquake studies and simply called 'stress drop'. Yet they are equal to each other only for ruptures with spatially uniform stress drop, which results in an elliptical slip distribution for a circular rupture. Indeed, we find that other relatively simple slip shapes\u2014such as triangular, trapezoidal or sinusoidal\u2014already result in stress drop distributions with notable differences between \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM, \u0394\u03c3\u00af\u00af\u00af\u00af\u00afA, and \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE. Introduction of spatial slip heterogeneity results in further systematic differences between them, with \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE always being larger than \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM, a fact that we have proven theoretically, and \u0394\u03c3\u00af\u00af\u00af\u00af\u00afA almost always being the smallest. In particular, the value of the energy-related \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE significantly increases in comparison to the moment-based \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM with increasing roughness of the slip distribution over the fault. Previous studies used \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM in place of \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE in computing the radiation ratio \u03b7R that compares the radiated energy in earthquakes to a characteristic part of their strain energy change. Typical values of \u03b7R for large earthquakes were found to be from 0.25 to 1. Our finding that \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE\u2265\u0394\u03c3\u00af\u00af\u00af\u00af\u00afM allows us to interpret the values of \u03b7R as the upper bound. We determine the restrictions placed by such estimates on the evolution of stress with slip at the earthquake source. We also find that \u0394\u03c3\u00af\u00af\u00af\u00af\u00afE can be approximated by \u0394\u03c3\u00af\u00af\u00af\u00af\u00afM if the latter is computed based on a reduced rupture area.", "doi": "10.1093/gji/ggt074", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2013-06", "series_number": "3", "volume": "193", "issue": "3", "pages": "1691-1712" }, { "id": "authors:chfhq-maj45", "collection": "authors", "collection_id": "chfhq-maj45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130208-131948816", "type": "article", "title": "Stable creeping fault segments can become destructive as a result of dynamic weakening", "author": [ { "family_name": "Noda", "given_name": "Hiroyuki", "clpid": "Noda-Hiroyuki" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Faults in Earth's crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M_w = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids, allowing unstable slip to occur in segments that can creep between events. The model parameters are based on laboratory measurements on samples from the fault of the M_w\u20097.6 1999 Chi-Chi earthquake. The long-term slip behaviour of the model, which we examine using a unique numerical approach that includes all wave effects, reproduces and explains a number of both long-term and coseismic observations\u2014some of them seemingly contradictory\u2014about the faults at which the Tohoku-Oki and Chi-Chi earthquakes occurred, including there being more high-frequency radiation from areas of lower slip, the largest seismic slip in the Tohoku-Oki earthquake having occurred in a potentially creeping segment, the overall pattern of previous events in the area and the complexity of the Tohoku-Oki rupture. The implication that earthquake rupture may break through large portions of creeping segments, which are at present considered to be barriers, requires a re-evaluation of seismic hazard in many areas.", "doi": "10.1038/nature11703", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2013-01-24", "series_number": "7433", "volume": "493", "issue": "7433", "pages": "518-521" }, { "id": "authors:jwegq-85b59", "collection": "authors", "collection_id": "jwegq-85b59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160318-162707037", "type": "article", "title": "A Geostationary Optical Seismometer, Proof of Concept", "author": [ { "family_name": "Michel", "given_name": "R.", "clpid": "Michel-R" }, { "family_name": "Ampuero", "given_name": "J.-P.", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Avouac", "given_name": "J.-P.", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Leprince", "given_name": "S.", "orcid": "0000-0003-4555-8975", "clpid": "Leprince-S" }, { "family_name": "Redding", "given_name": "D. C.", "clpid": "Redding-D-C" }, { "family_name": "Somala", "given_name": "S. N.", "clpid": "Somala-S-N" } ], "abstract": "We discuss the possibility of imaging the propagation\nof seismic waves from a very large space-based optical telescope.\nImages of seismic waves propagating at the Earth's surface would\nbe an invaluable source of information for investigating earthquake\nphysics and the effect of the subsurface on earthquake\nground motions. This application would require ground displacement\nmeasurements at about every 100 m, with centimetric accuracy,\nand temporal sampling on the order of 1 Hz. A large field\nof view (> 10^5 km^2) is required to measure the full extent of a\nlarge earthquake in the areas of interest. A geostationary optical\ntelescope with a large aperture appears to be the most promising\nsystem. We establish preliminary technical requirements for such\na system, which lead us to consider a telescope with an angular\nfield of view of 0.8\u00b0 and with an aperture greater than 4 m.\nWe discuss and quantify the various sources of noise that would\nlimit such a system: atmospheric turbulence, evolution of ground\nreflectance and solar incidence angle, and stability of the platform\nat 1 Hz. We present numerical simulations, which account for\nthese sources of noise. They show that key details of the seismic\nwave field, hardly detectable using ground-based instruments,\nwould indeed be imaged by such a system. At the upper limit of\nmodern technology, data flow would be about 20\u201350 Gb \u00b7 s^(\u22121), and\ndata memory would be about 50 Tb.", "doi": "10.1109/TGRS.2012.2201487", "issn": "0196-2892", "publisher": "IEEE", "publication": "IEEE Transactions on Geoscience and Remote Sensing", "publication_date": "2013-01", "series_number": "1", "volume": "51", "issue": "1", "pages": "695-703" }, { "id": "authors:rknxz-cb876", "collection": "authors", "collection_id": "rknxz-cb876", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120521-080956348", "type": "article", "title": "Under the Hood of the Earthquake Machine: Toward Predictive Modeling of the Seismic Cycle", "author": [ { "family_name": "Barbot", "given_name": "Sylvain", "orcid": "0000-0003-4257-7409", "clpid": "Barbot-S" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "abstract": "Advances in observational, laboratory, and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power. To explore that possibility, we developed an integrative and fully dynamic model of the Parkfield segment of the San Andreas Fault. The model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude (M_w) 6.0 main shocks\u2014including events