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Sample records for california earthquake probabilities

  1. An empirical model for earthquake probabilities in the San Francisco Bay region, California, 2002-2031

    USGS Publications Warehouse

    Reasenberg, P.A.; Hanks, T.C.; Bakun, W.H.

    2003-01-01

    The moment magnitude M 7.8 earthquake in 1906 profoundly changed the rate of seismic activity over much of northern California. The low rate of seismic activity in the San Francisco Bay region (SFBR) since 1906, relative to that of the preceding 55 yr, is often explained as a stress-shadow effect of the 1906 earthquake. However, existing elastic and visco-elastic models of stress change fail to fully account for the duration of the lowered rate of earthquake activity. We use variations in the rate of earthquakes as a basis for a simple empirical model for estimating the probability of M ???6.7 earthquakes in the SFBR. The model preserves the relative magnitude distribution of sources predicted by the Working Group on California Earthquake Probabilities' (WGCEP, 1999; WGCEP, 2002) model of characterized ruptures on SFBR faults and is consistent with the occurrence of the four M ???6.7 earthquakes in the region since 1838. When the empirical model is extrapolated 30 yr forward from 2002, it gives a probability of 0.42 for one or more M ???6.7 in the SFBR. This result is lower than the probability of 0.5 estimated by WGCEP (1988), lower than the 30-yr Poisson probability of 0.60 obtained by WGCEP (1999) and WGCEP (2002), and lower than the 30-yr time-dependent probabilities of 0.67, 0.70, and 0.63 obtained by WGCEP (1990), WGCEP (1999), and WGCEP (2002), respectively, for the occurrence of one or more large earthquakes. This lower probability is consistent with the lack of adequate accounting for the 1906 stress-shadow in these earlier reports. The empirical model represents one possible approach toward accounting for the stress-shadow effect of the 1906 earthquake. However, the discrepancy between our result and those obtained with other modeling methods underscores the fact that the physics controlling the timing of earthquakes is not well understood. Hence, we advise against using the empirical model alone (or any other single probability model) for estimating the

  2. Earthquake Rate Model 2 of the 2007 Working Group for California Earthquake Probabilities, Magnitude-Area Relationships

    USGS Publications Warehouse

    Stein, Ross S.

    2008-01-01

    The Working Group for California Earthquake Probabilities must transform fault lengths and their slip rates into earthquake moment-magnitudes. First, the down-dip coseismic fault dimension, W, must be inferred. We have chosen the Nazareth and Hauksson (2004) method, which uses the depth above which 99% of the background seismicity occurs to assign W. The product of the observed or inferred fault length, L, with the down-dip dimension, W, gives the fault area, A. We must then use a scaling relation to relate A to moment-magnitude, Mw. We assigned equal weight to the Ellsworth B (Working Group on California Earthquake Probabilities, 2003) and Hanks and Bakun (2007) equations. The former uses a single logarithmic relation fitted to the M=6.5 portion of data of Wells and Coppersmith (1994); the latter uses a bilinear relation with a slope change at M=6.65 (A=537 km2) and also was tested against a greatly expanded dataset for large continental transform earthquakes. We also present an alternative power law relation, which fits the newly expanded Hanks and Bakun (2007) data best, and captures the change in slope that Hanks and Bakun attribute to a transition from area- to length-scaling of earthquake slip. We have not opted to use the alternative relation for the current model. The selections and weights were developed by unanimous consensus of the Executive Committee of the Working Group, following an open meeting of scientists, a solicitation of outside opinions from additional scientists, and presentation of our approach to the Scientific Review Panel. The magnitude-area relations and their assigned weights are unchanged from that used in Working Group (2003).

  3. California Fault Parameters for the National Seismic Hazard Maps and Working Group on California Earthquake Probabilities 2007

    USGS Publications Warehouse

    Wills, Chris J.; Weldon, Ray J., II; Bryant, W.A.

    2008-01-01

    This report describes development of fault parameters for the 2007 update of the National Seismic Hazard Maps and the Working Group on California Earthquake Probabilities (WGCEP, 2007). These reference parameters are contained within a database intended to be a source of values for use by scientists interested in producing either seismic hazard or deformation models to better understand the current seismic hazards in California. These parameters include descriptions of the geometry and rates of movements of faults throughout the state. These values are intended to provide a starting point for development of more sophisticated deformation models which include known rates of movement on faults as well as geodetic measurements of crustal movement and the rates of movements of the tectonic plates. The values will be used in developing the next generation of the time-independent National Seismic Hazard Maps, and the time-dependant seismic hazard calculations being developed for the WGCEP. Due to the multiple uses of this information, development of these parameters has been coordinated between USGS, CGS and SCEC. SCEC provided the database development and editing tools, in consultation with USGS, Golden. This database has been implemented in Oracle and supports electronic access (e.g., for on-the-fly access). A GUI-based application has also been developed to aid in populating the database. Both the continually updated 'living' version of this database, as well as any locked-down official releases (e.g., used in a published model for calculating earthquake probabilities or seismic shaking hazards) are part of the USGS Quaternary Fault and Fold Database http://earthquake.usgs.gov/regional/qfaults/ . CGS has been primarily responsible for updating and editing of the fault parameters, with extensive input from USGS and SCEC scientists.

  4. Maximum Magnitude and Probabilities of Induced Earthquakes in California Geothermal Fields: Applications for a Science-Based Decision Framework

    NASA Astrophysics Data System (ADS)

    Weiser, Deborah Anne

    Induced seismicity is occurring at increasing rates around the country. Brodsky and Lajoie (2013) and others have recognized anthropogenic quakes at a few geothermal fields in California. I use three techniques to assess if there are induced earthquakes in California geothermal fields; there are three sites with clear induced seismicity: Brawley, The Geysers, and Salton Sea. Moderate to strong evidence is found at Casa Diablo, Coso, East Mesa, and Susanville. Little to no evidence is found for Heber and Wendel. I develop a set of tools to reduce or cope with the risk imposed by these earthquakes, and also to address uncertainties through simulations. I test if an earthquake catalog may be bounded by an upper magnitude limit. I address whether the earthquake record during pumping time is consistent with the past earthquake record, or if injection can explain all or some of the earthquakes. I also present ways to assess the probability of future earthquake occurrence based on past records. I summarize current legislation for eight states where induced earthquakes are of concern. Unlike tectonic earthquakes, the hazard from induced earthquakes has the potential to be modified. I discuss direct and indirect mitigation practices. I present a framework with scientific and communication techniques for assessing uncertainty, ultimately allowing more informed decisions to be made.

  5. Earthquake Rate Model 2.2 of the 2007 Working Group for California Earthquake Probabilities, Appendix D: Magnitude-Area Relationships

    USGS Publications Warehouse

    Stein, Ross S.

    2007-01-01

    Summary To estimate the down-dip coseismic fault dimension, W, the Executive Committee has chosen the Nazareth and Hauksson (2004) method, which uses the 99% depth of background seismicity to assign W. For the predicted earthquake magnitude-fault area scaling used to estimate the maximum magnitude of an earthquake rupture from a fault's length, L, and W, the Committee has assigned equal weight to the Ellsworth B (Working Group on California Earthquake Probabilities, 2003) and Hanks and Bakun (2002) (as updated in 2007) equations. The former uses a single relation; the latter uses a bilinear relation which changes slope at M=6.65 (A=537 km2).

  6. Forecasting southern california earthquakes.

    PubMed

    Raleigh, C B; Sieh, K; Sykes, L R; Anderson, D L

    1982-09-17

    Since 1978 and 1979, California has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years. In the past such periods have also been associated with major destructive earthquakes, of magnitude 7 or greater, and the annual probability of occurrence of such an event is now 13 percent in California. The increase in seismicity is associated with a marked deviation in the pattern of strain accumulation, a correlation that is physically plausible. Although great earthquakes (magnitude greater than 7.5) are too infrequent to have clear associations with any pattern of seismicity that is now observed, the San Andreas fault in southern California has accumulated sufficient potential displacement since the last rupture in 1857 to generate a great earthquake along part or all of its length. PMID:17740956

  7. California earthquake history

    USGS Publications Warehouse

    Toppozada, T.; Branum, D.

    2004-01-01

    This paper presents an overview of the advancement in our knowledge of California's earthquake history since ??? 1800, and especially during the last 30 years. We first review the basic statewide research on earthquake occurrences that was published from 1928 through 2002, to show how the current catalogs and their levels of completeness have evolved with time. Then we review some of the significant new results in specific regions of California, and some of what remains to be done. Since 1850, 167 potentially damaging earthquakes of M ??? 6 or larger have been identified in California and its border regions, indicating an average rate of 1.1 such events per year. Table I lists the earthquakes of M ??? 6 to 6.5 that were also destructive since 1812 in California and its border regions, indicating an average rate of one such event every ??? 5 years. Many of these occurred before 1932 when epicenters and magnitudes started to be determined routinely using seismographs in California. The number of these early earthquakes is probably incomplete in sparsely populated remote parts of California before ??? 1870. For example, 6 of the 7 pre-1873 events in table I are of M ??? 7, suggesting that other earthquakes of M 6.5 to 6.9 occurred but were not properly identified, or were not destructive. The epicenters and magnitudes (M) of the pre-instrumental earthquakes were determined from isoseismal maps that were based on the Modified Mercalli Intensity of shaking (MMI) at the communities that reported feeling the earthquakes. The epicenters were estimated to be in the regions of most intense shaking, and values of M were estimated from the extent of the areas shaken at various MMI levels. MMI VII or greater shaking is the threshold of damage to weak buildings. Certain areas in the regions of Los Angeles, San Francisco, and Eureka were each shaken repeatedly at MMI VII or greater at least six times since ??? 1812, as depicted by Toppozada and Branum (2002, fig. 19).

  8. Long‐term time‐dependent probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3)

    USGS Publications Warehouse

    Field, Ned; Biasi, Glenn P.; Bird, Peter; Dawson, Timothy E.; Felzer, Karen R.; Jackson, David A.; Johnson, Kaj M.; Jordan, Thomas H.; Madden, Christopher; Michael, Andrew J.; Milner, Kevin; Page, Morgan T.; Parsons, Thomas E.; Powers, Peter; Shaw, Bruce E.; Thatcher, Wayne R.; Weldon, Ray J., II; Zeng, Yuehua

    2015-01-01

    The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model, published previously, renewal models are utilized to represent elastic-rebound-implied probabilities. A new methodology has been developed that solves applicability issues in the previous approach for un-segmented models. The new methodology also supports magnitude-dependent aperiodicity and accounts for the historic open interval on faults that lack a date-of-last-event constraint. Epistemic uncertainties are represented with a logic tree, producing 5,760 different forecasts. Results for a variety of evaluation metrics are presented, including logic-tree sensitivity analyses and comparisons to the previous model (UCERF2). For 30-year M≥6.7 probabilities, the most significant changes from UCERF2 are a threefold increase on the Calaveras fault and a threefold decrease on the San Jacinto fault. Such changes are due mostly to differences in the time-independent models (e.g., fault slip rates), with relaxation of segmentation and inclusion of multi-fault ruptures being particularly influential. In fact, some UCERF2 faults were simply too long to produce M 6.7 sized events given the segmentation assumptions in that study. Probability model differences are also influential, with the implied gains (relative to a Poisson model) being generally higher in UCERF3. Accounting for the historic open interval is one reason. Another is an effective 27% increase in the total elastic-rebound-model weight. The exact factors influencing differences between UCERF2 and UCERF3, as well as the relative importance of logic-tree branches, vary throughout the region, and depend on the evaluation metric of interest. For example, M≥6.7 probabilities may not be a good proxy for other hazard or loss measures. This sensitivity, coupled with the

  9. Earthquake education in California

    USGS Publications Warehouse

    MacCabe, M. P.

    1980-01-01

    In a survey of community response to the earthquake threat in southern California, Ralph Turner and his colleagues in the Department of Sociology at the University of California, Los Angeles, found that the public very definitely wants to be educated about the kinds of problems and hazards they can expect during and after a damaging earthquake; and they also want to know how they can prepare themselves to minimize their vulnerability. Decisionmakers, too, are recognizing this new wave of public concern. 

  10. The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2)

    USGS Publications Warehouse

    2007 Working Group on California Earthquake Probabilities

    2008-01-01

    California?s 35 million people live among some of the most active earthquake faults in the United States. Public safety demands credible assessments of the earthquake hazard to maintain appropriate building codes for safe construction and earthquake insurance for loss protection. Seismic hazard analysis begins with an earthquake rupture forecast?a model of probabilities that earthquakes of specified magnitudes, locations, and faulting types will occur during a specified time interval. This report describes a new earthquake rupture forecast for California developed by the 2007 Working Group on California Earthquake Probabilities (WGCEP 2007).

  11. Computing Earthquake Probabilities on Global Scales

    NASA Astrophysics Data System (ADS)

    Holliday, James R.; Graves, William R.; Rundle, John B.; Turcotte, Donald L.

    2016-03-01

    Large devastating events in systems such as earthquakes, typhoons, market crashes, electricity grid blackouts, floods, droughts, wars and conflicts, and landslides can be unexpected and devastating. Events in many of these systems display frequency-size statistics that are power laws. Previously, we presented a new method for calculating probabilities for large events in systems such as these. This method counts the number of small events since the last large event and then converts this count into a probability by using a Weibull probability law. We applied this method to the calculation of large earthquake probabilities in California-Nevada, USA. In that study, we considered a fixed geographic region and assumed that all earthquakes within that region, large magnitudes as well as small, were perfectly correlated. In the present article, we extend this model to systems in which the events have a finite correlation length. We modify our previous results by employing the correlation function for near mean field systems having long-range interactions, an example of which is earthquakes and elastic interactions. We then construct an application of the method and show examples of computed earthquake probabilities.

  12. Uniform California earthquake rupture forecast, version 2 (UCERF 2)

    USGS Publications Warehouse

    Field, E.H.; Dawson, T.E.; Felzer, K.R.; Frankel, A.D.; Gupta, V.; Jordan, T.H.; Parsons, T.; Petersen, M.D.; Stein, R.S.; Weldon, R.J.; Wills, C.J.

    2009-01-01

    The 2007 Working Group on California Earthquake Probabilities (WGCEP, 2007) presents the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2). This model comprises a time-independent (Poisson-process) earthquake rate model, developed jointly with the National Seismic Hazard Mapping Program and a time-dependent earthquake-probability model, based on recent earthquake rates and stress-renewal statistics conditioned on the date of last event. The models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular, extensible Open Seismic Hazard Analysis framework. The rate model satisfies integrating measures of deformation across the plate-boundary zone and is consistent with historical seismicity data. An overprediction of earthquake rates found at intermediate magnitudes (6.5 ??? M ???7.0) in previous models has been reduced to within the 95% confidence bounds of the historical earthquake catalog. A logic tree with 480 branches represents the epistemic uncertainties of the full time-dependent model. The mean UCERF 2 time-dependent probability of one or more M ???6.7 earthquakes in the California region during the next 30 yr is 99.7%; this probability decreases to 46% for M ???7.5 and to 4.5% for M ???8.0. These probabilities do not include the Cascadia subduction zone, largely north of California, for which the estimated 30 yr, M ???8.0 time-dependent probability is 10%. The M ???6.7 probabilities on major strike-slip faults are consistent with the WGCEP (2003) study in the San Francisco Bay Area and the WGCEP (1995) study in southern California, except for significantly lower estimates along the San Jacinto and Elsinore faults, owing to provisions for larger multisegment ruptures. Important model limitations are discussed.

  13. Virtual California: studying earthquakes through simulation

    NASA Astrophysics Data System (ADS)

    Sachs, M. K.; Heien, E. M.; Turcotte, D. L.; Yikilmaz, M. B.; Rundle, J. B.; Kellogg, L. H.

    2012-12-01

    Virtual California is a computer simulator that models earthquake fault systems. The design of Virtual California allows for fast execution so many thousands of events can be generated over very long simulated time periods. The result is a rich dataset, including simulated earthquake catalogs, which can be used to study the statistical properties of the seismicity on the modeled fault systems. We describe the details of Virtual California's operation and discuss recent results from Virtual California simulations.

  14. SCEC Earthquake Simulator Comparison Results for California

    NASA Astrophysics Data System (ADS)

    Tullis, T. E.; Richards-Dinger, K. B.; Barall, M.; Dieterich, J. H.; Field, E. H.; Heien, E. M.; Kellogg, L. H.; Pollitz, F. F.; Rundle, J. B.; Sachs, M. K.; Turcotte, D. L.; Ward, S. N.; Zielke, O.

    2011-12-01

    This is our first report on comparisons of earthquake simulator results with one another and with actual earthquake data for all of California, excluding Cascadia. Earthquake simulators are computer programs that simulate long sequences of earthquakes and therefore allow study of a much longer earthquake history than is possible from instrumental, historical and paleoseismic data. The usefulness of simulated histories for anticipating the probabilities of future earthquakes and for contributing to public policy decisions depends on whether simulated earthquake catalogs properly represent actual earthquakes. Thus, we compare simulated histories generated by five different earthquake simulators with one another and with what is known about actual earthquake history in order to evaluate the usefulness of the simulator results. Although sharing common features, our simulators differ from one another in their details in many important ways. All simulators use the same fault geometry and the same ~15,000, 3x3 km elements to represent the strike-slip and thrust faults in California. The set of faults and the input slip rates on them are essentially those of the UCERF2 fault and deformation model; we will switch to the UCERF3 model once it is available. All simulators use the boundary element method to compute stress transfer between elements. Differences between the simulators include how they represent fault friction and what assumptions they make to promote rupture propagation from one element to another. The behavior of the simulators is encouragingly similar and the results are similar to what is known about real earthquakes, although some refinements are being made to some of the simulators to improve these comparisons as a result of our initial results. The frequency magnitude distributions of simulated events from M6 to M7.5 for a 30,000 year simulated history agree well with instrumental observations for all of California. Scaling relations, as seen on plots of

  15. Prospective Tests of Southern California Earthquake Forecasts

    NASA Astrophysics Data System (ADS)

    Jackson, D. D.; Schorlemmer, D.; Gerstenberger, M.; Kagan, Y. Y.; Helmstetter, A.; Wiemer, S.; Field, N.

    2004-12-01

    We are testing earthquake forecast models prospectively using likelihood ratios. Several investigators have developed such models as part of the Southern California Earthquake Center's project called Regional Earthquake Likelihood Models (RELM). Various models are based on fault geometry and slip rates, seismicity, geodetic strain, and stress interactions. Here we describe the testing procedure and present preliminary results. Forecasts are expressed as the yearly rate of earthquakes within pre-specified bins of longitude, latitude, magnitude, and focal mechanism parameters. We test models against each other in pairs, which requires that both forecasts in a pair be defined over the same set of bins. For this reason we specify a standard "menu" of bins and ground rules to guide forecasters in using common descriptions. One menu category includes five-year forecasts of magnitude 5.0 and larger. Contributors will be requested to submit forecasts in the form of a vector of yearly earthquake rates on a 0.1 degree grid at the beginning of the test. Focal mechanism forecasts, when available, are also archived and used in the tests. Interim progress will be evaluated yearly, but final conclusions would be made on the basis of cumulative five-year performance. The second category includes forecasts of earthquakes above magnitude 4.0 on a 0.1 degree grid, evaluated and renewed daily. Final evaluation would be based on cumulative performance over five years. Other types of forecasts with different magnitude, space, and time sampling are welcome and will be tested against other models with shared characteristics. Tests are based on the log likelihood scores derived from the probability that future earthquakes would occur where they do if a given forecast were true [Kagan and Jackson, J. Geophys. Res.,100, 3,943-3,959, 1995]. For each pair of forecasts, we compute alpha, the probability that the first would be wrongly rejected in favor of the second, and beta, the probability

  16. Results of the Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California

    PubMed Central

    Lee, Ya-Ting; Turcotte, Donald L.; Holliday, James R.; Sachs, Michael K.; Rundle, John B.; Chen, Chien-Chih; Tiampo, Kristy F.

    2011-01-01

    The Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California was the first competitive evaluation of forecasts of future earthquake occurrence. Participants submitted expected probabilities of occurrence of M≥4.95 earthquakes in 0.1° × 0.1° cells for the period 1 January 1, 2006, to December 31, 2010. Probabilities were submitted for 7,682 cells in California and adjacent regions. During this period, 31 M≥4.95 earthquakes occurred in the test region. These earthquakes occurred in 22 test cells. This seismic activity was dominated by earthquakes associated with the M = 7.2, April 4, 2010, El Mayor–Cucapah earthquake in northern Mexico. This earthquake occurred in the test region, and 16 of the other 30 earthquakes in the test region could be associated with it. Nine complete forecasts were submitted by six participants. In this paper, we present the forecasts in a way that allows the reader to evaluate which forecast is the most “successful” in terms of the locations of future earthquakes. We conclude that the RELM test was a success and suggest ways in which the results can be used to improve future forecasts. PMID:21949355

  17. Earthquake probabilities: theoretical assessments and reality

    NASA Astrophysics Data System (ADS)

    Kossobokov, V. G.

    2013-12-01

    It is of common knowledge that earthquakes are complex phenomena which classification and sizing remain serious problems of the contemporary seismology. In general, their frequency-magnitude distribution exhibit power law scaling. This scaling differs significantly when different time and/or space domains are considered. At the scale of a particular earthquake rupture zone the frequency of similar size events is usually estimated to be about once in several hundred years. Evidently, contemporary seismology does not possess enough reported instrumental data for any reliable quantification of an earthquake probability at a given place of expected event. Regretfully, most of the state-of-the-art theoretical approaches to assess probability of seismic events are based on trivial (e.g. Poisson, periodic, etc) or, conversely, delicately-designed (e.g. STEP, ETAS, etc) models of earthquake sequences. Some of these models are evidently erroneous, some can be rejected by the existing statistics, and some are hardly testable in our life-time. Nevertheless such probabilistic counts including seismic hazard assessment and earthquake forecasting when used on practice eventually mislead to scientifically groundless advices communicated to decision makers and inappropriate decisions. As a result, the population of seismic regions continues facing unexpected risk and losses. The international project Global Earthquake Model (GEM) is on the wrong track, if it continues to base seismic risk estimates on the standard, mainly probabilistic, methodology to assess seismic hazard. It is generally accepted that earthquakes are infrequent, low-probability events. However, they keep occurring at earthquake-prone areas with 100% certainty. Given the expectation of seismic event once per hundred years, the daily probability of occurrence on a certain date may range from 0 to 100% depending on a choice of probability space (which is yet unknown and, therefore, made by a subjective lucky chance

  18. Real-time forecasts of tomorrow's earthquakes in California

    USGS Publications Warehouse

    Gerstenberger, M.C.; Wiemer, S.; Jones, L.M.; Reasenberg, P.A.

    2005-01-01

    Despite a lack of reliable deterministic earthquake precursors, seismologists have significant predictive information about earthquake activity from an increasingly accurate understanding of the clustering properties of earthquakes. In the past 15 years, time-dependent earthquake probabilities based on a generic short-term clustering model have been made publicly available in near-real time during major earthquake sequences. These forecasts describe the probability and number of events that are, on average, likely to occur following a mainshock of a given magnitude, but are not tailored to the particular sequence at hand and contain no information about the likely locations of the aftershocks. Our model builds upon the basic principles of this generic forecast model in two ways: it recasts the forecast in terms of the probability of strong ground shaking, and it combines an existing time-independent earthquake occurrence model based on fault data and historical earthquakes with increasingly complex models describing the local time-dependent earthquake clustering. The result is a time-dependent map showing the probability of strong shaking anywhere in California within the next 24 hours. The seismic hazard modelling approach we describe provides a better understanding of time-dependent earthquake hazard, and increases its usefulness for the public, emergency planners and the media.

  19. The 2004 Parkfield, CA Earthquake: A Teachable Moment for Exploring Earthquake Processes, Probability, and Earthquake Prediction

    NASA Astrophysics Data System (ADS)

    Kafka, A.; Barnett, M.; Ebel, J.; Bellegarde, H.; Campbell, L.

    2004-12-01

    The occurrence of the 2004 Parkfield earthquake provided a unique "teachable moment" for students in our science course for teacher education majors. The course uses seismology as a medium for teaching a wide variety of science topics appropriate for future teachers. The 2004 Parkfield earthquake occurred just 15 minutes after our students completed a lab on earthquake processes and earthquake prediction. That lab included a discussion of the Parkfield Earthquake Prediction Experiment as a motivation for the exercises they were working on that day. Furthermore, this earthquake was recorded on an AS1 seismograph right in their lab, just minutes after the students left. About an hour after we recorded the earthquake, the students were able to see their own seismogram of the event in the lecture part of the course, which provided an excellent teachable moment for a lecture/discussion on how the occurrence of the 2004 Parkfield earthquake might affect seismologists' ideas about earthquake prediction. The specific lab exercise that the students were working on just before we recorded this earthquake was a "sliding block" experiment that simulates earthquakes in the classroom. The experimental apparatus includes a flat board on top of which are blocks of wood attached to a bungee cord and a string wrapped around a hand crank. Plate motion is modeled by slowly turning the crank, and earthquakes are modeled as events in which the block slips ("blockquakes"). We scaled the earthquake data and the blockquake data (using how much the string moved as a proxy for time) so that we could compare blockquakes and earthquakes. This provided an opportunity to use interevent-time histograms to teach about earthquake processes, probability, and earthquake prediction, and to compare earthquake sequences with blockquake sequences. We were able to show the students, using data obtained directly from their own lab, how global earthquake data fit a Poisson exponential distribution better

  20. The parkfield, california, earthquake prediction experiment.

    PubMed

    Bakun, W H; Lindh, A G

    1985-08-16

    Five moderate (magnitude 6) earthquakes with similar features have occurred on the Parkfield section of the San Andreas fault in central California since 1857. The next moderate Parkfield earthquake is expected to occur before 1993. The Parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process; observations and reports of seismicity and aseismic slip associated with the last moderate Parkfield earthquake in 1966 constitute much of the basis of the design of the experiment. PMID:17739363

  1. Seismicity alert probabilities at Parkfield, California, revisited

    USGS Publications Warehouse

    Michael, A.J.; Jones, L.M.

    1998-01-01

    For a decade, the US Geological Survey has used the Parkfield Earthquake Prediction Experiment scenario document to estimate the probability that earthquakes observed on the San Andreas fault near Parkfield will turn out to be foreshocks followed by the expected magnitude six mainshock. During this time, we have learned much about the seismogenic process at Parkfield, about the long-term probability of the Parkfield mainshock, and about the estimation of these types of probabilities. The probabilities for potential foreshocks at Parkfield are reexamined and revised in light of these advances. As part of this process, we have confirmed both the rate of foreshocks before strike-slip earthquakes in the San Andreas physiographic province and the uniform distribution of foreshocks with magnitude proposed by earlier studies. Compared to the earlier assessment, these new estimates of the long-term probability of the Parkfield mainshock are lower, our estimate of the rate of background seismicity is higher, and we find that the assumption that foreshocks at Parkfield occur in a unique way is not statistically significant at the 95% confidence level. While the exact numbers vary depending on the assumptions that are made, the new alert probabilities are lower than previously estimated. Considering the various assumptions and the statistical uncertainties in the input parameters, we also compute a plausible range for the probabilities. The range is large, partly due to the extra knowledge that exists for the Parkfield segment, making us question the usefulness of these numbers.

  2. Probability based earthquake load and resistance factor design criteria for offshore platforms

    SciTech Connect

    Bea, R.G.

    1996-12-31

    This paper describes a probability reliability based formulation to determine earthquake Load and Resistance Factor Design (LRFD) parameters for conventional, steel, pile supported, tubular membered platforms that is proposed as a basis for earthquake design criteria and guidelines for offshore platforms that are intended to have worldwide applicability. The formulation is illustrated with application to platforms located in five areas: offshore California, Venezuela (Rio Caribe), the East Coast of Canada, in the Caspian Sea (Azeri), and the Norwegian sector of the North Sea.

  3. California earthquakes: why only shallow focus?

    PubMed

    Brace, W F; Byerlee, J D

    1970-06-26

    Frictional sliding on sawcuts and faults in laboratory samples of granite and gabbro is markedly temperature-dependent. At pressures from 1 to 5 kilobars, stick-slip gave way to stable sliding as temperature was increased from 200 to 500 degrees Celsius. Increased temperature with depth could thus cause the abrupt disappearance of earthquakes noted at shallow depths in California. PMID:17759338

  4. A physically-based earthquake recurrence model for estimation of long-term earthquake probabilities

    USGS Publications Warehouse

    Ellsworth, William L.; Matthews, Mark V.; Nadeau, Robert M.; Nishenko, Stuart P.; Reasenberg, Paul A.; Simpson, Robert W.

    1999-01-01

    A physically-motivated model for earthquake recurrence based on the Brownian relaxation oscillator is introduced. The renewal process defining this point process model can be described by the steady rise of a state variable from the ground state to failure threshold as modulated by Brownian motion. Failure times in this model follow the Brownian passage time (BPT) distribution, which is specified by the mean time to failure, μ, and the aperiodicity of the mean, α (equivalent to the familiar coefficient of variation). Analysis of 37 series of recurrent earthquakes, M -0.7 to 9.2, suggests a provisional generic value of α = 0.5. For this value of α, the hazard function (instantaneous failure rate of survivors) exceeds the mean rate for times > μ⁄2, and is ~ ~ 2 ⁄ μ for all times > μ. Application of this model to the next M 6 earthquake on the San Andreas fault at Parkfield, California suggests that the annual probability of the earthquake is between 1:10 and 1:13.

  5. Migration of historical earthquakes in California

    USGS Publications Warehouse

    King, C.-Y.; Ma, Z.

    1988-01-01

    Most large earthquakes of magnitude ???6.0 in California during 1852-1987 appear to show a southeast-to-northwest tendency of epicenter migration. This finding is consistent with earlier findings of Savage (1971) for a relatively few large earthquakes along the west coast of North America, and of Wood and Allen (1973) for smaller events along the San Andreas fault in central California. The average speed of migration is approximately 130 km/yr, which is within the range of speeds observed for other major seismic zones in the world. The epicenter migration in California may be the result of some small but broad-scaled episodic strain changes associated with creep waves induced by magma injections at the East Pacific Rise and propagating northwestwardly along a broad transform boundary between the Pacific and North American plates at subseismogenic depths as proposed by Savage (1971). ?? 1988 Birkha??user Verlag.

  6. Time‐dependent renewal‐model probabilities when date of last earthquake is unknown

    USGS Publications Warehouse

    Field, Edward H.; Jordan, Thomas H.

    2015-01-01

    We derive time-dependent, renewal-model earthquake probabilities for the case in which the date of the last event is completely unknown, and compare these with the time-independent Poisson probabilities that are customarily used as an approximation in this situation. For typical parameter values, the renewal-model probabilities exceed Poisson results by more than 10% when the forecast duration exceeds ~20% of the mean recurrence interval. We also derive probabilities for the case in which the last event is further constrained to have occurred before historical record keeping began (the historic open interval), which can only serve to increase earthquake probabilities for typically applied renewal models.We conclude that accounting for the historic open interval can improve long-term earthquake rupture forecasts for California and elsewhere.

  7. Conditional Probabilities for Large Events Estimated by Small Earthquake Rate

    NASA Astrophysics Data System (ADS)

    Wu, Yi-Hsuan; Chen, Chien-Chih; Li, Hsien-Chi

    2016-01-01

    We examined forecasting quiescence and activation models to obtain the conditional probability that a large earthquake will occur in a specific time period on different scales in Taiwan. The basic idea of the quiescence and activation models is to use earthquakes that have magnitudes larger than the completeness magnitude to compute the expected properties of large earthquakes. We calculated the probability time series for the whole Taiwan region and for three subareas of Taiwan—the western, eastern, and northeastern Taiwan regions—using 40 years of data from the Central Weather Bureau catalog. In the probability time series for the eastern and northeastern Taiwan regions, a high probability value is usually yielded in cluster events such as events with foreshocks and events that all occur in a short time period. In addition to the time series, we produced probability maps by calculating the conditional probability for every grid point at the time just before a large earthquake. The probability maps show that high probability values are yielded around the epicenter before a large earthquake. The receiver operating characteristic (ROC) curves of the probability maps demonstrate that the probability maps are not random forecasts, but also suggest that lowering the magnitude of a forecasted large earthquake may not improve the forecast method itself. From both the probability time series and probability maps, it can be observed that the probability obtained from the quiescence model increases before a large earthquake and the probability obtained from the activation model increases as the large earthquakes occur. The results lead us to conclude that the quiescence model has better forecast potential than the activation model.

  8. Building the Southern California Earthquake Center

    NASA Astrophysics Data System (ADS)

    Jordan, T. H.; Henyey, T.; McRaney, J. K.

    2004-12-01

    Kei Aki was the founding director of the Southern California Earthquake Center (SCEC), a multi-institutional collaboration formed in 1991 as a Science and Technology Center (STC) under the National Science Foundation (NSF) and the U. S. Geological Survey (USGS). Aki and his colleagues articulated a system-level vision for the Center: investigations by disciplinary working groups would be woven together into a "Master Model" for Southern California. In this presentation, we will outline how the Master-Model concept has evolved and how SCEC's structure has adapted to meet scientific challenges of system-level earthquake science. In its first decade, SCEC conducted two regional imaging experiments (LARSE I & II); published the "Phase-N" reports on (1) the Landers earthquake, (2) a new earthquake rupture forecast for Southern California, and (3) new models for seismic attenuation and site effects; it developed two prototype "Community Models" (the Crustal Motion Map and Community Velocity Model) and, perhaps most important, sustained a long-term, multi-institutional, interdisciplinary collaboration. The latter fostered pioneering numerical simulations of earthquake ruptures, fault interactions, and wave propagation. These accomplishments provided the impetus for a successful proposal in 2000 to reestablish SCEC as a "stand alone" center under NSF/USGS auspices. SCEC remains consistent with the founders' vision: it continues to advance seismic hazard analysis through a system-level synthesis that is based on community models and an ever expanding array of information technology. SCEC now represents a fully articulated "collaboratory" for earthquake science, and many of its features are extensible to other active-fault systems and other system-level collaborations. We will discuss the implications of the SCEC experience for EarthScope, the USGS's program in seismic hazard analysis, NSF's nascent Cyberinfrastructure Initiative, and other large collaboratory programs.

  9. Infrasonic observations of the Northridge, California, earthquake

    SciTech Connect

    Mutschlecner, J.P.; Whitaker, R.W.

    1994-09-01

    Infrasonic waves from the Northridge, California, earthquake of 17 January 1994 were observed at the St. George, Utah, infrasound array of the Los Alamos National Laboratory. The distance to the epicenter was 543 kilometers. The signal shows a complex character with many peaks and a long duration. An interpretation is given in terms of several modes of signal propagation and generation including a seismic-acoustic secondary source mechanism. A number of signals from aftershocks are also observed.

  10. Space- and Time-Dependent Probabilities for Earthquake Fault Systems from Numerical Simulations: Feasibility Study and First Results

    NASA Astrophysics Data System (ADS)

    van Aalsburg, Jordan; Rundle, John B.; Grant, Lisa B.; Rundle, Paul B.; Yakovlev, Gleb; Turcotte, Donald L.; Donnellan, Andrea; Tiampo, Kristy F.; Fernandez, Jose

    2010-08-01

    In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed "model steering". Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California.

  11. Estimating the Probability of Earthquake-Induced Landslides

    NASA Astrophysics Data System (ADS)

    McRae, M. E.; Christman, M. C.; Soller, D. R.; Sutter, J. F.

    2001-12-01

    The development of a regionally applicable, predictive model for earthquake-triggered landslides is needed to improve mitigation decisions at the community level. The distribution of landslides triggered by the 1994 Northridge earthquake in the Oat Mountain and Simi Valley quadrangles of southern California provided an inventory of failures against which to evaluate the significance of a variety of physical variables in probabilistic models of static slope stability. Through a cooperative project, the California Division of Mines and Geology provided 10-meter resolution data on elevation, slope angle, coincidence of bedding plane and topographic slope, distribution of pre-Northridge landslides, internal friction angle and cohesive strength of individual geologic units. Hydrologic factors were not evaluated since failures in the study area were dominated by shallow, disrupted landslides in dry materials. Previous studies indicate that 10-meter digital elevation data is required to properly characterize the short, steep slopes on which many earthquake-induced landslides occur. However, to explore the robustness of the model at different spatial resolutions, models were developed at the 10, 50, and 100-meter resolution using classification and regression tree (CART) analysis and logistic regression techniques. Multiple resampling algorithms were tested for each variable in order to observe how resampling affects the statistical properties of each grid, and how relationships between variables within the model change with increasing resolution. Various transformations of the independent variables were used to see which had the strongest relationship with the probability of failure. These transformations were based on deterministic relationships in the factor of safety equation. Preliminary results were similar for all spatial scales. Topographic variables dominate the predictive capability of the models. The distribution of prior landslides and the coincidence of slope

  12. Earthquake Simulations and Historical Patterns of Events: Forecasting the Next Great Earthquake in California

    NASA Astrophysics Data System (ADS)

    Sachs, M. K.; Rundle, J. B.; Heien, E. M.; Turcotte, D. L.; Yikilmaz, M.; Kellogg, L. H.

    2013-12-01

    The fault system in California combined with some of the United States most densely populated regions is a recipe for devastation. It has been estimated that a repeat of the 1906 m=7.8 San Francisco earthquake could cause as much as $84 billion in damage. Earthquake forecasting can help alleviate the effects of these events by targeting disaster relief and preparedness in regions that will need it the most. However, accurate earthquake forecasting has proven difficult. We present a forecasting technique that uses simulated earthquake catalogs generated by Virtual California and patterns of historical events. As background, we also describe internal details of the Virtual California earthquake simulator.

  13. Earthquake probabilities in the San Francisco Bay Region: 2000 to 2030 - a summary of findings

    USGS Publications Warehouse

    Working Group on California Earthquake Probabilities

    1999-01-01

    The San Francisco Bay region sits astride a dangerous “earthquake machine,” the tectonic boundary between the Pacific and North American Plates. The region has experienced major and destructive earthquakes in 1838, 1868, 1906, and 1989, and future large earthquakes are a certainty. The ability to prepare for large earthquakes is critical to saving lives and reducing damage to property and infrastructure. An increased understanding of the timing, size, location, and effects of these likely earthquakes is a necessary component in any effective program of preparedness. This study reports on the probabilities of occurrence of major earthquakes in the San Francisco Bay region (SFBR) for the three decades 2000 to 2030. The SFBR extends from Healdsberg on the northwest to Salinas on the southeast and encloses the entire metropolitan area, including its most rapidly expanding urban and suburban areas. In this study a “major” earthquake is defined as one with M≥6.7 (where M is moment magnitude). As experience from the Northridge, California (M6.7, 1994) and Kobe, Japan (M6.9, 1995) earthquakes has shown us, earthquakes of this size can have a disastrous impact on the social and economic fabric of densely urbanized areas. To reevaluate the probability of large earthquakes striking the SFBR, the U.S. Geological Survey solicited data, interpretations, and analyses from dozens of scientists representing a wide crosssection of the Earth-science community (Appendix A). The primary approach of this new Working Group (WG99) was to develop a comprehensive, regional model for the long-term occurrence of earthquakes, founded on geologic and geophysical observations and constrained by plate tectonics. The model considers a broad range of observations and their possible interpretations. Using this model, we estimate the rates of occurrence of earthquakes and 30-year earthquake probabilities. Our study considers a range of magnitudes for earthquakes on the major faults in the

  14. Operational earthquake forecasting in California: A prototype system combining UCERF3 and CyberShake

    NASA Astrophysics Data System (ADS)

    Milner, K. R.; Jordan, T. H.; Field, E. H.

    2014-12-01

    Operational earthquake forecasting (OEF) is the dissemination of authoritative information about time-dependent earthquake probabilities to help communities prepare for potentially destructive earthquakes. The goal of OEF is to inform the decisions that people and organizations must continually make to mitigate seismic risk and prepare for potentially destructive earthquakes on time scales from days to decades. To attain this goal, OEF must provide a complete description of the seismic hazard—ground motion exceedance probabilities as well as short-term rupture probabilities—in concert with the long-term forecasts of probabilistic seismic hazard analysis. We have combined the Third Uniform California Earthquake Rupture Forecast (UCERF3) of the Working Group on California Earthquake Probabilities (Field et al., 2014) with the CyberShake ground-motion model of the Southern California Earthquake Center (Graves et al., 2011; Callaghan et al., this meeting) into a prototype OEF system for generating time-dependent hazard maps. UCERF3 represents future earthquake activity in terms of fault-rupture probabilities, incorporating both Reid-type renewal models and Omori-type clustering models. The current CyberShake model comprises approximately 415,000 earthquake rupture variations to represent the conditional probability of future shaking at 285 geographic sites in the Los Angeles region (~236 million horizontal-component seismograms). This combination provides significant probability gains relative to OEF models based on empirical ground-motion prediction equations (GMPEs), primarily because the physics-based CyberShake simulations account for the rupture directivity, basin effects, and directivity-basin coupling that are not represented by the GMPEs.

  15. Bayesian probabilities of earthquake occurrences in Longmenshan fault system (China)

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Zhang, Keyin; Gan, Qigang; Zhou, Wen; Xiong, Liang; Zhang, Shihua; Liu, Chao

    2015-01-01

    China has a long history of earthquake records, and the Longmenshan fault system (LFS) is a famous earthquake zone. We believed that the LFS could be divided into three seismogenic zones (north, central, and south zones) based on the geological structures and the earthquake catalog. We applied the Bayesian probability method using extreme-value distribution of earthquake occurrences to estimate the seismic hazard in the LFS. The seismic moment, slip rate, earthquake recurrence rate, and magnitude were considered as the basic parameters for computing the Bayesian prior estimates of the seismicity. These estimates were then updated in terms of Bayes' theorem and historical estimates of seismicity in the LFS. Generally speaking, the north zone seemingly is quite peaceful compared with the central and south zones. The central zone is the most dangerous; however, the periodicity of earthquake occurrences for M s = 8.0 is quite long (1,250 to 5,000 years). The selection of upper bound probable magnitude influences the result, and the upper bound magnitude of the south zone maybe 7.5. We obtained the empirical relationship of magnitude conversion for M s and ML, the values of the magnitude of completeness Mc (3.5), and the Gutenberg-Richter b value before applying the Bayesian extreme-value distribution of earthquake occurrences method.

  16. Earthquakes and faults in southern California (1970-2010)

    USGS Publications Warehouse

    Sleeter, Benjamin M.; Calzia, James P.; Walter, Stephen R.

    2012-01-01

    The map depicts both active and inactive faults and earthquakes magnitude 1.5 to 7.3 in southern California (1970–2010). The bathymetry was generated from digital files from the California Department of Fish And Game, Marine Region, Coastal Bathymetry Project. Elevation data are from the U.S. Geological Survey National Elevation Database. Landsat satellite image is from fourteen Landsat 5 Thematic Mapper scenes collected between 2009 and 2010. Fault data are reproduced with permission from 2006 California Geological Survey and U.S. Geological Survey data. The earthquake data are from the U.S. Geological Survey National Earthquake Information Center.

  17. Fundamental questions of earthquake statistics, source behavior, and the estimation of earthquake probabilities from possible foreshocks

    USGS Publications Warehouse

    Michael, Andrew J.

    2012-01-01

    Estimates of the probability that an ML 4.8 earthquake, which occurred near the southern end of the San Andreas fault on 24 March 2009, would be followed by an M 7 mainshock over the following three days vary from 0.0009 using a Gutenberg–Richter model of aftershock statistics (Reasenberg and Jones, 1989) to 0.04 using a statistical model of foreshock behavior and long‐term estimates of large earthquake probabilities, including characteristic earthquakes (Agnew and Jones, 1991). I demonstrate that the disparity between the existing approaches depends on whether or not they conform to Gutenberg–Richter behavior. While Gutenberg–Richter behavior is well established over large regions, it could be violated on individual faults if they have characteristic earthquakes or over small areas if the spatial distribution of large‐event nucleations is disproportional to the rate of smaller events. I develop a new form of the aftershock model that includes characteristic behavior and combines the features of both models. This new model and the older foreshock model yield the same results when given the same inputs, but the new model has the advantage of producing probabilities for events of all magnitudes, rather than just for events larger than the initial one. Compared with the aftershock model, the new model has the advantage of taking into account long‐term earthquake probability models. Using consistent parameters, the probability of an M 7 mainshock on the southernmost San Andreas fault is 0.0001 for three days from long‐term models and the clustering probabilities following the ML 4.8 event are 0.00035 for a Gutenberg–Richter distribution and 0.013 for a characteristic‐earthquake magnitude–frequency distribution. Our decisions about the existence of characteristic earthquakes and how large earthquakes nucleate have a first‐order effect on the probabilities obtained from short‐term clustering models for these large events.

  18. Detection of hydrothermal precursors to large northern california earthquakes.

    PubMed

    Silver, P G; Valette-Silver, N J

    1992-09-01

    During the period 1973 to 1991 the interval between eruptions from a periodic geyser in Northern California exhibited precursory variations 1 to 3 days before the three largest earthquakes within a 250-kilometer radius of the geyser. These include the magnitude 7.1 Loma Prieta earthquake of 18 October 1989 for which a similar preseismic signal was recorded by a strainmeter located halfway between the geyser and the earthquake. These data show that at least some earthquakes possess observable precursors, one of the prerequisites for successful earthquake prediction. All three earthquakes were further than 130 kilometers from the geyser, suggesting that precursors might be more easily found around rather than within the ultimate rupture zone of large California earthquakes. PMID:17738277

  19. A post-Tohoku earthquake review of earthquake probabilities in the Southern Kanto District, Japan

    NASA Astrophysics Data System (ADS)

    Somerville, Paul G.

    2014-12-01

    The 2011 Mw 9.0 Tohoku earthquake generated an aftershock sequence that affected a large part of northern Honshu, and has given rise to widely divergent forecasts of changes in earthquake occurrence probabilities in northern Honshu. The objective of this review is to assess these forecasts as they relate to potential changes in the occurrence probabilities of damaging earthquakes in the Kanto Region. It is generally agreed that the 2011 Mw 9.0 Tohoku earthquake increased the stress on faults in the southern Kanto district. Toda and Stein (Geophys Res Lett 686, 40: doi:10.1002, 2013) further conclude that the probability of earthquakes in the Kanto Corridor has increased by a factor of 2.5 for the time period 11 March 2013 to 10 March 2018 in the Kanto Corridor. Estimates of earthquake probabilities in a wider region of the Southern Kanto District by Nanjo et al. (Geophys J Int, doi:10.1093, 2013) indicate that any increase in the probability of earthquakes is insignificant in this larger region. Uchida et al. (Earth Planet Sci Lett 374: 81-91, 2013) conclude that the Philippine Sea plate the extends well north of the northern margin of Tokyo Bay, inconsistent with the Kanto Fragment hypothesis of Toda et al. (Nat Geosci, 1:1-6,2008), which attributes deep earthquakes in this region, which they term the Kanto Corridor, to a broken fragment of the Pacific plate. The results of Uchida and Matsuzawa (J Geophys Res 115:B07309, 2013)support the conclusion that fault creep in southern Kanto may be slowly relaxing the stress increase caused by the Tohoku earthquake without causing more large earthquakes. Stress transfer calculations indicate a large stress transfer to the Off Boso Segment as a result of the 2011 Tohoku earthquake. However, Ozawa et al. (J Geophys Res 117:B07404, 2012) used onshore GPS measurements to infer large post-Tohoku creep on the plate interface in the Off-Boso region, and Uchida and Matsuzawa (ibid.) measured similar large creep off the Boso

  20. A 30-year history of earthquake crisis communication in California and lessons for the future

    NASA Astrophysics Data System (ADS)

    Jones, L.

    2015-12-01

    The first statement from the US Geological Survey to the California Office of Emergency Services quantifying the probability of a possible future earthquake was made in October 1985 about the probability (approximately 5%) that a M4.7 earthquake located directly beneath the Coronado Bay Bridge in San Diego would be a foreshock to a larger earthquake. In the next 30 years, publication of aftershock advisories have become routine and formal statements about the probability of a larger event have been developed in collaboration with the California Earthquake Prediction Evaluation Council (CEPEC) and sent to CalOES more than a dozen times. Most of these were subsequently released to the public. These communications have spanned a variety of approaches, with and without quantification of the probabilities, and using different ways to express the spatial extent and the magnitude distribution of possible future events. The USGS is re-examining its approach to aftershock probability statements and to operational earthquake forecasting with the goal of creating pre-vetted automated statements that can be released quickly after significant earthquakes. All of the previous formal advisories were written during the earthquake crisis. The time to create and release a statement became shorter with experience from the first public advisory (to the 1988 Lake Elsman earthquake) that was released 18 hours after the triggering event, but was never completed in less than 2 hours. As was done for the Parkfield experiment, the process will be reviewed by CEPEC and NEPEC (National Earthquake Prediction Evaluation Council) so the statements can be sent to the public automatically. This talk will review the advisories, the variations in wording and the public response and compare this with social science research about successful crisis communication, to create recommendations for future advisories

  1. The magnitude distribution of declustered earthquakes in Southern California

    PubMed Central

    Knopoff, Leon

    2000-01-01

    The binned distribution densities of magnitudes in both the complete and the declustered catalogs of earthquakes in the Southern California region have two significantly different branches with crossover magnitude near M = 4.8. In the case of declustered earthquakes, the b-values on the two branches differ significantly from each other by a factor of about two. The absence of self-similarity across a broad range of magnitudes in the distribution of declustered earthquakes is an argument against the application of an assumption of scale-independence to models of main-shock earthquake occurrence, and in turn to the use of such models to justify the assertion that earthquakes are unpredictable. The presumption of scale-independence for complete local earthquake catalogs is attributable, not to a universal process of self-organization leading to future large earthquakes, but to the universality of the process that produces aftershocks, which dominate complete catalogs. PMID:11035770

  2. Comparison of Short-term and Long-term Earthquake Forecast Models for Southern California

    NASA Astrophysics Data System (ADS)

    Helmstetter, A.; Kagan, Y. Y.; Jackson, D. D.

    2004-12-01

    Many earthquakes are triggered in part by preceding events. Aftershocks are the most obvious examples, but many large earthquakes are preceded by smaller ones. The large fluctuations of seismicity rate due to earthquake interactions thus provide a way to improve earthquake forecasting significantly. We have developed a model to estimate daily earthquake probabilities in Southern California, using the Epidemic Type Earthquake Sequence model [Kagan and Knopoff, 1987; Ogata, 1988]. The forecasted seismicity rate is the sum of a constant external loading and of the aftershocks of all past earthquakes. The background rate is estimated by smoothing past seismicity. Each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and which decreases with time following Omori's law. We use an isotropic kernel to model the spatial distribution of aftershocks for small (M≤5.5) mainshocks, and a smoothing of the location of early aftershocks for larger mainshocks. The model also assumes that all earthquake magnitudes follow the Gutenberg-Richter law with a unifom b-value. We use a maximum likelihood method to estimate the model parameters and tests the short-term and long-term forecasts. A retrospective test using a daily update of the forecasts between 1985/1/1 and 2004/3/10 shows that the short-term model decreases the uncertainty of an earthquake occurrence by a factor of about 10.

  3. FORESHOCKS AND TIME-DEPENDENT EARTHQUAKE HAZARD ASSESSMENT IN SOUTHERN CALIFORNIA.

    USGS Publications Warehouse

    Jones, Lucile M.

    1985-01-01

    The probability that an earthquake in southern California (M greater than equivalent to 3. 0) will be followed by an earthquake of larger magnitude within 5 days and 10 km (i. e. , will be a foreshock) is 6 plus or minus 0. 5 per cent (1 S. D. ), and is not significantly dependent on the magnitude of the possible foreshock between M equals 3 and M equals 5. The probability that an earthquake will be followed by an M greater than equivalent to 5. 0 main shock, however, increases with magnitude of the foreshock from less than 1 per cent at M greater than equivalent to 3 to 6. 5 plus or minus 2. 5 per cent (1 S. D. ) at M greater than equivalent to 5. The main shock will most likely occur in the first hour after the foreshock, and the probability that a main shock will occur in the first hour decreases with elapsed time from the occurrence of the possible foreshock by approximately the inverse of time. Thus, the occurrence of an earthquake of M greater than equivalent to 3. 0 in southern California increases the earthquake hazard within a small space-time window several orders of magnitude above the normal background level.

  4. Estimating earthquake-induced failure probability and downtime of critical facilities.

    PubMed

    Porter, Keith; Ramer, Kyle

    2012-01-01

    Fault trees have long been used to estimate failure risk in earthquakes, especially for nuclear power plants (NPPs). One interesting application is that one can assess and manage the probability that two facilities - a primary and backup - would be simultaneously rendered inoperative in a single earthquake. Another is that one can calculate the probabilistic time required to restore a facility to functionality, and the probability that, during any given planning period, the facility would be rendered inoperative for any specified duration. A large new peer-reviewed library of component damageability and repair-time data for the first time enables fault trees to be used to calculate the seismic risk of operational failure and downtime for a wide variety of buildings other than NPPs. With the new library, seismic risk of both the failure probability and probabilistic downtime can be assessed and managed, considering the facility's unique combination of structural and non-structural components, their seismic installation conditions, and the other systems on which the facility relies. An example is offered of real computer data centres operated by a California utility. The fault trees were created and tested in collaboration with utility operators, and the failure probability and downtime results validated in several ways. PMID:22576139

  5. Keeping the History in Historical Seismology: The 1872 Owens Valley, California Earthquake

    SciTech Connect

    Hough, Susan E.

    2008-07-08

    The importance of historical earthquakes is being increasingly recognized. Careful investigations of key pre-instrumental earthquakes can provide critical information and insights for not only seismic hazard assessment but also for earthquake science. In recent years, with the explosive growth in computational sophistication in Earth sciences, researchers have developed increasingly sophisticated methods to analyze macroseismic data quantitatively. These methodological developments can be extremely useful to exploit fully the temporally and spatially rich information source that seismic intensities often represent. For example, the exhaustive and painstaking investigations done by Ambraseys and his colleagues of early Himalayan earthquakes provides information that can be used to map out site response in the Ganges basin. In any investigation of macroseismic data, however, one must stay mindful that intensity values are not data but rather interpretations. The results of any subsequent analysis, regardless of the degree of sophistication of the methodology, will be only as reliable as the interpretations of available accounts - and only as complete as the research done to ferret out, and in many cases translate, these accounts. When intensities are assigned without an appreciation of historical setting and context, seemingly careful subsequent analysis can yield grossly inaccurate results. As a case study, I report here on the results of a recent investigation of the 1872 Owen's Valley, California earthquake. Careful consideration of macroseismic observations reveals that this event was probably larger than the great San Francisco earthquake of 1906, and possibly the largest historical earthquake in California. The results suggest that some large earthquakes in California will generate significantly larger ground motions than San Andreas fault events of comparable magnitude.

  6. California Earthquakes: Science, Risks, and the Politics of Hazard Mitigation

    NASA Astrophysics Data System (ADS)

    Shedlock, Kaye M.

    "Politics" should be the lead word in the sub-title of this engrossing study of the emergence and growth of the California and federal earthquake hazard reduction infrastructures. Beginning primarily with the 1906 San Francisco earthquake, scientists, engineers, and other professionals cooperated and clashed with state and federal officials, the business community, " boosters," and the general public to create programs, agencies, and commissions to support earthquake research and hazards mitigation. Moreover, they created a "regulatory-state" apparatus that governs human behavior without sustained public support for its creation. The public readily accepts that earthquake research and mitigation are government responsibilities. The government employs or funds the scientists, engineers, emergency response personnel, safety officials, building inspectors, and others who are instrumental in reducing earthquake hazards. This book clearly illustrates how, and why all of this came to pass.

  7. Discrepancy between earthquake rates implied by historic earthquakes and a consensus geologic source model for California

    USGS Publications Warehouse

    Petersen, M.D.; Cramer, C.H.; Reichle, M.S.; Frankel, A.D.; Hanks, T.C.

    2000-01-01

    We examine the difference between expected earthquake rates inferred from the historical earthquake catalog and the geologic data that was used to develop the consensus seismic source characterization for the state of California [California Department of Conservation, Division of Mines and Geology (CDMG) and U.S. Geological Survey (USGS) Petersen et al., 1996; Frankel et al., 1996]. On average the historic earthquake catalog and the seismic source model both indicate about one M 6 or greater earthquake per year in the state of California. However, the overall earthquake rates of earthquakes with magnitudes (M) between 6 and 7 in this seismic source model are higher, by at least a factor of 2, than the mean historic earthquake rates for both southern and northern California. The earthquake rate discrepancy results from a seismic source model that includes earthquakes with characteristic (maximum) magnitudes that are primarily between M 6.4 and 7.1. Many of these faults are interpreted to accommodate high strain rates from geologic and geodetic data but have not ruptured in large earthquakes during historic time. Our sensitivity study indicates that the rate differences between magnitudes 6 and 7 can be reduced by adjusting the magnitude-frequency distribution of the source model to reflect more characteristic behavior, by decreasing the moment rate available for seismogenic slip along faults, by increasing the maximum magnitude of the earthquake on a fault, or by decreasing the maximum magnitude of the background seismicity. However, no single parameter can be adjusted, consistent with scientific consensus, to eliminate the earthquake rate discrepancy. Applying a combination of these parametric adjustments yields an alternative earthquake source model that is more compatible with the historic data. The 475-year return period hazard for peak ground and 1-sec spectral acceleration resulting from this alternative source model differs from the hazard resulting from the

  8. Historic Ground Failures in Northern California Triggered by Earthquakes

    USGS Publications Warehouse

    Youd, T. Leslie; Hoose, Seena N.

    1978-01-01

    A major source of earthquake-related damage and casualties in northern California has been ground failures generated by the seismic shaking, including landslides, lateral spreads, ground settlement, and surface cracks. The historical record shows that, except for offshore shocks, the geographic area affected and the quantity and general severity of ground failures increase markedly with Richter magnitude. Hence, the largest historical event, the 1906 San Francisco earthquake, has been the most important generator of ground failures. Because of recent population growth and land development in northern California, the potential for damage in future events is enormous compared with that existing in 1906. Reports of the 1906 San Francisco earthquake and other northern California earthquakes and descriptions of ground failures therein are used to (1) identify and clarify the types of ground failures associated with earthquakes, (2) provide a guide for engineers, planners, and others responsible for minimizing seismic hazards, and (3) form a data base for other geotechnical studies of earthquake-triggered pound failures. Geologic, hydrologic, and topographic setting have an important influence on ground failure development as well as distance from the causative fault. Areas especially vulnerable to ground failure in northern California have been oversteepened slopes, such as mountain cliffs, streambanks, and coastal bluffs, and lowland deposits, principally Holocene fluvial deposits, deltaic deposits, and poorly compacted fills. Liquefaction has been the direct cause of most lowland failures. The historical record suggests that ground failures during future large earthquakes are most likely to occur at the same or geologically similar locations as failures during previous earhquakes.

  9. Depth dependence of earthquake frequency-magnitude distributions in California: Implications for rupture initiation

    USGS Publications Warehouse

    Mori, J.; Abercrombie, R.E.

    1997-01-01

    Statistics of earthquakes in California show linear frequency-magnitude relationships in the range of M2.0 to M5.5 for various data sets. Assuming Gutenberg-Richter distributions, there is a systematic decrease in b value with increasing depth of earthquakes. We find consistent results for various data sets from northern and southern California that both include and exclude the larger aftershock sequences. We suggest that at shallow depth (???0 to 6 km) conditions with more heterogeneous material properties and lower lithospheric stress prevail. Rupture initiations are more likely to stop before growing into large earthquakes, producing relatively more smaller earthquakes and consequently higher b values. These ideas help to explain the depth-dependent observations of foreshocks in the western United States. The higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock. At greater depth (9-15 km), any rupture initiation is more likely to continue growing into a larger event, so there are fewer foreshocks. If one assumes that frequency-magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake, then a small (M2) rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a M5.5 or larger event, compared to the same small rupture initiation at 0 to 3 km. Copyright 1997 by the American Geophysical Union.

  10. The initial subevent of the 1994 Northridge, California, earthquake: Is earthquake size predictable?

    USGS Publications Warehouse

    Kilb, Debi; Gomberg, J.

    1999-01-01

    We examine the initial subevent (ISE) of the M?? 6.7, 1994 Northridge, California, earthquake in order to discriminate between two end-member rupture initiation models: the 'preslip' and 'cascade' models. Final earthquake size may be predictable from an ISE's seismic signature in the preslip model but not in the cascade model. In the cascade model ISEs are simply small earthquakes that can be described as purely dynamic ruptures. In this model a large earthquake is triggered by smaller earthquakes; there is no size scaling between triggering and triggered events and a variety of stress transfer mechanisms are possible. Alternatively, in the preslip model, a large earthquake nucleates as an aseismically slipping patch in which the patch dimension grows and scales with the earthquake's ultimate size; the byproduct of this loading process is the ISE. In this model, the duration of the ISE signal scales with the ultimate size of the earthquake, suggesting that nucleation and earthquake size are determined by a more predictable, measurable, and organized process. To distinguish between these two end-member models we use short period seismograms recorded by the Southern California Seismic Network. We address questions regarding the similarity in hypocenter locations and focal mechanisms of the ISE and the mainshock. We also compare the ISE's waveform characteristics to those of small earthquakes and to the beginnings of earthquakes with a range of magnitudes. We find that the focal mechanisms of the ISE and mainshock are indistinguishable, and both events may have nucleated on and ruptured the same fault plane. These results satisfy the requirements for both models and thus do not discriminate between them. However, further tests show the ISE's waveform characteristics are similar to those of typical small earthquakes in the vicinity and more importantly, do not scale with the mainshock magnitude. These results are more consistent with the cascade model.

  11. Dynamics of Liquefaction during the 1987 Superstition Hills, California, Earthquake

    NASA Astrophysics Data System (ADS)

    Holzer, T. L.; Youd, T. L.; Hanks, T. C.

    1989-04-01

    Simultaneous measurements of seismically induced pore-water pressure changes and surface and subsurface accelerations at a site undergoing liquefaction caused by the Superstition Hills, California, earthquake (24 November 1987; M = 6.6) reveal that total pore pressures approached lithostatic conditions, but, unexpectedly, after most of the strong motion ceased. Excess pore pressures were generated once horizontal acceleration exceeded a threshold value.

  12. Earthquakes near Parkfield, California: Comparing the 1934 and 1966 Sequences.

    PubMed

    Bakun, W H; McEvilly, T V

    1979-09-28

    Moderate-sized earthquakes (Richter magnitude M(L) 5(1/2)) have occurred four times this century (1901, 1922, 1934, and 1966) on the San Andreas fault near Parkfield in central California. In many respects the June 1966 sequence was a remarkably detailed repetition of the June 1934 sequence, suggesting a recurring recognizable pattern of stress and fault zone behavior. PMID:17732330

  13. Dynamics of liquefaction during the 1987 Superstition Hills, California, earthquake

    USGS Publications Warehouse

    Holzer, T.L.; Youd, T.L.; Hanks, T.C.

    1989-01-01

    Simultaneous measurements of seismically induced pore-water pressure changes and surface and subsurface accelerations at a site undergoing liquefaction caused by the Superstition Hills, California, earthquake (24 November 1987; M = 6.6) reveal that total pore pressures approached lithostatic conditions, but, unexpectedly, after most of the strong motion ceased. Excess pore pressures were generated once horizontal acceleration exceeded a threshold value.

  14. Search for seismic forerunners to earthquakes in central California

    USGS Publications Warehouse

    Wesson, R.L.; Robinson, R.; Bufe, C.G.; Ellsworth, W.L.; Pfluke, J.H.; Steppe, J.A.; Seekins, L.C.

    1977-01-01

    The relatively high seismicity of the San Andreas fault zone in central California provides an excellent opportunity to search for seismic forerunners to moderate earthquakes. Analysis of seismic traveltime and earthquake location data has resulted in the identification of two possible seismic forerunners. The first is a period of apparently late (0.3 sec) P-wave arrival times lasting several weeks preceding one earthquake of magnitude 5.0. The rays for these travel paths passed through - or very close to - the aftershock volume of the subsequent earthquake. The sources for these P-arrival time data were earthquakes in the distance range 20-70 km. Uncertainties in the influence of small changes in the hypocenters of the source earthquakes and in the identification of small P-arrivals raise the possibility that the apparantly delayed arrivals are not the result of a decrease in P-velocity. The second possible precursor is an apparent increase in the average depth of earthquakes preceding two moderate earthquakes. This change might be only apparent, caused by a location bias introduced by a decrease in P-wave velocity, but numerical modeling for realistic possible changes in velocity suggests that the observed effect is more likely a true migration of earthquakes. To carry out this work - involving the manipulation of several thousand earthquake hypocenters and several hundred thousand readings of arrival time - a system of data storage was designed and manipulation programs for a large digital computer have been executed. This system allows, for example, the automatic selection of earthquakes from a specific region, the extraction of all the observed arrival times for these events, and their relocation under a chosen set of assumptions. ?? 1977.

  15. Chapter F. The Loma Prieta, California, Earthquake of October 17, 1989 - Tectonic Processes and Models

    USGS Publications Warehouse

    Simpson, Robert W.

    1994-01-01

    If there is a single theme that unifies the diverse papers in this chapter, it is the attempt to understand the role of the Loma Prieta earthquake in the context of the earthquake 'machine' in northern California: as the latest event in a long history of shocks in the San Francisco Bay region, as an incremental contributor to the regional deformation pattern, and as a possible harbinger of future large earthquakes. One of the surprises generated by the earthquake was the rather large amount of uplift that occurred as a result of the reverse component of slip on the southwest-dipping fault plane. Preearthquake conventional wisdom had been that large earthquakes in the region would probably be caused by horizontal, right-lateral, strike-slip motion on vertical fault planes. In retrospect, the high topography of the Santa Cruz Mountains and the elevated marine terraces along the coast should have provided some clues. With the observed ocean retreat and the obvious uplift of the coast near Santa Cruz that accompanied the earthquake, Mother Nature was finally caught in the act. Several investigators quickly saw the connection between the earthquake uplift and the long-term evolution of the Santa Cruz Mountains and realized that important insights were to be gained by attempting to quantify the process of crustal deformation in terms of Loma Prieta-type increments of northward transport and fault-normal shortening.

  16. Transient Response of Seismicity and Earthquake Probabilities to Stress Transfer in a Brownian Earthquake Model

    NASA Astrophysics Data System (ADS)

    Ellsworth, W. L.; Matthews, M. V.; Simpson, R. W.

    2001-12-01

    A statistical mechanical description of elastic rebound is used to study earthquake interaction and stress transfer effects in a point process model of earthquakes. The model is a Brownian Relaxation Oscillator (BRO) in which a random walk (standard Brownian motion) is added to a steady tectonic loading to produce a stochastic load state process. Rupture occurs in this model when the load state reaches a critical value. The load state is a random variable and may be described at any point in time by its probability density. Load state evolves toward the failure threshold due to tectonic loading (drift), and diffuses due to Brownian motion (noise) according to a diffusion equation. The Brownian perturbation process formally represents the sum total of all factors, aside from tectonic loading, that govern rupture. Physically, these factors may include effects of earthquakes external to the source, aseismic loading, interaction effects within the source itself, healing, pore pressure evolution, etc. After a sufficiently long time, load state always evolves to a steady state probability density that is independent of the initial condition and completely described by the drift rate and noise scale. Earthquake interaction and stress transfer effects are modeled by an instantaneous change in the load state. A negative step reduces the probability of failure, while a positive step may either immediately trigger rupture or increase the failure probability (hazard). When the load state is far from failure, the effects are well-approximated by ``clock advances'' that shift the unperturbed hazard down or up, as appropriate for the sign of the step. However, when the load state is advanced in the earthquake cycle, the response is a sharp, temporally localized decrease or increase in hazard. Recovery of the hazard is characteristically ``Omori like'' ( ~ 1/t), which can be understood in terms of equilibrium thermodynamical considerations since state evolution is diffusion with

  17. Crustal deformation in great California earthquake cycles

    NASA Technical Reports Server (NTRS)

    Li, Victor C.; Rice, James R.

    1986-01-01

    Periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model: A depth L (less than or similiar to H) extending downward from the Earth's surface at a transform boundary between uniform elastic lithospheric plates of thickness H is locked between earthquakes. It slips an amount consistent with remote plate velocity V sub pl after each lapse of earthquake cycle time T sub cy. Lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress. The plates are coupled at their base to a Maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions, compatible with plate velocity, are transmitted to the surface plates. The coupling is described approximately through a generalized Elsasser model. It is argued that the model gives a more realistic physical description of tectonic loading, including the time dependence of deep slip and crustal stress build up throughout the earthquake cycle, than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone.

  18. Long Period Earthquakes Beneath California's Young and Restless Volcanoes

    NASA Astrophysics Data System (ADS)

    Pitt, A. M.; Dawson, P. B.; Shelly, D. R.; Hill, D. P.; Mangan, M.

    2013-12-01

    The newly established USGS California Volcano Observatory has the broad responsibility of monitoring and assessing hazards at California's potentially threatening volcanoes, most notably Mount Shasta, Medicine Lake, Clear Lake Volcanic Field, and Lassen Volcanic Center in northern California; and Long Valley Caldera, Mammoth Mountain, and Mono-Inyo Craters in east-central California. Volcanic eruptions occur in California about as frequently as the largest San Andreas Fault Zone earthquakes-more than ten eruptions have occurred in the last 1,000 years, most recently at Lassen Peak (1666 C.E. and 1914-1917 C.E.) and Mono-Inyo Craters (c. 1700 C.E.). The Long Valley region (Long Valley caldera and Mammoth Mountain) underwent several episodes of heightened unrest over the last three decades, including intense swarms of volcano-tectonic (VT) earthquakes, rapid caldera uplift, and hazardous CO2 emissions. Both Medicine Lake and Lassen are subsiding at appreciable rates, and along with Clear Lake, Long Valley Caldera, and Mammoth Mountain, sporadically experience long period (LP) earthquakes related to migration of magmatic or hydrothermal fluids. Worldwide, the last two decades have shown the importance of tracking LP earthquakes beneath young volcanic systems, as they often provide indication of impending unrest or eruption. Herein we document the occurrence of LP earthquakes at several of California's young volcanoes, updating a previous study published in Pitt et al., 2002, SRL. All events were detected and located using data from stations within the Northern California Seismic Network (NCSN). Event detection was spatially and temporally uneven across the NCSN in the 1980s and 1990s, but additional stations, adoption of the Earthworm processing system, and heightened vigilance by seismologists have improved the catalog over the last decade. LP earthquakes are now relatively well-recorded under Lassen (~150 events since 2000), Clear Lake (~60 events), Mammoth Mountain

  19. In the shadow of 1857-the effect of the great Ft. Tejon earthquake on subsequent earthquakes in southern California

    USGS Publications Warehouse

    Harris, R.A.; Simpson, R.W.

    1996-01-01

    The great 1857 Fort Tejon earthquake is the largest earthquake to have hit southern California during the historic period. We investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake. When post-1857 earthquakes with unknown focal mechanisms were assigned strike-slip mechanisms with strike and rake determined by the nearest active fault, 13 of the 13 southern California M???5.5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture. When post-1857 earthquakes in the Transverse Ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike-slip, 11 of the 13 earthquakes were encouraged by the 1857 earthquake. These results show significant correlations between static stress changes and seismicity patterns. The correlation disappears around 1907, suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century.

  20. Crustal deformation in Great California Earthquake cycles

    NASA Technical Reports Server (NTRS)

    Li, Victor C.; Rice, James R.

    1987-01-01

    A model in which coupling is described approximately through a generalized Elsasser model is proposed for computation of the periodic crustal deformation associated with repeated strike-slip earthquakes. The model is found to provide a more realistic physical description of tectonic loading than do simpler kinematic models. Parameters are chosen to model the 1857 and 1906 San Andreas ruptures, and predictions are found to be consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces. Results indicate that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps the crust-mantle transition zone.

  1. Southern California Earthquake Center (SCEC) Summer Internship Programs

    NASA Astrophysics Data System (ADS)

    Benthien, M. L.; Perry, S.; Jordan, T. H.

    2004-12-01

    For the eleventh consecutive year, the Southern California Earthquake Center (SCEC) coordinated undergraduate research experiences in summer 2004, allowing 35 students with a broad array of backgrounds and interests to work with the world's preeminent earthquake scientists and specialists. Students participate in interdisciplinary, system-level earthquake science and information technology research, and several group activities throughout the summer. Funding for student stipends and activities is made possible by the NSF Research Experiences for Undergraduates (REU) program. SCEC coordinates two intern programs: The SCEC Summer Undergraduate Research Experience (SCEC/SURE) and the SCEC Undergraduate Summer in Earthquake Information Technology (SCEC/USEIT). SCEC/SURE interns work one-on-one with SCEC scientists at their institutions on a variety of earthquake science research projects. The goals of the program are to expand student participation in the earth sciences and related disciplines, encourage students to consider careers in research and education, and to increase diversity of students and researchers in the earth sciences. 13 students participated in this program in 2004. SCEC/USEIT is an NSF REU site that brings undergraduate students from across the country to the University of Southern California each summer. SCEC/USEIT interns interact in a team-oriented research environment and are mentored by some of the nation's most distinguished geoscience and computer science researchers. The goals of the program are to allow undergraduates to use advanced tools of information technology to solve problems in earthquake research; close the gap between computer science and geoscience; and engage non-geoscience majors in the application of earth science to the practical problems of reducing earthquake risk. SCEC/USEIT summer research goals are structured around a grand challenge problem in earthquake information technology. For the past three years the students have

  2. MOHO ORIENTATION BENEATH CENTRAL CALIFORNIA FROM REGIONAL EARTHQUAKE TRAVEL TIMES.

    USGS Publications Warehouse

    Oppenheimer, David H.; Eaton, Jerry P.

