[ { "id": "authors:65vb5-ef595", "collection": "authors", "collection_id": "65vb5-ef595", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-143219524", "type": "article", "title": "Relationship of the 1979 Southern California Radon Anomaly to a possible regional strain event", "author": [ { "family_name": "Shapiro", "given_name": "M. H.", "clpid": "Shapiro-M-H" }, { "family_name": "Melvin", "given_name": "J. D.", "clpid": "Melvin-J-D" }, { "family_name": "Tombrello", "given_name": "T. A.", "clpid": "Tombrello-T-A" }, { "family_name": "Mendenhall", "given_name": "M. H.", "clpid": "Mendenhall-M-H" }, { "family_name": "Larson", "given_name": "P. B.", "clpid": "Larson-P-B" }, { "family_name": "Whitcomb", "given_name": "J. H.", "clpid": "Whitcomb-J-H" } ], "abstract": "During the second half of 1979, anomalously high emanation of radon was recorded at two stations of the automated radon-thoron monitoring network operated by the W. K. Kellogg Radiation Laboratory of the California Institute of Technology. The two stations exhibiting major anomalies, Kresge and Dalton Canyon, are located approximately 30 km apart on the frontal fault system of the Transverse Ranges of southern California. At Kresge the anomaly began on June 21, 1979, and continued through December 1979. At Dalton Canyon the anomaly started about 3 weeks later and also continued through December 1979. At both sites the anomalous levels of radon decreased (but did not return entirely to normal values) shortly before October 15, 1979. During the week of October 15, 1979, a 6.6-M earthquake occurred about 290 km to the southeast of the two stations, and later in that week, earthquakes of magnitude 4.2 and 4.1 occurred at Malibu and Lytle Creek. The latter two events were within 60 km of the monitors. A radon-thoron monitor at Lytle Creek recorded no long-term anomaly but did record a sharp spikelike decrease in the radon level on October 13, 1979. Coincident with our observations of anomalous radon levels, other investigators have reported anomalies or suspected anomalies in several other geodetic, geophysical, and geochemical signals from the same general region. The rapid temporal development of several of the anomalies together with the large area over which they were observed suggests that a large-scale strain event took place which may have been responsible both for the widespread anomalies and for the seismicity that occurred in the region subsequent to the onset of the anomalies.", "doi": "10.1029/JB086iB03p01725", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1981-03-10", "series_number": "B3", "volume": "86", "issue": "B3", "pages": "1725-1730" }, { "id": "authors:52yrz-ag853", "collection": "authors", "collection_id": "52yrz-ag853", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-150207252", "type": "article", "title": "Automated radon monitoring at a hard-rock site in the southern California transverse ranges", "author": [ { "family_name": "Shapiro", "given_name": "M. H.", "clpid": "Shapiro-M-H" }, { "family_name": "Melvin", "given_name": "J. D.", "clpid": "Melvin-J-D" }, { "family_name": "Tombrello", "given_name": "T. A.", "clpid": "Tombrello-T-A" }, { "family_name": "Whitcomb", "given_name": "J. H.", "clpid": "Whitcomb-J-H" } ], "abstract": "Data are presented from 20 months of near-real-time (three samples per day) radon monitoring at a hard-rock site in the Transverse Ranges of southern California. An annual cycle is evident in the data which is attributed to thermoelastic strains in the vicinity of the borehole site. Between April 1, 1977, and October 31, 1978, there were 11 earthquakes with magnitudes \u22652.0 within 25 km of the monitoring site. Three of these events appeared to be preceded by precursory signals, four were preceded by 'possible' precursory signals, and four were not preceded by any apparent precursors. Before the 4.6 M Malibu earthquake of January 1, 1979, a 'possible' precursory signal sequence of 40\u201350 days' duration was observed.", "doi": "10.1029/JB085iB06p03058", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1980-06-10", "series_number": "B6", "volume": "85", "issue": "B6", "pages": "3058-3064" }, { "id": "authors:96jfy-8c363", "collection": "authors", "collection_id": "96jfy-8c363", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-143740373", "type": "article", "title": "A local earthquake coda magnitude and its relation to duration, moment M_o, and local Richter magnitude M_L", "author": [ { "family_name": "Suteau", "given_name": "Anne