Tectonic plates move at a steady velocity of several centimeters per year, which is intermittently interrupted by great megathrust earthquakes with rapid slip up to tens of meters. These large rupture events are driven by the slow tectonic loading and can substantially alter the deformation rate and state of stress in adjacent regions. With advances in computational algorithms, we develop cross-scale finite-element models that self-consistently integrate long-term motion of entire plates and the intervening space-time evolution associated with great earthquakes. The objectives are two-fold: firstly, to gain insight into the occurrence and magnitude of great earthquakes and their relationship with large-scale tectonic processes, and secondly, to constrain rheological properties of the solid Earth with multi-scale geophysical observations.
\r\n\r\nWe begin with formulating a generic subduction model that simultaneously resolves the dynamics of plate motions and megathrust seismic cycles (Chapter 2). Driven by internal buoyancy forces and governed by a nonlinear visco-elasto-plastic rheology, the predicted plate convergence and seismic cycle behavior align with observations in subduction zones. Using an efficient 2.5-dimensional approach, we show that the along-strike resistance arising from slip variations plays a key role in modulating the earthquake magnitude. In Chapter 3, we vary the rupture dimensions, rheological parameters and subduction characteristics to examine their influence on the plate velocity and coseismic slip. In Chapter 4, we build a three-dimensional model tailored to the Chilean Subduction Zone, and reproduce both the long-term motion of the Nazca Plate and post-seismic deformation in the adjacent non-ruptured segment after the 2010 Maule earthquake (Mw = 8.8). Combining these multi-scale geodetic observations as constraints significantly improves the uniqueness of inferred mantle viscosity structure. Following the previous work, we implement a margin-resolving global model of plate motions and earthquakes using the highly scalable finite-element code Rhea (Chapter 5). Constrained by both background plate motions and transient earthquake-related deformations, the model quantifies the sensitivity of different geodetic observations to the rheology of the megathrust, lithosphere and underlying mantle. In Chapter 6, we incorporate a true free surface and link plate motions, surface topography and off-megathrust stress state to Earth's nonlinear rheology within a unified cross-scale model. Our work demonstrates the potential for assimilating multi-scale geophysical observations in unified, physics-based models to better characterize Earth's internal structure and assess seismic hazards.
", "doi": "10.7907/c31c-fg36", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:16630", "collection": "thesis", "collection_id": "16630", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08132024-035518437", "primary_object_url": { "basename": "MyCaltechThesis_TaehoKim.pdf", "content": "final", "filesize": 102966987, "license": "other", "mime_type": "application/pdf", "url": "/16630/2/MyCaltechThesis_TaehoKim.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Modeling Frictional Processes in the Presence of Fluids: From Earthquakes in the Laboratory to Induced Seismicity in Geothermal Reservoirs", "author": [ { "family_name": "Kim", "given_name": "Taeho", "orcid": "0000-0002-2560-7728", "clpid": "Kim-Taeho" } ], "thesis_advisor": [ { "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" } ], "thesis_committee": [ { "family_name": "Fu", "given_name": "Xiaojing", "orcid": "0000-0001-7120-704X", "clpid": "Fu-Xiaojing" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "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" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Induced seismicity - earthquakes driven by injections of fluids into the subsurface - is of growing societal importance in its impact on clean energy technology. Advancements central to the world\u2019s transition to a greener economy such as geothermal energy and long-term geologic storage of CO2 are hampered by a lack of understanding and control of the associated seismic hazards. In its mechanics, frictional processes in the presence of fluids is a difficult problem to model given the challenges of studying frictionally unstable material in a controlled environment. Unstable gouge material is commonly found along faults in nature, due to pulverization of brittle rock in to granular layers called `gouge.' This thesis approaches the challenge at two different scales: 1. at the scale of the localized shear layer along the interface between two faults where we model laboratory earthquakes in the presence of pressurized fluids, and 2. at the scale of a reservoir where we model the rate of earthquakes given the injection/extraction schedule.
\r\n\r\nIn order to infer the frictional properties of unstable gouge material from laboratory experiments, we develop a probabilistic model based on a spring-slider representation of the experiment along with the rate-and-state friction law. Inversions indicate that the presence of pressurized pore fluids stabilizes the gouge - by an increase in the strength of the contacts and a lesser decrease in the grain size with slip - even under the same effective normal stress. Assuming purely slip-dependent healing of friction leads to an evolution of parameters with slip that is consistent with previously established interpretations of rate-and-state parameters. The best fitting spring-slider model still shows significant discrepancies to the experiment in the evolution of creep and in the dependence on loading rate. A quasi-static finite-element model with the same rate-and-state properties suggests that the gouge in the sample likely slides in a spatially uniform manner. Thus, the discrepancies between the spring-slider model and the experiment can likely be attributed to flaws in the rate-and-state formalism and the slip law rather than the idealization of a finite geometry to a single-degree-of-freedom system. The results prove that quantitative analysis of frictional processes of gouge in the unstable regime is possible, and that future development of constitutive relationships for friction should aim to reproduce key features of stick-slip in detail.
\r\n\r\nTo model seismicity induced by a geothermal well stimulation, we develop physical and statistical models of the seismicity rate. The physical models are based on rate-and-state friction and stress changes due to pore-pressure diffusion. The statistical model performs a convolution of a kernel function inspired by Omori law decay with the injection rate. Both models successfully reproduce the seismicity observed during the 2018 enhanced geothermal system (EGS) simulation in Otaniemi, Finland. We find that the effect of time-dependent nucleation from rate-and-state friction is crucial in reproducing the temporal and spatial patterns of the observed seismicity. We also find that the effect of finite nucleation cannot be approximated well by introducing a stress threshold in the standard Coulomb friction model, at least in the context of rapid variations of injection rates common in EGS operations.
\r\n\r\nWe highlight the major assumptions of the Dieterich seismicity rate model and examine how they may bias interpretations of induced seismicity observed in real reservoirs by comparing it directly to a Discrete Fault Network (DFN) model. The spatio-temporal pattern of seismicity in the finite setting is not only dependent on fluid transport properties and its combination with nucleation characteristics but also the distribution of initial conditions of the fault network. The back-propagation front, in particular, occurs co-injection if the time to instability for the minimum slip rate is shorter than the injection duration. The relocated catalogue of the 1993 GPK1 stimulation in Soultz-Sous-Forets shows such a back-front which can be fit qualitatively using the time to instability measure. A simple model for the rate of magnitudes that accounts for the evolution of frictional stability reproduces the apparent increase in the source radius of induced events in Soultz-Sous-Forets. The rate of larger events is overestimated by the model, possibly due to an overestimation of maximum magnitudes by the volume of stimulation. The comparisons reveal that parameters of the Dieterich model lack clear physical meaning in the finite analogue and highlight the importance of using realistic physics, especially in models at large scales where uncertainty due to assumptions at smaller scales may be amplified.
\r\n \r\nWe end the thesis with the application of rate-and-state friction to dynamic rupture modeling of seismic data from distributed acoustic sensing (DAS). The modeling of the high-frequency DAS recordings of a Magnitude 6.0 earthquake suggests a highly heterogeneous underlying fault with several prominent asperities and barriers that may control rupture dynamics. The model demonstrates how the high-stress patches both inhibit and promote the overall rupture, while also contributing to a significant amount of the energy release themselves. The successful interpretations of modern seismological data encourage future development efficient models that can be used for dynamic inversions.