    1984-01-01

    This paper examines relative Pn arrival times, recorded by the U. S. Geological Survey seismic network in central and northern California from an azimuthally distributed set of regional earthquakes. Improved estimates are presented of upper mantle velocities in the Coast Ranges, Great Valley, and Sierra Nevada foothills and estimates of the orientation of the Moho throughout this region. Finally, the azimuthal distribution of apparent velocities, corrected for dip and individual station travel time effects, is then studied for evidence of upper mantle velocity anisotropy and for indications of lower crustal structure in central California.

  3. Tidal stress triggering of earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Bucholc, Magda; Steacy, Sandy

    2016-05-01

    We analyse the influence of the solid Earth tides and ocean loading on the occurrence time of Southern California earthquakes. For each earthquake, we calculate tidal Coulomb failure stress and stress rate on a fault plane that is assumed to be controlled by the orientation of the adjacent fault. To reduce bias when selecting data for testing the tide-earthquake relationship, we create four earthquake catalogues containing events within 1, 1.5, 2.5 and 5 km of nearest faults. We investigate the difference in seismicity rates at times of positive and negative tidal stresses/stress rates given three different cases. We consider seismicity rates during times of positive versus negative stress and stress rate, as well as 2 and 3 hr surrounding the local tidal stress extremes. We find that tidal influence on earthquake occurrence is found to be statistically non-random only in close proximity to tidal extremes meaning that magnitude of tidal stress plays an important role in tidal triggering. A non-random tidal signal is observed for the reverse events. Along with a significant increase in earthquake rates around tidal Coulomb stress maxima, the strength of tidal correlation is found to be closely related to the amplitude of the peak tidal Coulomb stress (τp). The most effective tidal triggering is found for τp ≥ 1 kPa, which is much smaller than thresholds suggested for static and dynamic triggering of aftershocks.

  4. Dynamic models of an earthquake and tsunami offshore Ventura, California

    USGS Publications Warehouse

    Kenny J. Ryan; Geist, Eric L.; Barall, Michael; David D. Oglesby

    2015-01-01

    The Ventura basin in Southern California includes coastal dip-slip faults that can likely produce earthquakes of magnitude 7 or greater and significant local tsunamis. We construct a 3-D dynamic rupture model of an earthquake on the Pitas Point and Lower Red Mountain faults to model low-frequency ground motion and the resulting tsunami, with a goal of elucidating the seismic and tsunami hazard in this area. Our model results in an average stress drop of 6 MPa, an average fault slip of 7.4 m, and a moment magnitude of 7.7, consistent with regional paleoseismic data. Our corresponding tsunami model uses final seafloor displacement from the rupture model as initial conditions to compute local propagation and inundation, resulting in large peak tsunami amplitudes northward and eastward due to site and path effects. Modeled inundation in the Ventura area is significantly greater than that indicated by state of California's current reference inundation line.

  5. Losses to single-family housing from ground motions in the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Wesson, R.L.; Perkins, D.M.; Leyendecker, E.V.; Roth, R.J., Jr.; Petersen, M.D.

    2004-01-01

    The distributions of insured losses to single-family housing following the 1994 Northridge, California, earthquake for 234 ZIP codes can be satisfactorily modeled with gamma distributions. Regressions of the parameters in the gamma distribution on estimates of ground motion, derived from ShakeMap estimates or from interpolated observations, provide a basis for developing curves of conditional probability of loss given a ground motion. Comparison of the resulting estimates of aggregate loss with the actual aggregate loss gives satisfactory agreement for several different ground-motion parameters. Estimates of loss based on a deterministic spatial model of the earthquake ground motion, using standard attenuation relationships and NEHRP soil factors, give satisfactory results for some ground-motion parameters if the input ground motions are increased about one and one-half standard deviations above the median, reflecting the fact that the ground motions for the Northridge earthquake tended to be higher than the median ground motion for other earthquakes with similar magnitude. The results give promise for making estimates of insured losses to a similar building stock under future earthquake loading. ?? 2004, Earthquake Engineering Research Institute.

  6. Dynamics of liquefaction during the 1987 superstition hills, california, earthquake.

    PubMed

    Holzer, T L; Hanks, T C; Youd, T L

    1989-04-01

    Simultaneous measurements of seismically induced pore-water pressure changes and surface and subsurface accelerations at a site undergoing liquefaction caused by the Superstition Hills, California, earthquake (24 November 1987; M = 6.6) reveal that total pore pressures approached lithostatic conditions, but, unexpectedly, after most of the strong motion ceased. Excess pore pressures were generated once horizontal acceleration exceeded a threshold value. PMID:17818846

  7. Nonlinear site response in medium magnitude earthquakes near Parkfield, California

    USGS Publications Warehouse

    Rubinstein, Justin L.

    2011-01-01

    Careful analysis of strong-motion recordings of 13 medium magnitude earthquakes (3.7 ≤ M ≤ 6.5) in the Parkfield, California, area shows that very modest levels of shaking (approximately 3.5% of the acceleration of gravity) can produce observable changes in site response. Specifically, I observe a drop and subsequent recovery of the resonant frequency at sites that are part of the USGS Parkfield dense seismograph array (UPSAR) and Turkey Flat array. While further work is necessary to fully eliminate other models, given that these frequency shifts correlate with the strength of shaking at the Turkey Flat array and only appear for the strongest shaking levels at UPSAR, the most plausible explanation for them is that they are a result of nonlinear site response. Assuming this to be true, the observation of nonlinear site response in small (M M 6.5 San Simeon earthquake and the 2004 M 6 Parkfield earthquake).

  8. Intensity earthquake scenario (scenario event - a damaging earthquake with higher probability of occurrence) for the city of Sofia

    NASA Astrophysics Data System (ADS)

    Aleksandrova, Irena; Simeonova, Stela; Solakov, Dimcho; Popova, Maria

    2014-05-01

    Among the many kinds of natural and man-made disasters, earthquakes dominate with regard to their social and economical impact on the urban environment. Global seismic risk to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to effects of strong earthquakes. Additionally, the uncontrolled growth of mega cities in highly seismic areas around the world is often associated with the construction of seismically unsafe buildings and infrastructures, and undertaken with an insufficient knowledge of the regional seismicity peculiarities and seismic hazard. The assessment of seismic hazard and generation of earthquake scenarios is the first link in the prevention chain and the first step in the evaluation of the seismic risk. The earthquake scenarios are intended as a basic input for developing detailed earthquake damage scenarios for the cities and can be used in earthquake-safe town and infrastructure planning. The city of Sofia is the capital of Bulgaria. It is situated in the centre of the Sofia area that is the most populated (the population is of more than 1.2 mil. inhabitants), industrial and cultural region of Bulgaria that faces considerable earthquake risk. The available historical documents prove the occurrence of destructive earthquakes during the 15th-18th centuries in the Sofia zone. In 19th century the city of Sofia has experienced two strong earthquakes: the 1818 earthquake with epicentral intensity I0=8-9 MSK and the 1858 earthquake with I0=9-10 MSK. During the 20th century the strongest event occurred in the vicinity of the city of Sofia is the 1917 earthquake with MS=5.3 (I0=7-8 MSK). Almost a century later (95 years) an earthquake of moment magnitude 5.6 (I0=7-8 MSK) hit the city of Sofia, on May 22nd, 2012. In the present study as a deterministic scenario event is considered a damaging earthquake with higher probability of occurrence that could affect the city with intensity less than or equal to VIII

  9. Combining earthquakes and GPS data to estimate the probability of future earthquakes with magnitude Mw ≥ 6.0

    NASA Astrophysics Data System (ADS)

    Chen, K.-P.; Tsai, Y.-B.; Chang, W.-Y.

    2013-10-01

    According to Wyss et al. (2000) result indicates that future main earthquakes can be expected along zones characterized by low b values. In this study we combine Benioff strain with global positioning system (GPS) data to estimate the probability of future Mw ≥ 6.0 earthquakes for a grid covering Taiwan. An approach similar to the maximum likelihood method was used to estimate Gutenberg-Richter parameters a and b. The two parameters were then used to estimate the probability of simulating future earthquakes of Mw ≥ 6.0 for each of the 391 grids (grid interval = 0.1°) covering Taiwan. The method shows a high probability of earthquakes in western Taiwan along a zone that extends from Taichung southward to Nantou, Chiayi, Tainan and Kaohsiung. In eastern Taiwan, there also exists a high probability zone from Ilan southward to Hualian and Taitung. These zones are characterized by high earthquake entropy, high maximum shear strain rates, and paths of low b values. A relation between entropy and maximum shear strain rate is also obtained. It indicates that the maximum shear strain rate is about 4.0 times the entropy. The results of this study should be of interest to city planners, especially those concerned with earthquake preparedness. And providing the earthquake insurers to draw up the basic premium.

  10. Cascadia Earthquake and Tsunami Scenario for California's North Coast

    NASA Astrophysics Data System (ADS)

    Dengler, L.

    2006-12-01

    In 1995 the California Division of Mines and Geology (now the California Geological Survey) released a planning scenario for an earthquake on the southern portion of the Cascadia subduction zone (CSZ). This scenario was the 8th and last of the Earthquake Planning Scenarios published by CDMG. It was the largest magnitude CDMG scenario, an 8.4 earthquake rupturing the southern 200 km of the CSZ, and it was the only scenario to include tsunami impacts. This scenario event has not occurred in historic times and depicts impacts far more severe than any recent earthquake. The local tsunami hazard is new; there is no written record of significant local tsunami impact in the region. The north coast scenario received considerable attention in Humboldt and Del Norte Counties and contributed to a number of mitigation efforts. The Redwood Coast Tsunami Work Group (RCTWG), an organization of scientists, emergency managers, government agencies, and businesses from Humboldt, Mendocino, and Del Norte Counties, was formed in 1996 to assist local jurisdictions in understanding the implications of the scenario and to promote a coordinated, consistent mitigation program. The group has produced print and video materials and promoted response and evacuation planning. Since 1997 the RCTWG has sponsored an Earthquake Tsunami Education Room at county fairs featuring preparedness information, hands-on exhibits and regional tsunami hazard maps. Since the development of the TsunamiReady Program in 2001, the RCTWG facilitates community TsunamiReady certification. To assess the effectiveness of mitigation efforts, five telephone surveys between 1993 and 2001 were conducted by the Humboldt Earthquake Education Center. A sixth survey is planned for this fall. Each survey includes between 400 and 600 respondents. Over the nine year period covered by the surveys, the percent with houses secured to foundations has increased from 58 to 80 percent, respondents aware of a local tsunami hazard increased

  11. Accessing Data From the Southern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

    Yu, E.; Kahler, K.; Clayton, R. W.

    2001-12-01

    The Southern California Earthquake Data Center (SCEDC) archives and provides public access to earthquake parametric and waveform data gathered by the TriNet seismic network, southern California's earthquake monitoring network since January 1 2001. The parametric data includes earthquake locations, magnitudes, moment-tensor solutions (for some events), and phase picks. The waveform data consists of continuous recordings of 150 broadband stations, and triggered seismograms from 200 accelerometers and 200 short-period instruments. Since the Data Center and TriNet have the same Oracle database system, users can have access to earthquake data in near real-time, which usually means within a few minutes of the origin time. Catalog searches of the modern data can be done through the web interface http://www.scecdc.scec.org/catalog-search. User access to the data is via STP (Seismic Transfer Program) which can be accessed through a interactive web interface at the URL http://www.scedc.scedc.org/stp.html or through a client program that directly connects to the Data Center. The latter is a simple 'C' program for Solaris and Linux platforms and is downloadable from http://www.scecdc.scec.org/software.html. With STP, the waveform data is directly transfered to the user's computer and is converted to a number of formats, including SAC and MiniSEED. Byte-swapping is automatically taken care of. The older data is still available through the 'dbsort' program. These data are being converted to the new database over the coming year and will be uniformly accessible with the new interfaces.

  12. Chapter C. The Loma Prieta, California, Earthquake of October 17, 1989 - Landslides

    USGS Publications Warehouse

    Keefer, David K., (Edited By)

    1998-01-01

    Central California, in the vicinity of San Francisco and Monterey Bays, has a history of fatal and damaging landslides, triggered by heavy rainfall, coastal and stream erosion, construction activity, and earthquakes. The great 1906 San Francisco earthquake (MS=8.2-8.3) generated more than 10,000 landslides throughout an area of 32,000 km2; these landslides killed at least 11 people and caused substantial damage to buildings, roads, railroads, and other civil works. Smaller numbers of landslides, which caused more localized damage, have also been reported from at least 20 other earthquakes that have occurred in the San Francisco Bay-Monterey Bay region since 1838. Conditions that make this region particularly susceptible to landslides include steep and rugged topography, weak rock and soil materials, seasonally heavy rainfall, and active seismicity. Given these conditions and history, it was no surprise that the 1989 Loma Prieta earthquake generated thousands of landslides throughout the region. Landslides caused one fatality and damaged at least 200 residences, numerous roads, and many other structures. Direct damage from landslides probably exceeded $30 million; additional, indirect economic losses were caused by long-term landslide blockage of two major highways and by delays in rebuilding brought about by concern over the potential long-term instability of some earthquake-damaged slopes.

  13. The California Post-Earthquake Information Clearinghouse: A Plan to Learn From the Next Large California Earthquake

    NASA Astrophysics Data System (ADS)

    Loyd, R.; Walter, S.; Fenton, J.; Tubbesing, S.; Greene, M.

    2008-12-01

    In the rush to remove debris after a damaging earthquake, perishable data related to a wide range of impacts on the physical, built and social environments can be lost. The California Post-Earthquake Information Clearinghouse is intended to prevent this data loss by supporting the earth scientists, engineers, and social and policy researchers who will conduct fieldwork in the affected areas in the hours and days following the earthquake to study these effects. First called for by Governor Ronald Reagan following the destructive M6.5 San Fernando earthquake in 1971, the concept of the Clearinghouse has since been incorporated into the response plans of the National Earthquake Hazard Reduction Program (USGS Circular 1242). This presentation is intended to acquaint scientists with the purpose, functions, and services of the Clearinghouse. Typically, the Clearinghouse is set up in the vicinity of the earthquake within 24 hours of the mainshock and is maintained for several days to several weeks. It provides a location where field researchers can assemble to share and discuss their observations, plan and coordinate subsequent field work, and communicate significant findings directly to the emergency responders and to the public through press conferences. As the immediate response effort winds down, the Clearinghouse will ensure that collected data are archived and made available through "lessons learned" reports and publications that follow significant earthquakes. Participants in the quarterly meetings of the Clearinghouse include representatives from state and federal agencies, universities, NGOs and other private groups. Overall management of the Clearinghouse is delegated to the agencies represented by the authors above.

  14. Physical model for earthquakes, 2. Application to southern California

    SciTech Connect

    Rundle, J.B.

    1988-06-10

    The purpose of this paper is to apply ideas developed in a previous paper to the construction of a detailed model for earthquake dynamics in southern California. The basis upon which the approach is formulated is that earthquakes are perturbations on, or more specifically fluctuations about, the long-term motions of the plates. This concept is made mathematically precise by means of a ''fluctuation hypothesis,'' which states that all physical quantities associated with earthquakes can be expressed as integral expansions in a fluctuating quantity called the ''offset phase.'' While in general, the frictional stick-slip properties of the complex, interacting faults should properly come out of the underlying physics, a simplification is made here, and a simple, spatially varying friction law is assumed. Together with the complex geometry of the major active faults, an assumed, spatially varying Earth rheology, the average rates of long-term offsets on all the major faults, and the friction coefficients, one can generate synthetic earthquake histories for comparison to the real data.

  15. The Virtual Quake Earthquake Simulator: Earthquake Probability Statistics for the El Mayor-Cucapah Region and Evidence of Predictability in Simulated Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Schultz, K.; Yoder, M. R.; Heien, E. M.; Rundle, J. B.; Turcotte, D. L.; Parker, J. W.; Donnellan, A.

    2015-12-01

    We introduce a framework for developing earthquake forecasts using Virtual Quake (VQ), the generalized successor to the perhaps better known Virtual California (VC) earthquake simulator. We discuss the basic merits and mechanics of the simulator, and we present several statistics of interest for earthquake forecasting. We also show that, though the system as a whole (in aggregate) behaves quite randomly, (simulated) earthquake sequences limited to specific fault sections exhibit measurable predictability in the form of increasing seismicity precursory to large m > 7 earthquakes. In order to quantify this, we develop an alert based forecasting metric similar to those presented in Keilis-Borok (2002); Molchan (1997), and show that it exhibits significant information gain compared to random forecasts. We also discuss the long standing question of activation vs quiescent type earthquake triggering. We show that VQ exhibits both behaviors separately for independent fault sections; some fault sections exhibit activation type triggering, while others are better characterized by quiescent type triggering. We discuss these aspects of VQ specifically with respect to faults in the Salton Basin and near the El Mayor-Cucapah region in southern California USA and northern Baja California Norte, Mexico.

  16. ERTS Applications in earthquake research and mineral exploration in California

    NASA Technical Reports Server (NTRS)

    Abdel-Gawad, M.; Silverstein, J.

    1973-01-01

    Examples that ERTS imagery can be effectively utilized to identify, locate, and map faults which show geomorphic evidence of geologically recent breakage are presented. Several important faults not previously known have been identified. By plotting epicenters of historic earthquakes in parts of California, Sonora, Mexico, Arizona, and Nevada, we found that areas known for historic seismicity are often characterized by abundant evidence of recent fault and crustal movements. There are many examples of seismically quiet areas where outstanding evidence of recent fault movements is observed. One application is clear: ERTS-1 imagery could be effectively utilized to delineate areas susceptible to earthquake recurrence which, on the basis of seismic data alone, may be misleadingly considered safe. ERTS data can also be utilized in planning new sites in the geophysical network of fault movement monitoring and strain and tilt measurements.

  17. Earthquake epicenters and fault intersections in central and southern California

    NASA Technical Reports Server (NTRS)

    Abdel-Gawad, M. (Principal Investigator); Silverstein, J.

    1972-01-01

    The author has identifed the following significant results. ERTS-1 imagery provided evidence for the existence of short transverse fault segments lodged between faults of the San Andreas system in the Coast Ranges, California. They indicate that an early episode of transverse shear has affected the Coast Ranges prior to the establishment of the present San Andreas fault. The fault has been offset by transverse faults of the Transverse Ranges. It appears feasible to identify from ERTS-1 imagery geomorphic criteria of recent fault movements. Plots of historic earthquakes in the Coast Ranges and western Transverse Ranges show clusters in areas where structures are complicated by interaction of tow active fault systems. A fault lineament apparently not previously mapped was identified in the Uinta Mountains, Utah. Part of the lineament show evidence of recent faulting which corresponds to a moderate earthquake cluster.

  18. A more precise chronology of earthquakes produced by the San Andreas fault in southern California

    SciTech Connect

    Sieh, K. ); Stuiver, M. ); Brillinger, D. )

    1989-01-10

    Improved methods of radiocarbon analysis have enabled the authors to date more precisely the earthquake ruptures of the San Andreas fault that are recorded in the sediments at Pallett Creek. New error limits are less than 23 calendar years for all but two of the dated event. The new date ranges, with one exception, fall within the broader ranges estimated previously, but the estimate of the average interval between the latest 10 episodes of faulting is now about 132 years. Five of the nine intervals are shorter than a century: Three of the remaining four intervals are about two to three centuries long. Despite the wide range of these intervals, a pattern in the occurrence of large earthquakes at Pallett Creek is apparent in the new data. The past 10 earthquakes occur in four clusters, each of which consists of two or three events. Earthquakes within the clusters are separated by periods of several decades, but the clusters are separated by dormant periods of two to three centuries. This pattern may reflect important mechanical aspects of the fault's behavior. If this pattern continues into the future, the current period of dormancy will probably be greater than two centuries. This would mean that the section of the fault represented by the Pallett Creek site is currently in the middle of one of its longer periods of repose between clusters, and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in California. The greater precision of dates now available for large earthquakes recorded at the Pallett Creek site enables speculative correlation of events between paleoseismic sites along the southern half of the San Andreas fault. A history of great earthquakes with overlapping rupture zones along the Mojave section of the fault remains one of the more attractive possibilities.

  19. Teleseismic tomography of the Loma Prieta Earthquake Region, California: Implications for strain partitioning

    NASA Astrophysics Data System (ADS)

    Takauchi, Y.; Evans, John R.

    From teleseismic travel times we derive three-dimensional velocity models of the upper 71 km in the 1989 Loma Prieta earthquake region, central California. Shallow crustal structure is consistent with local-earthquake tomography. Horizontal velocity gradients at all depths suggest that the San Andreas fault was a deep shear locus, at least at one time. A large low-velocity feature near the Moho beneath Loma Prieta probably is caused by a crustal root. Two low-velocity features at about 45-70 km depth are offset right-laterally along the San Andreas by about 45 km. Cooling of this portion of the upper mantle [Furlong et al., 1989] could have frozen in displacements in this region within a few million years after passage of the Mendocino Triple Junction. These results are consistent with Furlong et al.'s model.

  20. A non-stationary earthquake probability assessment with the Mohr-Coulomb failure criterion

    NASA Astrophysics Data System (ADS)

    Wang, J. P.; Xu, Y.

    2015-10-01

    From theory to experience, earthquake probability associated with an active fault should be gradually increasing with time since the last event. In this paper, a new non-stationary earthquake assessment motivated/derived from the Mohr-Coulomb failure criterion is introduced. Different from other non-stationary earthquake analyses, the new model can more clearly define and calculate the stress states between two characteristic earthquakes. In addition to the model development and the algorithms, this paper also presents an example calculation to help explain and validate the new model. On the condition of best-estimate model parameters, the example calculation shows a 7.6 % probability for the Meishan fault in central Taiwan to induce a major earthquake in years 2015-2025, and if the earthquake does not occur by 2025, the earthquake probability will increase to 8 % in 2025-2035, which validates the new model that can calculate non-stationary earthquake probability as it should vary with time.

  1. Earthquake!

    ERIC Educational Resources Information Center

    Hernandez, Hildo

    2000-01-01

    Examines the types of damage experienced by California State University at Northridge during the 1994 earthquake and what lessons were learned in handling this emergency are discussed. The problem of loose asbestos is addressed. (GR)

  2. Rupture directivity of moderate earthquakes in northern California

    USGS Publications Warehouse

    Seekins, Linda C.; Boatwright, John

    2010-01-01

    We invert peak ground velocity and acceleration (PGV and PGA) to estimate rupture direction and rupture velocity for 47 moderate earthquakes (3.5≥M≥5.4) in northern California. We correct sets of PGAs and PGVs recorded at stations less than 55–125 km, depending on source depth, for site amplification and source–receiver distance, then fit the residual peak motions to the unilateral directivity function of Ben-Menahem (1961). We independently invert PGA and PGV. The rupture direction can be determined using as few as seven peak motions if the station distribution is sufficient. The rupture velocity is unstable, however, if there are no takeoff angles within 30° of the rupture direction. Rupture velocities are generally subsonic (0.5β–0.9β); for stability, we limit the rupture velocity at v=0.92β, the Rayleigh wave speed. For 73 of 94 inversions, the rupture direction clearly identifies one of the nodal planes as the fault plane. The 35 strike-slip earthquakes have rupture directions that range from nearly horizontal (6 events) to directly updip (5 events); the other 24 rupture partly along strike and partly updip. Two strike-slip earthquakes rupture updip in one inversion and downdip in the other. All but 1 of the 11 thrust earthquakes rupture predominantly updip. We compare the rupture directions for 10 M≥4.0 earthquakes to the relative location of the mainshock and the first two weeks of aftershocks. Spatial distributions of 8 of 10 aftershock sequences agree well with the rupture directivity calculated for the mainshock.

  3. Relative Contributions of Geothermal Pumping and Long-Term Earthquake Rate to Seismicity at California Geothermal Fields

    NASA Astrophysics Data System (ADS)

    Weiser, D. A.; Jackson, D. D.

    2015-12-01

    In a tectonically active area, a definitive discrimination between geothermally-induced and tectonic earthquakes is difficult to achieve. We focus our study on California's 11 major geothermal fields: Amedee, Brawley, Casa Diablo, Coso, East Mesa, The Geysers, Heber, Litchfield, Salton Sea, Susanville, and Wendel. The Geysers geothermal field is the world's largest geothermal energy producer. California's Department of Oil Gas and Geothermal Resources provides field-wide monthly injection and production volumes for each of these sites, which allows us to study the relationship between geothermal pumping activities and seismicity. Since many of the geothermal fields began injecting and producing before nearby seismic stations were installed, we use smoothed seismicity since 1932 from the ANSS catalog as a proxy for tectonic earthquake rate. We examine both geothermal pumping and long-term earthquake rate as factors that may control earthquake rate. Rather than focusing only on the largest earthquake, which is essentially a random occurrence in time, we examine how M≥4 earthquake rate density (probability per unit area, time, and magnitude) varies for each field. We estimate relative contributions to the observed earthquake rate of M≥4 from both a long-term earthquake rate (Kagan and Jackson, 2010) and pumping activity. For each geothermal field, respective earthquake catalogs (NCEDC and SCSN) are complete above at least M3 during the test period (which we tailor to each site). We test the hypothesis that the observed earthquake rate at a geothermal site during the test period is a linear combination of the long-term seismicity and pumping rates. We use a grid search to determine the confidence interval of the weighting parameters.

  4. The 1868 Hayward fault, California, earthquake: Implications for earthquake scaling relations on partially creeping faults

    USGS Publications Warehouse

    Hough, Susan E.; Martin, Stacey

    2015-01-01

    The 21 October 1868 Hayward, California, earthquake is among the best-characterized historical earthquakes in California. In contrast to many other moderate-to-large historical events, the causative fault is clearly established. Published magnitude estimates have been fairly consistent, ranging from 6.8 to 7.2, with 95% confidence limits including values as low as 6.5. The magnitude is of particular importance for assessment of seismic hazard associated with the Hayward fault and, more generally, to develop appropriate magnitude–rupture length scaling relations for partially creeping faults. The recent reevaluation of archival accounts by Boatwright and Bundock (2008), together with the growing volume of well-calibrated intensity data from the U.S. Geological Survey “Did You Feel It?” (DYFI) system, provide an opportunity to revisit and refine the magnitude estimate. In this study, we estimate the magnitude using two different methods that use DYFI data as calibration. Both approaches yield preferred magnitude estimates of 6.3–6.6, assuming an average stress drop. A consideration of data limitations associated with settlement patterns increases the range to 6.3–6.7, with a preferred estimate of 6.5. Although magnitude estimates for historical earthquakes are inevitably uncertain, we conclude that, at a minimum, a lower-magnitude estimate represents a credible alternative interpretation of available data. We further discuss implications of our results for probabilistic seismic-hazard assessment from partially creeping faults.

  5. Helium soil-gas variations associated with recent central California earthquakes: precursor or coincidence?

    USGS Publications Warehouse

    Reimer, G.M.

    1981-01-01

    Decreases in the helium concentration of soil-gas have been observed to precede six of eight recent central California earthquakes. Ten monitoring stations were established near Hollister, California and along the San Andreas Fault to permit gas collection. The data showed decreases occurring a few weeks before the earthquakes and concentratiosn returned to prequake levels either shortly before or after the earthquakes.-Author

  6. Virtual California: Earthquake Statistics, Surface Deformation Patterns, Surface Gravity Changes and InSAR Interferograms for Arbitrary Fault Geometries

    NASA Astrophysics Data System (ADS)

    Schultz, K.; Sachs, M. K.; Heien, E. M.; Rundle, J. B.; Fernandez, J.; Turcotte, D.; Donnellan, A.

    2014-12-01

    With the ever increasing number of geodetic monitoring satellites, it is vital to have a variety of geophysical numerical simulators to produce sample/model datasets. Just as hurricane forecasts are derived from the consensus among multiple atmospheric models, earthquake forecasts cannot be derived from a single comprehensive model. Here we present the functionality of Virtual California, a numerical simulator that can generate sample surface deformations, surface gravity changes, and InSAR interferograms in addition to producing earthquake statistics and forecasts.Virtual California is a boundary element code designed to explore the seismicity of today's fault systems. For arbitrary input fault geometry, Virtual California can output simulated seismic histories of 50,000 years or more. Using co-seismic slips from the output data, we generate surface deformation maps, surface gravity change maps, and InSAR interferograms as viewed by an orbiting satellite. Furthermore, using the times between successive earthquakes we generate probability distributions and earthquake forecasts.Virtual California is now supported by the Computational Infrastructure for Geodynamics. The source code is available for download and it comes with a users' manual. The manual includes instructions on how to generate fault models from scratch, how to deploy the simulator across a parallel computing environment, etc.http://geodynamics.org/cig/software/vc/

  7. Aftershocks and triggered events of the Great 1906 California earthquake

    USGS Publications Warehouse

    Meltzner, A.J.; Wald, D.J.

    2003-01-01

    The San Andreas fault is the longest fault in California and one of the longest strike-slip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the Mw 7.8 San Francisco earthquake on 18 April 1906. We conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake. We examined existing catalogs and historical documents for the period April 1906 to December 1907, compiling data on the first 20 months of the aftershock sequence. We grouped felt reports temporally and assigned modified Mercalli intensities for the larger events based on the descriptions judged to be the most reliable. For onshore and near-shore events, a grid-search algorithm (derived from empirical analysis of modern earthquakes) was used to find the epicentral location and magnitude most consistent with the assigned intensities. For one event identified as far offshore, the event's intensity distribution was compared with those of modern events, in order to contrain the event's location and magnitude. The largest aftershock within the study period, an M ???6.7 event, occurred ???100 km west of Eureka on 23 April 1906. Although not within our study period, another M ???6.7 aftershock occurred near Cape Mendocino on 28 October 1909. Other significant aftershocks included an M ???5.6 event near San Juan Bautista on 17 May 1906 and an M ???6.3 event near Shelter Cove on 11 August 1907. An M ???4.9 aftershock occurred on the creeping segment of the San Andreas fault (southeast of the mainshock rupture) on 6 July 1906. The 1906 San Francisco earthquake also triggered events in southern California (including separate events in or near the Imperial Valley, the Pomona Valley, and Santa Monica Bay), in western Nevada, in southern central Oregon, and in western Arizona, all within 2 days of the mainshock. Of these trigerred events, the largest were an M ???6.1 earthquake near Brawley

  8. SCIGN; new Southern California GPS network advances the study of earthquakes

    USGS Publications Warehouse

    Hudnut, Ken; King, Nancy

    2001-01-01

    Southern California is a giant jigsaw puzzle, and scientists are now using GPS satellites to track the pieces. These puzzle pieces are continuously moving, slowly straining the faults in between. That strain is then eventually released in earthquakes. The innovative Southern California Integrated GPS Network (SCIGN) tracks the motions of these pieces over most of southern California with unprecedented precision. This new network greatly improves the ability to assess seismic hazards and quickly measure the larger displacements that occur during and immediatelyafter earthquakes.

  9. 1957 Gobi-Altay, Mongolia, earthquake as a prototype for southern California's most devastating earthquake

    USGS Publications Warehouse

    Bayarsayhan, C.; Bayasgalan, A.; Enhtuvshin, B.; Hudnut, K.W.; Kurushin, R.A.; Molnar, P.; Olziybat, M.

    1996-01-01

    The 1957 Gobi-Altay earthquake was associated with both strike-slip and thrust faulting, processes similar to those along the San Andreas fault and the faults bounding the San Gabriel Mountains just north of Los Angeles, California. Clearly, a major rupture either on the San Andreas fault north of Los Angeles or on the thrust faults bounding the Los Angeles basin poses a serious hazard to inhabitants of that area. By analogy with the Gobi-Altay earthquake, we suggest that simultaneous rupturing of both the San Andreas fault and the thrust faults nearer Los Angeles is a real possibility that amplifies the hazard posed by ruptures on either fault system separately.

  10. Identification and Characterization of Earthquake Swarms in Southern California

    NASA Astrophysics Data System (ADS)

    Shearer, P. M.; Zhang, Q.

    2015-12-01

    Earthquake swarms are space-time clusters of seismicity that cannot easily be explained by typical aftershock behavior, and are likely triggered by external processes such as fluid migration and/or slow slip. However, swarm properties are not fully understood and how much swarm occurrence is related to the tectonic environment (e.g., heat flow, stressing rate) or source characteristics (e.g., focal mechanism, stress drop) is unclear. Systematic study of large numbers of swarms and their source properties should help to resolve these issues, but is hampered by the challenge of identifying swarms at a range of spatiotemporal scales from a large earthquake catalog. We have developed a new method to search for clusters by comparing the number of neighboring events to the background events in scalable space/time windows, similar to the idea of STA/LTA algorithms, and then discriminating swarms from aftershock clustering. We first apply this method to the San Jacinto Fault Zone (SJFZ) and find ten times more swarms than a previous study using fixed spatiotemporal windows. The most striking spatial pattern of our identified swarm events is a higher fraction of swarms at the northern and southern ends of the SJFZ than its central segment, which correlates with an increased proportion of normal faulting earthquakes. We then apply our method to search the entire southern California catalog of 433,737 events with M ≥ 1 from 1981 to 2014. Preliminary results indicate that swarms are heterogeneously distributed in space and time, but that higher swarm rates are generally found in regions of normal faulting. We will explore other swarm properties, such as event stress drops, spatial migration behavior, distribution of moment release, and relation to foreshock sequences in order to better understand the driving physical mechanisms of swarms and improve earthquake forecasts.

  11. Catalog of earthquakes along the San Andreas fault system in Central California, April-June 1972

    USGS Publications Warehouse

    Wesson, R.L.; Bennett, R.E.; Lester, F.W.

    1973-01-01

    Numerous small earthquakes occur each day in the coast ranges of Central California. The detailed study of these earthquakes provides a tool for gaining insight into the tectonic and physical processes responsible for the generation of damaging earthquakes. This catalog contains the fundamental parameters for earthquakes located within and adjacent to the seismograph network operated by the National Center for Earthquake Research (NCER), U.S. Geological Survey, during the period April - June, 1972. The motivation for these detailed studies has been described by Pakiser and others (1969) and by Eaton and others (1970). Similar catalogs of earthquakes for the years 1969, 1970 and 1971 have been prepared by Lee and others (1972 b, c, d). A catalog for the first quarter of 1972 has been prepared by Wesson and others (1972). The basic data contained in these catalogs provide a foundation for further studies. This catalog contains data on 910 earthquakes in Central California. A substantial portion of the earthquakes reported in this catalog represents a continuation of the sequence of earthquakes in the Bear Valley area which began in February, 1972 (Wesson and others, 1972). Arrival times at 126 seismograph stations were used to locate the earthquakes listed in this catalog. Of these, 101 are telemetered stations operated by NCER. Readings from the remaining 25 stations were obtained through the courtesy of the Seismographic Stations, University of California, Berkeley (UCB); the Earthquake Mechanism Laboratory, National Oceanic and Atmospheric Administration, San Francisco (EML); and the California Department of Water Resources, Sacramento. The Seismographic Stations of the University of California, Berkeley, have for many years published a bulletin describing earthquakes in Northern California and the surrounding area, and readings at UCB Stations from more distant events. The purpose of the present catalog is not to replace the UCB Bulletin, but rather to supplement

  12. Catalog of earthquakes along the San Andreas fault system in Central California: January-March, 1972

    USGS Publications Warehouse

    Wesson, R.L.; Bennett, R.E.; Meagher, K.L.

    1973-01-01

    Numerous small earthquakes occur each day in the Coast Ranges of Central California. The detailed study of these earthquakes provides a tool for gaining insight into the tectonic and physical processes responsible for the generation of damaging earthquakes. This catalog contains the fundamental parameters for earthquakes located within and adjacent to the seismograph network operated by the National Center for Earthquake Research (NCER), U.S. Geological Survey, during the period January - March, 1972. The motivation for these detailed studies has been described by Pakiser and others (1969) and by Eaton and others (1970). Similar catalogs of earthquakes for the years 1969, 1970 and 1971 have been prepared by Lee and others (1972 b,c,d). The basic data contained in these catalogs provide a foundation for further studies. This catalog contains data on 1,718 earthquakes in Central California. Of particular interest is a sequence of earthquakes in the Bear Valley area which contained single shocks with local magnitudes of S.O and 4.6. Earthquakes from this sequence make up roughly 66% of the total and are currently the subject of an interpretative study. Arrival times at 118 seismograph stations were used to locate the earthquakes listed in this catalog. Of these, 94 are telemetered stations operated by NCER. Readings from the remaining 24 stations were obtained through the courtesy of the Seismographic Stations, University of California, Berkeley (UCB); the Earthquake Mechanism Laboratory, National Oceanic and Atmospheric Administration, San Francisco (EML); and the California Department of Water Resources, Sacramento. The Seismographic Stations of the University of California, Berkeley,have for many years published a bulletin describing earthquakes in Northern California and the surrounding area, and readings at UCB Stations from more distant events. The purpose of the present catalog is not to replace the UCB Bulletin, but rather to supplement it, by describing the

  13. Simulations of the 1906 San Francisco Earthquake and Scenario Earthquakes in Northern California

    NASA Astrophysics Data System (ADS)

    Larsen, S.; Dreger, D.; Dolenc, D.

    2006-12-01

    3-D simulations of seismic ground motions are performed to better characterize the 1906 San Francisco earthquake and to investigate the seismic consequences from scenario events in northern California. Specifically, we perform simulations of: 1) the 1906 earthquake, which bilaterally ruptured a 480-km segment of the San Andreas fault from San Juan Bautista to Cape Mendocino (epicenter a few kilometers off the coast of San Francisco); 2) large scenario San Andreas events with different epicentral locations; and 3) smaller scenario events along faults local to the San Francisco Bay Area. Simulations of the 1906 earthquake indicate that significant ground motion occurred up and down the northern California coast and out into the Central Valley. Comparisons between the simulated motions and observed data (e.g., shaking intensities, Boatwright and Bundock, 2005), suggest that the moment magnitude of this event was between M7.8 and M7.9. Simulations of 1906-like scenario events along the San Andreas fault reveal that ground motions in the San Francisco Bay Area and in the Sacramento Delta region would be significantly stronger for earthquakes initiating along the northern section of the fault and rupturing to the southeast. Simulations of smaller scenario events in the San Francisco Bay Area indicate areas of concentrated shaking. These simulations are performed using a recently developed 3-D geologic model of northern California (Brocher and Thurber, 2005; Jachens et al., 2005), together with finite-difference codes (E3D and a new public domain package). The effects of topography and attenuation are included. The full computational domain spans most of the geologic model and is 630x320x50 km3. The minimum S-wave velocity is constrained to 500 m/s, except in water. Frequencies up to 1.0 Hz are modeled. The grid spacing ranges from 75 m to 200 m. High performance supercomputers are used for the simulations, which include models of over 23 billion grid nodes using 2000

  14. Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey

    USGS Publications Warehouse

    Parsons, T.

    2004-01-01

    New earthquake probability calculations are made for the Sea of Marmara region and the city of Istanbul, providing a revised forecast and an evaluation of time-dependent interaction techniques. Calculations incorporate newly obtained bathymetric images of the North Anatolian fault beneath the Sea of Marmara [Le Pichon et al., 2001; Armijo et al., 2002]. Newly interpreted fault segmentation enables an improved regional A.D. 1500-2000 earthquake catalog and interevent model, which form the basis for time-dependent probability estimates. Calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 August 1999 M = 7.4 Izmit earthquake to investigate effects of stress transfer on seismic hazard. Probability changes caused by the 1999 shock depend on Marmara Sea fault-stressing rates, which are calculated with a new finite element model. The combined 2004-2034 regional Poisson probability of M≥7 earthquakes is ~38%, the regional time-dependent probability is 44 ± 18%, and incorporation of stress transfer raises it to 53 ± 18%. The most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a M ??? 7 earthquake affecting Istanbul. The 30 year Poisson probability at Istanbul is 21%, and the addition of time dependence and stress transfer raises it to 41 ± 14%. The ranges given on probability values are sensitivities of the calculations to input parameters determined by Monte Carlo analysis; 1000 calculations are made using parameters drawn at random from distributions. Sensitivities are large relative to mean probability values and enhancements caused by stress transfer, reflecting a poor understanding of large-earthquake aperiodicity.

  15. Northern California Earthquake Data Center: Data Sets and Data Services

    NASA Astrophysics Data System (ADS)

    Neuhauser, D. S.; Allen, R. M.; Zuzlewski, S.

    2015-12-01

    The Northern California Earthquake Data Center (NCEDC) provides a permanent archive and real-time data distribution services for a unique and comprehensive data set of seismological and geophysical data sets encompassing northern and central California. We provide access to over 85 terabytes of continuous and event-based time series data from broadband, short-period, strong motion, and strain sensors as well as continuous and campaign GPS data at both standard and high sample rates. The Northen California Seismic System (NCSS), operated by UC Berkeley and USGS Menlo Park, has recorded over 900,000 events from 1984 to the present, and the NCEDC serves catalog, parametric information, moment tensors and first motion mechanisms, and time series data for these events. We also serve event catalogs, parametric information, and event waveforms for DOE enhanced geothermal system monitoring in northern California and Nevada. The NCEDC provides a several ways for users to access these data. The most recent development are web services, which provide interactive, command-line, or program-based workflow access to data. Web services use well-established server and client protocols and RESTful software architecture that allow users to easily submit queries and receive the requested data in real-time rather than through batch or email-based requests. Data are returned to the user in the appropriate format such as XML, RESP, simple text, or MiniSEED depending on the service and selected output format. The NCEDC supports all FDSN-defined web services as well as a number of IRIS-defined and NCEDC-defined services. We also continue to support older email-based and browser-based access to data. NCEDC data and web services can be found at http://www.ncedc.org and http://service.ncedc.org.

  16. Scenario earthquake hazards for the Long Valley Caldera-Mono Lake area, east-central California

    USGS Publications Warehouse

    Chen, Rui; Branum, David M.; Wills, Chris J.; Hill, David P.

    2014-01-01

    As part of the U.S. Geological Survey’s (USGS) multi-hazards project in the Long Valley Caldera-Mono Lake area, the California Geological Survey (CGS) developed several earthquake scenarios and evaluated potential seismic hazards, including ground shaking, surface fault rupture, liquefaction, and landslide hazards associated with these earthquake scenarios. The results of these analyses can be useful in estimating the extent of potential damage and economic losses because of potential earthquakes and in preparing emergency response plans. The Long Valley Caldera-Mono Lake area has numerous active faults. Five of these faults or fault zones are considered capable of producing magnitude ≥6.7 earthquakes according to the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2) developed by the 2007 Working Group of California Earthquake Probabilities (WGCEP) and the USGS National Seismic Hazard Mapping (NSHM) Program. These five faults are the Fish Slough, Hartley Springs, Hilton Creek, Mono Lake, and Round Valley Faults. CGS developed earthquake scenarios for these five faults in the study area and for the White Mountains Fault to the east of the study area. Earthquake scenarios are intended to depict the potential consequences of significant earthquakes. They are not necessarily the largest or most damaging earthquakes possible. Earthquake scenarios are both large enough and likely enough that emergency planners should consider them in regional emergency response plans. Earthquake scenarios presented here are based on fault geometry and activity data developed by the WGCEP, and are consistent with the 2008 Update of the United States National Seismic Hazard Maps (NSHM).For the Hilton Creek Fault, two alternative scenarios were developed in addition to the NSHM scenario to account for different opinions in how far north the fault extends into the Long Valley Caldera. For each scenario, ground motions were calculated using the current standard practice

  17. The Northern California Earthquake Data Center: Seismic and Geophysical Data for Northern California and Beyond

    NASA Astrophysics Data System (ADS)

    Neuhauser, D.; Klein, F.; Zuzlewski, S.; Gee, L.; Oppenheimer, D.; Romanowicz, B.

    2004-12-01

    The Northern California Earthquake Data Center (NCEDC) is an archive and distribution center for geophysical data for networks in northern and central California. The NCEDC provides timeseries data from seismic, strain, electro-magnetic, a variety of creep, tilt, and environmental sensors, and continuous and campaign GPS data in raw and RINEX formats. The NCEDC has a wide variety of interfaces for data retrieval. Timeseries data are available via a web interface and standard queued request methods such as NetDC (developed in collaboration with the IRIS DMC and other international data centers), BREQ_FAST, and EVT_FAST. Interactive data retrieval methods include STP, developed by the SCEDC, and FISSURES DHI (Data Handling Interface), an object-oriented interface developed by IRIS. The Sandia MATSEIS system is being adapted to use the FISSURES DHI interface to provide an enhanced GUI-based seismic analysis system for MATLAB. Northern California and prototype ANSS worldwide earthquake catalogs are searchable from web interfaces, and supporting phase and amplitude data can be retrieved when available. Future data sets planned for the NCEDC are seismic and strain data from the EarthScope Plate Boundary Observatory (PBO) and SAFOD. The NCEDC is a joint project of the UC Berkeley Seismological Laboratory and USGS Menlo Park.

  18. Large LOCA-earthquake event combination probability assessment - Load Combination Program Project I summary report

    SciTech Connect

    Lu, S.; Streit, R.D.; Chou, C.K.

    1980-12-10

    This report summarizes work performed to establish a technical basis for the NRC to use in reassessing its requirement that earthquake and large loss-of-coolant accident (LOCA) loads be combined in the design of nucelar power plants. A systematic probabilistic approach is used to treat the random nature of earthquake and transient loading to estimate the probability of large LOCAs that are directly and indirectly induced by earthquakes. A large LOCA is defined in this report as a double-ended guillotine break of the primary reactor coolant loop piping (the hot leg, cold leg, and crossover) of a pressurized water reactor (PWR). Unit 1 of the Zion Nuclear Power Plant, a four-loop PWR-1, is used for this study. To estimate the probability of a large LOCA directly induced by earthquakes, only fatigue crack growth resulting from the combined effects of thermal, pressure, seismic, and other cyclic loads is considered. Fatigue crack growth is simulated with a deterministic fracture mechanics model that incorporates stochastic inputs of initial crack size distribution, material properties, stress histories, and leak detection probability. Results of the simulation indicate that the probability of a double-ended guillotine break, either with or without an earthquake, is very small (on the order of 10/sup -12/). The probability of a leak was found to be several orders of magnitude greater than that of a complete pipe rupture.

  19. Probability estimates of seismic event occurrence compared to health hazards - Forecasting Taipei's Earthquakes

    NASA Astrophysics Data System (ADS)

    Fung, D. C. N.; Wang, J. P.; Chang, S. H.; Chang, S. C.

    2014-12-01

    Using a revised statistical model built on past seismic probability models, the probability of different magnitude earthquakes occurring within variable timespans can be estimated. The revised model is based on Poisson distribution and includes the use of best-estimate values of the probability distribution of different magnitude earthquakes recurring from a fault from literature sources. Our study aims to apply this model to the Taipei metropolitan area with a population of 7 million, which lies in the Taipei Basin and is bounded by two normal faults: the Sanchaio and Taipei faults. The Sanchaio fault is suggested to be responsible for previous large magnitude earthquakes, such as the 1694 magnitude 7 earthquake in northwestern Taipei (Cheng et. al., 2010). Based on a magnitude 7 earthquake return period of 543 years, the model predicts the occurrence of a magnitude 7 earthquake within 20 years at 1.81%, within 79 years at 6.77% and within 300 years at 21.22%. These estimates increase significantly when considering a magnitude 6 earthquake; the chance of one occurring within the next 20 years is estimated to be 3.61%, 79 years at 13.54% and 300 years at 42.45%. The 79 year period represents the average lifespan of the Taiwan population. In contrast, based on data from 2013, the probability of Taiwan residents experiencing heart disease or malignant neoplasm is 11.5% and 29%. The inference of this study is that the calculated risk that the Taipei population is at from a potentially damaging magnitude 6 or greater earthquake occurring within their lifetime is just as great as of suffering from a heart attack or other health ailments.

  20. Inventory of landslides triggered by the 1994 Northridge, California earthquake

    USGS Publications Warehouse

    Harp, Edwin L.; Jibson, Randall W.

    1995-01-01

    The 17 January 1994 Northridge, California, earthquake (M=6.7) triggered more than 11,000 landslides over an area of about 10,000 km?. Most of the landslides were concentrated in a 1,000-km? area that includes the Santa Susana Mountains and the mountains north of the Santa Clara River valley. We mapped landslides triggered by the earthquake in the field and from 1:60,000-scale aerial photography provided by the U.S. Air Force and taken the morning of the earthquake; these were subsequently digitized and plotted in a GIS-based format, as shown on the accompanying maps (which also are accessible via Internet). Most of the triggered landslides were shallow (1-5 m), highly disrupted falls and slides in weakly cemented Tertiary to Pleistocene clastic sediment. Average volumes of these types of landslides were less than 1,000 m?, but many had volumes exceeding 100,000 m?. Many of the larger disrupted slides traveled more than 50 m, and a few moved as far as 200 m from the bases of steep parent slopes. Deeper ( >5 m) rotational slumps and block slides numbered in the hundreds, a few of which exceeded 100,000 m? in volume. The largest triggered landslide was a block slide having a volume of 8X10E06 m?. Triggered landslides damaged or destroyed dozens of homes, blocked roads, and damaged oil-field infrastructure. Analysis of landslide distribution with respect to variations in (1) landslide susceptibility and (2) strong shaking recorded by hundreds of instruments will form the basis of a seismic landslide hazard analysis of the Los Angeles area.

  1. Catalog of earthquakes along the San Andreas fault system in Central California, July-September 1972

    USGS Publications Warehouse

    Wesson, R.L.; Meagher, K.L.; Lester, F.W.

    1973-01-01

    Numerous small earthquakes occur each day in the coast ranges of Central California. The detailed study of these earthquakes provides a tool for gaining insight into the tectonic and physical processes responsible for the generation of damaging earthquakes. This catalog contains the fundamental parameters for earthquakes located within and adjacent to the seismograph network operated by the National Center for Earthquake Research (NCER), U.S. Geological Survey, during the period July - September, 1972. The motivation for these detailed studies has been described by Pakiser and others (1969) and by Eaton and others (1970). Similar catalogs of earthquakes for the years 1969, 1970 and 1971 have been prepared by Lee and others (1972 b, c, d). Catalogs for the first and second quarters of 1972 have been prepared by Wessan and others (1972 a & b). The basic data contained in these catalogs provide a foundation for further studies. This catalog contains data on 1254 earthquakes in Central California. Arrival times at 129 seismograph stations were used to locate the earthquakes listed in this catalog. Of these, 104 are telemetered stations operated by NCER. Readings from the remaining 25 stations were obtained through the courtesy of the Seismographic Stations, University of California, Berkeley (UCB), the Earthquake Mechanism Laboratory, National Oceanic and Atmospheric Administration, San Francisco (EML); and the California Department of Water Resources, Sacramento. The Seismographic Stations of the University of California, Berkeley, have for many years published a bulletin describing earthquakes in Northern California and the surrounding area, and readings at UCB Stations from more distant events. The purpose of the present catalog is not to replace the UCB Bulletin, but rather to supplement it, by describing the seismicity of a portion of central California in much greater detail.

  2. Formulation and Application of a Physically-Based Rupture Probability Model for Large Earthquakes on Subduction Zones: A Case Study of Earthquakes on Nazca Plate

    NASA Astrophysics Data System (ADS)

    Mahdyiar, M.; Galgana, G.; Shen-Tu, B.; Klein, E.; Pontbriand, C. W.

    2014-12-01

    Most time dependent rupture probability (TDRP) models are basically designed for a single-mode rupture, i.e. a single characteristic earthquake on a fault. However, most subduction zones rupture in complex patterns that create overlapping earthquakes of different magnitudes. Additionally, the limited historic earthquake data does not provide sufficient information to estimate reliable mean recurrence intervals for earthquakes. This makes it difficult to identify a single characteristic earthquake for TDRP analysis. Physical models based on geodetic data have been successfully used to obtain information on the state of coupling and slip deficit rates for subduction zones. Coupling information provides valuable insight into the complexity of subduction zone rupture processes. In this study we present a TDRP model that is formulated based on subduction zone slip deficit rate distribution. A subduction zone is represented by an integrated network of cells. Each cell ruptures multiple times from numerous earthquakes that have overlapping rupture areas. The rate of rupture for each cell is calculated using a moment balance concept that is calibrated based on historic earthquake data. The information in conjunction with estimates of coseismic slip from past earthquakes is used to formulate time dependent rupture probability models for cells. Earthquakes on the subduction zone and their rupture probabilities are calculated by integrating different combinations of cells. The resulting rupture probability estimates are fully consistent with the state of coupling of the subduction zone and the regional and local earthquake history as the model takes into account the impact of all large (M>7.5) earthquakes on the subduction zone. The granular rupture model as developed in this study allows estimating rupture probabilities for large earthquakes other than just a single characteristic magnitude earthquake. This provides a general framework for formulating physically

  3. The vertical fingerprint of earthquake cycle loading in southern California

    NASA Astrophysics Data System (ADS)

    Howell, Samuel; Smith-Konter, Bridget; Frazer, Neil; Tong, Xiaopeng; Sandwell, David

    2016-08-01

    The San Andreas Fault System, one of the best-studied transform plate boundaries on Earth, is well known for its complex network of locked faults that slowly deform the crust in response to large-scale plate motions. Horizontal interseismic motions of the fault system are largely predictable, but vertical motions arising from tectonic sources remain enigmatic. Here we show that when carefully treated for spatial consistency, global positioning system-derived vertical velocities expose a small-amplitude (+/-2 mm yr-1), but spatially considerable (200 km), coherent pattern of uplift and subsidence straddling the fault system in southern California. We employ the statistical method of model selection to isolate this vertical velocity field from non-tectonic signals that induce velocity variations in both magnitude and direction across small distances (less than tens of kilometres; ref. ), and find remarkable agreement with the sense of vertical motions predicted by physical earthquake cycle models spanning the past few centuries. We suggest that these motions reveal the subtle, but identifiable, tectonic fingerprint of far-field flexure due to more than 300 years of fault locking and creeping depth variability. Understanding this critical component of interseismic deformation at a complex strike-slip plate boundary will better constrain regional mechanics and crustal rheology, improving the quantification of seismic hazards in southern California and beyond.

  4. Comparision of the different probability distributions for earthquake hazard assessment in the North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Yilmaz, Şeyda; Bayrak, Erdem; Bayrak, Yusuf

    2016-04-01

    In this study we examined and compared the three different probabilistic distribution methods for determining the best suitable model in probabilistic assessment of earthquake hazards. We analyzed a reliable homogeneous earthquake catalogue between a time period 1900-2015 for magnitude M ≥ 6.0 and estimated the probabilistic seismic hazard in the North Anatolian Fault zone (39°-41° N 30°-40° E) using three distribution methods namely Weibull distribution, Frechet distribution and three-parameter Weibull distribution. The distribution parameters suitability was evaluated Kolmogorov-Smirnov (K-S) goodness-of-fit test. We also compared the estimated cumulative probability and the conditional probabilities of occurrence of earthquakes for different elapsed time using these three distribution methods. We used Easyfit and Matlab software to calculate these distribution parameters and plotted the conditional probability curves. We concluded that the Weibull distribution method was the most suitable than other distribution methods in this region.

  5. Tsunami Hazard in Crescent City, California from Kuril Islands earthquakes

    NASA Astrophysics Data System (ADS)

    Dengler, L.; Uslu, B.; Barberopoulou, A.

    2007-12-01

    On November 15, Crescent City in Del Norte County, California was hit by a series of tsunami surges generated by the M = 8.3 Kuril Islands earthquake causing an estimated 9.7 million (US dollars) in damages to the small boat basin. This was the first significant tsunami loss on US territory since the 1964 Alaska tsunami. The damage occurred nearly 8 hours after the official tsunami alert bulletins had been cancelled. The tsunami caused no flooding and did not exceed the ambient high tide level. All of the damage was caused by strong currents, estimated at 12 to 15 knots, causing the floating docks to be pinned against the pilings and water to flow over them. The event highlighted problems in warning criteria and communications for a marginal event with the potential for only localized impacts, the vulnerability of harbors from a relatively modest tsunami, and the particular exposure of the Crescent City harbor area to tsunamis. It also illustrated the poor understanding of local officials of the duration of tsunami hazard. As a result of the November tsunami, interim changes were made by WCATWC to address localized hazards in areas like Crescent City. On January 13, 2007 when a M = 8.1 earthquake occurred in the Kuril Islands, a formal procedure was in place for hourly conference calls between WCATWC, California State Office of Emergency Services officials, local weather Service Offices and local emergency officials, significantly improving the decision making process and the communication among the federal, state and local officials. Kuril Island tsunamis are relatively common at Crescent City. Since 1963, five tsunamis generated by Kuril Island earthquakes have been recorded on the Crescent City tide gauge, two with amplitudes greater than 0.5 m. We use the MOST model to simulate the 2006, 2007 and 1994 events and to examine the difference between damaging and non-damaging events at Crescent City. Small changes in the angle of the rupture zone results can result

  6. UCERF3: A new earthquake forecast for California's complex fault system

    USGS Publications Warehouse

    Field, Edward H.; 2014 Working Group on California Earthquake Probabilities

    2015-01-01

    With innovations, fresh data, and lessons learned from recent earthquakes, scientists have developed a new earthquake forecast model for California, a region under constant threat from potentially damaging events. The new model, referred to as the third Uniform California Earthquake Rupture Forecast, or "UCERF" (http://www.WGCEP.org/UCERF3), provides authoritative estimates of the magnitude, location, and likelihood of earthquake fault rupture throughout the state. Overall the results confirm previous findings, but with some significant changes because of model improvements. For example, compared to the previous forecast (Uniform California Earthquake Rupture Forecast 2), the likelihood of moderate-sized earthquakes (magnitude 6.5 to 7.5) is lower, whereas that of larger events is higher. This is because of the inclusion of multifault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously. The public-safety implications of this and other model improvements depend on several factors, including site location and type of structure (for example, family dwelling compared to a long-span bridge). Building codes, earthquake insurance products, emergency plans, and other risk-mitigation efforts will be updated accordingly. This model also serves as a reminder that damaging earthquakes are inevitable for California. Fortunately, there are many simple steps residents can take to protect lives and property.

  7. Earthquakes, Tsunamis, and Storms Recorded at Crescent City, California, USA

    NASA Astrophysics Data System (ADS)

    Kelsey, H. M.; Hemphill-Haley, E.; Loofbourrow, C.; Caldwell, D. J.; Graehl, N. A.; Robinson, M.

    2015-12-01

    Stratigraphic evidence for coseismic land-level change, tsunamis, and storms is found beneath freshwater marshes in coastal northern California at Crescent City (CC). Previous studies at CC have focused on tsunamis, including the 1964 farfield tsunami from the Alaska earthquake, and nearfield tsunamis from earthquakes in the Cascadia subduction zone (CSZ). In addition to new data on tsunami inundation and coseismic land-level change, evidence for deposition by large storms shows another significant coastal hazard for the area. Our results are from three freshwater wetland sites at CC: Marhoffer Creek, Elk Creek, and Sand Mine. Marhoffer Creek marsh is adjacent to the coast about 5 km north of CC, and at an elevation of > 3.4 m above NAVD88 (>1 m above highest tides). C-14 and diatom data show it has been a freshwater wetland for at least the past 1,800 yr. We identify tsunami deposits associated with two CSZ earthquakes (1700 C.E. and 1,650 yr BP) at Marhoffer Creek. Diatom data show that coseismic subsidence accompanied the 1700 C.E. earthquake; the tsunami deposit from that event extends 550 m inland from the beach. Cs-137 data show that thin sand layers about 70 m from the beach and 20 cm below the marsh surface were deposited by the farfield tsunami in 1964. Intercalated between the 1964 and 1700 tsunami deposits, and extending as far inland as the 1964 deposit, are storm deposits consisting of discontinuous layers of sand and detrital peat. The deposits are found in an interval about 0.5 m thick, and are perched at elevations above the highest winter tides. We surmise that at least some of these deposits record the catastrophic ARkStorm of 1861-1862. At Elk Creek wetland, diatom data confirm coseismic subsidence in 1700 in addition to tsunami deposition. The 1964 tsunami deposit is thin and found only proximal to the Elk Creek channel. At Sand Mine marsh, association with coseismic subsidence is used to differentiate CSZ tsunamis in a complex ~100 m wide

  8. Heightened odds of large earthquakes near Istanbul: an interaction-based probability calculation

    USGS Publications Warehouse

    Parsons, T.; Toda, S.; Stein, R.S.; Barka, A.; Dieterich, J.H.

    2000-01-01

    We calculate the probability of strong shaking in Istanbul, an urban center of 10 million people, from the description of earthquakes on the North Anatolian fault system in the Marmara Sea during the past 500 years and test the resulting catalog against the frequency of damage in Istanbul during the preceding millennium, departing from current practice, we include the time-dependent effect of stress transferred by the 1999 moment magnitude M = 7.4 Izmit earthquake to faults nearer to Istanbul. We find a 62 ± 15% probability (one standard deviation) of strong shaking during the next 30 years and 32 ± 12% during the next decade.

  9. What to Expect from the Virtual Seismologist: Delay Times and Uncertainties of Initial Earthquake Alerts in California

    NASA Astrophysics Data System (ADS)

    Behr, Y.; Cua, G. B.; Clinton, J. F.; Racine, R.; Meier, M.; Cauzzi, C.

    2013-12-01

    The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) originally formulated by Cua and Heaton (2007). Implementation of VS into real-time EEW codes has been an on-going effort of the Swiss Seismological Service at ETH Zürich since 2006, with support from ETH Zürich, various European projects, and the United States Geological Survey (USGS). VS is one of three EEW algorithms that form the basis of the California Integrated Seismic Network (CISN) ShakeAlert system, a USGS-funded prototype end-to-end EEW system that could potentially be implemented in California. In Europe, VS is currently operating as a real-time test system in Switzerland, western Greece and Istanbul. As part of the on-going EU project REAKT (Strategies and Tools for Real-Time Earthquake Risk Reduction), VS installations in southern Italy, Romania, and Iceland are planned or underway. The possible use cases for an EEW system will be determined by the speed and reliability of earthquake source parameter estimates. A thorough understanding of both is therefore essential to evaluate the usefulness of VS. For California, we present state-wide theoretical alert times for hypothetical earthquakes by analyzing time delays introduced by the different components in the VS EEW system. Taking advantage of the fully probabilistic formulation of the VS algorithm we further present an improved way to describe the uncertainties of every magnitude estimate by evaluating the width and shape of the probability density function that describes the relationship between waveform envelope amplitudes and magnitude. We evaluate these new uncertainty values for past seismicity in California through off-line playbacks and compare them to the previously defined static definitions of uncertainty based on real-time detections. Our results indicate where VS alerts are most useful in California and also suggest where most effective improvements to the VS EEW system

  10. Monte Carlo method for determining earthquake recurrence parameters from short paleoseismic catalogs: Example calculations for California

    USGS Publications Warehouse

    Parsons, T.

    2008-01-01

    Paleoearthquake observations often lack enough events at a given site to directly define a probability density function (PDF) for earthquake recurrence. Sites with fewer than 10-15 intervals do not provide enough information to reliably determine the shape of the PDF using standard maximum-likelihood techniques (e.g., Ellsworth et al., 1999). In this paper I present a method that attempts to fit wide ranges of distribution parameters to short paleoseismic series. From repeated Monte Carlo draws, it becomes possible to quantitatively estimate most likely recurrence PDF parameters, and a ranked distribution of parameters is returned that can be used to assess uncertainties in hazard calculations. In tests on short synthetic earthquake series, the method gives results that cluster around the mean of the input distribution, whereas maximum likelihood methods return the sample means (e.g., NIST/SEMATECH, 2006). For short series (fewer than 10 intervals), sample means tend to reflect the median of an asymmetric recurrence distribution, possibly leading to an overestimate of the hazard should they be used in probability calculations. Therefore a Monte Carlo approach may be useful for assessing recurrence from limited paleoearthquake records. Further, the degree of functional dependence among parameters like mean recurrence interval and coefficient of variation can be established. The method is described for use with time-independent and time-dependent PDFs, and results from 19 paleoseismic sequences on strike-slip faults throughout the state of California are given.

  11. Monte Carlo Method for Determining Earthquake Recurrence Parameters from Short Paleoseismic Catalogs: Example Calculations for California

    USGS Publications Warehouse

    Parsons, Tom

    2008-01-01

    Paleoearthquake observations often lack enough events at a given site to directly define a probability density function (PDF) for earthquake recurrence. Sites with fewer than 10-15 intervals do not provide enough information to reliably determine the shape of the PDF using standard maximum-likelihood techniques [e.g., Ellsworth et al., 1999]. In this paper I present a method that attempts to fit wide ranges of distribution parameters to short paleoseismic series. From repeated Monte Carlo draws, it becomes possible to quantitatively estimate most likely recurrence PDF parameters, and a ranked distribution of parameters is returned that can be used to assess uncertainties in hazard calculations. In tests on short synthetic earthquake series, the method gives results that cluster around the mean of the input distribution, whereas maximum likelihood methods return the sample means [e.g., NIST/SEMATECH, 2006]. For short series (fewer than 10 intervals), sample means tend to reflect the median of an asymmetric recurrence distribution, possibly leading to an overestimate of the hazard should they be used in probability calculations. Therefore a Monte Carlo approach may be useful for assessing recurrence from limited paleoearthquake records. Further, the degree of functional dependence among parameters like mean recurrence interval and coefficient of variation can be established. The method is described for use with time-independent and time-dependent PDF?s, and results from 19 paleoseismic sequences on strike-slip faults throughout the state of California are given.

  12. Monte Carlo method for determining earthquake recurrence parameters from short paleoseismic catalogs: Example calculations for California

    NASA Astrophysics Data System (ADS)

    Parsons, Tom

    2008-03-01

    Paleoearthquake observations often lack enough events at a given site to directly define a probability density function (PDF) for earthquake recurrence. Sites with fewer than 10-15 intervals do not provide enough information to reliably determine the shape of the PDF using standard maximum-likelihood techniques (e.g., Ellsworth et al., 1999). In this paper I present a method that attempts to fit wide ranges of distribution parameters to short paleoseismic series. From repeated Monte Carlo draws, it becomes possible to quantitatively estimate most likely recurrence PDF parameters, and a ranked distribution of parameters is returned that can be used to assess uncertainties in hazard calculations. In tests on short synthetic earthquake series, the method gives results that cluster around the mean of the input distribution, whereas maximum likelihood methods return the sample means (e.g., NIST/SEMATECH, 2006). For short series (fewer than 10 intervals), sample means tend to reflect the median of an asymmetric recurrence distribution, possibly leading to an overestimate of the hazard should they be used in probability calculations. Therefore a Monte Carlo approach may be useful for assessing recurrence from limited paleoearthquake records. Further, the degree of functional dependence among parameters like mean recurrence interval and coefficient of variation can be established. The method is described for use with time-independent and time-dependent PDFs, and results from 19 paleoseismic sequences on strike-slip faults throughout the state of California are given.

  13. LLNL earthquake impact analysis committee report on the Livermore, California, earthquakes of January 24 and 26, 1980

    SciTech Connect

    Not Available

    1980-07-15

    The overall effects of the earthquakes of January 24 and 26, 1980, at the Lawrence Livermore National Laboratory in northern California are outlined. The damage caused by those earthquakes and how employees responded are discussed. The immediate emergency actions taken by management and the subsequent measures to resume operations are summarized. Long-range plans for recovery and repair, and the seisic history of the Livermore Valley region, various investigations concerning the design-basis earthquake (DBE), and seismic criteria for structures are reviewed. Following an analysis of the Laboratory's earthquake preparedness, emergency response, and related matters a series of conclusions and recommendations are presented. Appendixes provide additional information, such as persons interviewed, seismic and site maps, and a summary of the estimated costs incurred from the earthquakes.

  14. Earthquake alarm; operating the seismograph station at the University of California, Berkeley.

    USGS Publications Warehouse

    Stump, B.

    1980-01-01

    At the University of California seismographic stations, the task of locating and determining magnitudes for both local and distant earthquakes is a continuous one. Teleseisms must be located rapidly so that events that occur in the Pacific can be identified and the Pacific Tsunami Warning System alerted. For great earthquakes anywhere, there is a responsibility to notify public agencies such as the California Office of Emergency Services, the Federal Disaster Assistance Administration, the Earthquake Engineering Research Institute, the California Seismic Safety Commission, and the American Red Cross. In the case of damaging local earthquakes, it is necessary to alert also the California Department of Water Resources, California Division of Mines and Geology, U.S Army Corps of Engineers, Federal Bureau of Reclamation, and the Bay Area Rapid Transit. These days, any earthquakes that are felt in northern California cause immediate inquiries from the news media and an interested public. The series of earthquakes that jolted the Livermore area from January 24 to 26 1980, is a good case in point. 

  15. Unacceptable Risk: Earthquake Hazard Mitigation in One California School District. Hazard Mitigation Case Study.

    ERIC Educational Resources Information Center

    California State Office of Emergency Services, Sacramento.

    Earthquakes are a perpetual threat to California's school buildings. School administrators must be aware that hazard mitigation means much more than simply having a supply of water bottles in the school; it means getting everyone involved in efforts to prevent tragedies from occurring in school building in the event of an earthquake. The PTA in…

  16. Earthquake prediction research at the Seismological Laboratory, California Institute of Technology

    USGS Publications Warehouse

    Spall, H.

    1979-01-01

    Nevertheless, basic earthquake-related information has always been of consuming interest to the public and the media in this part of California (fig. 2.). So it is not surprising that earthquake prediction continues to be a significant reserach program at the laboratory. Several of the current spectrum of projects related to prediction are discussed below. 

  17. Variation of P-Wave Velocity before the Bear Valley, California, Earthquake of 24 February 1972.

    PubMed

    Robinson, R; Wesson, R L; Ellsworth, W L

    1974-06-21

    Residuals for P-wave traveltimes at a seismnograph station near Bear Valley, California, for small, precisely located local earthquakes at distances of 20 to 70 kilometers show a sharp increase of nearly 0.3 second about 2 months before a magnitude 5.0 earthquake that occurred within a few kilometers of the station. This indicates that velocity changes observed elsewhere premonitory to earthquakes, possibly related to dilatancy, occur along the central section of the San Andreas fault system. PMID:17784227

  18. Current Development at the Southern California Earthquake Data Center (SCEDC)

    NASA Astrophysics Data System (ADS)

    Appel, V. L.; Clayton, R. W.

    2005-12-01

    Over the past year, the SCEDC completed or is near completion of three featured projects: Station Information System (SIS) Development: The SIS will provide users with an interface into complete and accurate station metadata for all current and historic data at the SCEDC. The goal of this project is to develop a system that can interact with a single database source to enter, update and retrieve station metadata easily and efficiently. The system will provide accurate station/channel information for active stations to the SCSN real-time processing system, as will as station/channel information for stations that have parametric data at the SCEDC i.e., for users retrieving data via STP. Additionally, the SIS will supply information required to generate dataless SEED and COSMOS V0 volumes and allow stations to be added to the system with a minimum, but incomplete set of information using predefined defaults that can be easily updated as more information becomes available. Finally, the system will facilitate statewide metadata exchange for both real-time processing and provide a common approach to CISN historic station metadata. Moment Tensor Solutions: The SCEDC is currently archiving and delivering Moment Magnitudes and Moment Tensor Solutions (MTS) produced by the SCSN in real-time and post-processing solutions for events spanning back to 1999. The automatic MTS runs on all local events with magnitudes > 3.0, and all regional events > 3.5. The distributed solution automatically creates links from all USGS Simpson Maps to a text e-mail summary solution, creates a .gif image of the solution, and updates the moment tensor database tables at the SCEDC. Searchable Scanned Waveforms Site: The Caltech Seismological Lab has made available 12,223 scanned images of pre-digital analog recordings of major earthquakes recorded in Southern California between 1962 and 1992 at http://www.data.scec.org/research/scans/. The SCEDC has developed a searchable web interface that allows

  19. THE GREAT SOUTHERN CALIFORNIA SHAKEOUT: Earthquake Science for 22 Million People

    NASA Astrophysics Data System (ADS)

    Jones, L.; Cox, D.; Perry, S.; Hudnut, K.; Benthien, M.; Bwarie, J.; Vinci, M.; Buchanan, M.; Long, K.; Sinha, S.; Collins, L.