M.", "clpid": "Suteau-A-M" }, { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "abstract": "A relationship is found between the seismic moment, M_o, of shallow local earthquakes, coda amplitudes, and the total duration of the signal, t, in seconds, measured from the earthquake origin time. Following Aki, we assume that the end of the coda is composed of backscattering surface waves due to lateral heterogeneity in the shallow crust. Using the linear relationship between the logarithm of M_o and the local Richter magnitude M_L, we obtain a relationship between M_L and t, of the form: M_L = a_0 + a_1 log t + a_2t^(1/3) + f(t), where a_0, a_1, a_2 are constants depending on an attenuation parameter (effective Q) and geometric spreading; and f(t) is a function of the instrument response and a (weak) function of the scattering process. This relationship is different from the empirical one generally used M_L = a_0 + a_1 log \u03c4 + a_2(log \u03c4)^2 + a_3\u0394, where \u03c4 is the duration measured from the first P arrival time and \u0394 is epicentral distance in kilometers. In the theoretical relationship, the dependence on epicentral distance is implicit in t. The theoretical relationship is used to calculate a coda magnitude M_C that is compared to M_L for southern California earthquakes which occurred during the period from 1972 to 1975. This comparison is made independently at six stations of the CIT network. At all stations, a good linear fit (M_L = C_0 + C_1M_C) is obtained. The standard errors range from 0.2 to 0.3 and the correlation coefficients from 0.80 to 0.90. Once station gain is accounted for, station correction terms are less than 0.17 magnitude unit when comparing M_L and M_c. M_c calculation is not limited to a duration measurement but can utilize the entire earthquake coda in order to increase by many times the statistical confidence in an estimate of an earthquake's magnitude.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1979-04", "series_number": "2", "volume": "69", "issue": "2", "pages": "353-368" }, { "id": "authors:672x5-mx517", "collection": "authors", "collection_id": "672x5-mx517", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-145847045", "type": "article", "title": "Elsinore fault seismicity: The September 13, 1973, Agua Caliente Springs, California, earthquake series", "author": [ { "family_name": "Allison", "given_name": "M. Lee", "clpid": "Allison-M-L" }, { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" }, { "family_name": "Cheatum", "given_name": "Craig E.", "clpid": "Cheatum-C-E" }, { "family_name": "McEuen", "given_name": "Robert B.", "clpid": "McEuen-R-B" } ], "abstract": "A relatively small M_L = 4.8 earthquake and its aftershock series on the southern portion of the Elsinore Fault Zone in eastern San Diego County, California, provided a rare opportunity to study an area that has been subjected to variable tectonic interpretations in the past. Within 12 to 26 hours after the main shock, a network of four portable seismograph stations was established around the main event near Agua Caliente Springs to supplement the stations of the Southern California Seismographic Network. Four days after the main shock, seven additional portable seismograph stations were installed. In addition to the main event, 45 subsequent events were studied, ranging in magnitude from about 1.0 to 3.7. Of these, 36 could be termed aftershocks by their close proximity to the main event, whose proper location was determined by analysis of the aftershock series. Of the two branches of the Elsinore Fault in this region, the south branch is associated with the earthquake series. Focal mechanisms are consistent with right-lateral strike-slip along the south branch, with northeast dip at latitude 32\u00b051\u2032N. These conclusions are supported by hypocentral locations. Thrust activity on the two fault branches may be developing a horst between them, accounting for elevation and tilt changes observed near Agua Caliente.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1978-04", "series_number": "2", "volume": "68", "issue": "2", "pages": "429-440" }, { "id": "authors:ajmz6-j4f37", "collection": "authors", "collection_id": "ajmz6-j4f37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-154038994", "type": "article", "title": "P- and S-phase data from local earthquakes in Southern California for 1966 to 1975", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "abstract": "The purpose of this note is to describe a card-image computer tape now available\nwith earthquake epicenter and P- and S-phase data for local earthquakes in\nSouthern California during the 10-year period of 1966 through 1975. The tape is\nreadable on an IBM 370/158 computer using standard FORTRAN READ statements.