similar to the ones in 1966 and 2004\u2014and provides an excellent match for the detailed interseismic, coseismic, and postseismic observations collected along this fault during the most recent earthquake cycle. Such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins.", "doi": "10.1126/science.1218796", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2012-05-11", "series_number": "6082", "volume": "336", "issue": "6082", "pages": "707-710" }, { "id": "authors:erd5a-74007", "collection": "authors", "collection_id": "erd5a-74007", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120522-091602624", "type": "article", "title": "On Averaging Interface Response During Dynamic Rupture and Energy Partitioning Diagrams for Earthquakes", "author": [ { "family_name": "Noda", "given_name": "Hiroyuki", "clpid": "Noda-Hiroyuki" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Earthquakes occur as dynamic shear cracks and convert part of the elastic strain energy into radiated and dissipated energy. Local evolution of shear strength that governs this process, which is variable in space and time, can be studied from laboratory experiments and rupture models. At the same time, increasingly accurate measurements of radiated energy and other quantities characterize earthquakes in a rupture-averaged way. Here, we present and study two approaches to averaging frictional dissipation during dynamic rupture. The first one is based on the actual progression of dissipation, but the associated averaged shear stress does not reflect the local friction behavior. The second one is constructed to preserve prevailing features of local stress-slip response and performs well in the examples studied. The developed approach should be useful for visualizing energy partitioning in dynamic models and linking them to observations using diagrams that reflect dominant features of local stress evolution.", "doi": "10.1115/1.4005964", "issn": "0021-8936", "publisher": "American Society Mechanical Engineers", "publication": "Journal of Applied Mechanics", "publication_date": "2012-05", "series_number": "3", "volume": "79", "issue": "3", "pages": "031026" }, { "id": "authors:1s5cm-6pg74", "collection": "authors", "collection_id": "1s5cm-6pg74", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120518-141701118", "type": "article", "title": "Special Issue Honoring Professor James R. Rice", "author": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Dunham", "given_name": "Eric", "clpid": "Dunham-E" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X", "clpid": "Gao-Huajian" } ], "abstract": "This issue of the Journal of Applied Mechanics is dedicated, with our admiration and affection, to Professor Jim Rice of Harvard University. It serves as the proceedings of the 3 days symposium on Mechanics in Geophysical and Materials Sciences, which was held at the California Institute of Technology during Jan. 20\u201322, 2011 to celebrate Jim's brilliant career on the occasion of his 70th birthday.", "doi": "10.1115/1.4005965", "issn": "0021-8936", "publisher": "American Society Mechanical Engineers", "publication": "Journal of Applied Mechanics", "publication_date": "2012-05", "series_number": "3", "volume": "79", "issue": "3", "pages": "Art. No. 030301" }, { "id": "authors:q3anv-n4v64", "collection": "authors", "collection_id": "q3anv-n4v64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111121-115155076", "type": "article", "title": "Spectral-element simulations of long-term fault slip: Effect of low-rigidity layers on earthquake-cycle dynamics", "author": [ { "family_name": "Kaneko", "given_name": "Y.", "clpid": "Kaneko-Y" }, { "family_name": "Ampuero", "given_name": "J.-P.", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "We develop a spectral element method for the simulation of long-term histories of spontaneous seismic and aseismic slip on faults subjected to tectonic loading. Our approach reproduces all stages of earthquake cycles: nucleation and propagation of earthquake rupture, postseismic slip and interseismic creep. We apply the developed methodology to study the effects of low-rigidity layers on the dynamics of the earthquake cycle in 2-D. We consider two cases: small (M ~ 1) earthquakes on a fault surrounded by a damaged fault zone and large (M ~ 7) earthquakes on a vertical strike-slip fault that cuts through shallow low-rigidity layers. Our results indicate how the source properties of repeating earthquakes are affected by the presence of a damaged fault zone with low rigidity. Compared to faults in homogeneous media, we find (1) reduction in the earthquake nucleation size, (2) amplification of slip rates during dynamic rupture propagation, (3) larger recurrence interval, and (4) smaller amount of aseismic slip. Based on linear stability analysis, we derive a theoretical estimate of the nucleation size as a function of the width and rigidity reduction of the fault zone layer, which is in good agreement with simulated nucleation sizes. We further examine the effects of vertically-stratified layers (e.g., sedimentary basins) on the nature of shallow coseismic slip deficit. Our results suggest that low-rigidity shallow layers alone do not lead to coseismic slip deficit. While the low-rigidity layers result in lower interseismic stress accumulation, they also cause dynamic amplification of slip rates, with the net effect on slip being nearly zero.", "doi": "10.1029/2011JB008395", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2011-10", "series_number": "B10", "volume": "116", "issue": "B10", "pages": "Art. No. B10313" }, { "id": "authors:ep27x-rqf95", "collection": "authors", "collection_id": "ep27x-rqf95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110118-135848695", "type": "article", "title": "Three-dimensional earthquake sequence simulations with evolving temperature and pore pressure due to shear heating: Effect of heterogeneous hydraulic diffusivity", "author": [ { "family_name": "Noda", "given_name": "Hiroyuki", "clpid": "Noda-Hiroyuki" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "A new methodology for three-dimensional (3-D) simulations of earthquake sequences is presented that accounts not only for inertial effects during seismic events but also for shear-induced temperature variations on the fault and the associated evolution of pore fluid pressure. In particular, the methodology allows to capture thermal pressurization (TP) due to frictional heating in a shear zone. One-dimensional (1-D) diffusion of heat and pore fluids in the fault-normal direction is incorporated using a spectral method, which is unconditionally stable, accurate with affordable computational resources, and highly suitable to earthquake sequence calculations that use variable time steps. The approach is used to investigate the effect of heterogeneous hydraulic properties by considering a fault model with two regions of different hydraulic diffusivities and hence different potential for TP. We find that the region of more efficient TP produces larger slip in model-spanning events. The slip deficit in the other region is filled with more frequent smaller events, creating spatiotemporal complexity of large events on the fault. Interestingly, the area of maximum