[ { "id": "https://authors.library.caltech.edu/records/57vx0-8p458", "eprint_id": 24924, "eprint_status": "archive", "datestamp": "2023-08-19 15:01:11", "lastmod": "2024-01-13 05:20:22", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Don V." } }, { "id": "Ni-Sidao", "name": { "family": "Ni", "given": "Sidao" }, "orcid": "0000-0003-2988-4850" } ] }, "title": "Seismic Modeling Constraints on the South African Super Plume", "ispublished": "unpub", "full_text_status": "public", "note": "\u00a9 2005 American Geophysical Union. We thank Lianxing Wen and Ed Garnero for their excellent reviews, Evelina Cui for her efforts in producing this manuscript, and the editors of this book, in particular, Rob van der Hilst and production coordinator Virginia Marcum. This research was supported by NSF Grant EAR-0229885. Contribution Number 9116 of the Division of Geological and Planetary Sciences,\nCalifornia Institute of Technology.\n\n
Published - Helmberger2005p9757Earthquakes_Radiated_Energy_And_The_Physics_Of_Faulting.pdf
", "abstract": "Tomographic studies of the structure of the lower mantle beneath South Africa reveal large-scale low velocities above the core-mantle boundary. Predicted SKS delay patterns (up to 3 s) for some of these models fit observations (Kaapvaal Array data) quite well except for magnitude level, explaining less than one-half the\nobserved anomaly. Moreover, the sharpness in travel-time offsets and waveform complications require that nearly vertical walls separate the anomalous structure from the normal preliminary reference Earth model (PREM) mantle. We present numerous record sections along with 2D and 3D synthetics displaying multipathing of arrivals (S_(d') SKS, SKKS, S, and ScS), based on a large-scale 3D structure.\nThis kidney-shaped structure has one apex beneath the Indian Ocean (Kerguelen) and the other extending beneath the Mid-Atlantic (Cape Verde). The structure is about 1200 km wide beneath South Africa and extends upward to at least 1000 km through the lower mantle, similar to Grand's model but with an average uniform velocity decrease of about 3% relative to PREM. We have not found any evidences for ultra-low-velocity zones (ULVZ) beneath the main structure but ample evidence at some locations near the edges. We also analyzed Pd and the differentials between PcP travel times and P travel times (PcP-P) along the same great circle paths from the same events. The P-velocity is not very anomalous, perhaps -0.5%. The sharpness of the lateral boundaries (walls) and the large contrast in P and S velocities can be used in arguments for a thermochemical origin.", "date": "2005", "date_type": "published", "publisher": "American Geophysical Union", "place_of_pub": "Washington, DC", "pagerange": "63-81", "id_number": "CaltechAUTHORS:20110818-084011694", "isbn": "0-87590-425-4", "book_title": "Earth's Deep Mantle: Structure, Composition, and Evolution", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110818-084011694", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "funders": { "items": [ { "agency": "NSF", "grant_number": "EAR-0229885" } ] }, "other_numbering_system": { "items": [ { "id": "9116", "name": "Caltech Division of Geological and Planetary Sciences" } ] }, "contributors": { "items": [ { "id": "van-Der-Hilst-R-D", "name": { "family": "van Der Hilst", "given": "R. D." } }, { "id": "Bass-J-D", "name": { "family": "Bass", "given": "J. D." } }, { "id": "Matas-J", "name": { "family": "Matas", "given": "J." } }, { "id": "Trampert-J", "name": { "family": "Trampert", "given": "J." } } ] }, "doi": "10.1029/160GM06", "primary_object": { "basename": "Helmberger2005p9757Earthquakes_Radiated_Energy_And_The_Physics_Of_Faulting.pdf", "url": "https://authors.library.caltech.edu/records/57vx0-8p458/files/Helmberger2005p9757Earthquakes_Radiated_Energy_And_The_Physics_Of_Faulting.pdf" }, "resource_type": "book_section", "pub_year": "2005", "author_list": "Helmberger, Don V. and Ni, Sidao" }, { "id": "https://authors.library.caltech.edu/records/z8694-cca09", "eprint_id": 35758, "eprint_status": "archive", "datestamp": "2023-08-20 06:54:03", "lastmod": "2023-10-20 20:37:03", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Don V." } }, { "id": "Zhao-L-S", "name": { "family": "Zhao", "given": "Lian-She" } }, { "id": "Garnero-E-J", "name": { "family": "Garnero", "given": "Edward J." } } ] }, "title": "Construction of Synthetics for 2D structures; core phases", "ispublished": "unpub", "full_text_status": "restricted", "note": "\u00a9 1996 Editrice compositori.