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1

Southern California regional earthquake probability estimated from continuous GPS geodetic data  

Microsoft Academic Search

Current seismic hazard estimates are primarily based on seismic and geologic data, but geodetic measurements from large, dense arrays such as the Southern California Integrated GPS Network (SCIGN) can also be used to estimate earthquake probabilities and seismic hazard. Geodetically-derived earthquake probability estimates are particularly important in regions with poorly-constrained fault slip rates. In addition, they are useful because such

G. Anderson

2002-01-01

2

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

USGS Publications Warehouse

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).

Stein, Ross S.

2008-01-01

3

Earthquake Probability Mapping  

NSDL National Science Digital Library

This mapping tool allows users to generate Earthquake Probability Maps (EPMs) for a region within 50 kilometers of a location specified by latitude and longitude or by ZIP code. The maps are color-coded; higher earthquake probabilities are indicated by orange and red colors, while lower probabilities are indicated by green or blue. Fault traces are marked in white; rivers are in blue. The maps are also produced in downloadable, printable format (PDF).

4

Earthquake Probability Mapping  

NSDL National Science Digital Library

This mapping tool allows users to generate Earthquake Probability Maps (EPMs) for a region within 50 kilometers of a location specified by latitude and longitude or by ZIP code. The maps are color-coded; higher earthquake probabilities are indicated by orange and red colors, while lower probabilities are indicated by green or blue. Fault traces are marked in white; rivers are in blue. The maps are also produced in downloadable, printable format (PDF).

2010-12-27

5

Parkfield, California: Earthquake History  

NSDL National Science Digital Library

This report describes the history of seismic activity at Parkfield, California, which is situated on the San Andreas Fault. It points out that moderate-size earthquakes have occurred on the Parkfield section of the San Andreas fault at fairly regular intervals, and that the earthquakes may have been 'characteristic' in the sense that they occurred with some regularity (mean repetition time of about 22 years). This indicates that they may have repeatedly ruptured the same area on the fault. A diagram shows the timing of the earthquakes, and illustrations of the seismic waveforms show the similarities between earthquakes occurring in 1922, 1934, and 1966.

6

Cosmogenic beryllium-10 exposure dating of probable earthquake-triggered rock avalanches in Yosemite Valley, California  

NASA Astrophysics Data System (ADS)

In Yosemite Valley, rock falls commonly originate from the glacially-steepened walls. Deposition of the smaller rock falls, from hundreds up to tens of thousands of cubic meters, is typically limited to the active talus slopes beneath the cliffs. The floor of Yosemite Valley, however, preserves at least seven extremely large rock fall deposits, here termed rock avalanches, up to several million cubic meters in volume. These deposits extend far beyond the base of active talus slopes onto the valley floor, and have occurred since the retreat of Last Glacial Maximum glaciers circa 15-17 ka. Using airborne LiDAR data that resolves individual boulders, we mapped the rock avalanche deposits in the field and in ArcGIS. Minimum exposed volumes range from hundreds of thousands to several million cubic meters. To assess the frequency of rock avalanche occurrence, we employed cosmogenic beryllium-10 surface exposure dating of large (>4 cubic meters) boulders embedded within the deposits. These deposits are ideal targets for cosmogenic 10Be exposure dating, as they are instantaneous events that excavate deep-seated quartz-rich granitic rocks, and once deposited, are essentially immune to post-depositional erosion or modification. Mean exposure ages indicate that failures occurred at 1.0, 1.8, 2.3, 3.7, 4.4, 6.4, and 11.6 ka. At least three of the deposits appear to represent two or more failures, separated in time by hundreds to thousands of years. Synchronous rock avalanches (within the uncertainty of the exposure ages (<200 yrs)) at different locations within the valley appear to have occurred at 3.7 ka, and possibly at 2.3 ka, suggesting possible coseismic triggering. Age correlations from paleoseismic work tentatively identify large earthquakes originating from the eastern Sierra Nevada or western Nevada as possible triggers for at least half of the rock avalanches. These unique and robust age data provide key information for accurately mapping rock avalanches in Yosemite Valley and for quantifying their recurrence intervals.

Thompson, J. A.; Stock, G. M.; Rood, D.; Frankel, K. L.