", "doi": "10.7907/pp3a-2609", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16637", "collection": "thesis", "collection_id": "16637", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08142024-141724425", "primary_object_url": { "basename": "Shengduo_Liu_Thesis_Final.pdf", "content": "final", "filesize": 68545231, "license": "other", "mime_type": "application/pdf", "url": "/16637/1/Shengduo_Liu_Thesis_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Numerical Analyses of Frictional Sliding on Rate-and-State Interfaces: Fluid Effects, Dynamic Weakening, and Potential-Based Formulation Through Machine Learning", "author": [ { "family_name": "Liu", "given_name": "Shengduo", "orcid": "0009-0009-5259-0966", "clpid": "Liu-Shengduo" } ], "thesis_advisor": [ { "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" } ], "thesis_committee": [ { "family_name": "Fu", "given_name": "Xiaojing", "orcid": "0000-0001-7120-704X", "clpid": "Fu-Xiaojing" }, { "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" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Rate-and-state friction formulations have been widely used to reproduce a number of observations on faulting in the earth's crust, including earthquake nucleation, creeping fault segments, dynamic earthquake rupture, aftershock sequences, and episodic slow slip events. The formulations have also been used to explain the motion of landslides and glaciers. In this thesis, we use numerical simulations to study various factors that can affect the stability of fault slip with rate-and-state friction, including poroelastic bulk properties and dilatation/compaction of the fault material in the presence of fluids, fault healing, injection rate when there is fluid injected into the fault, as well as dynamic weakening of the fault gouge. We also seek to optimize simulations with rate-and-state friction by developing a potential-based formulation using machine learning.
\r\n\r\nFirst, we study the stability of frictional fault slip in the presence of fluids, with a focus on fault loading due to fluid injection into the fault as done in many field and laboratory experiments. In Chapter 2, we present a boundary-integral approach on simulating frictional fault slip in a permeable shear layer surrounded by poroelastic bulk. The approach is then used to explore the effects of poroelasticity and inelastic dilatancy on the stability of frictional fault slip in a fluid-injection problem. We find that the diffusion into and poroelastic properties of the bulk can significantly stabilize fault slip, with the stabilization by bulk diffusion and poroelastic properties comparable to the well-known stabilizing effects of the dilatancy mechanism.
\r\n \r\nIn Chapter 3, we further develop the boundary integral code to allow for purely elastic bulk with the same fluid transport properties as the poroelastic bulk material and consider the effect of fault healing and fluid injection rate on fault slip. We show that the poroelastic bulk effects can be very closely captured by using the undrained value of Poisson\u2019s ratio in an elastic bulk model with the same fluid mass diffusivity of the bulk. We find that fault healing significantly delays the onset of dynamic slip events and restricts their spatial extent, making the initial response of the fault to fluid injection much different than its longer-term response. While this is an expected conclusion, fault healing is not typically accounted for in fluid injection modeling which often uses simpler slip-dependent friction laws. We also find that faster or intermittent injection rates lead to more frequent but more spatially constrained dynamic slip events, for the same injected fluid mass, motivating further investigations into injection strategies that would optimize fault stability.
\r\n \r\nSecond, in Chapter 4, we numerically simulate a laboratory experiment of spontaneous dynamic rupture by developing a 3D finite-element model of the experiment with rate-and-state friction. In the experiment, a dynamic rupture is initiated on a Homalite-100 interface and then produces an intermittent slip in the rock gouge embedded into a part of the interface. Our simulations show that the laboratory findings are consistent with rock gouge which is rate-strengthening at low slip rates but dynamically weakening at high slip rates through the mechanism similar to flash heating. However, to fit the experimental results, the traditional flash-heating formulation needs to be substantially modified, potentially due to effects of localization and delocalization of slip in the rock gouge.
\r\n\r\nThe third part of the thesis focuses on identifying a potential-based formulation for the rate-and-state friction laws. Due to their empirical derivation, the rate-and-state friction laws cannot be written as the gradients of a potential, which leads to difficulties in implicit solution of dynamic frictional problems. In Chapter 5, we present a potential-based formulation for the rate-and-state friction law through Neural Network approximation and training on datasets generated by a one-degree of-freedom spring-slider system with the rate-and-state friction law. The learnt potential is able to reproduce the results with rate-and-state friction law, and indeed facilitates an implicit solution of dynamic problems. However, the training of the potential requires a much larger dataset than fitting the original rate-and-state friction law.
\r\n\r\nOverall, our modeling significantly advances our understanding of the factors that control stability of frictional sliding on natural faults and suggests promising machine-learning directions in replacing the empirical rate-and-state formulations with the ones based on thermodynamic potentials.
", "doi": "10.7907/1tzb-pn69", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:14998", "collection": "thesis", "collection_id": "14998", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08082022-055217161", "primary_object_url": { "basename": "Oliver_Stephenson_Thesis_2023.pdf", "content": "final", "filesize": 119182132, "license": "other", "mime_type": "application/pdf", "url": "/14998/1/Oliver_Stephenson_Thesis_2023.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Investigating the Earthquake Cycle on Multiple Temporal and Spatial Scales Using Satellites and Simulations", "author": [ { "family_name": "Stephenson", "given_name": "Oliver Laurent", "orcid": "0000-0002-5509-090X", "clpid": "Stephenson-Oliver-Laurent" } ], "thesis_advisor": [ { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The motion of the Earth's tectonic plates creates a gradual accumulation of stress at their boundaries, followed by a rapid release in earthquakes, a process known as the earthquake cycle. Studying this process is important because of the hazards earthquakes pose, but presents challenges due to the multi-scale nature of the problem\u2014stresses build up over hundreds to thousands of years, while earthquakes break narrow fault zones in a matter of seconds. In this thesis, we combine a variety of techniques to study the earthquake cycle on multiple temporal and spatial scales, including satellite-based interferometric synthetic aperture radar (InSAR) to observe the slow deformation of the Earth over wide areas, and high-performance computational simulations to model faults during earthquakes. We begin by presenting a method for removing the signal of plate-tectonic motion in large-scale InSAR measurements, allowing for better observation of small ground deformations. We then use these corrections to study the Makran subduction zone, on the Iran-Pakistan border. Our InSAR-derived ground velocity map can resolve motions at the level of millimeters per year over an area of nearly one million square kilometers, and we use it to place constraints on the degree of coupling on the subduction megathrust. Next, we show how InSAR can be combined with deep learning techniques to rapidly map earthquake damage in all weather conditions, day and night. Such products will hopefully prove useful in future disaster response. Finally, we present computational simulations of dynamic earthquake ruptures with enhanced dynamic weakening due to thermal pressurization. We apply our simplified model to the creeping section of the San Andreas Fault, which is generally thought to be a barrier to earthquake rupture. Our results show how thermal pressurization can allow earthquakes to propagate partially or completely through the creeping section for a range of physically reasonable parameters. Our work illustrates how results from multiple fields can be combined to deliver new insights into the earthquake cycle and the hazards that it poses.", "doi": "10.7907/ha9m-4p17", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14651", "collection": "thesis", "collection_id": "14651", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302022-071239478", "primary_object_url": { "basename": "PhD_thesis_Stacy_Larochelle.pdf", "content": "final", "filesize": 94832965, "license": "other", "mime_type": "application/pdf", "url": "/14651/1/PhD_thesis_Stacy_Larochelle.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Mechanical Interactions Between Water and the Solid Earth: from Quasi-Static Geodetic Deformation to Dynamic Fault Slip", "author": [ { "family_name": "Larochelle", "given_name": "Stacy", "orcid": "0000-0001-6161-5605", "clpid": "Larochelle-Stacy" } ], "thesis_advisor": [ { "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" } ], "thesis_committee": [ { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "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" } ], "local_group": [ { "literal": "Center for Geomechanics and Mitigation of Geohazards (GMG)" }, { "literal": "div_gps" } ], "abstract": "Mechanical interactions between Earth's solid interior and its hydrosphere are central to many geophysical problems of crucial societal importance: Changing conditions in the global water cycle deform the solid Earth; the groundwater storage capacity of aquifer systems is controlled by its interaction with geological materials; and crustal water - either natural occurring or added through anthropogenic activities - affects earthquakes and fault slip processes. In this thesis, we investigate some of these interactions by harnessing recent developments in the fields of satellite geodesy, statistical data analysis and elastodynamic earthquake modelling. We start by developing a procedure to identify and extract seasonal deformation signals associated with hydrological loading of the solid Earth from geodetic time series in Chapter 1. In Chapters 2 and 3, we consider the examples of the Ozarks Plateau (central United States) and Sacramento Valley (California) to establish a methodology for characterizing poroelastic deformation arising from groundwater variations with space-based geodesy. Then, in Chapter 4, we develop a model to simulate fault slip due to crustal water injections and calibrate it against a well-instrumented field experiment on a natural fault. We conclude by deriving a theoretical understanding of these fault slip simulations by considering the simple case of a fixed-length pressurized zone in Chapter 5. Overall, our work provides key insights for extracting and using different sources of hydrogeodetic signals as well as for modeling and understanding fluid-induced fault slip processes, which is becoming increasingly important in a world faced with water scarcity, a changing climate and an increased reliance on groundwater and geoenergy resources.
