\n\n\n
The ShakeAlert earthquake early warning (EEW) system partners along with U.S. Geological Survey (USGS) licensed operators deliver EEW alerts to the public and trigger automated systems when a significant earthquake is expected to impact California, Oregon, or Washington. ShakeAlert’s primary goal is to provide usable warning times before the arrival of damaging shaking. EEW is most likely to achieve this goal in large\u2010magnitude earthquakes. In recent years, ShakeAlert has gone through a series of upgrades to its underlying scientific algorithms aimed at improved performance during large earthquakes. Version 3 of this software recently went live in the production system and includes improvements to all algorithms. The main seismic algorithms that detect an earthquake and characterize its location, magnitude, and fault rupture orientation are faster than older versions. Other key changes include: using real\u2010time geodetic data to characterize the magnitude growth in large earthquakes; the introduction of an alert pause procedure to compromise between speed near the epicenter and improved accuracy at larger distances; and the inclusion of a nonergodic site\u2010response model in the ground\u2010motion predictions. ShakeAlert has achieved its primary goal of usable warning times before strong shaking at some locations in real\u2010time operations in recent M 6 earthquakes. Using offline tests, we demonstrate usable warning times are possible for many sites with peak shaking values of modified Mercalli intensity (MMI) 7–8 in M 7+ earthquakes and also for many MMI 8–9 sites in M 8+ earthquakes. ShakeAlert partners use a variety of MMI and magnitude thresholds in deciding when to alert their users within bounds set by the USGS. Our study shows that there is room to raise the magnitude thresholds up to about M 5.5 without adversely affecting performance in large earthquakes. The ground\u2010motion criteria are more complex owing to a significant drop\u2010off in warning times between the MMI 4 and 5 levels of predicted shaking. However, widely used ShakeAlert products, such as the MMI 3 and 4 contour products, can provide sufficiently long warning times before strong shaking in moderate\u2010to\u2010great earthquakes to enable a range of protective actions.
\n\n
One of the exciting things we can do in modern seismology is to model the details of the slip on the causative fault during an earthquake. An earthquake is a rupture process that expands from an initial rupture at some point on the fault plane. The rupture does not occur instantaneously nor does it proceed uniformly along the fault plane. This article describes a method used to uncover the spatial and temporal details of the rupture process--the determination of the slip model.
",
"doi": "10.7907/5avh1-7rk53",
"issn": "0894-7163",
"publisher": "U. S. Geological Survey",
"publication": "Earthquakes and Volcanoes",
"publication_date": "1994-01-01",
"series_number": "1",
"volume": "25",
"issue": "1",
"pages": "42-47"
},
{
"id": "authors:tmnhr-7ha12",
"collection": "authors",
"collection_id": "tmnhr-7ha12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130204-090427264",
"type": "article",
"title": "Source study of the 1906 San Francisco earthquake",
"author": [
{
"family_name": "Wald",
"given_name": "David J.",
"clpid": "Wald-D-J"
},
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Helmberger",
"given_name": "Donald V.",
"clpid": "Helmberger-D-V"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "All quality teleseismic recordings of the great 1906 San Francisco earthquake archived in the 1908 Carnegie Report by the State Earthquake Investigation Commission were scanned and digitized. First order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated, similarly located, more recent earthquakes (1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta earthquakes) at nearly co-located modern stations. Peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1.5 \u00d7 10^(27) dyne-cm was responsible for producing the peak the teleseismic body wave arrivals. At longer periods (50 to 80 sec), we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 \u00d7 10^(27) dyne-cm for the 1906 earthquake, comparable to previous geodetic and surface wave estimates (Thatcher, 1975). We then made a more detailed source analysis using Morgan Hill S body waves as empirical Green's Functions in a finite fault subevent summation. The Morgan Hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture. From forward and inverse empirical summations of Morgan Hill Green's functions, we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km. Assuming the 1906 epicenter determined by Bolt (1968), this corresponds with a large asperity (on the order of the Loma Prieta earthquake) in the Golden Gate/San Francisco region and one about three times larger located northwest along strike between Point Reyes and Fort Ross. This model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation. Consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km. With rough constraints on the largest asperity (size and magnitude) we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the Loma Prieta earthquake but with three times as much slip. For purposes of comparison with the recent, abundant Loma Prieta strong motion data set, we \"moved\" the largest 1906 asperity into Loma Prieta region. Peak ground velocity amplitudes are substantially greater than those recorded during the Loma Prieta earthquake, and are comparable to those predicted by the attenuation relationship of Joyner and Boore (1988) for a magnitude M_W = 7.7 earthquake.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1993-08",
"series_number": "4",
"volume": "83",
"issue": "4",
"pages": "981-1019"
},
{
"id": "authors:v23rd-n3c69",
"collection": "authors",
"collection_id": "v23rd-n3c69",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130311-145649896",
"type": "article",
"title": "Near-Field Investigations of the Landers Earthquake Sequence, April to July 1992",
"author": [
{
"family_name": "Sieh",
"given_name": "Kerry",
"orcid": "0000-0002-7311-2447",
"clpid": "Sieh-K-E"
},
{
"family_name": "Jones",
"given_name": "Lucile",
"orcid": "0000-0002-2690-3051",
"clpid": "Jones-L-M"
},
{
"family_name": "Hauksson",
"given_name": "Egill",
"orcid": "0000-0002-6834-5051",
"clpid": "Hauksson-E"
},
{
"family_name": "Hudnut",
"given_name": "Kenneth",
"orcid": "0000-0002-3168-4797",
"clpid": "Hudnut-K-W"
},
{
"family_name": "Eberhard-Phillips",
"given_name": "Donna",
"clpid": "Eberhard-Phillips-D"
},
{
"family_name": "Heaton",
"given_name": "Thomas",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hough",
"given_name": "Susan",
"orcid": "0000-0002-5980-2986",
"clpid": "Hough-S-E"
},
{
"family_name": "Hutton",
"given_name": "Kate",
"clpid": "Hutton-K"
},
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Lilje",
"given_name": "Anne",
"clpid": "Lilje-A"
},
{
"family_name": "Lindvall",
"given_name": "Scott",
"clpid": "Lindvall-S-C"
},
{
"family_name": "McGill",
"given_name": "Sally F.",
"clpid": "McGill-S-F"
},
{
"family_name": "Mori",
"given_name": "James",
"clpid": "Mori-Jim"
},
{
"family_name": "Rubin",
"given_name": "Charles",
"clpid": "Rubin-C-M"
},
{
"family_name": "Spotila",
"given_name": "James A.",
"clpid": "Spotila-J-A"
},
{
"family_name": "Stock",
"given_name": "Joann",
"orcid": "0000-0003-4816-7865",
"clpid": "Stock-J-M"
},
{
"family_name": "Thio",
"given_name": "Hong Kie",
"clpid": "Thio-Hong-Kie"
},
{
"family_name": "Treiman",
"given_name": "Jerome",
"clpid": "Treiman-J"
},
{
"family_name": "Wernicke",
"given_name": "Brian",
"orcid": "0000-0002-7659-8358",
"clpid": "Wernicke-B-P"
},
{
"family_name": "Zachariasen",
"given_name": "Judith",
"clpid": "Zachariasen-J"
}
],
"abstract": "The Landers earthquake, which had a moment magnitude (M_w) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M_w 6.1 preshock and M_w 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.",
"doi": "10.1126/science.260.5105.171",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1993-04-09",
"series_number": "5105",
"volume": "260",
"issue": "5105",
"pages": "171-176"
},
{
"id": "authors:ctp96-14x06",
"collection": "authors",
"collection_id": "ctp96-14x06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-113646769",
"type": "article",
"title": "Determination of earthquake energy release and M_L using TERRAscope",
"author": [
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Mori",
"given_name": "Jim",
"clpid": "Mori-Jim"
},
{
"family_name": "Hauksson",
"given_name": "Egill",
"orcid": "0000-0002-6834-5051",
"clpid": "Hauksson-E"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hutton",
"given_name": "L. Katherine",
"clpid": "Hutton-K"
},
{
"family_name": "Jones",
"given_name": "Lucile M.",
"orcid": "0000-0002-2690-3051",
"clpid": "Jones-L-M"
}
],