slip in model-spanning events is not associated with the maximum temperature increase because of stronger dynamic weakening in that area. The region of more efficient TP has lower interseismic shear stress, which discourages rupture nucleation there, contrary to what was concluded in prior studies. Seismic events nucleate in the region of less efficient TP where interseismic shear stress is higher. In our model, hypocenters of large events do not occur in areas of large slip or large stress drop.", "doi": "10.1029/2010JB007780", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2010-12-10", "volume": "115", "pages": "Art. No. B12314" }, { "id": "authors:0qmj4-bxd18", "collection": "authors", "collection_id": "0qmj4-bxd18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110104-111925811", "type": "article", "title": "Rupture modes in laboratory earthquakes: Effect of fault prestress and nucleation conditions", "author": [ { "family_name": "Lu", "given_name": "Xiao", "clpid": "Lu-Xiao" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Seismic inversions show that earthquake risetimes may be much shorter than the overall rupture duration, indicating that earthquakes may propagate as self-healing, pulse-like ruptures. Several mechanisms for producing pulse-like ruptures have been proposed, including velocity-weakening friction, interaction of dynamic rupture with fault geometry and local heterogeneity, and effect of bimaterial contrast. We present experimental results on rupture mode selection in laboratory earthquakes occurring on frictional interfaces, which were prestressed both in compression and in shear. Our experiments demonstrate that pulse-like ruptures can exist in the absence of a bimaterial effect or of local heterogeneities. We find a systematic variation from crack-like to pulse-like rupture modes with both (1) decreasing nondimensional shear prestress and (2) decreasing absolute levels of shear and normal prestress for the same value of nondimensional shear prestress. Both pulse-like and crack-like ruptures can propagate with either sub-Rayleigh or supershear rupture speeds. Our experimental results are consistent with theories of ruptures on velocity-weakening interfaces, implying that velocity-weakening friction plays an important role in governing the dynamic behavior of earthquake ruptures. We show that there is no measurable fault-normal stress decrease on the fault plane due to the nucleation procedure employed in experiments, and hence, this is not a factor in the rupture mode selection. We find that pulse-like ruptures correspond to the levels of nondimensional shear prestress significantly lower than the static friction coefficient, suggesting that faults hosting pulse-like ruptures may operate at low levels of prestress compared to their static strength.", "doi": "10.1029/2009JB006833", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2010-12-01", "volume": "115", "pages": "Art. No. B12302" }, { "id": "authors:p8btb-p7644", "collection": "authors", "collection_id": "p8btb-p7644", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101220-135941841", "type": "article", "title": "Supershear transition due to a free surface in 3-D simulations of spontaneous dynamic rupture on vertical strike-slip faults", "author": [ { "family_name": "Kaneko", "given_name": "Y.", "clpid": "Kaneko-Y" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments. We study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike-slip faults. We find that locally supershear rupture near the free surface can occur due to (i) the generalized Burridge\u2013Andrews mechanism, that is, a supershear loading field between P- and SV-wave arrivals generated by the main rupture front at depths, and (ii) the phase conversion of SV to P-diffracted waves at the free surface. Weaker supershear slip due to the generalized Burridge\u2013Andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones. Dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion. Locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth. Such global supershear transition, which depends on prestress, can occur under prestress levels lower than the theoretical estimates for models with no free surface. Although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors, it may play an important role on natural faults, at least in those strike-slip earthquakes that accumulate significant surface slip.", "doi": "10.1016/j.tecto.2010.06.015", "issn": "0040-1951", "publisher": "Elsevier", "publication": "Tectonophysics", "publication_date": "2010-10-18", "series_number": "3-4", "volume": "493", "issue": "3-4", "pages": "272-284" }, { "id": "authors:6snq5-sbf24", "collection": "authors", "collection_id": "6snq5-sbf24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101213-113244215", "type": "article", "title": "Postseismic variations in seismic moment and recurrence interval of repeating earthquakes", "author": [ { "family_name": "Chen", "given_name": "Kate Huihusan", "clpid": "Chen-Kate-Huihusan" }, { "family_name": "B\u00fcrgmann", "given_name": "Roland", "orcid": "0000-0002-3560-044X", "clpid": "B\u00fcrgmann-R" }, { "family_name": "Nadeau", "given_name": "Robert M.", "clpid": "Nadeau-R-M" }, { "family_name": "Chen", "given_name": "Ting", "orcid": "0000-0002-9599-871X", "clpid": "Chen-Ting" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "In laboratory experiments, longer stationary contact time leads to larger seismic moment during repeated ruptures. However, not all observations in natural fault systems agree with the prediction. We analyze a subset of 34 M\u22120.4\u20132.1 repeating earthquake sequences (RES) from 1987 to 2009 at Parkfield to examine the variation of their recurrence properties in space and time. Following a 2004 M6 earthquake, many of the repeating events have greatly reduced recurrence intervals (Tr) that systematically increase with time. In addition to this change in timing, we also find systematic changes in seismic moment (Mo), where most sequences experienced an immediate increase in Mo and subsequent decay as Tr approached pre-quake durations. The RES at shallower depth tend to have a larger range in both Tr and Mo, whereas deeper RES show smaller variation. The shallowest RES with the greatest magnitude (M1.8\u20132.1) among the events we studied reveal a large variation in Tr but small variation in Mo. These observations are qualitatively consistent with earthquake simulations in 3D continuum fault models with rate- and state-dependent friction. In the models, RES are produced on velocity-weakening patches surrounded by velocity-strengthening fault areas. The models show that the degree of postseismic variation in Mo and Tr is a function of radius (r) and nucleation zone size (h*) of the velocity-weakening patch. A ratio of r/h* ~ 1 produces negative Mo\u2013Tr slopes, whereas larger ratios of r/h* yield weak positive slopes. Given the same nucleation size h* (i.e., the same frictional properties and effective normal stress), smaller radii and hence smaller seismic moments result in negative Mo\u2013Tr slopes, whereas larger radii and hence larger moments lead to weak positive Mo\u2013Tr slopes, which are consistent with observations. Conversely, with only