", "doi": "10.7907/2r5a-9277", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14507", "collection": "thesis", "collection_id": "14507", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02232022-193800084", "primary_object_url": { "basename": "Kavya_thesis_2022.pdf", "content": "final", "filesize": 39218273, "license": "other", "mime_type": "application/pdf", "url": "/14507/1/Kavya_thesis_2022.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Slip Patterns on Heterogeneous Frictional Interfaces", "author": [ { "family_name": "Sudhir", "given_name": "Kavya", "orcid": "0000-0001-6673-0979", "clpid": "Sudhir-Kavya" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "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" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Understanding the implications of heterogeneity on frictional interfaces for the resulting slip patterns is a challenging, highly nonlinear, and dynamic problem with special relevance to earthquake source processes. Natural fault surfaces are rarely homogeneous and host a spectrum of slip behaviors in response to slow tectonic loading where slow steady slip and earthquake ruptures are just the end members. Understanding how heterogeneous frictional properties translate into different slip patterns would enable us to constrain the heterogeneity of natural faults and get an insight into processes that are difficult to observe in the field such as earthquake nucleation, with important implications for the assessment of seismic hazard.
\r\n\r\nIn this thesis, we advance our understanding of fault heterogeneity and its effects by conducting numerical simulations of long-term slip histories on heterogeneous frictional interfaces. We first focus on how irregular fault geometry affects the variability in repeating sequences by investigating a specific example of the SF-LA repeaters in the Parkfield segment of the San Andreas Fault (SAF) in California. We then investigate the effect of increasing heterogeneity in the effective normal stress on earthquake nucleation processes, complexity of earthquake sequences, and features of larger-scale ruptures. In both cases, we incorporate the heterogeneity in physical properties into 2D planar faults governed by rate-and-state friction and embedded into 3D homogeneous elastic bulk. Fully dynamic simulations are used to numerically solve the resulting elastodynamic problems with friction as a nonlinear boundary condition.
\r\n\r\nOur models reproduce many observations about SF-LA repeating sequences, in- cluding their mean moment, mean recurrence times, stress drops, the observed non- trivial scaling between the seismic moment and recurrence times of the repeaters, the ranges of variability in moment and recurrence time, and the ranges of triggering times between the two sequences. Multiple models produce slip behaviors com- parable to observations, indicating that the models cannot be uniquely constrained based on available observations. We also study how small-scale features of hetero- geneity affect model response. We find that smoothing the distribution over scales smaller than governing length scales in the problem, such as the nucleation size in our case, changes the specific evolution of slip, but preserves its key characteristics, such as the range of event variability and triggering times between events. However, smoothing the distribution on larger scales modifies the response qualitatively.
\r\n\r\nOur study of the earthquake initiation processes on interfaces with normal stress heterogeneity reveals that systematic increase in heterogeneity induces a continuum of behaviors, ranging from purely fault-spanning events to persistent foreshock-like events interspersed between fault-spanning mainshocks. In models with strong heterogeneity, most smaller-scale and larger-scale events initiate from scales much smaller than the nucleation size estimates calculated for uniform interfaces with equivalent average properties. While the variations in normal stress induce inversely proportional variations in the instability length scale often called nucleation size, we find that the nucleation-size variations by themselves are insufficient to cause such behavior, and that the associated strong heterogeneity in frictional strength is also required. In models with uniform friction strength but the same nucleation-size variation, the nucleation processes of larger-scale events are similar to those on uniform interfaces, with an addition of multiple triggered small-scale earthquakes. Our simulations show that several hypothesized scenarios of earthquake nucleation and foreshocks on natural faults may be viable and reflect different types and levels of heterogeneity on different faults the effects of which, in addition, vary as fault conditions evolve. For example, even with strong fault heterogeneity, some large- scale events have foreshocks and some do not, in the same simulation.
\r\n\r\nThe increasing fault heterogeneity generally leads to increasing complexity of the resulting earthquake sequences and moment-rate release (also called source-time function) of large-scale, fault-spanning events, as intuitively expected, although with some saturation at the higher heterogeneity levels. We find that, in the presence of significant normal-stress heterogeneity, source-time functions of many larger-scale events exhibit prolonged seismic initiation phases, similar to some observations, as the events nucleate from the heterogeneity scale and re-rupture the areas pres-lipped quasi-statically and in foreshocks. The source-time functions also reveal that larger-scale events in our models -- that are arrested by velocity-strengthening barriers -- have a more abrupt arrest phase than natural earthquakes, which places constraints on rupture-arresting mechanisms that should be used in modeling. The initial moment rates are similar for events of different eventual sizes on interfaces with strong heterogeneity, implying that, in those cases, large events are just small events that ran away.
", "doi": "10.7907/xkbp-ks08", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14168", "collection": "thesis", "collection_id": "14168", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202021-190145895", "primary_object_url": { "basename": "Thesis-ValereLambert.pdf", "content": "final", "filesize": 170625558, "license": "other", "mime_type": "application/pdf", "url": "/14168/1/Thesis-ValereLambert.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Constraining Earthquake Source Processes Through Physics-Based Modeling", "author": [ { "family_name": "Lambert", "given_name": "Val\u00e8re R\u00e9gis Westbrooke", "orcid": "0000-0002-6174-9651", "clpid": "Lambert-Valere-Regis-Westbrooke" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "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": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Zhan", "given_name": "Zhongwen", "orcid": "0000-0002-5586-2607", "clpid": "Zhan-Zhongwen" } ], "local_group": [ { "literal": "Center for Geomechanics and Mitigation of Geohazards (GMG)" }, { "literal": "div_gps" } ], "abstract": "Determining principles and conditions governing motion along faults is crucial for assessing how earthquake ruptures start and how large they may ultimately become. This thesis aims to shed light on the physics governing earthquake source processes by (i) developing physics-based numerical models that combine geological observations and laboratory insight with theoretical developments, and (ii) using these models to examine how different physical mechanisms and conditions are reflected in a range of geophysical observations taken together, from heat-flow constraints and seismologically determined properties of earthquakes to geodetic inferences and earthquake frequency-magnitude statistics.
\r\n\r\nWe examine the behavior and observable characteristics of numerically simulated sequences of earthquakes and aseismic slip in fault models designed to reproduce well-known features of mature faults that produce large destructive earthquakes. In part, the models are consistent with the inferred low-stress, low-heat operation of mature faults, which host large earthquakes at much lower levels of stress than their expected static strength. We explore two potential explanations for such behavior, one that faults are indeed quasi-statically strong but experience dramatic weakening during earthquakes, or that faults are persistently weak, e.g., due to fluid overpressure. We find that the two classes of fault models can, in principle, be distinguished based on the amount of seismic energy radiated from earthquake ruptures. Dynamic ruptures in the form of self-healing pulses, which occur on quasi-statically strong but dynamically weak faults, result in much larger radiated energy than inferred teleseismically for megathrust events, whereas crack-like ruptures on persistently weak faults are consistent with the seismological observations. The larger radiated energy of self-healing pulses is similar to limited regional inferences for crustal strike-slip faults. Our results suggest that re-evaluating estimates of radiated energy and static stress drop would provide substantial insight into the driving physics of large earthquakes and the absolute stress conditions on faults, with potential differences between tectonic settings.
\r\n\r\nThe results also have significant implications for seismic hazard, since our modeling shows that fault models that experience efficient dynamic weakening during ruptures tend to predominantly produce large earthquakes, at the expense of smaller earthquakes. Such behavior is consistent with some mature fault segments, such as several segments of the San Andreas Fault in California that have hosted large earthquakes but are currently nearly seismically quiescent. These considerations can provide physical basis for improving earthquake early warning systems. If mature faults in California are indeed governed by enhanced dynamic weakening, then our results suggest that the likelihood of an earthquake on these faults becoming substantially larger is much higher than typical expectations based on Gutenberg-Richter statistics.