"abstract": "We estimated the energy radiated by earthquakes in southern California using on-scale very broadband recordings from TERRAscope. The method we used involves time integration of the squared ground-motion velocity and empirical determination of the distance attenuation function and the station corrections. The time integral is typically taken over a duration of 2 min after the P-wave arrival. The attenuation curve for the energy integral we obtained is given by q(r) = cr^(\u2212n)exp(\u2212kr)(r^2 = \u0394^2 + h_(ref)^2) with c = 0.49710, n = 1.0322, k = 0.0035 km^(\u22121), and h_(ref) = 8 km, where \u0394 is the epicentral distance. A similar method was used to determine M_L using TERRAscope data. The station corrections for M_L are determined such that the M_L values determined from TERRAscope agree with those from the traditional optical Wood-Anderson seismographs. For 1.5 < M_L < 6.0, a linear relationship log E_S = 1.96 M_L + 9.05 (E_S in ergs) was obtained. However, for events with M_L > 6.5, M_L saturates. The ratio E_S/M_0 (M_0: seismic moment), a measure of the average stress drop, for six earthquakes, the 1989 Montebello earthquake (M_L = 4.6), the 1989 Pasadena earthquake (M_L = 4.9), the 1990 Upland earthquake (M_L = 5.2), the 1991 Sierra Madre earthquake (M_L = 5.8), the 1992 Joshua Tree earthquake (M_L = 6.1), and the 1992 Landers earthquake (M_w = 7.3), are about 10 times larger than those of the others that include the aftershocks of the 1987 Whittier Narrows earthquake, the Sierra Madre earthquake, the Joshua Tree earthquake, and the two earthquakes on the San Jacinto fault. The difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times. The aftershocks, which occurred on the fault plane where the mainshock slippage occurred, had a very short time to heal, hence a low stress drop. The repeat time of the major earthquakes on the frontal fault systems in the Transverse Ranges in southern California is believed to be very long, a few thousand years. Hence, the events in the Transverse Ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times, such as the San Andreas fault and the San Jacinto fault. The observation that very high stress-drop events occur in the Transverse Ranges and the Los Angeles Basin has important implications for the regional seismic potential. The occurrence of these high stress-drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events. Characterization of earthquakes in terms of the E_S/M_0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the Los Angeles basin and the Transverse Ranges.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1993-04",
"series_number": "2",
"volume": "83",
"issue": "2",
"pages": "330-346"
},
{
"id": "authors:v6ma7-y6k70",
"collection": "authors",
"collection_id": "v6ma7-y6k70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-105330733",
"type": "article",
"title": "Initial investigation of the Landers, California, Earthquake of 28 June 1992 using TERRAscope",
"author": [
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Thio",
"given_name": "Hong-Kie",
"clpid": "Thio-Hong-Kie"
},
{
"family_name": "Dreger",
"given_name": "Doug",
"clpid": "Dreger-D-S"
},
{
"family_name": "Hauksson",
"given_name": "Egill",
"orcid": "0000-0002-6834-5051",
"clpid": "Hauksson-E"
},
{
"family_name": "Heaton",
"given_name": "Tom",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "The 1992 Landers earthquake (M_s =7.5, M_w =7.3) was recorded at six TERRAscope stations in southern California. Peak accelerations ranged from 0.16 g at SVD (\u0394=63 km) to 0.0092 g at ISA (\u0394=245 km), decreasing with distance away from the fault zone. The peak velocity showed a different pattern reflecting the rupture directivity from south to north. The largest peak velocity, 19 cm/sec, was observed at GSC (\u0394=125 km). Moment tensor inversion of long\u2010period surface waves yielded a mechanism with M_0=1.1\u00d710^(27) dyne\u2010cm (M_w =7.3), dip=74\u00b0, rake=\u2212176\u00b0, and strike=340\u00b0. Inversion of teleseismic P and S waves revealed two distinct sub\u2010events of 6 and 8 sec duration and about 10 sec apart. The source parameters for the first and second events are: M_0=1.9\u00d710^(26) dyne\u2010cm, dip=83\u00b0, rake=179\u00b0, strike=359\u00b0; and M_0=6.1\u00d710^(26) dyne\u2010cm, dip=87\u00b0, rake=178\u00b0, strike=333\u00b0, respectively. The radiated wave energy, E_S, was estimated as 4.3\u00d710^(23) ergs. The ratio E_s/M_0=3.9\u00d710^(\u22124) corresponds to a stress drop of 280 bars, and suggests that the Landers earthquake belongs to the group of high stress drop earthquakes, and occurred on a fault with a long recurrence time. The rupture directivity can be seen clearly in the records from PFO (\u0394=68 km) located to the south and GSC located to the north of the epicenter. The maximum displacement at PFO is only 13% of that at GSC despite the shorter epicentral distance to PFO than to GSC. The slip distribution determined with the empirical Green's function method indicates that the Landers earthquake consists of two distinct sub\u2010events about 30 km apart, with the second sub\u2010event to the north being about twice as large as the first one. This slip distribution is consistent with the teleseismic data and the surface offsets mapped in the field.",
"doi": "10.1029/92GL02320",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1992-11-20",
"series_number": "22",
"volume": "19",
"issue": "22",
"pages": "2267-2270"
},
{
"id": "authors:b4m5b-f8n47",
"collection": "authors",
"collection_id": "b4m5b-f8n47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121214-101544449",
"type": "article",
"title": "Seismic threat to the Pacific Northwest",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Which region of the contiguous United States has the potential for the largest earthquake? Surprisingly, the answer may not be California. With the possible exception of the Alaska subduction zone, the Cascadia subduction zone, extending 1,200 kilometers from Northern California to Vancouver Island, is the largest tectonically active fault system in North America.\n\nThe Cascadia subduction zone is currently gaining credence as a potential, major threat to Eureka, Portland, Seattle, and Vancouver. Because it is a relatively new focus of study, no existing building codes or regulations incorporate the force levels necessary to withstand a major event on the Cascadia zone. Design standards must be reevaluated to reflect and mitigate the catastrophic damage that could occur in the zone.",
"publisher": "EQE Engineering",
"publication": "EQE Review",
"publication_date": "1992-09",
"volume": "1992",
"pages": "13-18"
},
{
"id": "authors:q3nrq-gpm30",
"collection": "authors",
"collection_id": "q3nrq-gpm30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130507-093416832",
"type": "article",
"title": "Seismic excitation by space shuttles",
"author": [
{
"family_name": "Kanamori",
"given_name": "H.",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Mori",
"given_name": "J.",
"clpid": "Mori-Jim"
},
{
"family_name": "Sturtevant",
"given_name": "B.",
"clpid": "Sturtevant-B"
},
{
"family_name": "Anderson",
"given_name": "D. L.",
"clpid": "Anderson-D-L"
},
{
"family_name": "Heaton",
"given_name": "T.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Shock waves generated by the space shuttles\nColumbia (August 13, 1989), Atlantis (April 11, 1991) and\nDiscovery (September 18, 1991) on their return to Edwards\nAir Force Base, California, were recorded by TERRAscope\n(Caltech's broadband seismic network), the Caltech-U.S.G.S\nSouthern California Seismic Network (SCSN), and the University\nof Southern California (USC) Los Angeles Basin\nSeismic Network. The spatial pattern of the arrival limes\nexhibits hyperbolic shock fronts from which the path, velocity\nand altitude of the space shuttle could be determined.\nThe shock wave was acoustically coupled to the ground,\nconverted to a seismic wave, and recorded clearly at the\nbroadband TERRAscope stations. The acoustic coupling occurred\nvery differently depending on the conditions of the\nEarth's surface surrounding the station. For a seismic station\nlocated on hard bedrock, the shock wave (N wave)\nwas clearly recorded with little distortion. Aside from the N\nwave, very little acoustic coupling of the shock wave energy\nto the ground occurred at these sites. The observed N wave\nrecord was used to estimate the overpressure of the shock\nwave accurately; a pressure change of 0.5 to 2.2 mbars was\nobtained. For a seismic station located close to the ocean\nor soft sedimentary basins, a significant amount of shock\nwave energy was transferred to the ground through acoustic\ncoupling of the shock wave and the oceanic Rayleigh wave.\nA distinct topography such as a mountain range was found\neffective to couple the shock wave energy to the ground.\nShock wave energy was also coupled to the ground very\neffectively through large man made structures such as high\nrise buildings and offshore oil drilling platforms. For the\nspace shuttle Columbia, in particular, a distinct pulse having\na period of about 2 to 3 seconds was observed, 12.5 s before\nthe shock wave, with a broadband seismograph in Pasadena.\nThis pulse was probably excited by the high rise buildings\nin downtown Los Angeles which were simultaneously hit by\nthe space shuttle shock waves. The proximity of the natural\nperiods of the high rise buildings and the modal periods of\nthe Los Angeles basin enabled efficient energy transfer from\nshock wave to seismic wave.",
"doi": "10.1007/BF01415896",
"issn": "0938-1287",
"publisher": "Springer",
"publication": "Shock Waves",
"publication_date": "1992-06-01",
"series_number": "2",
"volume": "2",
"issue": "2",
"pages": "89-96"
},
{
"id": "authors:ak4kh-bd094",
"collection": "authors",
"collection_id": "ak4kh-bd094",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121212-100004230",
"type": "article",
"title": "TERRAscope and CUBE Project at Caltech",
"author": [
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Hauksson",
"given_name": "Egill",
"orcid": "0000-0002-6834-5051",
"clpid": "Hauksson-E"
},
{
"family_name": "Heaton",