2013-12-01

7

Paleoseismic event dating and the conditional probability of large earthquakes on the southern San Andreas fault, California  

USGS Publications Warehouse

We introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the Wrightwood and Pallett Creek sites on the southern San Andreas fault. We illustrate how stratigraphic ordering, sedimentological, and historical data can be used quantitatively in the process of estimating earthquake ages. Calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation. The method does not eliminate subjective judgements in event dating, but it does provide a means of systematically and objectively approaching the dating process. Date distributions for the most recent 14 events at Wrightwood are based on sample and contextual evidence in Fumal et al. (2002) and site context and slip history in Weldon et al. (2002). Pallett Creek event and dating descriptions are from published sources. For the five most recent events at Wrightwood, our results are consistent with previously published estimates, with generally comparable or narrower uncertainties. For Pallett Creek, our earthquake date estimates generally overlap with previous results but typically have broader uncertainties. Some event date estimates are very sensitive to details of data interpretation. The historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data. Radiocarbon ages, peat accumulation rates, and historical constraints at Pallett Creek for event X yield a date estimate in the earliest 1800s and preclude a date in the late 1600s. This event is almost certainly the historical 1812 earthquake, as previously concluded by Sieh et al. (1989). This earthquake also produced ground deformation at Wrightwood. All events at Pallett Creek, except for event T, about A.D. 1360, and possibly event I, about A.D. 960, have corresponding events at Wrightwood with some overlap in age ranges. Event T falls during a period of low sedimentation at Wrightwood when conditions were not favorable for recording earthquake evidence. Previously proposed correlations of Pallett Creek X with Wrightwood W3 in the 1690s and Pallett Creek event V with W5 around 1480 (Fumal et al., 1993) appear unlikely after our dating reevaluation. Apparent internal inconsistencies among event, layer, and dating relationships around events R and V identify them as candidates for further investigation at the site. Conditional probabilities of earthquake recurrence were estimated using Poisson, lognormal, and empirical models. The presence of 12 or 13 events at Wrightwood during the same interval that 10 events are reported at Pallett Creek is reflected in mean recurrence intervals of 105 and 135 years, respectively. Average Poisson model 30-year conditional probabilities are about 20% at Pallett Creek and 25% at Wrightwood. The lognormal model conditional probabilities are somewhat higher, about 25% for Pallett Creek and 34% for Wrightwood. Lognormal variance ??ln estimates of 0.76 and 0.70, respectively, imply only weak time predictability. Conditional probabilities of 29% and 46%, respectively, were estimated for an empirical distribution derived from the data alone. Conditional probability uncertainties are dominated by the brevity of the event series; dating uncertainty contributes only secondarily. Wrightwood and Pallett Creek event chronologies both suggest variations in recurrence interval with time, hinting that some form of recurrence rate modulation may be at work, but formal testing shows that neither series is more ordered than might be produced by a Poisson process.

Biasi, G. P.; Weldon, II. , R. J.; Fumal, T. E.; Seitz, G. G.

2002-01-01

8

Historic Earthquakes in Southern California  

NSDL National Science Digital Library

This page contains a map of southern California with epicenters of earthquakes shown as circles of different sizes and colors. The size and color of each earthquake symbol corresponds to its magnitude, as indicated by a scale on the map. Clicking on an epicenter takes the user to a page of information about that earthquake. Earthquakes dating back to 1812 are shown. Also available on this page are links to fault maps, earthquake animations, and other indexes of seismological information.

2011-04-06

9

Stress triggering and earthquake probability estimates  

Microsoft Academic Search

Stress triggering and fault interaction concepts are beginning to be incorporated into quantitative earthquake probability estimates. However, the current methods are limited in their range of compatible earthquake nucleation models. I introduce a new general method for translating stress changes into earthquake probability changes, which can potentially be used with any physical fault model. Given the large uncertainties in earthquake

Jeanne L. Hardebeck

2004-01-01

10

The Parkfield, California, Earthquake Experiment  

NSDL National Science Digital Library

This report decribes research being carried out in Parkfield, California whose purpose is to better understand the physics of earthquakes: what actually happens on the fault and in the surrounding region before, during and after an earthquake. Ultimately, scientists hope to better understand the earthquake process and, if possible, to provide a scientific basis for earthquake prediction. Topics include the scientific background for the experiment, including the tectonic setting at Parkfield, historical earthquake activity on this section of the San Andreas fault, the monitoring and data collecting activities currently being carried out, and plans for future research. Data are also available to view in real time and to download.