\r\n\r\nBy considering average fault stress before simulated earthquake ruptures, we find that critical stress conditions for earthquake occurrence depend on the size and style of motion (e.g. the degree of slip acceleration at the rupture front) during individual ruptures. In particular, the stress conditions required to propagate large earthquake ruptures can be considerably lower than those required for rupture nucleation, and standard notions of quasi-static fault strength based on laboratory studies. Our results demonstrate that the critical stress for earthquake occurrence is not governed by a simple condition such as a certain level of Coloumb stress, as commonly used in studies of stress interactions among faults and earthquake aftershocks patterns. More robust criteria for critical stress conditions would depend on the strength evolution during dynamic rupture and can be explored in numerical simulations.
\r\n\r\nFinally, evaluating the predictive power of numerical earthquake models for future hazards is a topic of great importance for physics-based seismic hazard assessment. Towards that end, we investigate the sensitivity of outcomes from numerical simulations of sequences of earthquakes and aseismic slip, including the long-term interaction of fault segments, to choices in numerical discretization and treatment of inertial, wave-mediated effects. In particular, we find that the rate of earthquake ruptures that manage to jump between two fault segments, a parameter routinely used in seismic hazard studies, is highly sensitive to numerical and physical modeling choices. These results suggest the need for developing different parameterization of seismic hazard than currently used, a task for which numerical modeling is well-suited.
", "doi": "10.7907/7s93-k485", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:10951", "collection": "thesis", "collection_id": "10951", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272018-175543580", "primary_object_url": { "basename": "Schaal_Natalie_thesis_2018.pdf", "content": "final", "filesize": 26842737, "license": "other", "mime_type": "application/pdf", "url": "/10951/1/Schaal_Natalie_thesis_2018.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Modeling of Nucleation and Dynamic Rupture on Heterogeneous Frictional Interfaces with Applications to Foreshocks", "author": [ { "family_name": "Schaal", "given_name": "Natalie Sarah Ann", "orcid": "0000-0003-4825-4344", "clpid": "Schaal-Natalie-Sarah-Ann" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Heaton", "given_name": "Thomas H.", "clpid": "Heaton-T-H" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "While many large earthquakes are preceded by observable foreshocks, the mechanisms responsible for the occurrence of these smaller-scale seismic events remain uncertain. One physical explanation of foreshocks with growing support is that they are produced by the interaction of slow slip, due to the nucleation of the upcoming mainshock, with fault patches of different properties. Having a better understanding of how earthquakes nucleate on heterogeneous faults would increase our capacity to forecast potentially hazardous events.\r\n
\r\n\r\nWith this motivation in mind, we seek to understand what conditions produce isolated microseismicity within the nucleating region of the mainshock and to study the mechanics of the resulting events. Inspired by the suggestion from laboratory experiments that foreshocks occur on asperities, i.e., local deviations from planarity that are flattened by the overall compression, we explore the behavior of asperity-type patches of higher compressive stress embedded in the larger seismogenic region of a rate-and-state fault model by conducting 3D numerical simulations of their slip over long-term sequences of aseismic and seismic slip. Our models do produce smaller-scale seismicity during the aseismic nucleation of much larger seismic events, and we explore their properties as well as the separation in length scales needed to produce them. These foreshock-like events have stress drops that are consistent with laboratory and field observations and approximately constant, despite the highly elevated compression assigned to the source patches. Two main factors contributing to the reasonable stress drops are the significant extent of the rupture into the region surrounding the patch and the aseismic stress release just prior to the seismic event.
\r\n\r\n\r\nWe also investigate the seismologically-derived properties of the asperity-type events using the spectral analysis commonly applied to natural microseismic events. We find that the seismological methods cannot adequately capture the properties of the simulated events. In part, the seismological estimates of their stress drops are significantly different from the actual stress drops determined from the on-fault stress changes. This is because our sources have more complex features than the standard models from which the current seismological methods have been built, including heterogeneous stress change over the rupture area with much larger initial stress change, and heterogeneous rupture speed. We identify features in the far-field seismograms of the asperity-type sources that differ from the standard models and can be potentially characteristic of the asperity-type sources.\r\n
\r\n\r\n\r\nOur asperity-type models of microseismicity sources provide insight into the conditions conducive for generating foreshocks on both natural and laboratory faults and the properties of the resulting events. The conclusions provided jointly by the two perspectives in this study -- dynamically simulating the behavior of seismic sources within heterogeneous fault models and seismologically analyzing their far-field source spectra -- have important implications that warrant further study. Topics for future research include the interaction among smaller-scale seismic events and their role in the mainshock nucleation process, the effect of timing on their source properties, and relation to the so-called seismic nucleation phase of the subsequent mainshock.\r\n
\r\n", "doi": "10.7907/YCVJ-PM21", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10988", "collection": "thesis", "collection_id": "10988", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-150338327", "type": "thesis", "title": "Laboratory Investigation of Shear Ruptures: Supersonic Propagation and Nucleation by Fluid Injection", "author": [ { "family_name": "Gori", "given_name": "Marcello", "orcid": "0000-0002-7380-3723", "clpid": "Gori-Marcello" } ], "thesis_advisor": [ { "family_name": "Rosakis", "given_name": "Ares J.", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Rosakis", "given_name": "Ares J.", "clpid": "Rosakis-A-J" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Shear rupture nucleation and dynamic propagation is a challenging, non- linear, highly interactive process with important practical implications. Here we focus on two aspects of this problem: propagation speeds and shock front radiation from the dynamic crack tip as well as nucleation of dynamic rupture due to fluid injection.
\r\n\r\nSpontaneously propagating cracks in solids emit pressure and shear waves and are, in part, driven by energy transfer due to them. 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. The equivalent scenario involving a pressure shock front should not be possible, since cracks should not be able to exceed the pressure wave speed, at least in an isotropic linear-elastic solid. Here we present full-field experimental evidence of dynamic shear cracks in viscoelastic polymers that result in the formation of a pressure shock front, in addition to the shear one. In that sense, the crack appears to be supersonic. The apparent violation of classic theories is explained by the strain-rate-dependent material behavior of polymers: the increased wave speeds within the highly- strained region around the crack tip allow for supersonic crack propagation with respect to the (lower) wave speeds at short distances away from the interface, resulting in the formation of the pressure shock front. The crack speed remains below the pressure wave speed prevailing locally, about its tip, in agreement with basic physics and energy considerations of linear-elastic theories.
\r\n\r\nWe find that the shock fronts emitted by the shear cracks in the viscoelastic materials are curved and propose a novel method to quantify the viscoelastic wave speeds of the solids in the dynamic range of strain rates based on the curvature. Only kinematic relationships are used in the method, without the need for the constitutive relationship of the material. Measuring or inferring the material properties at elevated strain rates in viscoelastic solids is a difficult task, because of practical limitations of obtaining accurate measurements in that regime. Under the quasi-elastic solid approximation, in which the strain-rate history is neglected, we use the pressure-wave speed measurements to infer the associated value of the Young\u2019s modulus, estimated by assuming a constant value of the Poisson\u2019s ratio. We complement these results with the characterization of the Young\u2019s modulus at lower strain rates via canonical compressive tests. Our results not only confirm previous findings that the Young\u2019s modulus dependence on the strain rate in PMMA is significant but also demonstrate that its variation is more pronounced in the dynamic strain-rate range, with important consequences for the design of structures employing viscoelastic materials that are required to withstand elevated strain rates.
\r\n\r\nThe second part of the study concentrates on the nucleation of shear dynamic rupture due to fluid injection or, more broadly, on the interaction of frictional faulting with fluids. Fluid overpressure is recognized to play a fundamental role in promoting fault motion. A large number of observations has shed light on the interplay between fluids and faulting, both in natural events and in earth-quakes induced by human activities, such as wastewater disposal associated with oil and gas extraction. Fluids can induce a variety of earthquake source behaviors ranging from unstable, dynamic motions to stable, quasi-static ones, which a number of field studies suggests that can coexist on the same fault areas at different times, depending on the local conditions. In fact, a higher pore pres-sure plays the dual role of reducing the frictional strength of the fault and of increasing the nucleation size, e.g., the critical length for a shear crack to transition from quasi-static to dynamic motions. However, due to the complexity of the frictional problem at the fault interface, the understanding of which of these two effects prevails remains elusive. The assumption of a critical nucleation length represents a powerful, yet simplified concept, which currently does not include the dependence on the rate of the pore pressure increase.