"given_name": "Tom",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "The TERRAscope project of the California Institute of Technology began in 1988 and now has six very broadband seismic stations (PAS, GSC, PFO, SBC, ISA, and SVD) in southern California (Figure 1). The goal of TERRAscope is to provide high-quality broadband data needed for significant advances in both regional and global seismology. TERRAscope will replace the old Caltech seismographic network in southern California, which dates back to the 1920s. In many cases, new stations are deployed in cooperation with local institutions. The goal is to encourage involvement of both students and researchers in the operation of the stations and analysis of new data. The station PAS is a joint project between Caltech, the University of Southern California, the U.S. Geological Survey (USGS), and the Incorporated Research Institutions for Seismology (IRIS). The station SBC was deployed in cooperation with the University of California at Santa Barbara. The station PFO is operated jointly with the University of California at San Diego, and the station SVD was installed and is operated by the USGS. Except for SVD, all of the stations are equipped with a broadband Streckeisen STS-1 seismometer and Quanterra data logger with a 24-bit digitizer and a Kinemetrics FBA-23 strong-motion sensor. The station SVD has a Streckeisen STS-2 seismometer and a Guralp CMG-5 accelerograph. The project is funded mainly by grants from the L. K. Whittier Foundation and the Arco Foundation. In addition to the automatic dial-up data retrieving system called Caltech Gopher (adapted from the IRIS Gopher system) has been implemented. The Caltech Gopher receives mail from NEIC for teleseisms and the SCSN with origin time, location, and magnitude for regional events. The Gopher retrieves data from all six TERRAscope stations for these events. The TERRAscope data reside in an FTP anonymous account (seismo.gps.caltech.edu; password: \"your e-mail address\") at the Caltech Seismological Laboratory, and are available to users through Internet. Usually the data are available within 30 minutes after a regional event and several hours after a teleseism. In the near future a new version of the Gopher software will be installed, which will also make some of the Gopher data available directly from the IRIS-DMC Gopher. When the Data Center of the Southern California Earthquake Center begins full operation in early 1992, it will take over the distribution of earthquake data from southern California, including both TERRAscope Gopher data and continuous data from the tape cartridges. The data will also be available from IRIS-DMC, and future improvements and changes in data access will be posted on the IRIS-DMC bulletin board.",
"doi": "10.1029/90EO00395",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "EOS Transactions",
"publication_date": "1991-12-10",
"series_number": "50",
"volume": "72",
"issue": "50",
"pages": "564-566"
},
{
"id": "authors:871pr-gyr75",
"collection": "authors",
"collection_id": "871pr-gyr75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121213-141842168",
"type": "article",
"title": "Rupture model of the 1989 Loma Prieta earthquake from the inversion of strong-motion and broadband teleseismic data",
"author": [
{
"family_name": "Wald",
"given_name": "David J.",
"clpid": "Wald-D-J"
},
{
"family_name": "Helmberger",
"given_name": "Donald V.",
"clpid": "Helmberger-D-V"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "We have used 24 broadband teleseismic and 48 components of local strong motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip. Separate inversions of the teleseismic data (periods 3-30 sec) or strong motion data (periods 1-5 sec) result in similar models. The data require bilateral rupture with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches; one centered 6 km northwest of the hypocenter at a depth of 12 km and with a maximum slip of 350 cm, and the other centered about 5 km southeast of the hypocenter at a depth of 16 km and with a maximum slip of 460 cm. The bilateral nature of the rupture results in large amplitude ground motions at sites located along the fault strike, both to the northwest and the southeast. However, the northwestern patch has a larger moment and overall stress drop and is, consequently, the source of the largest ground motion velocities, consistent with the observed recordings. This bilateral rupture also produces relatively modest ground motion amplitudes directly updip from the hypocenter, which is in agreement with the velocity ground motions observed at Corralitos. There is clear evidence of a foreshock (magnitude between 3.5 and 5.0) or a slow rupture nucleation about 2 seconds before the main part of the rupture; the origin time implied by strong motion trigger times is systematically 2 seconds later than the time predicted from the high-gain regional network data. The seismic moment obtained from either of the separate data sets or both sets combined is about 3.0 x 10^(26) dyne-cm and the potency is 0.95 km^3.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1991-10",
"series_number": "5",
"volume": "81",
"issue": "5",
"pages": "1540-1572"
},
{
"id": "authors:1sp6e-bmc33",
"collection": "authors",
"collection_id": "1sp6e-bmc33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121211-145014142",
"type": "article",
"title": "What Is the Southern California Earthquake Center?",
"author": [
{
"family_name": "Aki",
"given_name": "Keiiti",
"clpid": "Aki-Keiiti"
},
{
"family_name": "Henyey",
"given_name": "Thomas",
"clpid": "Henyey-T-L"
},
{
"family_name": "Heaton",
"given_name": "Thomas",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "On February 11, Congressman George E. Brown, Jr., Chairman of the House Committee on Science, Space and Technology, together with the National Science Foundation, the U.S. Geological Survey, and state and local officials, helped inaugurate the Southern California Earthquake Center (SCEC) on the campus of the University of Southern California. SCEC is one of 14 new NSF Science and Technology Centers and includes a substantial commitment from the USGS for FY91. The center is a consortium of seven core academic institutions-USC (coordinating institution), Caltech, Columbia University's Lamont-Doherty Geological Observatory, University of California at Los Angeles, University of California at Santa Barbara, University of California at Santa Cruz, and University of California at San Diego's Scripps Institution of Oceanography-in partnership with the USGS's Office of Earthquakes, Volcanoes, and Engineering (OEVE). The center grew out of an April 3-5, 1989, workshop at Lake Arrowhead, Calif., convened by the USGS to discuss the need for an expanded effort in earthquake research in southern California.",
"doi": "10.1029/90EO00304",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "EOS Transactions",
"publication_date": "1991-09-24",
"series_number": "39",
"volume": "72",
"issue": "39",
"pages": "417-421"
},
{
"id": "authors:tthsg-6r860",
"collection": "authors",
"collection_id": "tthsg-6r860",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-104344746",
"type": "article",
"title": "Lg and Rg Waves on the California Regional Networks From the December 23, 1985 Nahanni Earthquake",
"author": [
{
"family_name": "Wald",
"given_name": "Lisa A.",
"clpid": "Wald-L-A"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "We investigate Lg and Rg propagation in California using the central and southern California regional networks. Approximately 550 stations constitute these two short-period networks providing a dense coverage of almost the entire state. The waveforms recorded from the December 23, 1985, Nahanni, Canada, earthquake are used to construct three profiles along the propagation path (almost N-S) and three perpendicular to the propagation path (almost E-W) to look at the nature of propagation of these two types of surface waves. Groups of records from stations in various geological and tectonic provinces in California are also examined in order to establish regional characteristics of the surface waves. We find that the propagation characteristics of Lg differ from those of Rg across California; Lg waves are apparently more sensitive to crustal heterogeneities. The most striking observations are the similarity of coda for both the Lg and the Rg waves within geologic provinces and the marked difference in coda between regions. These differences are seen in the amplitudes, coda duration, shape of the energy envelope, frequency content, and sharpness of the phase initiation. In general, a decrease in the Moho depth near the Pacific Coast is correlated with a decrease in the surface wave amplitude, especially at higher frequencies (0.15\u20130.2 Hz). Most interesting is the association of the San Andreas fault with abrupt changes in the wave train amplitudes. The surface waves are amplified in the vicinity of the fault zone and then decrease in amplitude after the zone is crossed. In the Coast Ranges, amplitudes are low and waveform coherence is poor. The Rg phase dominates the record in the Sierra Nevada, and both surface waves are amplified by the thick sedimentary sequence of the Great Valley.",
"doi": "10.1029/91JB00920",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-07-10",
"series_number": "B7",
"volume": "96",
"issue": "B7",
"pages": "12099-12125"
},
{
"id": "authors:j1vy2-15651",
"collection": "authors",
"collection_id": "j1vy2-15651",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130415-144341134",
"type": "article",