a small percentage of its slip accumulated seismically, a small asperity appears to grow in Mo under high loading rate, which is contrary to the view that Mo should decrease due to a reduced strength recovery time.", "doi": "10.1016/j.epsl.2010.08.027", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "2010-10-15", "series_number": "1-2", "volume": "299", "issue": "1-2", "pages": "118-125" }, { "id": "authors:n7kpe-sfs51", "collection": "authors", "collection_id": "n7kpe-sfs51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100713-095100144", "type": "article", "title": "Pulse-like and crack-like dynamic shear ruptures on frictional interfaces: experimental evidence, numerical modeling, and implications", "author": [ { "family_name": "Lu", "given_name": "Xiao", "clpid": "Lu-Xiao" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" } ], "abstract": "Destructive large earthquakes occur as dynamic frictional ruptures along pre-existing interfaces (or faults) in the Earth's crust. One of the important issues in earthquake dynamics is the local duration of relative displacement or slip. Seismic inversions show that earthquakes may propagate as self-healing pulse-like ruptures, with local slip duration being much shorter than the overall rupture duration. Yet many classical models produce crack-like ruptures, with local slip durations comparable to the overall rupture duration. We study rupture modes in an experimental set up designed to mimic a fault prestressed both in compression and in shear. Our experiments demonstrate systematic variation from crack-like to pulse-like rupture modes as nondimensional shear prestress is decreased. The results of our experiments are consistent with theories of ruptures on interfaces with velocity-weakening friction. To consider the possibility that slip-weakening friction can also result in such rupture mode transition in the presence of the dynamic nucleation procedure employed by the experimental setup, we conduct numerical simulations with linear slip-weakening friction. In the simulations, we use the parameter regimes that were shown in previous studies to reproduce supershear transition distances obtained in the same experimental setup. We find that simulations with linear slip-weakening friction are unable to reproduce pulse-like ruptures, even in the presence of the dynamic initiation procedure. Our experimental results and simulations imply that velocity-weakening friction plays an important role in dynamic behavior of shear ruptures and needs to be included in earthquake models.", "doi": "10.1007/s10704-010-9479-4", "issn": "0376-9429", "publisher": "Springer", "publication": "International Journal of Fracture", "publication_date": "2010-05", "series_number": "1-2", "volume": "163", "issue": "1-2", "pages": "27-39" }, { "id": "authors:b90w9-nqx63", "collection": "authors", "collection_id": "b90w9-nqx63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100526-075511174", "type": "article", "title": "Towards inferring earthquake patterns from geodetic observations of interseismic coupling", "author": [ { "family_name": "Kaneko", "given_name": "Yoshihiro", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Ultimately, seismotectonic studies seek to provide ways of assessing the timing, magnitude and spatial extent of future earthquakes. Ample observations document the spatial variability in interseismic coupling, defined as a degree of locking of a fault during the period of stress build-up between seismic events: fully or nearly locked fault patches are often surrounded by aseismically creeping areas. However, it is unclear how these observations could help assess future earthquakes. Here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model. Our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction. We consider the long-term evolution of slip on a model fault where two seismogenic, locked segments are separated by an aseismically slipping patch where rupture is impeded. We find that the probability for a large earthquake to break through the rupture-impeding patch is correlated with the interseismic coupling averaged over this patch. In addition, the probability that an earthquake breaks through the rupture-impeding patch and interseismic coupling are both related to fault friction properties through a single non-dimensional parameter. Our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling, and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes.", "doi": "10.1038/NGEO843", "issn": "1752-0894", "publisher": "Nature Publishing Group", "publication": "Nature Geoscience", "publication_date": "2010-05", "series_number": "5", "volume": "3", "issue": "5", "pages": "363-369" }, { "id": "authors:y70h3-yw948", "collection": "authors", "collection_id": "y70h3-yw948", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091020-134142242", "type": "article", "title": "The roller coaster of fault friction", "author": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "During an earthquake, friction is a key control on the initiation, propagation and termination of fault motion.\nLaboratory experiments that use variable slip rates suggest that friction evolves in a more complex fashion than\ngenerally assumed.", "doi": "10.1038/ngeo645", "issn": "1752-0894", "publisher": "Nature Publishing Group", "publication": "Nature Geoscience", "publication_date": "2009-10", "series_number": "10", "volume": "2", "issue": "10", "pages": "676-677" }, { "id": "authors:2ypdb-w7626", "collection": "authors", "collection_id": "2ypdb-w7626", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091013-093449432", "type": "article", "title": "Three-dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip", "author": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Liu", "given_name": "Yi", "clpid": "Liu-Yi" } ], "abstract": "Fault processes involve complex patterns of seismic events and aseismic slip. This work develops a three-dimensional (3-D) methodology for simulating long-term history of spontaneous seismic and aseismic slip on a vertical planar strike-slip fault subjected to slow tectonic loading. Our approach reproduces all stages of earthquake cycles, from accelerating slip before dynamic instability, to rapid dynamic propagation of earthquake rupture, to postseismic slip, and to interseismic creep, including aseismic transients. We use the developed 3-D methodology to study interaction of fault slip with a small patch of higher normal stress over long-term slip history. For uniform initial prestress, dynamic rupture is significantly affected by the stronger patch in the first simulated event but not in subsequent ones. The change in behavior is due to redistribution of shear stress by prior slip, which demonstrates that distributions of fault strength and stress are related and illustrates the importance of simulating long slip histories even in studies of dynamic rupture. Despite no long-term effect on dynamic rupture, the small patch of higher normal stress influences nucleation processes and hence long-term slip patterns in the model. Comparison of the fully dynamic simulations and a widely used quasi-dynamic approach shows that the quasi-dynamic approach modifies long-term slip patterns in addition to