\r\n\r\nHere, we explore the effect of the rate of the pore pressure increase on the rupture nucleation. We find that elevated injection rates induce triggering of the rupture at lower pressure values and minimal volumes of the injected fluid, if compared to slow injection rates. For the slow injection rates, we experimentally observe a much larger portion of interface wetted by the fluid and a phase of accelerated slip prior to the dynamic event (quasi-dynamic nucleation process). In some cases, we record much smaller foreshock-like events at the injection site. These findings suggest the presence of a prominent quasi-static nucleation process over the interface. In cases of rapid pore pressure increase, the nucleation process is much shorter in time and much more compact in space, being highly concentrated around the injection location. The dynamic events, once initiated, are qualitatively similar across different injection rates, but quantitatively different, with the slow-injection ones experiencing higher stress drops and higher slips, perhaps due to the effect of fluids on the friction properties.\r\nThese findings suggest the need to develop nucleation size estimates that include the rate of the pore pressure increase and motivate further investigation of how friction properties depend on the presence of fluids. The details of the obtained experimental findings, once analyzed through numerical modeling, will place important constrains on the forms of the acceptable friction laws, including the effects of pore fluid pressure and its rate of change.
", "doi": "10.7907/AH9X-V905", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11027", "collection": "thesis", "collection_id": "11027", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06062018-071106334", "type": "thesis", "title": "Analyzing Stress Change and Energy Budget of Earthquakes Through Physics-Based Modeling", "author": [ { "family_name": "Perry", "given_name": "Stephen Michael", "orcid": "0000-0003-1748-1827", "clpid": "Perry-Stephen-Michael" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Tsai", "given_name": "Victor C.", "clpid": "Tsai-V-C" }, { "family_name": "Zhan", "given_name": "Zhongwen", "clpid": "Zhan-Zhongwen" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Researchers use concepts such as stress drop, breakdown energy, and available energy to describe earthquakes sources and study earthquake physics. These quantities represent the spatially and temporally varying dynamic events by single, event-averaged values. They are inferred indirectly from observations, often based on simplified models. Thus, their relationship to fault constitutive properties, which are local on the fault, is not straightforward.
\r\n\r\nHere, we use simulations of earthquake sequences in fault models with friction laws motivated by laboratory experiments to examine how the event-averaged observables arise from spatially and temporally varying earthquake rupture. In particular, we consider whether several typically used fault mechanisms, such as rate-and-state friction, thermal pressurization of pore fluids, and flash heating, are consistent with common observations such as magnitude-invariant stress drop, increasing breakdown energy with the event size, and radiation efficiencies of ~0.5.
\r\n \r\nStress drops, observed to be magnitude invariant, are a key characteristic used to describe natural earthquakes. Theoretical studies and lab experiments indicate that dynamic weakening, such as thermal pressurization of pore fluids, may be present on natural faults. At first glance, these two observations seem incompatible, since larger events may experience greater weakening and should thus have lower final stresses. We hypothesize that dynamic weakening can be reconciled with magnitude-invariant stress drops due to larger events having lower average prestress when compared to smaller events. The additional weakening would allow the final stresses to also be lower, but the stress drops may be similar.
\r\n\r\nTo explore this hypothesis, we study long-term earthquake sequences on a rate-and-state fault segment with enhanced dynamic weakening due to thermal pressurization using a fully dynamic simulation approach with a seismogenic segment that has uniform friction properties. Our results show, for a range of event sizes, that such models can explain both observationally inferred stress drop invariance and breakdown energy increase with event magnitude. Smaller events indeed have larger average initial stresses than medium-sized events, and we get nearly constant stress drops for events spanning up to five orders of magnitude in seismic moment. Segment-spanning events have more complex behavior, which is dependent on the properties of the velocity-strengthening (VS) region at the edges of the fault. Models with large values of velocity strengthening in their boundary regions do not allow ruptures to propagate much into the velocity-strengthening region, thus containing the rupture area and leading to higher stress drops for a larger amount of slip. Decreasing the velocity strengthening of the boundaries leads to farther rupture propagation into the velocity-strengthening region and thus lower stress drops.
\r\n\r\nIn all models with the thermal pressurization of pore fluids that we have examined, both the smaller and segment-spanning events exhibit increases in breakdown energy consistent with observations. The breakdown energy is the portion of the dissipated energy that governs the event dynamics, analogous to the fracture energy concept of fracture mechanics. The increase in the breakdown energy is due to continuous weakening of the fault with slip, as hypothesized in previous analytical studies.
\r\n\r\nWe also examine the accuracy of seismically estimated breakdown energies GSE for a range of models, by comparing the values computed directly from our fault models and indirectly from seismically available observations. Observationally, GSE is typically obtained as the difference between the seismically estimated available energy \u0394W0 per unit area and radiated energy ER. This defines the available energy \u0394WA as the sum of the breakdown energy and radiated energy. However, the seismically estimated available energy \u0394W0 is obtained as one-half of the product of the (average) stress drop and (average) final slip, based on a simplified model. As such, we examine the relation between the actual available energy \u0394WA and its seismic estimate \u0394W0 in our models. We find that, as rupture mode changes from crack-like to pulse-like, the actual available energy \u0394WA, becomes increasingly larger that the seismically estimated available energy \u0394W0, due to significant and increasing stress undershoot characteristic of pulse-like ruptures. The extra available energy for more pulse-like ruptures either makes the breakdown energy much larger than its seismically estimated value, or makes the radiated energy much larger than the seismically estimated available energy \u0394W0, or both. In the two latter cases, the radiation ratio \u03b7 (sometimes called radiation efficiency) between the radiated energy and seismically estimated available energy increases beyond 1, consistent with some observations that were previously thought to be aphysical.
\r\n\r\nOverall, we find that models with rate-and-state friction and thermal pressurization of pore fluids, when resulting in continuous weakening of fault with slip and crack-like ruptures, produce events with magnitude-invariant stress drops, increases in breakdown energies with the event sizes consistent with observations, radiation ratios consistent with observations, and available energies similar to the ones inferred seismically. More pulse-like ruptures, which result occasionally in such models and reliably in models that incorporate more severe enhanced weakening motivated by flash heating, have increasingly more significant undershoot and hence extra energy available for breakdown and radiation compared with the seismically estimated available energy. Therefore, current seismic estimates of their breakdown energy and radiation ratio are not reliable. More work is needed to understand the energy budget of pulse-like events obtained in realistic fault models, especially since one of the common paradigms in earthquake physics is that many large events occur as pulse-like ruptures.
", "doi": "10.7907/ryht-eb75", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:9983", "collection": "thesis", "collection_id": "9983", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11232016-044435496", "primary_object_url": { "basename": "SKYLui_PhD_Thesis_FINAL.pdf", "content": "final", "filesize": 49646596, "license": "other", "mime_type": "application/pdf", "url": "/9983/1/SKYLui_PhD_Thesis_FINAL.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Earthquake Source Characterization Through Seismic Observations and Numerical Modeling", "author": [ { "family_name": "Lui", "given_name": "Semechah Ka Yan", "orcid": "0000-0001-7801-3635", "clpid": "Lui-Semechah-Ka-Yan" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "thesis_committee": [ { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Tsai", "given_name": "Victor C.", "clpid": "Tsai-V-C" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In this thesis, I present a series of works on the characterization of source properties and physical mechanisms of various small to moderate earthquakes through both observational and numerical approaches. From the results, we find implications on a broader scheme of topics relating to larger earthquakes, shear zone structure, frictional properties of faults, and seismic hazard assessment.