"title": "Seismology in the United States, 1986-1990",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "In this volume, seven highly respected seismologists\nattempt to summarize seismological research in the U.S. in\nthe past four years. This is indeed a daunting task; the\nmere compilation and classification of the overwhelming\nvolume of new seismological literature is difficult enough,\nbut to confidently provide an overview of our new\nknowledge and understanding is almost impossible.\nAlthough the study of vibrations in the Earth (that is,\nseismology) may at first seem to be a scientific field of\nlimited scope, it encompasses a vast range of observations\nand problems in mathematical physics. Seismologists\ncurrently study waves varying in frequencies from 10^2 Hz\nto 10^(-4) Hz (20 octaves) and in acceleration amplitudes from\n1 g to 10^(-12) g (240 dB). These waves are observed at a wide\nvariety of distances as they travel through a very complex\nmedium, the interior of the Earth. Furthermore the waves\nare excited by numerous and often complex mechanisms,\nincluding earthquakes, man-made explosions, landslides,\nvolcanoes, and atmospheric disturbances. Seismologists\nstudy waves from earthquakes that range in energy over 15\norders of magnitude. These waves are studied to reveal the\nphysical properties of the Earth, the kinematics and\ndynamics of Earth deformation, the characteristics of\ndestructive earthquakes and volcanoes, and the occurrence of\nman-made explosions. When viewed from this perspective,\nit is little wonder that any individual seismologist can feel\noverwhelmed by the sheer volume of seismological\nresearch in the past four years.\nSeveral thousand seismological papers were published in\nthe past four years; Langston (this issue) alone lists 800\npapers pertaining to wave propagation problems. I confess\nthat I have only read a small fraction of these, and even if I\nhad read them all, I would not attempt to choose those\nhaving the greatest significance. Instead, I can only\nsummarize current trends in seismological research.",
"issn": "8755-1209",
"publisher": "American Geophysical Union",
"publication": "Reviews of Geophysics",
"publication_date": "1991-04",
"series_number": "S",
"volume": "29",
"issue": "S",
"pages": "659-661"
},
{
"id": "authors:76zxd-b8e31",
"collection": "authors",
"collection_id": "76zxd-b8e31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130418-110317308",
"type": "article",
"title": "Seismic excitation by the space shuttle Columbia",
"author": [
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Mori",
"given_name": "Jim",
"clpid": "Mori-Jim"
},
{
"family_name": "Anderson",
"given_name": "Don L.",
"clpid": "Anderson-D-L"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Seismic stations in southern California recorded the atmospheric shock waves generated by the space shuttle Columbia on its return to the Edwards Air Force base on 13 August 1989 (Fig. 1). In addition to the shock wave, the broad-band IRIS\u2013TERRAscope station at Pasadena recorded a distinct pulse with a period of ~2\u20133 seconds, which arrived 12.5 seconds before the shock wave (Fig. 2). This pulse was also recorded at the University of Southern California, near downtown Los Angeles, where it arrived 3 seconds after the shock wave. The origin of this pulse could not be readily identified. We show here that it was a seismic P wave excited by the motion of high-rise buildings in downtown Los Angeles, which were hit by the shock wave. The proximity of the natural period of the high-rise buildings to that of the Los Angeles basin enabled efficient energy transfer from shock wave to seismic wave.",
"doi": "10.1038/349781a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1991-02-28",
"series_number": "6312",
"volume": "349",
"issue": "6312",
"pages": "781-782"
},
{
"id": "authors:zycqh-fr298",
"collection": "authors",
"collection_id": "zycqh-fr298",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121120-105420644",
"type": "article",
"title": "Evidence for and implications of self-healing pulses of slip in earthquake rupture",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Dislocation time histories of models derived from waveforms of seven earthquakes are discussed. In each model, dislocation rise times (the duration of slip for a given point on the fault) are found to be short compared to the overall duration of the earthquake (\u223c 10%). However, in many crack-like numerical models of dynamic rupture, the slip duration at a given point is comparable to the overall duration of the rupture; i.e. slip at a given point continues until information is received that the rupture has stopped propagating. Alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are: (1) the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes; (2) earthquakes are composed of a sequence of small-dimension (short duration) events that are separated by locked regions (barriers); (3) rupture occurs in a narrow self-healing pulse of slip that travels along the fault surface. Evidence is discussed that suggests that slip durations are indeed short and that the self-healing slip-pulse model is the most appropriate explanation.\nA qualitative model is presented that produces self-healing slip pulses. The key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity. The model has the following features: high static strength of materials (kilobar range), low static stress drops (in the range of tens of bars), and relatively low frictional stress during slip (less than several hundreds of bars). It is suggested that the reason that the average dislocation scales with fault length is because large-amplitude slip pulses are difficult to stop and hence tend to propagate large distances. This model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes. It also qualitatively explains why the recurrence time for large earthquakes may be irregular.",
"doi": "10.1016/0031-9201(90)90002-F",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1990-11",
"series_number": "1",
"volume": "64",
"issue": "1",
"pages": "1-20"
},
{
"id": "authors:63wca-p9428",
"collection": "authors",
"collection_id": "63wca-p9428",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-130617628",
"type": "article",
"title": "The 3 December 1988, Pasadena earthquake (M_L = 4.9) recorded with the very broadband system in Pasadena",
"author": [
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
},
{
"family_name": "Mori",
"given_name": "Jim",
"clpid": "Mori-Jim"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Since 1 December 1987, a very broadband seismographic system has been in operation at the Kresge Laboratory of the California Institute of Technology. This system consists of the Streckeisen-1 very broadband sensor (Wielandt and Streckeisen, 1982), the Kinemetrics FBA-23 triaxial force balance accelerometer and a Quanterra data-logger with a 24-bit (for Streckeisen-1) and a 16-bit (for FBA-23) digitizer. The details of the data logger are described in Steim (1986). The overall dynamic range of this system is about 200 db. This system was constructed as a joint project between the California Institute of Technology, the U.S. Geological Survey, the University of Southern California and the International Research\nInstitution for Seismology (IRIS), and is an element of the IRIS global network as well as the TERRAscope network of California Institute of Technology. A brief description of the system is given by Given et al. (1989).",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1990-04",
"series_number": "2",
"volume": "80",
"issue": "2",
"pages": "483-487"
},
{
"id": "authors:rje8q-7a815",
"collection": "authors",
"collection_id": "rje8q-7a815",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130418-104533548",
"type": "article",
"title": "The calm before the quake?",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "With the exception of Alaska, the Cascadia subduction zone, extending 1,200 Km from northern California to Vancouver Island, is the largest tectonically active fault system in North America. Although is widely accepted that the North American continental plate is converging at a rate of 2.5-4.5cm yr^(-1), modern seismic activity has been minimal along the Cascadia Subduction zone. Are the Pacific oceanic plates sliding effortlessly below the continental margin? Or are the plates welded together, gradually accumulating elastic strain, to be released in another cataclysmic earthquake sometime in the coming centuries? There is geological evidence, much debated at a recent meeting, that there have been six massive earthquakes (energy magnitude M_w = 8.5-9.5: see box overleaf) in this region in the past 3,600 years, most recently sometime in 1680-90.",
"doi": "10.1038/343511a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1990-02-08",
"series_number": "6258",
"volume": "343",
"issue": "6258",
"pages": "511-512"
},
{
"id": "authors:39ffh-nrm98",
"collection": "authors",
"collection_id": "39ffh-nrm98",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121205-090612653",
"type": "article",
"title": "The fortnightly tide and the tidal triggering of earthquakes",
"author": [
{
"family_name": "Hartzell",
"given_name": "Stephen",
"clpid": "Hartzell-S-H"
},
{
"family_name": "Heaton",
"given_name": "Thomas",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "In this paper we test the southern California network earthquake catalog and the\nworld-wide earthquake catalog for a fortnightly tidal periodicity and find none. In\nstudies that test the hypothesis of tidal triggering of earthquakes, it is usually\nnecessary to resolve the tidal shear stress onto the plane of the fault and in the\ndirection of the slip vector to determine if the stress is compatible with the fault\nmotion (Heaton, 1975, 1982). This analysis requires accurate focal mechanisms and\nknowledge of the focal plane on which slip occurred for as many earthquakes as\npossible to improve the statistical sampling of the data set. However, if we consider\nthe fortnightly tide, which is a simple amplitude modulation, focal mechanism\ninformation is not required. Our analysis assumes that we have a large data base of\nearthquakes with varying mechanisms. The alignment of the slip vector with the\ntidal shear stress will vary from earthquake to earthquake. However, if tidal\ntriggering of earthquakes does occur, more earthquakes should be triggered out of\nthe total population when the tidal stress is large than when it is small. If the\nlargest semi-diurnal tide is normalized to an amplitude of 1.0, the fortnightly tide\nwould have an amplitude of 0.17 on this scale and a period of about 2 weeks (Munk\nand MacDonald, 1960). Therefore, the effect on the occurrence of earthquakes by\nthe tidal shear stress will be modulated with a 2 week period. Considering the\nfortnightly tide allows us to utilize entire catalogs of data to test the tidal triggering\nhypothesis without knowledge of the focal mechanisms.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1989-08",