    2008-12-01

    Earthquake science is being communicated to and used by the 22 million residents of southern California to improve resiliency to future earthquakes through the Great Southern California ShakeOut. The ShakeOut began when the USGS partnered with the California Geological Survey, Southern California Earthquake Center and many other organizations to bring 300 scientists and engineers together to formulate a comprehensive description of a plausible major earthquake, released in May 2008, as the ShakeOut Scenario, a description of the impacts and consequences of a M7.8 earthquake on the Southern San Andreas Fault (USGS OFR2008-1150). The Great Southern California ShakeOut was a week of special events featuring the largest earthquake drill in United States history. The ShakeOut drill occurred in houses, businesses, and public spaces throughout southern California at 10AM on November 13, 2008, when southern Californians were asked to pretend that the M7.8 scenario earthquake had occurred and to practice actions that could reduce the impact on their lives. Residents, organizations, schools and businesses registered to participate in the drill through www.shakeout.org where they could get accessible information about the scenario earthquake and share ideas for better reparation. As of September 8, 2008, over 2.7 million confirmed participants had been registered. The primary message of the ShakeOut is that what we do now, before a big earthquake, will determine what our lives will be like after. The goal of the ShakeOut has been to change the culture of earthquake preparedness in southern California, making earthquakes a reality that are regularly discussed. This implements the sociological finding that 'milling,' discussing a problem with loved ones, is a prerequisite to taking action. ShakeOut milling is taking place at all levels from individuals and families, to corporations and governments. Actions taken as a result of the ShakeOut include the adoption of earthquake

  20. Estimated ground motion from the 1994 Northridge, California, earthquake at the site of interstate 10 and La Cienega Boulevard bridge collapse, West Los Angeles, California

    USGS Publications Warehouse

    Boore, D.M.; Gibbs, J.F.; Joyner, W.B.; Tinsley, J.C.; Ponti, D.J.

    2003-01-01

    We have estimated ground motions at the site of a bridge collapse during the 1994 Northridge, California, earthquake. The estimated motions are based on correcting motions recorded during the mainshock 2.3 km from the collapse site for the relative site response of the two sites. Shear-wave slownesses and damping based on analysis of borehole measurements at the two sites were used in the site response analysis. We estimate that the motions at the collapse site were probably larger, by factors ranging from 1.2 to 1.6, than at the site at which the ground motion was recorded, for periods less than about 1 sec.

  1. Liquefaction at Oceano, California, during the 2003 San Simeon earthquake

    USGS Publications Warehouse

    Holzer, T.L.; Noce, T.E.; Bennett, M.J.; Tinsley, J. C., III; Rosenberg, L.I.

    2005-01-01

    The 2003 M 6.5 San Simeon, California, earthquake caused liquefaction-induced lateral spreading at Oceano at an unexpectedly large distance from the seismogenic rupture. We conclude that the liquefaction was caused by ground motion that was enhanced by both rupture directivity in the mainshock and local site amplification by unconsolidated fine-grained deposits. Liquefaction occurred in sandy artificial fill and undisturbed eolian sand and fluvial deposits. The largest and most damaging lateral spread was caused by liquefaction of artificial fill; the head of this lateral spread coincided with the boundary between the artificial fill and undisturbed eolian sand deposits. Values of the liquefaction potential index, in general, were greater than 5 at liquefaction sites, the threshold value that has been proposed for liquefaction hazard mapping. Although the mainshock ground motion at Oceano was not recorded, peak ground acceleration was estimated to range from 0.25 and 0.28g on the basis of the liquefaction potential index and aftershock recordings. The estimates fall within the range of peak ground acceleration values associated with the modified Mercalli intensity = VII reported at the U.S. Geological Survey (USGS) "Did You Feel It?" web site.

  2. Influence of static stress changes on earthquake locations in southern California

    NASA Astrophysics Data System (ADS)

    Harris, Ruth A.; Simpson, Robert W.; Reasenberg, Paul A.

    1995-05-01

    EARTHQUAKES induce changes in static stress on neighbouring faults that may delay, hasten or even trigger subsequent earthquakes1-10. The length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment, but is presently unknown. Here we use an elastic half-space model11 to estimate the static stress changes generated by damaging (magnitude M>=5) earthquakes in southern California over the past 26 years, and to investigate the influence of these changes on subsequent earthquake activity. We find that, in the 1.5-year period following a M>=5 earthquake, any subsequent nearby M>=5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake. After this period, damaging earthquakes are equally likely to rupture loaded and relaxed faults. Our results suggest that there is a short period of time following a damaging earthquake in southern California in which simple Coulomb failure stress models could be used to identify regions of increased seismic hazard.

  3. Operational Earthquake Forecasting and Decision-Making in a Low-Probability Environment

    NASA Astrophysics Data System (ADS)

    Jordan, T. H.; the International Commission on Earthquake ForecastingCivil Protection

    2011-12-01

    Operational earthquake forecasting (OEF) is the dissemination of authoritative information about the time dependence of seismic hazards to help communities prepare for potentially destructive earthquakes. Most previous work on the public utility of OEF has anticipated that forecasts would deliver high probabilities of large earthquakes; i.e., deterministic predictions with low error rates (false alarms and failures-to-predict) would be possible. This expectation has not been realized. An alternative to deterministic prediction is probabilistic forecasting based on empirical statistical models of aftershock triggering and seismic clustering. During periods of high seismic activity, short-term earthquake forecasts can attain prospective probability gains in excess of 100 relative to long-term forecasts. The utility of such information is by no means clear, however, because even with hundredfold increases, the probabilities of large earthquakes typically remain small, rarely exceeding a few percent over forecasting intervals of days or weeks. Civil protection agencies have been understandably cautious in implementing OEF in this sort of "low-probability environment." The need to move more quickly has been underscored by recent seismic crises, such as the 2009 L'Aquila earthquake sequence, in which an anxious public was confused by informal and inaccurate earthquake predictions. After the L'Aquila earthquake, the Italian Department of Civil Protection appointed an International Commission on Earthquake Forecasting (ICEF), which I chaired, to recommend guidelines for OEF utilization. Our report (Ann. Geophys., 54, 4, 2011; doi: 10.4401/ag-5350) concludes: (a) Public sources of information on short-term probabilities should be authoritative, scientific, open, and timely, and need to convey epistemic uncertainties. (b) Earthquake probabilities should be based on operationally qualified, regularly updated forecasting systems. (c) All operational models should be evaluated

  4. The Influence of the Geometry of the San Andreas Fault System on Earthquakes in California

    NASA Astrophysics Data System (ADS)

    Li, Q.; Liu, M.

    2004-12-01

    The San Andreas Fault is believed to be the main surface trace of the plate boundary between the North American and the Pacific plates. From 1800 to present, three large historical earthquakes (1857 M7.9, 1906 M8.25, and 1989 M7.1) ruptured the San Andreas Fault. At the same time, more than a dozen M>7.0 earthquakes occurred outside the main trace of the San Andreas Fault. Most of the off-main-trace large earthquakes were scattered in Southern California, whereas in northern and central California, earthquakes were clustered along the main trace of the San Andreas Fault. Such a seismic distribution may be related to the geometry of the San Andreas Fault, which is curved with a major bending in southern California. In this study, we constructed a finite element model to explore the influence of the geometry of the San Andreas Fault system on stress distribution and seismicity in California. In the model, the San Andreas Fault is simulated with a weak zone that obeys the Coulomb Friction Law. The model results show that along relative straight segments of the San Andreas Fault in northern and central California, fault slip on the main fault trace causes low level stresses in nearby regions. Along the bended San Andreas Fault in southern California, however, the relative plate motion causes significant off-main-trace stress buildup, consistent with the distribution of large historical earthquakes outside the San Andreas Fault.

  5. Tilt precursors before earthquakes on the San Andreas fault, California

    USGS Publications Warehouse

    Johnston, M.J.S.; Mortensen, C.E.

    1974-01-01

    An array of 14 biaxial shallow-borehole tiltmeters (at 10-7 radian sensitivity) has been installed along 85 kilometers of the San Andreas fault during the past year. Earthquake-related changes in tilt have been simultaneously observed on up to four independent instruments. At earthquake distances greater than 10 earthquake source dimensions, there are few clear indications of tilt change. For the four instruments with the longest records (>10 months), 26 earthquakes have occurred since July 1973 with at least one instrument closer than 10 source dimensions and 8 earthquakes with more than one instrument within that distance. Precursors in tilt direction have been observed before more than 10 earthquakes or groups of earthquakes, and no similar effect has yet been seen without the occurrence of an earthquake.

  6. Tilt Precursors before Earthquakes on the San Andreas Fault, California.

    PubMed

    Johnston, M J; Mortensen, C E

    1974-12-13

    An array of 14 biaxial shallow-borehole tiltmeters (at 1O(-7) radian sensitivity) has been installed along 85 kilometers of the San Andreas fault during the past year. Earthquake-related changes in tilt have been simultaneously observed on up to four independent instruments. At earthquake distances greater than 10 earthquake source dimensions, there are few clear indications of tilt change. For the four instruments with the longest records (> 10 months), 26 earthquakes have occurred since July 1973 with at least one instrument closer than 10 source dimensions and 8 earthquakes with more than one instrument within that distance. Precursors in tilt direction have been observed before more than 10 earthquakes or groups of earthquakes, and no similar effect has yet been seen without the occurrence of an earthquake. PMID:17843056

  7. A search for long-term periodicities in large earthquakes of southern and coastal central California

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1990-01-01

    It has been occasionally suggested that large earthquakes may follow the 8.85-year and 18.6-year lunar-solar tidal cycles and possibly the approximately 11-year solar activity cycle. From a new study of earthquakes with magnitudes greater than 5.5 in southern and coastal central California during the years 1855-1983, it is concluded that, at least in this selected area of the world, no statistically significant long-term periodicities in earthquake frequency occur. The sample size used is about twice that used in comparable earlier studies of this region, which concentrated on large earthquakes.

  8. Factors Affecting the Probability of Default: Student Loans in California.

    ERIC Educational Resources Information Center

    Woo, Jennie H.

    2002-01-01

    Linked a database of California student borrowers with background financial and demographic information and post-college employment data to examine factors that predict default for borrowers in the federal Family Education Loan program. Found that background demographic and financial characteristics, leaving school without a degree, having low…

  9. California Earthquake Clearinghouse Activation for August 24, 2014, M6.0 South Napa Earthquake

    NASA Astrophysics Data System (ADS)

    Rosinski, A.; Parrish, J.; Mccrink, T. P.; Tremayne, H.; Ortiz, M.; Greene, M.; Berger, J.; Blair, J. L.; Johnson, M.; Miller, K.; Seigel, J.; Long, K.; Turner, F.

    2014-12-01

    The Clearinghouse's principal functions are to 1) coordinate field investigations of earth scientists, engineers, and other participating researchers; 2) facilitate sharing of observations through regular meetings and through the Clearinghouse website; and 3) notify disaster responders of crucial observations or results. Shortly after 3:20 a.m., on August 24, 2014, Clearinghouse management committee organizations, the California Geological Survey (CGS), the Earthquake Engineering Research Institute (EERI), the United States Geological Survey (USGS), the California Office of Emergency Services (CalOES), and the California Seismic Safety Commission (CSSC), authorized activation of a virtual Clearinghouse and a physical Clearinghouse location. The California Geological Survey, which serves as the permanent, lead coordination organization for the Clearinghouse, provided all coordination with the state for all resources required for Clearinghouse activation. The Clearinghouse physical location, including mobile satellite communications truck, was opened at a Caltrans maintenance facility located at 3161 Jefferson Street, in Napa. This location remained active through August 26, 2014, during which time it drew the participation of over 100 experts from more than 40 different organizations, and over 1730 remote visitors via the Virtual Clearinghouse and online data compilation map. The Clearinghouse conducted three briefing calls each day with the State Operations Center (SOC) and Clearinghouse partners, and also conducted nightly briefings, accessible to remote participants via webex, with field personnel. Data collected by field researchers was compiled into a map through the efforts of EERI and USGS volunteers in the Napa Clearinghouse. EERI personnel continued to provide updates to the compilation map over an extended period of time following de-activation of the Clearinghouse. In addition, EERI managed the Clearinghouse website. Two overflights were conducted, for

  10. Occurrence probability assessment of earthquake-triggered landslides with Newmark displacement values and logistic regression: The Wenchuan earthquake, China

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Song, Chongzhen; Lin, Qigen; Li, Juan

    2016-04-01

    The Newmark displacement model has been used to predict earthquake-triggered landslides. Logistic regression (LR) is also a common landslide hazard assessment method. We combined the Newmark displacement model and LR and applied them to Wenchuan County and Beichuan County in China, which were affected by the Ms. 8.0 Wenchuan earthquake on May 12th, 2008, to develop a mechanism-based landslide occurrence probability model and improve the predictive accuracy. A total of 1904 landslide sites in Wenchuan County and 3800 random non-landslide sites were selected as the training dataset. We applied the Newmark model and obtained the distribution of permanent displacement (Dn) for a 30 × 30 m grid. Four factors (Dn, topographic relief, and distances to drainages and roads) were used as independent variables for LR. Then, a combined model was obtained, with an AUC (area under the curve) value of 0.797 for Wenchuan County. A total of 617 landslide sites and non-landslide sites in Beichuan County were used as a validation dataset with AUC = 0.753. The proposed method may also be applied to earthquake-induced landslides in other regions.

  11. Earthquake prediction comes of age

    SciTech Connect

    Lindth, A. . Office of Earthquakes, Volcanoes, and Engineering)

    1990-02-01

    In the last decade, scientists have begun to estimate the long-term probability of major earthquakes along the San Andreas fault. In 1985, the U.S. Geological Survey (USGS) issued the first official U.S. government earthquake prediction, based on research along a heavily instrumented 25-kilometer section of the fault in sparsely populated central California. Known as the Parkfield segment, this section of the Sand Andreas had experienced its last big earthquake, a magnitude 6, in 1966. Estimated probabilities of major quakes along the entire San Andreas by a working group of California earthquake experts, using new geologic data and careful analysis of past earthquakes, are reported.

  12. Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes

    USGS Publications Warehouse

    Toppozada, Tousson R.; Real, Charles R.; Bezore, Stephen P.; Parke, David L.

    1981-01-01

    This is the second annual report of a three year project to clarify the earthquake history of California for the period before 1900. More than four thousand additional newspaper issues were searched for earthquake reports, bringing the total number of issues examined to more than eleven thousand. About one quarter of the issues searched have provided earthquake reports. Summaries of these reports, emphasizing the information used to assign earthquake intensities, were prepared. The strength and spatial distribution of the reported earthquake effects were used to estimate the magnitude and epicentral location of the earthquakes. The third annual report, projected for August 1981, will provide isoseismal maps showing the distribution of the intensity reports which control the estimates of magnitude and epicenter.

  13. Liquefaction caused by the 2009 Olancha, California (USA), M5.2 earthquake

    USGS Publications Warehouse

    Holzer, T.L.; Jayko, A.S.; Hauksson, E.; Fletcher, J.P.B.; Noce, T.E.; Bennett, M.J.; Dietel, C.M.; Hudnut, K.W.

    2010-01-01

    The October 3, 2009 (01:16:00 UTC), Olancha M5.2 earthquake caused extensive liquefaction as well as permanent horizontal ground deformation within a 1.2 km2area earthquake in Owens Valley in eastern California (USA). Such liquefaction is rarely observed during earthquakes of M ≤ 5.2. We conclude that subsurface conditions, not unusual ground motion, were the primary factors contributing to the liquefaction. The liquefaction occurred in very liquefiable sands at shallow depth (< 2 m) in an area where the water table was near the land surface. Our investigation is relevant to both geotechnical engineering and geology. The standard engineering method for assessing liquefaction potential, the Seed–Idriss simplified procedure, successfully predicted the liquefaction despite the small earthquake magnitude. The field observations of liquefaction effects highlight a need for caution by earthquake geologists when inferring prehistoric earthquake magnitudes from paleoliquefaction features because small magnitude events may cause such features.

  14. Differential Energy Radiation from Two Earthquakes with Similar Mw: The Baja California 2010 and Haiti 2010 Earthquakes

    NASA Astrophysics Data System (ADS)

    Meng, L.; Shi, B.

    2010-12-01

    The Baja, Mexico, earthquake of the April 4, 2010, Mw 7.2 occurred in northern Baja California at shallow depth along the principal plate boundary between the North American and Pacific plates, 2 people killed in the Mexicali area. The January 12, 2010, Mw 7.0, Haiti, earthquake occurred in the vicinity of Port-au-Prince, the capital of Haiti, on the Enriquillo Plantain Garden Fault, and with estimates of almost 250,000 deaths. International media reports of such kind of disasters by Haiti earthquake is just resulted from poor building structure design comparing with Mexicali area. Although the moment magnitude of the Haiti earthquake is similar as the Baja earthquake, but the radiated energy of the Haiti earthquake almost as 15 times as the Baja earthquake, resulting stronger near-fault ground motions. For the Haiti earthquake and Baja earthquake with the similar moment magnitude, two special finite fault models are constructed to simulate the near-fault strong ground motion for comparison purpose. We propose a new technique based on the far-field energy integrand over a simple finite fault to estimate S-wave energy radiation with associated the composite source model. The fault slip distributions on both faults are generated based on the composite source model in which the subevent-source-function is described by Brune’s pulse. The near-field peak ground accelerations (PGAs) including the shallow velocity structures (V30, average shear-velocity down to 30 m ) from the Haiti earthquake is almost as 20 times as from Baja earthquake, while the peak ground velocities (PGVs) including the shallow velocity structures from Yushu earthquake is almost as 8 times as from the Baja earthquake. Therefore, the radiated seismic energy plays a significant role in determining the levels of strong grounds in which stronger ground accelerations usually could cause much more property damages on the ground. The source rupture dynamics related to the frictional overshoot and

  15. The loma prieta, california, earthquake: an anticipated event.

    PubMed

    1990-01-19

    The first major earthquake on the San Andreas fault since 1906 fulfilled a long-term forecast for its rupture in the southern Santa Cruz Mountains. Severe damage occurred at distances of up to 100 kilometers from the epicenter in areas underlain by ground known to be hazardous in strong earthquakes. Stronger earthquakes will someday strike closer to urban centers in the United States, most of which also contain hazardous ground. The Loma Prieta earthquake demonstrated that meaningful predictions can be made of potential damage patterns and that, at least in well-studied areas, long-term forecasts can be made of future earthquake locations and magnitudes. Such forecasts can serve as a basis for action to reduce the threat major earthquakes pose to the United States. PMID:17735847

  16. Forecasting California's earthquakes: What can we expect in the next 30 years?

    USGS Publications Warehouse

    Field, Edward H.; Milner, Kevin R.; The 2007 Working Group on California Earthquake Probabilities

    2008-01-01

    In a new comprehensive study, scientists have determined that the chance of having one or more magnitude 6.7 or larger earthquakes in the California area over the next 30 years is greater than 99%. Such quakes can be deadly, as shown by the 1989 magnitude 6.9 Loma Prieta and the 1994 magnitude 6.7 Northridge earthquakes. The likelihood of at least one even more powerful quake of magnitude 7.5 or greater in the next 30 years is 46%?such a quake is most likely to occur in the southern half of the State. Building codes, earthquake insurance, and emergency planning will be affected by these new results, which highlight the urgency to prepare now for the powerful quakes that are inevitable in California?s future.

  17. Database of potential sources for earthquakes larger than magnitude 6 in Northern California

    USGS Publications Warehouse

    Working Group on Northern California Earthquake Potential

    1996-01-01

    The Northern California Earthquake Potential (NCEP) working group, composed of many contributors and reviewers in industry, academia and government, has pooled its collective expertise and knowledge of regional tectonics to identify potential sources of large earthquakes in northern California. We have created a map and database of active faults, both surficial and buried, that forms the basis for the northern California portion of the national map of probabilistic seismic hazard. The database contains 62 potential sources, including fault segments and areally distributed zones. The working group has integrated constraints from broadly based plate tectonic and VLBI models with local geologic slip rates, geodetic strain rate, and microseismicity. Our earthquake source database derives from a scientific consensus that accounts for conflict in the diverse data. Our preliminary product, as described in this report brings to light many gaps in the data, including a need for better information on the proportion of deformation in fault systems that is aseismic.

  18. Paleoseismologic evidence for late Holocene earthquakes on the Southern Panamint Valley fault zone: Implications for earthquake clustering in the Eastern California Shear Zone north of the Garlock fault

    NASA Astrophysics Data System (ADS)

    McAuliffe, L. J.; Dolan, J. F.; Kirby, E.; Haravitch, B.; Alm, S.

    2010-12-01

    New paleoseismological data from two trenches excavated across the southern end of the Panamint Valley fault (PVF), the most active of the three major faults in the eastern California shear zone (ECSZ) north of the Garlock fault, reveal the occurrence of at least two, and probably three, surface ruptures during the late Holocene. These trenches were designed to test the hypothesis that the earthquake clusters and intervening seismic lulls observed in the Mojave section of the ECSZ (Rockwell et al. 2000, Ganev et al. 2010) at 8-9.5 ka, 5-6 ka and during the past ~1-1.5 ka, also involved the fault systems of the ECSZ north of the Garlock fault. Well stratified playa sands, silts and clays exposed in the trench allowed precise identification of two event horizons; a likely third event horizon occurred during a period of soil development across the playa. Calibrated radiocarbon dates from 25 charcoal samples constrain the dates of the most recent event (MRE) to ~1450-1500 AD and the ante-penultimate event at 3.2-3.6 ka. The penultimate event occurred during a period of soil development spanning ~350-1400 AD. The presence of large blocks of soil in what appears to be scarp-derived colluvium in a large fissure opened during this event require that it occurred late during soil development, probably only a few hundred years before the MRE. The timing of the three events indicate that the southern PVF has ruptured at least once, and probably twice during the ongoing seismic cluster in the Mojave region. The PVF earthquakes also are similar in age to the 1872 Owens Valley earthquakes and the geomorphically youthful, but undated MRE in central Death Valley. Although we were unable to excavate deeply enough at this site to expose mid-to lower - Holocene playa strata, the timing of the ante-penultimate earthquake at our site shows that the PVF has ruptured at least once during the well-defined 2-5 ka seismic lull in the Mojave section of the ECSZ. Interestingly the 3.2-3.6 ka

  19. Real-time forecasts of tomorrow's earthquakes in California: a new mapping tool

    USGS Publications Warehouse

    Gerstenberger, Matt; Wiemer, Stefan; Jones, Lucy

    2004-01-01

    We have derived a multi-model approach to calculate time-dependent earthquake hazard resulting from earthquake clustering. This file report explains the theoretical background behind the approach, the specific details that are used in applying the method to California, as well as the statistical testing to validate the technique. We have implemented our algorithm as a real-time tool that has been automatically generating short-term hazard maps for California since May of 2002, at http://step.wr.usgs.gov

  20. UAVSAR and GPS Observations of Crustal Deformation in Southern California and Implications for Earthquake Risk

    NASA Astrophysics Data System (ADS)

    Donnellan, A.; Parker, J. W.; Lyzenga, G. A.; Rundle, J. B.; Grant Ludwig, L.; Granat, R. A.; Glasscoe, M. T.; Heflin, M. B.

    2010-12-01

    The 2010 El-Mayor Cucapah earthquake was the first earthquake to be observed with UAVSAR. UAVSAR observations, GPS time series analysis, and simulations suggest that the fault that ruptured in the earthquake is coupled to the Elsinore, San Jacinto, and San Andreas faults to the north. GPS and UAVSAR observations indicate a zone of shear that extends southward from the Big Bend of the San Andreas fault near Gorman through the San Fernando Valley towards the Newport-Inglewood fault. The zone steps over to the region of the Elsinore or San Jacinto faults, though the partitioning of strain between the two faults is not as clear. State changes in GPS time series data fall in line with the shear zone through the San Fernando Valley and extend northward from the El Mayor-Cucapah earthquake rupture. Seismicity hotspots also indicate elevated earthquake hazard near the San Fernando Valley and in the Inland Empire near the Elsinore and San Jacinto faults. Inversions of GPS velocity vectors favor a fault underlying the shear zone extending from the Big Bend to the Newport-Inglewood fault over substantial slip on the San Andreas fault under north of Los Angeles. Virtual California simulations of southern California are being analyzed for fault activity associated with the identified shear zone and for subsequent earthquakes that may be related to El Mayor-Cucapah type earthquakes in Baja.

  1. Changes in static stress on southern California faults after the 1992 Landers earthquake

    USGS Publications Warehouse

    Harris, R.A.; Simpson, R.W.

    1992-01-01

    THE magnitude 7.5 Landers earthquake of 28 June 1992 was the largest earthquake to strike California in 40 years. The slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults; these changes in stress should in turn affect the likelihood of future earthquakes. Stress changes that load faults towards failure have been cited as the cause of small1-5, moderate6 and large7 earthquakes; conversely, those that relax neighbouring faults have been related to a decrease in seismicity5. Here we use an elastic half-space model8 to estimate the stress changes produced by the Landers earthquake on selected southern California faults, including the San Andreas. We find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4.5, and that the largest changes (1-10 bar), occurring on part of the San Bernardino segment of the San Andreas fault, may have decreased the time to the next magnitude 8 earthquake by about 14 years.

  2. Changes in state of stress on the southern san andreas fault resulting from the california earthquake sequence of april to june 1992.

    PubMed

    Jaumé, S C; Sykes, L R

    1992-11-20

    The April to June 1992 Landers earthquake sequence in southern California modified the state of stress along nearby segments of the San Andreas fault, causing a 50-kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near San Gorgonio Pass. The decrease in compressive normal stress may also have reduced fluid pressures along that fault segment. As pressures are reequilibrated by diffusion, that fault segment should move closer to failure with time. That fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years. PMID:17778355

  3. FORECAST MODEL FOR MODERATE EARTHQUAKES NEAR PARKFIELD, CALIFORNIA.

    USGS Publications Warehouse

    Stuart, William D.; Archuleta, Ralph J.; Lindh, Allan G.

    1985-01-01

    The paper outlines a procedure for using an earthquake instability model and repeated geodetic measurements to attempt an earthquake forecast. The procedure differs from other prediction methods, such as recognizing trends in data or assuming failure at a critical stress level, by using a self-contained instability model that simulates both preseismic and coseismic faulting in a natural way. In short, physical theory supplies a family of curves, and the field data select the member curves whose continuation into the future constitutes a prediction. Model inaccuracy and resolving power of the data determine the uncertainty of the selected curves and hence the uncertainty of the earthquake time.

  4. Southern California Earthquake Center--Virtual Display of Objects (SCEC-VDO): An Earthquake Research and Education Tool

    NASA Astrophysics Data System (ADS)

    Perry, S.; Maechling, P.; Jordan, T.

    2006-12-01

    Interns in the program Southern California Earthquake Center/Undergraduate Studies in Earthquake Information Technology (SCEC/UseIT, an NSF Research Experience for Undergraduates Site) have designed, engineered, and distributed SCEC-VDO (Virtual Display of Objects), an interactive software used by earthquake scientists and educators to integrate and visualize global and regional, georeferenced datasets. SCEC-VDO is written in Java/Java3D with an extensible, scalable architecture. An increasing number of SCEC-VDO datasets are obtained on the fly through web services and connections to remote databases; and user sessions may be saved in xml-encoded files. Currently users may display time-varying sequences of earthquake hypocenters and focal mechanisms, several 3-dimensional fault and rupture models, satellite imagery - optionally draped over digital elevation models - and cultural datasets including political boundaries. The ability to juxtapose and interactively explore these data and their temporal and spatial relationships has been particularly important to SCEC scientists who are evaluating fault and deformation models, or who must quickly evaluate the menace of evolving earthquake sequences. Additionally, SCEC-VDO users can annotate the display, plus script and render animated movies with adjustable compression levels. SCEC-VDO movies are excellent communication tools and have been featured in scientific presentations, classrooms, press conferences, and television reports.

  5. Precise estimation of repeating earthquake moment: Example from parkfield, california

    USGS Publications Warehouse

    Rubinstein, J.L.; Ellsworth, W.L.

    2010-01-01

    We offer a new method for estimating the relative size of repeating earthquakes using the singular value decomposition (SVD). This method takes advantage of the highly coherent waveforms of repeating earthquakes and arrives at far more precise and accurate descriptions of earthquake size than standard catalog techniques allow. We demonstrate that uncertainty in relative moment estimates is reduced from ??75% for standard coda-duration techniques employed by the network to an uncertainty of ??6.6% when the SVD method is used. This implies that a single-station estimate of moment using the SVD method has far less uncertainty than the whole-network estimates of moment based on coda duration. The SVD method offers a significant improvement in our ability to describe the size of repeating earthquakes and thus an opportunity to better understand how they accommodate slip as a function of time.

  6. Source parameters of the 1980 Mammoth Lakes, California earthquake sequence

    SciTech Connect

    Archuleta, R.J.; Cranswick, E.; Muller, C.; Spudich, P.

    1982-06-10

    From the more than 1500 Mammoth Lakes earthquakes recorded on three-component digital seismographs (Spudich et al., 1981), 150 were used in an analysis of the locations, mechanism, and source parameters. A composite fault plane solution of nine earthquakes 3.9< or =M< or =5.1 defines a right-lateral strike slip mechanism on a steeply dipping nearly east-west plane striking S75 /sup 0/E or left-lateral strike slip on a nearly north-south plane striking N10 /sup 0/E. Vertical cross sections of well-located aftershocks indicate possible three east-west planes that coincide with the locations of the four largest earthquakes with M/sub L/> or =6.0. Using the spectral analysis of S waves (Brune, 1970), source parameters for 67 earthquakes were determined. Forty-eight had magnitudes greater than or equal to 3.0. Seismic moments ranges from 9.20 x 10/sup 18/ dyn cm to 2.33 x 10/sup 24/ dyn cm. Earthquakes with seismic moment greater than about 1.0 x 10/sup 21/ dyn cm had nearly constant stress drops (approx. =50 bars); earthquakes with seismic moment less than about 1.0 x 10/sup 21/ dyn cm had stress drop that apparetnly decrease as seismic moment decreases.

  7. Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Forecasts

    USGS Publications Warehouse

    Harris, Ruth A.

    1998-01-01

    The magnitude (Mw) 6.9 Loma Prieta earthquake struck the San Francisco Bay region of central California at 5:04 p.m. P.d.t. on October 17, 1989, killing 62 people and generating billions of dollars in property damage. Scientists were not surprised by the occurrence of a destructive earthquake in this region and had, in fact, been attempting to forecast the location of the next large earthquake in the San Francisco Bay region for decades. This paper summarizes more than 20 scientifically based forecasts made before the 1989 Loma Prieta earthquake for a large earthquake that might occur in the Loma Prieta area. The forecasts geographically closest to the actual earthquake primarily consisted of right-lateral strike-slip motion on the San Andreas Fault northwest of San Juan Bautista. Several of the forecasts did encompass the magnitude of the actual earthquake, and at least one approximately encompassed the along-strike rupture length. The 1989 Loma Prieta earthquake differed from most of the forecasted events in two ways: (1) it occurred with considerable dip-slip in addition to strike-slip motion, and (2) it was much deeper than expected.

  8. Statistical Properties of Induced and Triggered Earthquakes at The Geysers, California

    NASA Astrophysics Data System (ADS)

    Hawkins, A. K.; Turcotte, D. L.; Kellogg, L. H.

    2015-12-01

    This study considers the statistics of induced and triggered seismicity at The Geysers geothermal field, California. Data is considered from the regional Northern California Seismic Network (NCSN) and local Lawrence Berkeley National Laboratory Network (LBNLN). Both data sets give good GR data fits for 2009-2014 but NCSN data have b=1.15 and LBNLN data have b=1.36. Comparing 18,000 individual earthquakes we find on average MLBNLN = MNCSN+0.5. Thus care must be taken when both data sets are used. We hypothesize that the strain accumulated due to the plate motions is a balance by the strain released in earthquakes with a maximum upper limit Mmax. We compare the strain associated with seismicity with the tectonic GPS strain being accumulated in the region. Taking the NCSN GR data with an upper magnitude cutoff, we find this cutoff to be Mmax=4.74. This is consistent with an observed upper magnitude limit to The Geysers seismicity at about M=5. We present studies of aftershock statistics of four M = 4.43, 4.16, 4.62, and 4.53 earthquakes. We find both GR and Omori Law statistics to be typical of tectonic earthquakes. We suggest that the four earthquakes release accumulated tectonic stresses but injected fluids reduce the stress required for rupture initiation. We also consider triggered seismicity caused by three remote earthquakes. We obtain excellent data for the 2010 M=7.2 El Mayor-Cucapah and the M=6.0 South Napa earthquakes. In the first case a M=3.37 event was triggered and in the second case a M=4.48 event was triggered. We conclude that the observed seismicity consists primarily of aftershocks of the large triggered earthquakes and that the directly triggered earthquakes do not satisfy GR frequency-magnitude statistics.

  9. Properties of the probability distribution associated with the largest event in an earthquake cluster and their implications to foreshocks

    SciTech Connect

    Zhuang Jiancang; Ogata, Yosihiko

    2006-04-15

    The space-time epidemic-type aftershock sequence model is a stochastic branching process in which earthquake activity is classified into background and clustering components and each earthquake triggers other earthquakes independently according to certain rules. This paper gives the probability distributions associated with the largest event in a cluster and their properties for all three cases when the process is subcritical, critical, and supercritical. One of the direct uses of these probability distributions is to evaluate the probability of an earthquake to be a foreshock, and magnitude distributions of foreshocks and nonforeshock earthquakes. To verify these theoretical results, the Japan Meteorological Agency earthquake catalog is analyzed. The proportion of events that have 1 or more larger descendants in total events is found to be as high as about 15%. When the differences between background events and triggered event in the behavior of triggering children are considered, a background event has a probability about 8% to be a foreshock. This probability decreases when the magnitude of the background event increases. These results, obtained from a complicated clustering model, where the characteristics of background events and triggered events are different, are consistent with the results obtained in [Ogata et al., Geophys. J. Int. 127, 17 (1996)] by using the conventional single-linked cluster declustering method.

  10. Evidence for dyke intrusion earthquake mechanisms near long valley caldera, California

    USGS Publications Warehouse

    Julian, B.R.

    1983-01-01

    A re-analysis of the magnitude 6 earthquakes that occurred near Long Valley caldera in eastern California on 25 and 27 May 1980, suggests that at least two of them, including the largest, were probably caused by fluid injection along nearly vertical surfaces and not by slip on faults. Several investigators 1,2 have reported difficulty in explaining both the long-period surface-wave amplitudes and phases and the locally recorded short-period body-wave first motions from these events, using conventional double-couple (shear fault) source models. They attributed this difficulty to: (1) complex sources, not representable by single-fault models; (2) artefacts of the analysis methods used; or (3) effects of wave propagation through hypothetical structures beneath the caldera. We show here that the data agree well with the predictions for a compensated linear-vector dipole (CLVD) equivalent-force system3 with its principal extensional axis horizontal and trending N 55-65?? E. Such a mechanism is what would be expected for fluid injection into dykes striking N 25-35?? W, which is the approximate strike of numerous normal faults in the area. ?? 1983 Nature Publishing Group.

  11. Liquefaction-induced lateral spreading in Oceano, California, during the 2003 San Simeon Earthquake

    USGS Publications Warehouse

    Holzer, Thomas L.; Noce, Thomas E.; Bennett, Michael J.; Di Alessandro, Carola; Boatwright, John; Tinsley, John C., III; Sell, Russell W.; Rosenberg, Lewis I.

    2004-01-01

    The December 22, 2003, San Simeon, California, (M6.5) earthquake caused damage to houses, road surfaces, and underground utilities in Oceano, California. The community of Oceano is approximately 50 miles (80 km) from the earthquake epicenter. Damage at this distance from a M6.5 earthquake is unusual. To understand the causes of this damage, the U.S. Geological Survey conducted extensive subsurface exploration and monitoring of aftershocks in the months after the earthquake. The investigation included 37 seismic cone penetration tests, 5 soil borings, and aftershock monitoring from January 28 to March 7, 2004. The USGS investigation identified two earthquake hazards in Oceano that explain the San Simeon earthquake damage?site amplification and liquefaction. Site amplification is a phenomenon observed in many earthquakes where the strength of the shaking increases abnormally in areas where the seismic-wave velocity of shallow geologic layers is low. As a result, earthquake shaking is felt more strongly than in surrounding areas without similar geologic conditions. Site amplification in Oceano is indicated by the physical properties of the geologic layers beneath Oceano and was confirmed by monitoring aftershocks. Liquefaction, which is also commonly observed during earthquakes, is a phenomenon where saturated sands lose their strength during an earthquake and become fluid-like and mobile. As a result, the ground may undergo large permanent displacements that can damage underground utilities and well-built surface structures. The type of displacement of major concern associated with liquefaction is lateral spreading because it involves displacement of large blocks of ground down gentle slopes or towards stream channels. The USGS investigation indicates that the shallow geologic units beneath Oceano are very susceptible to liquefaction. They include young sand dunes and clean sandy artificial fill that was used to bury and convert marshes into developable lots. Most of

  12. Intermediate-term, pre-earthquake phenomena in California, 1975-1986, and preliminary forecast of seismicity for the next decade

    USGS Publications Warehouse

    Wesson, R.L.; Nicholson, C.

    1988-01-01

    Intermediate-term observations preceding earthquakes of magnitude 5.7 or greater in California from 1975 through 1986 suggest that: (1) The sudden appearance of earthquakes in a previously inactive area indicates an increased likelihood of a significant earthquake in that area for a period from days to years; (2) these larger earthquakes tend to occur towards the ends of creeping fault segments; (3) one large earthquake in a region increases the likelihood of a subsequent significant event in the adjacent area; and (4) marginal evidence for the occurrence of a regional deformation event suggests that such events increase the probability of earthquake occurrence throughout the entire area. A common element in many of these observed patterns appears to be the transmission and amplification of tectonic stress changes by the mechanism of fault creep, and suggests that surface fault creep is a sensitive indicator of changes in stress. The preceding critieria are used to construct a preliminary 'forecast' of the likely locations of significant earthquakes over the next decade. ?? 1988 Birkha??user Verlag.

  13. Products and Services Available from the Southern California Earthquake Data Center (SCEDC) and the Southern California Seismic Network (SCSN)

    NASA Astrophysics Data System (ADS)

    Yu, E.; Chen, S.; Chowdhury, F.; Bhaskaran, A.; Hutton, K.; Given, D.; Hauksson, E.; Clayton, R. W.

    2009-12-01

    The SCEDC archives continuous and triggered data from nearly 3000 data channels from 375 SCSN recorded stations. The SCSN and SCEDC process and archive an average of 12,000 earthquakes each year, contributing to the southern California earthquake catalog that spans from 1932 to present. The SCEDC provides public, searchable access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP, NETDC and DHI. New data products: ● The SCEDC is distributing synthetic waveform data from the 2008 ShakeOut scenario (Jones et al., USGS Open File Rep., 2008-1150) and (Graves et al. 2008; Geophys. Res. Lett.) This is a M 7.8 earthquake on the southern San Andreas fault. Users will be able to download 40 sps velocity waveforms in SAC format from the SCEDC website. The SCEDC is also distributing synthetic GPS data (Crowell et al., 2009; Seismo. Res. Letters.) for this scenario as well. ● The SCEDC has added a new web page to show the latest tomographic model of Southern California. This model is based on Tape et al., 2009 Science. New data services: ● The SCEDC is exporting data in QuakeML format. This is an xml format that has been adopted by the Advanced National Seismic System (ANSS). This data will also be available as a web service. ● The SCEDC is exporting data in StationXML format. This is an xml format created by the SCEDC and adopted by ANSS to fully describe station metadata. This data will also be available as a web service. ● The stp 1.6 client can now access both the SCEDC and the Northern California Earthquake Data Center (NCEDC) earthquake and waveform archives. In progress - SCEDC to distribute 1 sps GPS data in miniSEED format: ● As part of a NASA Advanced Information Systems Technology project in collaboration with Jet Propulsion Laboratory and Scripps Institution of Oceanography, the SCEDC will receive real time 1 sps streams of GPS displacement solutions from the California

  14. Prediction of central California earthquakes from soil-gas helium fluctuations

    USGS Publications Warehouse

    Reimer, G.M.

    1985-01-01

    The observations of short-term decreases in helium soil-gas concentrations along the San Andreas Fault in central California have been correlated with subsequent earthquake activity. The area of study is elliptical in shape with radii approximately 160??80 km, centered near San Benito, and with the major axis parallel to the Fault. For 83 percent of the M>4 earthquakes in this area a helium decrease preceded seismic activity by 1.5 to 6.5 weeks. There were several earthquakes without a decrease and several decreases without a corresponding earthquake. Owing to complex and unresolved interaction of many geophysical and geochemical parameters, no suitable model is yet developed to explain the observations. ?? 1985 Birkha??user Verlag.

  15. Annual modulation of triggered seismicity following the 1992 Landers earthquake in California

    PubMed

    Gao; Silver; Linde; Sacks

    2000-08-01

    The mechanism responsible for the triggering of earthquakes remains one of the least-understood aspects of the earthquake process. The magnitude-7.3 Landers, California earthquake of 28 June 1992 was followed for several weeks by triggered seismic activity over a large area, encompassing much of the western United States. Here we show that this triggered seismicity marked the beginning of a five-year trend, consisting of an elevated microearthquake rate that was modulated by an annual cycle, decaying with time. The annual cycle is mainly associated with several hydrothermal or volcanic regions where short-term triggering was also observed. These data indicate that the Landers earthquake produced long-term physical changes in these areas, and that an environmental source of stress--plausibly barometric pressure--might be responsible for the annual variation. PMID:10952308

  16. Constraining depth range of S wave velocity decrease after large earthquakes near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Wu, Chunquan; Delorey, Andrew; Brenguier, Florent; Hadziioannou, Celine; Daub, Eric G.; Johnson, Paul

    2016-06-01

    We use noise correlation and surface wave inversion to measure the S wave velocity changes at different depths near Parkfield, California, after the 2003 San Simeon and 2004 Parkfield earthquakes. We process continuous seismic recordings from 13 stations to obtain the noise cross-correlation functions and measure the Rayleigh wave phase velocity changes over six frequency bands. We then invert the Rayleigh wave phase velocity changes using a series of sensitivity kernels to obtain the S wave velocity changes at different depths. Our results indicate that the S wave velocity decreases caused by the San Simeon earthquake are relatively small (~0.02%) and access depths of at least 2.3 km. The S wave velocity decreases caused by the Parkfield earthquake are larger (~0.2%), and access depths of at least 1.2 km. Our observations can be best explained by material damage and healing resulting mainly from the dynamic stress perturbations of the two large earthquakes.

  17. Hydrothermal response to a volcano-tectonic earthquake swarm, Lassen, California

    USGS Publications Warehouse

    Ingebritsen, Steven E.; Shelly, David R.; Hsieh, Paul A.; Clor, Laura; P.H. Seward; Evans, William C.

    2015-01-01

    The increasing capability of seismic, geodetic, and hydrothermal observation networks allows recognition of volcanic unrest that could previously have gone undetected, creating an imperative to diagnose and interpret unrest episodes. A November 2014 earthquake swarm near Lassen Volcanic National Park, California, which included the largest earthquake in the area in more than 60 years, was accompanied by a rarely observed outburst of hydrothermal fluids. Although the earthquake swarm likely reflects upward migration of endogenous H2O-CO2 fluids in the source region, there is no evidence that such fluids emerged at the surface. Instead, shaking from the modest sized (moment magnitude 3.85) but proximal earthquake caused near-vent permeability increases that triggered increased outflow of hydrothermal fluids already present and equilibrated in a local hydrothermal aquifer. Long-term, multiparametric monitoring at Lassen and other well-instrumented volcanoes enhances interpretation of unrest and can provide a basis for detailed physical modeling.

  18. Hydrothermal response to a volcano-tectonic earthquake swarm, Lassen, California

    NASA Astrophysics Data System (ADS)

    Ingebritsen, S. E.; Shelly, D. R.; Hsieh, P. A.; Clor, L. E.; Seward, P. H.; Evans, W. C.

    2015-11-01

    The increasing capability of seismic, geodetic, and hydrothermal observation networks allows recognition of volcanic unrest that could previously have gone undetected, creating an imperative to diagnose and interpret unrest episodes. A November 2014 earthquake swarm near Lassen Volcanic National Park, California, which included the largest earthquake in the area in more than 60 years, was accompanied by a rarely observed outburst of hydrothermal fluids. Although the earthquake swarm likely reflects upward migration of endogenous H2O-CO2 fluids in the source region, there is no evidence that such fluids emerged at the surface. Instead, shaking from the modest sized (moment magnitude 3.85) but proximal earthquake caused near-vent permeability increases that triggered increased outflow of hydrothermal fluids already present and equilibrated in a local hydrothermal aquifer. Long-term, multiparametric monitoring at Lassen and other well-instrumented volcanoes enhances interpretation of unrest and can provide a basis for detailed physical modeling.

  19. Nonvolcanic tremor evolution and the San Simeon and Parkfield, California, earthquakes.

    PubMed

    Nadeau, Robert M; Guilhem, Aurélie

    2009-07-10

    Nonvolcanic tremors occur adjacent to locked faults and may be closely related to the generation of earthquakes. Monitoring of the San Andreas Fault in the Parkfield, California, region revealed that after two strong earthquakes, tremor activity increased in a nearly dormant tremor zone, increased and became periodic in a previously active zone, and has remained elevated and periodic for over 4 years. Static shear- and Coulomb-stress increases of 6 to 14 kilopascals from these two earthquakes are coincident with sudden increases in tremor rates. The persistent changes in tremor suggest that stress is now accumulating more rapidly beneath this part of the San Andreas Fault, which ruptured in the moment magnitude 7.8 Ft. Tejon earthquake of 1857. PMID:19589999

  20. Earthquake Swarm Along the San Andreas Fault near Palmdale, Southern California, 1976 to 1977.

    PubMed

    McNally, K C; Kanamori, H; Pechmann, J C; Fuis, G

    1978-09-01

    Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 8(1/4)+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown. PMID:17738534

  1. Earthquake swarm along the San Andreas fault near Palmdale, Southern California, 1976 to 1977

    USGS Publications Warehouse

    Mcnally, K.C.; Kanamori, H.; Pechmann, J.C.; Fuis, G.

    1978-01-01

    Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude ??? 3) occurred on or near the San Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 81/4+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown. Copyright ?? 1978 AAAS.

  2. Instability model for recurring large and great earthquakes in southern California

    USGS Publications Warehouse

    Stuart, W.D.

    1985-01-01

    The locked section of the San Andreas fault in southern California has experienced a number of large and great earthquakes in the past, and thus is expected to have more in the future. To estimate the location, time, and slip of the next few earthquakes, an earthquake instability model is formulated. The model is similar to one recently developed for moderate earthquakes on the San Andreas fault near Parkfield, California. In both models, unstable faulting (the earthquake analog) is caused by failure of all or part of a patch of brittle, strain-softening fault zone. In the present model the patch extends downward from the ground surface to about 12 km depth, and extends 500 km along strike from Parkfield to the Salton Sea. The variation of patch strength along strike is adjusted by trial until the computed sequence of instabilities matches the sequence of large and great earthquakes since a.d. 1080 reported by Sieh and others. The last earthquake was the M=8.3 Ft. Tejon event in 1857. The resulting strength variation has five contiguous sections of alternately low and high strength. From north to south, the approximate locations of the sections are: (1) Parkfield to Bitterwater Valley, (2) Bitterwater Valley to Lake Hughes, (3) Lake Hughes to San Bernardino, (4) San Bernardino to Palm Springs, and (5) Palm Springs to the Salton Sea. Sections 1, 3, and 5 have strengths between 53 and 88 bars; sections 2 and 4 have strengths between 164 and 193 bars. Patch section ends and unstable rupture ends usually coincide, although one or more adjacent patch sections may fail unstably at once. The model predicts that the next sections of the fault to slip unstably will be 1, 3, and 5; the order and dates depend on the assumed length of an earthquake rupture in about 1700. ?? 1985 Birkha??user Verlag.

  3. Injuries and Traumatic Psychological Exposures Associated with the South Napa Earthquake - California, 2014.

    PubMed

    Attfield, Kathleen R; Dobson, Christine B; Henn, Jennifer B; Acosta, Meileen; Smorodinsky, Svetlana; Wilken, Jason A; Barreau, Tracy; Schreiber, Merritt; Windham, Gayle C; Materna, Barbara L; Roisman, Rachel

    2015-01-01

    On August 24, 2014, at 3:20 a.m., a magnitude 6.0 earthquake struck California, with its epicenter in Napa County (1). The earthquake was the largest to affect the San Francisco Bay area in 25 years and caused significant damage in Napa and Solano counties, including widespread power outages, five residential fires, and damage to roadways, waterlines, and 1,600 buildings (2). Two deaths resulted (2). On August 25, Napa County Public Health asked the California Department of Public Health (CDPH) for assistance in assessing postdisaster health effects, including earthquake-related injuries and effects on mental health. On September 23, Solano County Public Health requested similar assistance. A household-level Community Assessment for Public Health Emergency Response (CASPER) was conducted for these counties in two cities (Napa, 3 weeks after the earthquake, and Vallejo, 6 weeks after the earthquake). Among households reporting injuries, a substantial proportion (48% in Napa and 37% in western Vallejo) reported that the injuries occurred during the cleanup period, suggesting that increased messaging on safety precautions after a disaster might be needed. One fifth of respondents overall (27% in Napa and 9% in western Vallejo) reported one or more traumatic psychological exposures in their households. These findings were used by Napa County Mental Health to guide immediate-term mental health resource allocations and to conduct public training sessions and education campaigns to support persons with mental health risks following the earthquake. In addition, to promote community resilience and future earthquake preparedness, Napa County Public Health subsequently conducted community events on the earthquake anniversary and provided outreach workers with psychological first aid training. PMID:26355257

  4. Guide and Checklist for Nonstructural Earthquake Hazards in California Schools.

    ERIC Educational Resources Information Center

    2003

    The recommendations included in this document are intended to reduce seismic hazards associated with the non-structural components of schools buildings, including mechanical systems, ceiling systems, partitions, light fixtures, furnishings, and other building contents. It identifies potential earthquake hazards and provides recommendations for…

  5. The 1936, 1945-1947, and 1950 earthquake sequences near Lassen Peak, California

    USGS Publications Warehouse

    Norris, R.D.; Weaver, C.S.

    1997-01-01

    Three vigorous earthquake sequences occurred near Lassen Peak in 1936, between 1945 and 1947, and in 1950; the latter two sequences included mainshocks of magnitude 5.0 and 5.5, respectively, and thousands of smaller events. No comparable earthquake sequences have occurred near Lassen Peak since 1950. The epicentral area lies within 20 km of the southern boundary of Lassen Volcanic National Park, in a northwest striking seismic zone that extends from Lake Tahoe to the vicinity of Mount Shasta. In comparing their time history and magnitude distribution with other earthquake sequences that have occurred in regions of Cenozoic volcanism within and east of the Cascade Range and the Sierra Nevada, we find that the Lassen earthquake sequences show similar characteristics to two earthquake sequences that occurred on Basin and Range faults near Herlong, California, and Klamath Falls, Oregon. We interpret this similarity as evidence that the Lassen earthquakes were caused by Basin and Range extension and may have occurred on one or more Basin and Range faults in the Lassen region. However, the limitations of the data do not allow other possible sources, such as magmatic injection, to be ruled out. The most important implication of the Lassen earthquake sequences is that earthquakes of M 5 or greater may occur in the Lassen region, perhaps quite close to Lassen Peak or other volcanoes. The record of Holocene volcanism and fault displacements in the region indicates that earthquake sequences driven by either tectonic or magmatic processes may occur near Lassen Peak, and any significant earthquake sequence should be carefully monitored to assess its nature.

  6. Improving Estimates of Coseismic Subsidence from southern Cascadia Subduction Zone Earthquakes at northern Humboldt Bay, California

    NASA Astrophysics Data System (ADS)

    Padgett, J. S.; Engelhart, S. E.; Hemphill-Haley, E.; Kelsey, H. M.; Witter, R. C.

    2015-12-01

    Geological estimates of subsidence from past earthquakes help to constrain Cascadia subduction zone (CSZ) earthquake rupture models. To improve subsidence estimates for past earthquakes along the southern CSZ, we apply transfer function analysis on microfossils from 3 intertidal marshes in northern Humboldt Bay, California, ~60 km north of the Mendocino Triple Junction. The transfer function method uses elevation-dependent intertidal foraminiferal and diatom assemblages to reconstruct relative sea-level (RSL) change indicated by shifts in microfossil assemblages. We interpret stratigraphic evidence associated with sudden shifts in microfossils to reflect sudden RSL rise due to subsidence during past CSZ earthquakes. Laterally extensive (>5 km) and sharp mud-over-peat contacts beneath marshes at Jacoby Creek, Mad River Slough, and McDaniel Slough demonstrate widespread earthquake subsidence in northern Humboldt Bay. C-14 ages of plant macrofossils taken from above and below three contacts that correlate across all three sites, provide estimates of the times of subsidence at ~250 yr BP, ~1300 yr BP and ~1700 yr BP. Two further contacts observed at only two sites provide evidence for subsidence during possible CSZ earthquakes at ~900 yr BP and ~1100 yr BP. Our study contributes 20 AMS radiocarbon ages, of identifiable plant macrofossils, that improve estimates of the timing of past earthquakes along the southern CSZ. We anticipate that our results will provide more accurate and precise reconstructions of RSL change induced by southern CSZ earthquakes. Prior to our work, studies in northern Humboldt Bay provided subsidence estimates with vertical uncertainties >±0.5 m; too imprecise to adequately constrain earthquake rupture models. Our method, applied recently in coastal Oregon, has shown that subsidence during past CSZ earthquakes can be reconstructed with a precision of ±0.3m and substantially improves constraints on rupture models used for seismic hazard

  7. On the reported ionospheric precursor of the 1999 Hector Mine, California earthquake

    USGS Publications Warehouse

    Thomas, Jeremy N.; Love, Jeffrey J.; Komjathy, Attila; Verkhoglyadova, Olga P.; Butala, Mark; Rivera, Nicholas

    2012-01-01

    Using Global Positioning System (GPS) data from sites near the 16 Oct. 1999 Hector Mine, California earthquake, Pulinets et al. (2007) identified anomalous changes in the ionospheric total electron content (TEC) starting one week prior to the earthquake. Pulinets (2007) suggested that precursory phenomena of this type could be useful for predicting earthquakes. On the other hand, and in a separate analysis, Afraimovich et al. (2004) concluded that TEC variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake. In an investigation of these very different results, we examine TEC time series of long duration from GPS stations near and far from the epicenter of the Hector Mine earthquake, and long before and long after the earthquake. While we can reproduce the essential time series results of Pulinets et al., we find that the signal they identify as anomalous is not actually anomalous. Instead, it is just part of normal global-scale TEC variation. We conclude that the TEC anomaly reported by Pulinets et al. is unrelated to the Hector Mine earthquake.

  8. History of Modern Earthquake Hazard Mapping and Assessment in California Using a Deterministic or Scenario Approach

    NASA Astrophysics Data System (ADS)

    Mualchin, Lalliana

    2011-03-01

    Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In DSHA, seismic hazard in the event of the Maximum Credible Earthquake (MCE) magnitude from each of the known seismogenic faults within and near the state are assessed. The likely occurrence of the MCE has been assumed qualitatively by using late Quaternary and younger faults that are presumed to be seismogenic, but not when or within what time intervals MCE may occur. MCE is the largest or upper-bound potential earthquake in moment magnitude, and it supersedes and automatically considers all other possible earthquakes on that fault. That moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships, and for calculating ground motions as in neo-DSHA (Z uccolo et al., 2008). The first deterministic California earthquake hazard map was published in 1974 by the California Division of Mines and Geology (CDMG) which has been called the California Geological Survey (CGS) since 2002, using the best available fault information and ground motion attenuation relationships at that time. The California Department of Transportation (Caltrans) later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists, seismologists, and engineers for many years. Some engineers involved in the siting process of large important projects, for example, dams and nuclear power plants, continued to challenge the map(s). The second edition map was completed in 1985 incorporating more faults, improving MCE's estimation method, and using new ground motion attenuation relationships from the latest published

  9. Superficial simplicity of the 2010 El Mayorg-Cucapah earthquake of Baja California in Mexico

    USGS Publications Warehouse

    Wei, S.; Fielding, E.; Leprince, S.; Sladen, A.; Avouac, J.-P.; Helmberger, D.; Hauksson, E.; Chu, R.; Simons, M.; Hudnut, K.; Herring, T.; Briggs, R.

    2011-01-01

    The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures1-6. The fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the Mw 7.2 2010 El Mayorg-Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault. Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130 ??E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  10. One hundred years of earthquake recording at the University of California

    USGS Publications Warehouse

    Bolt, B. A.

    1987-01-01

    The best seismographs then available arrived from England in 1887 and were installed at Lick Observatory on Mt.Hamilton and at the Students Astronomical Observatory on the Berkeley campus. The first California earthquake recorded by the Lick instrument was on April 24, 1887. These seismographic stations have functioned continuously from their founding to the present day, with improvements in instruments from time to time as technology advanced. Now they are part of a sesimogrpahic network of 16 stations recording with great completeness both local and distant earthquakes

  11. A record of large earthquakes during the past two millennia on the southern Green Valley Fault, California

    USGS Publications Warehouse

    Lienkaemper, James J.; Baldwin, John N.; Turner, Robert; Sickler, Robert R.; Brown, Johnathan

    2013-01-01

    We document evidence for surface-rupturing earthquakes (events) at two trench sites on the southern Green Valley fault, California (SGVF). The 75-80-km long dextral SGVF creeps ~1-4 mm/yr. We identify stratigraphic horizons disrupted by upward-flowering shears and in-filled fissures unlikely to have formed from creep alone. The Mason Rd site exhibits four events from ~1013 CE to the Present. The Lopes Ranch site (LR, 12 km to the south) exhibits three events from 18 BCE to Present including the most recent event (MRE), 1610 ±52 yr CE (1σ) and a two-event interval (18 BCE-238 CE) isolated by a millennium of low deposition. Using Oxcal to model the timing of the 4-event earthquake sequence from radiocarbon data and the LR MRE yields a mean recurrence interval (RI or μ) of 199 ±82 yr (1σ) and ±35 yr (standard error of the mean), the first based on geologic data. The time since the most recent earthquake (open window since MRE) is 402 yr ±52 yr, well past μ~200 yr. The shape of the probability density function (pdf) of the average RI from Oxcal resembles a Brownian Passage Time (BPT) pdf (i.e., rather than normal) that permits rarer longer ruptures potentially involving the Berryessa and Hunting Creek sections of the northernmost GVF. The model coefficient of variation (cv, σ/μ) is 0.41, but a larger value (cv ~0.6) fits better when using BPT. A BPT pdf with μ of 250 yr and cv of 0.6 yields 30-yr rupture probabilities of 20-25% versus a Poisson probability of 11-17%.

  12. The effect of stress changes on time-dependent earthquake probability: an example from the Wasatch Fault Zone, Utah, USA.

    NASA Astrophysics Data System (ADS)

    Verdecchia, Alessandro; Carena, Sara; Pace, Bruno; DuRoss, Christopher

    2016-04-01

    Static and quasi-static Coulomb stress changes produced by large earthquakes can modify the probability of occurrence of subsequent events on neighbouring faults. In order to better understand and minimize the uncertainties in this kind of approach based on physical (Coulomb stress changes) and statistical (probability calculations) models, we focused our study on the Wasatch fault zone (WFZ), a well-studied active normal fault system having abundant geologic and paleoseismic data. Paleoseismic trench investigations of the WFZ indicate that at least 24 large, surface-faulting earthquakes have ruptured the fault's five central, 35-59-km long segments since ~7 ka. Our goal is to determine if the stress changes due to selected paleoevents have significantly modified the present-day probability of occurrence of large earthquakes on each of the segments. For each segment, we modeled the cumulative (coseismic + postseismic) Coulomb stress changes (∆CFScum) due to earthquakes younger than the most recent event and applied the resulting values to the time-dependent probability calculations. Results from the probability calculations predict high percentages of occurrence for the Brigham City and Salt Lake City segments, due to their long elapsed times (>1-2 kyr) when compared to the Weber, Provo, and Nephi segments (< 1 kyr). We also found that the Brigham City, Salt Lake City, and Provo segments have accumulated ∆CFScum larger than 10 bar, whereas the Weber segment has experienced a stress drop of 5 bar. Our results indicate that the ∆CFScum resulting from earthquakes postdating the youngest events on the segments significantly affect the probability calculations only for the Brigham City, Salt Lake City, and Provo segments. In particular, the probability of occurrence of a large earthquake in the next 50 years on these three segments may be underestimated if a time-independent approach, or a time-dependent approach that does not consider ∆CFS, is adopted.

  13. Stress transferred by the 1995 Mw = 6.9 Kobe, Japan, shock: Effect on aftershocks and future earthquake probabilities

    USGS Publications Warehouse

    Toda, S.; Stein, R.S.; Reasenberg, P.A.; Dieterich, J.H.; Yoshida, A.

    1998-01-01

    The Kobe earthquake struck at the edge of the densely populated Osaka-Kyoto corridor in southwest Japan. We investigate how the earthquake transferred stress to nearby faults, altering their proximity to failure and thus changing earthquake probabilities. We find that relative to the pre-Kobe seismicity, Kobe aftershocks were concentrated in regions of calculated Coulomb stress increase and less common in regions of stress decrease. We quantify this relationship by forming the spatial correlation between the seismicity rate change and the Coulomb stress change. The correlation is significant for stress changes greater than 0.2-1.0 bars (0.02-0.1 MPa), and the nonlinear dependence of seismicity rate change on stress change is compatible with a state- and rate-dependent formulation for earthquake occurrence. We extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of Kobe and calculating the change in probability caused by these stress changes. Transient effects of the stress changes are incorporated by the state-dependent constitutive relation, which amplifies the permanent stress changes during the aftershock period. Earthquake probability framed in this manner is highly time-dependent, much more so than is assumed in current practice. Because the probabilities depend on several poorly known parameters of the major faults, we estimate uncertainties of the probabilities by Monte Carlo simulation. This enables us to include uncertainties on the elapsed time since the last earthquake, the repeat time and its variability, and the period of aftershock decay. We estimate that a calculated 3-bar (0.3-MPa) stress increase on the eastern section of the Arima-Takatsuki Tectonic Line (ATTL) near Kyoto causes fivefold increase in the 30-year probability of a subsequent large earthquake near Kyoto; a 2-bar (0.2-MPa) stress decrease on the western section of the ATTL results in a reduction in probability by a factor of 140 to

  14. Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Highway Systems

    USGS Publications Warehouse

    Yashinsky, Mark

    1998-01-01

    This paper summarizes the impact of the Loma Prieta earthquake on highway systems. City streets, urban freeways, county roads, state routes, and the national highway system were all affected. There was damage to bridges, roads, tunnels, and other highway structures. The most serious damage occurred in the cities of San Francisco and Oakland, 60 miles from the fault rupture. The cost to repair and replace highways damaged by this earthquake was $2 billion. About half of this cost was to replace the Cypress Viaduct, a long, elevated double-deck expressway that had a devastating collapse which resulted in 42 deaths and 108 injuries. The earthquake also resulted in some positive changes for highway systems. Research on bridges and earthquakes began to be funded at a much higher level. Retrofit programs were started to upgrade the seismic performance of the nation's highways. The Loma Prieta earthquake changed earthquake policy and engineering practice for highway departments not only in California, but all over the world.

  15. Dynamic Models of Earthquakes and Tsunamis in the Santa Barbara Channel, California

    NASA Astrophysics Data System (ADS)

    Oglesby, David; Ryan, Kenny; Geist, Eric

    2016-04-01

    The Santa Barbara Channel and the adjacent Ventura Basin in California are the location of a number of large faults that extend offshore and could potentially produce earthquakes of magnitude greater than 7. The area is also home to hundreds of thousands of coastal residents. To properly evaluate the earthquake and tsunami hazard in this region requires the characterization of possible earthquake sources as well as the analysis of tsunami generation, propagation and inundation. Toward this end, we perform spontaneous dynamic earthquake rupture models of potential events on the Pitas Point/Lower Red Mountain faults, a linked offshore thrust fault system. Using the 3D finite element method, a realistic nonplanar fault geometry, and rate-state friction, we find that this fault system can produce an earthquake of up to magnitude 7.7, consistent with estimates from geological and paleoseismological studies. We use the final vertical ground deformation from our models as initial conditions for the generation and propagation of tsunamis to the shore, where we calculate inundation. We find that path and site effects lead to large tsunami amplitudes northward and eastward of the fault system, and in particular we find significant tsunami inundation in the low-lying cities of Ventura and Oxnard. The results illustrate the utility of dynamic earthquake modeling to produce physically plausible slip patterns and associated seafloor deformation that can be used for tsunami generation.

  16. Fluid‐driven seismicity response of the Rinconada fault near Paso Robles, California, to the 2003 M 6.5 San Simeon earthquake

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2012-01-01

    The 2003 M 6.5 San Simeon, California, earthquake caused significant damage in the city of Paso Robles and a persistent cluster of aftershocks close to Paso Robles near the Rinconada fault. Given the importance of secondary aftershock triggering in sequences of large events, a concern is whether this cluster of events could trigger another damaging earthquake near Paso Robles. An epidemic‐type aftershock sequence (ETAS) model is fit to the Rinconada seismicity, and multiple realizations indicate a 0.36% probability of at least one M≥6.0 earthquake during the next 30 years. However, this probability estimate is only as good as the projection into the future of the ETAS model. There is evidence that the seismicity may be influenced by fluid pressure changes, which cannot be forecasted using ETAS. The strongest evidence for fluids is the delay between the San Simeon mainshock and a high rate of seismicity in mid to late 2004. This delay can be explained as having been caused by a pore pressure decrease due to an undrained response to the coseismic dilatation, followed by increased pore pressure during the return to equilibrium. Seismicity migration along the fault also suggests fluid involvement, although the migration is too slow to be consistent with pore pressure diffusion. All other evidence, including focal mechanisms and b‐value, is consistent with tectonic earthquakes. This suggests a model where the role of fluid pressure changes is limited to the first seven months, while the fluid pressure equilibrates. The ETAS modeling adequately fits the events after July 2004 when the pore pressure stabilizes. The ETAS models imply that while the probability of a damaging earthquake on the Rinconada fault has approximately doubled due to the San Simeon earthquake, the absolute probability remains low.

  17. Earthquake swarms and local crustal spreading along major strike-slip faults in California

    USGS Publications Warehouse

    Weaver, C.S.; Hill, D.P.

    1978-01-01

    Earthquake swarms in California are often localized to areas within dextral offsets in the linear trend in active fault strands, suggesting a relation between earthquake swarms and local crustal spreading. Local crustal spereading is required by the geometry of dextral offsets when, as in the San Andreas system, faults have dominantly strike-slip motion with right-lateral displacement. Three clear examples of this relation occur in the Imperial Valley, Coso Hot Springs, and the Danville region, all in California. The first two of these areas are known for their Holocene volcanism and geothermal potential, which is consistent with crustal spreading and magmatic intrusion. The third example, however, shows no evidence for volcanism or geothermal activity at the surface. ?? 1978 Birkha??user Verlag.

  18. The north-northwest aftershock pattern of the June 28, 1992 Landers earthquake and the probability of large earthquakes in Indian Wells Valley

    SciTech Connect

    Roquemore, G.R. . Dept. of Geosciences); Simila, G.A. . Dept. of Geological Sciences)

    1993-04-01

    Immediately following the June 28, 1992 Landers earthquake, a strong north-northwest pattern of aftershocks and triggered earthquakes developed. The most intense pattern developed between the north end of primary rupture on the Emerson fault and southern Owens Valley. The trend of seismicity cuts through the east-west trending Garlock fault at a high angle. The Garlock fault has no apparent affect on the trend or pattern. Within the aftershock zone, south of the Garlock fault, the Calico and Blackwater faults provide the most likely pathway for the Mojave shear zone into Indian Wells and Owens Valleys. In Indian Wells Valley the seismically active Little Lake fault aligns well with the Blackwater fault to the south and the southern Owens Valley fault zone to the north. Several recent research papers suggest that Optimum Coulomb failure stress changes caused by the Landers earthquake have enhanced the probability of earthquakes within the north-northwest trending aftershock zone. This increase has greater significance when the presumed Optimum Coulomb failure stress changes caused by the 1872 Owens Valley earthquake and its affects on Indian Wells Valley are considered. Indian Wells Valley and the Coso Volcanic field may have received two significant stress increases from earthquakes of magnitude 7.5 or greater in the last 120 years. If these two earthquakes increased the shear stress of aults in the Indian Wells/Coso areas, the most likely site for the next large earthquake within the Mojave shear zone may be there. The rate of seismicity within Indian Wells Valley had increased since 1980 including a magnitude 5.0 earthquake in 1982.

  19. Earthquake and Tsunami planning, outreach and awareness in Humboldt County, California

    NASA Astrophysics Data System (ADS)

    Ozaki, V.; Nicolini, T.; Larkin, D.; Dengler, L.

    2008-12-01

    Humboldt County has the longest coastline in California and is one of the most seismically active areas of the state. It is at risk from earthquakes located on and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ), other regional fault systems, and from distant sources elsewhere in the Pacific. In 1995 the California Division of Mines and Geology published the first earthquake scenario to include both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of representatives from government agencies, tribes, service groups, academia and the private sector from the three northern coastal California counties, was formed in 1996 to coordinate and promote earthquake and tsunami hazard awareness and mitigation. The RCTWG and its member agencies have sponsored a variety of projects including education/outreach products and programs, tsunami hazard mapping, signage and siren planning, and has sponsored an Earthquake - Tsunami Education Room at the Humboldt County fair for the past eleven years. Three editions of Living on Shaky Ground an earthquake-tsunami preparedness magazine for California's North Coast, have been published since 1993 and a fourth is due to be published in fall 2008. In 2007, Humboldt County was the first region in the country to participate in a tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD and the first area in California to conduct a full-scale tsunami evacuation drill. The County has conducted numerous multi-agency, multi-discipline coordinated exercises using county-wide tsunami response plan. Two Humboldt County communities were recognized as TsunamiReady by the National Weather Service in 2007. Over 300 tsunami hazard zone signs have been posted in Humboldt County since March 2008. Six assessment surveys from 1993 to 2006 have tracked preparedness actions and personal

  20. Historigraphical analysis of the 1857 Ft. Tejon earthquake, San Andreas Fault, California: Preliminary results

    NASA Astrophysics Data System (ADS)

    Martindale, D.; Evans, J. P.

    2002-12-01

    Past historical analyses of the 1857 Forth Tejon earthquake include Townley and Allen (1939); Wood (1955) re-examined the earthquake and added some additional new material, and Agnew and Sieh (1978) published an extensive review of the previous publications and included primary sources not formerly known. Since 1978, most authors have reiterated the findings of Agnew and Sieh, with the exception of Meltzner and Wald's 1998 work that built on Sieh's foreshock research and included an extensive study of aftershocks. Approximately twenty-five years has past since the last full investigation of the event. In the last several decades, libraries and archives have continued to gather additional documents. Staff members continually inventory new and existing collections, making them accessible to researchers today. As a result, we are conducting an updated examination, with the hope of new insight regarding the 1857 Fort Tejon earthquake. We use a new approached to the topic: the research skills of a historian in collaboration with a geologist to generate quantitative data on the nature and location of ground shaking associated with the earthquake. We analyze documents from the Huntington Library, California State Historical Society, California State Library-California Room, Utah Historical Association Information Center, the Church of Jesus Christ of Latter-day Saints (LDS) Archives and Historical Department, Cal Tech Archives, the National Archives, and the Fort Tejon State Park. New facilities reviewed also include Utah State University, University of Utah, and the LDS Family History Center. Each facility not only provided formerly quoted sources, but many offered new materials. For example, previous scholars examined popular, well-known newspapers; yet, publications in smaller towns and in languages other than English, also existed. Thirty newspapers published in January 1857 were located. We find records of the event at least one year after the earthquake. One outcome

  1. The 2014 Mw 6.0 Napa Earthquake, California: Observations from Real-time GPS-enhanced Earthquake Early Warning

    NASA Astrophysics Data System (ADS)

    Johanson, I. A.; Grapenthin, R.; Allen, R. M.

    2014-12-01

    Recently, progress has been made to demonstrate feasibility and benefits of including real-time GPS (rtGPS) in earthquake early warning and rapid response systems. While most concepts have yet to be integrated into operational environments, the Berkeley Seismological Laboratory is currently running an rtGPS based finite fault inversion scheme in true real-time, which is triggered by the seismic-based ShakeAlert system and then sends updated earthquake alerts to a test receiver. The Geodetic Alarm System (G-larmS) was online and responded to the 2014 Mw6.0 South Napa earthquake in California. We review G-larmS' performance during this event and for 13 aftershocks, and we present rtGPS observations and real-time modeling results for the main shock. The first distributed slip model and a magnitude estimate of Mw5.5 were available 24 s after the event origin time, which could be reduced to 14 s after a bug fix (~8 s S-wave travel time, ~6 s data latency). The system continued to re-estimate the magnitude once every second: it increased to Mw5.9 3 s after the first alert and stabilized at Mw5.8 after 15 s. G-larmS' solutions for the subsequent small magnitude aftershocks demonstrate that Mw~6.0 is the current limit for alert updates to contribute back to the seismic-based early warning system.

  2. The Southern California Earthquake Center/Undergraduate Studies in Earthquake Information Technology (SCEC/UseIT) Internship Program

    NASA Astrophysics Data System (ADS)

    Perry, S.; Jordan, T.