11

Next-Day Earthquake Forecasts for California  

NASA Astrophysics Data System (ADS)

We implemented a daily forecast of m > 4 earthquakes for California in the format suitable for testing in community-based earthquake predictability experiments: Regional Earthquake Likelihood Models (RELM) and the Collaboratory for the Study of Earthquake Predictability (CSEP). The forecast is based on near-real time earthquake reports from the ANSS catalog above magnitude 2 and will be available online. The model used to generate the forecasts is based on the Epidemic-Type Earthquake Sequence (ETES) model, a stochastic model of clustered and triggered seismicity. Our particular implementation is based on the earlier work of Helmstetter et al. (2006, 2007), but we extended the forecast to all of Cali-fornia, use more data to calibrate the model and its parameters, and made some modifications. Our forecasts will compete against the Short-Term Earthquake Probabilities (STEP) forecasts of Gersten-berger et al. (2005) and other models in the next-day testing class of the CSEP experiment in California. We illustrate our forecasts with examples and discuss preliminary results.

Werner, M. J.; Jackson, D. D.; Kagan, Y. Y.

2008-12-01

12

Southern California Earthquake Center (SCEC)  

NSDL National Science Digital Library

The Southern California Earthquake Center (SCEC), a National Science Foundation (NSF) Science and Technology Center, aims to reduce earthquake hazard by defining the locations of future earthquakes, calculating expected ground motions, and conveying this information to the general public. The SCECùs homepage contains access to research and data, including links to databases for strong motion and seismograms, and a searchable and sortable bibliographic database of publications. Also available are GPS data and a network of GPS stations. A link to the Earthquake Information Network provides a searchable list of up-to-date internet earthquakes resources. Note, in order to access the SCEC Publications Database, a username and password are required. Use your own name for the username, and enter -webview as the password. SCEC is a first rate resource for earthquake engineers.

13

How Do Scientists Determine Earthquake Probabilities?  

NSDL National Science Digital Library

This provides many links to articles, graphics, scientific papers and podcasts to help students understand how scientists determine probabilities for earthquake occurrences. Topics include the locations of faults and how much they need to move in order to release the strain that accumulates; the study of past earthquakes on each fault to predict the size of possible earthquakes that could occur in the future; and using information on how long it's been since the last earthquake to estimate the probability that an earthquake will occur in the next few years. Links to additional information are embedded in the text.

14

Southern California Earthquake Data Center Home  

NSDL National Science Digital Library

The Southern California Eathquake Center features a variety of links to information on recent and historic earthquakes and faults, as well as seismological data from analog and digital stations and instruments. Materials include an interactive map of southern California showing recent earthquake activity (last hour, last day, last week), a searchable catalog of data on earthquakes from 1932-present, an interactive map of faults in southern California, and interactive map showing historic earthquakes for the region as far back as 1812.

2010-06-18

15

Southern California Earthquake Center (SCEC) Home Page  

NSDL National Science Digital Library

This is the home page of the Southern California Earthquake Center (SCEC), a consortium of universities and research institutions dedicated to gathering information about earthquakes in Southern California, integrate that knowledge into a comprehensive and predictive understanding of earthquake phenomena, and communicate this understanding to end-users and the general public in order to increase earthquake awareness, reduce economic losses, and save lives. News of recent earthquake research, online resources and educational information is available here.

16

USGS Earthquake Hazards Program-Northern California: Special Features  

NSDL National Science Digital Library

This page describes current special features on seismology, faults, and earthquakes. The current articles covered the topics shake maps for Northern and Southern California, Real-time display of seismograms for Northern California, an Earthquake probability study for the San Francisco Bay area, Landscape, seascape and faults of the San Francisco Bay area, and the Scientific expedition for the earthquake in Turkey 1999. Visitors who feel significant earthquakes in this area are invited to participate in an internet survey of ground shaking and damage. Visitors may also view previous features.

17

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

USGS Publications Warehouse

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.

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

18

Northern California Earthquake Data Center  

NSDL National Science Digital Library

A project between the University of California Berkeley Seismological Laboratory and the United State Geological Survey, the Northern California Earthquake Data Center (NCEDC) "is a long-term archive and distribution center for seismological and geodetic data for Northern and Central California." Educators and students can examine recent seismograms from the Berkeley Digital Seismic Network. Researchers will benefit from the site's enormous amount of data collections including BARD; a system of 67 constantly operating Global Positioning System receivers in Northern California. By reading the annual reports, educators will also learn about the center's many outreach activities from talks and lab tours to the production of classroom resources for kindergarten through twelfth grade teachers. This site is also reviewed in the October 17, 2003 NSDL Physical Sciences Report.

19

Northern California Earthquake Data Center (NCEDC)  

NSDL National Science Digital Library

This is the home page of the Northern California Earthquake Data Center (NCEDC) which is a joint project of the University of California Berkeley Seismological Laboratory and the U. S. Geological Survey at Menlo Park. The NCEDC is an archive for seismological and geodetic data for Northern and Central California. Accessible through this page are news items, recent earthquake information, links to earthquake catalogs, seismic waveform data sets, and Global Positioning System information. Most data sets are accessible for downloading via ftp.