"series_number": "4",
"volume": "79",
"issue": "4",
"pages": "1282-1286"
},
{
"id": "authors:9h02s-ekd66",
"collection": "authors",
"collection_id": "9h02s-ekd66",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-133559557",
"type": "article",
"title": "Static deformations from point forces and force couples located in welded elastic Poissonian half-spaces: Implications for seismic moment tensors",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Heaton",
"given_name": "Robert E.",
"clpid": "Heaton-R-E"
}
],
"abstract": "We present analytic expressions for the static deformations produced by point forces and point force couples embedded in two elastic Poissonian half-spaces that are welded on a horizontal interface. We show that the deformations from point forces and from vertically dipping strike-slip point double couples vary continuously (except at the strike-slip source) as the source is moved across the welded interface. We show that the pattern of deformations from vertically dipping (or horizontally dipping) dip-slip point double couples also vary continuously as the source is moved across the welded interface, but the amplitude of the deformations jumps by the ratio of the rigidities. Finally, we show that the pattern of deformation from a point explosion source or from a point double-couple source dipping at angles other than 0\u00b0 or 90\u00b0 jumps as the source is moved across the boundary. We demonstrate that integration of point double-couple sources on a plane of finite extent mimics the deformation of slip on a fault plane where the total moment of the double-couples is \u03bcAD. We also demonstrate that deformations from a distribution of double couples on a horizontally dipping finite plane just above the interface are indistinguishable from the deformations produced by a similar distribution of double couples located just below the interface but with a total moment that is different by the ratio of the rigidities. This demonstrates that the moment of a dislocation that occurs between two materials is ambiguously defined. We discuss reasons why seismic moment is not a very satisfying way to parameterize the size of an earthquake. We show that potency, defined to be the integral of the slip over the rupture surface, is a more natural size scaling parameter than seismic moment.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1989-06",
"series_number": "3",
"volume": "79",
"issue": "3",
"pages": "813-841"
},
{
"id": "authors:ksemv-j7z19",
"collection": "authors",
"collection_id": "ksemv-j7z19",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130305-094649151",
"type": "article",
"title": "Estimation of strong ground motions from hypothetical earthquakes on the Cascadia subduction zone, Pacific Northwest",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
}
],
"abstract": "Strong ground motions are estimated for the Pacific Northwest assuming that large shallow earthquakes, similar to those experienced in southern Chile, southwestern Japan, and Colombia, may also occur on the Cascadia subduction zone. Fifty-six strong motion recordings for twenty-five subduction earthquakes of M_s \u2265 7.0 are used to estimate the response spectra that may result from earthquakes M_w <8 1/4. Large variations in observed ground motion levels are noted for a given site distance and earthquake magnitude. When compared with motions that have been observed in the western United States, large subduction zone earthquakes produce relatively large ground motions at surprisingly large distances. An earthquake similar to the 22 May 1960 Chilean earthquake (M_w 9.5) is the largest event that is considered to be plausible for the Cascadia subduction zone. This event has a moment which is two orders of magnitude larger than the largest earthquake for which we have strong motion records. The empirical Green's function technique is used to synthesize strong ground motions for such giant earthquakes. Observed teleseismic P-waveforms from giant earthquakes are also modeled using the empirical Green's function technique in order to constrain model parameters. The teleseismic modeling in the period range of 1.0 to 50 sec strongly suggests that fewer Green's functions should be randomly summed than is required to match the long-period moments of giant earthquakes. It appears that a large portion of the moment associated with giant earthquakes occurs at very long periods that are outside the frequency band of interest for strong ground motions. Nevertheless, the occurrence of a giant earthquake in the Pacific Northwest may produce quite strong shaking over a very large region.",
"doi": "10.1007/BF00874626",
"issn": "0033-4553",
"publisher": "Springer",
"publication": "Pure and Applied Geophysics",
"publication_date": "1989",
"series_number": "1-2",
"volume": "129",
"issue": "1-2",
"pages": "131-201"
},
{
"id": "authors:byvxn-xt189",
"collection": "authors",
"collection_id": "byvxn-xt189",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130207-113106326",
"type": "article",
"title": "Earthquake Ground Motions",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
}
],
"abstract": "In this review, we discuss some of the many phenomena that can determine the nature of strong ground motion. Some of these phenomena have been inferred from the study of existing ground-motion records, and others are inferred from theoretical models of earthquake sources and wave\npropagation.",
"doi": "10.1146/annurev.ea.16.050188.001005",
"issn": "0084-6597",
"publisher": "Annual Reviews",
"publication": "Annual Review of Earth and Planetary Sciences",
"publication_date": "1988-05",
"volume": "16",
"pages": "121-145"
},
{
"id": "authors:11xa4-q8z20",
"collection": "authors",
"collection_id": "11xa4-q8z20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-115204715",
"type": "article",
"title": "Failure of self-similarity for large (M_w > 8 1/4) earthquakes",
"author": [
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "We compare teleseismic P-wave records for earthquakes in the magnitude range from 6.0 to 9.5 with synthetics for a self-similar, \u03c9^2 source model and conclude that the energy radiated by very large earthquakes (M_w > 8 1/4) is not self-similar to that radiated from smaller earthquakes (M_w < 8 1/4). Furthermore, in the period band from 2 sec to several tens of seconds, we conclude that large subduction earthquakes have an average spectral decay rate of \u03c9^(-1.5). This spectral decay rate is consistent with a previously noted tendency of the \u03c9^2 model to overestimate Ms for large earthquakes.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1988-04",
"series_number": "2",
"volume": "78",
"issue": "2",
"pages": "478-488"
},
{
"id": "authors:728se-n2480",
"collection": "authors",
"collection_id": "728se-n2480",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121212-095209080",
"type": "article",
"title": "Earthquake Hazards on the Cascadia Subduction Zone",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
}
],
"abstract": "Large subduction earthquakes on the Cascadia subduction zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being subducted beneath North America at a rate of approximately 4 centimeters per year. The Cascadia subduction zone shares many characteristics with subduction zones in southern Chile, southwestern Japan, and Colombia, where comparably young oceanic lithosphere is also subducting. Very large subduction earthquakes, ranging in energy magnitude (M_w) between 8 and 9.5, have occurred along these other subduction zones. If the Cascadia subduction zone is also storing elastic energy, a sequence of several great earthquakes (M_w 8) or a giant earthquake (M_w 9) would be necessary to fill this 1200-kilometer gap. The nature of strong ground motions recorded during subduction earthquakes of Mw less than 8.2 is discussed. Strong ground motions from even larger earthquakes (M_w up to 9.5) are estimated by simple simulations. If large subduction earthquakes occur in the Pacific Northwest, relatively strong shaking can be expected over a large region. Such earthquakes may also be accompanied by large local tsunamis.",
"doi": "10.1126/science.236.4798.162",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1987-04-10",
"series_number": "4798",
"volume": "236",
"issue": "4798",
"pages": "162-168"
},
{
"id": "authors:ym5d2-ne474",
"collection": "authors",
"collection_id": "ym5d2-ne474",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-103555819",
"type": "article",
"title": "Rupture history of the 1984 Morgan Hill, California, earthquake from the inversion of strong motion records",
"author": [
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Near-source strong motion velocity records and teleseismic short-period P waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 Morgan Hill earthquake. Both forward modeling and constrained, least-squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0.2 to 2.0 Hz. These data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine-tenths of the local S-wave velocity. The majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions, each with an extent of about 5 km with their centers separated by about 12 km. However, each of the sources has detailed structure of its own, and a simple two-point-source model is not an accurate representation of the Morgan Hill earthquake. The second source occurs about 4.5 sec after the first and is approximately 3 times larger. The maximum dislocation on the fault plane is about 1 m. The total moment of the earthquake is estimated to be 2.1 \u00d7 10^(25) dyne-cm. The Morgan Hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike-slip faults.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1986-06",