resulting in much smaller slip velocities and rupture speeds during dynamic events. We show that the response of quasi-dynamic formulations with reduced radiation damping terms can be scaled to match the results of the standard quasi-dynamic formulation and hence cannot improve the comparison.", "doi": "10.1029/2008JB005934", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2009-09-16", "series_number": "B9", "volume": "114", "issue": "B9", "pages": "B09303" }, { "id": "authors:pz1pb-snr66", "collection": "authors", "collection_id": "pz1pb-snr66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090706-134648271", "type": "article", "title": "Analysis of supershear transition regimes in rupture experiments : the effect of nucleation conditions and friction parameters", "author": [ { "family_name": "Lu", "given_name": "Xiao", "clpid": "Lu-Xiao" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" } ], "abstract": "We consider the effect of the rupture initiation procedure on supershear transition of Mode II ruptures on interfaces governed by linear slip-weakening friction. Our study is motivated by recent experiments, which demonstrated the transition of spontaneous ruptures from sub-Rayleigh to supershear speeds in the laboratory. In these works the experiments were analysed using the Burridge\u2013Andrews model of supershear transition, in which a supershear daughter crack is nucleated in front of the main mother rupture. It was concluded that the critical slip of the linear slip-weakening formulation needs to be pressure-dependent for a good match with experiments. However, the dynamic rupture initiation mechanism in the experiments was conceptually different from the quasi-static one adopted in the numerical work used for comparison. Here, our goal is to determine the effect of the nucleation by numerically modelling the experiments using a rupture initiation procedure that captures the dynamic nature of the wire explosion mechanism used in the experiments. We find parameter regimes that match the experimentally observed transition distances for the entire range of experimental conditions. Our simulations show that the dynamic rupture initiation procedure significantly affects the resulting transition distances, shortening them by about 30\u201350 per cent compared to those predicted through the quasi-static rupture initiation process. Moreover, for some cases, the dynamic initiation procedure changes the very mode of transition, causing a direct supershear transition at the tip of the main rupture instead of the mother\u2013daughter mechanism. We find reasonable parameter regimes which match experimentally determined transition distances with both direct supershear transition at the rupture tip and the Burridge\u2013Andrews (mother\u2013daughter) mechanism, using both pressure-independent and pressure-dependent critical slip. The results show that there are trade-offs between the parameters of the rupture initiation procedure and the properties of interface friction. This underscores the importance of quantifying experimental parameters for proper interpretation of the experiments and highlights the importance of the rupture initiation procedure, in simulations of both experiments and real-life earthquake events.", "doi": "10.1111/j.1365-246X.2009.04091.x", "issn": "0956-540X", "publisher": "Royal Astronomical Society", "publication": "Geophysical Journal International", "publication_date": "2009-05", "series_number": "2", "volume": "177", "issue": "2", "pages": "717-732" }, { "id": "authors:yjfr4-bnr63", "collection": "authors", "collection_id": "yjfr4-bnr63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHEjgrb09", "type": "article", "title": "Scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model", "author": [ { "family_name": "Chen", "given_name": "Ting", "orcid": "0000-0002-9599-871X", "clpid": "Chen-Ting" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Because of short recurrence times and known locations, small repeating earthquakes present a rare predictable opportunity for detailed field observations. They are used to study fault creeping velocities, earthquake nucleation, stress drops, and other aspects of tectonophysics, earthquake mechanics, and seismology. An intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment, which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip. Here we show that a model of repeating earthquakes based on laboratory-derived rate and state friction laws reproduces the observed scaling. In the model, a small fault patch governed by steady state velocity-weakening friction is surrounded by a much larger velocity-strengthening region. Long-term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events. The model results in repeating earthquakes with typical stress drops and sizes comparable with observations. For a fixed set of friction parameters, the observed scaling is reproduced by varying the size of the velocity-weakening patch. In simulations, a significant part of slip on the velocity-weakening patches is accumulated aseismically, even though the patches also produce seismic events. The proposed model supplies a laboratory-based framework for interpreting the wealth of observations about repeating earthquakes, provides indirect evidence that rate and state friction acts on natural faults, and has important implications for possible scenarios of slip partition into seismic and aseismic parts.", "doi": "10.1029/2008JB005749", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2009-01", "series_number": "B1", "volume": "114", "issue": "B1", "pages": "Art. No. B01311" }, { "id": "authors:v2f42-7qd58", "collection": "authors", "collection_id": "v2f42-7qd58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:HARsrl09", "type": "article", "title": "The SCEC/USGS Dynamic Earthquake Rupture Code Verification Exercise", "author": [ { "family_name": "Harris", "given_name": "R. A.", "clpid": "Harris-R-A" }, { "family_name": "Barall", "given_name": "M.", "clpid": "Barall-M" }, { "family_name": "Archuleta", "given_name": "R.", "clpid": "Archuleta-R" }, { "family_name": "Dunham", "given_name": "E.", "clpid": "Dunham-E" }, { "family_name": "Aagaard", "given_name": "B. T.", "orcid": "0000-0002-8795-9833", "clpid": "Aagaard-B-T" }, { "family_name": "Ampuero", "given_name": "J. P.", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Bhat", "given_name": "H.", "clpid": "Bhat-H" }, { "family_name": "Cruz-Atienza", "given_name": "V.", "clpid": "Cruz-Atienza-V" }, { "family_name": "Dalguer", "given_name": "L.", "clpid": "Dalguer-L" }, { "family_name": "Dawson", "given_name": "P.", "clpid": "Dawson-P" }, { "family_name": "Day", "given_name": "S.", "clpid": "Day-S" }, { "family_name": "Duan", "given_name": "B.", "clpid": "Duan-B" }, { "family_name": "Ely", "given_name": "G.", "clpid": "Ely-G" }, { "family_name": "Kaneko", "given_name": "Y.", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" }, { "family_name": "Kase", "given_name": "Y.", "clpid": "Kase-Y" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Liu", "given_name": "Y.", "clpid": "Liu-Y" }, { "family_name": "Ma", "given_name": "S.", "clpid": "Ma-S" }, { "family_name": "Oglesby", "given_name": "D.", "clpid": "Oglesby-D" }, { "family_name": "Olsen", "given_name": "K.", "clpid": "Olsen-Kim" }, { "family_name": "Pitarka", "given_name": "A.", "clpid": "Pitarka-A" }, { "family_name": "Song", "given_name": "S.", "clpid": "Song-S" }, { "family_name": "Templeton", "given_name": "E.", "clpid": "Templeton-E" } ], "abstract": "Numerical