20

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

PubMed Central

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.

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

2011-01-01

21

Revisiting the 1872 Owens Valley, California, Earthquake  

Microsoft Academic Search

The 26 March 1872 Owens Valley earthquake is among the largest his- torical earthquakes in California. The felt area and maximum fault displacements have long been regarded as comparable to, if not greater than, those of the great San Andreas fault earthquakes of 1857 and 1906, but mapped surface ruptures of the latter two events were 2-3 times longer than

S. E. Hough; Kate Hutton

2008-01-01

22

Earthquake probabilities: theoretical assessments and reality  

NASA Astrophysics Data System (ADS)

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). How many days are needed to distinguish 0 from the average probability of 0.000027? Is it theoretically admissible to apply average when seismic events, including mega-earthquakes, are evidently clustered in time and space displaying behaviors that are far from independent? Is it possible to ignore possibly fractal, definitely, far from uniform distribution in space when mapping seismic probability density away from the empirical earthquake locus embedded onto the boundaries of the lithosphere blocks? These are simple questions to those who advocate the existing probabilistic products for seismic hazard assessment and forecasting. Fortunately, the situation is not hopeless due to deterministic pattern recognition approaches applied to available geological evidences, specifically, when intending to predict predictable, but not the exact size, site, date, and probability of a target event. Understanding by modeling the complexity of non-linear dynamics of hierarchically organized systems of blocks-and-faults has led already to methodologies of neo-deterministic seismic hazard analysis and intermediate-term middle- to narrow-range earthquake prediction algorithms tested in real-time applications over the last decades.

Kossobokov, V. G.

2013-12-01

23

Real-time forecasts of tomorrow's earthquakes in California  

USGS Publications Warehouse

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.

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

2005-01-01

24

Differences between spontaneous and triggered earthquakes: Their influences on foreshock probabilities  

Microsoft Academic Search

In this study we investigate the foreshock probabilities calculated from earthquake catalogs from Japan, southern California, and New Zealand. Unlike conventional studies on foreshocks, we use a probability-based declustering method to separate each catalog into stochastic versions of family trees, such that each event is classified as either having been triggered by a preceding event or being a spontaneous event.

Jiancang Zhuang; Annemarie Christophersen; Martha K. Savage; David Vere-Jones; Yosihiko Ogata; David D. Jackson

2008-01-01

25

Estimation of Future Earthquake Losses in California  

NASA Astrophysics Data System (ADS)

Recent developments in earthquake hazards and damage modeling, computing, and data management and processing, have made it possible to develop estimates of the levels of damage from earthquakes that may be expected in the future in California. These developments have been mostly published in the open literature, and provide an opportunity to estimate the levels of earthquake damage Californians can expect to suffer during the next several decades. Within the past 30 years, earthquake losses have increased dramatically, mostly because our exposure to earthquake hazards has increased. All but four of the recent damaging earthquakes have occurred distant from California's major population centers. Two, the Loma Prieta earthquake and the San Fernando earthquake, occurred on the edges of major populated areas. Loma Prieta caused significant damage in the nearby Santa Cruz and in the more distant, heavily populated, San Francisco Bay area. The 1971 San Fernando earthquake had an epicenter in the lightly populated San Gabriel Mountains, but caused slightly over 2 billion dollars in damage in the Los Angeles area. As urban areas continue to expand, the population and infrastructure at risk increases. When earthquakes occur closer to populated areas, damage is more significant. The relatively minor Whittier Narrows earthquake of 1987 caused over 500 million dollars in damage because it occurred in the Los Angeles metropolitan area, not at its fringes. The Northridge earthquake had fault rupture directly beneath the San Fernando Valley, and caused about 46 billion dollars in damage. This vast increase in damage from the San Fernando earthquake reflected both the location of the earthquake directly beneath the populated area and the 23 years of continued development and resulting greater exposure to potential damage. We have calculated losses from potential future earthquake, both as scenarios of potential earthquakes and as annualized losses considering all the potential earthquake sources included in the national seismic hazard maps. Initial results give an expected annual loss in California of 2.2 billion dollars. This estimate is based on the 2002 CGS-USGS ground motion data and the 1997 NEHRP soil amplification factors. It should be pointed out that these results are very sensitive to the soil amplification factors used in the analysis. Using amplification factors from Boore, Joyner and Fumal, 1997, which had been used in previous CGS loss estimation studies, the state wide estimated annual loss becomes roughly 3.3 billion dollars. The estimates presented in this study include only structural and non-structural damage to buildings. Experience with real earthquakes suggest that when associated losses, such as losses to contents, inventory and income, are included, the total expected annual would be considerably larger.