    2006-12-01

    Our undergraduate research program, SCEC/UseIT, an NSF Research Experience for Undergraduates site, provides software for earthquake researchers and educators, movies for outreach, and ways to strengthen the technical career pipeline. SCEC/UseIT motivates diverse undergraduates towards science and engineering careers through team-based research in the exciting field of earthquake information technology. UseIT provides the cross-training in computer science/information technology (CS/IT) and geoscience needed to make fundamental progress in earthquake system science. Our high and increasing participation of women and minority students is crucial given the nation"s precipitous enrollment declines in CS/IT undergraduate degree programs, especially among women. UseIT also casts a "wider, farther" recruitment net that targets scholars interested in creative work but not traditionally attracted to summer science internships. Since 2002, SCEC/UseIT has challenged 79 students in three dozen majors from as many schools with difficult, real-world problems that require collaborative, interdisciplinary solutions. Interns design and engineer open-source software, creating increasingly sophisticated visualization tools (see "SCEC-VDO," session IN11), which are employed by SCEC researchers, in new curricula at the University of Southern California, and by outreach specialists who make animated movies for the public and the media. SCEC-VDO would be a valuable tool for research-oriented professional development programs.

  3. The Loma Prieta earthquake of October 17, 1989 : a brief geologic view of what caused the Loma Prieta earthquake and implications for future California earthquakes: What happened ... what is expected ... what can be done.

    USGS Publications Warehouse

    Ward, Peter L.; Page, Robert A.

    1990-01-01

    The San Andreas fault, in California, is the primary boundary between the North American plate and the Pacific plate. Land west of the fault has been moving northwestward relative to land on the east at an average rate of 2 inches per year for millions of years. This motion is not constant but occurs typically in sudden jumps during large earthquakes. This motion is relentless; therefore earthquakes in California are inevitable.

  4. New Continuous Timeseries Data at the Northern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

    Neuhauser, D. S.; Dietz, L.; Zuzlewski, S.; Kohler, W.; Gee, L.; Oppenheimer, D.; Romanowicz, B.

    2005-12-01

    The Northern California Earthquake Data Center (NCEDC) is an archive and distribution center for geophysical data for networks in northern and central California. Recent discovery of non-volcanic tremors in northern and central California has sparked user interest in access to a wider range of continuous seismic data in the region. The NCEDC has responded by expanding its archiving and distribution to all new available continuous data from northern California seismic networks (the USGS NCSN, the UC Berkeley BDSN, the Parkfield HRSN borehole network, and local USArray stations) at all available sample rates, to provide access to all recent real-time timeseries data, and to restore from tape and archive all NCSN continuous data from 2001-present. All new continuous timeseries data will also be available in near-real-time from the NCEDC via the DART (Data Available in Real Time) system, which allows users to directly download daily Telemetry MiniSEED files or to extract and retrieve the timeseries of their selection. The NCEDC will continue to create and distribute event waveform collections for all events detected by the Northern California Seismic System (NCSS), the northern California component of the California Integrated Seismic Network (CISN). All new continuous and event timeseries will be archived in daily intervals and are accessible via the same data request tools (NetDC, BREQ_FAST, EVT_FAST, FISSURES/DHI, STP) as previously archived waveform data. The NCEDC is a joint project of the UC Berkeley Seismological Laboratory and USGS Menlo Park.

  5. Earthquake-induced sediment failures on a 0.25o slope, Klamath River delta, California.

    USGS Publications Warehouse

    Field, M.E.; Gardner, J.V.; Jennings, A.E.; Edwards, B.D.

    1982-01-01

    On Nov. 8, 1980, a major earthquake (magnitude 6.5-7.2) occurred 60 km off the coast of N California. A survey of the area using high-resolution seismic-reflection and side-scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping (less than 0.25o) Klamath River delta.-from Authors

  6. Processed seismic motion records from earthquakes (1982--1993): Recorded at Scotty`s Castle, California

    SciTech Connect

    Lum, P K; Honda, K K

    1993-10-01

    The 8mm data tape contains the processed seismic data of earthquakes recorded at Scotty`s Castle, California. The seismic data were recorded by seismographs maintained by the DOE/NV in Southern Nevada. Four files were generated from each seismic recorder. They are ``Uncorrected acceleration time histories, 2. corrected acceleration, velocity and displacement time histories, 3. original recording, and 4. Fourier amplitude spectra of acceleration.

  7. DEFORMATION NEAR THE EPICENTER OF THE 1984 ROUND VALLEY, CALIFORNIA, EARTHQUAKE.

    USGS Publications Warehouse

    Gross, W.K.; Savage, J.C.

    1985-01-01

    A trilateration network extending from near Mammoth Lakes to Bishop, California, was resurveyed following the November 23, 1984, Round Valley earthquake (M//L equals 5. 8). The network had previously been surveyed in 1982. Deformation apparently associated with the Round Valley earthquake was detected as well as deformation due to the expansion of a magma chamber 8 km beneath the resurgent dome in the Long Valley caldera and right-lateral slip on the uppermost 2 km of the 1983 rupture surface in the south moat of the caldera. The deformation associated with Round Valley earthquake suggests left-lateral slip on the north-northeasterly striking vertical plane defined by the aftershock hypocenters. (Edted author abstract) Refs.

  8. New Tools for Quality Assessment of Modern Earthquake Catalogs: Examples From California and Japan.

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Wiemer, S.; Giardini, D.

    2002-12-01

    Earthquake catalogs provide a comprehensive knowledge database for studies related to seismicity, seismotectonic, earthquake physics, and hazard analysis. We introduce a set of tools and new software for improving the quality of modern catalogs of microseismicty. Surprisingly little research on detecting seismicity changes and analyzing the causes has been performed in recent years. Especially the discrimination between artificial and natural causes responsible for transients in seismicity, such as rate changes or alternations in the earthquake size distribution (b-value), often remains difficult. Thus, significant changes in reporting homogeneity are often detected only years after they occurred. We believe that our tools, used regularly and automatically in a ?real time mode?, allow addressing such problems shortly after they occurred. Based on our experience in analyzing earthquake catalogs, and building on the groundbreaking work by Habermann in the 1980?s, we propose a recipe for earthquake catalog quality assessment: 1) Decluster as a tool to homogenize the data; 2) Identify and remove blast contamination; 3) Estimate completeness as a function of space and time; 4) Assess reporting homogeneity as a function of space and time using self-consistency and, if possible, comparison with other independent data sources. During this sequence of analysis steps, we produce a series of maps that portray for a given period the magnitude of completeness, seismicity rate changes, possible shifts and stretches in the magnitude distribution and the degree of clustering. We apply our algorithms for quality assessment to data sets from California and Japan addressing the following questions: 1) Did the 1983 Coalinga earthquake change the rate of small events on the Parkfield segment of the San Andreas system? 2) Did the Kobe earthquake change the rate of earthquakes or the b-value in nearby volumes?

  9. Cruise report for A1-98-SC southern California Earthquake Hazards Project

    USGS Publications Warehouse

    Normark, William R.; Bohannon, Robert G.; Sliter, Ray; Dunhill, Gita; Scholl, David W.; Laursen, Jane; Reid, Jane A.; Holton, David

    1999-01-01

    The focus of the Southern California Earthquake Hazards project, within the Western Region Coastal and Marine Geology team (WRCMG), is to identify the landslide and earthquake hazards and related ground-deformation processes that can potentially impact the social and economic well-being of the inhabitants of the Southern California coastal region, the most populated urban corridor along the U.S. Pacific margin. The primary objective is to help mitigate the earthquake hazards for the Southern California region by improving our understanding of how deformation is distributed (spatially and temporally) in the offshore with respect to the onshore region. To meet this overall objective, we are investigating the distribution, character, and relative intensity of active (i.e., primarily Holocene) deformation within the basins and along the shelf adjacent to the most highly populated areas (see Fig. 1). In addition, the project will examine the Pliocene-Pleistocene record of how this deformation has shifted in space and time. The results of this study should improve our knowledge of shifting deformation for both the long-term (105 to several 106 yr) and short-term (<50 ky) time frames and enable us to identify actively deforming structures that may constitute current significant seismic hazards.

  10. [Engineering aspects of seismic behavior of health-care facilities: lessons from California earthquakes].

    PubMed

    Rutenberg, A

    1995-03-15

    The construction of health-care facilities is similar to that of other buildings. Yet the need to function immediately after an earthquake, the helplessness of the many patients and the high and continuous occupancy of these buildings, require that special attention be paid to their seismic performance. Here the lessons from the California experience are invaluable. In this paper the behavior of California hospitals during destructive earthquakes is briefly described. Adequate structural design and execution, and securing of nonstructural elements are required to ensure both safety of occupants, and practically uninterrupted functioning of equipment, mechanical and electrical services and other vital systems. Criteria for post-earthquake functioning are listed. In view of the hazards to Israeli hospitals, in particular those located along the Jordan Valley and the Arava, a program for the seismic evaluation of medical facilities should be initiated. This evaluation should consider the hazards from nonstructural elements, the safety of equipment and systems, and their ability to function after a severe earthquake. It should not merely concentrate on safety-related structural behavior. PMID:7750814

  11. Analysis of Earthquake Recordings Obtained from the Seafloor Earthquake Measurement System (SEMS) Instruments Deployed off the Coast of Southern California

    USGS Publications Warehouse

    Boore, D.M.; Smith, C.E.

    1999-01-01

    For more than 20 years, a program has been underway to obtain records of earthquake shaking on the seafloor at sites offshore of southern California, near oil platforms. The primary goal of the program is to obtain data that can help determine if ground motions at offshore sites are significantly different than those at onshore sites; if so, caution may be necessary in using onshore motions as the basis for the seismic design of oil platforms. We analyze data from eight earthquakes recorded at six offshore sites; these are the most important data recorded on these stations to date. Seven of the earthquakes were recorded at only one offshore station; the eighth event was recorded at two sites. The earthquakes range in magnitude from 4.7 to 6.1. Because of the scarcity of multiple recordings from any one event, most of the analysis is based on the ratio of spectra from vertical and horizontal components of motion. The results clearly show that the offshore motions have very low vertical motions compared to those from an average onshore site, particularly at short periods. Theoretical calculations find that the water layer has little effect on the horizontal components of motion but that it produces a strong spectral null on the vertical component at the resonant frequency of P waves in the water layer. The vertical-to-horizontal ratios for a few selected onshore sites underlain by relatively low shear-wave velocities are similar to the ratios from offshore sites for frequencies less than about one-half the water layer P-wave resonant frequency, suggesting that the shear-wave velocities beneath a site are more important than the water layer in determining the character of the ground motions at lower frequencies.

  12. Geophysical Investigations Along the Hayward Fault, Northern California, and Their Implications on Earthquake Hazards

    NASA Astrophysics Data System (ADS)

    Ponce, D. A.; Graymer, R. W.; Hildenbrand, T. G.; Jachens, R. C.; Simpson, R. W.

    2007-12-01

    Geophysical studies indicate that the Hayward Fault follows a pre-existing basement structure and that local geologic features play an important role in earthquake seismicity. The recent creeping trace of the Hayward Fault extends for about 90 km from San Pablo Bay in the northwest to Fremont in the southeast, and together with its northern extension, the Rodgers Creek Fault, is regarded as one of the most hazardous faults in northern California. The Hayward Fault is predominantly a right-lateral strike-slip fault that forms the western boundary of the East Bay Hills and separates Franciscan Complex rocks on the southwest from Coast Range Ophiolite and Great Valley Sequence basement rocks on the northeast. The Hayward Fault is characterized by distinct linear gravity and magnetic anomalies that correlate with changes in geology, structural trends, creep rates, and clusters of seismicity. These correlations indicate the existence of fault-zone discontinuities that probably reflect changes in mechanical properties. These fault-zone discontinuities may play a role in defining fault segments--locations where recurring seismic ruptures may tend to nucleate or terminate. Along the central part of the Hayward Fault, a prominent gravity and magnetic anomaly correlates with an exposed gabbro body, the San Leandro gabbro. Modeling of these anomalies reveals that the San Leandro gabbro is much more extensive in the subsurface than the outcrop pattern suggests, extending to a depth of about 6-8 km. The inferred extent of the San Leandro gabbro, it's geologic setting, and associated seismicity suggest that the Hayward Fault evolved from a pre-existing basement feature, similar to the ancestral Coast Range Fault. Combined modeling and relocated double-difference seismicity data indicate that the dip of the fault surface varies from near vertical in the north to about 75 degrees in the central part to about 50 degrees in the south near Fremont and ultimately connects with the

  13. Cruise report for 01-99-SC: southern California earthquake hazards project

    USGS Publications Warehouse

    Normark, William R.; Reid, Jane A.; Sliter, Ray W.; Holton, David; Gutmacher, Christina E.; Fisher, Michael A.; Childs, Jonathan R.

    1999-01-01

    The focus of the Southern California Earthquake Hazards project is to identify the landslide and earthquake hazards and related ground-deformation processes occurring in the offshore areas that have significant potential to impact the inhabitants of the Southern California coastal region. The project activity is supported through the Coastal and Marine Geology Program of the Geologic Division of the U. S. Geological Survey (USGS) and is a component of the Geologic Division's Science Strategy under Goal 1—Conduct Geologic Hazard Assessments for Mitigation Planning (Bohlen et al., 1998). The project research is specifically stated under Activity 1.1.2 of the Science Strategy: Earthquake Hazard Assessments and Loss Reduction Products in Urban Regions. This activity involves "research, seismic and geodetic monitoring, field studies, geologic mapping, and analyses needed to provide seismic hazard assessments of major urban centers in earthquake-prone regions including adjoining coastal and offshore areas." The southern California urban areas, which form the most populated urban corridor along the U.S. Pacific margin, are among a few specifically designated for special emphasis under the Division's science strategy (Bohlen et al., 1998). The primary objective of the project is to help mitigate the earthquake hazards for the Southern California region by improving our understanding of how deformation is distributed (spatially and temporally) in the offshore with respect to the onshore region. To meet this objective, we are conducting field investigations to observe the distribution, character, and relative intensity of active (i.e., primarily Holocene) deformation within the basins and along the shelf adjacent to the most highly populated areas (Fig. 1). In addition, acoustic imaging should help determine the subsurface dimensions of the faults and identify the size and frequency of submarine landslides, both of which are necessary for evaluating the potential for

  14. Slip budget and potential for a M7 earthquake in central California

    NASA Astrophysics Data System (ADS)

    Harris, Ruth A.; Archuleta, Ralph J.

    1988-10-01

    The slip rate budget of the San Andreas fault (SAF) in central California, which is approximately 33 mm/yr, is accounted for by a change in the slip release mechanism along the fault. In the NW section of the fault, between Bear Valley and Monarch Peak, creep apparently accounts for the slip budget with the seismicity contributing negligibly. The section at Parkfield marks the transition from a creeping to a locked fault trace. Since the M8 1857 earthquake five M6 earthquakes have occurred but have not completely accounted for the slip budget. Southeast of Parkfield, the SAF has been locked since 1857. From Cholame to Bitterwater Valley this section now lags the deep slip by the amount of slip released in 1857; consequently faulting in this section could occur at the time of the next Parkfield earthquake. If this earthquake releases the slip deficit accumulated in the transition zone and in the locked zone, the earthquake will have a moment-magnitude M7.2.

  15. Moderate, strong and strongest earthquake-prone areas in the Caucasus, California and the Andes

    NASA Astrophysics Data System (ADS)

    Dzeboev, Boris; Gvishiani, Alexei

    2016-04-01

    We present this study on recognition of areas of possible occurrence of strong earthquakes. The study deals with the earthquake-prone areas in three regions with different geological and tectonic structures located in different parts of the world. The authors created a new method (FCAZ - Fuzzy Clustering and Zoning) for recognition of highly seismic areas, where epicenters of earthquakes with magnitude M≥M0 can occur. The magnitude threshold M0 depends on the seismic activity of the region. The objects of clustering are earthquake epicenters. The new method allows us to implement uniformly necessary clustering of the recognition objects respectively for moderate, strong and strongest events. Suggested approach consists of two steps: clustering of known earthquake epicenters by the original DPS (Discrete Perfect Sets) algorithm and delineating highly seismic zones around the recognized clusters by another original E2XT algorithm. By means of this method we detected the areas of possible occurrence of the epicenters of strong earthquakes in the Caucasus (M≥5), in California (M≥6.5) and in the mountain belt of the Andes (M≥7.75). The latter case relates to the possible areas of natural disaster occurence. Reliability of the results is confirmed by numerous control experiments, including individual and complete seismic history. Two strongest recent Chilean earthquakes occurred in 2014 and 2015 after the moment the results were published. Their epicenters belong to the zone recognized as high seismically hazardous. It is a strong independent argument which confirms the reliability of the results. The presented results integrate most recent outcomes of more than 40 years of research in pattern recognition and systems analysis for seismic zoning implemented in Russian Academy of Science. This research is supported by the Russian Science Foundation (project № 15-17-30020).

  16. The Earthquake Cycle on the San Andreas Fault System in northern California

    NASA Astrophysics Data System (ADS)

    Yikilmaz, M. B.; Turcotte, D. L.; Beketova, O.; Kellogg, L. H.; Rundle, J. B.

    2012-12-01

    An important aspect of the tectonics in northern California is the northward migration of the triple junction across the region which gave birth to the San Andreas transform fault about 28 Myrs ago. The triple junction has formed by the subduction of a spreading ridge that once bounded the Farallon and the Pacific plates. A "slab window" has also been formed during this subduction event. Due to the high heat flow caused by this slab window, a soft zone of deformation with a width of ~100 km has been generated. This deformation zone is bounded on the west by the near rigid Pacific Plate and on the east by the near rigid Sierra-Nevada Central Valley Plate. Continuous and campaign GPS measurements indicate a near-uniform shear strain in this zone of deformation. We propose a hypothesis for the deformation pattern associated with great earthquakes and the linear strain field discussed above. We separate the earthquake cycle into three parts, beginning with the great 1906 earthquake on the San Andreas Fault, these are: 1) The coseismic behavior associated with the great earthquake. We take the slip to be 4 m and the associated stress drop extends some 15 km on either side of the fault. 2) Stress relaxation following the earthquake. This relaxation results in a near uniform state of stress across the zone of deformation and a reloading of the San Andreas Fault. 3)Uniform shear stress loading until the next great earthquake occurs in agreement with the GPS observations. We attribute this near uniform shear to fluid-like behavior beneath the brittle upper lithosphere in which earthquakes occur.

  17. Calculation of the Rate of M>6.5 Earthquakes for California and Adjacent Portions of Nevada and Mexico

    USGS Publications Warehouse

    Frankel, Arthur; Mueller, Charles

    2008-01-01

    One of the key issues in the development of an earthquake recurrence model for California and adjacent portions of Nevada and Mexico is the comparison of the predicted rates of earthquakes with the observed rates. Therefore, it is important to make an accurate determination of the observed rate of M>6.5 earthquakes in California and the adjacent region. We have developed a procedure to calculate observed earthquake rates from an earthquake catalog, accounting for magnitude uncertainty and magnitude rounding. We present a Bayesian method that corrects for the effect of the magnitude uncertainty in calculating the observed rates. Our recommended determination of the observed rate of M>6.5 in this region is 0.246 ? 0.085 (for two sigma) per year, although this rate is likely to be underestimated because of catalog incompleteness and this uncertainty estimate does not include all sources of uncertainty.

  18. Surface fault slip associated with the 2004 Parkfield, California, earthquake

    USGS Publications Warehouse

    Rymer, M.J.; Tinsley, J. C., III; Treiman, J.A.; Arrowsmith, J.R.; Ciahan, K.B.; Rosinski, A.M.; Bryant, W.A.; Snyder, H.A.; Fuis, G.S.; Toke, N.A.; Bawden, G.W.

    2006-01-01

    Surface fracturing occurred along the San Andreas fault, the subparallel Southwest Fracture Zone, and six secondary faults in association with the 28 September 2004 (M 6.0) Parkfield earthquake. Fractures formed discontinuous breaks along a 32-km-long stretch of the San Andreas fault. Sense of slip was right lateral; only locally was there a minor (1-11 mm) vertical component of slip. Right-lateral slip in the first few weeks after the event, early in its afterslip period, ranged from 1 to 44 mm. Our observations in the weeks following the earthquake indicated that the highest slip values are in the Middle Mountain area, northwest of the mainshock epicenter (creepmeter measurements indicate a similar distribution of slip). Surface slip along the San Andreas fault developed soon after the mainshock; field checks in the area near Parkfield and about 5 km to the southeast indicated that surface slip developed more than 1 hr but generally less than 1 day after the event. Slip along the Southwest Fracture Zone developed coseismically and extended about 8 km. Sense of slip was right lateral; locally there was a minor to moderate (1-29 mm) vertical component of slip. Right-lateral slip ranged from 1 to 41 mm. Surface slip along secondary faults was right lateral; the right-lateral component of slip ranged from 3 to 5 mm. Surface slip in the 1966 and 2004 events occurred along both the San Andreas fault and the Southwest Fracture Zone. In 1966 the length of ground breakage along the San Andreas fault extended 5 km longer than that mapped in 2004. In contrast, the length of ground breakage along the Southwest Fracture Zone was the same in both events, yet the surface fractures were more continuous in 2004. Surface slip on secondary faults in 2004 indicated previously unmapped structural connections between the San Andreas fault and the Southwest Fracture Zone, further revealing aspects of the structural setting and fault interactions in the Parkfield area.

  19. Real time test of the long-range aftershock algorithm as a tool for mid-term earthquake prediction in Southern California

    NASA Astrophysics Data System (ADS)

    Prozorov, A. G.; Schreider, S. Yu.

    1990-04-01

    Result of the algorithm of earthquake prediction, published in 1982, is examined in this paper. The algorithm is based on the hypothesis of long-range interaction between strong and moderate earthquakes in a region. It has been applied to the prediction of earthquakes with M≥6.4 in Southern California for the time interval 1932 1979. The retrospective results were as follows: 9 out of 10 strong earthquakes were predicted with average spatial accuracy of 58 km and average delay time (the time interval between a strong earthquake and its best precursor) 9.4 years varying from 0.8 to 27.9 years. During the time interval following the period studied in that publication, namely in 1980 1988, four earthquakes occurred in the region which had a magnitude of M≥6.4 at least in one of the catalogs: Caltech or NOAA. Three earthquakes—Coalinga of May, 1983, Chalfant Valley of July, 1985 and Superstition Hills of November, 1987—were successfully predicted by the published algorithm. The missed event is a couple of two Mammoth Lake earthquakes of May, 1980 which we consider as one event due to their time-space closeness. This event occurred near the northern boundary of the region, and it also would have been predicted if we had moved the northern boundary from 38°N to the 39°N; the precision of the prediction in this case would be 30 km. The average area declared by the algorithm as the area of increased probability of strong earthquake, e.g., the area within 111-km distance of all long-range aftershocks currently present on the map of the region during 1980 1988 is equal to 47% of the total area of the region if the latter is measured in accordance with the density distribution of earthquakes in California, approximated by the catalog of earthquakes with M≥5. In geometrical terms it is approximately equal to 17% of the total area. Thus the result of the real time test shows a 1.6 times increase of the occurrence of C-events in the alarmed area relative to the

  20. Seismic velocity structure and earthquake relocation for the magmatic system beneath Long Valley Caldera, eastern California

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    2015-04-01

    A new three-dimensional (3-D) seismic velocity model and high-precision location catalog for earthquakes between 1984 and 2014 are presented for Long Valley Caldera and its adjacent fault zones in eastern California. The simul2000 tomography algorithm is applied to derive the 3-D Vp and Vp/Vs models using first-arrivals of 1004 composite earthquakes obtained from the original seismic data at the Northern California Earthquake Data Center. The resulting Vp model reflects geological structures and agrees with previous local tomographic studies. The simultaneously resolved Vp/Vs model is a major contribution of this study providing an important complement to the Vp model for the interpretation of structural heterogeneities and physical properties in the study area. The caldera is dominated by low Vp anomalies at shallow depths due to postcaldera fill. High Vp and low Vp/Vs values are resolved from the surface to ~ 3.4 km depth beneath the center of the caldera, corresponding to the structural uplift of the Resurgent Dome. An aseismic body with low Vp and high Vp/Vs anomalies at 4.2-6.2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on Vp models only and the inflation source locations based on geodetic modeling. The Sierran crystalline rocks outside the caldera are generally characterized with high Vp and low Vp/Vs values. The newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high-precision earthquake catalog based on similar-event cluster analysis and waveform cross-correlation data. The fine-scale velocity structure and precise earthquake relocations are useful for investigating magma sources, seismicity and stress interaction and other seismological studies in Long Valley.

  1. Web Services and Other Enhancements at the Northern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

    Neuhauser, D. S.; Zuzlewski, S.; Allen, R. M.

    2012-12-01

    The Northern California Earthquake Data Center (NCEDC) provides data archive and distribution services for seismological and geophysical data sets that encompass northern California. The NCEDC is enhancing its ability to deliver rapid information through Web Services. NCEDC Web Services use well-established web server and client protocols and REST software architecture to allow users to easily make queries using web browsers or simple program interfaces and to receive the requested data in real-time rather than through batch or email-based requests. Data are returned to the user in the appropriate format such as XML, RESP, or MiniSEED depending on the service, and are compatible with the equivalent IRIS DMC web services. The NCEDC is currently providing the following Web Services: (1) Station inventory and channel response information delivered in StationXML format, (2) Channel response information delivered in RESP format, (3) Time series availability delivered in text and XML formats, (4) Single channel and bulk data request delivered in MiniSEED format. The NCEDC is also developing a rich Earthquake Catalog Web Service to allow users to query earthquake catalogs based on selection parameters such as time, location or geographic region, magnitude, depth, azimuthal gap, and rms. It will return (in QuakeML format) user-specified results that can include simple earthquake parameters, as well as observations such as phase arrivals, codas, amplitudes, and computed parameters such as first motion mechanisms, moment tensors, and rupture length. The NCEDC will work with both IRIS and the International Federation of Digital Seismograph Networks (FDSN) to define a uniform set of web service specifications that can be implemented by multiple data centers to provide users with a common data interface across data centers. The NCEDC now hosts earthquake catalogs and waveforms from the US Department of Energy (DOE) Enhanced Geothermal Systems (EGS) monitoring networks. These

  2. Earthquake Education and Public Information Centers: A Collaboration Between the Earthquake Country Alliance and Free-Choice Learning Institutions in California

    NASA Astrophysics Data System (ADS)

    Degroot, R. M.; Springer, K.; Brooks, C. J.; Schuman, L.; Dalton, D.; Benthien, M. L.

    2009-12-01

    In 1999 the Southern California Earthquake Center initiated an effort to expand its reach to multiple target audiences through the development of an interpretive trail on the San Andreas fault at Wallace Creek and an earthquake exhibit at Fingerprints Youth Museum in Hemet. These projects and involvement with the San Bernardino County Museum in Redlands beginning in 2007 led to the creation of Earthquake Education and Public Information Centers (EPIcenters) in 2008. The impetus for the development of the network was to broaden participation in The Great Southern California ShakeOut. In 2009 it has grown to be more comprehensive in its scope including its evolution into a statewide network. EPIcenters constitute a variety of free-choice learning institutions, representing museums, science centers, libraries, universities, parks, and other places visited by a variety of audiences including families, seniors, and school groups. They share a commitment to demonstrating and encouraging earthquake preparedness. EPIcenters coordinate Earthquake Country Alliance activities in their county or region, lead presentations or organize events in their communities, or in other ways demonstrate leadership in earthquake education and risk reduction. The San Bernardino County Museum (Southern California) and The Tech Museum of Innovation (Northern California) serve as EPIcenter regional coordinating institutions. They interact with over thirty institutional partners who have implemented a variety of activities from displays and talks to earthquake exhibitions. While many activities are focused on the time leading up to and just after the ShakeOut, most EPIcenter members conduct activities year round. Network members at Kidspace Museum in Pasadena and San Diego Natural History Museum have formed EPIcenter focus groups on early childhood education and safety and security. This presentation highlights the development of the EPIcenter network, synergistic activities resulting from this

  3. The 2014 Mw 6.0 Napa earthquake, California: Observations from real-time GPS-enhanced earthquake early warning

    NASA Astrophysics Data System (ADS)

    Grapenthin, Ronni; Johanson, Ingrid; Allen, Richard M.

    2014-12-01

    Recently, progress has been made to demonstrate feasibility and benefits of including real-time GPS (rtGPS) in earthquake early warning and rapid response systems. Most concepts, however, have yet to be integrated into operational environments. The Berkeley Seismological Laboratory runs an rtGPS-based finite fault inversion scheme in real time. This system (G-larmS) detected the 2014 Mw 6.0 South Napa earthquake in California. We review G-larmS' performance during this event and 13 aftershocks and present rtGPS observations and real-time modeling results for the main shock. The first distributed slip model and magnitude estimates were available 24s after the event origin time, which, after optimizations, was reduced to 14s (≈8s S wave travel time, ≈6s data latency). G-larmS' solutions for the aftershocks (that had no measurable surface displacements) demonstrate that, in combination with the seismic early warning magnitude, Mw 6.0 is our current resolution limit.

  4. Rupture process of four medium-sized earthquakes that occurred in the Gulf of California

    NASA Astrophysics Data System (ADS)

    RodríGuez-Lozoya, HéCtor E.; Quintanar, Luis; Ortega, Roberto; Rebollar, Cecilio J.; Yagi, Yuji

    2008-10-01

    Four medium-sized earthquakes (Mw Global CMT project 5.5, 5.6, 5.9, 6.3; hereinafter named Topolobampo, Angel de la Guarda, San Lorenzo, and Loreto earthquakes, respectively) located in the Gulf of California Extensional Province were studied to obtain their kinematic rupture processes. A network of broadband seismic stations located around the Gulf of California recorded the events (Network of Autonomously Recording Seismographs-Baja and Red Sísmica de Banda Ancha). Inversion of the seismic moment tensor and body waveform modeling were used to obtain the fault geometry and slip distribution on the fault plane, respectively. From these analyses, we obtained source depths of the order of 5.5 ± 0.5 km. We found also that the source rupture processes of the Topolobampo and Angel de la Guarda events have simple moment rate functions and source time durations of 5.0 ± 1.2 and 4.2 ± 1.2 s, respectively. The Topolobampo event was a right-lateral strike-slip event, and Angel de la Guarda was a normal event. The San Lorenzo and Loreto shocks show a rather complex rupture, with source time durations of 7.5 ± 1.2 and 9.0 ± 1.2 s, respectively. For these earthquakes, we tested the resolution of numerical results, performing an extra inversion with smoother waveforms. The new inversions do not show the separated patches of slip, as in the first analysis, but the slip distribution has an elongated shape not characteristic of simple events. We cannot therefore conclude rupture propagation for the San Lorenzo event, although the extent of the patch for the Loreto earthquake agrees with aftershock locations. Estimates of source time durations for these earthquakes are at the upper limit of the values found for earthquakes elsewhere. Directions of P axes are in the same order of magnitude as the maximum horizontal stress obtained for the so-called Gulf of California stress province from borehole elongations, focal plane solutions, and fault slip data.

  5. Impact of a Large San Andreas Fault Earthquake on Tall Buildings in Southern California

    NASA Astrophysics Data System (ADS)

    Krishnan, S.; Ji, C.; Komatitsch, D.; Tromp, J.

    2004-12-01

    In 1857, an earthquake of magnitude 7.9 occurred on the San Andreas fault, starting at Parkfield and rupturing in a southeasterly direction for more than 300~km. Such a unilateral rupture produces significant directivity toward the San Fernando and Los Angeles basins. The strong shaking in the basins due to this earthquake would have had a significant long-period content (2--8~s). If such motions were to happen today, they could have a serious impact on tall buildings in Southern California. In order to study the effects of large San Andreas fault earthquakes on tall buildings in Southern California, we use the finite source of the magnitude 7.9 2001 Denali fault earthquake in Alaska and map it onto the San Andreas fault with the rupture originating at Parkfield and proceeding southward over a distance of 290~km. Using the SPECFEM3D spectral element seismic wave propagation code, we simulate a Denali-like earthquake on the San Andreas fault and compute ground motions at sites located on a grid with a 2.5--5.0~km spacing in the greater Southern California region. We subsequently analyze 3D structural models of an existing tall steel building designed in 1984 as well as one designed according to the current building code (Uniform Building Code, 1997) subjected to the computed ground motion. We use a sophisticated nonlinear building analysis program, FRAME3D, that has the ability to simulate damage in buildings due to three-component ground motion. We summarize the performance of these structural models on contour maps of carefully selected structural performance indices. This study could benefit the city in laying out emergency response strategies in the event of an earthquake on the San Andreas fault, in undertaking appropriate retrofit measures for tall buildings, and in formulating zoning regulations for new construction. In addition, the study would provide risk data associated with existing and new construction to insurance companies, real estate developers, and

  6. The Redwood Coast Tsunami Work Group: Promoting Earthquake and Tsunami Resilience on California's North Coast

    NASA Astrophysics Data System (ADS)

    Dengler, L. A.; Henderson, C.; Larkin, D.; Nicolini, T.; Ozaki, V.

    2014-12-01

    In historic times, Northern California has suffered the greatest losses from tsunamis in the U.S. contiguous 48 states. 39 tsunamis have been recorded in the region since 1933, including five that caused damage. This paper describes the Redwood Coast Tsunami Work Group (RCTWG), an organization formed in 1996 to address the tsunami threat from both near and far sources. It includes representatives from government agencies, public, private and volunteer organizations, academic institutions, and individuals interested in working to reduce tsunami risk. The geographic isolation and absence of scientific agencies such as the USGS and CGS in the region, and relatively frequent occurrence of both earthquakes and tsunami events has created a unique role for the RCTWG, with activities ranging from basic research to policy and education and outreach programs. Regional interest in tsunami issues began in the early 1990s when there was relatively little interest in tsunamis elsewhere in the state. As a result, the group pioneered tsunami messaging and outreach programs. Beginning in 2008, the RCTWG has partnered with the National Weather Service and the California Office of Emergency Services in conducting the annual "live code" tsunami communications tests, the only area outside of Alaska to do so. In 2009, the RCTWG joined with the Southern California Earthquake Alliance and the Bay Area Earthquake Alliance to form the Earthquake Country Alliance to promote a coordinated and consistent approach to both earthquake and tsunami preparedness throughout the state. The RCTWG has produced and promoted a variety of preparedness projects including hazard mapping and sign placement, an annual "Earthquake - Tsunami Room" at County Fairs, public service announcements and print material, assisting in TsunamiReady community recognition, and facilitating numerous multi-agency, multidiscipline coordinated exercises, and community evacuation drills. Nine assessment surveys from 1993 to 2013

  7. Earthquake.

    PubMed

    Cowen, A R; Denney, J P

    1994-04-01

    On January 25, 1 week after the most devastating earthquake in Los Angeles history, the Southern California Hospital Council released the following status report: 928 patients evacuated from damaged hospitals. 805 beds available (136 critical, 669 noncritical). 7,757 patients treated/released from EDs. 1,496 patients treated/admitted to hospitals. 61 dead. 9,309 casualties. Where do we go from here? We are still waiting for the "big one." We'll do our best to be ready when Mother Nature shakes, rattles and rolls. The efforts of Los Angeles City Fire Chief Donald O. Manning cannot be overstated. He maintained department command of this major disaster and is directly responsible for implementing the fire department's Disaster Preparedness Division in 1987. Through the chief's leadership and ability to forecast consequences, the city of Los Angeles was better prepared than ever to cope with this horrendous earthquake. We also pay tribute to the men and women who are out there each day, where "the rubber meets the road." PMID:10133439

  8. Credible occurrence probabilities for extreme geophysical events: earthquakes, volcanic eruptions, magnetic storms

    USGS Publications Warehouse

    Love, Jeffrey J.

    2012-01-01

    Statistical analysis is made of rare, extreme geophysical events recorded in historical data -- counting the number of events $k$ with sizes that exceed chosen thresholds during specific durations of time $\\tau$. Under transformations that stabilize data and model-parameter variances, the most likely Poisson-event occurrence rate, $k/\\tau$, applies for frequentist inference and, also, for Bayesian inference with a Jeffreys prior that ensures posterior invariance under changes of variables. Frequentist confidence intervals and Bayesian (Jeffreys) credibility intervals are approximately the same and easy to calculate: $(1/\\tau)[(\\sqrt{k} - z/2)^{2},(\\sqrt{k} + z/2)^{2}]$, where $z$ is a parameter that specifies the width, $z=1$ ($z=2$) corresponding to $1\\sigma$, $68.3\\%$ ($2\\sigma$, $95.4\\%$). If only a few events have been observed, as is usually the case for extreme events, then these "error-bar" intervals might be considered to be relatively wide. From historical records, we estimate most likely long-term occurrence rates, 10-yr occurrence probabilities, and intervals of frequentist confidence and Bayesian credibility for large earthquakes, explosive volcanic eruptions, and magnetic storms.

  9. Credible occurrence probabilities for extreme geophysical events: Earthquakes, volcanic eruptions, magnetic storms

    NASA Astrophysics Data System (ADS)

    Love, Jeffrey J.

    2012-05-01

    Statistical analysis is made of rare, extreme geophysical events recorded in historical data - counting the number of events k with sizes that exceed chosen thresholds during specific durations of time τ. Under transformations that stabilize data and model-parameter variances, the most likely Poisson-event occurrence rate, k/τ, applies for frequentist inference and, also, for Bayesian inference with a Jeffreys prior that ensures posterior invariance under changes of variables. Frequentist confidence intervals and Bayesian (Jeffreys) credibility intervals are approximately the same and easy to calculate: (1/τ)(k-z/2)2,(k+z/2)2, where z is a parameter that specifies the width, z = 1 (z = 2) corresponding to 1σ, 68.3% (2σ, 95.4%). If only a few events have been observed, as is usually the case for extreme events, then these “error-bar” intervals might be considered to be relatively wide. From historical records, we estimate most likely long-term occurrence rates, 10-yr occurrence probabilities, and intervals of frequentist confidence and Bayesian credibility for large earthquakes, explosive volcanic eruptions, and magnetic storms.

  10. Timing and slip for prehistoric earthquakes on the Superstition Mountain Fault, Imperial Valley, southern California

    NASA Astrophysics Data System (ADS)

    Gurrola, Larry D.; Rockwell, Thomas K.

    1996-03-01

    Trenches excavated across the Superstition Mountain fault in the Imperial Valley, California, have exposed evidence for four prehistorical earthquakes preserved in displaced lacustrine stratigraphy associated with ancient Lake Cahuilla. The presence of shoreline peat accumulations along with abundant detrital charcoal allows for high-precision age determination of some stratigraphic units, thereby providing constraints on the timing of three of the paleoearthquakes. These three events occurred within a 480- to 820-year interval during the past 1200 years. The most recent earthquake (event 1) occurred during a fluvial phase of deposition between A.D. 1440-1637, immediately prior to the inundation of the Cahuilla basin at about A.D. 1480 and 1660. A channel margin was offset 2.2 +0.4/-0.15 m in this rupture, suggesting an earthquake with a magnitude ≥7. The penultimate event (event 2) also occurred during fluvial deposition after A.D. 1280 but before another lakestand at A.D. 1440-1640. Lateral slip could not be resolved for event 2. However, based on juxtaposition of dissimilar units and the amount of deformation produced by this event, it is presumed that this was also a large earthquake. The timing of event 3 is constrained to have occurred between about A.D. 820 and 1280. This event is represented by several fractures and small displacements that rupture up to a distinct stratigraphic level or event horizon. Slip was not resolved for this event. Finally, the timing of event 4 is very poorly constrained to between A.D. 964 and 4670 B.C. Undoubtedly, many events may have occurred during this period. Notably, the past three earthquakes occurred within a period of less than 820 years, and it has been over 350 years since the last earthquake.

  11. Broadband records of earthquakes in deep gold mines and a comparison with results from SAFOD, California

    USGS Publications Warehouse

    McGarr, A.; Boettcher, M.; Fletcher, Joe B.; Sell, R.; Johnston, M.J.S.; Durrheim, R.; Spottiswoode, S.; Milev, A.

    2009-01-01

    For one week during September 2007, we deployed a temporary network of field recorders and accelerometers at four sites within two deep, seismically active mines. The ground-motion data, recorded at 200 samples/sec, are well suited to determining source and ground-motion parameters for the mining-induced earthquakes within and adjacent to our network. Four earthquakes with magnitudes close to 2 were recorded with high signal/noise at all four sites. Analysis of seismic moments and peak velocities, in conjunction with the results of laboratory stick-slip friction experiments, were used to estimate source processes that are key to understanding source physics and to assessing underground seismic hazard. The maximum displacements on the rupture surfaces can be estimated from the parameter Rv, where v is the peak ground velocity at a given recording site, and R is the hypocentral distance. For each earthquake, the maximum slip and seismic moment can be combined with results from laboratory friction experiments to estimate the maximum slip rate within the rupture zone. Analysis of the four M 2 earthquakes recorded during our deployment and one of special interest recorded by the in-mine seismic network in 2004 revealed maximum slips ranging from 4 to 27 mm and maximum slip rates from 1.1 to 6:3 m=sec. Applying the same analyses to an M 2.1 earthquake within a cluster of repeating earthquakes near the San Andreas Fault Observatory at Depth site, California, yielded similar results for maximum slip and slip rate, 14 mm and 4:0 m=sec.

  12. Earthquake Interactions at Different Scales: an Example from Eastern California and Western Nevada, USA.

    NASA Astrophysics Data System (ADS)

    Verdecchia, A.; Carena, S.

    2015-12-01

    Earthquakes in diffuse plate boundaries occur in spatially and temporally complex patterns. The region east of the Sierra Nevada that encompasses the northern Eastern California Shear Zone (ECSZ), Walker Lane (WL), and the westernmost part of the Basin and Range province (B&R) is such a kind of plate boundary. In order to better understand the relationship between moderate-to major earthquakes in this area, we modeled the evolution of coseismic, postseismic and interseismic Coulomb stress changes (∆CFS) in this region at two different spatio-temporal scales. In the first example we examined seven historical and instrumental Mw ≥ 6 earthquakes that struck the region around Owens Valley (northern ECSZ) in the last 150 years. In the second example we expanded our study area to all of the northern ECSZ, WL and western B&R, examining seventeen paleoseismological and historical major surface-rupturing earthquakes (Mw ≥ 6.5) that occurred in the last 1400 years. We show that in both cases the majority of the studied events (100% in the first case and 80% in the second) are located in areas of combined coseismic and postseismic positive ∆CFS. This relationship is robust, as shown by control tests with random earthquake sequences. We also show that the White Mountain fault has accumulated up to 30 bars of total ∆CFS (coseismic + postseismic + interseismic) in the last 150 years, and the Hunter Mountain, Fish Lake Valley, Black Mountain, and Pyramid Lake faults have accumulated 40, 45, 54 and 37 bars respectively in the last 1400 years. Such values are comparable to the average stress drop in a major earthquake, and all these faults may be therefore close to failure.

  13. Premonitory patterns of seismicity months before a large earthquake: Five case histories in Southern California

    PubMed Central

    Keilis-Borok, V. I.; Shebalin, P. N.; Zaliapin, I. V.

    2002-01-01

    This article explores the problem of short-term earthquake prediction based on spatio-temporal variations of seismicity. Previous approaches to this problem have used precursory seismicity patterns that precede large earthquakes with “intermediate” lead times of years. Examples include increases of earthquake correlation range and increases of seismic activity. Here, we look for a renormalization of these patterns that would reduce the predictive lead time from years to months. We demonstrate a combination of renormalized patterns that preceded within 1–7 months five large (M ≥ 6.4) strike-slip earthquakes in southeastern California since 1960. An algorithm for short-term prediction is formulated. The algorithm is self-adapting to the level of seismicity: it can be transferred without readaptation from earthquake to earthquake and from area to area. Exhaustive retrospective tests show that the algorithm is stable to variations of its adjustable elements. This finding encourages further tests in other regions. The final test, as always, should be advance prediction. The suggested algorithm has a simple qualitative interpretation in terms of deformations around a soon-to-break fault: the blocks surrounding that fault began to move as a whole. A more general interpretation comes from the phenomenon of self-similarity since our premonitory patterns retain their predictive power after renormalization to smaller spatial and temporal scales. The suggested algorithm is designed to provide a short-term approximation to an intermediate-term prediction. It remains unclear whether it could be used independently. It seems worthwhile to explore similar renormalizations for other premonitory seismicity patterns. PMID:12482945

  14. Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake

    SciTech Connect

    Johnson, A.M.; Cruikshank, K.M. |; Fleming, R.W.

    1993-12-31

    Surface rupturing during the 28 June 1992, Landers, California earthquake, east of Los Angeles, accommodated right-lateral offsets up to about 6 m along segments of distinct, en echelon fault zones with a total length of about 80 km. The offsets were accommodated generally not by faults -- distinct slip surfaces -- but rather by shear zones, tabular bands of localized shearing. In long, straight stretches of fault zones at Landers the rupture is characterized by telescoping of shear zones and intensification of shearing: broad shear zones of mild shearing, containing narrow shear zones of more intense shearing, containing even-narrower shear zones of very intense shearing, which may contain a fault. Thus the ground ruptured across broad belts of shearing with subparallel walls, oriented NW. Each broad belt consists of a broad zone of mild shearing, extending across its entire width (50 to 200 m), and much narrower (a few m wide) shear zones that accommodate most of the offset of the belt and are portrayed by en echelon tension cracks. In response to right-lateral shearing, the slices of ground bounded by the tension cracks rotated in a clockwise sense, producing left lateral shearing, and the slices were forced against the walls of the shear zone, producing thrusting. Even narrower shear zones formed within the narrow shear zones, and some of these were faults. Although the narrower shear zones probably are indicators to right-lateral fault segments at depth, the surface rupturing during the earthquake is characterized not by faulting, but by zones of shearing at various scales. Furthermore, understanding of the formation of the shear zones may be critical to understanding of earthquake faulting because, where faulting is associated with the formation of a shear zone, the faulting occurs late in the development of the shear zone. The faulting occurs after a shear zone or a belt of shear zones forms.

  15. Products and Services Available from the Southern California Earthquake Data Center (SCEDC) and the Southern California Seismic Network (SCSN)

    NASA Astrophysics Data System (ADS)

    Yu, E.; Bhaskaran, A.; Chen, S.; Chowdhury, F. R.; Meisenhelter, S.; Hutton, K.; Given, D.; Hauksson, E.; Clayton, R. W.

    2010-12-01

    Currently the SCEDC archives continuous and triggered data from nearly 5000 data channels from 425 SCSN recorded stations, processing and archiving an average of 12,000 earthquakes each year. The SCEDC provides public access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP and DHI. This poster will describe the most significant developments at the SCEDC in the past year. Updated hardware: ● The SCEDC has more than doubled its waveform file storage capacity by migrating to 2 TB disks. New data holdings: ● Waveform data: Beginning Jan 1, 2010 the SCEDC began continuously archiving all high-sample-rate strong-motion channels. All seismic channels recorded by SCSN are now continuously archived and available at SCEDC. ● Portable data from El Mayor Cucapah 7.2 sequence: Seismic waveforms from portable stations installed by researchers (contributed by Elizabeth Cochran, Jamie Steidl, and Octavio Lazaro-Mancilla) have been added to the archive and are accessible through STP either as continuous data or associated with events in the SCEDC earthquake catalog. This additional data will help SCSN analysts and researchers improve event locations from the sequence. ● Real time GPS solutions from El Mayor Cucapah 7.2 event: Three component 1Hz seismograms of California Real Time Network (CRTN) GPS stations, from the April 4, 2010, magnitude 7.2 El Mayor-Cucapah earthquake are available in SAC format at the SCEDC. These time series were created by Brendan Crowell, Yehuda Bock, the project PI, and Mindy Squibb at SOPAC using data from the CRTN. The El Mayor-Cucapah earthquake demonstrated definitively the power of real-time high-rate GPS data: they measure dynamic displacements directly, they do not clip and they are also able to detect the permanent (coseismic) surface deformation. ● Triggered data from the Quake Catcher Network (QCN) and Community Seismic Network (CSN): The SCEDC in

  16. Investigation of temporal variations in stress orientations before and after four major earthquakes in California

    NASA Astrophysics Data System (ADS)

    Provost, Ann-Sophie; Houston, Heidi

    2003-10-01

    Orientations of the principal stresses before and after four major earthquakes in the greater San Francisco Bay Area were determined by inversions of 34 suites of focal mechanisms of about 1500 small earthquakes recorded by the Northern California Seismic Network over three decades. Stress orientations are expected to rotate due to the release of shear stress in a major earthquake. The degree of rotation can place some constraints on the ambient level of stress in the crust surrounding the mainshock. For the four earthquakes studied here, the 1986 Mt. Lewis, 1984 Morgan Hill, 1979 Coyote Lake, and 1989 Loma Prieta events, modest rotations of the maximum compressive stress SH to a higher angle (i.e., an orientation closer to fault-normal) appear to occur at the time of the mainshock. In some cases, SH eventually rotates back towards its original orientation. However, due to relatively large uncertainties obtained on the stress orientations, the constraints that can be inferred on the absolute levels of stress surrounding the mainshock regions are rather weak. By considering the largest stress change permitted by the confidence limits, we obtain lower bounds on the background deviatoric stress of 3-12 MPa, levels only slightly greater than the mainshock static stress drops.

  17. Wastewater disposal and earthquake swarm activity at the southern end of the Central Valley, California

    NASA Astrophysics Data System (ADS)

    Goebel, T. H. W.; Hosseini, S. M.; Cappa, F.; Hauksson, E.; Ampuero, J. P.; Aminzadeh, F.; Saleeby, J. B.

    2016-02-01

    Fracture and fault zones can channel fluid flow and transmit injection-induced pore pressure changes over large distances (>km), at which seismicity is rarely suspected to be human induced. We use seismicity analysis and hydrogeological models to examine the role of seismically active faults in inducing earthquakes. We analyze a potentially injection-induced earthquake swarm with three events above M4 near the White Wolf fault (WWF). The swarm deviates from classic main aftershock behavior, exhibiting uncharacteristically low Gutenberg-Richter b of 0.6, and systematic migration patterns. Some smaller events occurred southeast of the WWF in an area of several disposal wells, one of which became active just 5 months before the main swarm activity. Hydrogeological modeling revealed that wastewater disposal likely contributed to seismicity via localized pressure increase along a seismically active fault. Our results suggest that induced seismicity may remain undetected in California without detailed analysis of local geologic setting, seismicity, and fluid diffusion.

  18. Cruise report for A1-00-SC southern California earthquake hazards project, part A

    USGS Publications Warehouse

    Gutmacher, Christina E.; Normark, William R.; Ross, Stephanie L.; Edwards, Brian D.; Sliter, Ray; Hart, Patrick; Cooper, Becky; Childs, Jon; Reid, Jane A.

    2000-01-01

    A three-week cruise to obtain high-resolution boomer and multichannel seismic-reflection profiles supported two project activities of the USGS Coastal and Marine Geology (CMG) Program: (1) evaluating the earthquake and related geologic hazards posed by faults in the near offshore area of southern California and (2) determining the pathways through which sea-water is intruding into aquifers of Los Angeles County in the area of the Long Beach and Los Angeles harbors. The 2000 cruise, A1-00-SC, is the third major data-collection effort in support of the first objective (Normark et al., 1999a, b); one more cruise is planned for 2002. This report deals primarily with the shipboard operations related to the earthquake-hazard activity. The sea-water intrusion survey is confined to shallow water and the techniques used are somewhat different from that of the hazards survey (see Edwards et al., in preparation).

  19. Source properties of earthquakes near the Salton Sea triggered by the 16 October 1999 M 7.1 Hector Mine, California, earthquake

    USGS Publications Warehouse

    Hough, S.E.; Kanamori, H.

    2002-01-01

    We analyze the source properties of a sequence of triggered earthquakes that occurred near the Salton Sea in southern California in the immediate aftermath of the M 7.1 Hector Mine earthquake of 16 October 1999. The sequence produced a number of early events that were not initially located by the regional network, including two moderate earthquakes: the first within 30 sec of the P-wave arrival and a second approximately 10 minutes after the mainshock. We use available amplitude and waveform data from these events to estimate magnitudes to be approximately 4.7 and 4.4, respectively, and to obtain crude estimates of their locations. The sequence of small events following the initial M 4.7 earthquake is clustered and suggestive of a local aftershock sequence. Using both broadband TriNet data and analog data from the Southern California Seismic Network (SCSN), we also investigate the spectral characteristics of the M 4.4 event and other triggered earthquakes using empirical Green's function (EGF) analysis. We find that the source spectra of the events are consistent with expectations for tectonic (brittle shear failure) earthquakes, and infer stress drop values of 0.1 to 6 MPa for six M 2.1 to M 4.4 events. The estimated stress drop values are within the range observed for tectonic earthquakes elsewhere. They are relatively low compared to typically observed stress drop values, which is consistent with expectations for faulting in an extensional, high heat flow regime. The results therefore suggest that, at least in this case, triggered earthquakes are associated with a brittle shear failure mechanism. This further suggests that triggered earthquakes may tend to occur in geothermal-volcanic regions because shear failure occurs at, and can be triggered by, relatively low stresses in extensional regimes.

  20. Earthquake!

    ERIC Educational Resources Information Center

    Markle, Sandra

    1987-01-01

    A learning unit about earthquakes includes activities for primary grade students, including making inferences and defining operationally. Task cards are included for independent study on earthquake maps and earthquake measuring. (CB)

  1. Earthquakes

    MedlinePlus

    An earthquake happens when two blocks of the earth suddenly slip past one another. Earthquakes strike suddenly, violently, and without warning at any time of the day or night. If an earthquake occurs in a ...

  2. Earthquakes

    MedlinePlus

    An earthquake happens when two blocks of the earth suddenly slip past one another. Earthquakes strike suddenly, violently, and without warning at any time of the day or night. If an earthquake occurs in a populated area, it may cause ...

  3. Investigating earthquake cycle vertical deformation recorded by GPS and regional tide gauge stations in California

    NASA Astrophysics Data System (ADS)

    Hardy, S.; Konter, B.

    2013-12-01

    Geodetic and tide gauge measurements of vertical deformation record localized zones of uplift and subsidence that may document critical components of both long and short-period earthquake cycle deformation. In this study, we compare vertical tide gauge data from the Permanent Service for Mean Sea Level (PSMSL) and vertical GPS data from the EarthScope Plate Boundary Observatory (PBO) for 10 approximately co-located station pairs along coastal California from Point Reyes, CA to Ensenada, Mexico. To compare these two datasets, we first truncate both datasets so that they span a common time frame for all stations (2007 - 2012). PSMSL data are treated for both average global sea level rise (~1.8 mm/yr) and global isostatic adjustment. We then calculate a 2-month running mean for tide gauge and a 1-month running mean for GPS datasets to smooth out daily oceanographic or anthropologic disturbances but maintain the overall trend of each dataset. As major ocean-climate signals, such as El Nino, are considered regional features of the Pacific Ocean and likely common to all California tide gauge stations, we subtract a reference sea level record (San Francisco station) from all other stations to eliminate this signal. The GPS and tide gauge data show varying degrees of correlation spanning both 3-month and 4-year time-scales. We infer that the slope of vertical displacements are largely controlled by interseismic motions, however displacements from major earthquakes are evident and are required to explain some of the unique signatures in the tide gauge and GPS data. Specifically, we find that stations from both datasets in Southern California show an anomalous trend since the 2010 Baja California earthquake. To further investigate this trend and others, we compare these data to vertical motions estimated by a suite of 3-D viscoelastic earthquake cycle deformation models. Long-term tide gauge time series are well simulated by the models, but short-term time series are not as

  4. Potential for Large Transpressional Earthquakes along the Santa Cruz-Catalina Ridge, California Continental Borderland

    NASA Astrophysics Data System (ADS)

    Legg, M.; Kohler, M. D.; Weeraratne, D. S.; Castillo, C. M.

    2015-12-01

    Transpressional fault systems comprise networks of high-angle strike-slip and more gently-dipping oblique-slip faults. Large oblique-slip earthquakes may involve complex ruptures of multiple faults with both strike-slip and dip-slip. Geophysical data including high-resolution multibeam bathymetry maps, multichannel seismic reflection (MCS) profiles, and relocated seismicity catalogs enable detailed mapping of the 3-D structure of seismogenic fault systems offshore in the California Continental Borderland. Seafloor morphology along the San Clemente fault system displays numerous features associated with active strike-slip faulting including scarps, linear ridges and valleys, and offset channels. Detailed maps of the seafloor faulting have been produced along more than 400 km of the fault zone. Interpretation of fault geometry has been extended to shallow crustal depths using 2-D MCS profiles and to seismogenic depths using catalogs of relocated southern California seismicity. We examine the 3-D fault character along the transpressional Santa Cruz-Catalina Ridge (SCCR) section of the fault system to investigate the potential for large earthquakes involving multi-fault ruptures. The 1981 Santa Barbara Island (M6.0) earthquake was a right-slip event on a vertical fault zone along the northeast flank of the SCCR. Aftershock hypocenters define at least three sub-parallel high-angle fault surfaces that lie beneath a hillside valley. Mainshock rupture for this moderate earthquake appears to have been bilateral, initiating at a small discontinuity in the fault geometry (~5-km pressure ridge) near Kidney Bank. The rupture terminated to the southeast at a significant releasing step-over or bend and to the northeast within a small (~10-km) restraining bend. An aftershock cluster occurred beyond the southeast asperity along the East San Clemente fault. Active transpression is manifest by reverse-slip earthquakes located in the region adjacent to the principal displacement zone

  5. Open Access to Decades of NCSN Waveforms at the Northern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

    Neuhauser, D.; Klein, F.; Zuzlewski, S.; Jensen, E. G.; Oppenheimer, D.; Gee, L.; Romanowicz, B.

    2003-12-01

    The USGS in Menlo Park has operated the Northern California Seismic Network (NCSN) since 1967 and has generated digital seismograms since 1984. Since its inception, the NCSN has recorded 2900 distinct channels at over 500 distinct sites. Although originally used only for earthquake location and coda magnitude, these seismograms are now of interest to seismologists for studying earth structure, precision relocations through cross correlation timing, and analysis of strong motion records. Until recently, the NCSN waveform data were available only through research accounts and special request methods due to incomplete instrument responses. Over the past 2 years, the USGS has assembled the necessary descriptions for both historic and current NCSN instrumentation. The NCEDC and USGS jointly developed a procedure to assemble the hardware attributes and instrument responses for the NCSN data channels using a combination of a simple spreadsheet that defines the attributes of each data channel, and a limited number of attribute files for classes of sensors and shared digitizers. These files are used by programs developed by the NCEDC to populate the NCEDC hardware tracking database tables and then to generate both the simple response and the full SEED instrument response database tables. As a result, the NCSN waveform data can now be distributed in SEED format with any of the NCEDC standard waveform request methods. The NCEDC provides access to waveform data through Web forms, email requests, and programming interfaces. The SeismiQuery Web interface provides information about data holdings. NetDC allows users to retrieve inventory information, instrument responses, and waveforms in SEED format. STP provides both a Web and programming interface to retrieve data in SEED or other user-friendly formats. Through the California Integrated Seismic Network, we are working with the SCEDC to provide unified access to California earthquake data. The NCEDC is a joint project of the UC

  6. Archiving and Distributing Seismic Data at the Southern California Earthquake Data Center (SCEDC)

    NASA Astrophysics Data System (ADS)

    Appel, V. L.

    2002-12-01

    The Southern California Earthquake Data Center (SCEDC) archives and provides public access to earthquake parametric and waveform data gathered by the Southern California Seismic Network and since January 1, 2001, the TriNet seismic network, southern California's earthquake monitoring network. The parametric data in the archive includes earthquake locations, magnitudes, moment-tensor solutions and phase picks. The SCEDC waveform archive prior to TriNet consists primarily of short-period, 100-samples-per-second waveforms from the SCSN. The addition of the TriNet array added continuous recordings of 155 broadband stations (20 samples per second or less), and triggered seismograms from 200 accelerometers and 200 short-period instruments. Since the Data Center and TriNet use the same Oracle database system, new earthquake data are available to the seismological community in near real-time. Primary access to the database and waveforms is through the Seismogram Transfer Program (STP) interface. The interface enables users to search the database for earthquake information, phase picks, and continuous and triggered waveform data. Output is available in SAC, miniSEED, and other formats. Both the raw counts format (V0) and the gain-corrected format (V1) of COSMOS (Consortium of Organizations for Strong-Motion Observation Systems) are now supported by STP. EQQuest is an interface to prepackaged waveform data sets for select earthquakes in Southern California stored at the SCEDC. Waveform data for large-magnitude events have been prepared and new data sets will be available for download in near real-time following major events. The parametric data from 1981 to present has been loaded into the Oracle 9.2.0.1 database system and the waveforms for that time period have been converted to mSEED format and are accessible through the STP interface. The DISC optical-disk system (the "jukebox") that currently serves as the mass-storage for the SCEDC is in the process of being replaced

  7. Marine geology and earthquake hazards of the San Pedro Shelf region, southern California

    USGS Publications Warehouse

    Fisher, Michael A.; Normark, William R.; Langenheim, V.E.; Calvert, Andrew J.; Sliter, Ray

    2004-01-01

    High-resolution seismic-reflection data have been com- bined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro Shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington Graben, the Palos Verdes Fault Zone, various faults below the western part of the shelf and slope, and the deep-water San Pedro Basin. The structure of the Palos Verdes Fault Zone changes mark- edly southeastward across the San Pedro Shelf and slope. Under the northern part of the shelf, this fault zone includes several strands, but the main strand dips west and is probably an oblique-slip fault. Under the slope, this fault zone con- sists of several fault strands having normal separation, most of which dip moderately east. To the southeast near Lasuen Knoll, the Palos Verdes Fault Zone locally is a low-angle fault that dips east, but elsewhere near this knoll the fault appears to dip steeply. Fresh sea-floor scarps near Lasuen Knoll indi- cate recent fault movement. The observed regional structural variation along the Palos Verdes Fault Zone is explained as the result of changes in strike and fault geometry along a master strike-slip fault at depth. The shallow summit and possible wavecut terraces on Lasuen knoll indicate subaerial exposure during the last sea-level lowstand. Modeling of aeromagnetic data indicates the presence of a large magnetic body under the western part of the San Pedro Shelf and upper slope. This is interpreted to be a thick body of basalt of Miocene(?) age. Reflective sedimentary rocks overlying the basalt are tightly folded, whereas folds in sedimentary rocks east of the basalt have longer wavelengths. This difference might mean that the basalt was more competent during folding than the encasing sedimentary rocks. West of the Palos Verdes Fault Zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these

  8. Space-Time Clustering and Correlations of Major Earthquakes

    SciTech Connect

    Holliday, James R.; Rundle, John B.; Turcotte, Donald L.; Klein, William; Tiampo, Kristy F.; Donnellan, Andrea

    2006-12-08

    Earthquake occurrence in nature is thought to result from correlated elastic stresses, leading to clustering in space and time. We show that the occurrence of major earthquakes in California correlates with time intervals when fluctuations in small earthquakes are suppressed relative to the long term average. We estimate a probability of less than 1% that this coincidence is due to random clustering.

  9. GPS Time Series Analysis of Southern California Associated with the 2010 M7.2 El Mayor/Cucapah Earthquake

    NASA Technical Reports Server (NTRS)

    Granat, Robert; Donnellan, Andrea

    2011-01-01

    The Magnitude 7.2 El-Mayor/Cucapah earthquake the occurred in Mexico on April 4, 2012 was well instrumented with continuous GPS stations in California. Large Offsets were observed at the GPS stations as a result of deformation from the earthquake providing information about the co-seismic fault slip as well as fault slip from large aftershocks. Information can also be obtained from the position time series at each station.

  10. Calculation of earthquake rupture histories using a hybrid global search algorithm: Application to the 1992 Landers, California, earthquake

    USGS Publications Warehouse

    Hartzell, S.; Liu, P.

    1996-01-01

    A method is presented for the simultaneous calculation of slip amplitudes and rupture times for a finite fault using a hybrid global search algorithm. The method we use combines simulated annealing with the downhill simplex method to produce a more efficient search algorithm then either of the two constituent parts. This formulation has advantages over traditional iterative or linearized approaches to the problem because it is able to escape local minima in its search through model space for the global optimum. We apply this global search method to the calculation of the rupture history for the Landers, California, earthquake. The rupture is modeled using three separate finite-fault planes to represent the three main fault segments that failed during this earthquake. Both the slip amplitude and the time of slip are calculated for a grid work of subfaults. The data used consist of digital, teleseismic P and SH body waves. Long-period, broadband, and short-period records are utilized to obtain a wideband characterization of the source. The results of the global search inversion are compared with a more traditional linear-least-squares inversion for only slip amplitudes. We use a multi-time-window linear analysis to relax the constraints on rupture time and rise time in the least-squares inversion. Both inversions produce similar slip distributions, although the linear-least-squares solution has a 10% larger moment (7.3 ?? 1026 dyne-cm compared with 6.6 ?? 1026 dyne-cm). Both inversions fit the data equally well and point out the importance of (1) using a parameterization with sufficient spatial and temporal flexibility to encompass likely complexities in the rupture process, (2) including suitable physically based constraints on the inversion to reduce instabilities in the solution, and (3) focusing on those robust rupture characteristics that rise above the details of the parameterization and data set.

  11. Products and Services Available from the Southern California Earthquake Data Center (SCEDC) and the Southern California Seismic Network (SCSN)

    NASA Astrophysics Data System (ADS)

    Chen, S. E.; Yu, E.; Bhaskaran, A.; Chowdhury, F. R.; Meisenhelter, S.; Hutton, K.; Given, D.; Hauksson, E.; Clayton, R. W.

    2011-12-01

    Currently, the SCEDC archives continuous and triggered data from nearly 8400 data channels from 425 SCSN recorded stations, processing and archiving an average of 6.4 TB of continuous waveforms and 12,000 earthquakes each year. The SCEDC provides public access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP and DHI. This poster will describe the most significant developments at the SCEDC during 2011. New website design: ? The SCEDC has revamped its website. The changes make it easier for users to search the archive, discover updates and new content. These changes also improve our ability to manage and update the site. New data holdings: ? Post processing on El Mayor Cucapah 7.2 sequence continues. To date there have been 11847 events reviewed. Updates are available in the earthquake catalog immediately. ? A double difference catalog (Hauksson et. al 2011) spanning 1981 to 6/30/11 will be available for download at www.data.scec.org and available via STP. ? A focal mechanism catalog determined by Yang et al. 2011 is available for distribution at www.data.scec.org. ? Waveforms from Southern California NetQuake stations are now being stored in the SCEDC archive and available via STP as event associated waveforms. Amplitudes from these stations are also being stored in the archive and used by ShakeMap. ? As part of a NASA/AIST project in collaboration with JPL and SIO, the SCEDC will receive real time 1 sps streams of GPS displacement solutions from the California Real Time Network (http://sopac.ucsd.edu/projects/realtime; Genrich and Bock, 2006, J. Geophys. Res.). These channels will be archived at the SCEDC as miniSEED waveforms, which then can be distributed to the user community via applications such as STP. Improvements in the user tool STP: ? STP sac output now includes picks from the SCSN. New archival methods: ? The SCEDC is exploring the feasibility of archiving and distributing

  12. Caltech/USGS Southern California Seismic Network (SCSN): Infrastructure upgrade to support Earthquake Early Warning (EEW)

    NASA Astrophysics Data System (ADS)

    Bhadha, R. J.; Hauksson, E.; Boese, M.; Felizardo, C.; Thomas, V. I.; Yu, E.; Given, D. D.; Heaton, T. H.; Hudnut, K. W.

    2013-12-01

    The SCSN is the modern digital ground motion seismic network in Southern California and performs the following tasks: 1) Operates remote seismic stations and the central data processing systems in Pasadena; 2) Generates and reports real-time products including location, magnitude, ShakeMap, aftershock probabilities and others; 3) Responds to FEMA, CalOES, media, and public inquiries about earthquakes; 4) Manages the production, archival, and distribution of waveforms, phase picks, and other data at the SCEDC; 5) Contributes to development and implementation of the demonstration EEW system called CISN ShakeAlert. Initially, the ShakeAlert project was funded through the US Geological Survey (USGS) and in early 2012, the Gordon and Betty Moore Foundation provided three years of new funding for EEW research and development for the US west coast. Recently, we have also received some Urban Areas Security Initiative (UASI) funding to enhance the EEW capabilities for the local UASI region by making our system overall faster, more reliable and redundant than the existing system. The additional and upgraded stations will be capable of decreasing latency and ensuring data delivery by using more reliable and redundant telemetry pathways. Overall, this will enhance the reliability of the earthquake early warnings by providing denser station coverage and more resilient data centers than before. * Seismic Datalogger upgrade: replaces existing dataloggers with modern equipment capable of sending one-second uncompressed packets and utilizing redundant Ethernet telemetry. * GPS upgrade: replaces the existing GPS receivers and antennas, especially at "zipper array" sites near the major faults, with receivers that perform on-board precise point positioning to calculate position and velocity in real time and stream continuous data for use in EEW calculations. * New co-located seismic/GPS stations: increases station density and reduces early warning delays that are incurred by travel

  13. The 1999 Mw 7.1 Hector Mine, California, earthquake: A test of the stress shadow hypothesis?

    USGS Publications Warehouse

    Harris, R.A.; Simpson, R.W.

    2002-01-01

    We test the stress shadow hypothesis for large earthquake interactions by examining the relationship between two large earthquakes that occurred in the Mojave Desert of southern California, the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes. We want to determine if the 1999 Hector Mine earthquake occurred at a location where the Coulomb stress was increased (earthquake advance, stress trigger) or decreased (earthquake delay, stress shadow) by the previous large earthquake. Using four models of the Landers rupture and a range of possible hypocentral planes for the Hector Mine earthquake, we discover that most scenarios yield a Landers-induced relaxation (stress shadow) on the Hector Mine hypocentral plane. Although this result would seem to weigh against the stress shadow hypothesis, the results become considerably more uncertain when the effects of a nearby Landers aftershock, the 1992 ML 5.4 Pisgah earthquake, are taken into account. We calculate the combined static Coulomb stress changes due to the Landers and Pisgah earthquakes to range from -0.3 to +0.3 MPa (- 3 to +3 bars) at the possible Hector Mine hypocenters, depending on choice of rupture model and hypocenter. These varied results imply that the Hector Mine earthquake does not provide a good test of the stress shadow hypothesis for large earthquake interactions. We use a simple approach, that of static dislocations in an elastic half-space, yet we still obtain a wide range of both negative and positive Coulomb stress changes. Our findings serve as a caution that more complex models purporting to explain the triggering or shadowing relationship between the 1992 Landers and 1999 Hector Mine earthquakes need to also consider the parametric and geometric uncertainties raised here.

  14. Earthquakes.

    ERIC Educational Resources Information Center

    Walter, Edward J.

    1977-01-01

    Presents an analysis of the causes of earthquakes. Topics discussed include (1) geological and seismological factors that determine the effect of a particular earthquake on a given structure; (2) description of some large earthquakes such as the San Francisco quake; and (3) prediction of earthquakes. (HM)

  15. Earthquakes.

    ERIC Educational Resources Information Center

    Pakiser, Louis C.

    One of a series of general interest publications on science topics, the booklet provides those interested in earthquakes with an introduction to the subject. Following a section presenting an historical look at the world's major earthquakes, the booklet discusses earthquake-prone geographic areas, the nature and workings of earthquakes, earthquake…

  16. Basin Waves on a Seafloor Recording of the 1990 Upland, California, Earthquake: Implications for Ground Motions from a Larger Earthquake

    USGS Publications Warehouse

    Boore, D.M.

    1999-01-01

    The velocity and displacement time series from a recording on the seafloor at 74 km from the 1990 Upland earthquake (M = 5.6) are dominated by late-arriving waves with periods of 6 to 7 sec. These waves are probably surface waves traveling across the Los Angeles basin. Response spectra for the recording are in agreement with predictions from empirical regression equations and theoretical models for periods less than about 1 sec but are significantly larger than those predictions for longer periods. The longer-period spectral amplitudes are controlled by the late-arriving waves, which are not included in the theoretical models and are underrepresented in the data used in the empirical analyses. When the motions are scaled to larger magnitude, the results are in general agreement with simulations of wave propagation in the Los Angeles basin by Graves (1998).

  17. Introducing ShakeMap to potential users in Puerto Rico using scenarios of damaging historical and probable earthquakes

    NASA Astrophysics Data System (ADS)

    Huerfano, V. A.; Cua, G.; von Hillebrandt, C.; Saffar, A.

    2007-12-01

    The island of Puerto Rico has a long history of damaging earthquakes. Major earthquakes from off-shore sources have affected Puerto Rico in 1520, 1615, 1670, 1751, 1787, 1867, and 1918 (Mueller et al, 2003; PRSN Catalogue). Recent trenching has also yielded evidence of possible M7.0 events inland (Prentice, 2000). The high seismic hazard, large population, high tsunami potential and relatively poor construction practice can result in a potentially devastating combination. Efficient emergency response in event of a large earthquake will be crucial to minimizing the loss of life and disruption of lifeline systems in Puerto Rico. The ShakeMap system (Wald et al, 2004) developed by the USGS to rapidly display and disseminate information about the geographical distribution of ground shaking (and hence potential damage) following a large earthquake has proven to be a vital tool for post earthquake emergency response efforts, and is being adopted/emulated in various seismically active regions worldwide. Implementing a robust ShakeMap system is among the top priorities of the Puerto Rico Seismic Network. However, the ultimate effectiveness of ShakeMap in post- earthquake response depends not only on its rapid availability, but also on the effective use of the information it provides. We developed ShakeMap scenarios of a suite of damaging historical and probable earthquakes that severely impact San Juan, Ponce, and Mayagüez, the 3 largest cities in Puerto Rico. Earthquake source parameters were obtained from McCann and Mercado (1998); and Huérfano (2004). For historical earthquakes that generated tsunamis, tsunami inundation maps were generated using the TIME method (Shuto, 1991). The ShakeMap ground shaking maps were presented to local and regional governmental and emergency response agencies at the 2007 Annual conference of the Puerto Rico Emergency Management and Disaster Administration in San Juan, PR, and at numerous other emergency management talks and training

  18. Earthquake source mechanisms and transform fault tectonics in the Gulf of California

    NASA Technical Reports Server (NTRS)

    Goff, John A.; Bergman, Eric A.; Solomon, Sean C.