simulations of earthquake rupture dynamics are now common, yet it has been difficult to test the validity of thesesimulations because there have been few field observations and no analytic solutions with which to compare the results. This paper describes the Southern California Earthquake Center/U.S. Geological Surve(SCEC/USGS) Dynamic Earthquake Rupture Code Verification Exercise, where codes that simulate spontaneous rupture dynamics in three dimensions are evaluated and the results produced by these codes are compared using Web-based tools. This is the first time that a broad and rigorous examination of numerous spontaneous rupture codes has been performed\u2014a significant advance in this science. The automated process developed to attain this achievement provides for a future where testing of codes is easily accomplished. \n\nScientists who use computer simulations to understand earthquakes utilize a range of techniques. Most of these assume that earthquakes are caused by slip at depth on faults in the Earth, but hereafter the strategies vary. Among the methods used in earthquake mechanics studies are kinematic approaches and dynamic approaches. \n \nThe kinematic approach uses a computer code that prescribes the spatial and temporal evolution of slip on the causative fault (or faults). These types of simulations are very helpful, especially since they can be used in seismic data inversions to relate the ground motions recorded in the field to slip on the fault(s) at depth. However, these kinematic solutions generally provide no insight into the physics driving the fault slip or information about why the involved fault(s) slipped that much (or that little). In other words, these kinematic solutions may lack information about the physical dynamics of earthquake rupture that will be most helpful in forecasting future events. \n\nTo help address this issue, some researchers use computer codes to numerically simulate earthquakes and construct dynamic, spontaneous rupture (hereafter called \"spontaneous rupture\") solutions. For these types of numerical simulations, rather than prescribing the slip function at each location on the fault(s), just the friction constitutive properties and initial stress conditions are prescribed. The subsequent stresses and fault slip spontaneously evolve over time as part of the elasto-dynamic solution. Therefore, spontaneous rupture computer simulations of earthquakes allow us to include everything that we know, or think that we know, about earthquake dynamics and to test these ideas against earthquake observations.", "doi": "10.1785/gssrl.80.1.119", "issn": "0895-0695", "publisher": "Seismological Society of America", "publication": "Seismological Research Letters", "publication_date": "2009-01", "series_number": "1", "volume": "80", "issue": "1", "pages": "119-126" }, { "id": "authors:2nv6g-3aq10", "collection": "authors", "collection_id": "2nv6g-3aq10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:KANjgrb08b", "type": "article", "title": "Variability of earthquake nucleation in continuum models of rate-and-state faults and implications for aftershock rates", "author": [ { "family_name": "Kaneko", "given_name": "Y.", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Using two continuum models of rate-and-state faults, one with a weaker patch and the other with rheological transition from steady state velocity-weakening to velocity-strengthening friction, we simulate several scenarios of spontaneous earthquake nucleation plausible for natural faults, investigate their response to static shear stress steps, and infer the corresponding aftershock rates. Overall, nucleation processes at weaker patches behave similarly to theories based on spring-slider models, with some notable deviations. In particular, nucleation and aftershock rates are affected by normal stress heterogeneity in the nucleation zone. Nucleation processes at rheological transitions behave differently, producing complex slip velocity histories, nonmonotonic responses to static stress changes, and aftershock rates with pronounced peaks and seismic quiescence. For such processes, positive stress steps sometimes delay nucleation of seismic events by inducing aseismic transients that relieve stress and postpone seismic slip. Superposition of the complex aftershock response for spatially variable stress changes results in Omori's law for a period of time followed by seismic quiescence. Such behavior was observed at the base of the seismogenic zone near the 1984 Morgan Hill earthquake. We show that the computed aftershock rates are linked to unperturbed slip velocity evolution in the nucleation zone and construct simplified analytical scenarios that explain some features of the response. The qualitative differences that we find between the two nucleation models indicate that aftershock response of rate-and-state faults to static stress changes would depend on the conditions under which nucleation occurs on natural faults and may be different from predictions based on spring-slider models.", "doi": "10.1029/2007JB005154", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2008-12-31", "series_number": "B12", "volume": "113", "issue": "B12", "pages": "B12312" }, { "id": "authors:ef0e7-2dd15", "collection": "authors", "collection_id": "ef0e7-2dd15", "cite_using_url": "https://resolver.caltech.edu/CaltechSOLIDS:2008.001", "type": "article", "title": "Spectral-element modeling of spontaneous earthquake rupture on rate and state faults: Effect of velocity-strengthening friction at shallow depths", "author": [ { "family_name": "Kaneko", "given_name": "Y.", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" }, { "family_name": "Lapusta", "given_name": "N.", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Ampuero", "given_name": "J.-P.", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" } ], "abstract": "We develop a spectral-element methodology (SEM) for simulating dynamic rupture on rate and state faults and use it to study how the rupture is affected by a shallow fault region of steady-state velocity-strengthening friction. Our comparison of the developed SEM and a spectral boundary-integral method (BIM) for an anti-plane (two-dimensional) test problem shows that the two methods produce virtually identical solutions for the finest resolution we use and that the convergence with grid reduction of the developed SEM methodology is comparable to that of BIM. We also use the test problem to compare numerical resolution required for different state evolution laws and for linear slip-weakening friction. Using our three-dimensional implementation of the methodology, we find that a shallow velocity-strengthening fault region can significantly alter dynamic rupture and ground motion. The velocity-strengthening region suppresses supershear propagation at the free surface occurring in the absence of such region, which could explain the lack of universally