\nThe tape is currently being used for several research projects including event\nrelocation, velocity, P-delay, and magnitude studies. This research resource is being\nmade available to all scientific investigators.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1978-04", "series_number": "2", "volume": "68", "issue": "2", "pages": "523-525" }, { "id": "authors:1a6qx-0g345", "collection": "authors", "collection_id": "1a6qx-0g345", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160513-123454078", "type": "article", "title": "New vertical geodesy", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "abstract": "Vertical geodesy is undergoing a revolution because of two factors. First, new precise three-dimensional position measurement techniques used over very long distances and based on extraterrestrial reference systems provide a new class and precision of geometric data previously unavailable for geophysical investigations. Second, physical models in tectonic theory for large earthquakes predict crustal distortions that violate the conventional assumptions used to interpret gravity and leveling data. Leveling and geometric elevation measurements are not directly comparable because the interpretation of leveling data is density-model dependent. Estimates of pre-1971 San Fernando earthquake elevation changes based on leveling of about 10 cm may be as much as 3 cm, or 40%, too large. Pre-1964 Niigata earthquake leveling surveys, previously used as confirmation of the dilatancy model, do not require dilatancy as an explanation and easily allow an alternative model with a subsurface density increase. Gravity is also not a dependable estimator of elevation change. But a combination of gravity with either leveling, if the dimensions of the distorted body are known or small, or geometric elevation measurements is essential for the determination of crustal density and strain changes. The 1965\u20131967 Matsushiro earthquake swarm leveling and gravity data show a significant dilatant strain of 0.6\u20131.8\u00d710^(\u22124) if the proper model dimensions are used. This dilatant strain would be adequate to cause the observed drop in V_p/V_s, even if the crust were initially saturated prior to distortion. The combination of gravity, leveling, and the new geometric elevation measurements provides a useful parameter, gravitational potential, for the inversion of subsurface density distributions. Use of this parameter, defined as the free-air elevation anomaly, is illustrated for a nearly compensated mountain root structure and shows that this technique holds significant promise for the study of large, deep structures in the crust and upper mantle.", "doi": "10.1029/JB081i026p04937", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1976-09-10", "series_number": "26", "volume": "81", "issue": "26", "pages": "4937-4944" }, { "id": "authors:s6h8d-x1463", "collection": "authors", "collection_id": "s6h8d-x1463", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150220-070523447", "type": "article", "title": "Time-Dependent Seismology", "author": [ { "family_name": "Anderson", "given_name": "Don L.", "clpid": "Anderson-D-L" }, { "family_name": "Whitcomb", "given_name": "J. H.", "clpid": "Whitcomb-J-H" } ], "abstract": "The time variation of crustal velocities in tectonic regions is most reasonably attributed to stress induced variations in crack porosity. The decrease in V_p/V_s before earthquakes is due primarily to a large decrease in V_p. This supports the Nur dilatancy hypothesis but not the effective stress hypothesis. New data from the San Fernando region verify the V_p drop, show that this drop cannot be entirely due to source depth effects, and give strong support to the explanation of material property, or path effect, rather than source effect variations. Calculations show that the crack-widening model works even for mid crustal depths in saturated rock. Narrow cracks of low aspect ratio are required to satisfy the velocity and uplift constraints. The recovery of velocity prior to fracture can be due to fluid flow or crack closure. The t \u223c L^2 relation does not require diffusion. Diffusion of groundwater or crack closure leads to increased pore pressure and rock weakening. Observations of gravity, conductivity, and crustal distortions along with velocities should narrow the choice of models. The crust in regions of