\nWe would like to thank Xiaoming Ding for his help in generating a number\nof these figures. This research was supported by the National Science Foundation,\ngrant EAR93-16441, and by the Air Force Office of Scientific Research under\ngrant F49620-92-10221. Contribution 5340, Division of Geological and Planetary\nSciences, California Institute of Technology, Pasadena, California, 91125.", "abstract": "Recent studies have emphasized the prominence of anomalous high and low\nvelocity regions in the lower mantle. For example, slower than average seismic\nshear wave velocities beneath the central Pacific accompanied by surrounding\nhigher than average velocities is common to most tomographic studies (e.g., see\nTanimoto, 1990; Masters et al., 1992; Su and Dziewonski, 1994). Images from\nthese reports indicate long wavelength (> 3000 km) structures with velocity\nanomalies of up to \u00b1 2.5%. A particularly prominent slow region occurs just north\nof the Fiji-Tonga region in all of these models and has been noted by many authors\nwith respect to differential times of body waves, such as ScS-S by Sipkin and\nJordan (1980), S-SKS by Garnero and Helmberger (1993) and others. The latter\nstudy demonstrates that S-SKS time predictions made from present 3D models do\nnot agree with all of the observations. Since this anomaly may well be associated\nwith up-welling currents in the mantle, the seismic details become particularly important\nespecially at the shorter wavelengths associated with body waves (5-100\nkm). Thus, better methods of generating realistic synthetics for these types of\ncomplex models would be useful and are addressed in this study.", "date": "1996", "date_type": "published", "publisher": "Editrice compositori", "place_of_pub": "Bologna, Italy", "pagerange": "183-221", "id_number": "CaltechAUTHORS:20121203-095459179", "isbn": "978-8877940803", "book_title": "Seismic modelling of earth structure", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121203-095459179", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "funders": { "items": [ { "agency": "NSF", "grant_number": "EAR93-16441" }, { "agency": "Air Force Office of Scientific Research (AFOSR)", "grant_number": "F49620-92-10221" } ] }, "other_numbering_system": { "items": [ { "id": "5340", "name": "Caltech Division of Geological and Planetary Sciences" } ] }, "contributors": { "items": [ { "id": "Boschi-E", "name": { "family": "Boschi", "given": "Enzo" } }, { "id": "Ekstr\u00f6m-G", "name": { "family": "Ekstr\u00f6m", "given": "G\u00f6ran" } }, { "id": "Morelli-A", "name": { "family": "Morelli", "given": "A." } } ] }, "resource_type": "book_section", "pub_year": "1996", "author_list": "Helmberger, Don V.; Zhao, Lian-She; et el." }, { "id": "https://authors.library.caltech.edu/records/mbawm-q7k21", "eprint_id": 35757, "eprint_status": "archive", "datestamp": "2023-08-20 06:53:56", "lastmod": "2024-01-13 05:57:34", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Don V." } }, { "id": "Woods-B", "name": { "family": "Woods", "given": "Brad" } } ] }, "title": "Regional Source Parameters, Seismic Energy, and Discrimination", "ispublished": "unpub", "full_text_status": "restricted", "note": "\u00a9 1996 Kluwer Academic Publishers.\n\nWe thank Evelina Cui for producing this camera-ready manuscript and Dave Harkrider for his review. This research was supported by the Department of Defense as monitored by the Air Force Office of Scientific Research under contract F49620-93-1-0221. Contribution no. 5472, Division of Geological & Planetary Sciences, Caltech, Pasadena,\nCA.", "abstract": "We have examined broadband waveforms from a large number of NTS explosions and\nearthquakes throughout the southwestern United States in order to characterize seismic\nsources. Explosions were found to be richer in coda energy than earthquakes. Most\nearthquakes show relatively little long-period (T>4 sec) coda energy and tend to be richer\nin long-period and shear-wave energy than explosions. We have developed several\nseismic discriminants based on these observations and our modeling experience. One\npromising discriminant is the ratio of short-period vertical component, P-wavetrain\nenergy, to long-period surface wave energy, averaged over three components. Explosions\ntend to have a higher ratio than do earthquakes, essentially an extension of m_b:M_s.