    1987-01-01

    The source parameters of 19 large earthquakes in the Gulf of California were determined from inversions of long-period P and SH waveforms. The goal was to understand the recent slip history of this dominantly transform boundary between the Pacific and North American plates as well as the effect on earthquake characteristics of the transition from young oceanic to continental lithosphere. For the better recorded transform events, the fault strike is resolved to + or - 4 deg at 90 percent confidence. The slip vectors thus provide important constraints on the direction of relative plate motion. Most centroid depths are poorly resolved because of tradeoffs between depth and source time function. On the basis of waveform modeling, historical seismicity, and other factors, it is appropriate to divide the Gulf into three distinct zones. The difference in seismic character among the three zones is likely the result of differing levels of maturity of the processes of rifting, generation of oceanic crust, and formation of stable oceanic transform faults. The mechanism of an earthquake on the Tres Marias Escarpment is characterized by thrust faulting and likely indicates the direction of relative motion between the Rivera and North American plates. This mechanism requires revision in plate velocity models which predict strike slip motion at this location.

  19. The 1979 Homestead Valley earthquake sequence, California: control of aftershocks and postseismic deformation.

    USGS Publications Warehouse

    Stein, R.S.; Lisowski, M.

    1983-01-01

    The coseismic slip and geometry of the March 15, 1979, Homestead Valley, California, earthquake sequence are well constrained by precise horizontal and vertical geodetic observations and by data from a dense local seismic network. These observations indicate 0.52 + or - 0.10 m of right-lateral slip and 0.17 + or - 0.04 m of reverse slip on a buried vertical 6-km-long and 5-km-deep fault and yield a mean static stress drop of 7.2 + or -1.3 MPa. The largest shock had Ms = 5.6. Observations of the ground rupture revealed up to 0.1 m of right-lateral slip on two mapped faults that are subparallel to the modeled seismic slip plane. In the 1.9 years since the earthquakes, geodetic network displacements indicate that an additional 60+ or -10 mm of postseismic creep took place. The rate of postseismic shear strain (0.53 + or - 0.13 mu rad/yr) measured within a 30 X 30-km network centered on the principal events was anomalously high compared to its preearthquake value and the postseismic rate in the adjacent network. This transient cannot be explained by postseismic slip on the seismic fault but rather indicates that broadside release of strain followed the earthquake sequence. -Authors

  20. Cross-fault triggering in the November 1987 Superstition Hills earthquake sequence, southern California

    SciTech Connect

    Hudnut, K.W.; Pacheco, J. Columbia University, New York, NY ); Seeber, L. )

    1989-02-01

    Two large strike-slip ruptures 11.4 hours apart occurred on intersecting, nearly orthogonal, vertical faults during the November 1987 Superstition Hills earthquake sequence in southern California. This sequence is the latest in a northwestward progression of earthquakes (1979, 1981, and 1987) rupturing a set of parallel left-lateral cross-faults that trend northeast between the Brawley seismic zone and Superstition Hills fault, a northwest trending main strand of the San Jacinto fault zone. The first large event (M{sub s} = 6.2) in the 1987 sequence ruptured the Elmore Ranch fault, a cross-fault that strikes northeasterly between the Brawley seismic zone and the Superstition Hills main fault. The second event (M{sub s} = 6.6) initiated its rupture at the intersection of the cross-fault and main fault and propagated towards the southeast along the main fault. The following hypotheses are advanced; (1) slip on the cross-fault locally decreased normal stress on the main fault, and triggered the main fault rupture after a delay; and (2) the delay was caused by fluid diffusion. It is inferred that the observed northwestward progression of ruptures on cross-faults may continue. The next cross-fault expected to rupture intersects both the San Andreas fault and the San Jacinto fault zone. The authors hypothesize that rupture of this cross-fault may trigger rupture on either of these main faults by a mechanism similar to that which occurred in the Superstition Hills earthquake sequence.

  1. Spatial-temporal variation of low-frequency earthquake bursts near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Wu, Chunquan; Guyer, Robert; Shelly, David; Trugman, Daniel; Frank, William; Gomberg, Joan; Johnson, Paul

    2015-08-01

    Tectonic tremor (TT) and low-frequency earthquakes (LFEs) have been found in the deeper crust of various tectonic environments globally in the last decade. The spatial-temporal behaviour of LFEs provides insight into deep fault zone processes. In this study, we examine recurrence times from a 12-yr catalogue of 88 LFE families with ˜730 000 LFEs in the vicinity of the Parkfield section of the San Andreas Fault (SAF) in central California. We apply an automatic burst detection algorithm to the LFE recurrence times to identify the clustering behaviour of LFEs (LFE bursts) in each family. We find that the burst behaviours in the northern and southern LFE groups differ. Generally, the northern group has longer burst duration but fewer LFEs per burst, while the southern group has shorter burst duration but more LFEs per burst. The southern group LFE bursts are generally more correlated than the northern group, suggesting more coherent deep fault slip and relatively simpler deep fault structure beneath the locked section of SAF. We also found that the 2004 Parkfield earthquake clearly increased the number of LFEs per burst and average burst duration for both the northern and the southern groups, with a relatively larger effect on the northern group. This could be due to the weakness of northern part of the fault, or the northwesterly rupture direction of the Parkfield earthquake.

  2. A physical model for earthquakes. I - Fluctuations and interactions. II - Application to southern California

    NASA Technical Reports Server (NTRS)

    Rundle, John B.

    1988-01-01

    The idea that earthquakes represent a fluctuation about the long-term motion of plates is expressed mathematically through the fluctuation hypothesis, under which all physical quantities which pertain to the occurance of earthquakes are required to depend on the difference between the present state of slip on the fault and its long-term average. It is shown that under certain circumstances the model fault dynamics undergo a sudden transition from a spatially ordered, temporally disordered state to a spatially disordered, temporally ordered state, and that the latter stages are stable for long intervals of time. For long enough faults, the dynamics are evidently chaotic. The methods developed are then used to construct a detailed model for earthquake dynamics in southern California. The result is a set of slip-time histories for all the major faults, which are similar to data obtained by geological trenching studies. Although there is an element of periodicity to the events, the patterns shift, change and evolve with time. Time scales for pattern evolution seem to be of the order of a thousand years for average recurring intervals of about a hundred years.

  3. High precision earthquake locations reveal seismogenic structure beneath Mammoth Mountain, California

    USGS Publications Warehouse

    Prejean, S.; Stork, A.; Ellsworth, W.; Hill, D.; Julian, B.

    2003-01-01

    In 1989, an unusual earthquake swarm occurred beneath Mammoth Mountain that was probably associated with magmatic intrusion. To improve our understanding of this swarm, we relocated Mammoth Mountain earthquakes using a double difference algorithm. Relocated hypocenters reveal that most earthquakes occurred on two structures, a near-vertical plane at 7-9 km depth that has been interpreted as an intruding dike, and a circular ring-like structure at ???5.5 km depth, above the northern end of the inferred dike. Earthquakes on this newly discovered ring structure form a conical section that dips outward away from the aseismic interior. Fault-plane solutions indicate that in 1989 the seismicity ring was slipping as a ring-normal fault as the center of the mountain rose with respect to the surrounding crust. Seismicity migrated around the ring, away from the underlying dike at a rate of ???0.4 km/month, suggesting that fluid movement triggered seismicity on the ring fault. Copyright 2003 by the American Geophysical Union.

  4. Holocene paleoseismicity, temporal clustering, and probabilities of future large (M > 7) earthquakes on the Wasatch fault zone, Utah

    USGS Publications Warehouse

    McCalpin, J.P.; Nishenko, S.P.

    1996-01-01

    The chronology of M>7 paleoearthquakes on the central five segments of the Wasatch fault zone (WFZ) is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years. Repeat times for individual segments vary by a factor of 2, and range from about 1200 to 2600 years. Four of the central five segments ruptured between ??? 620??30 and 1230??60 calendar years B.P. The remaining segment (Brigham City segment) has not ruptured in the past 2120??100 years. Comparison of the WFZ space-time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability (depending on model assumptions) of reflecting random coincidence as opposed to intersegment contagion. Regional seismicity suggests that for exposure times of 50 and 100 years, the probability for an earthquake of M>7 anywhere within the Wasatch Front region, based on a Poisson model, is 0.16 and 0.30, respectively. A fault-specific WFZ model predicts 50 and 100 year probabilities for a M>7 earthquake on the WFZ itself, based on a Poisson model, as 0.13 and 0.25, respectively. In contrast, segment-specific earthquake probabilities that assume quasi-periodic recurrence behavior on the Weber, Provo, and Nephi segments are less (0.01-0.07 in 100 years) than the regional or fault-specific estimates (0.25-0.30 in 100 years), due to the short elapsed times compared to average recurrence intervals on those segments. The Brigham City and Salt Lake City segments, however, have time-dependent probabilities that approach or exceed the regional and fault specific probabilities. For the Salt Lake City segment, these elevated probabilities are due to the elapsed time being approximately equal to the average late Holocene recurrence time. For the Brigham City segment, the elapsed time is significantly longer than the segment-specific late Holocene recurrence time.

  5. Characterization and stochastic modeling of earthquake faulting in California. Final Report

    SciTech Connect

    Kiremidjian, A.S.; Lutz, K.A.; Thrainsson, H.

    1995-06-01

    The objective of this report is to develop a time- and space-dependent probabilistic earthquake occurrence model for seismic hazard analysis. In order to study the space and time behavior of earthquakes along major faults, project investigators first evaluated slip rate and event interarrival time data for the San Andreas fault. These data were considered in the context of a model of the fault comprised of a series of segments that can rupture either independently or together with other segments. In Part One of this report, a slip-predictable model with random slip was used to generate probabilities of occurrences for all segments of the fault. In Part Two, a generalized semi-Markov model was developed that describes the temporal and spatial dependence of seismic events. Using the first model, investigators found large probabilities of occurrence of magnitude 6.5 or greater earthquakes for many segments of the fault. Using the second model, investigators found that the North Coast and South Santa Cruz Mountains segments of the fault typically generate quakes of magnitude 7.8 to 8.2 and 6.9 to 7.2 respectively.

  6. Earthquake geology of the northern San Andreas Fault near Point Arena, California

    SciTech Connect

    Prentice, C.S.

    1989-01-01

    Excavations into a Holocene alluvial fan provided exposures of a record of prehistoric earthquakes near Point Arena, California. At least five earthquakes were recognized in the section. All of these occurred since the deposition of a unit that is approximately 2000 years old. Radiocarbon dating allows constraints to be placed on the dates of these earthquakes. A buried Holocene (2356-2709 years old) channel has been offset a maximum of 64 {plus minus} 2 meters. This implies a maximum slip rate of 25.5 {plus minus} 2.5 mm/yr. These data suggest that the average recurrence interval for great earthquakes on this segment of the San Andreas fault is long - between about 200 and 400 years. Offset marine terrace risers near Point Arena and an offset landslide near Fort Ross provide estimates of the average slip rate since Late Pleistocene time. Near Fort Ross, an offset landslide implies a slip rate of less than 39 mm/yr. Correlation and age estimates of two marine terrace risers across the San Andreas fault near Point Arena suggest slip rates of about 18-19 mm/yr since Late Pleistocene time. Tentative correlation of the Pliocene Ohlson Ranch Formation in northwestern Sonoma County with deposits 50 km to the northwest near Point Arean, provides piercing points to use in calculation of a Pliocene slip rate for the northern San Andreas fault. A fission-track age 3.3 {plus minus} 0.8 Ma was determined for zicrons separated from a tuff collected from the Ohlson Ranch Formation. The geomorphology of the region, especially of the two major river drainages, supports the proposed 50 km Pliocene offset. This implies a Pliocene slip rate of at least 12-20 mm/yr. These rates for different time periods imply that much of the Pacific-North American plate motion must be accommodated on other structures at this latitude.

  7. Crustal velocities near Coalinga, California, modeled from a combined earthquake/explosion refraction profile

    USGS Publications Warehouse

    Macgregor-Scott, N.; Walter, A.

    1988-01-01

    Crustal velocity structure for the region near Coalinga, California, has been derived from both earthquake and explosion seismic phase data recorded along a NW-SE seismic-refraction profile on the western flank of the Great Valley east of the Diablo Range. Comparison of the two data sets reveals P-wave phases in common which can be correlated with changes in the velocity structure below the earthquake hypocenters. In addition, the earthquake records reveal secondary phases at station ranges of less than 20 km that could be the result of S- to P-wave conversions at velocity interfaces above the earthquake hypocenters. Two-dimensional ray-trace modeling of the P-wave travel times resulted in a P-wave velocity model for the western flank of the Great Valley comprised of: 1) a 7- to 9-km thick section of sedimentary strata with velocities similar to those found elsewhere in the Great Valley (1.6 to 5.2 km s-1); 2) a middle crust extending to about 14 km depth with velocities comparable to those reported for the Franciscan assemblage in the Diablo Range (5.6 to 5.9 km s-1); and 3) a 13- to 14-km thick lower crust with velocities similar to those reported beneath the Diablo Range and the Great Valley (6.5 to 7.30 km s-1). This lower crust may have been derived from subducted oceanic crust that was thickened by accretionary underplating or crustal shortening. -Authors

  8. A new method to identify earthquake swarms applied to seismicity near the San Jacinto Fault, California

    NASA Astrophysics Data System (ADS)

    Zhang, Qiong; Shearer, Peter M.

    2016-02-01

    Understanding earthquake clustering in space and time is important but also challenging because of complexities in earthquake patterns and the large and diverse nature of earthquake catalogs. Swarms are of particular interest because they likely result from physical changes in the crust, such as slow slip or fluid flow. Both swarms and clusters resulting from aftershock sequences can span a wide range of spatial and temporal scales. Here we test and implement a new method to identify seismicity clusters of varying sizes and discriminate them from randomly occurring background seismicity. Our method searches for the closest neighboring earthquakes in space and time and compares the number of neighbors to the background events in larger space/time windows. Applying our method to California's San Jacinto Fault Zone (SJFZ), we find a total of 89 swarm-like groups. These groups range in size from 0.14 to 7.23 km and last from 15 minutes to 22 days. The most striking spatial pattern is the larger fraction of swarms at the northern and southern ends of the SJFZ than its central segment, which may be related to more normal-faulting events at the two ends. In order to explore possible driving mechanisms, we study the spatial migration of events in swarms containing at least 20 events by fitting with both linear and diffusion migration models. Our results suggest that SJFZ swarms are better explained by fluid flow because their estimated linear migration velocities are far smaller than those of typical creep events while large values of best-fitting hydraulic diffusivity are found.

  9. Source processes of industrially-induced earthquakes at the Geysers geothermal area, California

    USGS Publications Warehouse

    Ross, A.; Foulger, G.R.; Julian, B.R.

    1999-01-01

    Microearthquake activity at The Geysers geothermal area, California, mirrors the steam production rate, suggesting that the earthquakes are industrially induced. A 15-station network of digital, three-component seismic stations was operated for one month in 1991, and 3,900 earthquakes were recorded. Highly-accurate moment tensors were derived for 30 of the best recorded earthquakes by tracing rays through tomographically derived 3-D VP and VP / VS structures, and inverting P-and S-wave polarities and amplitude ratios. The orientations of the P-and T-axes are very scattered, suggesting that there is no strong, systematic deviatoric stress field in the reservoir, which could explain why the earthquakes are not large. Most of the events had significant non-double-couple (non-DC) components in their source mechanisms with volumetric components up to ???30% of the total moment. Explosive and implosive sources were observed in approximately equal numbers, and must be caused by cavity creation (or expansion) and collapse. It is likely that there is a causal relationship between these processes and fluid reinjection and steam withdrawal. Compensated linear vector dipole (CLVD) components were up to 100% of the deviatoric component. Combinations of opening cracks and shear faults cannot explain all the observations, and rapid fluid flow may also be involved. The pattern of non-DC failure at The Geysers contrasts with that of the Hengill-Grensdalur area in Iceland, a largely unexploited water-dominated field in an extensional stress regime. These differences are poorly understood but may be linked to the contrasting regional stress regimes and the industrial exploitation at The Geysers.

  10. Geodetic constraints on frictional properties and earthquake hazard in the Imperial Valley, Southern California

    NASA Astrophysics Data System (ADS)

    Lindsey, Eric O.; Fialko, Yuri

    2016-02-01

    We analyze a suite of geodetic observations across the Imperial Fault in southern California that span all parts of the earthquake cycle. Coseismic and postseismic surface slips due to the 1979 M 6.6 Imperial Valley earthquake were recorded with trilateration and alignment surveys by Harsh (1982) and Crook et al. (1982), and interseismic deformation is measured using a combination of multiple interferometric synthetic aperture radar (InSAR)-viewing geometries and continuous and survey-mode GPS. In particular, we combine more than 100 survey-mode GPS velocities with InSAR data from Envisat descending tracks 84 and 356 and ascending tracks 77 and 306 (149 total acquisitions), processed using a persistent scatterers method. The result is a dense map of interseismic velocities across the Imperial Fault and surrounding areas that allows us to evaluate the rate of interseismic loading and along-strike variations in surface creep. We compare available geodetic data to models of the earthquake cycle with rate- and state-dependent friction and find that a complete record of the earthquake cycle is required to constrain key fault properties including the rate-dependence parameter (a - b) as a function of depth, the extent of shallow creep, and the recurrence interval of large events. We find that the data are inconsistent with a high (>30 mm/yr) slip rate on the Imperial Fault and investigate the possibility that an extension of the San Jacinto-Superstition Hills Fault system through the town of El Centro may accommodate a significant portion of the slip previously attributed to the Imperial Fault. Models including this additional fault are in better agreement with the available observations, suggesting that the long-term slip rate of the Imperial Fault is lower than previously suggested and that there may be a significant unmapped hazard in the western Imperial Valley.

  11. Satellite IR Thermal Measurements Prior to the September 2004 Earthquakes in Central California

    NASA Technical Reports Server (NTRS)

    Ouzounov, D.; Logan, T.; Taylor, Patrick

    2004-01-01

    We present and discuss observed variations in thermal transients and radiation fields prior to the earthquakes of September 18 near Bodie (M5.5) and September 28,2004 near Parkfield(M6.0) in California. Previous analysis of earthquake events have indicated the presence of a thermal anomaly, where temperatures increased or did not return to its usual nighttime value. The procedures used in our work is to analyze weather satellite data taken at night and to record the general condition where the ground cools after sunset. Two days before the Bodie earthquake lower temperature radiation was observed by the NOAA/AVHRR satellite. This occurred when the entire region was relatively cloud-free. IR land surface nighttime temperature from the MODIS instrument rose to +4 C in a 100 km radius around the Bodie epicenter. The thermal transient field recorded by MODIS in the vicinity of Parkfield, also with a cloud free environment, was around +l C and it is significantly smaller than the Parkfield epicenter, however, for that period showed a steady increase 4 days prior to the earthquake and a significant drop of the night before the quake. Geosynchronous weather satellite thermal IR measurements taken every half hour from sunset to dawn, were also recorded for 10 days prior to the Parkfield event and 5 days after as well as the day of the quake. To establish a baseline we also obtained GOES data for the same Julian sets were then used to systematically observe and record any thermal anomaly prior to the events that deviated from the baseline. Our recent results support the hypothesis of a possible relationship between an thermodynamic processes produced by increasing tectonic stress in the Earth's crust and a subsequent electro-chemical interaction between this crust and the atmosphere/ionosphere.

  12. A new method to identify earthquake swarms applied to seismicity near the San Jacinto Fault, California

    NASA Astrophysics Data System (ADS)

    Zhang, Qiong; Shearer, Peter M.

    2016-05-01

    Understanding earthquake clustering in space and time is important but also challenging because of complexities in earthquake patterns and the large and diverse nature of earthquake catalogues. Swarms are of particular interest because they likely result from physical changes in the crust, such as slow slip or fluid flow. Both swarms and clusters resulting from aftershock sequences can span a wide range of spatial and temporal scales. Here we test and implement a new method to identify seismicity clusters of varying sizes and discriminate them from randomly occurring background seismicity. Our method searches for the closest neighbouring earthquakes in space and time and compares the number of neighbours to the background events in larger space/time windows. Applying our method to California's San Jacinto Fault Zone (SJFZ), we find a total of 89 swarm-like groups. These groups range in size from 0.14 to 7.23 km and last from 15 min to 22 d. The most striking spatial pattern is the larger fraction of swarms at the northern and southern ends of the SJFZ than its central segment, which may be related to more normal-faulting events at the two ends. In order to explore possible driving mechanisms, we study the spatial migration of events in swarms containing at least 20 events by fitting with both linear and diffusion migration models. Our results suggest that SJFZ swarms are better explained by fluid flow because their estimated linear migration velocities are far smaller than those of typical creep events while large values of best-fitting hydraulic diffusivity are found.

  13. Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California

    USGS Publications Warehouse

    DeLong, Stephen B.; Lienkaemper, James J.; Pickering, Alexandra J; Avdievitch, Nikita N.

    2015-01-01

    The A.D. 2014 M6.0 South Napa earthquake, despite its moderate magnitude, caused significant damage to the Napa Valley in northern California (USA). Surface rupture occurred along several mapped and unmapped faults. Field observations following the earthquake indicated that the magnitude of postseismic surface slip was likely to approach or exceed the maximum coseismic surface slip and as such presented ongoing hazard to infrastructure. Using a laser scanner, we monitored postseismic deformation in three dimensions through time along 0.5 km of the main surface rupture. A key component of this study is the demonstration of proper alignment of repeat surveys using point cloud–based methods that minimize error imposed by both local survey errors and global navigation satellite system georeferencing errors. Using solid modeling of natural and cultural features, we quantify dextral postseismic displacement at several hundred points near the main fault trace. We also quantify total dextral displacement of initially straight cultural features. Total dextral displacement from both coseismic displacement and the first 2.5 d of postseismic displacement ranges from 0.22 to 0.29 m. This range increased to 0.33–0.42 m at 59 d post-earthquake. Furthermore, we estimate up to 0.15 m of vertical deformation during the first 2.5 d post-earthquake, which then increased by ∼0.02 m at 59 d post-earthquake. This vertical deformation is not expressed as a distinct step or scarp at the fault trace but rather as a broad up-to-the-west zone of increasing elevation change spanning the fault trace over several tens of meters, challenging common notions about fault scarp development in strike-slip systems. Integrating these analyses provides three-dimensional mapping of surface deformation and identifies spatial variability in slip along the main fault trace that we attribute to distributed slip via subtle block rotation. These results indicate the benefits of laser scanner surveys along

  14. Westward-derived conglomerates in Moenkopi formation of Southeastern California, and their probable tectonic significance

    SciTech Connect

    Walker, J.D.; Burchfiel, B.C.; Royden, L.H.

    1983-02-01

    The upper part of the Moenkopi Formation in the Northern Clark Mountains, Southeastern California, contains conglomerate beds whose clasts comprise igneous, metamorphic, and sedimentary rocks. Metamorphic clasts include foliated granite, meta-arkose, and quarzite, probably derived from older Precambrian basement and younger Precambrian clastic rocks. Volcanic clasts are altered plagioclase-bearing rocks, and sedimentary clasts were derived from Paleozoic miogeoclinal rocks. Paleocurrent data indicate that the clasts had a source to the southwest. An age of late Early or early Middle Triassic has been tentatively assigned to these conglomerates. These conglomerates indicate that Late Permian to Early Triassic deformational events in this part of the orogen affected rocks much farther east than has been previously recognized.

  15. M≥7 Earthquake rupture forecast and time-dependent probability for the Sea of Marmara region, Turkey

    USGS Publications Warehouse

    Murru, Maura; Akinci, Aybige; Falcone, Guiseppe; Pucci, Stefano; Console, Rodolfo; Parsons, Thomas E.

    2016-01-01

    We forecast time-independent and time-dependent earthquake ruptures in the Marmara region of Turkey for the next 30 years using a new fault-segmentation model. We also augment time-dependent Brownian Passage Time (BPT) probability with static Coulomb stress changes (ΔCFF) from interacting faults. We calculate Mw > 6.5 probability from 26 individual fault sources in the Marmara region. We also consider a multisegment rupture model that allows higher-magnitude ruptures over some segments of the Northern branch of the North Anatolian Fault Zone (NNAF) beneath the Marmara Sea. A total of 10 different Mw=7.0 to Mw=8.0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation. We use Gaussian random distributions to treat parameter uncertainties (e.g., aperiodicity, maximum expected magnitude, slip rate, and consequently mean recurrence time) of the statistical distributions associated with each fault source. We then estimate uncertainties of the 30-year probability values for the next characteristic event obtained from three different models (Poisson, BPT, and BPT+ΔCFF) using a Monte Carlo procedure. The Gerede fault segment located at the eastern end of the Marmara region shows the highest 30-yr probability, with a Poisson value of 29%, and a time-dependent interaction probability of 48%. We find an aggregated 30-yr Poisson probability of M >7.3 earthquakes at Istanbul of 35%, which increases to 47% if time dependence and stress transfer are considered. We calculate a 2-fold probability gain (ratio time-dependent to time-independent) on the southern strands of the North Anatolian Fault Zone.

  16. M ≥ 7 earthquake rupture forecast and time-dependent probability for the sea of Marmara region, Turkey

    NASA Astrophysics Data System (ADS)

    Murru, M.; Akinci, A.; Falcone, G.; Pucci, S.; Console, R.; Parsons, T.

    2016-04-01

    We forecast time-independent and time-dependent earthquake ruptures in the Marmara region of Turkey for the next 30 years using a new fault segmentation model. We also augment time-dependent Brownian passage time (BPT) probability with static Coulomb stress changes (ΔCFF) from interacting faults. We calculate Mw > 6.5 probability from 26 individual fault sources in the Marmara region. We also consider a multisegment rupture model that allows higher-magnitude ruptures over some segments of the northern branch of the North Anatolian Fault Zone beneath the Marmara Sea. A total of 10 different Mw = 7.0 to Mw = 8.0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation. We use Gaussian random distributions to treat parameter uncertainties (e.g., aperiodicity, maximum expected magnitude, slip rate, and consequently mean recurrence time) of the statistical distributions associated with each fault source. We then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models (Poisson, BPT, and BPT + ΔCFF) using a Monte Carlo procedure. The Gerede fault segment located at the eastern end of the Marmara region shows the highest 30 year probability, with a Poisson value of 29% and a time-dependent interaction probability of 48%. We find an aggregated 30 year Poisson probability of M > 7.3 earthquakes at Istanbul of 35%, which increases to 47% if time dependence and stress transfer are considered. We calculate a twofold probability gain (ratio time dependent to time independent) on the southern strands of the North Anatolian Fault Zone.

  17. Earthquakes

    ERIC Educational Resources Information Center

    Roper, Paul J.; Roper, Jere Gerard

    1974-01-01

    Describes the causes and effects of earthquakes, defines the meaning of magnitude (measured on the Richter Magnitude Scale) and intensity (measured on a modified Mercalli Intensity Scale) and discusses earthquake prediction and control. (JR)

  18. Tests of RTG (Real Time GIPSY) for Earthquake Early Warning and Response Applications in Southern California

    NASA Astrophysics Data System (ADS)

    King, N.; Hudnut, K.; Stark, K.; Aspiotes, A.

    2008-12-01

    Recent developments in high-rate real-time GPS technology and processing promise to improve the application of GPS to earthquake early warning and response. Point positioning processing algorithms, which do not require a reference station, are particularly attractive for these applications since any reference station will itself be displaced during a large earthquake. USGS Pasadena is testing one such software package, Real Time GIPSY (RTG), developed and supported by the Jet Propulsion Laboratory (JPL). JPL uses RTG for precise real-time satellite orbit and clock determination, formats the results as corrections to the GPS broadcast orbit, and provides a real-time stream over the Internet. In our tests we use a locally- installed copy of RTG to compute real-time positions of GPS stations at a sampling rate of 1 second. In clean sections of the position time series are good, with rms scatter of 2 to 4 cm in the north and east components, and 5 to 10 cm in the vertical. Current work is designed to understand and handle occasional convergence delays and large outliers; many outliers repeat every sidereal day and may be correlated with multipath or with the rising or setting of individual satellites. The test site is in a less-than-ideal setting, and we are experimenting with the software setup and with different sites with fewer sources of multipath and better sky view. USGS Pasadena currently operates about 90 permanent continuously-operating GPS stations, about 20 of which are real-time. With funding from the USGS MultiHazards Demonstration Project, USGS Pasadena is cooperating with the California Integrated Seismic Network to co-locate approximately eight real-time GPS receivers at new seismic stations along the southern San Andreas fault. The Plate Boundary Observatory (PBO) is also converting many of its southern California stations to real-time operation. These real-time data and software such as RTG promise to improve USGS Pasasdena's geodetic response to

  19. Uniform California earthquake rupture forecast, version 3 (UCERF3): the time-independent model

    USGS Publications Warehouse

    Field, Edward H.; Biasi, Glenn P.; Bird, Peter; Dawson, Timothy E.; Felzer, Karen R.; Jackson, David D.; Johnson, Kaj M.; Jordan, Thomas H.; Madden, Christopher; Michael, Andrew J.; Milner, Kevin R.; Page, Morgan T.; Parsons, Thomas; Powers, Peter M.; Shaw, Bruce E.; Thatcher, Wayne R.; Weldon, Ray J., II; Zeng, Yuehua; Working Group on CA Earthquake Probabilities

    2013-01-01

    In this report we present the time-independent component of the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), which provides authoritative estimates of the magnitude, location, and time-averaged frequency of potentially damaging earthquakes in California. The primary achievements have been to relax fault segmentation assumptions and to include multifault ruptures, both limitations of the previous model (UCERF2). The rates of all earthquakes are solved for simultaneously, and from a broader range of data, using a system-level "grand inversion" that is both conceptually simple and extensible. The inverse problem is large and underdetermined, so a range of models is sampled using an efficient simulated annealing algorithm. The approach is more derivative than prescriptive (for example, magnitude-frequency distributions are no longer assumed), so new analysis tools were developed for exploring solutions. Epistemic uncertainties were also accounted for using 1,440 alternative logic tree branches, necessitating access to supercomputers. The most influential uncertainties include alternative deformation models (fault slip rates), a new smoothed seismicity algorithm, alternative values for the total rate of M≥5 events, and different scaling relationships, virtually all of which are new. As a notable first, three deformation models are based on kinematically consistent inversions of geodetic and geologic data, also providing slip-rate constraints on faults previously excluded because of lack of geologic data. The grand inversion constitutes a system-level framework for testing hypotheses and balancing the influence of different experts. For example, we demonstrate serious challenges with the Gutenberg-Richter hypothesis for individual faults. UCERF3 is still an approximation of the system, however, and the range of models is limited (for example, constrained to stay close to UCERF2). Nevertheless, UCERF3 removes the apparent UCERF2 overprediction of

  20. G-larmS: An Infrastructure for Geodetic Earthquake Early Warning, applied to Northern California

    NASA Astrophysics Data System (ADS)

    Johanson, I. A.; Grapenthin, R.; Allen, R. M.

    2014-12-01

    Integrating geodetic data into seismic earthquake early warning (EEW) is critical for accurately resolving magnitude and finite fault dimensions in the very largest earthquakes (M>7). We have developed G-larmS, the Geodetic alarm System, as part of our efforts to incorporate geodetic data into EEW for Northern California. G-larmS is an extensible geodetic EEW infrastructure that analyzes positioning time series from real-time GPS processors, such as TrackRT or RTNET. It is currently running in an operational mode at the Berkeley Seismological Laboratory (BSL) where we use TrackRT to produce high sample rate displacement time series for 62 GPS stations in the greater San Francisco Bay Area with 3-4 second latency. We employ a fully triangulated network scheme, which provides resiliency against an outage or telemetry loss at any individual station, for a total of 165 basestation-rover pairs. G-larmS is tightly integrated into seismic alarm systems (CISN ShakeAlert, ElarmS) as it uses their P-wave detection alarms to trigger its own processing and sends warning messages back to the ShakeAlert decision module. Once triggered, G-larmS estimates the static offset at each station pair and inputs these into an inversion for fault slip, which is updated once per second. The software architecture and clear interface definitions of this Python implementation enable straightforward extensibility and exchange of specific algorithms that operate in the individual modules. For example, multiple modeling instances can be called in parallel, each of which applying a different strategy to infer fault and magnitude information (e.g., pre-defined fault planes, full grid search, least squares inversion, etc.). This design enables, for example, quick tests, expansion and algorithm comparisons. Here, we present the setup and report results of the first months of operation in Northern California. This includes analysis of system latencies, noise, and G-larmS' response to actual events. We

  1. A public health issue related to collateral seismic hazards: The valley fever outbreak triggered by the 1994 Northridge, California earthquake

    USGS Publications Warehouse

    Jibson, R.W.

    2002-01-01

    Following the 17 January 1994 Northridge. California earthquake (M = 6.7), Ventura County, California, experienced a major outbreak of coccidioidomycosis (CM), commonly known as valley fever, a respiratory disease contracted by inhaling airborne fungal spores. In the 8 weeks following the earthquake (24 January through 15 March), 203 outbreak-associated cases were reported, which is about an order of magnitude more than the expected number of cases, and three of these cases were fatal. Simi Valley, in easternmost Ventura County, had the highest attack rate in the county, and the attack rate decreased westward across the county. The temporal and spatial distribution of CM cases indicates that the outbreak resulted from inhalation of spore-contaminated dust generated by earthquake-triggered landslides. Canyons North East of Simi Valley produced many highly disrupted, dust-generating landslides during the earthquake and its aftershocks. Winds after the earthquake were from the North East, which transported dust into Simi Valley and beyond to communities to the West. The three fatalities from the CM epidemic accounted for 4 percent of the total earthquake-related fatalities.

  2. Data Sets and Data Services at the Northern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

    Neuhauser, D. S.; Zuzlewski, S.; Allen, R. M.

    2014-12-01

    The Northern California Earthquake Data Center (NCEDC) houses a unique and comprehensive data archive and provides real-time services for a variety of seismological and geophysical data sets that encompass northern and central California. We have over 80 terabytes of continuous and event-based time series data from broadband, short-period, strong motion, and strain sensors as well as continuous and campaign GPS data at both standard and high sample rates in both raw and RINEX format. The Northen California Seismic System (NCSS), operated by UC Berkeley and USGS Menlo Park, has recorded over 890,000 events from 1984 to the present, and the NCEDC provides catalog, parametric information, moment tensors and first motion mechanisms, and time series data for these events. We also host and provide event catalogs, parametric information, and event waveforms for DOE enhanced geothermal system monitoring in northern California and Nevada. The NCEDC provides a variety of ways for users to access these data. The most recent development are web services, which provide interactive, command-line, or program-based workflow access to data. Web services use well-established server and client protocols and RESTful software architecture that allow users to easily submit queries and receive the requested data in real-time rather than through batch or email-based requests. Data are returned to the user in the appropriate format such as XML, RESP, simple text, or MiniSEED depending on the service and selected output format. The NCEDC supports all FDSN-defined web services as well as a number of IRIS-defined and NCEDC-defined services. We also continue to support older email-based and browser-based access to data. NCEDC data and web services can be found at http://www.ncedc.org and http://service.ncedc.org.

  3. Sonographs of submarine sediment failure caused by the 1980 earthquake off northern California

    USGS Publications Warehouse

    Field, M.E.; Hall, R.K.

    1982-01-01

    In 1980, a large earthquake caused extensive sediment failure on the shallow continental shelf off the Klamath River in northern California. Side-scan sonography was used to complement detailed geophysical profiling in identifying specific features and resolving modes of failure. The features include a nearly flat failure terrace mantled with sand boils, collapse craters and sediment flows, and bounded on the seaward side by a meandering continuous toe ridge. Seaward of the terrace lies a compression zone delineated by small pressure ridges. Our findings indicate a temporal progression of failure from lique-faction of shallow subsurface sand to lateral spread of intact blocks to sediment collapse and flow. ?? 1982 A. M. Dowden, Inc.

  4. Data and Visualizations in the Southern California Earthquake Center's Fault Information System

    NASA Astrophysics Data System (ADS)

    Perry, S.

    2003-12-01

    The Southern California Earthquake Center's Fault Information System (FIS) provides a single point of access to fault-related data and models from multiple databases and datasets. The FIS is built of computer code, metadata and Web interfaces based on Web services technology, which enables queries and data interchange irrespective of computer software or platform. Currently we have working prototypes of programmatic and browser-based access. The first generation FIS may be searched and downloaded live, by automated processes, as well as interactively, by humans using a browser. Users get ascii data in plain text or encoded in XML. Via the Earthquake Information Technology (EIT) Interns (Juve and others, this meeting), we are also testing the effectiveness of querying multiple databases using a fault database ontology. For more than a decade, the California Geological Survey (CGS), SCEC, and the U. S. Geological Survey (USGS) have put considerable, shared resources into compiling and assessing published fault data, then providing the data on the Web. Several databases now exist, with different formats, datasets, purposes, and users, in various stages of completion. When fault databases were first envisioned, the full power of today's internet was not yet recognized, and the databases became the Web equivalents of review papers, where one could read an overview summation of a fault, then copy and paste pertinent data. Today, numerous researchers also require rapid queries and downloads of data. Consequently, the first components of the FIS are MySQL databases that deliver numeric values from earlier, text-based databases. Another essential service provided by the FIS is visualizations of fault representations such as those in SCEC's Community Fault Model. The long term goal is to provide a standardized, open-source, platform-independent visualization technique. Currently, the FIS makes available fault model viewing software for users with access to Matlab or Java3D

  5. Frequency-magnitude statistics and spatial correlation dimensions of earthquakes at Long Valley caldera, California

    NASA Astrophysics Data System (ADS)

    Barton, D. J.; Foulger, G. R.; Henderson, J. R.; Julian, B. R.

    1999-08-01

    Intense earthquake swarms at Long Valley caldera in late 1997 and early 1998 occurred on two contrasting structures. The first is defined by the intersection of a north-northwesterly array of faults with the southern margin of the resurgent dome, and is a zone of hydrothermal upwelling. Seismic activity there was characterized by high b-values and relatively low values of D, the spatial fractal dimension of hypocentres. The second structure is the pre-existing South Moat fault, which has generated large-magnitude seismic activity in the past. Seismicity on this structure was characterized by low b-values and relatively high D. These observations are consistent with low-magnitude, clustered earthquakes on the first structure, and higher-magnitude, diffuse earthquakes on the second structure. The first structure is probably an immature fault zone, fractured on a small scale and lacking a well-developed fault plane. The second zone represents a mature fault with an extensive, coherent fault plane.

  6. Frequency-magnitude statistics and spatial correlation dimensions of earthquakes at Long Valley caldera, California

    USGS Publications Warehouse

    Barton, D.J.; Foulger, G.R.; Henderson, J.R.; Julian, B.R.

    1999-01-01

    Intense earthquake swarms at Long Valley caldera in late 1997 and early 1998 occurred on two contrasting structures. The first is defined by the intersection of a north-northwesterly array of faults with the southern margin of the resurgent dome, and is a zone of hydrothermal upwelling. Seismic activity there was characterized by high b-values and relatively low values of D, the spatial fractal dimension of hypocentres. The second structure is the pre-existing South Moat fault, which has generated large-magnitude seismic activity in the past. Seismicity on this structure was characterized by low b-values and relatively high D. These observations are consistent with low-magnitude, clustered earthquakes on the first structure, and higher-magnitude, diffuse earthquakes on the second structure. The first structure is probably an immature fault zone, fractured on a small scale and lacking a well-developed fault plane. The second zone represents a mature fault with an extensive, coherent fault plane.

  7. Probable Post-Traumatic Stress Disorder and Its Predictors in Disaster-Bereaved Survivors: A Longitudinal Study After the Sichuan Earthquake.

    PubMed

    Hu, Xiuying; Cao, Xiaoyi; Wang, Heng; Chen, Qian; Liu, Maoqiong; Yamamoto, Aiko

    2016-04-01

    This study examined the trajectory of probable PTSD prevalence and severity, and analyzed the predictors for PTSD severity in bereaved survivors at 6 months and 18 months after the 2008 Sichuan earthquake. This was a longitudinal study with 226 bereaved survivors sampled at 6 months and 18 months post-earthquake. The instrument used in the study was the revised version of the Impact of Event Scale. The results showed that the prevalence of probable PTSD in bereaved survivors decreased significantly from 38.9% at 6 months to 16.8% at 18 months post-earthquake. Loss of a child, being directly exposed to the death of family members and property loss during the earthquake, and mental health services utilization after the earthquake were significant predictors for PTSD severity at both assessments. These findings can contribute to post-disaster psychological rescue work. The bereaved survivors at high risk for more severe PTSD should be particularly targeted. PMID:26992870

  8. Evidence of shallow fault zone strengthening after the 1992 M7.5 Landers, California, earthquake

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.; Aki, K.; Xu, Fei; Burdette, T.

    1998-01-01

    Repeated seismic surveys of the Landers, California, fault zone that ruptured in the magnitude (M) 7.5 earthquake of 1992 reveal an increase in seismic velocity with time. P, S, and fault zone trapped waves were excited by near-surface explosions in two locations in 1994 and 1996, and were recorded on two linear, three-component seismic arrays deployed across the Johnson Valley fault trace. The travel times of P and S waves for identical shot-receiver pairs decreased by 0.5 to 1.5 percent from 1994 to 1996, with the larger changes at stations located within the fault zone. These observations indicate that the shallow Johnson Valley fault is strengthening after the main shock, most likely because of closure of cracks that were opened by the 1992 earthquake. The increase in velocity is consistent with the prevalence of dry over wet cracks and with a reduction in the apparent crack density near the fault zone by approximately 1.0 percent from 1994 to 1996.

  9. Rupture propagation of the 2004 Parkfield, California, earthquake from observations at the UPSAR

    USGS Publications Warehouse

    Fletcher, Joe B.; Spudich, P.; Baker, L.M.

    2006-01-01

    Using a short-baseline seismic array (U.S. Geological Survey Parkfield Dense Seismograph Array [UPSAR]) about 12 km west of the rupture initiation of the 28 September 2004 M 6.0 Parkfield, California, earthquake, we have observed the movement of the rupture front of this earthquake on the San Andreas fault. The sources of high-frequency arrivals at UPSAR, which we use to identify the rupture front, are mapped onto the San Andreas fault using their apparent velocity and back azimuth. Measurements of apparent velocity and back azimuth are calibrated using aftershocks, which have a compact source and known location. Aftershock back azimuths show considerable lateral refraction, consistent with a high-velocity ridge on the southwest side of the fault. We infer that the initial mainshock rupture velocity was approximately the Rayleigh speed (with respect to slower side of the fault), and the rupture then slowed to about 0.66?? near the town of Parkfield after 2 sec. The last well-correlated pulse, 4 sec after S, is the largest at UPSAR, and its source is near the region of large accelerations recorded by strong-motion accelerographs and close to northern extent of continuous surface fractures on the southwest fracture zone. Coincidence of sources with preshock and aftershock distributions suggests fault material properties control rupture behavior. High-frequency sources approximately correlate with the edges of asperities identified as regions of high slip derived from inversion of strong-motion waveforms.

  10. A Double-difference Earthquake location algorithm: Method and application to the Northern Hayward Fault, California

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2000-01-01

    We have developed an efficient method to determine high-resolution hypocenter locations over large distances. The location method incorporates ordinary absolute travel-time measurements and/or cross-correlation P-and S-wave differential travel-time measurements. Residuals between observed and theoretical travel-time differences (or double-differences) are minimized for pairs of earthquakes at each station while linking together all observed event-station pairs. A least-squares solution is found by iteratively adjusting the vector difference between hypocentral pairs. The double-difference algorithm minimizes errors due to unmodeled velocity structure without the use of station corrections. Because catalog and cross-correlation data are combined into one system of equations, interevent distances within multiplets are determined to the accuracy of the cross-correlation data, while the relative locations between multiplets and uncorrelated events are simultaneously determined to the accuracy of the absolute travel-time data. Statistical resampling methods are used to estimate data accuracy and location errors. Uncertainties in double-difference locations are improved by more than an order of magnitude compared to catalog locations. The algorithm is tested, and its performance is demonstrated on two clusters of earthquakes located on the northern Hayward fault, California. There it colapses the diffuse catalog locations into sharp images of seismicity and reveals horizontal lineations of hypocenter that define the narrow regions on the fault where stress is released by brittle failure.

  11. Overview of the Uniform California Earthquake Rupture Forecast Version 3 (UCERF3) Time-Independent Model

    NASA Astrophysics Data System (ADS)

    Field, E. H.; Arrowsmith, R.; Biasi, G. P.; Bird, P.; Dawson, T. E.; Felzer, K. R.; Jackson, D. D.; Johnson, K. M.; Jordan, T. H.; Madugo, C. M.; Michael, A. J.; Milner, K. R.; Page, M. T.; Parsons, T.; Powers, P.; Shaw, B. E.; Thatcher, W. R.; Weldon, R. J.; Zeng, Y.

    2013-12-01

    We present the time-independent component of the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), where the primary achievements have been to relax fault segmentation and include multi-fault ruptures, both limitations of UCERF2. The rates of all earthquakes are solved for simultaneously, and from a broader range of data, using a system-level 'grand inversion' that is both conceptually simple and extensible. The inverse problem is large and underdetermined, so a range of models is sampled using an efficient simulated annealing algorithm. The approach is more derivative than prescriptive (e.g., magnitude-frequency distributions are no longer assumed), so new analysis tools were developed for exploring solutions. Epistemic uncertainties were also accounted for using 1440 alternative logic tree branches, necessitating access to supercomputers. The most influential uncertainties include alternative deformation models (fault slip rates), a new smoothed seismicity algorithm, alternative values for the total rate of M≥5 events, and different scaling relationships, virtually all of which are new. As a notable first, three deformation models are based on kinematically consistent inversions of geodetic and geologic data, also providing slip-rate constraints on faults previously excluded due to lack of geologic data. The grand inversion constitutes a system-level framework for testing hypotheses and balancing the influence of different experts. For example, we demonstrate serious challenges with the Gutenberg-Richter hypothesis for individual faults. UCERF3 is still an approximation of the system, however, and the range of models is limited (e.g., constrained to stay close to UCERF2). Nevertheless, UCERF3 removes the apparent UCERF2 over-prediction of M6.5-7 earthquake rates, and also includes types of multi-fault ruptures seen in nature. While UCERF3 fits the data better than UCERF2 overall, there may be areas that warrant further site

  12. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  13. Comparison of four moderate-size earthquakes in southern California using seismology and InSAR

    USGS Publications Warehouse

    Mellors, R.J.; Magistrale, H.; Earle, P.; Cogbill, A.H.

    2004-01-01

    Source parameters determined from interferometric synthetic aperture radar (InSAR) measurements and from seismic data are compared from four moderate-size (less than M 6) earthquakes in southern California. The goal is to verify approximate detection capabilities of InSAR, assess differences in the results, and test how the two results can be reconciled. First, we calculated the expected surface deformation from all earthquakes greater than magnitude 4 in areas with available InSAR data (347 events). A search for deformation from the events in the interferograms yielded four possible events with magnitudes less than 6. The search for deformation was based on a visual inspection as well as cross-correlation in two dimensions between the measured signal and the expected signal. A grid-search algorithm was then used to estimate focal mechanism and depth from the InSAR data. The results were compared with locations and focal mechanisms from published catalogs. An independent relocation using seismic data was also performed. The seismic locations fell within the area of the expected rupture zone for the three events that show clear surface deformation. Therefore, the technique shows the capability to resolve locations with high accuracy and is applicable worldwide. The depths determined by InSAR agree with well-constrained seismic locations determined in a 3D velocity model. Depth control for well-imaged shallow events using InSAR data is good, and better than the seismic constraints in some cases. A major difficulty for InSAR analysis is the poor temporal coverage of InSAR data, which may make it impossible to distinguish deformation due to different earthquakes at the same location.

  14. Winnetka deformation zone: Surface expression of coactive slip on a blind fault during the Northridge earthquake sequence, California. Evidence that coactive faulting occurred in the Canoga Park, Winnetka, and Northridge areas during the 17 January 1994, Northridge, California earthquake

    SciTech Connect

    Cruikshank, K.M.; Johnson, A.M.; Fleming, R.W.; Jones, R.L.

    1996-12-31

    Measurements of normalized length changes of streets over an area of 9 km{sup 2} in San Fernando Valley of Los Angeles, California, define a distinctive strain pattern that may well reflect blind faulting during the 1994 Northridge earthquake. Strain magnitudes are about 3 {times} 10{sup {minus}4}, locally 10{sup {minus}3}. They define a deformation zone trending diagonally from near Canoga Park in the southwest, through Winnetka, to near Northridge in the northeast. The deformation zone is about 4.5 km long and 1 km wide. The northwestern two-thirds of the zone is a belt of extension of streets, and the southeastern one-third is a belt of shortening of streets. On the northwest and southeast sides of the deformation zone the magnitude of the strains is too small to measure, less than 10{sup {minus}4}. Complete states of strain measured in the northeastern half of the deformation zone show that the directions of principal strains are parallel and normal to the walls of the zone, so the zone is not a strike-slip zone. The magnitudes of strains measured in the northeastern part of the Winnetka area were large enough to fracture concrete and soils, and the area of larger strains correlates with the area of greater damage to such roads and sidewalks. All parts of the pattern suggest a blind fault at depth, most likely a reverse fault dipping northwest but possibly a normal fault dipping southeast. The magnitudes of the strains in the Winnetka area are consistent with the strains produced at the ground surface by a blind fault plane extending to depth on the order of 2 km and a net slip on the order of 1 m, within a distance of about 100 to 500 m of the ground surface. The pattern of damage in the San Fernando Valley suggests a fault segment much longer than the 4.5 km defined by survey data in the Winnetka area. The blind fault segment may extend several kilometers in both directions beyond the Winnetka area. This study of the Winnetka area further supports

  15. Monitoring of the stress state variations of the Southern California for the purpose of earthquake prediction

    NASA Astrophysics Data System (ADS)

    Gokhberg, M.; Garagash, I.; Bondur, V.; Steblov, G. M.

    2014-12-01

    The three-dimensional geomechanical model of Southern California was developed, including a mountain relief, fault tectonics and characteristic internal features such as the roof of the consolidated crust and Moho surface. The initial stress state of the model is governed by the gravitational forces and horizontal tectonic motions estimated from GPS observations. The analysis shows that the three-dimensional geomechanical models allows monitoring of the changes in the stress state during the seismic process in order to constrain the distribution of the future places with increasing seismic activity. This investigation demonstrates one of possible approach to monitor upcoming seismicity for the periods of days - weeks - months. Continuous analysis of the stress state was carried out during 2009-2014. Each new earthquake with М~1 and above from USGS catalog was considered as the new defect of the Earth crust which has some definite size and causes redistribution of the stress state. Overall calculation technique was based on the single function of the Earth crust damage, recalculated each half month. As a result each half month in the upper crust layers and partially in the middle layers we revealed locations of the maximal values of the stress state parameters: elastic energy density, shear stress, proximity of the earth crust layers to their strength limit. All these parameters exhibit similar spatial and temporal distribution. How follows from observations all four strongest events with М ~ 5.5-7.2 occurred in South California during the analyzed period were prefaced by the parameters anomalies in peculiar advance time of weeks-months in the vicinity of 10-50 km from the upcoming earthquake. After the event the stress state source disappeared. The figure shows migration of the maximums of the stress state variations gradients (parameter D) in the vicinity of the epicenter of the earthquake 04.04.2010 with М=7.2 in the period of 01.01.2010-01.05.2010. Grey lines

  16. Artefacts of earthquake location errors and short-term incompleteness on seismicity clusters in southern California

    NASA Astrophysics Data System (ADS)

    Zaliapin, Ilya; Ben-Zion, Yehuda

    2015-09-01

    We document and quantify effects of two types of catalogue uncertainties-earthquake location errors and short-term incompleteness-on results of statistical cluster analyses of seismicity in southern California. In the main part of the study we analyse 117 076 events with m ≥ 2 in southern California during 1981-2013 from the waveform-relocated catalogue of Hauksson et al. We present statistical evidence for three artefacts caused by the absolute and relative location errors: (1) Increased distance between offspring and parents. (2) Underestimated clustering, quantified by the number of offspring per event, the total number of clustered events, and some other statistics. (3) Overestimated background rates. We also find that short-term incompleteness leads to (4) Apparent magnitude dependence and temporal fluctuations of b-values. The reported artefacts are robustly observed in three additional catalogues of southern California: the relocated catalogue of Richards-Dinger & Shearer during 1975-1998, and the two subcatalogues-1961-1981 and 1981-2013-of the Advances National Seismic System catalogue. This implies that the reported artefacts are not specific to a particular (re)location method. The comparative quality of the four examined catalogues is reflected in the magnitude of the artefacts. The location errors in the examined catalogues mostly affect events with m < 3.5, while for larger magnitudes the location error effects are negligible. This is explained by comparing the location error and rupture lengths of events and their parents. Finally, our analysis suggests that selected aggregated cluster statistics (e.g. proportion of singles) are less prone to location artefacts than individual statistics (e.g. the distance to parent or parent-offspring assignment). The results can inform a range of studies focused on small-magnitude seismicity patterns in the presence of catalogue uncertainties.

  17. Survey of strong motion earthquake effects on thermal power plants in California with emphasis on piping systems. Volume 2, Appendices

    SciTech Connect

    Stevenson, J.D.

    1995-11-01

    Volume 2 of the ``Survey of Strong Motion Earthquake Effects on Thermal Power Plants in California with Emphasis on Piping Systems`` contains Appendices which detail the detail design and seismic response of several power plants subjected to strong motion earthquakes. The particular plants considered include the Ormond Beach, Long Beach and Seal Beach, Burbank, El Centro, Glendale, Humboldt Bay, Kem Valley, Pasadena and Valley power plants. Included is a typical power plant piping specification and photographs of typical power plant piping specification and photographs of typical piping and support installations for the plants surveyed. Detailed piping support spacing data are also included.

  18. CRUSTAL REFRACTION PROFILE OF THE LONG VALLEY CALDERA, CALIFORNIA, FROM THE JANUARY 1983 MAMMOTH LAKES EARTHQUAKE SWARM.

    USGS Publications Warehouse

    Luetgert, James H.; Mooney, Walter D.

    1985-01-01

    Seismic-refraction profiles recorded north of Mammoth Lakes, California, using earthquake sources from the January 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the Long Valley caldera. Eight earthquakes from a depth range of 4. 9 to 8. 0 km confirm the observation of basement rocks with seismic velocities ranging from 5. 8 to 6. 4 km/sec extending at least to depths of 20 km. The data provide further evidence for the existence of a partial melt zone beneath Long Valley caldera and constrain its geometry. Refs.

  19. Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations

    NASA Astrophysics Data System (ADS)

    Waldhauser, Felix; Ellsworth, William L.

    2002-03-01

    The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggests that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when

  20. Fault structure and mechanics of the Hayward Fault, California from double-difference earthquake locations

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2002-01-01

    The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggest that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital

  1. Timing of large earthquakes since A.D. 800 on the Mission Creek strand of the San Andreas fault zone at Thousand Palms Oasis, near Palm Springs, California

    USGS Publications Warehouse

    Fumal, T.E.; Rymer, M.J.; Seitz, G.G.

    2002-01-01

    Paleoseismic investigations across the Mission Creek strand of the San Andreas fault at Thousand Palms Oasis indicate that four and probably five surface-rupturing earthquakes occurred during the past 1200 years. Calendar age estimates for these earthquakes are based on a chronological model that incorporates radio-carbon dates from 18 in situ burn layers and stratigraphic ordering constraints. These five earthquakes occurred in about A.D. 825 (770-890) (mean, 95% range), A.D. 982 (840-1150), A.D. 1231 (1170-1290), A.D. 1502 (1450-1555), and after a date in the range of A.D. 1520-1680. The most recent surface-rupturing earthquake at Thousand Palms is likely the same as the A.D. 1676 ?? 35 event at Indio reported by Sieh and Williams (1990). Each of the past five earthquakes recorded on the San Andreas fault in the Coachella Valley strongly overlaps in time with an event at the Wrightwood paleoseismic site, about 120 km northwest of Thousand Palms Oasis. Correlation of events between these two sites suggests that at least the southernmost 200 km of the San Andreas fault zone may have ruptured in each earthquake. The average repeat time for surface-rupturing earthquakes on the San Andreas fault in the Coachella Valley is 215 ?? 25 years, whereas the elapsed time since the most recent event is 326 ?? 35 years. This suggests the southernmost San Andreas fault zone likely is very near failure. The Thousand Palms Oasis site is underlain by a series of six channels cut and filled since about A.D. 800 that cross the fault at high angles. A channel margin about 900 years old is offset right laterally 2.0 ?? 0.5 m, indicating a slip rate of 4 ?? 2 mm/yr. This slip rate is low relative to geodetic and other geologic slip rate estimates (26 ?? 2 mm/yr and about 23-35 mm/yr, respectively) on the southernmost San Andreas fault zone, possibly because (1) the site is located in a small step-over in the fault trace and so the rate is not be representative of the Mission Creek fault

  2. TriNet "ShakeMaps": Rapid generation of peak ground motion and intensity maps for earthquakes in southern California

    USGS Publications Warehouse

    Wald, D.J.; Quitoriano, V.; Heaton, T.H.; Kanamori, H.; Scrivner, C.W.; Worden, C.B.

    1999-01-01

    Rapid (3-5 minutes) generation of maps of instrumental ground-motion and shaking intensity is accomplished through advances in real-time seismographic data acquisition combined with newly developed relationships between recorded ground-motion parameters and expected shaking intensity values. Estimation of shaking over the entire regional extent of southern California is obtained by the spatial interpolation of the measured ground motions with geologically based frequency and amplitude-dependent site corrections. Production of the maps is automatic, triggered by any significant earthquake in southern California. Maps are now made available within several minutes of the earthquake for public and scientific consumption via the World Wide Web; they will be made available with dedicated communications for emergency response agencies and critical users.

  3. Bayesian probabilities for Mw 9.0+ earthquakes in the Aleutian Islands from a regionally scaled global rate

    NASA Astrophysics Data System (ADS)

    Butler, Rhett; Frazer, L. Neil; Templeton, William J.

    2016-05-01

    We use the global rate of Mw ≥ 9.0 earthquakes, and standard Bayesian procedures, to estimate the probability of such mega events in the Aleutian Islands, where they pose a significant risk to Hawaii. We find that the probability of such an earthquake along the Aleutians island arc is 6.5% to 12% over the next 50 years (50% credibility interval) and that the annualized risk to Hawai'i is about $30 M. Our method (the regionally scaled global rate method or RSGR) is to scale the global rate of Mw 9.0+ events in proportion to the fraction of global subduction (units of area per year) that takes place in the Aleutians. The RSGR method assumes that Mw 9.0+ events are a Poisson process with a rate that is both globally and regionally stationary on the time scale of centuries, and it follows the principle of Burbidge et al. (2008) who used the product of fault length and convergence rate, i.e., the area being subducted per annum, to scale the Poisson rate for the GSS to sections of the Indonesian subduction zone. Before applying RSGR to the Aleutians, we first apply it to five other regions of the global subduction system where its rate predictions can be compared with those from paleotsunami, paleoseismic, and geoarcheology data. To obtain regional rates from paleodata, we give a closed-form solution for the probability density function of the Poisson rate when event count and observation time are both uncertain.

  4. Processed seismic motion records from Big Bear, California earthquake of June 28, 1992, recorded at seismograph stations in southern Nevada

    SciTech Connect

    Lum, P.K.; Honda, K.K.

    1993-04-01

    The 8mm data-tape contains the processed seismic data of the Big Bear, California earthquake of June 28, 1992. The seismic data were recorded by 15 seismographs maintained by the DOE/NV in Southern Nevada. Four files were generated from each seismic recorder. They are ``Uncorrected acceleration time histories, 2. Corrected acceleration, velocity and displacement time histories, 3. Pseudo response velocity spectra, and 4. Fourier amplitude spectra of acceleration.``

  5. Processed seismic motion records from Landers, California earthquake of June 28, 1992, recorded at seismograph stations in southern Nevada

    SciTech Connect

    Lum, P.K.; Honda, K.K.

    1993-04-01

    The 8mm data tape contains the processed seismic data of the Landers, California earthquake of June 28, 1992. The seismic, data were recorded by 19 seismographs maintained by the DOE/NV in Southern Nevada. Four files were generated from each seismic recorder. They are ``Uncorrected acceleration time histories, 2. Corrected acceleration, velocity and displacement time histories, 3. Pseudo response velocity spectra, and 4. Fourier amplitude spectra of acceleration.``

  6. Dynamic deformations and the M6.7, Northridge, California earthquake

    USGS Publications Warehouse

    Gomberg, J.

    1997-01-01

    A method of estimating the complete time-varying dynamic formation field from commonly available three-component single station seismic data has been developed and applied to study the relationship between dynamic deformation and ground failures and structural damage using observations from the 1994 Northridge, California earthquake. Estimates from throughout the epicentral region indicate that the horizontal strains exceed the vertical ones by more than a factor of two. The largest strains (exceeding ???100 ??strain) correlate with regions of greatest ground failure. There is a poor correlation between structural damage and peak strain amplitudes. The smallest strains, ???35 ??strain, are estimated in regions of no damage or ground failure. Estimates in the two regions with most severe and well mapped permanent deformation, Potrero Canyon and the Granada-Mission Hills regions, exhibit the largest strains; peak horizontal strains estimates in these regions equal ???139 and ???229 ??strain respectively. Of note, the dynamic principal strain axes have strikes consistent with the permanent failure features suggesting that, while gravity, sub-surface materials, and hydrologic conditions undoubtedly played fundamental roles in determining where and what types of failures occurred, the dynamic deformation field may have been favorably sized and oriented to initiate failure processes. These results support other studies that conclude that the permanent deformation resulted from ground shaking, rather than from static strains associated with primary or secondary faulting. They also suggest that such an analysis, either using data or theoretical calculations, may enable observations of paleo-ground failure to be used as quantitative constraints on the size and geometry of previous earthquakes. ?? 1997 Elsevier Science Limited.

  7. Detailed observations of California foreshock sequences: Implications for the earthquake initiation process

    USGS Publications Warehouse

    Dodge, D.A.; Beroza, G.C.; Ellsworth, W.L.

    1996-01-01

    We find that foreshocks provide clear evidence for an extended nucleation process before some earthquakes. In this study, we examine in detail the evolution of six California foreshock sequences, the 1986 Mount Lewis (ML, = 5.5), the 1986 Chalfant (ML = 6.4), the. 1986 Stone Canyon (ML = 4.7), the 1990 Upland (ML = 5.2), the 1992 Joshua Tree (MW= 6.1), and the 1992 Landers (MW = 7.3) sequence. Typically, uncertainties in hypocentral parameters are too large to establish the geometry of foreshock sequences and hence to understand their evolution. However, the similarity of location and focal mechanisms for the events in these sequences leads to similar foreshock waveforms that we cross correlate to obtain extremely accurate relative locations. We use these results to identify small-scale fault zone structures that could influence nucleation and to determine the stress evolution leading up to the mainshock. In general, these foreshock sequences are not compatible with a cascading failure nucleation model in which the foreshocks all occur on a single fault plane and trigger the mainshock by static stress transfer. Instead, the foreshocks seem to concentrate near structural discontinuities in the fault and may themselves be a product of an aseismic nucleation process. Fault zone heterogeneity may also be important in controlling the number of foreshocks, i.e., the stronger the heterogeneity, the greater the number of foreshocks. The size of the nucleation region, as measured by the extent of the foreshock sequence, appears to scale with mainshock moment in the same manner as determined independently by measurements of the seismic nucleation phase. We also find evidence for slip localization as predicted by some models of earthquake nucleation. Copyright 1996 by the American Geophysical Union.

  8. Potential Effects of a Scenario Earthquake on the Economy of Southern California: Small Business Exposure and Sensitivity Analysis to a Magnitude 7.8 Earthquake

    USGS Publications Warehouse

    Sherrouse, Benson C.; Hester, David J.; Wein, Anne M.

    2008-01-01

    The Multi-Hazards Demonstration Project (MHDP) is a collaboration between the U.S. Geological Survey (USGS) and various partners from the public and private sectors and academia, meant to improve Southern California's resiliency to natural hazards (Jones and others, 2007). In support of the MHDP objectives, the ShakeOut Scenario was developed. It describes a magnitude 7.8 (M7.8) earthquake along the southernmost 300 kilometers (200 miles) of the San Andreas Fault, identified by geoscientists as a plausible event that will cause moderate to strong shaking over much of the eight-county (Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura) Southern California region. This report contains an exposure and sensitivity analysis of small businesses in terms of labor and employment statistics. Exposure is measured as the absolute counts of labor market variables anticipated to experience each level of Instrumental Intensity (a proxy measure of damage). Sensitivity is the percentage of the exposure of each business establishment size category to each Instrumental Intensity level. The analysis concerns the direct effect of the earthquake on small businesses. The analysis is inspired by the Bureau of Labor Statistics (BLS) report that analyzed the labor market losses (exposure) of a M6.9 earthquake on the Hayward fault by overlaying geocoded labor market data on Instrumental Intensity values. The method used here is influenced by the ZIP-code-level data provided by the California Employment Development Department (CA EDD), which requires the assignment of Instrumental Intensities to ZIP codes. The ZIP-code-level labor market data includes the number of business establishments, employees, and quarterly payroll categorized by business establishment size.

  9. Multifractal Omori law for earthquake triggering: new tests on the California, Japan and worldwide catalogues

    NASA Astrophysics Data System (ADS)

    Ouillon, G.; Sornette, D.; Ribeiro, E.

    2009-07-01

    The Multifractal Stress-Activated model is a statistical model of triggered seismicity based on mechanical and thermodynamic principles. It predicts that, above a triggering magnitude cut-off M0, the exponent p of the Omori law for the time decay of the rate of aftershocks is a linear increasing function p(M) = a0M + b0 of the main shock magnitude M. We previously reported empirical support for this prediction, using the Southern California Earthquake Center (SCEC) catalogue. Here, we confirm this observation using an updated, longer version of the same catalogue, as well as new methods to estimate p. One of this methods is the newly defined Scaling Function Analysis (SFA), adapted from the wavelet transform. This method is able to measure a mathematical singularity (hence a p-value), erasing the possible regular part of a time-series. The SFA also proves particularly efficient to reveal the coexistence and superposition of several types of relaxation laws (typical Omori sequences and short-lived swarms sequences) which can be mixed within the same catalogue. Another new method consists in monitoring the largest aftershock magnitude observed in successive time intervals, and thus shortcuts the problem of missing events with small magnitudes in aftershock catalogues. The same methods are used on data from the worldwide Harvard Centroid Moment Tensor (CMT) catalogue and show results compatible with those of Southern California. For the Japan Meteorological Agency (JMA) catalogue, we still observe a linear dependence of p on M, but with a smaller slope. The SFA shows however that results for this catalogue may be biased by numerous swarm sequences, despite our efforts to remove them before the analysis.

  10. Probability of failure in BWR reactor coolant piping: Guillotine break indirectly induced by earthquakes

    SciTech Connect

    Hardy, G.S.; Campbell, R.D.; Ravindra, M.K.

    1986-12-01

    The requirements to design nuclear power plants for the effects of an instantaneous double-ended guillotine break (DEGB) of the reactor coolant piping have led to excessive design costs, interference with normal plant operation and maintenance, and unnecessary radiation exposure of plant maintenance personnel. This report describes an aspect of the NRC/Lawrence Livermore National laboratory-sponsored research program aimed at investigating whether the probability of DEGB in Reactor Coolant Loop Piping of nuclear power plants is acceptably small such that the requirements to design for the DEGB effects (e.g., provision of pipe whip restraints) may be removed. This study estimates the probability of indirect DEGB in Reactor Coolant piping as a consequence of seismic-induced structural failures within the containment of the GE supplied boiling water reactor at the Brunswick nuclear power plant. The median probability of indirect DEGB was estimated to be 2 x 10/sup -8/ per year. Using conservation assumptions, the 90% subjective probability value (confidence) of P/sub DEGB/ was found to be less than 5 x 10/sup -7/ per year.

  11. Cruise report for A1-02-SC southern California CABRILLO project, Earthquake Hazards Task

    USGS Publications Warehouse

    Normark, William R.; Fisher, Michael A.; Gutmacher, Christina E.; Sliter, Ray; Hibbeler, Lori; Feingold, Beth; Reid, Jane A.

    2003-01-01

    A two-week marine geophysical survey obtained sidescan-sonar images and multiple sets of high-resolution seismic-reflection profiles in the southern California offshore area between Point Arguello and Point Dume. The data were obtained to support two project activities of the United States Geological Survey (USGS) Coastal and Marine Geology (CMG) Program: (1) the evaluation of the geologic hazards posed by earthquake faults and landslides in the offshore areas of Santa Barbara Channel and western Santa Monica Basin and (2) determine the location of active hydrocarbon seeps in the vicinity of Point Conception as part of a collaborative study with the Minerals Management Service (MMS). The 2002 cruise, A1-02- SC, is the fourth major data-collection effort in support of the first objective (Normark et al., 1999a, b; Gutmacher et al., 2000). A cruise to obtain sediment cores to constrain the timing of deformation interpreted from the geophysical records is planned for the summer of 2003.

  12. Disaster Response and Decision Support in Partnership with the California Earthquake Clearinghouse

    NASA Astrophysics Data System (ADS)

    Glasscoe, M. T.; Rosinski, A.; Vaughan, D.; Morentz, J.

    2014-12-01

    Getting the right information to the right people at the right time is critical during a natural disaster. E-DECIDER (Emergency Data Enhanced Cyber-Infrastructure for Disaster Evaluation and Response) is a NASA decision support system designed to produce remote sensing and geophysical modeling data products that are relevant to the emergency preparedness and response communities and serve as a gateway to enable the delivery of NASA decision support products to these communities. The E-DECIDER decision support system has several tools, services, and products that have been used to support end-user exercises in partnership with the California Earthquake Clearinghouse since 2012, including near real-time deformation modeling results and on-demand maps of critical infrastructure that may have been potentially exposed to damage by a disaster. E-DECIDER's underlying service architecture allows the system to facilitate delivery of NASA decision support products to the Clearinghouse through XchangeCore Web Service Data Orchestration that allows trusted information exchange among partner agencies. This in turn allows Clearinghouse partners to visualize data products produced by E-DECIDER and other NASA projects through incident command software such as SpotOnResponse or ArcGIS Online.

  13. Fault tectonics and earthquake hazards in the Peninsular Ranges, Southern California

    NASA Technical Reports Server (NTRS)

    Merifield, P. M.; Lamar, D. L. (Principal Investigator)

    1974-01-01

    The author has identified the following significant results. ERTS and Skylab images reveal a number of prominent lineaments in the basement terrane of the Peninsular Ranges, Southern California. The major, well-known, active, northwest trending, right-slip faults are well displayed, but northeast and west to west-northwest trending lineaments are also present. Study of large-scale airphotos followed by field investigations have shown that several of these lineaments represent previously unmapped faults. Pitches of striations on shear surfaces of the northeast and west trending faults indicate oblique-slip movement; data are insufficient to determine the net-slip. These faults are restricted to the pre-Tertiary basement terrane and are truncated by the major northwest trending faults; therefore, they may have formed in response to an earlier stress system. Future work should be directed toward determining whether the northeast and west trending faults are related to the presently active stress system or to an older inactive system, because this question relates to the earthquake risk in the vicinity of these faults.

  14. A rupture model for the 28 June 1992 Landers, California, earthquake

    NASA Astrophysics Data System (ADS)

    Campillo, Michel; Archuleta, Ralph J.

    1993-04-01

    We have modeled displacement time histories to infer the large-scale rupture process of the June 28, 1992 7.4-magnitude quake at Landers, California. We have used integrated accelerograms from four TERRAscope stations at distances between 70 and 150 km. The earthquake process consists of unilateral rupture propagation, 3 km/s, on two distinct segments with different strikes: N 10 deg W and N 40 deg W. The two segments are 20 and 30 km long, with constant slip of 3.5 m and 5.2 m, respectively. The excitation of surface waves, resulting from a low-velocity surficial layer, plays a critical role in matching the synthetic waveforms to the observed displacements. The displacements, due to both body waves and surface waves, are strongly affected by directivity. Matching the synthetics to the data requires a one second delay between the end of rupture on the first segment and the initiation of rupture on the second segment. The seismic moment of the subevents are 2.8 x 10 exp 19 N-m and 8.4 x 10 exp 19 N-m, leading to a total moment of 1.12 x 10 exp 20 N-m (magnitude of 7.4).

  15. Evaluation of Real-Time Performance of the Virtual Seismologist Earthquake Early Warning Algorithm in Switzerland and California

    NASA Astrophysics Data System (ADS)

    Behr, Y.; Cua, G. B.; Clinton, J. F.; Heaton, T. H.