observed supershear rupture near the free surface. In addition, the velocity-strengthening region promotes faster fall-off of slip velocity behind the rupture front and decreases final slip throughout the entire fault, causing a smaller average stress drop. The slip decrease is largest in the shallow parts of the fault, resulting in the depth profile of slip qualitatively consistent with observations of shallow co-seismic slip deficit. The shallow velocity-strengthening region also reduces the amplification of strong ground motion due to a low-velocity bulk structure.", "doi": "10.1029/2007JB005553", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2008-09", "series_number": "B9", "volume": "113", "issue": "B9", "pages": "Art. No. B09317" }, { "id": "authors:a5zqr-t1b55", "collection": "authors", "collection_id": "a5zqr-t1b55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130311-073945463", "type": "article", "title": "Transition of mode II cracks from sub-Rayleigh to intersonic\n speeds in the presence of favorable heterogeneity", "author": [ { "family_name": "Liu", "given_name": "Yi", "clpid": "Liu-Yi" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "abstract": "Understanding sub-Rayleigh-to-intersonic transition of mode II cracks is a fundamental problem in fracture mechanics with important practical implications for earthquake dynamics and seismic radiation. In the Burridge\u2013Andrews mechanism, an intersonic daughter crack nucleates, for sufficiently high prestress, at the shear stress peak traveling with the shear wave speed in front of the main crack. We find that sub-Rayleigh-to-intersonic transition and sustained intersonic propagation occurs in a number of other models that subject developing cracks to intersonic loading fields. We consider a spontaneously expanding sub-Rayleigh crack (or main crack) which advances, along a planar interface with linear slip-weakening friction, towards a place of favorable heterogeneity, such as a preexisting subcritical crack or a small patch of higher prestress (similar behavior is expected for a small patch of lower static strength). For a range of model parameters, a secondary dynamic crack nucleates at the heterogeneity and acquires intersonic speeds due to the intersonic stress field propagating in front of the main crack. Transition to intersonic speeds occurs directly at the tip of the secondary crack, with the tip accelerating rapidly to values numerically equal to the Rayleigh wave speed and then abruptly jumping to an intersonic speed. Models with favorable heterogeneity achieve intersonic transition and propagation for much lower prestress levels than the ones implied by the Burridge\u2013Andrews mechanism and have transition distances that depend on the position of heterogeneity. We investigate the dependence of intersonic transition and subsequent crack propagation on model parameters and discuss implications for earthquake dynamics.", "doi": "10.1016/j.jmps.2007.06.005", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2008-01", "series_number": "1", "volume": "56", "issue": "1", "pages": "25-50" }, { "id": "authors:yef3z-9cf18", "collection": "authors", "collection_id": "yef3z-9cf18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LUXpnas07", "type": "article", "title": "Pulse-like and crack-like ruptures in experiments mimicking crustal earthquakes", "author": [ { "family_name": "Lu", "given_name": "Xiao", "clpid": "Lu-Xiao" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "Ares J.", "orcid": "0000-0003-0559-0794", "clpid": "Rosakis-A-J" } ], "abstract": "Theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws, stress conditions on faults, energy partition and heat generation during earthquakes, scaling laws, and spatiotemporal complexity of fault slip. Early theoretical models treated earthquakes as crack-like ruptures, but seismic inversions indicate that earthquake ruptures may propagate in a self-healing pulse-like mode. A number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated. This study presents experimental observations of spontaneous pulse-like ruptures in a homogeneous linear-elastic setting that mimics crustal earthquakes; reveals how different rupture modes are selected based on the level of fault prestress; demonstrates that both rupture modes can transition to supershear speeds; and advocates, based on comparison with theoretical studies, the importance of velocity-weakening friction for earthquake dynamics.", "doi": "10.1073/pnas.0704268104", "pmcid": "PMC2141885", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2007-11-27", "series_number": "48", "volume": "104", "issue": "48", "pages": "18931-18936" }, { "id": "authors:z99mq-5pm27", "collection": "authors", "collection_id": "z99mq-5pm27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130416-143417195", "type": "article", "title": "Comparison of finite difference and boundary integral solutions to three-dimensional spontaneous rupture", "author": [ { "family_name": "Day", "given_name": "Steven M.", "clpid": "Day-S-M" }, { "family_name": "Dalguer", "given_name": "Luis A.", "clpid": "Dalguer-L-A" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Liu", "given_name": "Yi", "clpid": "Liu-Yi" } ], "abstract": "The spontaneously propagating shear crack on a frictional interface has proven to be a useful idealization of a natural earthquake. The corresponding boundary value problems are nonlinear and usually require computationally intensive numerical methods for their solution. Assessing the convergence and accuracy of the numerical methods is challenging, as we lack appropriate analytical solutions for comparison. As a complement to other methods of assessment, we compare solutions obtained by two independent numerical methods, a finite difference method and a boundary integral (BI) method. The finite difference implementation, called DFM, uses a traction-at-split-node formulation of the fault discontinuity. The BI implementation employs spectral representation of the stress transfer functional. The three-dimensional (3-D) test problem involves spontaneous rupture spreading on a planar interface governed by linear slip-weakening friction that essentially defines a cohesive law. To get a priori understanding of the spatial resolution that would be required in this and similar problems, we review and combine some simple estimates of the cohesive zone sizes which correspond quite well to the sizes observed in simulations. We have assessed agreement between the methods in terms of the RMS differences in rupture time, final slip, and peak slip rate and related these to median and minimum measures of the cohesive zone resolution observed in the numerical solutions. The BI and DFM methods give virtually indistinguishable solutions to the 3-D spontaneous rupture test problem when their grid spacing \u0394x is small enough so that the solutions adequately resolve the cohesive zone, with at least three points for BI and at least five node points for DFM. Furthermore, grid-dependent differences in the results, for each of the two methods taken separately, decay as a power law in \u0394x, with the same convergence rate for each method, the calculations apparently converging to a common, grid interval