\nMagnitude threshold for this discriminant is about 3.5. Another useful discriminant is\nbased on the total broadband energy to moment ratio where explosions are distinguished\nby their stronger energy levels relative to their long-period amplitudes. This approach\nrequires Green's functions, a source estimator program, and processes all events as\nearthquakes. For this method to be effective requires the calibration of the region using\nrelatively large earthquakes, M>5, but does not require calibrations of explosions.", "date": "1996", "date_type": "published", "publisher": "Kluwer Academic Publishers", "place_of_pub": "Boston", "pagerange": "365-383", "id_number": "CaltechAUTHORS:20121203-091244448", "isbn": "9780792338116", "book_title": "Monitoring a comprehensive test ban treaty", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121203-091244448", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "funders": { "items": [ { "agency": "Department of Defense" }, { "agency": "Air Force Office of Scientific Research (AFOSR)", "grant_number": "F49620-93-1-0221" } ] }, "other_numbering_system": { "items": [ { "id": "5472", "name": "Caltech Division of Geological and Planetary Sciences" } ] }, "contributors": { "items": [ { "id": "Husebye-E-S", "name": { "family": "Husebye", "given": "Eystein Sverre" } }, { "id": "Dainty-A-M", "name": { "family": "Dainty", "given": "A. M." } } ] }, "resource_type": "book_section", "pub_year": "1996", "author_list": "Helmberger, Don V. and Woods, Brad" }, { "id": "https://authors.library.caltech.edu/records/6mbme-6ns80", "eprint_id": 35645, "eprint_status": "archive", "datestamp": "2023-08-22 10:43:44", "lastmod": "2024-01-13 05:57:14", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Wald-D-J", "name": { "family": "Wald", "given": "David J." } }, { "id": "Heaton-T-H", "name": { "family": "Heaton", "given": "Thomas H." }, "orcid": "0000-0003-3363-2197" }, { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Donald V." } } ] }, "title": "Strong-Motion and Broadband Teleseismic Analysis of the Earthquake for Rupture Process and Hazards Assessment", "ispublished": "unpub", "full_text_status": "public", "note": "\u00a9 1986 Untied States Government Printing Office.\nThis work was supported by the U.S. Geological Survey\nunder contracts 14-08-0001-21912 and 14-08-0001-G1832. Reviews by Hiroo Kanamori, Paul Somerville,\nPaul Spudich, and Lisa Wald improved the manuscript.\nWe thank Steve Hartzell for useful discussions and advice\non the use of his inversion software, and Norm\nAbrahamson and Nancy Smith for providing programs to\ncompute the response-spectral bias.\n\nPublished - Heaton_PP1550A_p235.pdf
", "abstract": "We have used broadband records from 18 teleseismic\nstations and three-component records from 16 local strongmotion\nstations in a formal inversion to determine the\ntemporal and spatial distribution of slip during the earthquake.\nSeparate inversions of the teleseismic (periods, 3-30 s) \nand strong-motion (periods, 1-5 s) data sets result in\nsimilar source models. The data require bilateral rupture,\nwith relatively little slip in the region directly updip from\nthe hypocenter. Slip is concentrated in two patches: one\ncentered 6 km northwest of the hypocenter at 12-km depth\nwith an average slip amplitude of 250 cm, and the other\ncentered about 5 km southeast of the hypocenter at 16-km\ndepth with an average slip amplitude of 180 cm. This\nbilateral rupture results in large-amplitude ground motions\nat sites both to the northwest and southeast along\nthe fault strike. The northwestern patch, however, has a\nlarger seismic moment and overall stress drop and thus is\nthe source of the highest ground-motion velocities, a result\nconsistent with observations. The bilateral rupture also\nresults in relatively moderate ground motion directly updip\nfrom the hypocenter, in agreement with the ground motions\nobserved at Corralitos, Calif. Furthermore, there is\nclear evidence of a foreshock (M~4.5-5.0) or slow rupture\nnucleation about 2 s before the main rupture; the\norigin time implied by strong-motion trigger times is systematically\nnearly 2 s later than that predicted from the\nhigh-gain regional-network data. The seismic moment obtained\nfrom either or both data sets is about 3.0x10^(26)\ndyne-cm, and the seismic potency is 0.95 km^3. Our analysis\nindicates that the rupture model determined from the\nteleseismic data set alone, independent of the strong-motion\ndata set, is adequate to predict many characteristics\nof the local-strong-motion recordings.", "date": "1996", "date_type": "published", "publisher": "Untied States Government Printing Office", "id_number": "CaltechAUTHORS:20121126-145417758", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121126-145417758", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "funders": { "items": [ { "agency": "USGS", "grant_number": "14-08-0001-21912" }, { "agency": "USGS", "grant_number": "14-08-0001-G1832" } ] }, "local_group": { "items": [ { "id": "Division-of-Geological-and-Planetary-Sciences" } ] }, "contributors": { "items": [ { "id": "Spudich-P", "name": { "family": "Spudich", "given": "Paul" } }, { "id": "Bakun-W-H", "name": { "family": "Bakun", "given": "W. H." } }, { "id": "Prescott-W-H", "name": { "family": "Prescott", "given": "William H." } }, { "id": "Havach-G-A", "name": { "family": "Havach", "given": "George A." } } ] }, "primary_object": { "basename": "Heaton_PP1550A_p235.pdf", "url": "https://authors.library.caltech.edu/records/6mbme-6ns80/files/Heaton_PP1550A_p235.pdf" }, "resource_type": "book_section", "pub_year": "1996", "author_list": "Wald, David J.; Heaton, Thomas H.; et el." }, { "id": "https://authors.library.caltech.edu/records/k4936-q8e94", "eprint_id": 54388, "eprint_status": "archive", "datestamp": "2023-08-20 06:16:23", "lastmod": "2023-10-20 16:23:50", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Garnero-E-J", "name": { "family": "Garnero", "given": "Edward J." } }, { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Donald V." } } ] }, "title": "Seismic Resolution of the Earth's Outermost Core in Relation to Lower Mantle Heterogeneity", "ispublished": "unpub", "full_text_status": "restricted", "note": "\u00a9 1995 Elsevier Science B.V.", "abstract": "Issues concerning resolution of seismically determined outermost core properties are presented.\nParticular attention is given to effects of both large and small scale lower mantle heterogeneity\non seismic phases most commonly used for determining outermost core properties. The family\nof SmKS waves, which travel as S in the mantle, P in the core, reflecting (m-1) times at the\nunderside of the core-mantle boundary (CMB), are the outer core's equivalent to upper mantle\nmultiple S waves (S, SS, SSS, ... ), and are well-suited for studying outermost core structure.\nThe higher multiples of SmKS have outer core wave paths restricted to the outermost few\nhundred km of the core (see figure). Travel time and waveform behavior of SmKS waves are\nanalyzed over a large distance range (125\u00b0 - 165\u00b0) and correlated to overlying mantle structure.\nLong-period (LP) World Wide Seismographic Station Network data are utilized due to the\npresently unsurpassed \u224820 year time span of operation for global station coverage. This data\nset is augmented by available broadband data. In regions where lower mantle heterogeneity\nis predicted small, SmKS observations are well predicted by the PREM reference model, with\nthe addition of a slight reduction in Vp in the top 50 km of the core (1.5%). Such a reduction\nimplies chemical stratification in this 50 km zone, though this model feature is not uniquely\nresolved. Data having wave paths through areas of known D\" heterogeneity (\u00b1 2%) exhibit\nsystematic anomalies in SmKS differential times. 2-D wave propagation experiments using a\nmodified WKBJ method demonstrate how large scale lower mantle velocity perturbations can\nexplain long wavelength behavior of such anomalous SmKS times, though heterogeneity on\nsmaller scales may be responsible for the observed scatter about these trends. A 2-D model\nhaving anomalously slow lower mantle velocities beneath the Indonesia region produces SmKS\ndifferential time residuals that agree with observations of Fiji-Tonga events recorded in Eurasia\nand Africa. In general, information from previously published 3-D maps of mantle heterogeneity\ncan be used to construct starting models of 2-D cross sections appropriate for source-receiver\ngeometries of interest.", "date": "1995-09", "date_type": "published", "publisher": "Elsevier", "id_number": "CaltechAUTHORS:20150204-150153779", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150204-150153779", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "contributors": { "items": [ { "id": "Loper-D", "name": { "family": "Loper", "given": "D." } }, { "id": "Nataf-H-C", "name": { "family": "Nataf", "given": "H.-C." } } ] }, "resource_type": "book_section", "pub_year": "1995", "author_list": "Garnero, Edward J. and Helmberger, Donald V." }, { "id": "https://authors.library.caltech.edu/records/xsef7-ahg31", "eprint_id": 60557, "eprint_status": "archive", "datestamp": "2023-08-19 17:27:50", "lastmod": "2023-10-24 16:39:49", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Burdick-L-J", "name": { "family": "Burdick", "given": "L. J." } }, { "id": "Barker-J-S", "name": { "family": "Barker", "given": "J. S." } }, { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "D. V." } }, { "id": "Harkrider-D-G", "name": { "family": "Harkrider", "given": "D. G." } } ] }, "title": "Linear Elastic Waveform Modeling in the Inelastic Region of Underground Nuclear Explosions", "ispublished": "unpub", "full_text_status": "restricted", "note": "\u00a9 