"series_number": "3",
"volume": "76",
"issue": "3",
"pages": "649-674"
},
{
"id": "authors:k2m99-pzt76",
"collection": "authors",
"collection_id": "k2m99-pzt76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-132535295",
"type": "article",
"title": "Source characteristics of hypothetical subduction earthquakes in the northwestern United States",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
}
],
"abstract": "Historic earthquake sequences on subduction zones that are similar to the Cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern United States. Based on systematic comparisons of several physical characteristics, including physiography and seismicity, subduction zones that are deemed most similar to the Cascadia subduction zone are those in southern Chile, southwestern Japan, and Colombia. These zones have all experienced very large earthquake sequences, and if the Cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length, then earthquakes of very large size (M_w > 8 1/2) must be considered. Circumstantial evidence is presented that suggests (but does not prove) that large subduction earthquakes along the Cascadia subduction zone may have an average repeat time of 400 to 500 yr.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1986-06",
"series_number": "3",
"volume": "76",
"issue": "3",
"pages": "675-708"
},
{
"id": "authors:zqwa3-s4380",
"collection": "authors",
"collection_id": "zqwa3-s4380",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140225-152223066",
"type": "article",
"title": "Estimating ground motions using recorded accelerograms",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Tajima",
"given_name": "Fumiko",
"clpid": "Tajima-Fumiko"
},
{
"family_name": "Mori",
"given_name": "Wildestein",
"clpid": "Mori-Wildestein"
}
],
"abstract": "A procedure for estimating ground motions using recorded accelerograms is described. The premise of the study is the assumption that future ground motions will be similar to those observed for similar site and tectonic situations in the past. Direct techniques for scaling existing accelerograms have been developed, based on relative estimates of local magnitude, M_L. Design events are described deterministically in terms of fault dimension, tectonic setting (stress drop), fault distance, and site conditions. A combination of empirical and theoretical arguments is used to develop relationships between M_L and other earthquake magnitude scales. In order to minimize scaling errors due to lack of understanding of the physics of strong ground motion, the procedure employs as few intermediate scaling laws as possible. The procedure conserves a meaningful measure of the uncertainty inherent when predicting ground motions from simple parameterizations of earthquake sources and site conditions.",
"doi": "10.1007/BF01904051",
"issn": "0169-3298",
"publisher": "Springer",
"publication": "Surveys in Geophysics",
"publication_date": "1986-03-01",
"series_number": "1",
"volume": "8",
"issue": "1",
"pages": "25-83"
},
{
"id": "authors:seg3b-cys27",
"collection": "authors",
"collection_id": "seg3b-cys27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130115-110915450",
"type": "article",
"title": "Possible tsunami along the northwestern coast of the United States inferred from Indian traditions",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Snavely",
"given_name": "Parke D., Jr.",
"clpid": "Snavely-P-D-Jr"
}
],
"abstract": "Subduction of the Juan de Fuca and Gorda plates beneath western North America\npresents a paradox; despite the fact that there is good evidence of 3 to 4 cm/yr of\nongoing convergence, there is a remarkable paucity of either historic or instrumentally\nrecorded shallow subduction earthquakes. Steady aseismic slip along the entire\nCascadia subduction zone provides one explanation for this seismic quiescence.\nHowever, the Cascadia subduction zone shares many features, including temporal\nquiescence, with other subduction zones that have experienced very large shallow\nsubduction earthquakes (Heaton and Kanamori, 1984). Yet, there is no\ndirect geologic or historical evidence presently available to confirm that great\nshallow subduction earthquakes have occurred along the coast of Washington,\nOregon, and northern California. However, there are reports describing Indian\nlegends of great sea-level disturbances that may be related to large nearby earthquakes.\nIn this letter, we briefly review the history of exploration and settlement of\nthis region by nonnative people and then discuss legends from Indians in northern\nWashington and northern California.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1985-10",
"series_number": "5",
"volume": "75",
"issue": "5",
"pages": "1455-1460"
},
{
"id": "authors:p8wsq-zh934",
"collection": "authors",
"collection_id": "p8wsq-zh934",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130130-145105862",
"type": "article",
"title": "Teleseismic time functions for large, shallow subduction zone earthquakes",
"author": [
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Broadband vertical P-wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum-Pacific in the last 45 yr. Most of the records studied come from a common instrument, the Pasadena, California, Benioff 1-90 seismometer. Propagation and instrument effects are deconvolved from the P-wave records using a damped least-squares inversion to obtain the teleseismic source time function. The inversion has the additional constraint that the time function be positive everywhere. The period band over which the time functions are considered reliable is from 2.5 to 50 sec. Fourier displacement amplitude spectra computed for each of the 1-90 P-wave trains indicate spectral slopes measured between 2 and 50 sec of \u03c9^(\u22121.0) to \u03c9^(\u22122.25) with an average value of \u03c9^(\u22121.5). These values assume an average attenuation of t^* = 1.0. The seismic moments derived from the P-wave time functions compare well with other published values for earthquakes having moments smaller than 2.5 \u00d7 10^(28) dyne-cm (M_w = 8.2). Because the 1-90 seismometer has little response at very long periods, this technique underestimates the moments of the very largest events. The time functions are characterized using five parameters: (1) spectral slope between 2 and 50 sec; (2) roughness of the time function; (3) multiplicity of sources; (4) pulse widths of individual sources; and (5) overall signal duration. The 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere, convergence rates, and maximum size of earthquakes. Comparing the time function parameters with age, rate, and M_w of the subduction zone does not yield obvious global trends. However, most of the subduction zones do behave characteristically and can be grouped accordingly.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1985-08",
"series_number": "4",
"volume": "75",
"issue": "4",
"pages": "965-1004"
},
{
"id": "authors:9ztfb-9pv72",
"collection": "authors",
"collection_id": "9ztfb-9pv72",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121127-081300397",
"type": "article",
"title": "Reply to H. Acharya's \"Comments on 'Seismic potential associated with subduction in the Northwestern United States'\"",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
}
],
"abstract": "Subduction in the northwestern United States presents us with a dilemma. Although there is good evidence of 3 to 4 cm/yr of convergence between the Juan de Fuca and North American plates, the occurrence of either historic or instrumentally recorded shallow thrust earthquakes is remarkably low. Why aren't there more earthquakes? Aseismic slip along the entire plate boundary provides a convenient\nexplanation for this dilemma. Aseismic slip appears to be the predominant mode for plate interaction for many subduction zones. However, the Juan de Fuca subduction zone is clearly different from the most common class of aseismic\nsubduction zone that is characterized by the subduction of very old oceanic lithosphere (Heaton and Kanamori, 1984). We noted that, in general, the subduction of young lithosphere is characterized by strong interplate seismic coupling. The Juan de Fuca subduction zone can be considered as an end member in that it involves\nsome of the youngest subducted lithosphere observed anywhere. This, in itself, suggests that the Juan de Fuca subduction zone belongs in a class (perhaps aseismic)\nby itself. However, there are several other localities where comparably young crust appears to be subducting. These are southern Chile between 42\u00b0 and 45\u00b0 south\nlatitude, Colombia near 2\u00ba north latitude, and the Rivera plate off western Mexico. All of these regions are seismically active and, in the case of Colombia and southern\nChile, have involved earthquakes with energy magnitudes of 8.8 (1906) and 9.5 (southern half of the 1960 rupture zone), respectively. Furthermore, these regions of Colombia and southern Chile do not have bathymetric trenches, and there is no significant seismic activity deeper than 100 km observed on their Benioff-Wadati zones. There is also evidence that these regions have experienced significant periods of seismic quiescence. The NOAA catalog shows a remarkable absence of shallow activity between 41\u00ba and 45\u00b0 south latitude along the Chile trench for at least 30 yr\nprior to the 1960 M_w 9.5 Chilean earthquake. Unfortunately, this catalog is not sufficiently complete to allow a comparison of seismicity at small magnitude\nearthquakes. However, at a magnitude cutoff of 6, the rate of seismicity in the 50 yr preceding the 1960 earthquakes in the region between 41\u00ba and 45\u00ba south latitude seems comparable to that reported for the Juan de Fuca subduction zone's 150-yr history (the Juan de Fuca convergence rate is about one-third that of southern Chile).",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1985-06",