thrust tectonics is probably always dilatant to some degree. The aftershock region is smaller than the anomalous velocity region, which in turn must be smaller than the dilatant region. A simple relationship is derived for the relative sizes of the anomalous and aftershock regions.", "doi": "10.1029/JB080i011p01497", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1975-04-10", "series_number": "11", "volume": "80", "issue": "11", "pages": "1497-1503" }, { "id": "authors:fwzsd-qs863", "collection": "authors", "collection_id": "fwzsd-qs863", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190918-075239587", "type": "book_section", "title": "Seismological Studies of the San Fernando Earthquake and\n Their Tectonic Implications", "author": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Hanks", "given_name": "Thomas C.", "clpid": "Hanks-T-C" }, { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "contributor": [ { "family_name": "Oakeshott", "given_name": "Gordon B.", "clpid": "Oakeshott-G-B" } ], "abstract": "Improved hypocentral locations have been obtained for the San Fernando earthquake and its larger aftershocks through the use of data from portable stations installed in and around the aftershock area subsequent to the main shock. The main shock, at 14 00 41.8 GMT on 9 February 1971, is now assigned a magnitude (M_L) of 6.4 and a location at 34\u00b0 24.7' N, 118\u00b0 24.0' W, h = 8.4 km. Fifty-five aftershocks of magnitude 4.0 and greater had occurred through 31 December 1971. The lunate-shaped epicentral distribution of aftershocks is consistent with the idea of southward thrusting along a disc-shaped fault surface, and aftershock depths as well as aftershock focal mechanisms suggest that the thrust surface dips about 35\u00b0 toward N 20\u00b0 E. However, a distinct linear alignment of left-lateral strike-slip aftershocks parallel to the motion direction near the west boundary of activity suggests that the fault surface has a steep flexure along this line, down-stepped to the west, and both the planar distribution of aftershocks and the local geology support this concept.", "publisher": "California Division of Mines and Geology", "publication_date": "1975" }, { "id": "authors:ghyd1-w7719", "collection": "authors", "collection_id": "ghyd1-w7719", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130430-114455558", "type": "article", "title": "Point Mugu, California, Earthquake of 21 February 1973\n and Its Aftershocks", "author": [ { "family_name": "Ellsworth", "given_name": "W. L.", "clpid": "Ellsworth-W-L" }, { "family_name": "Campbell", "given_name": "R. H.", "clpid": "Campbell-R-H" }, { "family_name": "Hill", "given_name": "D. P.", "orcid": "0000-0001-7476-6306", "clpid": "Hill-D-P" }, { "family_name": "Page", "given_name": "R. A.", "clpid": "Page-R-A" }, { "family_name": "Alewine", "given_name": "R. W., III", "clpid": "Alewine-R-W-III" }, { "family_name": "Hanks", "given_name": "T. C.", "clpid": "Hanks-T-C" }, { "family_name": "Heaton", "given_name": "T. H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Hileman", "given_name": "J. A.", "clpid": "Hileman-J-A" }, { "family_name": "Kanamori", "given_name": "H.", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Minster", "given_name": "B.", "clpid": "Minster-B" }, { "family_name": "Whitcomb", "given_name": "J. H.", "clpid": "Whitcomb-J-H" } ], "abstract": "Seismological investigations show that the Point Mugu earthquake involved north-south crustal shortening deep within the complex fault zone that marks the southern front of the Transverse Ranges province. This earthquake sequence results from the same stress system responsible for the deformation in this province in the Pliocene through Holocene and draws attention to the significant earthquake hazard that the southern frontal fault system poses to the Los Angeles metropolitan area.", "doi": "10.1126/science.182.4117.1127", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1973-12-14", "series_number": "4117", "volume": "182", "issue": "4117", "pages": "1127-1129" }, { "id": "authors:dydj3-sx048", "collection": "authors", "collection_id": "dydj3-sx048", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140924-134415224", "type": "article", "title": "San Fernando Earthquake Series, 1971: Focal Mechanisms and Tectonics", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Garmany", "given_name": "Jan D.", "clpid": "Garmany-J-D" }, { "family_name": "Hileman", "given_name": "James A.", "clpid": "Hileman-J-A" } ], "abstract": "The largest events in the San Fernando earthquake