1985 Executive Graphic Services.", "abstract": "In an attempt to characterize the way in which linear elastic theory breaks\ndown within the inelastic region near underground nuclear explosions, we\nhave compared the observed velocity waveforms from the inelastic region with\npredictions of ordinary elastic generalized ray theory. In earlier studies, models for events at both Pahute Mesa and Amchitka were developed using ground\nmotion recordings from the 5 to 20 km distance range. The models consisted\nof a source time junction and a source strength, \u03c8\u221e for a point source in\na layered elastic crust. In this study the predictions of the models were evaluated\nat ranges from 0 to 5 km. Surprisingly, the elastic models predict the observed\npeak vertical velocity very accurately even in the spall zone. They also\npredict the rise times of the velocity pulses into surface zero. The elastic synthetic\nseismograms match the observed velocities up until the time when the\nspalled material begins to decelerate. The observed radial motions are much\nmore poorly modeled. Nevertheless, the results suggest that only low-order\ncorrections to elastic theory may be required to explain some of the phenomena\nwithin the inelastic region of contained nuclear explosions.\nVertical velocity waveforms within the spall zones of Amchitka and Pahute\nMesa events are well modeled by linear elastic theory during the compressive\npulse prior to spall. We introduce the definition of the \"compressive elastic radius.\"", "date": "1985", "date_type": "published", "publisher": "Executive Graphic Services", "id_number": "CaltechAUTHORS:20150928-081250895", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150928-081250895", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "contributors": { "items": [ { "id": "Kerr-A-U", "name": { "family": "Kerr", "given": "Ann U." } } ] }, "resource_type": "book_section", "pub_year": "1985", "author_list": "Burdick, L. J.; Barker, J. S.; et el." }, { "id": "https://authors.library.caltech.edu/records/ehfxb-f0392", "eprint_id": 35667, "eprint_status": "archive", "datestamp": "2023-08-22 01:37:07", "lastmod": "2023-10-20 20:08:58", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Heaton-T-H", "name": { "family": "Heaton", "given": "Thomas H." }, "orcid": "0000-0003-3363-2197" }, { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Donald V." } } ] }, "title": "Synthesis of San Fernando strong-motion records", "ispublished": "unpub", "full_text_status": "public", "note": "\u00a9 1978 National Science Foundation.\n\nPublished - Heaton_p52.pdf
", "abstract": "Three-dimensional models of a finite fault located in a half-space are constructed to\nstudy the ground motions from the 9 February 1971 earthquake as observed at JPL, Palmdale,\nand Lake Hughes (Array Station #4). The Cagniard-De Hoop Technique is used to compute the\nground motions due to infinitesimal point sources which are evenly distributed (0.5 km\nspacing) on the fault plane. The responses are summed with time lags determined by the\nassumed hypocentral solution and rupture velocity. Nonuniform fault displacement is\nmodeled by varying the weights of individual point sources. By investigating the motion\ndue to small sections of the fault it is possible to understand how various wave types\ninterfere to produce the motion due to the total fault. Recent modeling of teleseismic\nbody waves by Langston has indicated that the fault changes dip from 50\u00b0 to 30\u00b0 at a depth\nof approximately 5 km. This feature has been incorporated into our models. The assumed\nfault geometry and station locations are shown in Figure 1. In Figure 2, we display\nassumed fault displacements for a preliminary model which is used to explain the motions\nat JPL, PLM, and LKH. The overall moment for this model is 1.5 x 10^(26) ergs. The hypocenter\nis assumed to lie in the region of maximum displacement and a rupture velocity of\n1.8 km/sec (as suggested by Langston) is also assumed. Although stations LKH and JPL are\nsituated at roughly equal epicentral distances, there appears to be a dramatic difference\nin the character and amplitudes of ground motion seen for these stations. This can be\nseen in Figures 3 and 4. In these figures, the synthetic ground motions for the fault\nmodel described above are compared with the integrated accelerograms for these stations.