"series_number": "3",
"volume": "75",
"issue": "3",
"pages": "891-892"
},
{
"id": "authors:dy0a0-k4317",
"collection": "authors",
"collection_id": "dy0a0-k4317",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130108-151339368",
"type": "article",
"title": "A Model for a Seismic Computerized Alert Network",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "In large earthquakes, damaging ground motions may occur at large epicentral distances. Because of the relatively slow speed of seismic waves, it is possible to construct a system to provide short-term warning (as much as several tens of seconds) of imminent strong ground motions from major earthquakes. Automated safety responses could be triggered by users after receiving estimates of the arrival time and strength of shaking expected at an individual site. Although warning times are likely to be short for areas greatly damaged by relatively numerous earthquakes of moderate size, large areas that experience very strong shaking during great earthquakes would receive longer warning times.",
"doi": "10.1126/science.228.4702.987",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1985-05",
"series_number": "4702",
"volume": "228",
"issue": "4702",
"pages": "987-990"
},
{
"id": "authors:vhcs6-41351",
"collection": "authors",
"collection_id": "vhcs6-41351",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130228-101520253",
"type": "article",
"title": "Array analysis of the ground velocities and accelerations from the 1971 San Fernando, California, earthquake",
"author": [
{
"family_name": "Liu",
"given_name": "Hsui-Lin",
"clpid": "Liu-Hsui-Lin"
},
{
"family_name": "Heaton",
"given_name": "Thomas",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Profiles of ground velocity and acceleration, displayed as a function of epicentral distance, are analyzed for recordings of the 1971 San Fernando earthquake. Three long profiles (>50 km) and three short profiles (<2 km) are studied. Although there is considerable variation in waveforms and peak amplitudes observed along the long profiles, there are also many examples of coherent phases seen on adjacent stations. There are striking differences in the amplitudes and durations of ground velocity observed at stations located on hard rock sites as opposed to stations located within the large sedimentary basins of the Los Angeles area. Furthermore, the San Fernando Basin, which is adjacent to the source area, seems to respond quite differently from the Los Angeles Basin which is about 30 km from the earthquake source area. Ground acceleration profiles, however, show that there is no corresponding change in the duration or amplitude of high-frequency shaking with site characteristics. We infer that the excitation of surface waves within sedimentary basins is the reason that large peak velocities and displacements are observed for soft sites. The ground velocity waveforms are nearly identical along the three short profiles, which are all located within the Los Angeles Basin. Greater variation of waveforms and amplitudes are seen for ground acceleration along these short profiles, although strong phase coherence is still observed.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1984-10",
"series_number": "5",
"volume": "74",
"issue": "5",
"pages": "1951-1968"
},
{
"id": "authors:ahz5c-cnv07",
"collection": "authors",
"collection_id": "ahz5c-cnv07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121127-135005668",
"type": "article",
"title": "Seismic potential associated with subduction in the northwestern United States",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Kanamori",
"given_name": "Hiroo",
"orcid": "0000-0001-8219-9428",
"clpid": "Kanamori-H"
}
],
"abstract": "Despite good evidence of present-day convergence of the Juan de Fuca and North American plates, there has been remarkably little historical seismic activity along the shallow part of the Juan de Fuca subduction zone. Although we cannot completely rule out the possibility that the plate motion is being accommodated by aseismic creep, we find that the Juan de Fuca subduction zone shares many features with other subduction zones that have experienced great earthquakes.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1984-06",
"series_number": "3",
"volume": "74",
"issue": "3",
"pages": "933-941"
},
{
"id": "authors:9raxb-4vt71",
"collection": "authors",
"collection_id": "9raxb-4vt71",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130228-093912445",
"type": "article",
"title": "Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake",
"author": [
{
"family_name": "Hartzell",
"given_name": "Stephen H.",
"clpid": "Hartzell-S-H"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "A least-squares point-by-point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 Imperial Valley, California, earthquake. The Imperial fault is represented by a plane embedded in a half-space where the elastic properties vary with depth. The inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right-lateral strike-slip and normal dip-slip components of motion. Inversions are run for different fault dips and for both constant and variable rupture velocity models. Effects of different data sets are also investigated. Inversions are compared which use the strong ground motions alone, the teleseismic body waves alone, and simultaneously the strong ground motion and teleseismic records. The inversions are stabilized by adding both smoothing and positivity constraints.\nThe moment is estimated to be 5.0 \u00d7 10^(25) dyne-cm and the fault dip 90\u00b0 \u00b1 5\u00b0. Dislocation in the hypocentral region south of the United States-Mexican border is relatively small and almost dies out near the border. Dislocation then increases sharply north of the border to a maximum of about 2 m under Interstate 8. Dipslip motion is minor compared to strike-slip motion and is concentrated in the sediments. The best-fitting constant rupture velocity is 80 per cent of the local shear-wave velocity. However, there is a suggestion that the rupture front accelerated from the hypocenter northward. The 1979 Imperial Valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1983-12",
"series_number": "6",
"volume": "73",
"issue": "6",
"pages": "1553-1583"
},
{
"id": "authors:54xqh-fwj29",
"collection": "authors",
"collection_id": "54xqh-fwj29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121211-141241559",
"type": "article",
"title": "Ground failure along the New River caused by the October 1979 Imperial Valley earthquake sequence",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Anderson",
"given_name": "John G.",
"clpid": "Anderson-J-G"
},
{
"family_name": "German",
"given_name": "Peter T.",
"clpid": "German-P-T"
}
],
"abstract": "We recognized a number of ground failures along the south bank of the New River north of Brawley, California, following the 15 October 1979 Imperial Valley, California, earthquake sequence. The zone includes a large pond and numerous sand boils, apparently caused by liquefaction, near the Del Rio Country Club. These ground failures, together with failures at the New River bridge west of Brawley and at Wiest Lake, form a discontinuous zone 10 km long. While this zone appears to coincide with the aftershocks following the 16 October 1979, M_L 5.8, Brawley earthquake (the largest aftershock of the Imperial Valley earthquake), a cause and effect relationship cannot be demonstrated. No evidence of tectonic surface faulting could be found.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1983-08",
"series_number": "4",
"volume": "73",
"issue": "4",
"pages": "1161-1171"
},
{
"id": "authors:3p8xy-yg917",
"collection": "authors",
"collection_id": "3p8xy-yg917",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121205-081142449",
"type": "article",
"title": "The 1971 San Fernando earthquake: A double event?",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Evidence is presented which suggest that the 1971 San Fernando earthquake may have been a double event that occurred on two separate, subparallel thrust faults. It is postulated that the initial event took place at depth on the Sierra Madre fault zone which runs along the base of the San Gabriel Mountains. Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km. A second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the Sierra Madre fault zone. The surface trace of this fault coincides with the San Fernando fault zone which was the principal fault associated with surface rupture. It is postulated that rupture propagated from a depth of 8 km to the free surface. The moments of the first and second events are approximately 0.7 \u00d7 10^(26) dyne-cm and 1.0 \u00d7 10^(26) dyne-cm, respectively. This model is found to explain the combined data sets of strong ground motions, teleseismic P and S waveforms, and static offsets better than previous models, which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth. Nevertheless, many features of the observed motions remain unexplained, and considerable uncertainty still exists regarding the faulting history of the San Fernando earthquake.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1982-12",
"series_number": "6A",
"volume": "72",
"issue": "6A",
"pages": "2037-2062"
},
{