\r\n\r\nPart I consists of two studies using waveform modeling. In Chapter 2, we present an in-depth study of a series of intraslab earthquakes that occurred in a localized region near the downdip edge of the 2011 Mw Tohoku-Oki megathrust earthquake. By refining source parameters of selected events, simulating their rupture properties and comparing their mechanisms to stress changes caused by the main shock in the region, we are able to identify the true rupture plane and the reactivation of a subducted normal fault, enhancing our understanding on the downdip shear zone. In Chapter 3, based on similar techniques, we further develop a systematic methodology to perform fast assessments on important source properties as an earthquake occurs. For two Mw 4.4 earthquakes in Fontana, moment magnitude and focal mechanism can be accurately estimated with 3 to 6 s after the first P-wave arrival, while focal depth can be constrained upon the arrival of S waves. Rupture directivity can also be determined with as little as 3 seconds of P waves. This study opens the opportunity to predict ground motions ahead of time and can potentially be useful for Earthquake Early Warning.
\r\n\r\nPart II involves the modeling of seismic source properties and physical mechanisms of interacting earthquakes in dynamic rupture simulations. In particular, we focus on small repeating earthquake sequences that trigger one another. In Chapter 4, we quantify the relative importance of physical mechanisms that contribute to earthquake interaction and identify that the stress change caused by post seismic slip is the dominating factor. Our findings introduce the possibility to constrain frictional properties of the fault based on earthquake interactions. We further apply this working model in Chapter 5 to reproduce the actual interacting repeating sequences in Parkfield. We are able to identify possible physical mechanisms that cause the inferred high stress drops of these repeating events, as well as reproduce their synchronized seismic cycles. Results from our simulations are consistent with the observed scaling relation between the recurrence time interval and the seismic moment of these events. Our findings indicate that the difference between the observed and the theoretical scaling relations can be explained by the significant aseismic slip in the rupture area.
", "doi": "10.7907/Z9QN64QM", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9221", "collection": "thesis", "collection_id": "9221", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10142015-142502895", "type": "thesis", "title": "Probabilistic Imaging and Dynamic Modeling of Earthquake Source Processes", "author": [ { "family_name": "Jiang", "given_name": "Junle", "orcid": "0000-0002-8796-5846", "clpid": "Jiang-Junle" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Simons", "given_name": "Mark", "clpid": "Simons-M" } ], "thesis_committee": [ { "family_name": "Ampuero", "given_name": "Jean-Paul", "clpid": "Ampuero-J-P" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Heaton", "given_name": "Thomas H.", "clpid": "Heaton-T-H" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Simons", "given_name": "Mark", "clpid": "Simons-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Investigation of large, destructive earthquakes is challenged by their infrequent occurrence and the remote nature of geophysical observations. This thesis sheds light on the source processes of large earthquakes from two perspectives: robust and quantitative observational constraints through Bayesian inference for earthquake source models, and physical insights on the interconnections of seismic and aseismic fault behavior from elastodynamic modeling of earthquake ruptures and aseismic processes.
\r\n\r\nTo constrain the shallow deformation during megathrust events, we develop semi-analytical and numerical Bayesian approaches to explore the maximum resolution of the tsunami data, with a focus on incorporating the uncertainty in the forward modeling. These methodologies are then applied to invert for the coseismic seafloor displacement field in the 2011 Mw 9.0 Tohoku-Oki earthquake using near-field tsunami waveforms and for the coseismic fault slip models in the 2010 Mw 8.8 Maule earthquake with complementary tsunami and geodetic observations. From posterior estimates of model parameters and their uncertainties, we are able to quantitatively constrain the near-trench profiles of seafloor displacement and fault slip. Similar characteristic patterns emerge during both events, featuring the peak of uplift near the edge of the accretionary wedge with a decay toward the trench axis, with implications for fault failure and tsunamigenic mechanisms of megathrust earthquakes.
\r\n\r\nTo understand the behavior of earthquakes at the base of the seismogenic zone on continental strike-slip faults, we simulate the interactions of dynamic earthquake rupture, aseismic slip, and heterogeneity in rate-and-state fault models coupled with shear heating. Our study explains the long-standing enigma of seismic quiescence on major fault segments known to have hosted large earthquakes by deeper penetration of large earthquakes below the seismogenic zone, where mature faults have well-localized creeping extensions. This conclusion is supported by the simulated relationship between seismicity and large earthquakes as well as by observations from recent large events. We also use the modeling to connect the geodetic observables of fault locking with the behavior of seismicity in numerical models, investigating how a combination of interseismic geodetic and seismological estimates could constrain the locked-creeping transition of faults and potentially their co- and post-seismic behavior.
", "doi": "10.7907/Z9639MQC", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8861", "collection": "thesis", "collection_id": "8861", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05172015-152006825", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 13609562, "license": "other", "mime_type": "application/pdf", "url": "/8861/1/thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Collective Behavior of Asperities as a Model for Friction and Adhesion", "author": [ { "family_name": "Hulikal Sampath Kumaran", "given_name": "Srivatsan", "clpid": "Hulikal-Sampath-Kumaran-Srivatsan" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Understanding friction and adhesion in static and sliding contact of surfaces is important in numerous physical phenomena and technological applications. Most surfaces are rough at the microscale, and thus the real area of contact is only a fraction of the nominal area. The macroscopic frictional and adhesive response is determined by the collective behavior of the population of evolving and interacting microscopic contacts. This collective behavior can be very different from the behavior of individual contacts. It is thus important to understand how the macroscopic response emerges from the microscopic one.
\r\n\r\nIn this thesis, we develop a theoretical and computational framework to study the collective behavior. Our philosophy is to assume a simple behavior of a single asperity and study the collective response of an ensemble. Our work bridges the existing well-developed studies of single asperities with phenomenological laws that describe macroscopic rate-and-state behavior of frictional interfaces. We find that many aspects of the macroscopic behavior are robust with respect to the microscopic response. This explains why qualitatively similar frictional features are seen for a diverse range of materials.
\r\n\r\nWe first show that the collective response of an ensemble of one-dimensional independent viscoelastic elements interacting through a mean field reproduces many qualitative features of static and sliding friction evolution. The resulting macroscopic behavior is different from the microscopic one: for example, even if each contact is velocity-strengthening, the macroscopic behavior can be velocity-weakening. The framework is then extended to incorporate three-dimensional rough surfaces, long- range elastic interactions between contacts, and time-dependent material behaviors such as viscoelasticity and viscoplasticity. Interestingly, the mean field behavior dominates and the elastic interactions, though important from a quantitative perspective, do not change the qualitative macroscopic response. Finally, we examine the effect of adhesion on the frictional response as well as develop a force threshold model for adhesion and mode I interfacial cracks.