\nBecause the integrated accelerograms have been filtered with an 8 sec. Ormsby filter, the\nsynthetics are displayed both with and without the inclusion of this filter. Although it\nappears that the particular fault model used for Figures 3 and 4 is not, in detail, correct,\nit does well at explaining the differences in character and amplitude of ground motions as\nseen between JPL and LKH. An examination of Figure 5 helps one to appreciate the complex\ninterplay between source and wave propagational effects. In this figure the fault is\nsubdivided into 5 strips each of which has a width of 4 km. Also shown are synthetic\nmotions (JPL, North) for a single point source located in the middle of each subfault.\nAlthough these point sources produce easily interpreted specific arrivals, it is clear\nthat the JPL record results from complex and not easily interpreted interaction of both\nsource and propagation effects. These synthetics also demonstrate the dramatic effect\nof the free-surface. Rayleigh wave and sP head wave contributions are of great importance.", "date": "1978", "date_type": "published", "publisher": "National Science Foundation", "id_number": "CaltechAUTHORS:20121127-101407169", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121127-101407169", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "local_group": { "items": [ { "id": "Division-of-Geological-and-Planetary-Sciences" } ] }, "primary_object": { "basename": "Heaton_p52.pdf", "url": "https://authors.library.caltech.edu/records/ehfxb-f0392/files/Heaton_p52.pdf" }, "resource_type": "book_section", "pub_year": "1978", "author_list": "Heaton, Thomas H. and Helmberger, Donald V." }, { "id": "https://authors.library.caltech.edu/records/zgr40-xs756", "eprint_id": 49773, "eprint_status": "archive", "datestamp": "2023-08-19 08:13:12", "lastmod": "2024-01-13 16:09:33", "type": "book_section", "metadata_visibility": "show", "creators": { "items": [ { "id": "Allen-C-R", "name": { "family": "Allen", "given": "Clarence R." } }, { "id": "Helmberger-D-V", "name": { "family": "Helmberger", "given": "Donald V." } } ] }, "title": "Search for temporal changes in seismic velocities using large explosions in southern California", "ispublished": "unpub", "full_text_status": "public", "note": "\u00a9 1973 Stanford University.\n\nPublished - Allen_1973p436.pdf
", "abstract": "For many years, large explosions within the\nCaltech seismic network have occurred periodically at a\nquarry near Corona (75 km southeast of Pasadena) and at\nthe Eagle Mountain iron mine (240 km east of Pasadena).\nExplosions have taken place almost daily since 1948 at\nEagle Mountain. The long-established station at Hayfield,\nvery close to the mine, permits accurate determinations of\napparent velocities to distant stations such as Barrett,\nand this particular path crosses the epicentral region of\nthe 1968 Borrego Mountain earthquake (M = 6.4). The first\narrival at Barrett, at a distance of 172 km, is a refracted\nwave, but a distinct second arrival presumably represents a\ncrustal phase. There has been no systematic change in the\napparent P-wave velocity of either phase since 1962;\nmaximum observed variation from the mean velocities is less\nthan 2% for 32 events distributed throughout the 1962-1973\nperiod. Fewer but larger events have taken place at Corona\nsince 1949. Nine of these events at roughly three-year\nintervals were recorded throughout the network as well as\nonsite for timing purposes. The observed variation in\nP-wave velocity is less than 3-1/2% for all paths, and\nall variations can probably be explained by instrumental\nand reading inaccuracies. Because of the timing of events\nand their locations, the results from Eagle Mountain and\nCorona do not completely rule out dilatancy effects prior\nto the Borrego Mountain and San Fernando earthquakes --\nthe two major shocks of this period. But the observations\ndo put certain restrictions on the possible size and nature\nof any proposed dilatancy regions, and there are no\ndiscernible systematic trends in the 24 years of data along\nany paths.", "date": "1973", "date_type": "published", "publisher": "Stanford University", "id_number": "CaltechAUTHORS:20140917-094944198", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140917-094944198", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "other_numbering_system": { "items": [ { "id": "2371", "name": "Caltech Division of Geological and Planetary Sciences" } ] }, "contributors": { "items": [ { "id": "Kovach-R-L", "name": { "family": "Kovach", "given": "Robert L." } }, { "id": "Nur-A", "name": { "family": "Nur", "given": "Amos" } } ] }, "primary_object": { "basename": "Allen_1973p436.pdf", "url": "https://authors.library.caltech.edu/records/zgr40-xs756/files/Allen_1973p436.pdf" }, "resource_type": "book_section", "pub_year": "1973", "author_list": "Allen, Clarence R. and Helmberger, Donald V." } ]