    2012-12-01

    The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) originally formulated by Cua and Heaton (2007). Implementation of VS into real-time EEW codes has been an on-going effort of the Swiss Seismological Service at ETH Zürich since 2006, with support from ETH Zürich, various European projects, and the United States Geological Survey (USGS). VS is one of three EEW algorithms - the other two being ElarmS (Allen and Kanamori, 2003) and On-Site (Wu and Kanamori, 2005; Boese et al., 2008) algorithms - that form the basis of the California Integrated Seismic Network (CISN) ShakeAlert system, a USGS-funded prototype end-to-end EEW system that could potentially be implemented in California. In Europe, VS is currently operating as a real-time test system in Switzerland. As part of the on-going EU project REAKT (Strategies and Tools for Real-Time Earthquake Risk Reduction), VS will be installed and tested at other European networks. VS has been running in real-time on stations of the Southern California Seismic Network (SCSN) since July 2008, and on stations of the Berkeley Digital Seismic Network (BDSN) and the USGS Menlo Park strong motion network in northern California since February 2009. In Switzerland, VS has been running in real-time on stations monitored by the Swiss Seismological Service (including stations from Austria, France, Germany, and Italy) since 2010. We present summaries of the real-time performance of VS in Switzerland and California over the past two and three years respectively. The empirical relationships used by VS to estimate magnitudes and ground motion, originally derived from southern California data, are demonstrated to perform well in northern California and Switzerland. Implementation in real-time and off-line testing in Europe will potentially be extended to southern Italy, western Greece, Istanbul, Romania, and Iceland. Integration of the VS algorithm into both the CISN Advanced

  16. Physics-based Broadband Ground Motion Simulations for Probable M>7.0 earthquakes in the Marmara Sea Region (Turkey)

    NASA Astrophysics Data System (ADS)

    Akinci, Aybige; Aochi, Hideo; Herrero, Andre; Pischiutta, Marta; Karanikas, Dimitris

    2016-04-01

    The city of Istanbul is characterized by one of the highest levels of seismic risk in Europe and the Mediterranean region. The important source of the increased risk in Istanbul is the remarkable probability of the occurrence of a large earthquake, which stands at about 65% during the coming years due to the existing seismic gap and the post-1999 earthquake stress transfer at the western portion of the North Anatolian Fault Zone (NAFZ). In this study, we have simulated hybrid broadband time histories from two selected scenario earthquakes having magnitude M>7.0 in the Marmara Sea within 10-20 km of Istanbul believed to have generated devastating 1509 event in the region. The physics-based rupture scenarios, which may be an indication of potential future events, are adopted to estimate the ground motion characteristics and its variability in the region. Two simulation techniques (a full 3D wave propagation method to generate low-frequency seismograms, <~1 Hz and a stochastic technique to simulate high-frequency seismograms, >1Hz) are used to compute more realistic time series associated with scenario earthquakes having magnitudes Mw >7.0 in the Marmara Sea Region. A dynamic rupture is generated and computed with a boundary integral equation method and the propagation in the medium is realized through a finite difference approach (Aochi and Ulrich, 2015). The high frequency radiation is computed using stochastic finite-fault model approach based on a dynamic corner frequency (Motazedian and Atkinson, 2005; Boore, 2009). The results from the two simulation techniques are then merged by performing a weighted summation at intermediate frequencies to calculate broadband synthetic time series. The hybrid broadband ground motions computed with the proposed approach are validated by comparing peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration (SA) with recently proposed ground motion prediction equations (GMPE) in the region. Our

  17. Remotely triggered microearthquakes and tremor in central California following the 2010 Mw 8.8 Chile earthquake

    USGS Publications Warehouse

    Peng, Zhigang; Hill, David P.; Shelly, David R.; Aiken, Chastity

    2010-01-01

    We examine remotely triggered microearthquakes and tectonic tremor in central California following the 2010 Mw 8.8 Chile earthquake. Several microearthquakes near the Coso Geothermal Field were apparently triggered, with the largest earthquake (Ml 3.5) occurring during the large-amplitude Love surface waves. The Chile mainshock also triggered numerous tremor bursts near the Parkfield-Cholame section of the San Andreas Fault (SAF). The locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from Coso, but can be identified by applying high-pass or matched filters. Both triggered tremor along the SAF and the Ml 3.5 earthquake in Coso are consistent with frictional failure at different depths on critically-stressed faults under the Coulomb failure criteria. The triggered tremor, however, appears to be more phase-correlated with the surface waves than the triggered earthquakes, likely reflecting differences in constitutive properties between the brittle, seismogenic crust and the underlying lower crust.

  18. Changes in the discharge characteristics of thermal springs and fumaroles in the Long Valley Caldera, California, resulting from earthquakes on May 25-27, 1980

    USGS Publications Warehouse

    Sorey, M.L.; Clark, Mark D.

    1981-01-01

    Changes in flow rate and turbidity have been observed and measured in hot springs in the Long Valley caldera, California, following earthquakes with magnitudes up to 6.3 in May 1980. Increases in flow rate of some hot springs occurred within minutes of the earthquakes, followed by more gradual decreases in flow rate to pre-earthquake levels. Spring temperatures and chemistries also show no long-term variations following earthquakes. Transient changes in discharge characteristics of the hot springs appear to result from increases in the permeability of fault conduits transmitting the hot water to the surface. (USGS)

  19. Multifrequential periodogram analysis of earthquake occurrence: An alternative approach to the Schuster spectrum, with two examples in central California

    NASA Astrophysics Data System (ADS)

    Dutilleul, Pierre; Johnson, Christopher W.; Bürgmann, Roland; Wan, Yongge; Shen, Zheng-Kang

    2015-12-01

    Periodic earthquake occurrences may reflect links with semidiurnal to multiyear tides, seasonal hydrological loads, and ~14 month pole tide forcing. The Schuster spectrum is a recent extension of Schuster's traditional test for periodicity analysis in seismology. We present an alternative approach: the multifrequential periodogram analysis (MFPA), performed on time series of monthly earthquake numbers. We explore if seismicity in two central California regions, the Central San Andreas Fault near Parkfield (CSAF-PKD) and the Sierra Nevada-Eastern California Shear Zone (SN-ECSZ), exhibits periodic behavior at periods of 2 months to several years. Original and declustered catalogs spanning up to 26 years were analyzed with both methods. For CSAF-PKD, the MFPA resolves ~1 year periodicities, with additional statistically significant periods of ~6 and ~4 months; for SN-ECSZ, it finds a strong ~14 month periodic component. Unlike the Schuster spectrum, the MFPA has an exact modified statistic at non-Fourier frequencies. Informed by the MFPA period estimates, trigonometric models with periods of 12, 6, and 4 months (Model 1) and 14.24 and 12 months (Model 2) were fitted to time series of earthquake numbers. For CSAF-PKD, Model 1 shows a peak annual earthquake occurrence during August-November and a secondary peak in April. Similar peaks, or troughs, are found in annual and semiannual components of pole tide and tide-induced stress model time series and fault normal-stress reduction from seasonal hydrological unloading. For SN-ECSZ, the dominant ~14 month periodicity prevents regular annual peaking, and Model 2 provides a better fit (ΔR>¯adjusted2: 2.4%). This new MFPA application resolves several periodicities in earthquake catalogs that reveal external periodic forcing.

  20. Probability of inducing given-magnitude earthquakes by perturbing finite volumes of rocks

    NASA Astrophysics Data System (ADS)

    Shapiro, Serge A.; Krüger, Oliver S.; Dinske, Carsten

    2013-07-01

    Fluid-induced seismicity results from an activation of finite rock volumes. The finiteness of perturbed volumes influences frequency-magnitude statistics. Previously we observed that induced large-magnitude events at geothermal and hydrocarbon reservoirs are frequently underrepresented in comparison with the Gutenberg-Richter law. This is an indication that the events are more probable on rupture surfaces contained within the stimulated volume. Here we theoretically and numerically analyze this effect. We consider different possible scenarios of event triggering: rupture surfaces located completely within or intersecting only the stimulated volume. We approximate the stimulated volume by an ellipsoid or cuboid and derive the statistics of induced events from the statistics of random thin flat discs modeling rupture surfaces. We derive lower and upper bounds of the probability to induce a given-magnitude event. The bounds depend strongly on the minimum principal axis of the stimulated volume. We compare the bounds with data on seismicity induced by fluid injections in boreholes. Fitting the bounds to the frequency-magnitude distribution provides estimates of a largest expected induced magnitude and a characteristic stress drop, in addition to improved estimates of the Gutenberg-Richter a and b parameters. The observed frequency-magnitude curves seem to follow mainly the lower bound. However, in some case studies there are individual large-magnitude events clearly deviating from this statistic. We propose that such events can be interpreted as triggered ones, in contrast to the absolute majority of the induced events following the lower bound.

  1. Earthquakes, active faults, and geothermal areas in the Imperial Valley, California

    USGS Publications Warehouse

    Hill, D.P.; Mowinckel, P.; Peake, L.G.

    1975-01-01

    A dense seismograph network in the Imperial Valley recorded a series of earthquake swarms along the Imperial and Brawley faults and a diffuse pattern of earthquakes along the San Jacinto fault. Two known geothermal areas are closely associated with these earthquake swarms. This seismicity pattern demonstrates that seismic slip is occurring along both the Imperial-Brawley and San Jacinto fault systems.

  2. Earthquakes, active faults, and geothermal areas in the imperial valley, california.

    PubMed

    Hill, D P; Mowinckel, P; Peake, L G

    1975-06-27

    A dense seismograph network in the Imperial Valley recorded a series of earthquake swarms along the Imperial and Brawley faults and a diffuse pattern of earthquakes along the San Jacinto fault. Two known geothermal areas are closely associated with these earthquake swarms. This seismicity pattern demonstrates that seismic slip is occurring along both the Imperial-Brawley and San Jacinto fault systems. PMID:17772600

  3. Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer

    USGS Publications Warehouse

    Toda, S.; Stein, R.S.; Richards-Dinger, K.; Bozkurt, S.B.

    2005-01-01

    We develop a forecast model to reproduce the distibution of main shocks, aftershocks and surrounding seismicity observed during 1986-200 in a 300 ?? 310 km area centered on the 1992 M = 7.3 Landers earthquake. To parse the catalog into frames with equal numbers of aftershocks, we animate seismicity in log time increments that lengthen after each main shock; this reveals aftershock zone migration, expansion, and densification. We implement a rate/state algorithm that incorporates the static stress transferred by each M ??? 6 shock and then evolves. Coulomb stress changes amplify the background seismicity, so small stress changes produce large changes in seismicity rate in areas of high background seismicity. Similarly, seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates. Thus a key constituent of the model is the background seismicity rate, which we smooth from 1981 to 1986 seismicity. The mean correlation coefficient between observed and predicted M ??? 1.4 shocks (the minimum magnitude of completeness) is 0.52 for 1986-2003 and 0.63 for 1992-2003; a control standard aftershock model yields 0.54 and 0.52 for the same periods. Four M ??? 6.0 shocks struck during the test period; three are located at sites where the expected seismicity rate falls above the 92 percentile, and one is located above the 75 percentile. The model thus reproduces much, but certainly not all, of the observed spatial and temporal seismicity, from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades. Finally, we offer a M ??? 5 earthquake forecast for 2005-2015, assigning probabilities to 324 10 ?? 10 km cells.

  4. Directional topographic site response at Tarzana observed in aftershocks of the 1994 Northridge, California, earthquake: Implications for mainshock motions

    USGS Publications Warehouse

    Spudich, P.; Hellweg, M.; Lee, W.H.K.

    1996-01-01

    The Northridge earthquake caused 1.78 g acceleration in the east-west direction at a site in Tarzana, California, located about 6 km south of the mainshock epicenter. The accelerograph was located atop a hill about 15-m high, 500-m long, and 130-m wide, striking about N78??E. During the aftershock sequence, a temporary array of 21 three-component geophones was deployed in six radial lines centered on the accelerograph, with an average sensor spacing of 35 m. Station COO was located about 2 m from the accelerograph. We inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion. We identified a 3.2-Hz resonance that is a transverse oscillation of the hill (a directional topographic effect). The top/base amplification ratio at 3.2 Hz is about 4.5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill. This resonance is seen most strongly within 50 m of COO. Other resonant frequencies were also observed. A strong lateral variation in attenuation, probably associated with a fault, caused substantially lower motion at frequencies above 6 Hz at the east end of the hill. There may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill, causing particle motions (not spectral ratios) at the top of the hill to be rotated about 20?? away from the direction transverse to the hill. The resonant frequency, but not the amplitude, of our observed topographic resonance agrees well with theory, even for such a low hill. Comparisons of our observations with theoretical results indicate that the 3D shape of the hill and its internal structure are important factors affecting its response. The strong transverse resonance of the hill does not account for the large east-west mainshock motions. Assuming linear soil response, mainshock east-west motions at the Tarzana accelerograph

  5. Micro-earthquake Analysis for Reservoir Properties at the Prati-32 Injection Test, The Geysers, California

    NASA Astrophysics Data System (ADS)

    Hutchings, L. J.; Singh, A. K.

    2014-12-01

    The Prati-32 injection test offers a particular opportunity to test rock physics theories and tomography results as it occurred in a previously undisturbed portion of The Geysers, California. Within the northwest Geysers, there is a high temperature zone (HTZ) directly below the normal temperature reservoir (NTR) at ˜2.6 km below ground surface. We demonstrate an analysis of micro-earthquake data with rock physics theory to identify fractures, state of fluids, and permeable zones. We obtain earthquake source properties (hypocenters, magnitudes, stress drops, and moment tensors), 3D isotropic velocity (Vp and Vs) and attenuation (Qp and Qs seismic quality factors), derived elastic moduli (Lambda, Bulk and Young's moduli), and Poisson's ratio. After one month of injection changes in these parameters occur right at the point where injection occured, which confirms the accuracy of the tomography. Bulk modulus, Poisson's ratio, and Lambda increased. Vs decreased. Qp and Vp increased slightly and Qs did not change. We interpret this observation to indicate that there is fluid saturation along with fracturing around the well bottom. Fracturing would decrease Vs, while saturation would not affect Vs. Whereas, saturation would increase Vp, even with fracturing. Saturation and fracturing should have competing effect of intrinsic and extrinsic Q. Saturation should increase intrinsic Qp, but not affect extrinsic Qp. We can't explain the unchanged Qs, unless the effect of increasing intrinsic Qs is offset by a decrease in extrinsic Qs. Poisson's ratio, and Lambda increased, which is another indication of saturation. After two months of injection, as compared to one month before injection. Bulk modulus and Vp have returned to values comparable to before injection for the volume around the well bottom. A new anomaly in Vp has moved below the well. Vs continues to be low and Lambda and Poisson's ratio continue to be high compared to before injection. These changes have not moved

  6. Earthquake warning system for Japan Railways’ bullet train; implications for disaster prevention in California

    USGS Publications Warehouse

    Nakamura, Y.; Tucker, B. E.

    1988-01-01

    Today, Japanese society is well aware of the prediction of the Tokai earthquake. It is estimated by the Tokyo earthquake. It is estimated by the Tokyo muncipal government that this predicted earthquake could kill 30,000 people. (this estimate is viewed by many as conservative; other Japanese government agencies have made estimates but they have not been published.) Reduction in the number deaths from 120,000 to 30,000 between the Kanto earthquake and the predicted Tokai earthquake is due in large part to the reduction in the proportion of wooden construction (houses). 

  7. A three-step Maximum-A-Posterior probability method for InSAR data inversion of coseismic rupture with application to four recent large earthquakes in Asia

    NASA Astrophysics Data System (ADS)

    Sun, J.; Shen, Z.; Burgmann, R.; Liang, F.

    2012-12-01

    We develop a three-step Maximum-A-Posterior probability (MAP) method for coseismic rupture inversion, which aims at maximizing the a posterior probability density function (PDF) of elastic solutions of earthquake rupture. The method originates from the Fully Bayesian Inversion (FBI) and the Mixed linear-nonlinear Bayesian inversion (MBI) methods , shares the same a posterior PDF with them and keeps most of their merits, while overcoming its convergence difficulty when large numbers of low quality data are used and improving the convergence rate greatly using optimization procedures. A highly efficient global optimization algorithm, Adaptive Simulated Annealing (ASA), is used to search for the maximum posterior probability in the first step. The non-slip parameters are determined by the global optimization method, and the slip parameters are inverted for using the least squares method without positivity constraint initially, and then damped to physically reasonable range. This step MAP inversion brings the inversion close to 'true' solution quickly and jumps over local maximum regions in high-dimensional parameter space. The second step inversion approaches the 'true' solution further with positivity constraints subsequently applied on slip parameters using the Monte Carlo Inversion (MCI) technique, with all parameters obtained from step one as the initial solution. Then the slip artifacts are eliminated from slip models in the third step MAP inversion with fault geometry parameters fixed. We first used a designed model with 45 degree dipping angle and oblique slip, and corresponding synthetic InSAR data sets to validate the efficiency and accuracy of method. We then applied the method on four recent large earthquakes in Asia, namely the 2010 Yushu, China earthquake, the 2011 Burma earthquake, the 2011 New Zealand earthquake and the 2008 Qinghai, China earthquake, and compared our results with those results from other groups. Our results show the effectiveness of

  8. Recent developments in understanding the tectonic evolution of the Southern California offshore area: Implications for earthquake-hazard analysis

    USGS Publications Warehouse

    Fisher, M.A.; Langenheim, V.E.; Nicholson, C.; Ryan, H.F.; Sliter, R.W.

    2009-01-01

    During late Mesozoic and Cenozoic time, three main tectonic episodes affected the Southern California offshore area. Each episode imposed its unique structural imprint such that early-formed structures controlled or at least influenced the location and development of later ones. This cascaded structural inheritance greatly complicates analysis of the extent, orientation, and activity of modern faults. These fault attributes play key roles in estimates of earthquake magnitude and recurrence interval. Hence, understanding the earthquake hazard posed by offshore and coastal faults requires an understanding of the history of structural inheritance and modifi-cation. In this report we review recent (mainly since 1987) findings about the tectonic development of the Southern California offshore area and use analog models of fault deformation as guides to comprehend the bewildering variety of offshore structures that developed over time. This report also provides a background in regional tectonics for other chapters in this section that deal with the threat from offshore geologic hazards in Southern California. ?? 2009 The Geological Society of America.

  9. Potential Effects of a Scenario Earthquake on the Economy of Southern California: Intraregional Commuter, Worker, and Earnings Flow Analysis

    USGS Publications Warehouse

    Sherrouse, Benson C.; Hester, David J.

    2008-01-01

    The Multi-Hazards Demonstration Project (MHDP) is a collaboration between the U.S. Geological Survey (USGS) and various partners from the public and private sectors and academia, meant to improve Southern California's resiliency to natural hazards (Jones and others, 2007). In support of the MHDP objectives, the ShakeOut Scenario was developed. It describes a magnitude 7.8 (M7.8) earthquake along the southernmost 300 kilometers (200 miles) of the San Andreas Fault, identified by geoscientists as a plausible event that will cause moderate to strong shaking over much of the eight-county (Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura) Southern California region (Jones and others, 2008). This report uses selected datasets from the U.S. Census Bureau and the State of California's Employment Development Department to develop preliminary estimates of the number and spatial distribution of commuters who cross the San Andreas Fault and to characterize these commuters by the industries in which they work and their total earnings. The analysis concerns the relative exposure of the region's economy to the effects of the earthquake as described by the location, volume, and earnings of those commuters who work in each of the region's economic sectors. It is anticipated that damage to transportation corridors traversing the fault would lead to at least short-term disruptions in the ability of commuters to travel between their places of residence and work.

  10. Focal Mechanisms for Deep Crustal Earthquakes in the Central Foothills and Near Yosemite National Park in the Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Frassetto, A.; Hurd, O.; Zandt, G.; Gilbert, H.; Owens, T.; Jones, C.

    2008-12-01

    Past studies have observed seismicity occurring to depths near 40 km beneath the central Sierra Nevada in eastern California, but the cause of this unusual activity remains largely unknown. We use seismograms from a recent deployment of the Sierra Nevada EarthScope Project (SNEP) broadband array and interspersed USArray TA stations to study this deep crustal earthquake activity. From June of 2005 to May of 2006, we recorded 126 earthquakes in the central western flank of the Sierra Nevada that relocated in the depth range from 1.0 to 47.6 km. These earthquakes have small magnitudes (M < 3), occur at a rate of ~10 per month, and occasionally display repeating waveforms. The majority of the earthquakes fall into two distinct clusters. One cluster of earthquakes form a diffuse band under the low foothills north of Fresno and have focal depths mostly between 20 and 35 km. The second cluster underlies the higher western slope of the range in a more compact north-south band extending from the southern edge of Yosemite National Park to the San Joaquin River. These events have focal depths from near surface to 30 km, and are located above occasional deep, long-period (LP) events (Pitt, et al., SRL, 2002). We use P- and S-wave polarity picks and P/SH amplitude ratios to construct focal mechanisms for 23 of the larger, well-recorded earthquakes, 14 in the Foothills Cluster and 9 in the Yosemite Cluster. The focal mechanisms show dominantly near vertical and subhorizontal nodal planes, although several events do show clear normal or reverse mechanisms. Although there is some scatter, a majority of the mechanisms from the Foothills Cluster have S-to-SW steeply dipping T-axes. The majority of earthquakes in the Yosemite Cluster have P-axes moderately dipping to the SW and T-axes moderately dipping to the NE, similar to focal mechanisms of earthquakes associated with the recent magma intrusion event under Lake Tahoe (von Seggern, et al., BSSA, 2008). We suggest that the

  11. A model of earthquake triggering probabilities and application to dynamic deformations constrained by ground motion observations

    USGS Publications Warehouse

    Gomberg, J.; Felzer, K.

    2008-01-01

    We have used observations from Felzer and Brodsky (2006) of the variation of linear aftershock densities (i.e., aftershocks per unit length) with the magnitude of and distance from the main shock fault to derive constraints on how the probability of a main shock triggering a single aftershock at a point, P(r, D), varies as a function of distance, r, and main shock rupture dimension, D. We find that P(r, D) becomes independent of D as the triggering fault is approached. When r ??? D P(r, D) scales as Dm where m-2 and decays with distance approximately as r-n with n = 2, with a possible change to r-(n-1) at r > h, where h is the closest distance between the fault and the boundaries of the seismogenic zone. These constraints may be used to test hypotheses about the types of deformations and mechanisms that trigger aftershocks. We illustrate this using dynamic deformations (i.e., radiated seismic waves) and a posited proportionality with P(r, D). Deformation characteristics examined include peak displacements, peak accelerations and velocities (proportional to strain rates and strains, respectively), and two measures that account for cumulative deformations. Our model indicates that either peak strains alone or strain rates averaged over the duration of rupture may be responsible for aftershock triggering.

  12. Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

    SciTech Connect

    Templeton, D C; Nadeau, R; Burgmann, R

    2007-07-09

    Repeating earthquakes (REs) are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. We investigate the occurrence of these REs along faults in central California to determine which faults exhibit creep and the spatio-temporal distribution of this creep. At the juncture of the San Andreas and southern Calaveras-Paicines faults, both faults as well as a smaller secondary fault, the Quien Sabe fault, are observed to produce REs over the observation period of March 1984-May 2005. REs in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time. Cumulative slip over the observation period at individual sequence locations is determined to range from 5.5-58.2 cm on the San Andreas fault, 4.8-14.1 cm on the southern Calaveras-Paicines fault, and 4.9-24.8 cm on the Quien Sabe fault. Creep at depth appears to mimic the behaviors seen of creep on the surface in that evidence of steady slip, triggered slip, and episodic slip phenomena are also observed in the RE sequences. For comparison, we investigate the occurrence of REs west of the San Andreas fault within the southern Coast Range. Events within these RE sequences only occurred minutes to weeks apart from each other and then did not repeat again over the observation period, suggesting that REs in this area are not produced by steady aseismic creep of the surrounding fault surface.

  13. Response of the San Andreas fault to the 1983 Coalinga-Nuñez earthquakes: an application of interaction-based probabilities for Parkfield

    USGS Publications Warehouse

    Toda, Shinji; Stein, Ross S.

    2002-01-01

    The Parkfield-Cholame section of the San Andreas fault, site of an unfulfilled earthquake forecast in 1985, is the best monitored section of the world's most closely watched fault. In 1983, the M = 6.5 Coalinga and M = 6.0 Nuñez events struck 25 km northeast of Parkfield. Seismicity rates climbed for 18 months along the creeping section of the San Andreas north of Parkfield and dropped for 6 years along the locked section to the south. Right-lateral creep also slowed or reversed from Parkfield south. Here we calculate that the Coalinga sequence increased the shear and Coulomb stress on the creeping section, causing the rate of small shocks to rise until the added stress was shed by additional slip. However, the 1983 events decreased the shear and Coulomb stress on the Parkfield segment, causing surface creep and seismicity rates to drop. We use these observations to cast the likelihood of a Parkfield earthquake into an interaction-based probability, which includes both the renewal of stress following the 1966 Parkfield earthquake and the stress transfer from the 1983 Coalinga events. We calculate that the 1983 shocks dropped the 10-year probability of a M ∼ 6 Parkfield earthquake by 22% (from 54 ± 22% to 42 ± 23%) and that the probability did not recover until about 1991, when seismicity and creep resumed. Our analysis may thus explain why the Parkfield earthquake did not strike in the 1980s, but not why it was absent in the 1990s. We calculate a 58 ± 17% probability of a M ∼ 6 Parkfield earthquake during 2001–2011.

  14. In-situ fluid-pressure measurements for earthquake prediction: An example from a deep well at Hi Vista, California

    USGS Publications Warehouse

    Healy, J.H.; Urban, T.C.

    1985-01-01

    Short-term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes. Instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur, and it is now recognized that even to have the possibility of a reliable earthquake-prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals. We are conducting experiments to determine the maximum signal-to-noise improvement that can be obtained in drill holes. In a 592 m well in the Mojave Desert near Hi Vista, California, we measured water-level changes with amplitudes greater than 10 cm, induced by earth tides. By removing the effects of barometric pressure and the stress related to earth tides, we have achieved a sensitivity to volumetric strain rates of 10-9 to 10-10 per day. Further improvement may be possible, and it appears that a successful earthquake-prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km, assuming that the premonitory strain signals are, in fact, present. ?? 1985 Birkha??user Verlag.

  15. LLNL-Generated Content for the California Academy of Sciences, Morrison Planetarium Full-Dome Show: Earthquake

    SciTech Connect

    Rodgers, A J; Petersson, N A; Morency, C E; Simmons, N A; Sjogreen, B

    2012-01-23

    The California Academy of Sciences (CAS) Morrison Planetarium is producing a 'full-dome' planetarium show on earthquakes and asked LLNL to produce content for the show. Specifically the show features numerical ground motion simulations of the M 7.9 1906 San Francisco and a possible future M 7.05 Hayward fault scenario earthquake. The show also features concepts of plate tectonics and mantle convection using images from LLNL's G3D global seismic tomography. This document describes the data that was provided to the CAS in support of production of the 'Earthquake' show. The CAS is located in Golden Gate Park, San Francisco and hosts over 1.6 million visitors. The Morrison Planetarium, within the CAS, is the largest all digital planetarium in the world. It features a 75-foot diameter spherical section projection screen tilted at a 30-degree angle. Six projectors cover the entire field of view and give a three-dimensional immersive experience. CAS shows strive to use scientifically accurate digital data in their productions. The show, entitled simply 'Earthquake', will debut on 26 May 2012. They are working on graphics and animations based on the same data sets for display on LLNL powerwalls and flat-screens as well as for public release.

  16. In-situ fluid-pressure measurements for earthquake prediction: An example from a deep well at Hi Vista, California

    NASA Astrophysics Data System (ADS)

    Healy, John H.; Urban, T. C.

    1984-03-01

    Short-term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes. Instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur, and it is now recognized that even to have the possibility of a reliable earthquake-prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals. We are conducting experiments to determine the maximum signal-to-noise improvement that can be obtained in drill holes. In a 592 m well in the Mojave Desert near Hi Vista, California, we measured water-level changes with amplitudes greater than 10 cm, induced by earth tides. By removing the effects of barometric pressure and the stress related to earth tides, we have achieved a sensitivity to volumetric strain rates of 10-9 to 10-10 per day. Further improvement may be possible, and it appears that a successful earthquake-prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km, assuming that the premonitory strain signals are, in fact, present.

  17. Virtual California, ETAS, and OpenHazards web services: Responding to earthquakes in the age of Big Data

    NASA Astrophysics Data System (ADS)

    Yoder, M. R.; Schultz, K.; Rundle, J. B.; Glasscoe, M. T.; Donnellan, A.

    2014-12-01

    The response to the 2014 m=6 Napa earthquake showcased data driven services and technologies that aided first responders and decision makers to quickly assess damage, estimate aftershock hazard, and efficiently allocate resources where where they were most needed. These tools have been developed from fundamental research as part of a broad collaboration -- facilitated in no small party by the California Earthquake Clearinghouse, between researchers, policy makers, and executive decision makers and practiced and honed during numerous disaster response exercises over the past several years. On 24 August 2014, and the weeks following the m=6 Napa event, it became evident that these technologies will play an important role in the response to natural (and other) disasters in the 21st century. Given the continued rapid growth of computational capabilities, remote sensing technologies, and data gathering capacities -- including by unpiloted aerial vehicles (UAVs), it is reasonable to expect that both the volume and variety of data available during a response scenario will grow significantly in the decades to come. Inevitably, modern Data Science will be critical to effective disaster response in the 21st century. In this work, we discuss the roles that earthquake simulators, statistical seismicity models, and remote sensing technologies played in the the 2014 Napa earthquake response. We further discuss "Big Data" technologies and data models that facilitate the transformation of raw data into disseminable information and actionable products, and we outline a framework for the next generation of disaster response data infrastructure.

  18. The 1868 Hayward Earthquake Alliance: A Case Study - Using an Earthquake Anniversary to Promote Earthquake Preparedness

    NASA Astrophysics Data System (ADS)

    Brocher, T. M.; Garcia, S.; Aagaard, B. T.; Boatwright, J. J.; Dawson, T.; Hellweg, M.; Knudsen, K. L.; Perkins, J.; Schwartz, D. P.; Stoffer, P. W.; Zoback, M.

    2008-12-01

    Last October 21st marked the 140th anniversary of the M6.8 1868 Hayward Earthquake, the last damaging earthquake on the southern Hayward Fault. This anniversary was used to help publicize the seismic hazards associated with the fault because: (1) the past five such earthquakes on the Hayward Fault occurred about 140 years apart on average, and (2) the Hayward-Rodgers Creek Fault system is the most likely (with a 31 percent probability) fault in the Bay Area to produce a M6.7 or greater earthquake in the next 30 years. To promote earthquake awareness and preparedness, over 140 public and private agencies and companies and many individual joined the public-private nonprofit 1868 Hayward Earthquake Alliance (1868alliance.org). The Alliance sponsored many activities including a public commemoration at Mission San Jose in Fremont, which survived the 1868 earthquake. This event was followed by an earthquake drill at Bay Area schools involving more than 70,000 students. The anniversary prompted the Silver Sentinel, an earthquake response exercise based on the scenario of an earthquake on the Hayward Fault conducted by Bay Area County Offices of Emergency Services. 60 other public and private agencies also participated in this exercise. The California Seismic Safety Commission and KPIX (CBS affiliate) produced professional videos designed forschool classrooms promoting Drop, Cover, and Hold On. Starting in October 2007, the Alliance and the U.S. Geological Survey held a sequence of press conferences to announce the release of new research on the Hayward Fault as well as new loss estimates for a Hayward Fault earthquake. These included: (1) a ShakeMap for the 1868 Hayward earthquake, (2) a report by the U. S. Bureau of Labor Statistics forecasting the number of employees, employers, and wages predicted to be within areas most strongly shaken by a Hayward Fault earthquake, (3) new estimates of the losses associated with a Hayward Fault earthquake, (4) new ground motion

  19. Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake

    NASA Astrophysics Data System (ADS)

    Floyd, Michael A.; Walters, Richard J.; Elliott, John R.; Funning, Gareth J.; Svarc, Jerry L.; Murray, Jessica R.; Hooper, Andy J.; Larsen, Yngvar; Marinkovic, Petar; Bürgmann, Roland; Johanson, Ingrid A.; Wright, Tim J.

    2016-07-01

    Following earthquakes, faults are often observed to continue slipping aseismically. It has been proposed that this afterslip occurs on parts of the fault with rate-strengthening friction that are stressed by the main shock, but our understanding has been limited by a lack of immediate, high-resolution observations. Here we show that the behavior of afterslip following the 2014 South Napa earthquake in California varied over distances of only a few kilometers. This variability cannot be explained by coseismic stress changes alone. We present daily positions from continuous and survey GPS sites that we remeasured within 12 h of the main shock and surface displacements from the new Sentinel-1 radar mission. This unique geodetic data set constrains the distribution and evolution of coseismic and postseismic fault slip with exceptional resolution in space and time. We suggest that the observed heterogeneity in behavior is caused by lithological controls on the frictional properties of the fault plane.

  20. Borehole velocity measurements at five sites that recorded the Cape Mendocino, California earthquake of 25 April, 1992

    USGS Publications Warehouse

    Gibbs, James F.; Tinsley, John C., III; Boore, David M.

    2002-01-01

    The U.S. Geological Survey (USGS), as part of an ongoing program to acquire seismic velocity and geologic data at locations that recorded strong-ground motions during earthquakes, has investigated five sites in the Fortuna, California region (Figure 1). We selected drill sites at strong-motion stations that recorded high accelerations (Table 1) from the Cape Mendocino earthquake (M 7.0) of 25 April 1992 (Oppenheimer et al., 1993). The boreholes were drilled to a nominal depth of 95 meters (310 ft) and cased with schedule 80 pvc-casing grouted in place at each location. S-wave and P-wave data were acquired at each site using a surface source and a borehole three-component geophone. This report contains the velocity models interpreted from the borehole data and gives reference to locations and peak accelerations at the selected strong-motion stations.

  1. Potential Effects of a Scenario Earthquake on the Economy of Southern California: Labor Market Exposure and Sensitivity Analysis to a Magnitude 7.8 Earthquake

    USGS Publications Warehouse

    Sherrouse, Benson C.; Hester, David J.; Wein, Anne M.

    2008-01-01

    The Multi-Hazards Demonstration Project (MHDP) is a collaboration between the U.S. Geological Survey (USGS) and various partners from the public and private sectors and academia, meant to improve Southern California's resiliency to natural hazards (Jones and others, 2007). In support of the MHDP objectives, the ShakeOut Scenario was developed. It describes a magnitude 7.8 (M7.8) earthquake along the southernmost 300 kilometers (200 miles) of the San Andreas Fault, identified by geoscientists as a plausible event that will cause moderate to strong shaking over much of the eight-county (Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura) Southern California region. This report contains an exposure and sensitivity analysis of economic Super Sectors in terms of labor and employment statistics. Exposure is measured as the absolute counts of labor market variables anticipated to experience each level of Instrumental Intensity (a proxy measure of damage). Sensitivity is the percentage of the exposure of each Super Sector to each Instrumental Intensity level. The analysis concerns the direct effect of the scenario earthquake on economic sectors and provides a baseline for the indirect and interactive analysis of an input-output model of the regional economy. The analysis is inspired by the Bureau of Labor Statistics (BLS) report that analyzed the labor market losses (exposure) of a M6.9 earthquake on the Hayward fault by overlaying geocoded labor market data on Instrumental Intensity values. The method used here is influenced by the ZIP-code-level data provided by the California Employment Development Department (CA EDD), which requires the assignment of Instrumental Intensities to ZIP codes. The ZIP-code-level labor market data includes the number of business establishments, employees, and quarterly payroll categorized by the North American Industry Classification System. According to the analysis results, nearly 225,000 business

  2. Instrumental intensity distribution for the Hector Mine, California, and the Chi-Chi, Taiwan, earthquakes: Comparison of two methods

    USGS Publications Warehouse

    Sokolov, V.; Wald, D.J.

    2002-01-01

    We compare two methods of seismic-intensity estimation from ground-motion records for the two recent strong earthquakes: the 1999 (M 7.1) Hector Mine, California, and the 1999 (M 7.6) Chi-Chi, Taiwan. The first technique utilizes the peak ground acceleration (PGA) and velocity (PGV), and it is used for rapid generation of the instrumental intensity map in California. The other method is based on the revised relationships between intensity and Fourier amplitude spectrum (FAS). The results of using the methods are compared with independently observed data and between the estimations from the records. For the case of the Hector Mine earthquake, the calculated intensities in general agree with the observed values. For the case of the Chi-Chi earthquake, the areas of maximum calculated intensity correspond to the areas of the greatest damage and highest number of fatalities. However, the FAS method producees higher-intensity values than those of the peak amplitude method. The specific features of ground-motion excitation during the large, shallow, thrust earthquake may be considered a reason for the discrepancy. The use of PGA and PGV is simple; however, the use of FAS provides a natural consideration of site amplification by means of generalized or site-specific spectral ratios. Because the calculation of seismic-intensity maps requires rapid processing of data from a large network, it is very practical to generate a "first-order" map from the recorded peak motions. Then, a "second-order" map may be compiled using an amplitude-spectra method on the basis of available records and numerical modeling of the site-dependent spectra for the regions of sparse station spacing.

  3. Patterns of Seismicity Characterizing the Earthquake Cycle

    NASA Astrophysics Data System (ADS)

    Rundle, J. B.; Turcotte, D. L.; Yoder, M. R.; Holliday, J. R.; Schultz, K.; Wilson, J. M.; Donnellan, A.; Grant Ludwig, L.

    2015-12-01

    A number of methods to calculate probabilities of major earthquakes have recently been proposed. Most of these methods depend upon understanding patterns of small earthquakes preceding the large events. For example, the Natural Time Weibull method for earthquake forecasting (see www.openhazards.com) is based on the assumption that large earthquakes complete the Gutenberg-Richter scaling relation defined by the smallest earthquakes. Here we examine the scaling patterns of small earthquakes having magnitudes between cycles of large earthquakes. For example, in the region of California-Nevada between longitudes -130 to -114 degrees W, and latitudes 32 to 45 degrees North, we find 79 earthquakes having magnitudes M6 during the time interval 1933 - present, culminating with the most recent event, the M6.0 Napa, California earthquake of August 24, 2014. Thus we have 78 complete cycles of large earthquakes in this region. After compiling and stacking the smaller events occurring between the large events, we find a characteristic pattern of scaling for the smaller events. This pattern shows a scaling relation for the smallest earthquakes up to about 3earthquakes for 4.5earthquake having M~6.4. In addition, statistics indicate that departure of the successive earthquake cycles from their average pattern can be characterized by Coefficients of Variability and other measures. We discuss these ideas and apply them not only to California, but also to other seismically active areas in the world

  4. Southern California Earthquake Center - SCEC1: Final Report Summary Alternative Earthquake Source Characterization for the Los Angeles Region

    SciTech Connect

    Foxall, B

    2003-02-26

    The objective my research has been to synthesize current understanding of the tectonics and faults of the Los Angeles Basin and surrounding region to quantify uncertainty in the characterization of earthquake sources used for geologically- and geodetically-based regional earthquake likelihood models. This work has focused on capturing epistemic uncertainty; i.e. uncertainty stemming from ignorance of the true characteristics of the active faults in the region and of the tectonic forces that drive them. In the present context, epistemic uncertainty has two components: First, the uncertainty in source geometrical and occurrence rate parameters deduced from the limited geological, geophysical and geodetic observations available; and second. uncertainties that result from fundamentally different interpretations of regional tectonic deformation and faulting. Characterization of the large number of active and potentially active faults that need to be included in estimating earthquake occurrence likelihoods for the Los Angeles region requires synthesis and evaluation of large amounts of data and numerous interpretations. This was accomplished primarily through a series of carefully facilitated workshops, smaller meetings involving key researchers, and email groups. The workshops and meetings were made possible by the unique logistical and financial resources available through SCEC, and proved to be extremely effective forums for the exchange and critical debate of data and interpretations that are essential in constructing fully representative source models. The main products from this work are a complete source model that characterizes all know or potentially active faults in the greater Los Angeles region. which includes the continental borderland as far south as San Diego, the Ventura Basin, and the Santa Barbara Channel. The model constitutes a series of maps and representative cross-sections that define alternative fault geometries, a table containing rault

  5. The magnitude 6.7 Northridge, California, earthquake of 17 January 1994

    USGS Publications Warehouse

    Jones, L.; Aki, K.; Boore, D.; Celebi, M.; Donnellan, A.; Hall, J.; Harris, R.; Hauksson, E.; Heaton, T.; Hough, S.; Hudnut, K.; Hutton, K.; Johnston, M.; Joyner, W.; Kanamori, H.; Marshall, G.; Michael, A.; Mori, J.; Murray, M.; Ponti, D.; Reasenberg, P.; Schwartz, D.; Seeber, L.; Shakal, A.; Simpson, R.; Thio, H.; Tinsley, J.; Todorovska, M.; Trifunac, M.; Wald, D.; Zoback, M.L.

    1994-01-01

    The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.

  6. Earthquake-induced structures in sediments of Van Norman Lake, San Fernando, California

    USGS Publications Warehouse

    Sims, J.D.

    1973-01-01

    The 9 February 1971 earthquake in the San Fernando Valley damaged the Lower Van Norman Dam severely enough to warrant draining the reservoir. In March 1972 the sediment deposited on the reservoir floor was examined to determine whether the 1971 earthquake had induced sediment deformation and, if so, what types. A zone of deformational structures characterized by small-scale loads and slightly recumbent folds associated with the 1971 earthquake was discovered, in addition to two older zones of load structures. Each of the zones has been tentatively correlated with an historic earthquake.

  7. Damage and restoration of geodetic infrastructure caused by the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Hodgkinson, Kathleen M.; Stein, Ross S.; Hudnut, Kenneth W.; Satalich, Jay; Richards, John H.

    1996-01-01

    We seek to restore the integrity of the geodetic network in the San Fernando, Simi, Santa Clarita Valleys and in the northern Los Angeles Basin by remeasurement of the network and identification of BMs which experienced non-tectonic displacements associated with the Northridge earthquake. We then use the observed displacement of BMs in the network to portray or predict the permanent vertical and horizontal deformation associated with the 1994 Northridge earthquake throughout the area, including sites where we lack geodetic measurements. To accomplish this, we find the fault geometry and earthquake slip that are most compatible with the geodetic and independent seismic observations of the earthquake. We then use that fault model to predict the deformation everywhere at the earth's surface, both at locations where geodetic observations exist and also where they are absent. We compare displacements predicted for a large number of numerical models of the earthquake faulting to the coseismic displacements, treating the earthquake fault as a cut or discontinuity embedded in a stiff elastic solid. This comparison is made after non-tectonic deformation has been removed from the measured elevation changes. The fault slip produces strain in the medium and deforms the ground surface. The model compatible with seismic observations that best fits the geodetic data within their uncertainties is selected. The acceptable model fault bisects the mainshock focus, and the earthquake size , magnitude, is compatible with the earthquake size measured seismically. Our fault model was used to identify geodetic monuments on engineered structures that were anomalously displaced by the earthquake.

  8. Early Tertiary magmatism and probable Mesozoic fabrics in the Black Mountains, Death Valley, California

    NASA Astrophysics Data System (ADS)

    Miller, Martin G.; Friedman, Richard M.

    1999-01-01

    We report two early Tertiary U-Pb zircon ages for pegmatite from the Black Mountains of Death Valley, California. These ages, 54.7 ± 0.6 Ma and 56 ± 3 Ma, are unique for much of southeastern California. The samples belong to a pegmatite suite that occupies part of the footwall of the Badwater turtleback, a late Tertiary extensional feature; similar but undated pegmatite intrudes the footwalls of the Copper Canyon and Mormon Point turtlebacks farther south. The pegmatite suite demonstrates that fabric development on the turtlebacks was at least a two-stage process. Fabrics cut by these pegmatites likely formed during the Mesozoic, whereas those that involve them formed during late Tertiary extension.

  9. Current progress in using multiple electromagnetic indicators to determine location, time, and magnitude of earthquakes in California and Peru (Invited)

    NASA Astrophysics Data System (ADS)

    Bleier, T. E.; Dunson, C.; Roth, S.; Heraud, J.; Freund, F. T.; Dahlgren, R.; Bryant, N.; Bambery, R.; Lira, A.

    2010-12-01

    Since ultra-low frequency (ULF) magnetic anomalies were discovered prior to the 1989 Loma Prieta, Ca. M7.0 earthquake, QuakeFinder, a small R&D group based in Palo Alto California has systematically monitored ULF magnetic signals with a network of 3-axis induction magnetometers since 2000 in California. This raw magnetometer data was collected at 20-50 samples per sec., with no preprocessing, in an attempt to collect an accurate time history of electromagnetic waveforms prior to, during, and after large earthquakes within 30 km. of these sensors. Finally in October 2007, the QuakeFinder team observed a series of strange magnetic pulsations at the Alum Rock, California site, 14 days prior to M5.4 earthquake. These magnetic signals observed were relatively short, random pulsations, not continuous waveform signals like Pc1 or Pc3 micropulsations. The magnetic pulses have a characteristic uni-polar shapes and 0.5 sec. to 30 sec. durations, much longer than lightning signals. In May of 2010, very similar pulses were observed at Tacna, Peru, 13 days prior to a M6.2 earthquake, using a QuakeFinder station jointly operated under collaboration with the Catholic University in Lima Peru (PUCP). More examples of these pulsations were sought, and a historical review of older California magnetic data discovered fewer but similar pulsations occurred at the Hollister, Ca. site operated by UC Berkeley (e.g. San Juan Bautista M5.1 earthquake on August 12, 1998). Further analysis of the direction of arrival of the magnetic pulses showed an interesting “azimuth clustering” observed in both Alum Rock, Ca. and Tacna, Peru data. The complete time series of the Alum Rock data allowed the team to analyze subsequent changes observed in magnetometer “filter banks” (0.001 Hz to 10 Hz filter bands, similar to those used by Fraser-Smith in 1989), but this time using time-adjusted limits based on time of day, time of year, Kp, and site background noise. These site-customized limits

  10. Times of increased probability of strong earthquakes (M ge 7. 5) diagnosed by algorithm M8 in Japan and adjacent territories

    SciTech Connect

    Keilis-Borok, V.I.; Kossobokov, V.G. )

    1990-08-10

    This paper continues to explore the possibility of identifying the times of increased probability (TIPs) of occurrence of a strong earthquake by premonitory intermediate-term seismic activation in lower-magnitude range, as defined in the algorithm M8. A TIP refers to a 5-year period and an area whose linear size is several times larger than that of an incipient earthquake. In the course of the global test of the algorithm, the authors applied it retrospectively to the data from the National Earthquake Information Center worldwide earthquake catalog, related to the segment of circum-Pacific belt between latitudes 20{degree}N and 48{degree}N, from the south of Kuril arc to the Taiwan and Izu-Bonin arc. The worldwide catalog allows one to diagnose TIPs for earthquakes above magnitude 7.5 from 1975 on. Five out of six earthquakes with M {ge} 7.5 occurred within the TIPs diagnosed by the algorithm M8 with a priori fixed parameters. The missed earthquake occurred at the final stage of formation of the corresponding TIP. Application of the additional algorithm of localization, named Mendocino Scenario, indicates that the southern part of the Japan trench is an area deserving particular attention. The results obtained here by no means constitute the definitive earthquake prediction but merely outline the territories for more detailed and comprehensive analysis. If confirmed by regional data, the results may be used for implementation of some safety measures and evaluation of other precursors, including short-term ones.

  11. Cross-sections and maps showing double-difference relocated earthquakes from 1984-2000 along the Hayward and Calaveras faults, California

    USGS Publications Warehouse

    Simpson, Robert W.; Graymer, Russell W.; Jachens, Robert C.; Ponce, David A.; Wentworth, Carl M.

    2004-01-01

    We present cross-section and map views of earthquakes that occurred from 1984 to 2000 in the vicinity of the Hayward and Calaveras faults in the San Francisco Bay region, California. These earthquakes came from a catalog of events relocated using the double-difference technique, which provides superior relative locations of nearby events. As a result, structures such as fault surfaces and alignments of events along these surfaces are more sharply defined than in previous catalogs.

  12. Earthquake-by-earthquake fold growth above the Puente Hills blind thrust fault, Los Angeles, California: Implications for fold kinematics and seismic hazard

    USGS Publications Warehouse

    Leon, L.A.; Christofferson, S.A.; Dolan, J.F.; Shaw, J.H.; Pratt, T.L.

    2007-01-01

    Boreholes and high-resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the Puente Hills thrust fault (PHT) beneath Los Angeles, California, provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault. These data document fold growth within a discrete kink band that narrows upward from ???460 m at the base of the Quaternary section (200-250 m depth) to 82% at 250 m depth) folding and uplift occur within discrete kink bands, thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault. The borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site. We interpret the intervals of growth as occurring after the formation of now-buried paleofold scarps during three large PHT earthquakes in the past 8 kyr. The intervening intervals of no growth record periods of structural quiescence and deposition at the regional, near-horizontal stream gradient at the study site. Minimum uplift in each of the scarp-forming events, which occurred at 0.2-2.2 ka (event Y), 3.0-6.3 ka (event X), and 6.6-8.1 ka (event W), ranged from ???1.1 to ???1.6 m, indicating minimum thrust displacements of ???2.5 to 4.5 m. Such large displacements are consistent with the occurrence of large-magnitude earthquakes (Mw > 7). Cumulative, minimum uplift in the past three events was 3.3 to 4.7 m, suggesting cumulative thrust displacement of ???7 to 10.5 m. These values yield a minimum Holocene slip rate for the PHT of ???0.9 to 1.6 mm/yr. The borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally, such that older strata that have been deformed by more earthquakes dip more steeply than younger

  13. A possible explanation for deeper earthquakes under the Sacramento delta, California, in terms of its deep structure and thermal history

    NASA Astrophysics Data System (ADS)

    Mikhailov, V.; Parsons, T.; Simpson, R. W.; Timoshkina, E.; Williams, C.

    2003-04-01

    Hypocentral depth of earthquakes under the Sacramento River Delta region in Northern California extends to nearly 20 km, whereas in the Coast Ranges to the west it is less than 12-15 km. In order to better understand the origin of these deeper earthquakes and the potential earthquake hazard in the vicinity, we have used data from wells in the Sacramento Valley to construct and calibrate a model of tectonic subsidence and thermal evolution of this forearc basin. Our model assumes an oceanic basement with an initial thermal profile dependent on its age, subjected to a refrigeration effect caused by subducting slab, which age and rate could change in time. Subsidence obtained for the Sacramento Delta area is close to that expected for a forearc basin underlain by normal oceanic lithosphere of 150 My age. Observed subsidence at the eastern and northern borders of the Sacramento valley appears to be considerably less, corresponding to subsidence caused by the dynamics of the subduction zone alone. Thus, it appears that the lithosphere of the Sacramento Delta, being thinner and having undergone deeper long-term subsidence, differs from the lithosphere of other parts of the Sacramento valley. Strength diagrams based on the thermal model show that even under very slow deformation the upper part of the Sacramento Delta crystalline crust (at least down to 20-22 km) can fail in brittle fashion, which is in agreement with earthquake occurrence. Rheology of the mantle below the Moho also appears to be brittle. The greater width of the seismogenic zone in this area raises the possibility that for segments of comparable length, earthquakes of somewhat greater magnitude might occur than in the Coast Ranges to the west.

  14. The Loma Prieta, California, Earthquake of October 17, 1989: Performance of the Built Environment

    USGS Publications Warehouse

    Coordinated by Holzer, Thomas L.

    1998-01-01

    Professional Paper 1552 focuses on the response of buildings, lifelines, highway systems, and earth structures to the earthquake. Losses to these systems totaled approximated $5.9 billion. The earthquake displaced many residents from their homes and severely disrupted transportation systems. Some significant findings were: * Approximately 16,000 housing units were uninhabitable after the earthquake including 13,000 in the San Francisco Bay region. Another 30,000-35,000 units were moderately damaged in the earthquake. Renters and low-income residents were particularly hard hit. * Failure of highway systems was the single largest cause of loss of life during the earthquake. Forty-two of the 63 earthquake fatalities died when the Cypress Viaduct in Oakland collapsed. The cost to repair and replace highways damaged by the earthquake was $2 billion, about half of which was to replace the Cypress Viaduct. * Major bridge failures were the result of antiquated designs and inadequate anticipation of seismic loading. * Twenty one kilometers (13 mi) of gas-distribution lines had to be replaced in several communities and more than 1,200 leaks and breaks in water mains and service connections had to be excavated and repaired. At least 5 electrical substations were badly damaged, overwhelming the designed redundancy of the electrical system. * Instruments in 28 buildings recorded their response to earthquake shaking that provided opportunities to understand how different types of buildings responded, the importance of site amplification, and how buildings interact with their foundation when shaken (soil structure interaction).

  15. The Magnitude 6.7 Northridge, California, Earthquake of January 17, 1994

    NASA Technical Reports Server (NTRS)

    Donnellan, A.

    1994-01-01

    The most damaging earthquake in the United States since 1906 struck northern Los Angeles on January 17.1994. The magnitude 6.7 Northridge earthquake produced a maximum of more than 3 meters of reverse (up-dip) slip on a south-dipping thrust fault rooted under the San Fernando Valley and projecting north under the Santa Susana Mountains.

  16. Using Logistic Regression to Predict the Probability of Debris Flows in Areas Burned by Wildfires, Southern California, 2003-2006

    USGS Publications Warehouse

    Rupert, Michael G.; Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Helsel, Dennis R.

    2008-01-01

    Logistic regression was used to develop statistical models that can be used to predict the probability of debris flows in areas recently burned by wildfires by using data from 14 wildfires that burned in southern California during 2003-2006. Twenty-eight independent variables describing the basin morphology, burn severity, rainfall, and soil properties of 306 drainage basins located within those burned areas were evaluated. The models were developed as follows: (1) Basins that did and did not produce debris flows soon after the 2003 to 2006 fires were delineated from data in the National Elevation Dataset using a geographic information system; (2) Data describing the basin morphology, burn severity, rainfall, and soil properties were compiled for each basin. These data were then input to a statistics software package for analysis using logistic regression; and (3) Relations between the occurrence or absence of debris flows and the basin morphology, burn severity, rainfall, and soil properties were evaluated, and five multivariate logistic regression models were constructed. All possible combinations of independent variables were evaluated to determine which combinations produced the most effective models, and the multivariate models that best predicted the occurrence of debris flows were identified. Percentage of high burn severity and 3-hour peak rainfall intensity were significant variables in all models. Soil organic matter content and soil clay content were significant variables in all models except Model 5. Soil slope was a significant variable in all models except Model 4. The most suitable model can be selected from these five models on the basis of the availability of independent variables in the particular area of interest and field checking of probability maps. The multivariate logistic regression models can be entered into a geographic information system, and maps showing the probability of debris flows can be constructed in recently burned areas of

  17. Estimating Earthquake Hazards in the San Pedro Shelf Region, Southern California

    NASA Astrophysics Data System (ADS)

    Baher, S.; Fuis, G.; Normark, W. R.; Sliter, R.

    2003-12-01

    The San Pedro Shelf (SPS) region of the inner California Borderland offshore southern California poses a significant seismic hazard to the contiguous Los Angeles Area, as a consequence of late Cenozoic compressional reactivation of mid-Cenozoic extensional faults. The extent of the hazard, however, is poorly understood because of the complexity of fault geometries and uncertainties in earthquake locations. The major faults in the region include the Palos Verdes, THUMS Huntington Beach and the Newport-Inglewood fault zones. We report here the analysis and interpretation of wide-angle seismic-reflection and refraction data recorded as part of the Los Angeles Region Seismic Experiment line 1 (LARSE 1), multichannel seismic (MCS) reflection data obtained by the USGS (1998-2000) and industry borehole stratigraphy. The onshore-offshore velocity model, which is based on forward modeling of the refracted P-wave arrival times, is used to depth migrate the LARSE 1 section. Borehole stratigraphy allows correlation of the onshore and offshore velocity models because state regulations prevent collection of deep-penetration acoustic data nearshore (within 3 mi.). Our refraction study is an extension of ten Brink et al., 2000 tomographic inversion of LARSE I data. They found high velocities (> 6 km/sec) at about ~3.5 km depth from the Catalina Fault (CF) to the SPS. We find these velocities, shallower (around 2 km depth) beneath the Catalina Ridge (CR) and SPS, but at a depth 2.5-3.0 km elsewhere in the study region. This change in velocity structure can provide additional constraints for the tectonic processes of this region. The structural horizons observed in the LARSE 1 reflection data are tied to adjacent MCS lines. We find localized folding and faulting at depth (~2 km) southwest of the CR and on the SPS slope. Quasi-laminar beds, possible of pelagic origin follow the contours of earlier folded (wavelength ~1 km) and faulted Cenozoic sedimentary and volcanic rocks. Depth to

  18. Liquefaction and other ground failures in Imperial County, California, from the April 4, 2010, El Mayor-Cucapah earthquake

    USGS Publications Warehouse

    McCrink, Timothy P.; Pridmore, Cynthia L.; Tinsley, John C., III; Sickler, Robert R.; Brandenberg, Scott J.; Stewart, Jonathan P.

    2011-01-01

    The Colorado River Delta region of southern Imperial Valley, California, and Mexicali Valley, Baja California, is a tectonically dynamic area characterized by numerous active faults and frequent large seismic events. Significant earthquakes that have been accompanied by surface fault rupture and/or soil liquefaction occurred in this region in 1892 (M7.1), 1915 (M6.3; M7.1), 1930 (M5.7), 1940 (M6.9), 1950 (M5.4), 1957 (M5.2), 1968 (6.5), 1979 (6.4), 1980 (M6.1), 1981 (M5.8), and 1987 (M6.2; M6.8). Following this trend, the M7.2 El Mayor-Cucapah earthquake of April 4, 2010, ruptured approximately 120 kilometers along several known faults in Baja California. Liquefaction caused by the M7.2 El Mayor-Cucapah earthquake was widespread throughout the southern Imperial Valley but concentrated in the southwest corner of the valley, southwest of the city centers of Calexico and El Centro where ground motions were highest. Although there are few strong motion recordings in the very western part of the area, the recordings that do exist indicate that ground motions were on the order of 0.3 to 0.6g where the majority of liquefaction occurrences were found. More distant liquefaction occurrences, at Fites Road southwest of Brawley and along Rosita Canal northwest of Holtville were triggered where ground motions were about 0.2 g. Damage to roads was associated mainly with liquefaction of sandy river deposits beneath bridge approach fills, and in some cases liquefaction within the fills. Liquefaction damage to canal and drain levees was not always accompanied by vented sand, but the nature of the damage leads the authors to infer that liquefaction was involved in the majority of observed cases. Liquefaction-related damage to several public facilities - Calexico Waste Water Treatment Plant, Fig Lagoon levee system, and Sunbeam Lake Dam in particular - appears to be extensive. The cost to repair these facilities to prevent future liquefaction damage will likely be prohibitive. As

  19. Geodetic slip rate for the eastern California shear zone and the recurrence time of Mojave desert earthquakes

    USGS Publications Warehouse

    Sauber, J.; Thatcher, W.; Solomon, S.C.; Lisowski, M.

    1994-01-01

    Where the San Andreas fault passes along the southwestern margin of the Mojave desert, it exhibits a large change in trend, and the deformation associated with the Pacific/North American plate boundary is distributed broadly over a complex shear zone. The importance of understanding the partitioning of strain across this region, especially to the east of the Mojave segment of the San Andreas in a region known as the eastern California shear zone (ECSZ), was highlighted by the occurrence (on 28 June 1992) of the magnitude 7.3 Landers earthquake in this zone. Here we use geodetic observations in the central Mojave desert to obtain new estimates for the rate and distribution of strain across a segment of the ECSZ, and to determine a coseismic strain drop of ~770 ??rad for the Landers earthquake. From these results we infer a strain energy recharge time of 3,500-5,000 yr for a Landers-type earthquake and a slip rate of ~12 mm yr-1 across the faults of the central Mojave. The latter estimate implies that a greater fraction of plate motion than heretofore inferred from geodetic data is accommodated across the ECSZ.

  20. San Andreas fault geometry at Desert Hot Springs, California, and its effects on earthquake hazards and groundwater

    USGS Publications Warehouse

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Gandhok, G.

    2009-01-01

    The Mission Creek and Banning faults are two of the principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. Structural characteristics of the faults affect both regional earthquake hazards and local groundwater resources. We use seismic, gravity, and geological data to characterize the San Andreas fault zone in the vicinity of Desert Hot Springs. Seismic images of the upper 500 m of the Mission Creek fault at Desert Hot Springs show multiple fault strands distributed over a 500 m wide zone, with concentrated faulting within a central 200 m wide area of the fault zone. High-velocity (up to 5000 m=sec) rocks on the northeast side of the fault are juxtaposed against a low-velocity (6.0) earthquakes in the area (in 1948 and 1986) occurred at or near the depths (~10 to 12 km) of the merged (San Andreas) fault. Large-magnitude earthquakes that nucleate at or below the merged fault will likely generate strong shaking from guided waves along both fault zones and from amplified seismic waves in the low-velocity basin between the two fault zones. The Mission Creek fault zone is a groundwater barrier with the top of the water table varying by 60 m in depth and the aquifer varying by about 50 m in thickness across a 200 m wide zone of concentrated faulting.

  1. Comments on baseline correction of digital strong-motion data: Examples from the 1999 Hector Mine, California, earthquake

    USGS Publications Warehouse

    Boore, D.M.; Stephens, C.D.; Joyner, W.B.

    2002-01-01

    Residual displacements for large earthquakes can sometimes be determined from recordings on modern digital instruments, but baseline offsets of unknown origin make it difficult in many cases to do so. To recover the residual displacement, we suggest tailoring a correction scheme by studying the character of the velocity obtained by integration of zeroth-order-corrected acceleration and then seeing if the residual displacements are stable when the various parameters in the particular correction scheme are varied. For many seismological and engineering purposes, however, the residual displacement are of lesser importance than ground motions at periods less than about 20 sec. These ground motions are often recoverable with simple baseline correction and low-cut filtering. In this largely empirical study, we illustrate the consequences of various correction schemes, drawing primarily from digital recordings of the 1999 Hector Mine, California, earthquake. We show that with simple processing the displacement waveforms for this event are very similar for stations separated by as much as 20 km. We also show that a strong pulse on the transverse component was radiated from the Hector Mine earthquake and propagated with little distortion to distances exceeding 170 km; this pulse leads to large response spectral amplitudes around 10 sec.

  2. Offshore and onshore liquefaction at Moss Landing spit, central California - result of the October 17, 1989, Loma Prieta earthquake

    SciTech Connect

    Greene, H.G.; Chase, T.E.; Hicks, K.R. ); Gardner-Taggart, J.; Ledbetter, M.T.; Barminski, R. ); Baxter, C. )

    1991-09-01

    As a result of the October 17, 1989, Loma Prieta (Santa Cruz Mountains, California) earthquake, liquefaction of the fluvial, estuarine, eolian, and beach sediments under a sand spit destroyed the Moss Landing Marine Laboratories and damaged other structures and utilities. Initial studies suggested that the liquefaction was a local phenomenon. More detailed offshore investigations, however, indicate that it occurred over a large area (maximum 8 km{sup 2}) during or shortly after the earthquake with movement of unconsolidated sediment toward and into the head of Monterey submarine canyon. This conclusion is supported by side-scan sonographs, high-resolution seismic-reflection and bathymetric profiles, onshore and sea-floor photographs, and underwater video tapes. Many distinct lobate features were identified on the shallow shelf. These features almost certainly were the result of the October 17 earthquake; they were subsequently destroyed by winter storms. In addition, fresh slump scars and recently dislodged mud debris were found on the upper, southern wall of Monterey submarine canyon.

  3. 3-D P- and S-wave velocity structure and low-frequency earthquake locations in the Parkfield, California region

    NASA Astrophysics Data System (ADS)

    Zeng, Xiangfang; Thurber, Clifford H.; Shelly, David R.; Harrington, Rebecca M.; Cochran, Elizabeth S.; Bennington, Ninfa L.; Peterson, Dana; Guo, Bin; McClement, Kara

    2016-09-01

    To refine the 3-D seismic velocity model in the greater Parkfield, California region, a new data set including regular earthquakes, shots, quarry blasts and low-frequency earthquakes (LFEs) was assembled. Hundreds of traces of each LFE family at two temporary arrays were stacked with time-frequency domain phase weighted stacking method to improve signal-to-noise ratio. We extend our model resolution to lower crustal depth with LFE data. Our result images not only previously identified features but also low velocity zones (LVZs) in the area around the LFEs and the lower crust beneath the southern Rinconada Fault. The former LVZ is consistent with high fluid pressure that can account for several aspects of LFE behaviour. The latter LVZ is consistent with a high conductivity zone in magnetotelluric studies. A new Vs model was developed with S picks that were obtained with a new autopicker. At shallow depth, the low Vs areas underlie the strongest shaking areas in the 2004 Parkfield earthquake. We relocate LFE families and analyse the location uncertainties with the NonLinLoc and tomoDD codes. The two methods yield similar results.

  4. Chronology of Postglacial Eruptive Activity and Calculation of Eruption Probabilities for Medicine Lake Volcano, Northern California

    USGS Publications Warehouse

    Nathenson, Manuel; Donnelly-Nolan, Julie M.; Champion, Duane E.; Lowenstern, Jacob B.

    2007-01-01

    Medicine Lake volcano has had 4 eruptive episodes in its postglacial history (since 13,000 years ago) comprising 16 eruptions. Time intervals between events within the episodes are relatively short, whereas time intervals between the episodes are much longer. An updated radiocarbon chronology for these eruptions is presented that uses paleomagnetic data to constrain the choice of calibrated ages. This chronology is used with exponential, Weibull, and mixed-exponential probability distributions to model the data for time intervals between eruptions. The mixed exponential distribution is the best match to the data and provides estimates for the conditional probability of a future eruption given the time since the last eruption. The probability of an eruption at Medicine Lake volcano in the next year from today is 0.00028.

  5. Postearthquake relaxation and aftershock accumulation linearly related after the 2003 M 6.5 Chengkung, Taiwan, and the 2004 M 6.0 Parkfield, California, earthquakes

    USGS Publications Warehouse

    Savage, J.C.; Yu, S.-B.

    2007-01-01

    We treat both the number of earthquakes and the deformation following a mainshock as the superposition of a steady background accumulation and the post-earthquake process. The preseismic displacement and seismicity rates ru and rE are used as estimates of the background rates. Let t be the time after the mainshock, u(t) + u0 the postseismic displacement less the background accumulation rut, and ??N(t) the observed cumulative number of postseismic earthquakes less the background accumulation rE t. For the first 160 days (duration limited by the occurrence of another nearby earthquake) following the Chengkung (M 6.5, 10 December 2003, eastern Taiwan) and the first 560 days following the Parkfield (M 6.0, 28 September 2004, central California) earthquakes u(t) + u0 is a linear function of ??N(t). The aftershock accumulation ??N(t) for both earthquakes is described by the modified Omori Law d??N/dt ?? (1 + t/??)-p with p = 0.96 and ?? = 0.03 days. Although the Chengkung earthquake involved sinistral, reverse slip on a moderately dipping fault and the Parkfield earthquake right-lateral slip on a near-vertical fault, the earthquakes share an unusual feature: both occurred on faults exhibiting interseismic fault creep at the surface. The source of the observed postseismic deformation appears to be afterslip on the coseismic rupture. The linear relation between u(t) + u0 and N(t) suggests that this afterslip also generates the aftershocks. The linear relation between u(t) + u0 and ??N(t) obtains after neither the 1999 M 7.1 Hector Mine (southern California) nor the 1999 M 7.6 Chi-Chi (central Taiwan) earthquakes, neither of which occurred on fault segments exhibiting fault creep.

  6. Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Liquefaction

    USGS Publications Warehouse

    Holzer, Thomas L.

    1998-01-01

    The 1989 Loma Prieta earthquake both reconfirmed the vulnerability of areas in the San Francisco-Monterey Bay region to liquefaction and provided an opportunity to test methodologies for predicting liquefaction that have been developed since the mid-1970's. This vulnerability is documented in the chapter edited by O'Rourke and by the investigators in this chapter who describe case histories of liquefaction damage and warn us about the potential for even greater damage from liquefaction if an earthquake similar to the 1989 Loma Prieta earthquake, but located closer to their study sites, were to occur.

  7. Probable slow slips in the mid-crust of Hsinchu, northwestern Taiwan: Temporal correlation between normal faulting earthquakes and relative uplift

    NASA Astrophysics Data System (ADS)

    Pu, H. C.; Lin, C. H.

    2016-05-01

    To investigate the seismic behavior of crustal deformation, we deployed a dense seismic network at the Hsinchu area of northwestern Taiwan during the period between 2004 and 2006. Based on abundant local micro-earthquakes recorded at this seismic network, we have successfully determined 274 focal mechanisms among ∼1300 seismic events. It is very interesting to see that the dominant energy of both seismic strike-slip and normal faulting mechanisms repeatedly alternated with each other within two years. Also, the strike-slip and normal faulting earthquakes were largely accompanied with the surface slipping along N60°E and uplifting obtained from the continuous GPS data, individually. Those phenomena were probably resulted by the slow uplifts at the mid-crust beneath the northwestern Taiwan area. As the deep slow uplift was active below 10 km in depth along either the boundary fault or blind fault, the push of the uplifting material would simultaneously produce both of the normal faulting earthquakes in the shallow depths (0-10 km) and the slight surface uplifting. As the deep slow uplift was stop, instead, the strike-slip faulting earthquakes would be dominated as usual due to strongly horizontal plate convergence in the Taiwan. Since the normal faulting earthquakes repeatedly dominated in every 6 or 7 months between 2004 and 2006, it may conclude that slow slip events in the mid crust were frequent to release accumulated tectonic stress in the Hsinchu area.

  8. The M7 October 21, 1868 Hayward Earthquake, Northern California-140 Years Later

    NASA Astrophysics Data System (ADS)

    Brocher, T. M.; Boatwright, J.; Lienkaemper, J. J.; Schwartz, D. P.; Garcia, S.

    2007-12-01

    October 21, 2008 marks the 140th anniversary of the M7 1868 Hayward earthquake. This large earthquake, which occurred slightly before 8 AM, caused extensive damage to San Francisco Bay Area and remains the nation's 12th most lethal earthquake. Property loss was extensive and about 30 people were killed. This earthquake culminated a decade-long series of earthquakes in the Bay Area which started with an M~6 earthquake in the southern Peninsula in 1856, followed by a series of four M5.8 to M6.1 sized earthquakes along the northern Calaveras fault, and ended with a M~6.5 earthquake in the Santa Cruz Mountains in 1865. Despite this flurry of quakes, the shaking from the 1868 earthquake was the strongest that the new towns and growing cities of the Bay Area had ever experienced. The effect on the brick buildings of the time was devastating: walls collapsed in San Francisco, Oakland, and San Jose, and buildings cracked as far away as Napa, Santa Rosa, and Hollister. The area that was strongly shaken (at Modified Mercalli Intensity VII or higher) encompassed about 2,300 km2. Aftershocks continued into November 1868. Surface cracking of the ground along the southern end of the Hayward Fault was traced from Warm Springs in Fremont northward 32 km to San Leandro. As Lawson (1908) reports, "the evidence to the northward of San Leandro is not very satisfactory. The country was then unsettled, and the information consisted of reports of cow- boys riding on the range". Analysis of historical triangulation data suggest that the fault moved as far north as Berkeley, and from these data the average slip along the fault is inferred to be about 1.9 ± 0.4 meters. The paleoseismic record from the southern end of the Hayward Fault provides evidence for 10 earthquakes before 1868. The average interval between these earthquakes is 170 ± 80 years, but the last five earthquakes have had an average interval of only 140 ± 50 years. The 1868 Hayward earthquake and more recent analogs such

  9. Active Crustal Deformation in the Area of San Carlos, Baja California Sur, Mexico as Shown by Data of Local Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Munguía, Luis; González-Escobar, Mario; Navarro, Miguel; Valdez, Tito; Mayer, Sergio; Aguirre, Alfredo; Wong, Victor; Luna, Manuel

    2015-12-01

    We analyzed earthquakes of sequences that occurred at different times near San Carlos, a town of approximately 5000 inhabitants. The seismic sequences happened during March-April 1989, October 2000-June 2001, and 5-15 February 2004 at about 200 km west of the Pacific-North America plate boundary. The strong shaking from initial earthquakes of the first two sequences prompted the installation of temporary seismic stations in the area. With data recorded by these stations, we found an earthquake distribution that is consistent with the northwest segment of the Santa Margarita fault. Both the focal depth, that seemed to increase in E-NE direction, and a composite fault-plane solution, obtained from polarity data of the small earthquakes, were also consistent with the main characteristics of that fault. We also found that our normal-faulting mechanism (east side down) was quite similar to centroid moment tensor solutions for earthquakes with M w 5.4 and 5.3 that occurred in the area in February 2004. It is likely, then, that these larger earthquakes also occurred along the Santa Margarita Fault. To get some insight into the regional stress pattern, we compared the above mechanisms with mechanisms reported for other earthquakes of the Pacific margin of Baja California Sur and the Gulf of California regions. We observed that focal mechanisms of the two regions have T axes of stress that plunge sub horizontally in E-NE average direction. The corresponding P axes have N-NW average trend, but for the Pacific earthquakes these axes plunge at angles that are ~35° larger than those for the Gulf earthquakes. These more vertically inclined P axes of compressive stress mean substantial oblique fault motions. The mixture of oblique and strike-slip components of fault motions, as the focal mechanisms show, confirms a transtensional stress regime for the region. Before this research, we knew little about the seismicity and styles of faulting in the area. Now we know that

  10. Lower crustal earthquake swarms beneath Mammoth Mountain, California - evidence for the magmatic roots to the Mammoth Mountain mafic volcanic field?