", "doi": "10.7907/Z94M92HM", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:7953", "collection": "thesis", "collection_id": "7953", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09112013-133205322", "primary_object_url": { "basename": "PhD_thesis_thomas_marion_fontcor.pdf", "content": "final", "filesize": 260903591, "license": "other", "mime_type": "application/pdf", "url": "/7953/49/PhD_thesis_thomas_marion_fontcor.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Frictional Properties of Fault: From Observations on the Longitudinal Valley Fault, Taiwan, to Dynamic Simulations", "author": [ { "family_name": "Thomas", "given_name": "Marion Y.", "clpid": "Thomas-Marion-Y" } ], "thesis_advisor": [ { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Asimow", "given_name": "Paul David", "clpid": "Asimow-P-D" }, { "family_name": "Wernicke", "given_name": "Brian P.", "clpid": "Wernicke-B-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Heaton", "given_name": "Thomas H.", "clpid": "Heaton-T-H" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Faults can slip either aseismically or through episodic seismic ruptures, but we still do not understand the factors which determine the partitioning between these two modes of slip. This challenge can now be addressed thanks to the dense set of geodetic and seismological networks that have been deployed in various areas with active tectonics. The data from such networks, as well as modern remote sensing techniques, indeed allow documenting of the spatial and temporal variability of slip mode and give some insight. This is the approach taken in this study, which is focused on the Longitudinal Valley Fault (LVF) in Eastern Taiwan. This fault is particularly appropriate since the very fast slip rate (about 5 cm/yr) is accommodated by both seismic and aseismic slip. Deformation of anthropogenic features shows that aseismic creep accounts for a significant fraction of fault slip near the surface, but this fault also released energy seismically, since it has produced five M_w>6.8 earthquakes in 1951 and 2003. Moreover, owing to the thrust component of slip, the fault zone is exhumed which allows investigation of deformation mechanisms. In order to put constraint on the factors that control the mode of slip, we apply a multidisciplinary approach that combines modeling of geodetic observations, structural analysis and numerical simulation of the \"seismic cycle\". Analyzing a dense set of geodetic and seismological data across the Longitudinal Valley, including campaign-mode GPS, continuous GPS (cGPS), leveling, accelerometric, and InSAR data, we document the partitioning between seismic and aseismic slip on the fault. For the time period 1992 to 2011, we found that about 80-90% of slip on the LVF in the 0-26 km seismogenic depth range is actually aseismic. The clay-rich Lichi M\\'elange is identified as the key factor promoting creep at shallow depth. Microstructural investigations show that deformation within the fault zone must have resulted from a combination of frictional sliding at grain boundaries, cataclasis and pressure solution creep. Numerical modeling of earthquake sequences have been performed to investigate the possibility of reproducing the results from the kinematic inversion of geodetic and seismological data on the LVF. We first investigate the different modeling strategy that was developed to explore the role and relative importance of different factors on the manner in which slip accumulates on faults. We compare the results of quasi dynamic simulations and fully dynamic ones, and we conclude that ignoring the transient wave-mediated stress transfers would be inappropriate. We therefore carry on fully dynamic simulations and succeed in qualitatively reproducing the wide range of observations for the southern segment of the LVF. We conclude that the spatio-temporal evolution of fault slip on the Longitudinal Valley Fault over 1997-2011 is consistent to first order with prediction from a simple model in which a velocity-weakening patch is embedded in a velocity-strengthening area.", "doi": "10.7907/0AFX-WS57", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:7780", "collection": "thesis", "collection_id": "7780", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-210319511", "primary_object_url": { "basename": "SURENDRA_NADH_SOMALA_thesis.pdf", "content": "final", "filesize": 17191935, "license": "other", "mime_type": "application/pdf", "url": "/7780/1/SURENDRA_NADH_SOMALA_thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Source Imaging with Dense Sensor Networks: Inversions Based on Adjoint Methods", "author": [ { "family_name": "Somala", "given_name": "Surendra Nadh", "clpid": "Somala-Surendra-Nadh" } ], "thesis_advisor": [ { "family_name": "Ampuero", "given_name": "Jean-Paul", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Krishnan", "given_name": "Swaminathan", "clpid": "Krishnan-S" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "clpid": "Ampuero-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Inversions of earthquake source slip from the recorded ground motions typically impose a number of restrictions on the source parameterization, which are needed to stabilize the inverse problem with sparse data. Such restrictions may include smoothing, causality considerations, predetermined shapes of the local source-time function, and constant rupture speed. The best regional networks have sensor spacing in the tens of kilometers range, much larger than the wavelengths relevant to key aspects of earthquake physics. Novel approaches to providing orders-of-magnitude denser sensing include low-cost sensors (Community Seismic Network) and space-based optical imaging (Geostationary Optical Seismometer). This thesis aims to understand whether the inversion results could be substantially improved, with fewer constraints, by the availability of much denser sensor networks than currently available.
\r\n\r\nInversions that involve large number of sensors and 3D crustal velocity models are intractable with the current source inversion codes. Hence we have developed a new approach that can handle thousands of sensors in heterogeneous media. It employs iterative conjugate gradient optimization based on an adjoint method and involves iterative time-reversed 3D wave propagation simulations using the spectral element method (SPECFEM3D). We have also developed a variant of this adjoint-based method for layered media that utilizes pre-computed Green\u2019s functions instead of the time-reversed wave propagation. The developed methods have been applied to two problems: impact of crustal structure uncertainties on source inversion and resolution of rise time as a function of network spacing and rupture velocity. In the first part, we show that typical uncertainties in crustal velocity models represented by a von Karman distribution of 5 km correlation length and 5% standard deviation (with Hurst exponent of zero), severely degrade the quality of source inversion. However, if the velocity uncertainties have a correlation of 500 m or a standard deviation of 1%, then source inversion has an adequate quality. In the second part we find that supershear ruptures show almost identical source recovery in terms of width of the slip pulse for network spacings ranging from few km to tens of km, even for rise times as short as 1 sec, while subshear ruptures require a network spacing finer than a penetration length that depends on rupture velocity and rise time, as their peak ground velocity decay rapidly with distance from the fault.
\r\n\r\nIn summary, we have developed scalable source inversion tools that will enable exploiting the next generation of very dense earthquake observation systems, improvements in regional scale 3D tomography models and accelerated advancements in computing capabilities. These developments will be critical in resolving the fine spatio-temporal features of earthquake sources that are pertinent to fracture mechanics and earthquake physics. With the 3D iterative time-reversal imaging, one could aspire for extracting more information from the high frequency wavefield by considering joint improvement of source and structure.
\r\n", "doi": "10.7907/Z9WQ01S7", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:6870", "collection": "thesis", "collection_id": "6870", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03262012-175814763", "primary_object_url": { "basename": "TChenThesis.pdf", "content": "final", "filesize": 13489798, "license": "other", "mime_type": "application/pdf", "url": "/6870/1/TChenThesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Part I: Structure of Central and Southern Mexico from Velocity and Attenuation Tomography. Part II: Physics of Small Repeating Earthquakes ", "author": [ { "family_name": "Chen", "given_name": "Ting", "clpid": "Chen-Ting" } ], "thesis_advisor": [ { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "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": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In part I, the 3D velocity and attenuation structure of the Cocos subduction zone in Mexico is imaged using earthquakes recorded by two temporary seismic arrays and local stations. Inversion results reveal low-attenuation and high-velocity Cocos slab. The slab dip angle increases from almost flat in central Mexico near Mexico City to about 30 degrees in southern Mexico near the Isthmus of Tehuantepec. High attenuation and low velocity in the crust beneath the Trans-Mexico Volcanic Belt correlate with low resistivity, and are probably related to dehydration and melting process. The most pronounced high-attenuation, low-Vp and high-Vp/Vs anomaly is found in the crust beneath the Veracruz Basin. A high-velocity structure dipping southward from the Gulf of Mexico near the Isthmus of Tehuantepec coincides with a discontinuity from a receiver functions study, and provides an evidence for the collision between the Yucatan Block and Mexico in the Miocene.
\r\n\r\n\r\nIn part II, we show that a model of small repeating earthquakes based on laboratory-derived rate and state friction laws reproduces the observed scaling between the recurrence time and seismic moment. In the model, a small fault patch governed by velocity-weakening friction is surrounded by a much larger velocity-strengthening region. For a fixed set of friction parameters, the observed scaling is reproduced by varying the size of the velocity-weakening patch. We further investigate the behavior 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 vs. fully dynamic representation of inertial effects, and 2D vs. 3D simulations. We find that the simulated scalings between the recurrence time and seismic moment for these different scenarios are similar while differences do exist. We propose a theoretical model for the scaling between the recurrence time and seismic moment of small repeating earthquakes. 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": "10.7907/REJW-YJ88", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:1535", "collection": "thesis", "collection_id": "1535", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04282009-202026", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 5015961, "license": "other", "mime_type": "application/pdf", "url": "/1535/2/thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Investigations of Earthquake Source Processes Based on Fault Models with Variable Friction Rheology", "author": [ { "family_name": "Kaneko", "given_name": "Yoshihiro", "orcid": "0000-0003-2342-0131", "clpid": "Kaneko-Yoshihiro" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "clpid": "Ampuero-J-P" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Heaton", "given_name": "Thomas H.", "clpid": "Heaton-T-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Ample experimental and observational evidence suggests that friction properties on natural faults vary spatially. In the lab, rock friction depends on temperature and confining pressure and it can be either velocity weakening or velocity strengthening, leading to either unstable or stable slip. Such variations in friction rheology can explain patterns of seismic and aseismic fault slip inferred from field observations.