invariant solution. This result provides strong evidence for the accuracy of both methods. In addition, the specific solution presented here, by virtue of being demonstrably grid-independent and consistent between two very different numerical methods, may prove useful for testing new numerical methods for spontaneous rupture problems.", "doi": "10.1029/2005JB003813", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2005-12-23", "series_number": "B12", "volume": "110", "issue": "B12", "pages": "Art. No. B12307" }, { "id": "authors:7v4g1-tp143", "collection": "authors", "collection_id": "7v4g1-tp143", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130308-133521256", "type": "article", "title": "Nucleation and early seismic propagation of small and large events in a crustal earthquake model", "author": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rice", "given_name": "James R.", "clpid": "Rice-J-R" } ], "abstract": "Earthquake nucleation and early seismic propagation are studied in a two-dimensional strike-slip fault model with depth-variable properties. The fault is governed by the Dieterich-Ruina rate and state friction law. We use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by Lapusta et al. [2000]. We find that for decreasing values of the characteristic slip distance of the friction law, small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone. Small and large events have very similar nucleation phases in our simulations. Here, by \"nucleation phase\" we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic, seismically detectable event. Moment acceleration (to which velocity seismograms are proportional) in early stages of seismic propagation exhibits irregular fluctuations, in the form of speedups and slowdowns in the moment release rate, consistently with observations as reported by Ellsworth and Beroza [1995]. Our simulations show that such irregular moment acceleration can, at least in part, be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity-strengthening fault regions which inhibit seismic slip.", "doi": "10.1029/2001JB000793", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2003-04-18", "series_number": "B4", "volume": "108", "issue": "B4", "pages": "Art. No. 2205" }, { "id": "authors:5efnc-nm026", "collection": "authors", "collection_id": "5efnc-nm026", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130308-134151285", "type": "article", "title": "Rate and state dependent friction and the stability of sliding between elastically deformable solids", "author": [ { "family_name": "Rice", "given_name": "James R.", "clpid": "Rice-J-R" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Ranjith", "given_name": "K.", "clpid": "Ranjith-K" } ], "abstract": "We study the stability of steady sliding between elastically deformable continua using rate and state dependent friction laws. That is done for both elastically identical and elastically dissimilar solids. The focus is on linearized response to perturbations of steady-state sliding, and on studying how the positive direct effect (instantaneous increase or decrease of shear strength in response to a respective instantaneous increase or decrease of slip rate) of those laws allows the existence of a quasi-static range of response to perturbations at sufficiently low slip rate. We discuss the physical basis of rate and state laws, including the likely basis for the direct effect in thermally activated processes allowing creep slippage at asperity contacts, and estimate activation parameters for quartzite and granite. Also, a class of rate and state laws suitable for variable normal stress is presented. As part of the work, we show that compromises from the rate and state framework for describing velocity-weakening friction lead to paradoxical results, like supersonic propagation of slip perturbations, or to ill-posedness, when applied to sliding between elastically deformable solids. The case of sliding between elastically dissimilar solids has the inherently destabilizing feature that spatially inhomogeneous slip leads to an alteration of normal stress, hence of frictional resistance. We show that the rate and state friction laws nevertheless lead to stability of response to sufficiently short wavelength perturbations, at very slow slip rates. Further, for slow sliding between dissimilar solids, we show that there is a critical amplitude of velocity-strengthening above which there is stability to perturbations of all wavelengths.", "doi": "10.1016/S0022-5096(01)00042-4", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2001-09", "series_number": "9", "volume": "49", "issue": "9", "pages": "1865-1898" }, { "id": "authors:ber78-nkt41", "collection": "authors", "collection_id": "ber78-nkt41", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130308-135516190", "type": "article", "title": "Elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate- and state-dependent friction", "author": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Rice", "given_name": "James R.", "clpid": "Rice-J-R" }, { "family_name": "Ben-Zion", "given_name": "Yehuda", "orcid": "0000-0002-9602-2014", "clpid": "Ben-Zion-Y" }, { "family_name": "Zheng", "given_name": "Gutuan", "clpid": "Zheng-Gutan" } ], "abstract": "We present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure. This is done for a general class of rate- and state-dependent friction laws with positive direct velocity effect. The algorithm allows us to treat accurately, within a single computational procedure, loading intervals of thousands of years and to calculate, for each earthquake episode, initially aseismic accelerating slip prior to dynamic rupture, the rupture propagation itself, rapid post seismic deformation which follows, and also ongoing creep slippage throughout the loading period in velocity-strengthening fault regions. The methodology is presented using the two-dimensional (2-D) antiplane spectral formulation and can be readily extended to the 2-D in-plane and 3-D spectral formulations and, with certain modifications, to the space-time boundary integral formulations as well as to their discretized development using finite difference or finite element methods. The methodology can be used to address a number of important issues, such as fault operation under low overall stress, interaction of dynamic rupture propagation with pore pressure development, patterns of rupture propagation in events nucleated naturally as a part of a sequence, the earthquake nucleation process, earthquake sequences on faults with heterogeneous frictional properties and/or normal stress, and others. The procedure is illustrated for a 2-D crustal strike-slip fault model with depth-variable properties. For lower values of the state-evolution distance of the friction law, small events appear. The nucleation phases of the small and large events are very similar, suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself. We demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches, one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate.", "doi": "10.1029/2000JB900250", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "2000-10-10", "series_number": "B10", "volume": "105", "issue": "B10", "pages": "23765-23789" } ]