"id": "authors:r4esx-1qp34",
"collection": "authors",
"collection_id": "r4esx-1qp34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121205-082246121",
"type": "article",
"title": "Tidal triggering of earthquakes",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Analysis of the tidal stress tensor at the time of moderate to large earthquakes fails to confirm an earlier hypothesis that the origin times of shallow dip-slip earthquakes correlate with solid-earth tidal shear stress. Furthermore, no correlation is seen for either tidal shear stress or tidal normal-to-the-fault compressive stress with shallow strike-slip earthquakes or with deep earthquakes.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1982-12",
"series_number": "6A",
"volume": "72",
"issue": "6A",
"pages": "2181-2200"
},
{
"id": "authors:xhtpw-kaf53",
"collection": "authors",
"collection_id": "xhtpw-kaf53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121212-100833746",
"type": "article",
"title": "An evaluation of the seismic-window theory for earthquake prediction",
"author": [
{
"family_name": "McNutt",
"given_name": "Marcia",
"clpid": "McNutt-M"
},
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "The hypothesis that tides may trigger seismic events is not new. The conclusions\nfrom previous studies are mixed, but some negative results might be attributed to\nfailure in accounting for the variation in tidal phase and fault orientation over the\nsurface of the earth. The connection between tides and seismicity appears most\nconvincing for studies in which the investigators either correlated the earthquakes\nwith the magnitude and direction of tidal stress on the actual fault planes (Heaton,\n1975) or restricted the data set to events in a small region over which the earthquake\nmechanisms would be reasonably similar (Klein, 1976; Young and Zurn,\n1979). In general, these studies have dealt with only the semidiurnal fluctuations in\nthe tidal amplitude. The intent of this study was to determine whether earthquakes\nin the San Francisco Bay area respond to a fortnightly fluctuation in tidal\namplitude. A correlation between seismic events and any tidal period would contribute\nto the understanding of the earthquake process and the stress regime\nwithin which faulting occurs. But perhaps more importantly, correlations between\nthe longer tidal periods and seismicity might provide a useful tool for earthquake prediction.",
"issn": "0026-4555",
"publisher": "California Division of Mines and Geology",
"publication": "California Geology",
"publication_date": "1981-01",
"series_number": "1",
"volume": "34",
"issue": "1",
"pages": "12-16"
},
{
"id": "authors:7dc6r-g9z51",
"collection": "authors",
"collection_id": "7dc6r-g9z51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130204-115012596",
"type": "article",
"title": "Generalized ray models of the San Fernando Earthquake",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Helmberger",
"given_name": "Donald V.",
"clpid": "Helmberger-D-V"
}
],
"abstract": "The exact Cagniard-de Hoop solutions for a point dislocation in half-space are used to construct models of the strong ground motion observed during the February 9, 1971 San Fernando earthquake (M_L = 6.4). By summing point dislocations distributed over the fault plane, three-dimensional models of a finite fault located in a half-space are constructed to study the ground motions observed at JPL (Pasadena), Palmdale, Lake Hughes, and Pacoima Dam. Since the duration of faulting is comparable to the travel times for various wave types, very complex interference of these arrivals makes a detailed interpretation of these wave forms difficult. By investigating the motion due to small sections of the fault, it is possible to understand how various wave types interfere to produce the motion due to the total fault. Rayleigh waves as well as S to P head waves are shown to be important effects of the free surface. Near-field source effects are also quite dramatic. Strong directivity is required to explain the difference in amplitudes seen between stations to the north and stations to the south. Faulting appears to have begun north of Pacoima at a depth of 13 km. The rupture velocity, which is near 2.8 km/sec in the hypocentral region, appears to slow to 1.8 km/sec at a depth of 5 km. Displacements on the deeper sections of the fault are about 2.5 m. Fault offsets become very small at depths near 4 km and then grow again to 5 m near the surface rupture. The large velocity pulse seen at Pacoima is a far-field shear wave which is enhanced by directivity. Peak accelerations at Pacoima are probably associated with the large shallow faulting. The total moment is 1.4 \u00d7 10^(26) ergs.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1979-10",
"series_number": "5",
"volume": "69",
"issue": "5",
"pages": "1311-1341"
},
{
"id": "authors:00x1b-j8365",
"collection": "authors",
"collection_id": "00x1b-j8365",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-100923266",
"type": "article",
"title": "Predictability of strong ground motion in the Imperial Valley: Modeling the M4.9, November 4, 1976 Brawley earthquake",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Helmberger",
"given_name": "Donald V.",
"clpid": "Helmberger-D-V"
}
],
"abstract": "Strong-motion displacements, recorded at 33 km (IVC) and 36 km (ELC) from the November 4, 1976 Brawley earthquake, are modeled using the Cagniard-deHoop technique. The IVC record consists almost entirely of transversely polarized motion, whereas the ELC record contains an approximately equal proportion of transversely and radially polarized motion. A simplified shear-wave velocity model was determined from the compressional wave refraction studies of Biehler, Kovach, and Allen (1964). The epicentral location and focal mechanism computed from P-wave first-arrival studies were used to locate and orient a double-couple point source within the layered half-space. The far-field time function and source depth were the only parameters without good independent constraints. A triangular far-field time function with a duration of 1.5 sec and a source depth of 7 km were sufficient to model the first 25 sec of tangential ground motion. It appears that the effects of velocity structure on the propagation of long-period SH waves are predictable in the Imperial Valley. A study of the synthetic Fourier amplitude spectra indicates that wave propagation effects should be included in studies of source spectra and seismic wave attenuation.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1978-02",
"series_number": "1",
"volume": "68",
"issue": "1",
"pages": "31-48"
},
{
"id": "authors:fqn90-xg194",
"collection": "authors",
"collection_id": "fqn90-xg194",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121121-102148439",
"type": "article",
"title": "A study of the strong ground motion of the Borrego Mountain, California, earthquake",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
},
{
"family_name": "Helmberger",
"given_name": "Donald V.",
"clpid": "Helmberger-D-V"
}
],
"abstract": "Several synthetic models are constructed to fit the first 40 sec of the transversely polarized displacement, as recorded at El Centro, of the April 9, 1968 Borrego Mountain earthquake. The modeling is done in the time domain using the response computed for a distributed set of point shear dislocations embedded in a layered half-space. The beginning 10 sec of the observed record is used to model the spatial and temporal distribution of faulting whereas the remaining portion is used to determine the upper crustal structure based on surface-wave periodicity. A natural depth criterion was provided by comparing the amplitude of the direct arrival with the surface-wave excitations. Trade-offs are found to exist between source models and velocity structure models. Within the framework of a layer over a half-space model, faulting of finite vertical extent is required, whereas the horizontal dimensions of faulting are not resolvable. A model which is also consistent with the teleseismic results of Burdick and Mellman indicates massive faulting near a depth of 9 km with a fast rise time producing a 10-cm displacement pulse of 1 sec duration at El Centro. The faulting appears to slow down approaching the surface. The moment is calculated to be approximately 7 \u00d7 10^(25) dyne-cm which is somewhat smaller than the moment found by Burdick and Mellman (1976).",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1977-04",
"series_number": "2",
"volume": "67",
"issue": "2",
"pages": "315-330"
},
{
"id": "authors:ysm48-njp08",
"collection": "authors",
"collection_id": "ysm48-njp08",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130213-102823090",
"type": "article",
"title": "Tidal Triggering of Earthquakes",
"author": [
{
"family_name": "Heaton",
"given_name": "Thomas H.",
"orcid": "0000-0003-3363-2197",
"clpid": "Heaton-T-H"
}
],
"abstract": "Analysis of the tidal stress tensor at the time of moderate to large earthquakes strongly suggests that shallow (< 30 km) larger magnitude oblique-slip and dip-slip earthquakes are triggered by tidal stresses. No corresponding triggering effect is seen for shallow strike-slip earthquakes or for any type of intermediate or deep focus earthquakes which have been studied. Tidal triggering is also discussed from the viewpoint of the 'dilatancy-diffusion' model. Specifically, the model as usually stated, excludes the possibility of small earthquakes being tidally triggered.",
"doi": "10.1111/j.1365-246X.1975.tb00637.x",
"issn": "0956-540X",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal International",
"publication_date": "1975-11",
"series_number": "2",
"volume": "43",
"issue": "2",
"pages": "307-326"
},
{
"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"
}
]