    NASA Astrophysics Data System (ADS)

    Hill, D. P.; Shelly, D. R.

    2010-12-01

    Mammoth Mountain is a cluster of dacitic domes erupted ~ 68 ka. It stands on the SW topographic rim of Long Valley caldera in eastern CA. Structurally, it is outboard of the caldera ring-fracture system and its magmatic system is genetically distinct from that of the caldera. It resides within a field of mafic (basaltic) vents that erupted between 190 - 8 ka. A series of phreatic explosions from the north flank of the mountain some 700 ybp attest to the infusion of heat to shallow depths shortly prior to the 600 ybp eruptions of the Inyo Domes 6 to 12 km north of the Mountain. Unrest beneath Mammoth Mountain since 1980 has included 1) swarms of brittle-failure earthquakes in the upper 10 km of the crust that define concentric elliptical ring-like patterns centered beneath the summit, 2) mid-crustal (depths 10 to 20 km) long-period volcanic earthquakes, 3) the onset of diffuse CO2 degassing in 1990 following an 11-month-long swarm of shallow (<10 km), brittle-failure earthquakes in 1989, 4) occasional very-long-period earthquakes at depths of ~ 3 km, and 5) brief swarms of lower-crustal, brittle-failure earthquakes at depths of 20 to 30 km, including sizable episodes June 16-17, 2006 and September 29-30, 2009. Seismic waveform correlation analysis at multiple stations reveals that these lower-crustal, brittle-failure swarms consist of tens to hundreds of repeated similar events and also serves to identify many events not included in the Northern California Seismic Network (NCSN) catalog. In the case of the 2009 episode, an evolution in waveform is clearly discernible over the sequence, suggesting a corresponding evolution in source location or mechanism. Work is ongoing to take advantage of the waveform similarity to estimate precise hypocentral locations of these events in order to distinguish between these possibilities.We suggest that the brittle-failure earthquakes at depths of 20 to 30 km are occurring within the more mafic mid- to lower-crust, which can remain

  11. Birth of a fault: Connecting the Kern County and Walker Pass, California, earthquakes

    USGS Publications Warehouse

    Bawden, G.W.; Michael, A.J.; Kellogg, L.H.

    1999-01-01

    A band of seismicity transects the southern Sierra Nevada range between the northeastern end of the site of the 1952 MW (moment magnitude) 7.3 Kern County earthquake and the site of the 1946 MW 6.1 Walker Pass earthquake. Relocated earthquakes in this band, which lacks a surface expression, better delineate the northeast-trending seismic lineament and resolve complex structure near the Walker Pass mainshock. Left-lateral earthquake focal planes are rotated counterclockwise from the strike of the seismic lineament, consistent with slip on shear fractures such as those observed in the early stages of fault development in laboratory experiments. We interpret this seismic lineament as a previously unrecognized, incipient, currently blind, strike-slip fault, a unique example of a newly forming structure.

  12. Seismicity remotely triggered by the magnitude 7.3 landers, california, earthquake.

    PubMed

    Hill, D P; Reasenberg, P A; Michael, A; Arabaz, W J; Beroza, G; Brumbaugh, D; Brune, J N; Castro, R; Davis, S; Depolo, D; Ellsworth, W L; Gomberg, J; Harmsen, S; House, L; Jackson, S M; Johnston, M J; Jones, L; Keller, R; Malone, S; Munguia, L; Nava, S; Pechmann, J C; Sanford, A; Simpson, R W; Smith, R B; Stark, M; Stickney, M; Vidal, A; Walter, S; Wong, V; Zollweg, J

    1993-06-11

    The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma). PMID:17810202

  13. Seismicity remotely triggered by the magnitude 7.3 landers, california, earthquake

    USGS Publications Warehouse

    Hill, D.P.; Reasenberg, P.A.; Michael, A.; Arabaz, W.J.; Beroza, G.; Brumbaugh, D.; Brune, J.N.; Castro, R.; Davis, S.; Depolo, D.; Ellsworth, W.L.; Gomberg, J.; Harmsen, S.; House, L.; Jackson, S.M.; Johnston, M.J.S.; Jones, L.; Keller, Rebecca Hylton; Malone, S.; Munguia, L.; Nava, S.; Pechmann, J.C.; Sanford, A.; Simpson, R.W.; Smith, R.B.; Stark, M.; Stickney, M.; Vidal, A.; Walter, S.; Wong, V.; Zollweg, J.

    1993-01-01

    The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

  14. Chapter C. The Loma Prieta, California, Earthquake of October 17, 1989 - Building Structures

    USGS Publications Warehouse

    Celebi, Mehmet

    1998-01-01

    Several approaches are used to assess the performance of the built environment following an earthquake -- preliminary damage surveys conducted by professionals, detailed studies of individual structures, and statistical analyses of groups of structures. Reports of damage that are issued by many organizations immediately following an earthquake play a key role in directing subsequent detailed investigations. Detailed studies of individual structures and statistical analyses of groups of structures may be motivated by particularly good or bad performance during an earthquake. Beyond this, practicing engineers typically perform stress analyses to assess the performance of a particular structure to vibrational levels experienced during an earthquake. The levels may be determined from recorded or estimated ground motions; actual levels usually differ from design levels. If a structure has seismic instrumentation to record response data, the estimated and recorded response and behavior of the structure can be compared.

  15. Borehole strainmeter measurements spanning the 2014 Mw6.0 South Napa Earthquake, California: The effect from instrument calibration

    NASA Astrophysics Data System (ADS)

    Langbein, John

    2015-10-01

    The 24 August 2014 Mw6.0 South Napa, California earthquake produced significant offsets on 12 borehole strainmeters in the San Francisco Bay area. These strainmeters are located between 24 and 80 km from the source, and the observed offsets ranged up to 400 parts per billion (ppb), which exceeds their nominal precision by a factor of 100. However, the observed offsets of tidally calibrated strains differ by up to 130 ppb from predictions based on a moment tensor derived from seismic data. The large misfit can be attributed to a combination of poor instrument calibration and better modeling of the strain field from the earthquake. Borehole strainmeters require in situ calibration, which historically has been accomplished by comparing their measurements of Earth tides with the strain tides predicted by a model. Although the borehole strainmeter accurately measures the deformation within the borehole, the long-wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument. Previous analyses of surface-mounted, strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30%. The poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30% and making small adjustments to the point source model of the earthquake, which reduces the RMS misfit from 130 ppb to 18 ppb. This suggests that relying on tidal models to calibrate borehole strainmeters significantly reduces their accuracy.

  16. Borehole strainmeter measurements spanning the 2014, Mw6.0 South Napa Earthquake, California: The effect from instrument calibration

    USGS Publications Warehouse

    Langbein, John O.

    2015-01-01

    The 24 August 2014 Mw6.0 South Napa, California earthquake produced significant offsets on 12 borehole strainmeters in the San Francisco Bay area. These strainmeters are located between 24 and 80 km from the source and the observed offsets ranged up to 400 parts-per-billion (ppb), which exceeds their nominal precision by a factor of 100. However, the observed offsets of tidally calibrated strains differ by up to 130 ppb from predictions based on a moment tensor derived from seismic data. The large misfit can be attributed to a combination of poor instrument calibration and better modeling of the strain fit from the earthquake. Borehole strainmeters require in-situ calibration, which historically has been accomplished by comparing their measurements of Earth tides with the strain-tides predicted by a model. Although the borehole strainmeter accurately measure the deformation within the borehole, the long-wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument. Previous analyses of surface-mounted, strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30%. The poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30% and making small adjustments to the point-source model of the earthquake, which reduces the RMS misfit from 130 ppb to 18 ppb. This suggests that relying on tidal models to calibrate borehole strainmeters significantly reduces their accuracy.

  17. Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Lifelines

    USGS Publications Warehouse

    Schiff, Anshel J., (Edited By)

    1998-01-01

    To the general public who had their televisions tuned to watch the World Series, the 1989 Loma Prieta earthquake was a lifelines earthquake. It was the images seen around the world of the collapsed Cypress Street viaduct, with the frantic and heroic efforts to pull survivors from the structure that was billowing smoke; the collapsed section of the San Francisco-Oakland Bay Bridge and subsequent home video of a car plunging off the open span; and the spectacular fire in the Marina District of San Francisco fed by a broken gasline. To many of the residents of the San Francisco Bay region, the relation of lifelines to the earthquake was characterized by sitting in the dark because of power outage, the inability to make telephone calls because of network congestion, and the slow and snarled traffic. Had the public been aware of the actions of the engineers and tradespeople working for the utilities and other lifeline organizations on the emergency response and restoration of lifelines, the lifeline characteristics of this earthquake would have been even more significant. Unobserved by the public were the warlike devastation in several electrical-power substations, the 13 miles of gas-distribution lines that had to be replaced in several communities, and the more than 1,200 leaks and breaks in water mains and service connections that had to be excavated and repaired. Like the 1971 San Fernando, Calif., earthquake, which was a seminal event for activity to improve the earthquake performance of lifelines, the 1989 Loma Prieta earthquake demonstrated that the tasks of preparing lifelines in 'earthquake country' were incomplete-indeed, new lessons had to be learned.

  18. Near-field postseismic deformation associated with the 1992 Landers and 1999 Hector Mine, California, earthquakes

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Prescott, W.H.

    2003-01-01

    After the Landers earthquake (Mw = 7.3, 1992.489) a linear array of 10 monuments extending about 30 km N50??E on either side of the earthquake rupture plus a nearby offtrend reference monument were surveyed frequently by GPS until 2003.2. The array also spans the rupture of the subsequent Hector Mine earthquake (Mw = 7.1, 1999.792 . The pre-Landers velocities of monuments in the array relative to interior North America were estimated from earlier trilateration and very long baseline interferometry measurements. Except at the reference monument, the post-Landers velocities of the individual monuments in the array relaxed to their preseismic values within 4 years. Following the Hector Mine earthquake the velocities of the monuments relaxed to steady rates within 1 year. Those steady rates for the east components are about equal to the pre-Landers rates as is the steady rate for the north component of the one monument east of the Hector Mine rupture. However, the steady rates for the north components of the 10 monuments west of the rupture are systematically ???10 mm yr1 larger than the pre-Landers rates. The relaxation to a steady rate is approximately exponential with decay times of 0.50 ?? 0.10 year following the Landers earthquake and 0.32 ?? 0.18 year following the Hector Mine earthquake. The postearthquake motions of the Landers array following the Landers earthquake are not well approximated by the viscoelastic-coupling model of Pollitz et al. [2000]. A similar viscoelastic-coupling model [Pollitz et al., 2001] is more successful in representing the deformation after the Hector Mine earthquake.

  19. Paleoseismic evidence of clustered earthquakes on the San Andreas fault in the Carrizo Plain, California

    SciTech Connect

    Grant, L.B.; Sieh, K.

    1994-04-01

    Exposures we have excavated across the San Andreas fault contradict the hypothesis that part of the fault in the Carrizo Plain is unusually strong and experiences relatively infrequent rupture. The exposures record evidence of at least seven surface-rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in-situ plants. Five large earthquakes have occurred since 1218 A.D. The most recent earthquake, event A, was the 1857 Fort Tejon earthquake, which we have associated with 6.6-10 m of dextral slip along the main fault trace. The penultimate earthquake, event B, most likely occurred within the period A.D. 1405-1510. Slip from either events B and C combined or from event B alone, totals 7-11 m. Three earthquakes, events C, D, and E, occurred in a temporal cluster prior to event B and after approximately A.D. 1218. The average recurrence interval within this cluster is 73-116 years, depending on assumptions. Events F and G occurred after 200 years B.C. A depositional hiatus between events E and F may hide evidence of additional earthquakes. Events B and D within the Carrizo cluster of A.D. 1218-1510 may correlate with events T (A.D. 1329-1363) and V (A.D. 1465-1495) at Pallett Creek on the Mojave `segment` of the fault. This suggests two fault ruptures similar in length to that of 1857. Events C and E apparently did not rupture the Mojave section, which suggests that the Carrizo segment has ruptured independently or in combination with segments to the north. Irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic `supercycles.`

  20. Slip partitioning of the Calaveras fault, California, and prospects for future earthquakes

    SciTech Connect

    Oppenheimer, D.H.; Bakun, W.H.; Lindh, A.G. )

    1990-06-10

    Examination of main shock and microearthquake data from the Calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8-9 km near the base of the zone of microearthquakes. The spatial pattern of pre-main shock microseismicity surrounding the Coyote Lake and Morgan Hill hypocenters is similar to the pattern of the post-main shock microseismicity. Microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones. Estimates of the fault regions which slipped during the Coyote Lake Morgan Hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic. The authors propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes. From the pattern of microearthquake locations they recognize six aseismic zones where they expect future main shocks will rupture the Calaveras fault. From an analysis of historic seismic data they establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next M > 5 earthquakes. The first zone is located near Gilroy and was last ruptured by a M5.2 earthquake in 1949. The second zone is located south of Calaveras Reservoir and north of the 1988 M5.1 Alum Rock earthquake. It has not slipped seismically since at least 1903, and the size of the aseismic region is sufficiently large to sustain a M5.5 earthquake.

  1. Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Aftershocks and Postseismic Effects

    USGS Publications Warehouse

    Reasenberg, Paul A., (Edited By)

    1997-01-01

    While the damaging effects of the earthquake represent a significant social setback and economic loss, the geophysical effects have produced a wealth of data that have provided important insights into the structure and mechanics of the San Andreas Fault system. Generally, the period after a large earthquake is vitally important to monitor. During this part of the seismic cycle, the primary fault and the surrounding faults, rock bodies, and crustal fluids rapidly readjust in response to the earthquake's sudden movement. Geophysical measurements made at this time can provide unique information about fundamental properties of the fault zone, including its state of stress and the geometry and frictional/rheological properties of the faults within it. Because postseismic readjustments are rapid compared with corresponding changes occurring in the preseismic period, the amount and rate of information that is available during the postseismic period is relatively high. From a geophysical viewpoint, the occurrence of the Loma Prieta earthquake in a section of the San Andreas fault zone that is surrounded by multiple and extensive geophysical monitoring networks has produced nothing less than a scientific bonanza. The reports assembled in this chapter collectively examine available geophysical observations made before and after the earthquake and model the earthquake's principal postseismic effects. The chapter covers four broad categories of postseismic effect: (1) aftershocks; (2) postseismic fault movements; (3) postseismic surface deformation; and (4) changes in electrical conductivity and crustal fluids.

  2. School Site Preparedness for the Safety of California's Children K-12. Official Report of the Northridge Earthquake Task Force on Education.

    ERIC Educational Resources Information Center

    California State Legislature, Sacramento. Senate Select Committee on the Northridge Earthquake.

    This report asserts that disaster preparedness at all school sites must become a major and immediate priority. Should a disaster equaling the magnitude of the Northridge earthquake occur, the current varying levels of site preparedness may not adequately protect California's children. The report describes why the state's children are not safe and…

  3. The Redwood Coast Tsunami Work Group: a unique organization promoting earthquake and tsunami resilience on California's North Coast

    NASA Astrophysics Data System (ADS)

    Dengler, L.; Henderson, C.; Larkin, D.; Nicolini, T.; Ozaki, V.

    2012-12-01

    The Northern California counties of Del Norte, Humboldt, and Mendocino account for over 30% of California's coastline and is one of the most seismically active areas of the contiguous 48 states. The region is at risk from earthquakes located on- and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ) and from distant sources elsewhere in the Pacific. In 1995 the California Geological Survey (CGS) published a scenario for a CSZ earthquake that included both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of government agencies, tribes, service groups, academia and the private sector, was formed to coordinate and promote earthquake and tsunami hazard awareness and mitigation in the three-county region. The RCTWG and its member agencies projects include education/outreach products and programs, tsunami hazard mapping, signage and siren planning. Since 2008, RCTWG has worked with the California Emergency Management Agency (Cal EMA) in conducting tsunami warning communications tests on the North Coast. In 2007, RCTWG members helped develop and carry out the first tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD. The RCTWG has facilitated numerous multi-agency, multi-discipline coordinated exercises, and RCTWG county tsunami response plans have been a model for other regions of the state and country. Eight North Coast communities have been recognized as TsunamiReady by the National Weather Service, including the first National Park the first State Park and only tribe in California to be so recognized. Over 500 tsunami hazard zone signs have been posted in the RCTWG region since 2008. Eight assessment surveys from 1993 to 2010 have tracked preparedness actions and personal awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist

  4. The dependence of peak horizontal acceleration on magnitude, distance, and site effects for small-magnitude earthquakes in California and eastern North America

    USGS Publications Warehouse

    Campbell, K.W.

    1989-01-01

    One-hundred and ninety free-field accelerograms recorded on deep soil (>10 m deep) were used to study the near-source scaling characteristics of peak horizontal acceleration for 91 earthquakes (2.5 ??? ML ??? 5.0) located primarily in California. An analysis of residuals based on an additional 171 near-source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower acclerations, and that free-field accelerograms recorded on shallow soil (???10 m deep) have 82 per cent higher accelerations than free-field accelerograms recorded on deep soil. An analysis of residuals based on 27 selected strong-motion recordings from 19 earthquakes in Eastern North America indicated that near-source accelerations associated with frequencies less than about 25 Hz are consistent with predictions based on attenuation relationships derived from California. -from Author

  5. Statistical analysis of the induced Basel 2006 earthquake sequence: introducing a probability-based monitoring approach for Enhanced Geothermal Systems

    NASA Astrophysics Data System (ADS)

    Bachmann, C. E.; Wiemer, S.; Woessner, J.; Hainzl, S.

    2011-08-01

    Geothermal energy is becoming an important clean energy source, however, the stimulation of a reservoir for an Enhanced Geothermal System (EGS) is associated with seismic risk due to induced seismicity. Seismicity occurring due to the water injection at depth have to be well recorded and monitored. To mitigate the seismic risk of a damaging event, an appropriate alarm system needs to be in place for each individual experiment. In recent experiments, the so-called traffic-light alarm system, based on public response, local magnitude and peak ground velocity, was used. We aim to improve the pre-defined alarm system by introducing a probability-based approach; we retrospectively model the ongoing seismicity in real time with multiple statistical forecast models and then translate the forecast to seismic hazard in terms of probabilities of exceeding a ground motion intensity level. One class of models accounts for the water injection rate, the main parameter that can be controlled by the operators during an experiment. By translating the models into time-varying probabilities of exceeding various intensity levels, we provide tools which are well understood by the decision makers and can be used to determine thresholds non-exceedance during a reservoir stimulation; this, however, remains an entrepreneurial or political decision of the responsible project coordinators. We introduce forecast models based on the data set of an EGS experiment in the city of Basel. Between 2006 December 2 and 8, approximately 11 500 m3 of water was injected into a 5-km-deep well at high pressures. A six-sensor borehole array, was installed by the company Geothermal Explorers Limited (GEL) at depths between 300 and 2700 m around the well to monitor the induced seismicity. The network recorded approximately 11 200 events during the injection phase, more than 3500 of which were located. With the traffic-light system, actions where implemented after an ML 2.7 event, the water injection was

  6. Retardations in fault creep rates before local moderate earthquakes along the San Andreas fault system, central California

    USGS Publications Warehouse

    Burford, R.O.

    1988-01-01

    Records of shallow aseismic slip (fault creep) obtained along parts of the San Andreas and Calaveras faults in central California demonstrate that significant changes in creep rates often have been associated with local moderate earthquakes. An immediate postearthquake increase followed by gradual, long-term decay back to a previous background rate is generally the most obvious earthquake effect on fault creep. This phenomenon, identified as aseismic afterslip, usually is characterized by above-average creep rates for several months to a few years. In several cases, minor step-like movements, called coseismic slip events, have occurred at or near the times of mainshocks. One extreme case of coseismic slip, recorded at Cienega Winery on the San Andreas fault 17.5 km southeast of San Juan Bautista, consisted of 11 mm of sudden displacement coincident with earthquakes of ML=5.3 and ML=5.2 that occurred 2.5 minutes apart on 9 April 1961. At least one of these shocks originated on the main fault beneath the winery. Creep activity subsequently stopped at the winery for 19 months, then gradually returned to a nearly steady rate slightly below the previous long-term average. The phenomena mentioned above can be explained in terms of simple models consisting of relatively weak material along shallow reaches of the fault responding to changes in load imposed by sudden slip within the underlying seismogenic zone. In addition to coseismic slip and afterslip phenomena, however, pre-earthquake retardations in creep rates also have been observed. Onsets of significant, persistent decreases in creep rates have occurred at several sites 12 months or more before the times of moderate earthquakes. A 44-month retardation before the 1979 ML=5.9 Coyote Lake earthquake on the Calaveras fault was recorded at the Shore Road creepmeter site 10 km northwest of Hollister. Creep retardation on the San Andreas fault near San Juan Bautista has been evident in records from one creepmeter site for

  7. Processed seismic motion records from earthquakes (1982--1993): Recorded at Scotty`s Castle, California

    SciTech Connect

    Lum, P.K.; Honda, K.K.

    1993-10-01

    As part of the contract with the US Department of Energy, Nevada Operations Office (DOE/NV), URS/John A. Blume & Associates, Engineers (URS/Blume) maintained a network of seismographs to monitor the ground motion generated by the underground nuclear explosions (UNEs) at the Nevada Test Site (NTS). The seismographs were located in the communities surrounding the NTS and the Las Vegas valley. When these seismographs were not used for monitoring the UNE generated motions, a limited number of seismographs were maintained for monitoring motion generated by other than UNEs (e.g. motion generated by earthquakes, wind, blast). Scotty`s Castle was one of the selected earthquake monitoring station. During the period from 1982 through 1993, numerous earthquakes with varied in magnitudes and distances were recorded at Scotty`s Castle. The records from 24 earthquakes were processed and included in this report. Tables 1 and 2 lists the processed earthquakes in chronological order and in the order of epicentral distances, respectively. Figure 1 shows these epicenters and magnitudes. Due to the potential benefit of these data for the scientific community, DOE/NV and the National Park Service authorize the release of these records.

  8. Processed seismic motion records from earthquakes, 1982-1993: Recorded at Scotty's Castle, California

    NASA Astrophysics Data System (ADS)

    Lum, P. K.; Honda, K. K.

    1993-10-01

    As part of the contract with the US Department of Energy, Nevada Operations Office (DOE/NV), URS/John A. Blume & Associates, Engineers (URS/Blume) maintained a network of seismographs to monitor the ground motion generated by the underground nuclear explosions (UNE's) at the Nevada Test Site (NTS). The seismographs were located in the communities surrounding the NTS and the Las Vegas valley. When these seismographs were not used for monitoring the UNE generated motions, a limited number of seismographs were maintained for monitoring motion generated by other than UNE's (e.g. motion generated by earthquakes, wind, blast). Scotty's Castle was one of the selected earthquake monitoring stations. During the period from 1982 through 1993, numerous earthquakes which varied in magnitudes and distances were recorded at Scotty's Castle. The records from 24 earthquakes were processed and included in this report. The processed earthquakes are listed in chronological order and in the order of epicentral distances, respectively. These epicenters and magnitudes are shown. Due to the potential benefit of these data for the scientific community, DOE/NV and the National Park Service authorize the release of these records.

  9. Geodetic measurement of deformation in the Loma Prieta, California earthquake with Very Long Baseline Interferometry (VLBI)

    SciTech Connect

    Clark, T.A.; Ma, C.; Sauber, J.M.; Ryan, J.W. ); Gordon, D.; Caprette, D.S. ); Shaffer, D.B.; Vandenberg, N.R. )

    1990-07-01

    Following the Loma Prieta earthquake, two mobile Very Long Baseline Interferometry (VLBI) systems operated by the NASA Crustal Dynamics Project and the NOAA National Geodetic Survey were deployed at three previously established VLBI sites in the earthquake area: Fort Ord (near Monterey), the Presidio (in San Francisco) and Point Reyes. From repeated VLBI occupations of these sites since 1983, the pre-earthquake rates of deformation have been determined with respect to a North American reference frame with 1{sigma} formal standard errors of {approximately}1 mm/yr. The VLBI measurements immediately following the earthquake showed that the Fort Ord site was displaced 49 {plus minus} 4 mm at an azimuth of 11 {plus minus} 4{degree} and that the Presidio site was displaced 12 {plus minus} 5 mm at an azimuth of 148 {plus minus} 13{degree}. No anomalous change was detected at Point Reyes with 1{sigma} uncertainty of 4 mm. The estimated displacements at Fort Ord and the Presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment is shallower than slip on the more northern segment of the fault rupture. The authors also give the Cartesian positions at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the vicinity of the earthquake.

  10. Probability Assessment of Mega-thrust Earthquakes in Global Subduction Zones -from the View of Slip Deficit-

    NASA Astrophysics Data System (ADS)

    Ikuta, R.; Mitsui, Y.; Ando, M.

    2014-12-01

    We studied inter-plate slip history for about 100 years using earthquake catalogs. On assumption that each earthquake has stick-slip patch centered in its centroid, we regard cumulative seismic slips around the centroid as representing the inter-plate dislocation. We evaluated the slips on the stick-slip patches of over-M5-class earthquakes prior to three recent mega-thrust earthquakes, the 2004 Sumatra (Mw9.2), the 2010 Chile (Mw8.8), and the 2011 Tohoku (Mw9.0) around them. Comparing the cumulative seismic slips with the plate convergence, the slips before the mega-thrust events are significantly short in large area corresponding to the size of the mega-thrust events. We also researched cumulative seismic slips after other three mega-thrust earthquakes occurred in this 100 years, the 1952 Kamchatka (Mw9.0), the 1960 Chile (Mw9.5), the 1964 Alaska (Mw9.2). The cumulative slips have been significantly short in and around the focal area after their occurrence. The result should reflect persistency of the strong or/and large inter-plate coupled area capable of mega-thrust earthquakes. We applied the same procedure to global subduction zones to find that 21 regions including the focal area of above mega-thrust earthquakes show slip deficit over large area corresponding to the size of M9-class earthquakes. Considering that at least six M9-class earthquakes occurred in this 100 years and each recurrence interval should be 500-1000 years, it would not be surprised that from five to ten times of the already known regions (30 to 60 regions) are capable of M9 class earthquakes. The 21 regions as expected M9 class focal areas in our study is less than 5 to 10 times of the known 6, some of these regions may be divided into a few M9 class focal area because they extend to much larger area than typical M9 class focal area.

  11. Earthquake History of the Northern Imperial Fault, Imperial Valley, California, since the last Lake Cahuilla Highstand, circa A.D. 1680

    NASA Astrophysics Data System (ADS)

    Meltzner, A. J.; Rockwell, T. K.; Verdugo, D. M.

    2003-12-01

    The Imperial fault (IF) is the only fault in southern California to have ruptured in two major earthquakes in the 20th century. In 1940, it ruptured end-to-end (both north and south of the international border) in an M 6.9 earthquake, and in 1979, the northern segment of the fault (north of the border) ruptured again in an M 6.4 event. Slip in 1940 was highest (5-6 m) along the central portion of the fault and lowest (<1 m) along the northern portion, with a high slip gradient between these two segments just north of the border. The 1979 earthquake involved surface rupture along only the northern 30 km of the fault, with dextral offsets being <1 m and being nearly identical to 1940 offsets along the northern 20 km of the rupture. The similarities and differences of the two events led Sieh (1996) to propose a "slip-patch model" for the Imperial fault, whereby the fault ruptures with frequent moderate earthquakes along its northern end, like in 1979, and with less frequent larger events like 1940 along its entire length. According to the model, the central patch, which experienced high slip in 1940 and did not rupture in 1979, would rupture with relatively infrequent events (roughly every 260 years) with typically 5-6 m of slip per event; meanwhile, the northern patch, which corresponds to the 1979 rupture, would rupture more frequently (roughly every 40 years) with up to 1 m of slip per event. This model is consistent with the slip distribution observed in 1940 and in 1979. Paleoseismic investigations along the central patch also support this model, as the penultimate event there occurred shortly after the last Lake Cahuilla (LC) highstand at around A.D. 1680 (Thomas and Rockwell, 1996). Prior to the present investigation, however, there were no data on events prior to 1940 on the northern patch, which could serve to either support or refute the slip-patch model. We have opened a trench across the IF south of Harris Road, adjacent to Mesquite Basin, where the fault

  12. Triggered Fault Slip in Southern California Associated with the 2010 Sierra El Mayor-Cucapah, Baja California, Mexico, Earthquake

    NASA Astrophysics Data System (ADS)

    Rymer, M. J.; Treiman, J. A.; Kendrick, K. J.; Lienkaemper, J. J.; Wei, M.; Weldon, R. J.; Bilham, R. G.; Fielding, E. J.

    2010-12-01

    Surface fracturing (triggered slip) occurred in the central Salton Trough and to the southwest, in the Yuha Desert area—all in association with the 4 April 2010 (M7.2) El Mayor-Cucapah earthquake and its aftershocks. Triggered slip in the central Salton Trough occurred on the ‘frequent movers’: the southern San Andreas, Coyote Creek, Superstition Hills, and Imperial Faults, all of which have slipped in previous moderate to large, local and regional earthquakes in the past five decades. Other faults in the central Salton Trough that also slipped in 2010 include the Wienert Fault (southeastern section of the Superstition Hills Fault), the Kalin Fault (in the Brawley Seismic Zone), and the Brawley Fault Zone; triggered slip had not been reported on these faults in the past. Geologic measures of slip on faults in the central Salton Trough ranged from 1 to 18 mm, and everywhere was located where previous primary (tectonic) or triggered slip has occurred. Triggered slip in the Yuha Desert area occurred along at least two dozen faults, only some of which were known before the 4 April 2010 El Mayor-Cucapah earthquake. From east to northwest, slip occurred in seven general areas; 1) in the Northern Centinela Fault Zone (newly named), 2) along unnamed faults south of Pinto Wash, 3) along the Yuha Fault (newly named), 4) along both east and west branches of the Laguna Salada Fault, 5) along the Yuha Well Fault Zone (newly revised name), 6) along the Ocotillo Fault (newly named), and 7) along the southeastern-most section of the Elsinore Fault. Faults that slipped in the Yuha Desert area include northwest-trending right-lateral faults, northeast-trending left-lateral faults, and north-south faults, some of which had dominantly vertical slip. Triggered slip along the Ocotillo and Elsinore Faults occurred only in association with the 14 June 2010 (M5.7) aftershock, which also initiated slip along other faults near the town of Ocotillo. Triggered slip on faults in the Yuha

  13. Preseismic and coseismic deformation associated with the Coyote Lake, California, earthquake.

    USGS Publications Warehouse

    King, N.E.; Savage, J.C.; Lisowski, M.; Prescott, W.H.

    1981-01-01

    The Coyote Lake earthquake (ML=5.9; August 6, 1979; epicenter c100 km SE of San Francisco) occurred on the Calaveras fault within a geodetic network that had been surveyed annually since 1972 to monitor strain accumulation. The rupture surface as defined by aftershocks is a vertical rectangle 20 km in length extending from a depth of 4 km to c12 km. The observed deformation of the geodetic network constrains the average slip to be 0.33 + or - 0.05m right lateral. Although the geodetic data furnished an exceptionally detailed picture of the pre-earthquake deformation, no significant premonitory anomaly associated with the Coyote Lake earthquake can be identified.-Authors

  14. Deformation following the 1994 Northridge earthquake (M=6.7), southern California

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Prescott, W.H.; Hudnut, K.W.

    1998-01-01

    Following the 1994 MW=6.7 Northridge earthquake, a 65-km-long, north-south array of 11 geodetic monuments was established across the rupture. The array was surveyed with GPS ten times in the 4.25 yr after the earthquake. Although there is evidence for modest nonlinear postseismic relaxation in the first few weeks after the Northridge earthquake, the deformation in the subsequent four years can be adequately described by constant station velocities. The observed S70??E velocity components are consistent with the deformation expected from steady strain accumulation on the San Andreas fault. The N20??E velocity components indicate that the southern Northridge fault block is moving almost as a unit N20??E with repect to the northern fault block, the motion being accommodated by a zone of convergence (width 20 km) at the north end of the Northridge rupture.Following the 1994 Mw=6.7 Northridge earthquake, a 65-km-long, north-south array of 11 geodetic monuments was established across the rupture. The array was surveyed with GPS ten times in the 4.25 yr after the earthquake. Although there is evidence for modest nonlinear postseismic relaxation in the first few weeks after the Northridge earthquake, the deformation in the subsequent four years can be adequately described by constant station velocities. The observed S70??E velocity components are consistent with the deformation expected from steady strain accumulation on the San Andreas fault. The N20??E velocity components indicate that the southern Northridge fault block is moving almost as a unit N20??E with respect to the northern fault block, the motion being accommodated by a zone of convergence (width 20 km) at the north end of the Northridge rupture.

  15. Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day Earthquake, Hollister, California

    NASA Astrophysics Data System (ADS)

    Davis, Paul M.; Jackson, David D.; Johnston, Malcolm J. S.

    1980-07-01

    Seven weeks prior to the M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, an anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods of reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three, of the six stations analysed. Such changes have not been seen either previously or subsequently. The largest variation occurred at the two stations closest to the earthquake, but a change also occurred at a station 44 km to the south.

  16. Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day earthquake, Hollister, California

    SciTech Connect

    Davis, P.M.; Jackson, D.D.; Johnston, M.J.S.

    1980-07-01

    Seven weeks prior to he M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, and anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods or reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three of the six stations analysed. Such changes have not been seen either previously or subsequently. The largest variation occurred at the two stations closest to the earthquake, but a change also occurred at a station 44 km to the south.

  17. Chapter E. The Loma Prieta, California, Earthquake of October 17, 1989 - Geologic Setting and Crustal Structure

    USGS Publications Warehouse

    Wells, Ray E.

    2004-01-01

    Although some scientists considered the Ms=7.1 Loma Prieta, Calif., earthquake of 1989 to be an anticipated event, some aspects of the earthquake were surprising. It occurred 17 km beneath the Santa Cruz Mountains along a left-stepping restraining bend in the San Andreas fault system. Rupture on the southwest-dipping fault plane consisted of subequal amounts of right-lateral and reverse motion but did not reach the surface. In the area of maximum uplift, severe shaking and numerous ground cracks occurred along Summit Road and Skyland Ridge, several kilometers south of the main trace of the San Andreas fault. The relatively deep focus of the earthquake, the distribution of ground failure, the absence of throughgoing surface rupture on the San Andreas fault, and the large component of uplift raised several questions about the relation of the 1989 Loma Prieta earthquake to the San Andreas fault: Did the earthquake actually occur on the San Andreas fault? Where exactly is the San Andreas fault in the heavily forested Santa Cruz Mountains, and how does the fault relate to ground ruptures that occurred there in 1989 and 1906? What is the geometry of the San Andreas fault system at depth, and how does it relate to the major crustal blocks identified by geologic mapping? Subsequent geophysical and geologic investigations of crustal structure in the Loma Prieta region have addressed these and other questions about the relation of the earthquake to geologic structures observed in the southern Santa Cruz Mountains. The diverse papers in this chapter cover several topics: geologic mapping of the region, potential- field and electromagnetic modeling of crustal structure, and the velocity structure of the crust and mantle in and below the source region for the earthquake. Although these papers were mostly completed between 1992 and 1997, they provide critical documentation of the crustal structure of the Loma Prieta region. Together, they present a remarkably coherent, three

  18. Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Strong Ground Motion

    USGS Publications Warehouse

    Borcherdt, Roger D.

    1994-01-01

    Strong ground motion generated by the Loma Prieta, Calif., earthquake (MS~7.1) of October 17, 1989, resulted in at least 63 deaths, more than 3,757 injuries, and damage estimated to exceed $5.9 billion. Strong ground motion severely damaged critical lifelines (freeway overpasses, bridges, and pipelines), caused severe damage to poorly constructed buildings, and induced a significant number of ground failures associated with liquefaction and landsliding. It also caused a significant proportion of the damage and loss of life at distances as far as 100 km from the epicenter. Consequently, understanding the characteristics of the strong ground motion associated with the earthquake is fundamental to understanding the earthquake's devastating impact on society. The papers assembled in this chapter address this problem. Damage to vulnerable structures from the earthquake varied substantially with the distance from the causative fault and the type of underlying geologic deposits. Most of the damage and loss of life occurred in areas underlain by 'soft soil'. Quantifying these effects is important for understanding the tragic concentrations of damage in such areas as Santa Cruz and the Marina and Embarcadero Districts of San Francisco, and the failures of the San Francisco-Oakland Bay Bridge and the Interstate Highway 880 overpass. Most importantly, understanding these effects is a necessary prerequisite for improving mitigation measures for larger earthquakes likely to occur much closer to densely urbanized areas in the San Francisco Bay region. The earthquake generated an especially important data set for understanding variations in the severity of strong ground motion. Instrumental strong-motion recordings were obtained at 131 sites located from about 6 to 175 km from the rupture zone. This set of recordings, the largest yet collected for an event of this size, was obtained from sites on various geologic deposits, including a unique set on 'soft soil' deposits

  19. The 1989 earthquake swarm beneath Mammoth Mountain, California: an initial look at the 4 May through 30 September activity

    USGS Publications Warehouse

    Hill, D.P.

    1990-01-01

    Mammoth Mountain is a 50 000- to 200 000-yr-old cumulovolcano standing on the southwestern rim of Long Valley in eastern California. On 4 May 1989, two M=1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months. In addition to its longevity, noteworthy aspects of this persistent swarm are described. These aspects of the swarm, together with its location along the southern extension of the youthful Mono-Inyo volcanic chain, which last erupted 500 to 600 yr ago, point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath Mammoth Mountain. -from Authors

  20. Source inversion of the 1988 Upland, California, earthquake: determination of a fault plane for a small event

    USGS Publications Warehouse

    Mori, J.; Hartzell, S.

    1990-01-01

    We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4,6) earthquake near Upland, California. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 ?? 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. -from Authors

  1. Acceleration and volumetric strain generated by the Parkfield 2004 earthquake on the GEOS strong-motion array near Parkfield, California

    USGS Publications Warehouse

    Borcherdt, Rodger D.; Johnston, Malcolm J.S.; Dietel, Christopher; Glassmoyer, Gary; Myren, Doug; Stephens, Christopher

    2004-01-01

    An integrated array of 11 General Earthquake Observation System (GEOS) stations installed near Parkfield, CA provided on scale broad-band, wide-dynamic measurements of acceleration and volumetric strain of the Parkfield earthquake (M 6.0) of September 28, 2004. Three component measurements of acceleration were obtained at each of the stations. Measurements of collocated acceleration and volumetric strain were obtained at four of the stations. Measurements of velocity at most sites were on scale only for the initial P-wave arrival. When considered in the context of the extensive set of strong-motion recordings obtained on more than 40 analog stations by the California Strong-Motion Instrumentation Program (Shakal, et al., 2004 http://www.quake.ca.gov/cisn-edc) and those on the dense array of Spudich, et al, (1988), these recordings provide an unprecedented document of the nature of the near source strong motion generated by a M 6.0 earthquake. The data set reported herein provides the most extensive set of near field broad band wide dynamic range measurements of acceleration and volumetric strain for an earthquake as large as M 6 of which the authors are aware. As a result considerable interest has been expressed in these data. This report is intended to describe the data and facilitate its use to resolve a number of scientific and engineering questions concerning earthquake rupture processes and resultant near field motions and strains. This report provides a description of the array, its scientific objectives and the strong-motion recordings obtained of the main shock. The report provides copies of the uncorrected and corrected data. Copies of the inferred velocities, displacements, and Psuedo velocity response spectra are provided. Digital versions of these recordings are accessible with information available through the internet at several locations: the National Strong-Motion Program web site (http://agram.wr.usgs.gov/), the COSMOS Virtual Data Center Web site

  2. The SAFRR Tsunami Scenario: Improving Resilience for California from a Plausible M9 Earthquake near the Alaska Peninsula

    NASA Astrophysics Data System (ADS)

    Ross, S.; Jones, L.; Wilson, R. I.; Bahng, B.; Barberopoulou, A.; Borrero, J. C.; Brosnan, D.; Bwarie, J.; Geist, E. L.; Johnson, L.; Kirby, S. H.; Knight, W.; Long, K.; Lynett, P. J.; Miller, K.; Mortensen, C. E.; Nicolsky, D.; Oglesby, D. D.; Perry, S. C.; Plumlee, G. S.; Porter, K. A.; Real, C. R.; Ryan, K. J.; Suleimani, E.; Thio, H. K.; Titov, V.; Wein, A. M.; Whitmore, P.; Wood, N. J.

    2013-12-01

    The SAFRR Tsunami Scenario models a hypothetical but plausible tsunami, created by an Mw9.1 earthquake occurring offshore from the Alaskan peninsula, and its impacts on the California coast. We present the likely inundation areas, current velocities in key ports and harbors, physical damage and repair costs, economic consequences, environmental impacts, social vulnerability, emergency management, and policy implications for California associated with the tsunami scenario. The intended users are those who must make mitigation decisions before and rapid decisions during future tsunamis. Around a half million people would be present in the scenario's inundation area in residences, businesses, public venues, parks and beaches. Evacuation would likely be ordered for the State of California's maximum mapped tsunami inundation zone, evacuating an additional quarter million people from residences and businesses. Some island and peninsula communities would face particular evacuation challenges because of limited access options and short warning time, caused by the distance between Alaska and California. Evacuations may also be a challenge for certain dependent-care populations. One third of the boats in California's marinas could be damaged or sunk, costing at least 700 million in repairs to boats and docks, and potentially much more to address serious issues due to sediment transport and environmental contamination. Fires would likely start at many sites where fuel and petrochemicals are stored in ports and marinas. Tsunami surges and bores may travel several miles inland up coastal rivers. Debris clean-up and recovery of inundated and damaged areas will take days, months, or years depending on the severity of impacts and the available resources for recovery. The Ports of Los Angeles and Long Beach (POLA/LB) would be shut down for a miniμm of two days due to strong currents. Inundation of dry land in the ports would result in 100 million damages to cargo and additional

  3. Continuous GPS observations of postseismic deformation following the 16 October 1999 Hector Mine, California, earthquake (Mw 7.1)

    USGS Publications Warehouse

    Hudnutt, K.W.; King, N.E.; Galetzka, J.E.; Stark, K.F.; Behr, J.A.; Aspiotes, A.; van, Wyk S.; Moffitt, R.; Dockter, S.; Wyatt, F.

    2002-01-01

    Rapid field deployment of a new type of continuously operating Global Positioning System (GPS) network and data from Southern California Integrated GPS Network (SCIGN) stations that had recently begun operating in the area allow unique observations of the postseismic deformation associated with the 1999 Hector Mine earthquake. Innovative solutions in fieldcraft, devised for the 11 new GPS stations, provide high-quality observations with 1-year time histories on stable monuments at remote sites. We report on our results from processing the postseismic GPS data available from these sites, as well as 8 other SCIGN stations within 80 km of the event (a total of 19 sites). From these data, we analyze the temporal character and spatial pattern of the postseismic transients. Data from some sites display statistically significant time variation in their velocities. Although this is less certain, the spatial pattern of change in the postseismic velocity field also appears to have changed. The pattern now is similar to the pre-Landers (pre-1992) secular field, but laterally shifted and locally at twice the rate. We speculate that a 30 km ?? 50 km portion of crust (near Twentynine Palms), which was moving at nearly the North American plate rate (to within 3.5 mm/yr of that rate) prior to the 1992 Landers sequence, now is moving along with the crust to the west of it, as though it has been entrained in flow along with the Pacific Plate as a result of the Landers and Hector Mine earthquake sequence. The inboard axis of right-lateral shear deformation (at lower crustal to upper mantle depth) may have jumped 30 km farther into the continental crust at this fault junction that comprises the southern end of the eastern California shear zone.

  4. Rapid Centroid Moment Tensor (CMT) Inversion in 3D Earth Structure Model for Earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Chen, P.; Lee, E.; Jordan, T. H.; Maechling, P. J.

    2009-12-01

    Accurate and rapid CMT inversion is important for seismic hazard analysis. We have developed an algorithm for very rapid CMT inversions in a 3D Earth structure model and applied it on small to medium-sized earthquakes recorded by the Southern California Seismic Network (SCSN). Our CMT inversion algorithm is an integral component of the scattering-integral (SI) method for full-3D waveform tomography (F3DT). In the SI method for F3DT, the sensitivity (Fréchet) kernels are constructed through the temporal convolution between the earthquake wavefield (EWF) and the receiver Green tensor (RGT), which is the wavefield generated by 3 orthogonal unit impulsive body forces acting at the receiver location. The RGTs are also the partial derivatives of the waveform with respect to the moment tensors. In this study, our RGTs are computed in a 3D seismic structure model for Southern California (CVM4SI1) using the finite-difference method, which allows us to account for 3D path effects in our source inversion. We used three component broadband waveforms below 0.2 Hz. An automated waveform-picking algorithm based on continuous wavelet transform is applied on observed waveforms to pick P, S and surface waves. A multi-scale grid-searching algorithm is then applied on the picked waveforms to find the optimal strike, dip and rake values that minimize the amplitude misfit and maximize the correlation coefficient. In general, our CMT solutions agree with solutions inverted using other methods and provide better fit to the observed waveforms.

  5. Rapid Centroid Moment Tensor (CMT) Inversion in 3D Earth Structure Model for Earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Mu, D.; Lee, E.; Chen, P.; Jordan, T. H.; Maechling, P. J.

    2010-12-01

    Accurate and rapid CMT inversion is important for seismic hazard analysis. We have developed an algorithm for very rapid CMT inversions in a 3D Earth structure model and applied it on small to medium-sized earthquakes recorded by the Southern California Seismic Network (SCSN). Our CMT inversion algorithm is an integral component of the scattering-integral (SI) method for full-3D waveform tomography (F3DT). In the SI method for F3DT, the sensitivity (Fréchet) kernels are constructed through the temporal convolution between the earthquake wavefield (EWF) from the source and the receiver Green tensor (RGT) from the receiver. In this study, our RGTs were computed in a 3D seismic structure model for Southern California (CVM4SI1) using the finite-difference method, which allows us to account for 3D path effects in our source inversion. By storing the RGTs, synthetic seismograms for any source in our modeling volume could be generated rapidly by applying the reciprocity principle. An automated waveform-picking algorithm based on continuous wavelet transform is applied on observed waveforms to pick P, S and surface waves. A grid-searching algorithm is then applied on the picked waveforms to find an optimal focal mechanism that minimizes the amplitude misfit and maximize the weighted correlation coefficient. The grid-search result is then used as the initial solution in a gradient-based optimization algorithm that minimizes the L2 norm of the generalized seismological data functionals (GSDF), which quantifies waveform differences between observed and synthetic seismograms using frequencies-dependent phase-delay and amplitude anomalies. In general, our CMT solutions agree with solutions inverted using other methods and provide better fit to the observed waveforms.

  6. Formation of left-lateral fractures within the Summit Ridge shear zone, 1989 Loma Prieta, California, earthquake

    SciTech Connect

    Johnson, A.M.; Fleming, R.W. |

    1993-12-01

    The 1989 Loma Prieta, California, earthquake is characterized by the lack of major, throughgoing, coseismic, right-lateral faulting along strands of the San Andreas fault zone in the epicentral area. Instead, throughout the Summit Ridge area there are zones of tension cracks and left-lateral fracture zones oriented about N45 deg W, that is, roughly parallel to the San Andreas fault in this area. The left-lateral fractures zones are enigmatic because their left-lateral slip is opposite to the right-lateral sense of the relative motion between the Pacific and North American plates. We suggest that the enigmatic fractures can be understood if we assume that coesiesmic deformation was by right-lateral shear across a broad zone, about 0.5 km wide and 4 km long, beneath Summit Ridge. Contrary to most previous reports on the Loma Prieta earthquake, which assert that coseismic, right-lateral ground rupture was restricted to considerable (greater than 4 km) depths in the epicentral area, we find that nearly all the right-lateral offset is represented at the ground surface by the Summit Ridge shear zone.

  7. Late Holocene slip rate and recurrence of great earthquakes on the San Andreas fault in northern California

    SciTech Connect

    Niemi, T.M. Earth Sciences Associates, Palo Alto, CA ); Hall, N.T. )

    1992-03-01

    The slip rate of the San Andreas fault 45 km north of San Francisco at Olema, California, is determined by matching offset segments of a buried late Holocene stream channel. Stream deposits from 1,800 {plus minus} 78 yr B.P. are offset 42.5 {plus minus} 3.5 m across the active (1906) fault trace for a minimum late Holocene slip rate of 24 {plus minus} 3 mm/yr. When local maximum coseismic displacements of 4.9 to 5.5 m from the 1906 earthquake are considered with this slip rate, the recurrence of 1906-type earthquakes on the North Coast segment of the San Andreas fault falls within the interval of 221 {plus minus} 40 yr. Both comparable coseismic slip in 1906 and similar late Holocene geologic slip rates at the Olema site and a site 145 km northwest at Point Arena (Prentice, 1989) suggest that the North Coast segment behaves as a coherent rupture unit.

  8. Southern California Permanent GPS Geodetic Array: Continuous measurements of regional crustal deformation between the 1992 Landers and 1994 Northridge earthquakes

    USGS Publications Warehouse

    Bock, Y.; Wdowinski, S.; Fang, P.; Zhang, Jiahua; Williams, S.; Johnson, H.; Behr, J.; Genrich, J.; Dean, J.; Van Domselaar, M.; Agnew, D.; Wyatt, F.; Stark, K.; Oral, B.; Hudnut, K.; King, R.; Herring, T.; Dinardo, S.; Young, W.; Jackson, D.; Gurtner, W.

    1997-01-01

    The southern California Permanent GPS Geodetic Array (PGGA) was established in 1990 across the Pacific-North America plate boundary to continuously monitor crustal deformation. We describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19-month period between the June 28, 1992 (Mw=7.3), Landers and January 17, 1994 (Mw=6.7), Northridge earthquakes. We compare displacement rates at four site locations with those reported by Feigl et al. [1993], which were derived from an independent set of Global Positioning System (GPS) and very long baseline interferometry (VLBI) measurements collected over nearly a decade prior to the Landers earthquake. The velocity differences for three sites 65-100 km from the earthquake's epicenter are of order of 3-5 mm/yr and are systematically coupled with the corresponding directions of coseismic displacement. The fourth site, 300 km from the epicenter, shows no significant velocity difference. These observations suggest large-scale postseismic deformation with a relaxation time of at least 800 days. The statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets; two possible noise models fit the PGGA data equally well as described in the companion paper by Zhang et al. [this issue]; the pre-Landers data are too sparse and heterogeneous to derive a reliable noise model. Under a fractal white noise model for the PGGA data we find that the velocity differences for all three sites are statistically different at the 99% significance level. A white noise plus flicker noise model results in significance levels of only 94%, 43%, and 88%. Additional investigations of the pre-Landers data, and analysis of longer spans of PGGA data, could have an important effect on the significance of these results and will be addressed in future work. Copyright 1997 by the American Geophysical Union.

  9. Late Quaternary history of the Owens Valley fault zone, eastern California, and surface rupture associated with the 1872 earthquake

    SciTech Connect

    Beanland, S. . Earth Deformation Section); Clark, M.M. )

    1993-04-01

    The right-lateral Owens Valley fault zone (OVFZ) in eastern California extends north about 100 km from near the northwest shore of Owens Lake to beyond Big Pine. It passes through Lone Pine near the eastern base of the Alabama Hills and follows the floor of Owens Valley northward to the Poverty Hills, where it steps 3 km to the left and continues northwest across Crater Mountain and through Big Pine. Data from one site suggest an average net slip rate for the OVFZ of 1.5 [+-] 1 mm/yr for the past 300 ky. Several other sites yield an average Holocene net slip rate of 2 [+-] 1 mm/yr. The OVFZ apparently has experienced three major Holocene earthquakes. The minimum average recurrence interval is 5,000 years at the subsidiary Lone Pine fault, whereas it is 3,300 to 5,000 years elsewhere along the OVFZ. The prehistoric earthquakes are not dated, so an average recurrence interval need not apply. However, roughly equal (characteristic) displacement apparently happened during each Holocene earthquake. The Owens Valley fault zone accommodates some of the relative motion (dextral shear) between the North American and Pacific plates along a discrete structure. This shear occurs in the Walker Lane belt of normal and strike-slip faults within the mainly extensional Basin and Range Province. In Owens Valley displacement is partitioned between the OVFZ and the nearby, subparallel, and purely normal range-front faults of the Sierra Nevada. Compared to the OVFZ, these range-front normal faults are very discontinuous and have smaller Holocene slip rates of 0.1 to 0.8 mm/yr, dip slip. Contemporary activity on adjacent faults of such contrasting styles suggests large temporal fluctuations in the relative magnitudes of the maximum and intermediate principal stresses while the extension direction remains consistently east-west.

  10. Direct and indirect evidence for earthquakes; an example from the Lake Tahoe Basin, California-Nevada

    NASA Astrophysics Data System (ADS)

    Maloney, J. M.; Noble, P. J.; Driscoll, N. W.; Kent, G.; Schmauder, G. C.

    2012-12-01

    High-resolution seismic CHIRP data can image direct evidence of earthquakes (i.e., offset strata) beneath lakes and the ocean. Nevertheless, direct evidence often is not imaged due to conditions such as gas in the sediments, or steep basement topography. In these cases, indirect evidence for earthquakes (i.e., debris flows) may provide insight into the paleoseismic record. The four sub-basins of the tectonically active Lake Tahoe Basin provide an ideal opportunity to image direct evidence for earthquake deformation and compare it to indirect earthquake proxies. We present results from high-resolution seismic CHIRP surveys in Emerald Bay, Fallen Leaf Lake, and Cascade Lake to constrain the recurrence interval on the West Tahoe Dollar Point Fault (WTDPF), which was previously identified as potentially the most hazardous fault in the Lake Tahoe Basin. Recently collected CHIRP profiles beneath Fallen Leaf Lake image slide deposits that appear synchronous with slides in other sub-basins. The temporal correlation of slides between multiple basins suggests triggering by events on the WTDPF. If correct, we postulate a recurrence interval for the WTDPF of ~3-4 k.y., indicating that the WTDPF is near its seismic recurrence cycle. In addition, CHIRP data beneath Cascade Lake image strands of the WTDPF that offset the lakefloor as much as ~7 m. The Cascade Lake data combined with onshore LiDAR allowed us to map the geometry of the WTDPF continuously across the southern Lake Tahoe Basin and yielded an improved geohazard assessment.

  11. Seismicity and crustal structure studies of southern California: tectonic implications from improved earthquake locations

    SciTech Connect

    Corbett, E.J.

    1984-01-01

    The 5.1 M/sub L/ Santa Barbara earthquake of 13 August 1978 was located 3 km southeast of Santa Barbara at a focal depth of 12.7 km. The temporal-spatial development of the aftershock zone may indicate that the initial rupture plane was considerably smaller than that of the eventual aftershock zone. The aftershock hypocenters outline a nearly horizontal plane (dipping 15/sup 0/ or less) at 13-km depth and the preferred focal mechanism indicates north-over-south thrusting. To further test the decollement hypothesis, Caltech catalog locations were reviewed to determine the depth distribution of earthquakes in the Transverse Ranges. The seismogenic zone is thickest along the southern front of the Transverse Ranges and is thinnest in the southern Mojave Desert and at the east end of the Transverse Ranges. The seismicity of the western Transverse Ranges is typified by north-dipping planar structures and the eastern Transverse Ranges are typified by pervasive seismicity extending down to the floor of the seismogenic zone. Data from a large quarry explosion on Catalina Island were utilized to derive a 3-layer Continental Borderland velocity structure to improve the locations of the 1981 Santa Barbara Island earthquakes. The Santa Barbara Island earthquake (5.3 M/sub L/) occurred on September 4, 1981. Aftershocks exhibited a clear northwest-southeast alignment that coincides with the submarine escarpment of the Santa Cruz-Catalina fault and was consistent with focal mechanisms.

  12. Chapter E. The Loma Prieta, California, Earthquake of October 17, 1989 - Hydrologic Disturbances

    USGS Publications Warehouse

    Rojstaczer, Stuart A., (Edited By)

    1994-01-01

    Seismic events have long been known to cause changes in the level of oceans, streams, lakes, and the water table. The great San Francisco earthquake of 1906 induced significant hydrologic changes that were qualitatively similar to those changes observed for the Loma Prieta earthquake. What is different is that the hydrologic data sets collected from the Loma Prieta event have enough detail to enable hypotheses on the causes for these changes to be tested. The papers in this chapter document changes in ocean level, stream morphology and flow, water table height, and ground-water flow rates in response to the earthquake. Although hydrologic disturbances may have occurred about 1 hour before the main shock, the papers in this chapter deal strictly with postevent hydrologic changes. The hydrologic responses reported here reflect changes that are not the result of surface rupture. They appear to be the result of landslides, the static displacements induced by the earthquake, and changes in the permeability of the near surface.

  13. Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Public Response

    USGS Publications Warehouse

    Bolton, Patricia A., (Edited By)

    1993-01-01

    Major earthquakes provide seismologists and engineers an opportunity to examine the performance of the Earth and the man-made structures in response to the forces of the quake. So, too, do they provide social scientists an opportunity to delve into human responses evoked by the ground shaking and its physical consequences. The findings from such research can serve to guide the development and application of programs and practices designed to reduce death, injury, property losses, and social disruption in subsequent earthquakes. This chapter contains findings from studies focused mainly on public response to the Loma Prieta earthquake; that is, on the behavior and perceptions of the general population rather than on the activities of specific organizations or on the impact on procedures or policies. A major feature of several of these studies is that the information was collected from the population throughout the Bay area, not just from persons in the most badly damaged communities or who had suffered the greatest losses. This wide range serves to provide comparisons of behavior for those most directly affected by the earthquake with others who were less directly affected by it but still had to consider it very 'close to home.'

  14. Earthquake hazards of active blind-thrust faults under the central Los Angeles basin, California

    NASA Astrophysics Data System (ADS)

    Shaw, John H.; Suppe, John

    1996-04-01

    We document several blind-thrust faults under the Los Angeles basin that, if active and seismogenic, are capable of generating large earthquakes (M = 6.3 to 7.3). Pliocene to Quaternary growth folds imaged in seismic reflection profiles record the existence, size, and slip rates of these blind faults. The growth structures have shapes characteristic of fault-bend folds above blind thrusts, as demonstrated by balanced kinematic models, geologic cross sections, and axial-surface maps. We interpret the Compton-Los Alamitos trend as a growth fold above the Compton ramp, which extends along strike from west Los Angeles to at least the Santa Ana River. The Compton thrust is part of a larger fault system, including a decollement and ramps beneath the Elysian Park and Palos Verdes trends. The Cienegas and Coyote Hills growth folds overlie additional blind thrusts in the Elysian Park trend that are not closely linked to the Compton ramp. Analysis of folded Pliocene to Quaternary strata yields slip rates of 1.4 ± 0.4 mm/yr on the Compton thrust and 1.7 ± 0.4 mm/yr on a ramp beneath the Elysian Park trend. Assuming that slip is released in large earthquakes, we estimate magnitudes of 6.3 to 6.8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps. Multiple-segment ruptures could yield larger earthquakes (M = 6.9 to 7.3). Relations among magnitude, coseismic displacement, and slip rate yield an average recurrence interval of 380 years for single-segment earthquakes and a range of 400 to 1300 years for multiple-segment events. If these newly documented blind thrust faults are active, they will contribute substantially to the seismic hazards in Los Angeles because of their locations directly beneath the metropolitan area.

  15. Preliminary analysis of strong-motion recordings from the 28 September 2004 Parkfield, California earthquake

    USGS Publications Warehouse

    Shakal, A.; Graizer, V.; Huang, M.; Borcherdt, R.; Haddadi, H.; Lin, K.-W.; Stephens, C.; Roffers, P.

    2005-01-01

    The Parkfield 2004 earthquake yielded the most extensive set of strong-motion data in the near-source region of a magnitude 6 earthquake yet obtained. The recordings of acceleration and volumetric strain provide an unprecedented document of the near-source seismic radiation for a moderate earthquake. The spatial density of the measurements alon g the fault zone and in the linear arrays perpendicular to the fault is expected to provide an exceptional opportunity to develop improved models of the rupture process. The closely spaced measurements should help infer the temporal and spatial distribution of the rupture process at much higher resolution than previously possible. Preliminary analyses of the peak a cceleration data presented herein shows that the motions vary significantly along the rupture zone, from 0.13 g to more than 2.5 g, with a map of the values showing that the larger values are concentrated in three areas. Particle motions at the near-fault stations are consistent with bilateral rupture. Fault-normal pulses similar to those observed in recent strike-slip earthquakes are apparent at several of the stations. The attenuation of peak ground acceleration with distance is more rapid than that indicated by some standard relationships but adequately fits others. Evidence for directivity in the peak acceleration data is not strong. Several stations very near, or over, the rupturing fault recorded relatively low accelerations. These recordings may provide a quantitative basis to understand observations of low near-fault shaking damage that has been reported in other large strike-slip earthquak.

  16. Kinematic inversion of the Mw 6.0 2004 Parkfield, California, earthquake using elliptical sub-fault approximation

    NASA Astrophysics Data System (ADS)

    Twardzik, C.; Madariaga, R. I.; Das, S.; Custodio, S.; Archuleta, R. J.

    2011-12-01

    We explore a recently developed procedure for kinematic inversion based on elliptical sub-fault approximation. In this method, the slip is modelled by a small set of elliptical patches, each ellipse having a Gaussian distribution of slip. In addition to creating an intrinsically smooth slip distribution inside the slipping region, elliptical patches have the advantage of reducing the number of parameters to invert, since seven parameters are sufficient to describe each patch. We invert near-field strong ground motion data for the 28th September 2004 Parkfield, California, earthquake to test this approach. The dataset consists of 10 digital 3-components 18 s long accelerograms, which were integrated twice to obtain displacement records and filtered between 0.16Hz and 1Hz. Thirty-three digitized analog stations also recorded this earthquake but were not used in the inversion due to absence of absolute timing. However, these stations are used as a additional criteria to test our final model. However, some of these stations are difficult to fit as they lie very close to the fault and exhibit very strong site effects, for example, the influence of fault guided waves which are difficult to model. The best kinematic model is a slip pattern elongated in the strike direction with an average slip of about 0.55 m and a high-slip patch of 1.1 m located 20 km north-west of the hypocenter. Although some studies show evidence of high slip near the hypocenter, we find that the existence of this feature does not improve the fit to the data, and is therefore not resolvable using digital stations only. The final moment is 1.81 x 1018 N m, which is close to the CMT value of 1.13 x 1018 N m. We show that the data can be explained by a rupture propagating at a horizontal speed of 0.9Vs. Our slip distribution is perfectly aligned below a level delineated by small aftershocks at a depth of approximately 6 km, but this level does not coincide with any known structural boundary. By looking

  17. Faulting apparently related to the 1994 Northridge, California, earthquake and possible co-seismic origin of surface cracks in Potrero Canyon, Los Angeles County, California

    USGS Publications Warehouse

    Catchings, R.D.; Goldman, M.R.; Lee, W.H.K.; Rymer, M.J.; Ponti, D.J.

    1998-01-01

    Apparent southward-dipping, reverse-fault zones are imaged to depths of about 1.5 km beneath Potrero Canyon, Los Angeles County, California. Based on their orientation and projection to the surface, we suggest that the imaged fault zones are extensions of the Oak Ridge fault. Geologic mapping by others and correlations with seismicity studies suggest that the Oak Ridge fault is the causative fault of the 17 January 1994 Northridge earthquake (Northridge fault). Our seismically imaged faults may be among several faults that collectively comprise the Northridge thrust fault system. Unusually strong shaking in Potrero Canyon during the Northridge earthquake may have resulted from focusing of seismic energy or co-seismic movement along existing, related shallow-depth faults. The strong shaking produced ground-surface cracks and sand blows distributed along the length of the canyon. Seismic reflection and refraction images show that shallow-depth faults may underlie some of the observed surface cracks. The relationship between observed surface cracks and imaged faults indicates that some of the surface cracks may have developed from nontectonic alluvial movement, but others may be fault related. Immediately beneath the surface cracks, P-wave velocities are unusually low (<400 m/sec), and there are velocity anomalies consistent with a seismic reflection image of shallow faulting to depths of at least 100 m. On the basis of velocity data, we suggest that unconsolidated soils (<800 m/sec) extend to depths of about 15 to 20 m beneath our datum (<25 m below ground surface). The underlying rocks range in velocity from about 1000 to 5000 m/sec in the upper 100 m. This study illustrates the utility of high-resolution seismic imaging in assessing local and regional seismic hazards.

  18. Long Return Periods for Earthquakes in San Gorgonio Pass and Implications for Large Ruptures of the San Andreas Fault in Southern California

    NASA Astrophysics Data System (ADS)

    Yule, J.; McBurnett, P.; Ramzan, S.

    2011-12-01

    The largest discontinuity in the surface trace of the San Andreas fault occurs in southern California at San Gorgonio Pass. Here, San Andreas motion moves through a 20 km-wide compressive stepover on the dextral-oblique-slip thrust system known as the San Gorgonio Pass fault zone. This thrust-dominated system is thought to rupture during very large San Andreas events that also involve strike-slip fault segments north and south of the Pass region. A wealth of paleoseismic data document that the San Andreas fault segments on either side of the Pass, in the San Bernardino/Mojave Desert and Coachella Valley regions, rupture on average every ~100 yrs and ~200 yrs, respectively. In contrast, we report here a notably longer return period for ruptures of the San Gorgonio Pass fault zone. For example, features exposed in trenches at the Cabezon site reveal that the most recent earthquake occurred 600-700 yrs ago (this and other ages reported here are constrained by C-14 calibrated ages from charcoal). The rupture at Cabezon broke a 10 m-wide zone of east-west striking thrusts and produced a >2 m-high scarp. Slip during this event is estimated to be >4.5 m. Evidence for a penultimate event was not uncovered but presumably lies beneath ~1000 yr-old strata at the base of the trenches. In Millard Canyon, 5 km to the west of Cabezon, the San Gorgonio Pass fault zone splits into two splays. The northern splay is expressed by 2.5 ± 0.7 m and 5.0 ± 0.7 m scarps in alluvial terraces constrained to be ~1300 and ~2500 yrs old, respectively. The scarp on the younger, low terrace postdates terrace abandonment ~1300 yrs ago and probably correlates with the 600-700 yr-old event at Cabezon, though we cannot rule out that a different event produced the northern Millard scarp. Trenches excavated in the low terrace reveal growth folding and secondary faulting and clear evidence for a penultimate event ~1350-1450 yrs ago, during alluvial deposition prior to the abandonment of the low terrace

  19. Multi-sensor Integration of Space and Ground Observations of Pre-earthquake Anomalies Associated with M6.0, August 24, 2014 Napa, California

    NASA Astrophysics Data System (ADS)

    Ouzounov, Dimitar; Tramutoli, Valerio; Pulinets, Sergey; Liu, Tiger; Filizzola, Carolina; Genzano, Nicola; Lisi, Mariano; Petrov, Leonid; Kafatos, Menas

    2015-04-01

    We integrate multiple space-born and ground sensors for monitoring pre-earthquake geophysical anomalies that can provide significant early notification for earthquakes higher than M5.5 worldwide. The latest M6.0 event of August 24, 2014 in South Napa, California generated pre-earthquake signatures during our outgoing tests for California, and an experimental warning was documented about 17 days in advance. We process in controlled environment different satellite and ground data for California (and several other test areas) by using: a) data from the NPOES sensors recording OLR (Outgoing Longwave Radiation) in the infrared; b) 2/GNSS, FORMOSAT (GPS/TEC); c) Earth Observing System assimilation models from NASA; d) ground-based gas observations and meteorological data; e) TIR (Thermal Infrared) data from geostationary satellite (GOES). On Aug 4th, we detected (prospectively) a large anomaly of OLR transient field at the TOA over Northern California. The location was shifted in the northeast direction about 150 km from the Aug 23rd epicentral area. Compared to the reference field of August 2004 to 2014 the hotspot anomaly was the largest energy flux anomaly over the entire continental United States at this time. Based on the temporal and spatial estimates of the anomaly, on August 4th we issued an internal warning for a M5.5+ earthquake in Northern California within the next 1-4 weeks. TIR retrospective analysis showed significant (spatially extended and temporally persistent) sequences of TIR anomalies starting August 1st just in the future epicenter area and approximately in the same area affected by OLR anomalies in the following days. GPS/TEC retrospective analysis based on GIM and TGIM products show anomalies TEC variations 1-3 days, over region north form the Napa earthquake epicenter. The calculated index of atmospheric chemical potential based on the NASA numerical Assimilation weather model GEOS5 indicates for abnormal variations near the epicentral area days

  20. Three dimensional images of geothermal systems: local earthquake P-wave velocity tomography at the Hengill and Krafla geothermal areas, Iceland, and The Geysers, California

    USGS Publications Warehouse

    Julian, B.R.; Prisk, A.; Foulger, G.R.; Evans, J.R.

    1993-01-01

    Local earthquake tomography - the use of earthquake signals to form a 3-dimensional structural image - is now a mature geophysical analysis method, particularly suited to the study of geothermal reservoirs, which are often seismically active and severely laterally inhomogeneous. Studies have been conducted of the Hengill (Iceland), Krafla (Iceland) and The Geysers (California) geothermal areas. All three systems are exploited for electricity and/or heat production, and all are highly seismically active. Tomographic studies of volumes a few km in dimension were conducted for each area using the method of Thurber (1983).

  1. Triggered surface slips in southern California associated with the 2010 El Mayor-Cucapah, Baja California, Mexico, earthquake

    USGS Publications Warehouse

    Rymer, Michael J.; Treiman, Jerome A.; Kendrick, Katherine J.; Lienkaemper, James J.; Weldon, Ray J.; Bilham, Roger; Wei, Meng; Fielding, Eric J.; Hernandez, Janis L.; Olson, Brian P.E.; Irvine, Pamela J.; Knepprath, Nichole; Sickler, Robert R.; Tong, Xiaopeng; Siem, Martin E.

    2011-01-01

    Triggered slip in the Yuha Desert area occurred along more than two dozen faults, only some of which were recognized before the April 4, 2010, El Mayor-Cucapah earthquake. From east to northwest, slip occurred in seven general areas: (1) in the Northern Centinela Fault Zone (newly named), (2) along unnamed faults south of Pinto Wash, (3) along the Yuha Fault (newly named), (4) along both east and west branches of the Laguna Salada Fault, (5) along the Yuha Well Fault Zone (newly revised name) and related faults between it and the Yuha Fault, (6) along the Ocotillo Fault (newly named) and related faults to the north and south, and (7) along the southeasternmost section of the Elsinore Fault. Faults that slipped in the Yuha Desert area include northwest-trending right-lateral faults, northeast-trending left-lateral faults, and north-south faults, some of which had dominantly vertical offset. Triggered slip along the Ocotillo and Elsinore Faults appears to have occurred only in association with the June 14, 2010 (Mw5.7), aftershock. This aftershock also resulted in slip along other faults near the town of Ocotillo. Triggered offset on faults in the Yuha Desert area was mostly less than 20 mm, with three significant exceptions, including slip of about 50–60 mm on the Yuha Fault, 40 mm on a fault south of Pinto Wash, and about 85 mm on the Ocotillo Fault. All triggered slips in the Yuha Desert area occurred along preexisting faults, whether previously recognized or not.

  2. The Cape Mendocino, California, earthquakes of April 1992: Subduction at the triple junction

    USGS Publications Warehouse

    Oppenheimer, D.; Beroza, G.; Carver, G.; Dengler, L.; Eaton, J.; Gee, L.; Gonzalez, F.; Jayko, A.; Li, W.H.; Lisowski, M.; Magee, M.; Marshall, G.; Murray, M.; McPherson, R.; Romanowicz, B.; Satake, K.; Simpson, R.; Somerville, P.; Stein, R.; Valentine, D.

    1993-01-01

    The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demonstrated that the North America-Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the Cascadia region. The shock occurred just north of the Mendocino Triple Junction and caused strong ground motion and moderate damage in the immediate area. Rupture initiated onshore at a depth of 10.5 kilometers and propagated up-dip and seaward. Slip on steep faults in the Gorda plate generated two magnitude 6.6 aftershocks on 26 April. The main shock did not produce surface rupture on land but caused coastal uplift and a tsunami. The emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity.

  3. The 1987 Whittier Narrows earthquake in the Los Angeles metropolitan area, California

    USGS Publications Warehouse

    Hauksson, E.; Jones, L.M.; Davis, T.L.; Hutton, L.K.; Brady, A.G.; Reasenberg, P.A.; Michael, A.J.; Yerkes, R.F.; Williams, Pat; Reagor, G.; Stover, C.W.; Bent, A.L.; Shakal, A.K.; Etheredge, E.; Porcella, R.L.; Bufe, C.G.; Johnston, M.J.S.; Cranswick, E.