series, initiated by the main shock at 14h 00m 41.8s UT on February 9, 1971, were chosen for analysis from the first three months of activity, 87 events in all. C. R. Allen and his co-workers assigned the main shock parameters: 34\u00b024.7\u2032N, 118\u00b024.0\u2032W, focal depth h = 8.4 km, and local magnitude M_L = 6.4. The initial rupture location coincides with the lower, northernmost edge of the main north-dipping thrust fault and the aftershock distribution. The best focal mechanism fit to the main shock P wave first motions constrains the fault plane parameters to: strike, N67\u00b0(\u00b16\u00b0)W; dip, 52\u00b0(\u00b13\u00b0)NE; rake, 72\u00b0 (67\u00b0\u221295\u00b0) left lateral. Focal mechanisms of the aftershocks clearly outline a down step of the western edge of the main thrust fault surface along a northeast-trending flexure. Faulting on this down step is left lateral strike slip and dominates the strain release of the aftershock series, which indicates that the down step limited the main event rupture on the west. The main thrust fault surface dips at about 35\u00b0 to the northeast at shallow depths and probably steepens to 50\u00b0 below a depth of 8 km. This steep dip at depth is a characteristic of other thrust faults in the Transverse ranges and indicates the presence at depth of laterally varying vertical forces that are probably due to buckling or overriding that causes some upward redirection of a dominant north-south horizontal compression. Two sets of events exhibit normal dip slip motion with shallow hypocenters and correlate with areas of ground subsidence deduced from gravity data. One set in the northeastern aftershock area is related to shallow extensional stresses caused by the steepening of the main fault plane. The other set is probably caused by a deviation of displacements along the down step of the main fault surface that resulted in localized ground subsidence near the western end of the main fault break. Several lines of evidence indicate that a horizontal compressional stress in a north or north-northwest direction was added to the stresses in the aftershock area 12 days after the main shock. After this change, events were contained in bursts along the down step, and sequencing within the bursts provides evidence for an earthquake-triggering phenomenon that propagates with speeds of 5\u201315 km/day. Seismicity before the San Fernando series and the mapped structure of the area suggest that the down step of the main fault surface is not a localized discontinuity but is part of a zone of weakness extending from Point Dume, near Malibu, to Palmdale on the San Andreas fault. This zone is interpreted as a decoupling boundary between crustal blocks that permits them to deform separately in the prevalent crustal shortening mode of the Transverse ranges region.", "doi": "10.1029/RG011i003p00693", "issn": "8755-1209", "publisher": "American Geophysical Union", "publication": "Reviews of Geophysics", "publication_date": "1973-08", "series_number": "3", "volume": "11", "issue": "3", "pages": "693-730" }, { "id": "authors:ksfjm-4y612", "collection": "authors", "collection_id": "ksfjm-4y612", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150729-100956192", "type": "article", "title": "Earthquake Prediction: Variation of Seismic Velocities before the San Francisco Earthquake", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" }, { "family_name": "Garmany", "given_name": "Jan D.", "clpid": "Garmany-J-D" }, { "family_name": "Anderson", "given_name": "Don L.", "clpid": "Anderson-D-L" } ], "abstract": "A large precursory change in seismic body-wave velocities occurred before the earthquake in San Fernando, California. The discovery that this change is mainly in the P-wave velocity clearly relates the effect to the phenomenon of dilatancy in fluid-filled rocks. This interpretation is supported by the time-volume relation obtained by combining the present data with the data from previous studies. The duration of the precursor period is proportional to the square of an effective fault dimension, which indicates that a diffusive or fluid-flow phenomenon controls the time interval between the initiation of dilatancy and the return to a fully saturated condition which is required for rupture.", "doi": "10.1126/science.180.4086.632", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1973-05-11", "series_number": "4086", "volume": "180", "issue": "4086", "pages": "632-635" }, { "id": "authors:yfmrx-yps18", "collection": "authors", "collection_id": "yfmrx-yps18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-122837796", "type": "article", "title": "Asymmetric