\r\n\r\nThis thesis studies earthquake source processes using models with relatively simple but conceptually important patterns of velocity-weakening and velocity-strengthening friction that can arise on natural faults. Based on numerical and analytical modeling, we explore the consequences of such patterns for earthquake sequences, interseismic coupling, earthquake nucleation processes, aftershock occurrence, peak ground motion in the vicinity of active faults, and seismic slip budget at shallow depths. The velocity-dependence of friction is embedded into the framework of logarithmic rate and state friction laws.
\r\n\r\nIn addition to using existing boundary integral methods, which are accurate and efficient in simulating slip on planar faults embedded in homogeneous elastic media, the thesis develops spectral element methods to consider single dynamic ruptures and long-term histories of seismic and aseismic slip in models with layered bulk properties.
\r\n\r\nThe results of this thesis help to understand a number of observed fault slip phenomena, such as variability in earthquake patterns and its relation to interseismic coupling, seismic quiescence following decay of aftershocks at inferred rheological transitions, instances of poor correlation between static stress changes and aftershock occurrence, the lack of universally observed supershear rupture near the free surface, and coseismic slip deficit of large strike-slip earthquakes at shallow depths. The models, approaches, and numerical methods developed in the thesis motivate and enable consideration of many other earthquake source problems, such as the combined effect of two or more triggering mechanisms on aftershock rates, inferring friction properties on natural faults based on seismic and geodetic measurements, seismic hazard assessment based on observed interseismic coupling, and the effect of heterogeneous and/or nonelastic bulk properties on earthquake sequences.
\r\n\r\n", "doi": "10.7907/1WGT-6623", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:638", "collection": "thesis", "collection_id": "638", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02142009-181805", "primary_object_url": { "basename": "Thesis_YiLiu_Sep08.pdf", "content": "final", "filesize": 7225175, "license": "other", "mime_type": "application/pdf", "url": "/638/1/Thesis_YiLiu_Sep08.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Three-Dimensional Elastodynamic Modeling of Frictional Sliding with Application to Intersonic Transition", "author": [ { "family_name": "Liu", "given_name": "Yi", "clpid": "Liu-Yi" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" }, { "family_name": "Heaton", "given_name": "Thomas H.", "clpid": "Heaton-T-H" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Spontaneous slip on frictional interfaces involves both short-lived inertially-driven events and long-term quasi-static sliding. An example of considerable practical importance is the response of faults in the Earth's crust to tectonic loading. The response combines earthquakes that cause destructive ground motions and aseismic slip. Numerical models are needed to study the physics and mechanics of such complex behavior. In part, the models can help understand the observed slip patterns and interpret them in terms of constitutive properties of rocks determined in the lab.
\r\n\r\nThis thesis contains two main contributions. The first one is the development and implementation of a 3D methodology for simulations of spontaneous long-term interface slip punctuated by rapid inertially driven ruptures. Our approach is the first one to combine long-term deformation histories and the resulting stress redistribution on faults with full inclusion of inertial effects during simulated earthquakes in the context of 3D models. It reproduces all stages of earthquake cycles, from accelerating slip before dynamic instability, to rapid inertially driven propagation of earthquake rupture, to post-seismic slip, and to interseismic creep, including aseismic transients. The second main contribution is the discovery of the potentially dominating effect of favorable heterogeneity on intersonic transition in earthquakes, in both 2D models of single dynamic ruptures and 3D models of long-term fault slip. Studies of intersonic ruptures are practically important as they have the potential to cause strong ground motion farther from the fault than subsonic ruptures. Our conclusion that rheological boundaries promote transition to intersonic speeds in 3D rupture models is completely unexpected, as the neighboring stably slipping regions inhibit fast, inertially driven slip. The result could not be established in earlier studies, as it requires the computational methodology developed here that combines inertial effects, long-term slip histories, and 3D fault models. The thesis also develops test problems for dynamic rupture propagation and evaluates simplified quasi-dynamic approaches.
\r\n\r\nThe obtained results emphasize that dynamic ruptures should be considered in the context of the entire slip history of the fault, as such approach allows dynamic ruptures to occur under stress conditions established by prior slip, which leads to characteristic stress distributions that are not considered in single-event simulations. The developed 3D methodology can be applied to a number of problems in earthquake physics and mechanics that involve interaction of seismic and aseismic slip.
\r\n", "doi": "10.7907/JWCV-8V74", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:5207", "collection": "thesis", "collection_id": "5207", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05272009-165712", "primary_object_url": { "basename": "Ajay_Thesis.pdf", "content": "final", "filesize": 1453432, "license": "other", "mime_type": "application/pdf", "url": "/5207/1/Ajay_Thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Simulation of Dynamic Interface Fracture Using Spectral Boundary Integral Method", "author": [ { "family_name": "Harish", "given_name": "Ajay Bangalore", "clpid": "Harish-Ajay-Bangalore" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Simulation of three-dimensional dynamic fracture events constitutes one of the most challenging topics in the field of computational mechanics. Spontaneous dynamic fracture along the interface of two elastic solids is of great importance and interest to a number of disciplines in engineering and science. Applications include dynamic fractures in aircraft structures, earthquakes, thermal shocks in nuclear containment vessels and delamination in layered composite materials.
\r\n\r\nThis thesis presents numerical modeling of laboratory experiments on dynamic shear rupture, giving an insight into the experimental nucleation conditions. We describe a methodology of dynamic rupture simulation using spectral boundary integral method, including the theoretical background, numerical implementation and cohesive zone models relevant to the dynamic fracture problem. The developed numerical implementation is validated using the simulation of Lamb's problem of step loading on an elastic half space and mode I crack propagation along a bonded interface. Then the numerical model and its comparison with experimental measurements is used to investigate the initiation procedure of the dynamic rupture experiments. The inferred parameters of the initiation procedure can be used in future studies to model the experimental results on supershear transition and rupture models.
\r\n", "doi": "10.7907/B6P7-F707", "publication_date": "2009", "thesis_type": "engd", "thesis_year": "2009" }, { "id": "thesis:4240", "collection": "thesis", "collection_id": "4240", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10242008-070701", "primary_object_url": { "basename": "LuXiao_Thesis_Oct08.pdf", "content": "final", "filesize": 7721293, "license": "other", "mime_type": "application/pdf", "url": "/4240/1/LuXiao_Thesis_Oct08.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Combined Experimental and Numerical Study of Spontaneous Dynamic Rupture on Frictional Interfaces", "author": [ { "family_name": "Lu", "given_name": "Xiao", "clpid": "Lu-Xiao" } ], "thesis_advisor": [ { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" }, { "family_name": "Rosakis", "given_name": "Ares J.", "clpid": "Rosakis-A-J" } ], "thesis_committee": [ { "family_name": "Rosakis", "given_name": "Ares J.", "clpid": "Rosakis-A-J" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Knowles", "given_name": "James K.", "clpid": "Knowles-J-K" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Lapusta", "given_name": "Nadia", "clpid": "Lapusta-N" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The process of spontaneous dynamic frictional sliding along the interface of two elastic solids is of great interest to a number of disciplines in engineering and sciences. Applications include frictional rupture processes in earthquakes, delamination of layered composite materials, and sliding between soft membranes in biological systems. The transient nature of rupture dynamics presents an array of fascinating yet challenging questions, including the nucleation process, the mechanism of interface failure, and the speed and mode of rupture propagation.
\r\n\r\nThis thesis presents such a combined experimental and theoretical study aimed at understanding the conditions for selecting pulse-like vs. crack-like rupture modes and subshear vs. supershear rupture speeds. There are two major contributions in this work. The first one is high-resolution experimental study of the rupture modes on a frictional interface. The study presents first 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, importance of velocity-weakening friction for earthquake dynamics. The second major contribution is the numerical modeling of the rupture experiments that reveal the importance of the rupture nucleation mechanism and friction formulations. The modeling of sub-Rayleigh to supershear transition has demonstrated the influence of rupture nucleation mechanism on supershear transition distance, as well as on the mechanism of supershear transition. The modeling of pulse-like to crack-like rupture mode transition has confirmed the necessity of velocity weakening friction for producing pulse-like rupture to match the experimental observations.
\r\n", "doi": "10.7907/BGGT-MC04", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" } ]