    1988-01-01

    The Whittier Narrows earthquake sequence (local magnitude, ML=5.9), which caused over $358-million damage, indicates that assessments of earthquake hazards in the Los Angeles metropolitan area may be underestimated. The sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east-west length of the northern margin of the Los Angeles basin. Peak horizontal accelerations from the main shock, which were measured at ground level and in structures, were as high as 0.6g (where g is the acceleration of gravity at sea level) within 50 kilometers of the epicenter. The distribution of the modified Mercalli intensity VII reflects a broad north-south elongated zone of damage that is approximately centered on the main shock epicenter.

  4. Damage to urban infrastructure and other public property from the 1989 Loma Prieta (California) earthquake.

    PubMed

    French, S P

    1995-03-01

    This research project investigated the damage to public property caused by the 1989 Loma Prieta earthquake. The claims filed by state and local governments, special districts and non-profit organizations under the Federal Emergency Management Agency's (FEMA) disaster assistance program were analyzed to understand better the pattern of damage caused by the earthquake. These claims accounted for nearly $600 million. The damage distribution was very skewed with eleven agencies claiming more than 70 per cent of this total. Non-profit agencies accounted for a surprisingly large portion of overall damage. Heavy damage was concentrated in relatively few areas. The extent of damage in an area was a function of concentration of property, site conditions, characteristics of building stock, and distance from the epicenter. PMID:7735857

  5. Non-shear focal mechanisms of earthquakes at The Geysers, California and Hengill, Iceland, geothermal areas

    USGS Publications Warehouse

    Julian, B.R.; Miller, A.D.; Foulger, G.R.

    1993-01-01

    Several thousand earthquakes were recorded in each area. We report an initial investigation of the focal mechanisms based on P-wave polarities. Distortion by complicated three-dimensional crustal structure was minimized using tomographically derived three-dimensional crustal models. Events with explosive and implosive source mechanisms, suggesting cavity opening and collapse, have been tentatively identified at The Geysers. The new data show that some of these events do not fit the model of tensile cracking accompanied by isotropic pore pressure decreases that was suggested in earlier studies, but that they may instead involve combination of explosive and shear processes. However, the confirmation of earthquakes dominated by explosive components supports the model that the event are caused by crack opening induced by thermal contraction of the heat source.

  6. Surface Displacement of the 17 May 1993 Eureka Valley, California, Earthquake Observed by SAR Interferometry.

    PubMed

    Peltzer, G; Rosen, P

    1995-06-01

    Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The +/-3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event. These observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west-dipping, north-northeast fault plane, reactivating the largest escarpment in the Saline Range. PMID:17778980

  7. Triggered slip on the Calaveras fault during the magnitude 7. 1 Loma Prieta, California, earthquake

    SciTech Connect

    McClellan, P.H.; Hay, E.A.

    1990-07-01

    After the magnitude (M) 7.1 Loma Prieta earthquake on the San Andreas fault the authors inspected selected sites along the Calaveras fault for evidence of recent surface displacement. In two areas along the Calaveras fault they documented recent right-lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep. The areas are in the city of Hollister and at Highway 152 near San Felipe Lake, located approximately 25 km southeast and 18 km northeast, respectively, of the nearest part of the San Andreas rupture zone. On the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the Loma Prieta mainshock. They conclude that this earthquake on the San Andreas fault triggered surface rupture along at least a 17-km-long segment of the Calaveras fault. These geologic observations extend evidence of triggered slip from instrument stations within this zone of Calaveras fault rupture.

  8. The cape mendocino, california, earthquakes of april 1992: subduction at the triple junction.

    PubMed

    Oppenheimer, D; Eaton, J; Jayko, A; Lisowski, M; Marshall, G; Murray, M; Simpson, R; Stein, R; Beroza, G; Magee, M; Carver, G; Dengler, L; McPherson, R; Gee, L; Romanowicz, B; Gonzalez, F; Li, W H; Satake, K; Somerville, P; Valentine, D

    1993-07-23

    The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demonstrated that the North America-Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the Cascadia region. The shock occurred just north of the Mendocino Triple Junction and caused strong ground motion and moderate damage in the immediate area. Rupture initiated onshore at a depth of 10.5 kilometers and propagated up-dip and seaward. Slip on steep faults in the Gorda plate generated two magnitude 6.6 aftershocks on 26 April. The main shock did not produce surface rupture on land but caused coastal uplift and a tsunami. The emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity. PMID:17770022

  9. Earthquake recurrence on the Calaveras fault east of San Jose, California

    USGS Publications Warehouse

    Bufe, C.G.; Harsh, P.W.; Burford, R.O.

    1979-01-01

    Occurrence of small (3 ??? ML < 4) earthquakes on two 10-km segments of the Calaveras fault between Calaveras and Anderson reservoirs follows a simple linear pattern of elastic strain accumulation and release. The centers of these independent patches of earthquake activity are 20 km apart. Each region is characterized by a constant rate of seismic slip as computed from earthquake magnitudes, and is assumed to be an isolated locked patch on a creeping fault surface. By calculating seismic slip rates and the amount of seismic slip since the time of the last significant (M ??? 3) earthquake, it is possible to estimate the most likely date of the next (M ???- 3) event on each patch. The larger the last significant event, the longer the time until the next one. The recurrence time also appears to be increased according to the moment of smaller (2 < ML < 3) events in the interim. The anticipated times of future larger events on each patch, on the basis of preliminary location data through May 1977 and estimates of interim activity, are tabulated below with standard errors. The occurrence time for the southern zone is based on eight recurrent events since 1969, the northern zone on only three. The 95% confidence limits can be estimated as twice the standard error of the projected least-squares line. Events of M ??? 3 should not occur in the specified zones at times outside these limits. The central region between the two zones was the locus of two events (M = 3.6, 3.3) on July 3, 1977. These events occurred prior to a window based on the three point, post-1969 slip-time line for the central region. {A table is presented}. ?? 1979.

  10. Postseismic relaxation following the 1994 Mw6.7 Northridge earthquake, southern California

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.

    2010-01-01

    We have reexamined the postearthquake deformation of a 65 km long linear array of 11 geodetic monuments extending north–south across the rupture (reverse slip on a blind thrust dipping 40°S–20°W) associated with the 1994 Mw6.7 Northridge earthquake. That array was surveyed frequently in the interval from 4 to 2650 days after the earthquake. The velocity of each of the monuments over the interval 100–2650 days postearthquake appears to be constant. Moreover, the profile of those velocities along the length of the array is very similar to a preearthquake velocity profile for a nearby, similarly oriented array. We take this to indicate that significant postseismic relaxation is evident only in the first 100 days postseismic and that the subsequent linear trend is typical of the interseismic interval. The postseismic relaxation (postseismic displacement less displacement that would have occurred at the preseismic velocity) is found to be almost wholly parallel (N70°W) to the nearby (40 km) San Andreas Fault with only negligible relaxation in the direction of coseismic slip (N20°E) on the Northridge rupture. We suggest that the N70°W relaxation is caused by aseismic, right-lateral slip at depth on the San Andreas Fault, excess slip presumably triggered by the Northridge rupture. Finally, using the Dieterich (1994) stress-seismicity relation, we show that return to the preseismic deformation rate within 100 days following the earthquake could be consistent with the cumulative number of M > 2.5 earthquakes observed following the main shock.

  11. Paleoearthquakes on the southern San Andreas Fault, Wrightwood, California, 3000 to 1500 B.C.: A new method for evaluating paleoseismic evidence and earthquake horizons

    USGS Publications Warehouse

    Scharer, K.M.; Weldon, R.J., II; Fumal, T.E.; Biasi, G.P.

    2007-01-01

    We present evidence of 11-14 earthquakes that occurred between 3000 and 1500 B.C. on the San Andreas fault at the Wrightwood paleoseismic site. Earthquake evidence is presented in a novel form in which we rank (high, moderate, poor, or low) the quality of all evidence of ground deformation, which are called "event indicators." Event indicator quality reflects our confidence that the morphologic and sedimentologic evidence can be attributable to a ground-deforming earthquake and that the earthquake horizon is accurately identified by the morphology of the feature. In four vertical meters of section exposed in ten trenches, we document 316 event indicators attributable to 32 separate stratigraphic horizons. Each stratigraphic horizon is evaluated based on the sum of rank (Rs), maximum rank (Rm), average rank (Ra), number of observations (Obs), and sum of higher-quality event indicators (Rs>1). Of the 32 stratigraphic horizons, 14 contain 83% of the event indicators and are qualified based on the number and quality of event indicators; the remaining 18 do not have satisfactory evidence for further consideration. Eleven of the 14 stratigraphic horizons have sufficient number and quality of event indicators to be qualified as "probable" to "very likely" earthquakes; the remaining three stratigraphic horizons are associated with somewhat ambiguous features and are qualified as "possible" earthquakes. Although no single measurement defines an obvious threshold for designation as an earthquake horizon, Rs, Rm, and Rs>1 correlate best with the interpreted earthquake quality. Earthquake age distributions are determined from radio-carbon ages of peat samples using a Bayesian approach to layer dating. The average recurrence interval for the 10 consecutive and highest-quality earthquakes is 111 (93-131) years and individual intervals are ??50% of the average. With comparison with the previously published 14-15 earthquake record between A.D. 500 and present, we find no evidence

  12. Loss estimates for a Puente Hills blind-thrust earthquake in Los Angeles, California

    USGS Publications Warehouse

    Field, E.H.; Seligson, H.A.; Gupta, N.; Gupta, V.; Jordan, T.H.; Campbell, K.W.

    2005-01-01

    Based on OpenSHA and HAZUS-MH, we present loss estimates for an earthquake rupture on the recently identified Puente Hills blind-thrust fault beneath Los Angeles. Given a range of possible magnitudes and ground motion models, and presuming a full fault rupture, we estimate the total economic loss to be between $82 and $252 billion. This range is not only considerably higher than a previous estimate of $69 billion, but also implies the event would be the costliest disaster in U.S. history. The analysis has also provided the following predictions: 3,000-18,000 fatalities, 142,000-735,000 displaced households, 42,000-211,000 in need of short-term public shelter, and 30,000-99,000 tons of debris generated. Finally, we show that the choice of ground motion model can be more influential than the earthquake magnitude, and that reducing this epistemic uncertainty (e.g., via model improvement and/or rejection) could reduce the uncertainty of the loss estimates by up to a factor of two. We note that a full Puente Hills fault rupture is a rare event (once every ???3,000 years), and that other seismic sources pose significant risk as well. ?? 2005, Earthquake Engineering Research Institute.

  13. Creep Transients and Fault Interaction from Repeating Earthquakes Near San Juan Bautista, California

    NASA Astrophysics Data System (ADS)

    Turner, R. C.; Nadeau, R. M.; Burgmann, R.

    2012-12-01

    Along creeping sections of the San Andreas and other faults, small asperities in the fault zone load and fail in characteristic repeating earthquake sequences which can be used as subsurface creepmeters. Here, we use these virtual creepmeters to examine and compare slip rates on both the northwestern end of the creeping section of the San Andreas Fault near San Juan Bautista and on the nearby sub-parallel Sargent Fault, previously observed to have ~3mm/year of right-lateral creep. While creep on the San Andreas increases dramatically in response to the 1989 Loma Prieta earthquake and takes about ten years to resume interseismic rates, the Sargent shows little immediate response. The Sargent rather exhibits a very gradual increase of activity after the Loma Prieta earthquake, consistent with its generally lower interseismic slip rate and with static stress change models that show only a minor increase in the stress along the Sargent. When the SAF resumes its interseismic rate, it begins creeping coherently in time with the Sargent, indicating a mutual driving force in the system. Background seismicity in gray points, newly discovered repeaters in black circles (inset). Boxes show study area. Stars show epicenters of 1989 Loma Prieta EQ, 1998 San Juan Bautista EQ, and 2004 Parkfield EQ.

  14. Near-fault measurement of postseismic slip associated with the 1989 Loma Prieta, California, earthquake

    USGS Publications Warehouse

    Rymer, M.J.

    1990-01-01

    Five small-aperture (0.5 to 7.7 m) quadrilaterals were installed across the San Andreas fault and newly formed extensional cracks shortly after the October 17, 1989 Loma Prieta M7.1 earthquake. Measurements of line-length changes from as early as 4 d up to 184 d after the earthquake in nail quadrilaterals indicate a small amount of right-lateral postseismic slip on the San Andreas fault. The site near the southeast end of the 1989 aftershock zone on the San Andreas fault showed about 5??2 mm of postseismic right-lateral component of slip in addition to 23 mm of right-lateral coseismic movement. The site near the northwest end of aftershocks likewise showed about 5??2 mm of postseismic slip, but after only 5 mm of coseismic slip. The smal slip values, in spite of uncertainties, clearly show that the lack of coseismic surface slip associated with the earthquake was not followed by large postseismic slip. -from Author

  15. A century of oilfield operations and earthquakes in the greater Los Angeles Basin, southern California

    USGS Publications Warehouse

    Hauksson, Egill; Goebel, Thomas; Ampuero, Jean-Paul; Cochran, Elizabeth S.

    2015-01-01

    Most of the seismicity in the Los Angeles Basin (LA Basin) occurs at depth below the sediments and is caused by transpressional tectonics related to the big bend in the San Andreas fault. However, some of the seismicity could be associated with fluid extraction or injection in oil fields that have been in production for almost a century and cover ∼ 17% of the basin. In a recent study, first the influence of industry operations was evaluated by analyzing seismicity characteristics, including normalized seismicity rates, focal depths, and b-values, but no significant difference was found in seismicity characteristics inside and outside the oil fields. In addition, to identify possible temporal correlations, the seismicity and available monthly fluid extraction and injection volumes since 1977 were analyzed. Second, the production and deformation history of the Wilmington oil field were used to evaluate whether other oil fields are likely to experience similar surface deformation in the future. Third, the maximum earthquake magnitudes of events within the perimeters of the oil fields were analyzed to see whether they correlate with total net injected volumes, as suggested by previous studies. Similarly, maximum magnitudes were examined to see whether they exhibit an increase with net extraction volume. Overall, no obvious previously unidentified induced earthquakes were found, and the management of balanced production and injection of fluids appears to reduce the risk of induced-earthquake activity in the oil fields.

  16. Migrating swarms of brittle-failure earthquakes in the lower crust beneath Mammoth Mountain, California

    USGS Publications Warehouse

    Shelly, D.R.; Hill, D.P.

    2011-01-01

    Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. Where they occur, these earthquakes provide a rare opportunity to observe volcanic processes in the lower crust, such as fluid injection and migration, which may induce brittle faulting under these conditions. Here, we examine recent short-duration earthquake swarms deep beneath the southwestern margin of Long Valley Caldera, near Mammoth Mountain. We focus in particular on a swarm that occurred September 29-30, 2009. To maximally illuminate the spatial-temporal progression, we supplement catalog events by detecting additional small events with similar waveforms in the continuous data, achieving up to a 10-fold increase in the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the 2009 swarm exhibits systematically decelerating upward migration, with hypocenters shallowing from 21 to 19 km depth over approximately 12 hours. This relatively high migration rate, combined with a modest maximum magnitude of 1.4 in this swarm, suggests the trigger might be ascending CO2 released from underlying magma.

  17. Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Main Shock Characteristics

    USGS Publications Warehouse

    Spudich, Paul, (Edited By)

    1996-01-01

    The October 17, 1989, Loma Prieta, Calif., earthquake (0004:15.2 G.m.t. October 18; lat 37.036? N., long 121.883? W.; 19-km depth) had a local magnitude (ML) of about 6.7, a surface-wave magnitude (MS) of 7.1, a seismic moment of 2.2x1019 N-m to 3.5x1019 N-m, a source duration of 6 to 15 s, and an average stress drop of at least 50 bars. Slip occurred on a dipping fault surface about 35 km long and was largely confined to a depth of about 7 to 20 km. The slip vector had a large vertical component, and slip was distributed in two main regions situated northwest and southeast of the hypocenter. This slip distribution caused about half of the earthquake's energy to be focused toward the urbanized San Francisco Bay region, while the other half was focused toward the southeast. Had the rupture initiated at the southeast end of the aftershock zone, shaking in the bay region would have been both longer and stronger. These source parameters suggest that the earthquake was not a typical shallow San Andreas-type event but a deeper event on a different fault with a recurrence interval of many hundreds of years. Therefore, the potential for a damaging shallow event on the San Andreas fault in the Santa Cruz Mountains may still exist.

  18. Situated Preparedness: The Negotiation of a Future Catastrophic Earthquake in a California University

    ERIC Educational Resources Information Center

    Baker, Natalie Danielle

    2013-01-01

    This dissertation examines disaster preparedness as engaged at a large university in southern California using inductive research and grounded theory data collection and analysis methods. The thesis consists of three parts, all addressing the problem of disaster preparedness as enacted in this at-risk context. I use in-depth interviews, archival…

  19. Differentiating Tectonic and Anthropogenic Earthquakes in the Greater Los Angeles Basin, Southern California

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Goebel, T.; Cochran, E. S.; Ampuero, J. P.

    2014-12-01

    The 2014 flurry of moderate earthquakes in the Los Angeles region raised the concern if some of this or past seismicity was of anthropogenic origin as opposed to being caused by ongoing transpressional tectonics. The Mw5.1 La Habra sequence is located near several major oil fields but the Mw4.4 Encino sequence was located away from oil fields, within the Santa Monica Mountains. The last century of seismicity in the Los Angeles area consists of numerous small and large earthquakes. Most of these earthquakes occur beneath the basin sediments and are associated with transpressional tectonics, related to the big bend in the San Andreas fault, but some could be associated with large oil fields. In particular, both the 1933 Mw6.4 Long Beach and the 1987 Mw5.9 Whittier Narrows earthquakes were spatially associated with two major oil fields, the Huntington Beach and Montebello fields. Numerous large oil fields have been in production for more than 125 years. The geographical locations of the oil fields follow major tectonic trends such as the Newport-Inglewood fault, the Whittier fault, and the thrust belt located at the north edge of the Los Angeles basin. More than 60 fields have oil wells and some of these have both disposal and fracking wells. Before fluid injection became common, Kovach (1974) documented six damaging events induced by fluid extraction from 1947 to 1961 in the Wilmington oil field. Since 1981 the waveform-relocated earthquake catalog for the Los Angeles basin is complete on the average above M2.0. We compare the spatial distribution of these events and the proximity of nearby active oil fields. We will also analyze the seismicity in the context of available monthly fluid extraction and injection volumes and search for temporal correlations. The La Habra sequence apparently correlates with temporal changes in extraction and injection volumes in the Santa Fe Springs oil field but not with activities in other oil fields within closer spatial proximity.

  20. A study of microseismotectonics and earthquake sources in Long Valley Caldera, California

    NASA Astrophysics Data System (ADS)

    Stroujkova, Anastasia Felixovna

    It was noted by Aki (1992) that variety of conventional seismic methods fail in volcanic and geothermal environments due to complexity of structure and underlying processes. Custom-made combinations of data processing techniques should be designed for each particular geothermal site to gain a clear look at its internal structure. This thesis deals with various aspects of seismicity in the Long Valley Caldera, CA, observed during 1997 experiment in the Long Valley. Over 10,000 microearthquakes were detected and located as a result of this experiment. Hypocenters of several hundreds of swarm earthquakes were precisely relocated using the multiplet location technique. The relocation yielded elongated subvertical structures, pointing toward the geothermal plant. Based upon the earthquake relocation and focal mechanism study of these earthquakes, the major feature of this area is a series of sub-vertical faults. The majority of the seismicity in the Casa Diablo area was associated with advancing edges of this fault, failing in mode III (anti-plane). Analysis of about 2000 focal mechanisms showed that the seismicity is compatible with the regional stress field. Moment tensor study suggested that although most of the earthquakes could be explained in terms of double-couple mechanism, the statistical analysis revealed a possibility of a non-double-couple component present in the bulk seismicity. A number of unusual events with harmonic spectra occurred during the most active periods of the swarm. The source-time functions of these events consist of 2--3 sub-events with regular time delays between them, producing modulated, delay-dependent source spectra. The regularity of the delays suggests that the subevents are triggered by a fixed length/time scale process, an example being the length/inflation rate of a magmatic or hydrothermal flow structure. A number of earthquakes with unusual secondary phases were detected in the Casa Diablo area. Some of the phases were

  1. Estimating the probability of occurrence of earthquakes (M>6) in the Western part of the Corinth rift using fault-based and classical seismotectonic approaches.

    NASA Astrophysics Data System (ADS)

    Boiselet, Aurelien; Scotti, Oona; Lyon-Caen, Hélène

    2014-05-01

    The Corinth rift, Greece, is one of the regions with highest strain rates in the Euro-Mediterranean area and as such it has long been identified as a site of major importance for earthquake studies in Europe (20 years of research by the Corinth Rift Laboratory and 4 years of in-depth studies by the ANR-SISCOR project). This enhanced knowledge, acquired in particular, in the western part of the Gulf of Corinth, an area about 50 by 40 km, between the city of Patras to the west and the city of Aigion to the east, provides an excellent opportunity to compare fault-based and classical seismotectonic approaches currently used in seismic hazard assessment studies. A homogeneous earthquake catalogue was first constructed for the Greek territory based on two existing earthquake catalogues available for Greece (National Observatory of Athens and Thessaloniki). In spite of numerous documented damaging earthquakes, only a limited amount of macroseismic intensity data points are available in the existing databases for the damaging earthquakes affecting the west Corinth rift region. A re-interpretation of the macroseismic intensity field for numerous events was thus conducted, following an in-depth analysis of existing and newly found documentation (for details see Rovida et al. EGU2014-6346). In parallel, the construction of a comprehensive database of all relevant geological, geodetical and geophysical information (available in the literature and recently collected within the ANR-SISCOR project), allowed proposing rupture geometries for the different fault-systems identified in the study region. The combination of the new earthquake parameters and the newly defined fault geometries, together with the existing published paleoseismic data, allowed proposing a suite of rupture scenarios including the activation of multiple fault segments. The methodology used to achieve this goal consisted in setting up a logic tree that reflected the opinion of all the members of the ANR

  2. Slow rupture in Andaman during 2004 Sumatra-Andaman earthquake: a probable consequence of subduction of 90°E ridge

    NASA Astrophysics Data System (ADS)

    Gahalaut, V. K.; Subrahmanyam, C.; Kundu, B.; Catherine, J. K.; Ambikapathy, A.

    2010-03-01

    One of the most enigmatic features of the 2004 Sumatra-Andaman earthquake was the slow rupture speed and low slip on the northern part of the rupture under the Andaman region. We propose that the aseismic 90°E Ridge (NER) on the Indian Plate obliquely subducts under the Andaman frontal arc region. Though other possibilities also exist, we hypothesized that this ridge probably acted as a structural barrier influencing rupture characteristics of the earthquake. Here we present several features of the Andaman region that favour NER subduction under the region, which include (i) comparatively shallow bathymetry and trench depth, (ii) low seismicity, (iii) significant variation in the azimuths of coseismic horizontal offsets due to the 2004 Sumatra-Andaman earthquake, (iv) lack of post-seismic afterslip on the coseismic rupture in the Andaman frontal arc region, (v) low P wave with only small decrease in S wave speed from tomographic studies, (vi) gravity anomalies on the Indian Plate indicating continuation of the ridge under the Andaman frontal arc and (vii) lack of back arc volcanoes in the Andaman region.

  3. Earthquake stress drops and inferred fault strength on the Hayward Fault, east San Francisco Bay, California

    USGS Publications Warehouse

    Hardebeck, J.L.; Aron, A.

    2009-01-01

    We study variations in earthquake stress drop with respect to depth, faulting regime, creeping versus locked fault behavior, and wall-rock geology. We use the P-wave displacement spectra from borehole seismic recordings of M 1.0-4.2 earthquakes in the east San Francisco Bay to estimate stress drop using a stack-and-invert empirical Green's function method. The median stress drop is 8.7 MPa, and most stress drops are in the range between 0.4 and 130 MPa. An apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4-55 Hz. There is a trend of increasing stress drop with depth, with a median stress drop of ~5 MPa for 1-7 km depth, ~10 MPa for 7-13 km depth, and ~50 MPa deeper than 13 km. We use S=P amplitude ratios measured from the borehole records to better constrain the first-motion focal mechanisms. High stress drops are observed for a deep cluster of thrust-faulting earthquakes. The correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress. We compare the spatial distribution of stress drops on the Hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near Oakland. This also suggests a connection between stress drop and applied shear stress, as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher-strength material. The stress drops do not directly correlate with the strength of the proposed wall-rock geology at depth, suggesting that the relationship between fault strength and the strength of the wall rock is complex.

  4. Near-fault measurement of postseismic slip associated with the 1989 Loma Prieta, California, earthquake

    SciTech Connect

    Rymer, M.J. )

    1990-09-01

    Five small-aperture (0.5 to 7.7 m) quadrilaterals were installed across the San Andreas fault and newly formed extensional cracks shortly after the October 17, 1989 Loma Prieta M7.1 earthquake. Two quadrilaterals were installed across the San Andreas fault near the southeast and northwest ends of the 1989 rupture, and three were installed across dominantly extensional cracks in the Summit Road area near the main-shock epicenter and off the San Andreas fault. Measurements of line-length changes from as early as 4 d up to 184 d after the earthquake in the nail quadrilaterals indicate a small amount of right-lateral postseismic slip on the San Andreas fault. The site near the southeast end of the 1989 aftershock zone on the San Andreas fault showed about 5{plus minus}2 mm of postseismic right-lateral component of slip in addition to 23 mm of right-lateral coseismic movement. The site near the northwest end of aftershocks likewise showed about 5{plus minus}2 mm of postseismic slip, but after only 5 mm of coseismic slip. Measurements at sites across extensional cracks indicate possible minor left-lateral postseismic slips, and possible extensional/contractional motion. No measurements were made of possible vertical movements. Sites on extensional cracks showed similarly small amounts of possible postseismic lateral slip, from {approximately}2 to 10 mm, even though coseismic lateral slips were much greater (up to 410 mm) than on the surface trace of the San Andreas fault. The small slip values, in spite of uncertainties, clearly show that the lack of coseismic surface slip associated with the earthquake was not followed by large postseismic slip.

  5. Earthquakes, Segments, Bends, and Fault-Face Geology: Correlations Within the San Andreas System, California

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Simpson, R. W.; Thurber, C. H.; Murray, J. R.

    2006-12-01

    Three-dimensional geologic maps of regions surrounding parts of the San Andreas Fault system reveal correlations between fault face geology and both short- and long-term behavior of the faults. The Loma Prieta fault segment that ruptured during the 1989 M6.9 earthquake, as defined by its aftershocks, closely corresponds to the subsurface reach (80 km long) where a large body of Logan gabbro is truncated at the fault, as defined by its magnetic anomaly. This Jurassic ophiolitic gabbro and its related rocks occupy an unusual fault-bounded basement block within Salinaa, a largely Cretaceous granitic terrane SW of the San Andreas Fault. The along-fault reach of the Logan gabbro also coincides with essentially the entire Santa Cruz Mountains left-bend in the San Andreas Fault. Rejecting a chance coincidence, the position of the Logan gabbro with respect to the left bend implies that the bend is fixed relative to Salinia and that the block NE of the San Andreas Fault has been forced to negotiate around the bend as the blocks moved past each other. Thus the basement rocks of the Logan block appear to define (control?) the Loma Prieta segment in terms both of short-term behavior (earthquakes) and long-term behavior (restraining bend fault geometry). The Parkfield segment of the San Andreas Fault also closely corresponds to a characteristic geologic unit in the NE face of the fault, the greenstone-rich Permanente terrane of the Franciscan Complex. The along-fault subsurface extent of the Permanente terrane at the fault face, as inferred from a recent 3D tomographic wavespeed model, corresponds to the reach filled by the aftershocks of the 2004 Parkfield earthquake. Furthermore, the 2004 co-seismic slip inferred from geodetic observations also coincides with the Permanente terrane at the fault face. To test whether these observations are directly related to the presence of the Permanente terrane along the fault face, we looked at fault behavior at the location of its offset

  6. Three-Dimensional Geologic Map of Northern California: A Foundation for Earthquake Simulations and Other Predictive Modeling

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Simpson, R. W.; Graymer, R. W.; Wentworth, C. M.; Brocher, T. M.

    2006-12-01

    Detailed, realistic models of the subsurface are needed for predicting damage patterns from future earthquakes and simulating other phenomena affecting human safety and well being. The simple models used in the past are no longer adequate. In support of a planned simulation of the ground shaking from the Great 1906 San Francisco earthquake, we constructed a three-dimensional (3D) geologic map of northern California that consists of specific geologic units separated by discrete boundaries. It is based on a century of geologic mapping, 50 years of gravity and magnetic surveying, double-difference relocated seismicity, seismic soundings, P-wave tomography, and well logs. The map is a rules-based construction composed of faults that break the map volume into fault blocks, which in turn are populated with geologic units defined by surfaces that represent their tops. The rules define how the faults and tops truncate one another. The map is easily updated as new information becomes available. The 3D map is made up of two related parts. An inner detailed map of central California centered on San Francisco extends from Clear Lake to Monterey, from the edge of the continental shelf to the western Great Valley, and to a depth of 45 km. This is embedded in a less detailed regional map that extends from north of Cape Mendocino to Parkfield, from the ocean basin to the foothills of the Sierra Nevada and Cascade Ranges, and also to a depth of 45 km. The detailed map volume is broken by 25 major faults including the active San Andreas, Hayward, and Calaveras faults. The fault blocks are populated with geologic units in the following groups: water, Plio-Quaternary deposits, Tertiary (or undifferentiated Cenozoic) sedimentary and volcanic deposits, Mesozoic sedimentary or plutonic rocks, mafic lower crust, and mantle rocks. The primary purpose of the regional map is: 1) to provide coverage of the entire reach of the San Andreas Fault that ruptured in 1906 (including the major

  7. Forecasting the Next Great San Francisco Earthquake

    NASA Astrophysics Data System (ADS)

    Rundle, P.; Rundle, J. B.; Turcotte, D. L.; Donnellan, A.; Yakovlev, G.; Tiampo, K. F.

    2005-12-01

    The great San Francisco earthquake of 18 April 1906 and its subsequent fires killed more than 3,000 persons, and destroyed much of the city leaving 225,000 out of 400,000 inhabitants homeless. The 1906 earthquake occurred on a km segment of the San Andreas fault that runs from the San Juan Bautista north to Cape Mendocino and is estimated to have had a moment magnitude m ,l 7.9. Observations of surface displacements across the fault were in the range m. As we approach the 100 year anniversary of this event, a critical concern is the hazard posed by another such earthquake. In this talk we examine the assumptions presently used to compute the probability of occurrence of these earthquakes. We also present the results of a numerical simulation of interacting faults on the San Andreas system. Called Virtual California, this simulation can be used to compute the times, locations and magnitudes of simulated earthquakes on the San Andreas fault in the vicinity of San Francisco. Of particular importance are new results for the statistical distribution of interval times between great earthquakes, results that are difficult or impossible to obtain from a purely field-based approach. We find that our results are fit well under most circumstances by the Weibull statistical distribution, and we compute waiting times to future earthquakes based upon our simulation results. A contrasting approach to the same problem has been adopted by the Working Group on California Earthquake Probabilities, who use observational data combined with statistical assumptions to compute probabilities of future earthquakes.

  8. Along-strike variations in fault frictional properties along the San Andreas Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations

    USGS Publications Warehouse

    Harrington, R.M; Cochran, Elizabeth S.; Griffiths, E.M.; Zeng, X.; Thurber, C.

    2016-01-01

    Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San Andreas fault suggest slow‐slip earthquakes occur in a transition zone between the shallow fault, which accommodates slip by a combination of aseismic creep and earthquakes (<15  km depth), and the deep fault, which accommodates slip by stable sliding (>35  km depth). However, the spatial relationship between shallow earthquakes and LFEs remains unclear. Here, we present precise relocations of 34 earthquakes and 34 LFEs recorded during a temporary deployment of 13 broadband seismic stations from May 2010 to July 2011. We use the temporary array waveform data, along with data from permanent seismic stations and a new high‐resolution 3D velocity model, to illuminate the fine‐scale details of the seismicity distribution near Cholame and the relation to the distribution of LFEs. The depth of the boundary between earthquakes and LFE hypocenters changes along strike and roughly follows the 350°C isotherm, suggesting frictional behavior may be, in part, thermally controlled. We observe no overlap in the depth of earthquakes and LFEs, with an ∼5  km separation between the deepest earthquakes and shallowest LFEs. In addition, clustering in the relocated seismicity near the 2004 Mw 6.0 Parkfield earthquake hypocenter and near the northern boundary of the 1857 Mw 7.8 Fort Tejon rupture may highlight areas of frictional heterogeneities on the fault where earthquakes tend to nucleate.

  9. Interseismic Strain Accumulation in the Imperial Valley and Implications for Triggering of Large Earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Crowell, B. W.; Bock, Y.; Sandwell, D. T.

    2009-12-01

    From February, 2008 to March, 2009, we performed three rapid-static Global Positioning System (GPS) surveys of 115 geodetic monuments stretching from the United States-Mexico border into the Coachella Valley using the method of instantaneous positioning. The monuments are located in key areas near the Imperial, Superstition Hills, San Jacinto, San Andreas and Brawley Faults with nominal baselines generally less than 10 km. We perform a bicubic spline interpolation on the crustal motion vectors from the campaign measurements and 1005 continuous GPS monuments in western North America and solve for the velocity gradient tensor to look at the maximum shear strain, dilatation and rotation rates in the Imperial Valley. We then compare our computed strain field to that computed using the Southern California Earthquake Center Crustal Motion Map 3.0, which extends through 2003 and includes 840 measurements. We show that there is an interseismic strain transient that corresponds to an increase in the maximum shear strain rate of 0.7 μstrain/yr near Obsidian Buttes since 2003 along a fault referred to as the Obsidian Buttes Fault (OBF). A strong subsidence signal of 27 mm/yr and a left-lateral increase of 10 mm/yr are centered along the OBF. Changes in the dilatation and rotation rates confirm the increase in left-lateral motion, as well as infer a strong increase in spreading rate in the southern Salton Sea. The increase in spreading rate has caused an accelerated slip rate along the southern San Andreas near Durmid Hill as evidenced by continuous GPS, which has the potential for earthquake triggering.

  10. Interaction of the san jacinto and san andreas fault zones, southern california: triggered earthquake migration and coupled recurrence intervals.

    PubMed

    Sanders, C O

    1993-05-14

    Two lines of evidence suggest that large earthquakes that occur on either the San Jacinto fault zone (SJFZ) or the San Andreas fault zone (SAFZ) may be triggered by large earthquakes that occur on the other. First, the great 1857 Fort Tejon earthquake in the SAFZ seems to have triggered a progressive sequence of earthquakes in the SJFZ. These earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1.7 kilometers per year along the SJFZ after the 1857 earthquake. Second, the similarity in average recurrence intervals in the SJFZ (about 150 years) and in the Mojave segment of the SAFZ (132 years) suggests that large earthquakes in the northern SJFZ may stimulate the relatively frequent major earthquakes on the Mojave segment. Analysis of historic earthquake occurrence in the SJFZ suggests little likelihood of extended quiescence between earthquake sequences. PMID:17818388

  11. Coseismic deformation during the 1989 Loma Prieta earthquake and range-front thrusting along the southwestern margin of the Santa Clara Valley, California

    USGS Publications Warehouse

    Langenheim, V.E.; Schmidt, K.M.; Jachens, R.C.

    1997-01-01

    Damage patterns caused by the 1989 Loma Prieta earthquake along the southwestern margin of the Santa Clara Valley, California, form three zones that coincide with mapped and inferred traces of range-front thrust faults northeast of the San Andreas fault. Damage in these zones was largely contractional, consistent with past displacement associated with these faults. The damage zones coincide with gravity and aeromagnetic anomalies; modeling of the anomalies defines a southwest-dipping thrust fault that places the Franciscan Complex over Cenozoic sedimentary rocks to minimum depths of 2 km. Diffuse Loma Prieta earthquake aftershocks encompass the downward projection of this modeled thrust to depths of 9 km. Our results indicate that in this region the potential for concentrated damage arising from either primary deformation along the thrust faults themselves or by sympathetic motion triggered by earthquakes on the San Andreas fault may be higher than previously recognized.

  12. Average Stress Drops of Southern California Earthquakes in the Context of Crustal Geophysics: Implications for Fault Zone Healing

    NASA Astrophysics Data System (ADS)

    Hauksson, Egill

    2015-05-01

    To understand how fault healing processes affect earthquake stress drops, we search for a possible dependency of stress drops on crustal conditions and geophysical parameters. We reanalyze the stress drop values of ~60,000 earthquakes in southern California which were originally determined by Shearer et al. J Geophys Res 111:B06303, (2006) using a spectral method. We modify the dataset to include only stress drops that are derived from at least 10 spectra and with corner frequencies between 3 and 30 Hz, and correct the rupture velocity for increasing S-wave speed with depth. We see no dependence of stress drop on moment magnitude or depth, except for a small, poorly determined increase from 15 to 25 km. We use six crustal geophysics parameters to search for obvious correlations that may explain changes in the mean values of the stress drops: (1) crustal thickness, (2) isostatic gravity, (3) heat flow, (4) shear strain rate, (5) crustal stress regime, and (6) style of faulting. None of the variables reduce the scatter but most can explain up to 10-20 % variations in the mean stress drops. The geographical distribution of the grouped mean stress drops includes very high stress drops near Ridgecrest, eastern California, as well as near fault jogs within the San Andreas Fault system. Low stress drops dominate in trans-tensional regions. Heat flow and GPS-based shear strain rate estimates have the largest influence on stress drop variations. In the range of low to medium heat flow, the stress drops increase with increasing heat flow. In contrast, at high heat flow in thin crust, the stress drops decrease systematically with increasing heat flow. Increasing shear strain rate systematically correlates with decreasing stress drops. The crustal stress regime and style of faulting also influence the stress drops as demonstrated by lower stress drops for north-northeast trending principal horizontal stress and in areas of dip-slip faulting. The mean variations in stress drops

  13. Source complexity of the 1987 Whittier Narrows, California, earthquake from the inversion of strong motion records

    USGS Publications Warehouse

    Hartzell, S.; Iida, M.

    1990-01-01

    Strong motion records for the Whittier Narrows earthquake are inverted to obtain the history of slip. Both constant rupture velocity models and variable rupture velocity models are considered. The results show a complex rupture process within a relatively small source volume, with at least four separate concentrations of slip. Two sources are associated with the hypocenter, the larger having a slip of 55-90 cm, depending on the rupture model. These sources have a radius of approximately 2-3 km and are ringed by a region of reduced slip. The aftershocks fall within this low slip annulus. Other sources with slips from 40 to 70 cm each ring the central source region and the aftershock pattern. All the sources are predominantly thrust, although some minor right-lateral strike-slip motion is seen. The overall dimensions of the Whittier earthquake from the strong motion inversions is 10 km long (along the strike) and 6 km wide (down the dip). The preferred dip is 30?? and the preferred average rupture velocity is 2.5 km/s. Moment estimates range from 7.4 to 10.0 ?? 1024 dyn cm, depending on the rupture model. -Authors

  14. Survey of strong motion earthquake effects on thermal power plants in California with emphasis on piping systems. Volume 1, Main report

    SciTech Connect

    Stevenson, J.D.

    1995-11-01

    Since 1982, there has been a major effort expended to evaluate the susceptibility of nuclear Power plant equipment to failure and significant damage during seismic events. This was done by making use of data on the performance of electrical and mechanical equipment in conventional power plants and other similar industrial facilities during strong motion earthquakes. This report is intended as an extension of the seismic experience data collection effort and a compilation of experience data specific to power plant piping and supports designed and constructed US power piping code requirements which have experienced strong motion earthquakes. Eight damaging (Richter Magnitude 7.7 to 5.5) California earthquakes and their effects on 8 power generating facilities in use natural gas and California were reviewed. All of these facilities were visited and evaluated. Seven fossel-fueled (dual use natural gas and oil) and one nuclear fueled plants consisting of a total of 36 individual boiler or reactor units were investigated. Peak horizontal ground accelerations that either had been recorded on site at these facilities or were considered applicable to these power plants on the basis of nearby recordings ranged between 0.20g and 0.5lg with strong motion durations which varied from 3.5 to 15 seconds. Most US nuclear power plants are designed for a safe shutdown earthquake peak ground acceleration equal to 0.20g or less with strong motion durations which vary from 10 to 15 seconds.

  15. Deformation from the 1989 Loma Prieta earthquake near the southwest margin of the Santa Clara Valley, California

    USGS Publications Warehouse

    Schmidt, Kevin M.; Ellen, Stephen D.; Peterson, David M.

    2014-01-01

    To gain additional measurement of any permanent ground deformation that accompanied this damage, we compiled and conducted post-earthquake surveys along two 5-km lines of horizontal control and a 15-km level line. Measurements of horizontal distortion indicate approximately 0.1 m shortening in a NE-SW direction across the valley margin, similar to the amount measured in the channel lining. Evaluation of precise leveling by the National Geodetic Survey showed a downwarp, with an amplitude of >0.1 m over a span of >12 km, that resembled regional geodetic models of coseismic deformation. Although the leveling indicates broad, regional warping, abrupt discontinuities characteristic of faulting characterize both the broad-scale distribution of damage and the local deformation of the channel lining. Reverse movement largely along preexisting faults and probably enhanced significantly by warping combined with enhanced ground shaking, produced the documented coseismic ground deformation.

  16. Structural Constraints and Earthquake Recurrence Estimates for the West Tahoe-Dollar Point Fault, Lake Tahoe Basin, California

    NASA Astrophysics Data System (ADS)

    Maloney, J. M.; Driscoll, N. W.; Kent, G.; Brothers, D. S.; Baskin, R. L.; Babcock, J. M.; Noble, P. J.; Karlin, R. E.

    2011-12-01

    Previous work in the Lake Tahoe Basin (LTB), California, identified the West Tahoe-Dollar Point Fault (WTDPF) as the most hazardous fault in the region. Onshore and offshore geophysical mapping delineated three segments of the WTDPF extending along the western margin of the LTB. The rupture patterns between the three WTDPF segments remain poorly understood. Fallen Leaf Lake (FLL), Cascade Lake, and Emerald Bay are three sub-basins of the LTB, located south of Lake Tahoe, that provide an opportunity to image primary earthquake deformation along the WTDPF and associated landslide deposits. We present results from recent (June 2011) high-resolution seismic CHIRP surveys in FLL and Cascade Lake, as well as complete multibeam swath bathymetry coverage of FLL. Radiocarbon dates obtained from the new piston cores acquired in FLL provide age constraints on the older FLL slide deposits and build on and complement previous work that dated the most recent event (MRE) in Fallen Leaf Lake at ~4.1-4.5 k.y. BP. The CHIRP data beneath FLL image slide deposits that appear to correlate with contemporaneous slide deposits in Emerald Bay and Lake Tahoe. A major slide imaged in FLL CHIRP data is slightly younger than the Tsoyowata ash (7950-7730 cal yrs BP) identified in sediment cores and appears synchronous with a major Lake Tahoe slide deposit (7890-7190 cal yrs BP). The equivalent age of these slides suggests the penultimate earthquake on the WTDPF may have triggered them. If correct, we postulate a recurrence interval of ~3-4 k.y. These results suggest the FLL segment of the WTDPF is near its seismic recurrence cycle. Additionally, CHIRP profiles acquired in Cascade Lake image the WTDPF for the first time in this sub-basin, which is located near the transition zone between the FLL and Rubicon Point Sections of the WTDPF. We observe two fault-strands trending N45°W across southern Cascade Lake for ~450 m. The strands produce scarps of ~5 m and ~2.7 m, respectively, on the lake

  17. Post-earthquake relaxation evidence for laterally variable viscoelastic structure and elevated water concentration in the southwestern California mantle

    NASA Astrophysics Data System (ADS)

    Pollitz, F. F.

    2014-12-01

    I re-examine the lower crust and mantle relaxation following two large events in the Mojave Desert: the 1992 M7.3 Landers and 1999 M7.1 Hector Mine, California, earthquakes. More than a decade of GPS time series from regional sites out to 250 km from the ruptures are used to constrain models of postseismic relaxation. Crustal motions in the Mojave Desert region are elevated for several years following each event, with perturbations from a pre-Landers background of order mm to cm per year. I consider afterslip and relaxation of the ductile lower crust and mantle to explain these motions. To account for broad scale relaxation, the Burgers body model is employed, involving Kelvin (transient) viscosity and rigidity and Maxwell (steady state) viscosity and rigidity. I use the code VISCO2.5D to perform 2.5D modeling of the postseismic relaxation (3D quasi-static motions computed on 2D, laterally heterogeneous viscoelastic structures; Pollitz, 2014 GJI). Joint afterslip / postseismic relaxation modeling of continuous GPS time series up to 10.46 years following the Hector Mine earthquake (i.e. up to the time of the 2010 M7.2 El Mayor-Cucapah earthquake) reveals that a northwest-trending `southwest domain' that envelopes the San Andreas fault system and western Mojave Desert has ~4 times larger Maxwell mantle viscosity than the adjacent `northeast domain' that extends inland and envelopes the Landers and Hector Mine rupture areas in the central Mojave Desert. This pattern is counter to that expected from regional heat flow, which is higher in the northeast domain, but it is explicable by means of a non-linear rheology that includes dependence on both strain rate and water concentration. I infer that the southwest domain mantle has a relatively low steady-state viscosity because of its high strain rate and water content. The relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic

  18. Prevalence and Predictors of Somatic Symptoms among Child and Adolescents with Probable Posttraumatic Stress Disorder: A Cross-Sectional Study Conducted in 21 Primary and Secondary Schools after an Earthquake

    PubMed Central

    Zhang, Ye; Zhu, Shenyue; Du, Changhui

    2015-01-01

    Purpose To explore the prevalence rates and predictors of somatic symptoms among child and adolescent survivors with probable posttraumatic stress disorder (PTSD) after an earthquake. Methods A total of 3053 students from 21 primary and secondary schools in Baoxing County were administered the Patient Health Questionnaire-13 (PHQ-13), a short version of PHQ-15 without the two items about sexuality and menstruation, the Children's Revised Impact of Event Scale (CRIES), and the self-made Earthquake-Related Experience Questionnaire 3 months after the Lushan earthquake. Results Among child and adolescent survivors, the prevalence rates of all somatic symptoms were higher in the probable PTSD group compared with the controls. The most frequent somatic symptoms were trouble sleeping (83.2%), feeling tired or having low energy (74.4%), stomach pain (63.2%), dizziness (58.1%), and headache (57.7%) in the probable PTSD group. Older age, having lost family members, having witnessed someone get seriously injured, and having witnessed someone get buried were predictors for somatic symptoms among child and adolescent survivors with probable PTSD. Conclusions Somatic symptoms among child and adolescent earthquake survivors with probable PTSD in schools were common, and predictors of these somatic symptoms were identified. These findings may help those providing psychological health programs to find the child and adolescent students with probable PTSD who are at high risk of somatic symptoms in schools after an earthquake in China. PMID:26327455

  19. EFFECTS OF THE 1906 EARTHQUAKE ON THE BALD HILL OUTLET SYSTEM, SAN MATEO COUNTY, CALIFORNIA.

    USGS Publications Warehouse

    Pampeyan, Earl H.

    1986-01-01

    Following the earthquake of April 18, 1906, it was discovered that a brick forebay and other parts of the reservoir outlet system were in the slip zone of the San Andreas fault. The original outlet through which water was directed to San Francisco consisted of two tunnels joined at the brick forebay; one tunnel extends 2,820 ft to the east under Bald Hill on Buri Buri Ridge, and the other tunnel intersects the lake bottom about 250 ft west of the forebay. In 1897 a second intake was added to the system, also joining the original forebay. During the present study the accessible parts of this original outlet system were examined with the hope of learning how the system had been affected by fault slip in 1906.

  20. Non-double-couple earthquake mechanisms at the Geysers geothermal area, California

    USGS Publications Warehouse

    Ross, A.; Foulger, G.R.; Julian, B.R.

    1996-01-01

    Inverting P- and S-wave polarities and P:SH amplitude ratios using linear programming methods suggests that about 20% of earthquakes at The Geysers geothermal area have significantly non-double-couple focal mechanisms, with explosive volumetric components as large as 33% of the seismic moment. This conclusion contrasts with those of earlier studies, which interpreted data in terms of double couples. The non-double-couple mechanisms are consistent with combined shear and tensile faulting, possibly caused by industrial water injection. Implosive mechanisms, which might be expected because of rapid steam withdrawal, have not been found. Significant compensated-linear-vector-dipole (CLVD) components in some mechanisms may indicate rapid fluid flow accompanying crack opening. Copyright 1996 by the American Geophysical Union.

  1. Eruption probabilities for the Lassen Volcanic Center and regional volcanism, northern California, and probabilities for large explosive eruptions in the Cascade Range

    USGS Publications Warehouse

    Nathenson, Manuel; Clynne, Michael A.; Muffler, L.J. Patrick

    2012-01-01

    Chronologies for eruptive activity of the Lassen Volcanic Center and for eruptions from the regional mafic vents in the surrounding area of the Lassen segment of the Cascade Range are here used to estimate probabilities of future eruptions. For the regional mafic volcanism, the ages of many vents are known only within broad ranges, and two models are developed that should bracket the actual eruptive ages. These chronologies are used with exponential, Weibull, and mixed-exponential probability distributions to match the data for time intervals between eruptions. For the Lassen Volcanic Center, the probability of an eruption in the next year is 1.4x10-4 for the exponential distribution and 2.3x10-4 for the mixed exponential distribution. For the regional mafic vents, the exponential distribution gives a probability of an eruption in the next year of 6.5x10-4, but the mixed exponential distribution indicates that the current probability, 12,000 years after the last event, could be significantly lower. For the exponential distribution, the highest probability is for an eruption from a regional mafic vent. Data on areas and volumes of lava flows and domes of the Lassen Volcanic Center and of eruptions from the regional mafic vents provide constraints on the probable sizes of future eruptions. Probabilities of lava-flow coverage are similar for the Lassen Volcanic Center and for regional mafic vents, whereas the probable eruptive volumes for the mafic vents are generally smaller. Data have been compiled for large explosive eruptions (>≈ 5 km3 in deposit volume) in the Cascade Range during the past 1.2 m.y. in order to estimate probabilities of eruption. For erupted volumes >≈5 km3, the rate of occurrence since 13.6 ka is much higher than for the entire period, and we use these data to calculate the annual probability of a large eruption at 4.6x10-4. For erupted volumes ≥10 km3, the rate of occurrence has been reasonably constant from 630 ka to the present, giving

  2. Post seismic deformation associated with the 1992 Mω=7.3 Landers earthquake, southern California

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.

    1997-01-01

    Following the 1992 Mω=7.3 Landers earthquake, a linear array of 10 geodetic monuments at roughly 5-km spacing was established across the Emerson fault segment of the Landers rupture. The array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it. The array was surveyed by Global Positioning System 0.034, 0.048, 0.381, 1.27, 1.88, 2.60, and 3.42 years after the Landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation. The temporal behavior is described roughly by a short-term (decay time 84±23 days) exponential relaxation superimposed upon an apparently linear trend. Because the linear trend represents motions much more rapid than the observed preseismic motions, we attribute that trend to a slower (decay time greater than 5 years) postseismic relaxation, the curvature of which cannot be resolved in the short run (3.4 years) of postseismic data. About 100 mm of right-lateral displacement and 50 mm of fault-normal displacement accumulated across the geodetic array in the 3.4-year interval covered by the postseismic surveys. Those displacements are attributed to postseismic, right-lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace. The right-lateral slip amounted to about 1 m directly beneath the geodetic array, and the fault-normal displacement is apparently primarily a consequence of the curvature of the rupture. These conclusions are based upon dislocation models fit to the observed deformation. However, no dislocation model was found with rms residuals as small as the expected observational error.

  3. Deep Structure Of Long Valley, California, Based On Deep Reflections From Earthquakes

    SciTech Connect

    Zucca, J. J.; Kasameyer, P. W.

    1987-01-01

    Knowledge of the deep structure of Long Valley comes primarily from seismic studies. Most of these efforts have focused on delimiting the top of the inferred magma chamber. We present evidence for the location of the bottom of the low velocity layer (LVL). Two other studies have provided similar information. Steeples and Iyer (1976) inferred from teleseismic P-wave delays that low-velocity material extends from 7 km depth to 25 to 40 km, depending on the velocities assumed. Luetgert and Mooney (1985) have examined seismic refraction data from earthquake sources and have identified a reflection that appears to be from the lower boundary of a magma chamber. They detected the reflection with a linear array of single component stations, and assuming it traveled in a vertical plane, matched the travel time and apparent velocity (6.3 km/sec) to deduce that it was a P-P reflection from within a LVL. We recorded a similar phase with a 2-dimensional array of three-component stations, and carried out a similar analysis, but utilized additional information about the travel path, particle motions and amplitudes to constrain our interpretation. Our data comes from a passive seismic refraction experiment conducted during August 1982. Fourteen portable seismograph stations were deployed in a network with approximately 5 km station spacing in the Mono Craters region north of Long Valley (Figure 1). The network recorded earthquakes located south of Long Valley and in the south moat. Three components of motion were recorded at all sites. The data represent one of the few times that three-component data has been collected for raypaths through a magma chamber in the Long Valley area.

  4. Finite-fault analysis of the 2004 Parkfield, California, earthquake using Pnl waveforms

    USGS Publications Warehouse

    Mendoza, C.; Hartzell, S.

    2008-01-01

    We apply a kinematic finite-fault inversion scheme to Pnl displacement waveforms recorded at 14 regional stations (Δ<2°) to recover the distribution of coseismic slip for the 2004 Parkfield earthquake using both synthetic Green’s functions (SGFs) calculated for one-dimensional (1D) crustal-velocity models and empirical Green’s functions (EGFs) based on the recordings of a single Mw 5.0 aftershock. Slip is modeled on a rectangular fault subdivided into 2×2 km subfaults assuming a constant rupture velocity and a 0.5 sec rise time. A passband filter of 0.1–0.5 Hz is applied to both data and subfault responses prior to waveform inversion. The SGF inversions are performed such that the final seismic moment is consistent with the known magnitude (Mw 6.0) of the earthquake. For these runs, it is difficult to reproduce the entire Pnl waveform due to inaccuracies in the assumed crustal structure. Also, the misfit between observed and predicted vertical waveforms is similar in character for different rupture velocities, indicating that neither the rupture velocity nor the exact position of slip sources along the fault can be uniquely identified. The pattern of coseismic slip, however, compares well with independent source models derived using other data types, indicating that the SGF inversion procedure provides a general first-order estimate of the 2004 Parkfield rupture using the vertical Pnl records. The best-constrained slip model is obtained using the single-aftershock EGF approach. In this case, the waveforms are very well reproduced for both vertical and horizontal components, suggesting that the method provides a powerful tool for estimating the distribution of coseismic slip using the regional Pnl waveforms. The inferred slip model shows a localized patch of high slip (55 cm peak) near the hypocenter and a larger slip area (~50 cm peak) extending between 6 and 20 km to the northwest.

  5. Earthquake precursors: activation or quiescence?

    NASA Astrophysics Data System (ADS)

    Rundle, John B.; Holliday, James R.; Yoder, Mark; Sachs, Michael K.; Donnellan, Andrea; Turcotte, Donald L.; Tiampo, Kristy F.; Klein, William; Kellogg, Louise H.

    2011-10-01

    We discuss the long-standing question of whether the probability for large earthquake occurrence (magnitudes m > 6.0) is highest during time periods of smaller event activation, or highest during time periods of smaller event quiescence. The physics of the activation model are based on an idea from the theory of nucleation, that a small magnitude earthquake has a finite probability of growing into a large earthquake. The physics of the quiescence model is based on the idea that the occurrence of smaller earthquakes (here considered as magnitudes m > 3.5) may be due to a mechanism such as critical slowing down, in which fluctuations in systems with long-range interactions tend to be suppressed prior to large nucleation events. To illuminate this question, we construct two end-member forecast models illustrating, respectively, activation and quiescence. The activation model assumes only that activation can occur, either via aftershock nucleation or triggering, but expresses no choice as to which mechanism is preferred. Both of these models are in fact a means of filtering the seismicity time-series to compute probabilities. Using 25 yr of data from the California-Nevada catalogue of earthquakes, we show that of the two models, activation and quiescence, the latter appears to be the better model, as judged by backtesting (by a slight but not significant margin). We then examine simulation data from a topologically realistic earthquake model for California seismicity, Virtual California. This model includes not only earthquakes produced from increases in stress on the fault system, but also background and off-fault seismicity produced by a BASS-ETAS driving mechanism. Applying the activation and quiescence forecast models to the simulated data, we come to the opposite conclusion. Here, the activation forecast model is preferred to the quiescence model, presumably due to the fact that the BASS component of the model is essentially a model for activated seismicity. These

  6. History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland

    USGS Publications Warehouse

    Ryan, Holly F.; von Huene, Roland; Wells, Ray E.; Scholl, David W.; Kirby, Stephen; Draut, Amy E.

    2012-01-01

    During the past several years, devastating tsunamis were generated along subduction zones in Indonesia, Chile, and most recently Japan. Both the Chile and Japan tsunamis traveled across the Pacific Ocean and caused localized damage at several coastal areas in California. The question remains as to whether coastal California, in particular the California Continental Borderland, is vulnerable to more extensive damage from a far-field tsunami sourced along a Pacific subduction zone. Assuming that the coast of California is at risk from a far-field tsunami, its coastline is most exposed to a trans-Pacific tsunami generated along the eastern Aleutian-Alaska subduction zone. We present the background geologic constraints that could control a possible giant (Mw ~9) earthquake sourced along the eastern Aleutian-Alaska megathrust. Previous great earthquakes (Mw ~8) in 1788, 1938, and 1946 ruptured single segments of the eastern Aleutian-Alaska megathrust. However, in order to generate a giant earthquake, it is necessary to rupture through multiple segments of the megathrust. Potential barriers to a throughgoing rupture, such as high-relief fracture zones or ridges, are absent on the subducting Pacific Plate between the Fox and Semidi Islands. Possible asperities (areas on the megathrust that are locked and therefore subject to infrequent but large slip) are identified by patches of high moment release observed in the historical earthquake record, geodetic studies, and the location of forearc basin gravity lows. Global Positioning System (GPS) data indicate that some areas of the eastern Aleutian-Alaska megathrust, such as that beneath Sanak Island, are weakly coupled. We suggest that although these areas will have reduced slip during a giant earthquake, they are not really large enough to form a barrier to rupture. A key aspect in defining an earthquake source for tsunami generation is determining the possibility of significant slip on the updip end of the megathrust near

  7. Probabilities for large events in driven threshold systems

    NASA Astrophysics Data System (ADS)

    Rundle, John B.; Holliday, James R.; Graves, William R.; Turcotte, Donald L.; Tiampo, Kristy F.; Klein, William

    2012-08-01

    Many driven threshold systems display a spectrum of avalanche event sizes, often characterized by power-law scaling. An important problem is to compute probabilities of the largest events (“Black Swans”). We develop a data-driven approach to the problem by transforming to the event index frame, and relating this to Shannon information. For earthquakes, we find the 12-month probability for magnitude m>6 earthquakes in California increases from about 30% after the last event, to 40%-50% prior to the next one.

  8. Analysis of Injection-Induced Micro-Earthquakes in a Geothermal Steam Reservoir, The Geysers Geothermal Field, California

    SciTech Connect

    Rutqvist, Jonny; Rutqvist, J.; Oldenburg, C.M.

    2008-05-15

    In this study we analyze relative contributions to the cause and mechanism of injection-induced micro-earthquakes (MEQs) at The Geysers geothermal field, California. We estimated the potential for inducing seismicity by coupled thermal-hydrological-mechanical analysis of the geothermal steam production and cold water injection to calculate changes in stress (in time and space) and investigated if those changes could induce a rock mechanical failure and associated MEQs. An important aspect of the analysis is the concept of a rock mass that is critically stressed for shear failure. This means that shear stress in the region is near the rock-mass frictional strength, and therefore very small perturbations of the stress field can trigger an MEQ. Our analysis shows that the most important cause for injection-induced MEQs at The Geysers is cooling and associated thermal-elastic shrinkage of the rock around the injected fluid that changes the stress state in such a way that mechanical failure and seismicity can be induced. Specifically, the cooling shrinkage results in unloading and associated loss of shear strength in critically shear-stressed fractures, which are then reactivated. Thus, our analysis shows that cooling-induced shear slip along fractures is the dominant mechanism of injection-induced MEQs at The Geysers.

  9. Stress drop and its Uncertainty for Earthquakes M3.8-5.5 in Central California and Oklahoma

    NASA Astrophysics Data System (ADS)

    Ding, Luyuan

    Stress drop is the stress that is effectively available to drive fault motion. It is a key parameter in predicting peak ground acceleration (PGA), since PGA∝, and it is very important in estimating ground motion. However, it is difficult to get an accurate estimation of stress drop. In order to get a more stable measurement of stress drop, we test two methods in this thesis: the first one is the Brune stress drop, which is more commonly applied, and the second one is the Arms stress drop, which less applied before and theoretically should have less uncertainty. By comparing these two methods we would like to test the feasibility and stability of the Arms method. We applied these two methods to data of earthquakes M3-5.5 in California and Oklahoma. We found that, taking Oklahoma results as an example, the mean value of Brune stress drop is 0.38 MPa, with a multiplicative uncertainty of 3.12, and the mean value of Arms stress drop is 1.04, with a multiplicative uncertainty of 1.79. Therefore we concluded that the Arms method is a good estimator of stress drop, with a smaller uncertainty. We determine the path attenuation so that we can increase the source-station distance of events studied to be as much as 76 km. The path seismic attenuation is a critical parameter that must be included in the analysis.

  10. Transient stresses at Parkfield, California, produced by the M 7.4 Landers earthquake of June 28, 1992: Observations from the UPSAR dense seismograph array

    NASA Astrophysics Data System (ADS)

    Spudich, Paul; Steck, Lee K.; Hellweg, Margaret; Fletcher, J. B.; Baker, Lawrence M.

    1995-01-01

    The M 7.4 Landers earthquake triggered widespread seismicity in the western United States. Because the transient dynamic stresses induced at regional distances by the Landers surface waves are much larger than the expected static stresses, the magnitude and the characteristics of the dynamic stresses may bear upon the earthquake triggering mechanism. The Landers earthquake was recorded on the UPSAR (U.S. Geological Survey Parkfield Small Aperture Array) array, a group of 14 triaxial accelerometers located within a 1-square-km region 10 km southwest of the town of Parkfield, California, 412 km northwest of the Landers epicenter. No triggered earthquakes were observed at Parkfield. Multiple filter analysis shows that the displacements, obtained by double integrations, are dominated by the fundamental mode Love and Rayleigh modes, with some higher-mode contributions for periods shorter than 10 s. Most of the surface waves propagated along the great circle path from Landers, but a late arriving surface wave appears to have been scattered from the Sierra Nevada Mountains. We used a standard geodetic inversion procedure to determine the surface strain and stress tensors as functions of time from the observed displacements. Comparison of dynamic stresses induced by the Landers, Loma Prieta, and Petrolia earthquakes at a variety of sites indicates that the Landers stresses were not spectacularly larger than those induced by the other sources. Landers dynamic stresses were comparable to Coalinga static stresses at Parkfield. The effective strain caused by Landers at Parkfield, where no earthquakes were triggered, are the same amplitude as those at some sites in Nevada where earthquakes were triggered. Comparing various authors' observations of dynamic stresses, there is no obvious characteristic of these stresses that correlates with the triggered seismicity.

  11. Dynamic triggering of creep events in the Salton Trough, Southern California by regional M ≥ 5.4 earthquakes constrained by geodetic observations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Wei, Meng; Liu, Yajing; Kaneko, Yoshihiro; McGuire, Jeffrey J.; Bilham, Roger

    2015-10-01

    Since a regional earthquake in 1951, shallow creep events on strike-slip faults within the Salton Trough, Southern California have been triggered at least 10 times by M ≥ 5.4 earthquakes within 200 km. The high earthquake and creep activity and the long history of digital recording within the Salton Trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes. Here, we document the history of fault creep events on the Superstition Hills Fault based on data from creepmeters, InSAR, and field surveys since 1988. We focus on a subset of these creep events that were triggered by significant nearby earthquakes. We model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate- and state-dependent friction. We find that the static stress changes from the causal earthquakes are less than 0.1 MPa and too small to instantaneously trigger creep events. In contrast, we can reproduce the characteristics of triggered slip with dynamic perturbations alone. The instantaneous triggering of creep events depends on the peak and the time-integrated amplitudes of the dynamic Coulomb stress change. Based on observations and simulations, the stress change amplitude required to trigger a creep event of a 0.01-mm surface slip is about 0.6 MPa. This threshold is at least an order of magnitude larger than the reported triggering threshold of non-volcanic tremors (2-60 kPa) and earthquakes in geothermal fields (5 kPa) and near shale gas production sites (0.2-0.4 kPa), which may result from differences in effective normal stress, fault friction, the density of nucleation sites in these systems, or triggering mechanisms. We conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the Superstition Hills Fault.

  12. Moving Mountains and Deep Crustal Earthquakes: Evidence for Deep Magma Injection Beneath Lake Tahoe, Nevada-California

    NASA Astrophysics Data System (ADS)

    Blewitt, G.; Smith, K. D.; von Seggern, D.

    2004-12-01

    We recently reported [Smith et al., Science 305, 2004] an unusually deep swarm of 1611 earthquakes that occurred in late 2003 at Lake Tahoe, California (depth 29-33 kilometer; Richter Magnitude [ML] < 2.2; sum of the moment magnitude of all events is Mw 3.1). This swarm was coeval with a GPS transient displacement of 6 ± 0.3 mm horizontally outward from the swarm and 7.9 ± 1.0 mm upward measured at the GPS station on Slide Mountain, Nevada (SLID) 18 km to the northeast. Station SLID is a part of the 53-station Basin and Range Geodetic Network (BARGEN) network, continuously operating since 1996 and one of the PBO Nucleus stations. Here we focus on the results of the geodetic analysis for SLID, and other BARGEN stations within 200 km of SLID, starting on 1 January 2000. The SLID transient displacement is 9.8 mm in a direction normal to the planar structure defined by the deep earthquake swarm, spanning the same time period of the swarm. The geodetic displacement here is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters/second up-dip along a 40-km2 structure striking N30° W and dipping 50° to the northeast. Assuming a stress drop of 10 MPa (reasonable for upper crustal earthquakes), this event has an equivalent seismic moment to a magnitude (Mw) 6.0 earthquake with a displacement of ~1 meter at the source. Applying Okada's model for a tensile crack at 28 km depth in the source region, a potency equivalent to a volume of 3.7 × 107 m3, or volumetric moment equivalent of Mw 6.4, fits the SLID observations. As there is no established evidence of recent volcanism (<1 Ma) in the Tahoe region, this discovery suggests the hypothesis that such deep magmatic events in

  13. Moment-tensor solutions for the 24 November 1987 Superstition Hills, California, earthquakes

    USGS Publications Warehouse

    Sipkin, S.A.

    1989-01-01

    The teleseismic long-period waveforms recorded by the Global Digital Seismograph Network from the two largest Superstition Hills earthquakes are inverted using an algorithm based on optimal filter theory. These solutions differ slightly from those published in the Preliminary Determination of Epicenters Monthly Listing because a somewhat different, improved data set was used in the inversions and a time-dependent moment-tensor algorithm was used to investigate the complexity of the main shock. The foreshock (origin time 01:54:14.5, mb 5.7, Ms6.2) had a scalar moment of 2.3 ?? 1025 dyne-cm, a depth of 8km, and a mechanism of strike 217??, dip 79??, rake 4??. The main shock (origin time 13:15:56.4, mb 6.0, Ms6.6) was a complex event, consisting of at least two subevents, with a combined scalar moment of 1.0 ?? 1026 dyne-cm, a depth of 10km, and a mechanism of strike 303??, dip 89??, rake -180??. -Authors

  14. Measuring Possible Tsunami Currents from the April 1, 2014 Mw 8.2 Chile Earthquake in Crescent City, California

    NASA Astrophysics Data System (ADS)

    Admire, A. R.; Crawford, G. B.; Dengler, L. A.

    2014-12-01

    Crescent City, California has a long history of damaging tsunamis. Thirty-nine tsunamis have been recorded since 1933, including five that caused damage. Crescent City's harbor and small boat basin are particularly vulnerable to strong currents. Humboldt State University has installed Acoustic Doppler Profilers (ADPs) in order to directly measure water pressure fluctuations and currents caused by tsunamis. An instrument in Humboldt Bay, ~100 km south of Crescent City, recorded tsunamis generated by the 2010 Mw 8.7 Chile and 2011 Mw 9.0 Japan earthquakes and demonstrated the usefulness of ADPs in measuring tsunami currents. In 2013, an ADP was deployed in Crescent City's harbor adjacent to the NOAA tide gauge. On April 1, 2014, a Mw 8.2 earthquake occurred in northern Chile, producing a modest Pacific-wide tsunami and a 16 cm peak amplitude on the Crescent City tide gauge. We analyze the ADP data before and during the expected arrival of the April 2 tsunami to see if a tsunami signal is present. Tidal currents are generally small (5 cm/s or less). For two months before the tsunami, intermittent, high-frequency variability is present in velocity and pressure at periods on the order of 20, 9 and 5 min, which compare favorably to modal periods predicted using some simplified models of open-ended basins. For several hours after the tsunami arrival on April 2, spectral power levels in velocity and pressure around the 20 min period are notably enhanced. These results suggest that: (1) the observed periods of enhanced variability represent the first three modes (n=0, 1 and 2) of free oscillations in the harbor, (2) the dominant period of (non-tidal) oscillations observed during the April 2, 2014 tsunami (~20 min) and during previous tsunamis (e.g., the water level record for the March 11, 2011 tsunami; also ~20 min) represents harbor resonance corresponding to the lowest order mode, and (3) this event is very near the ADP limit of detectability with peak tsunami currents

  15. Correlation of ground motion and intensity for the 17 January 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Boatwright, J.; Thywissen, K.; Seekins, L.C.

    2001-01-01

    We analyze the correlations between intensity and a set of groundmotion parameters obtained from 66 free-field stations in Los Angeles County that recorded the 1994 Northridge earthquake. We use the tagging intensities from Thywissen and Boatwright (1998) because these intensities are determined independently on census tracts, rather than interpolated from zip codes, as are the modified Mercalli isoseismals from Dewey et al. (1995). The ground-motion parameters we consider are the peak ground acceleration (PGA), the peak ground velocity (PGV), the 5% damped pseudovelocity response spectral (PSV) ordinates at 14 periods from 0.1 to 7.5 sec, and the rms average of these spectral ordinates from 0.3 to 3 sec. Visual comparisons of the distribution of tagging intensity with contours of PGA, PGV, and the average PSV suggest that PGV and the average PSV are better correlated with the intensity than PGA. The correlation coefficients between the intensity and the ground-motion parameters bear this out: r = 0.75 for PGA, 0.85 for PGV, and 0.85 for the average PSV. Correlations between the intensity and the PSV ordinates, as a function of period, are strongest at 1.5 sec (r = 0.83) and weakest at 0.2 sec (r = 0.66). Regressing the intensity on the logarithms of these ground-motion parameters yields relations I ?? mlog?? with 3.0 ??? m ??? 5.2 for the parameters analyzed, where m = 4.4 ?? 0.7 for PGA, 3.4 ?? 0.4 for PGV, and 3.6 ?? 0.5 for the average PSV.

  16. Postearthquake relaxation after the 2004 M6 Parkfield, California, earthquake and rate-and-state friction

    USGS Publications Warehouse

    Savage, J.C.; Langbein, J.

    2008-01-01

    An unusually complete set of measurements (including rapid rate GPS over the first 10 days) of postseismic deformation is available at 12 continuous GPS stations located close to the epicenter of the 2004 M6.0 Parkfield earthquake. The principal component modes for the relaxation of the ensemble of those 12 GPS stations were determined. The first mode alone furnishes an adequate approximation to the data. Thus, the relaxation at all stations can be represented by the product of a common temporal function and distinct amplitudes for each component (north or east) of relaxation at each station. The distribution in space of the amplitudes indicates that the relaxation is dominantly strike slip. The temporal function, which spans times from about 5 min to 900 days postearthquake, can be fit by a superposition of three creep terms, each of the form ??l loge(1 + t/??l), with characteristic times ??, = 4.06, 0.11, and 0.0001 days. It seems likely that what is actually involved is a broad spectrum of characteristic times, the individual components of which arise from afterslip on different fault patches. Perfettini and Avouac (2004) have shown that an individual creep term can be explained by the spring-slider model with rate-dependent (no state variable) friction. The observed temporal function can also be explained using a single spring-slider model (i.e., single fault patch) that includes rate-and-state-dependent friction, a single-state variable, and either of the two commonly used (aging and slip) state evolution laws. In the latter fits, the rate-and-state friction parameter b is negative.

  17. The Non-Regularity of Earthquake Recurrence in California: Lessons From Long Paleoseismic Records in Simple vs Complex Fault Regions (Invited)

    NASA Astrophysics Data System (ADS)

    Rockwell, T. K.

    2010-12-01

    A long paleoseismic record at Hog Lake on the central San Jacinto fault (SJF) in southern C