P\u2032P\u2032: An alternative to P\u2032dP\u2032 reflections in the uppermost mantle (0 to 110 km)", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "abstract": "Precursors to P\u2032P\u2032 (PKPPKP), first interpreted as sub-surface reflections by Gutenberg in 1960 and studied in several later papers by other authors, precede the P\u2032P\u2032 phase by up to 200 sec. This phase, designated P\u2032dP\u2032 where d is the depth of reflection, has unique potential for giving new details of upper-mantle structure. However, as with any newly discovered seismic phase, the uniqueness of its interpretation must be well established. Asymmetric P\u2032P\u2032 phases reflecting from surface or near-surface dipping interfaces pose a challenge to this uniqueness because of their maximum-time nature. Simplified estimates of the amplitudes of asymmetric P\u2032P\u2032 rays are made, including consideration of the relative amplitudes of core phases and the finiteness of the reflecting surfaces of dipping interfaces. These estimates lead to the conclusion that the reading of asymmetric P\u2032P\u2032 at a single station is likely only in the 0- to 30-sec range before the main symmetric P\u2032P\u2032 phase. However, if array beam-forming is used, this range is reduced to 0 to 10 sec. The data indicate that both P\u2032dP\u2032 and asymmetric P\u2032P\u2032 are present at up to 30 sec lead time and array beam-forming is needed to differentiate between the two. A further effect of the maximum-time nature of P\u2032P\u2032 is that, in practice, the geographic location of the reflection point can be determined to within only a few degrees.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1973-02", "series_number": "1", "volume": "63", "issue": "1", "pages": "133-143" }, { "id": "authors:wz2xg-99x69", "collection": "authors", "collection_id": "wz2xg-99x69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-151015768", "type": "article", "title": "Preliminary seismological and geological studies of the San Fernando, California, earthquake of February 9 1971", "author": [ { "family_name": "Abrams", "given_name": "M.", "clpid": "Abrams-M" }, { "family_name": "Allen", "given_name": "C.", "clpid": "Allen-C-R" }, { "family_name": "Anderson", "given_name": "D.", "clpid": "Anderson-D-L" }, { "family_name": "Berkey", "given_name": "N.", "clpid": "Berkey-N" }, { "family_name": "Carey", "given_name": "D.", "clpid": "Carey-D" }, { "family_name": "Carter", "given_name": "B.", "clpid": "Carter-B" }, { "family_name": "Davies", "given_name": "G.", "clpid": "Davies-G" }, { "family_name": "Engen", "given_name": "G.", "clpid": "Engen-G-R" }, { "family_name": "Foley", "given_name": "M.", "clpid": "Foley-M-G" }, { "family_name": "Hanks", "given_name": "T.", "clpid": "Hanks-T-C" }, { "family_name": "Helmberger", "given_name": "D.", "clpid": "Helmberger-D-V" }, { "family_name": "Hileman", "given_name": "J.", "clpid": "Hileman-J-A" }, { "family_name": "Jordan", "given_name": "T.", "clpid": "Jordan-T" }, { "family_name": "Jungels", "given_name": "P.", "clpid": "Jungels-P" }, { "family_name": "Kamb", "given_name": "B.", "clpid": "Kamb-B" }, { "family_name": "Liu", "given_name": "H.", "clpid": "Liu-H" }, { "family_name": "Minster", "given_name": "B.", "clpid": "Minster-B" }, { "family_name": "Nordquist", "given_name": "J.", "clpid": "Nordquist-J-M" }, { "family_name": "Penrose", "given_name": "B.", "clpid": "Penrose-B" }, { "family_name": "Silver", "given_name": "L.", "clpid": "Silver-L-T" }, { "family_name": "Smith", "given_name": "R.", "clpid": "Smith-R" }, { "family_name": "Thatcher", "given_name": "W.", "clpid": "Thatcher-W" }, { "family_name": "Thomsen", "given_name": "L.", "clpid": "Thomsen-L" }, { "family_name": "Whitcomb", "given_name": "J.", "clpid": "Whitcomb-J-H" }, { "family_name": "Wood", "given_name": "S.", "clpid": "Wood-S" }, { "literal": "Caltech Division of Geological and Planetary Sciences" } ], "abstract": "The San Fernando earthquake was the largest earthquake to occur in the metropolitan Los\nAngeles area in more than 50 years. It has tentatively been assigned a magnitude, M_L of 6.6, a focal\ndepth of 13.0 km, and an epicentral location about 12 km east of Newhall, California, at 34\u00b024.0'N,\n118\u00b023.7'W (Figure 1), but these figures undoubtedly will be modified as further data become available.\nAlthough the focal depth is not as well defined as the epicenter, it is consistent with other\nobservations suggesting thrusting on a fault plane dipping north about 45 \u00b0 and breaking the surface\nin the Sylmar-San Fernando area (Figure 1). It should be emphasized that the hypocenter of\nthe main shock represents only the point of initial rupture. Breaking, presumably, then propagated\nsouthward and upward from this point, so that the main geological and engineering effects\nwere observed farther south where the fault was shallower and the displacement greater. The location\nof the main shock is based on readings from permanent stations of the Caltech network, as\nwell as the U. S. Geological Survey station at Point Mugu (SBLG) and the California Department\nof Water Resources stations at Pyramid (PYR) and Cedar Springs (CSP). Portable Caltech seismographs\nwere installed in the epicentral area as early as 3 hr following the main shock, and,\nwithin a few days, there were at least 30 portable units in the region operated by various groups\nand agencies.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1971-04", "series_number": "2", "volume": "61", "issue": "2", "pages": "491-495" }, { "id": "authors:8k5g2-wkh68", "collection": "authors", "collection_id": "8k5g2-wkh68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140430-094027139", "type": "article", "title": "Reflection of P'P' Seismic Waves from Discontinuities in the Mantle", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" }, { "family_name": "Anderson", "given_name": "Don L.", "clpid": "Anderson-D-L" } ], "abstract": "A systematic study of the travel times and apparent velocities of precursors of the seismic core phase PKPPKP indicate that these phases are reflections from the mantle. The strongest reflection is from a depth of 630 km. In order of confidence, other reflectors were found at depths of 280, 520, 940, 410 (very weak), and 1250 km (tentative). The weakness of the 410-km reflection was surprising in view of the large velocity increase at this depth indicated by refraction and Love-wave studies. This transition region must be broader than the others or must involve a smaller density jump. Reflections were observed that were possibly from the top and bottom of the low-velocity zone at depths of 50 and 130 km, respectively. The above reflections are interpreted in terms of the following solid-solid phase changes, in order of increasing depth: pyroxene-garnet solid solution, olivine \u2192 \u03b2 spinel, \u03b2 spinel \u2192 spinel and pyroxene \u2192 spinel + stishovite, spinel \u2192 post-spinel, and garnet \u2192 ilmenite or oxides. A spin-spin transition in Fe^(2+) may be responsible for one of the deeper discontinuities found by others.", "doi": "10.1029/JB075i029p05713", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1970-10-10", "series_number": "29", "volume": "75", "issue": "29", "pages": "5713-5728" }, { "id": "authors:zjw5c-3rj34", "collection": "authors", "collection_id": "zjw5c-3rj34", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140811-130115624", "type": "article", "title": "Array data processing techniques applied to long-period shear waves at Fennoscandian seismograph stations", "author": [ { "family_name": "Whitcomb", "given_name": "James H.", "clpid": "Whitcomb-J-H" } ], "abstract": "Array data processing is applied to long-period records of S waves at a network of five Fennoscandian seismograph stations (Uppsala, Ume\u00e5, Nurmij\u00e4rvi, Kongsberg, Copenhagen) with a maximum separation of 1300 km. Records of five earthquakes and one underground explosion are included in the study. The S motion is resolved into SH and SV, and after appropriate time shifts the individual traces are summed, both directly and after weighting.\n\nIn general, high signal correlation exists among the different stations involved resulting in more accurate time readings, especially for records which have amplitudes that are too small to be read normally. S-wave station residuals correlate with the general crustal type under each station. In addition, the Fennoscandian shield may have a higher SH/SV velocity ratio than the adjacent tectonic area to the northwest.SV-to-P conversion at the base of the crust can seriously interfere with picking the onset of Sin normal record reading.\n\nThe study demonstrates that, for epicentral distances beyond about 30\u00b0, existing networks of seismograph stations can be successfully used for array processing of long-period arrivals, especially the S arrivals.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1969-10", "series_number": "5", "volume": "59", "issue": "5", "pages": "1863-1887" } ]