Rowshandel, B.; Wills, C. J.; Cao, T.; Reichle, M.; Branum, D.

2003-12-01

26

Revisiting the 1872 Owens Valley, California, Earthquake  

USGS Publications Warehouse

The 26 March 1872 Owens Valley earthquake is among the largest historical earthquakes in California. The felt area and maximum fault displacements have long been regarded as comparable to, if not greater than, those of the great San Andreas fault earthquakes of 1857 and 1906, but mapped surface ruptures of the latter two events were 2-3 times longer than that inferred for the 1872 rupture. The preferred magnitude estimate of the Owens Valley earthquake has thus been 7.4, based largely on the geological evidence. Reinterpreting macroseismic accounts of the Owens Valley earthquake, we infer generally lower intensity values than those estimated in earlier studies. Nonetheless, as recognized in the early twentieth century, the effects of this earthquake were still generally more dramatic at regional distances than the macroseismic effects from the 1906 earthquake, with light damage to masonry buildings at (nearest-fault) distances as large as 400 km. Macroseismic observations thus suggest a magnitude greater than that of the 1906 San Francisco earthquake, which appears to be at odds with geological observations. However, while the mapped rupture length of the Owens Valley earthquake is relatively low, the average slip was high. The surface rupture was also complex and extended over multiple fault segments. It was first mapped in detail over a century after the earthquake occurred, and recent evidence suggests it might have been longer than earlier studies indicated. Our preferred magnitude estimate is Mw 7.8-7.9, values that we show are consistent with the geological observations. The results of our study suggest that either the Owens Valley earthquake was larger than the 1906 San Francisco earthquake or that, by virtue of source properties and/or propagation effects, it produced systematically higher ground motions at regional distances. The latter possibility implies that some large earthquakes in California will generate significantly larger ground motions than San Andreas fault events of comparable magnitude.

Hough, S. E.; Hutton, K.

2008-01-01

27

Combining earthquake forecast models using differential probability gains  

NASA Astrophysics Data System (ADS)

We propose a method to combine earthquake forecast models. The general procedure is to successively create new generations of a rate-based model by injecting into the current generation the additional knowledge carried by other input models. For a single iteration, we use the differential probability gain calculated in the Molchan diagram that evaluates the performance of the input model with respect to the current generation of the rate-based model. Then, at each point in space and time, the new rate is the product of the current rate times the local differential probability gain. The main advantage of our combining method is to produce high expected event rates using all types of numerical forecast models. The only restriction is that the input model has to bring additional amount of information with respect to the current generation of the alarm-based model. Here, we apply this method to EAST and EEPAS, two forecast models currently tested in the California testing center of the Collaboratory for the Study of Earthquake Predictability (CSEP). During the testing period from July 2009 to December 2011, the combined model shows better performance than the input model (EAST) and the initial rate-based model (EEPAS), both in terms of Molchan diagrams and likelihood tests. We show that a large number of events occurs in a limited space of higher forecasted rates. Most importantly, these rates are significantly higher than a linear combination of the two forecast models.

Shebalin, P.; Narteau, C.; Zechar, J.; Holschneider, M.

2012-04-01

28

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

USGS Publications Warehouse

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, ?, and the aperiodicity of the mean, ? (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 ? = 0.5. For this value of ?, the hazard function (instantaneous failure rate of survivors) exceeds the mean rate for times > ??2, and is ~ ~ 2 ? ? for all times > ?. 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.

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

1999-01-01

29

Infrasonic observations of the Northridge, California, earthquake  

SciTech Connect

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.

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

1994-09-01

30

The 1984 Morgan Hill, California, earthquake  

USGS Publications Warehouse

The Morgan Hill, California, earthquake (magnitude 6.1) of 24 April 1984 ruptured a 30-kilometer-long segment of the Calaveras fault zone to the east of San Jose. Although it was recognized in 1980 that an earthquake of magnitude 6 occurred on this segment in 1911 and that a repeat of this event might reasonably be expected, no short-term precursors were noted and so the time of the 1984 earthquake was not predicted. Unilateral rupture propagation toward the south-southeast and an energetic late source of seismic radiation located near the southeast end of the rupture zone contributed to the highly focused pattern of strong motion, including an exceptionally large horizontal acceleration of 1.29g at a site on a dam abutment near the southeast end of the rupture zone.

Bakun, W. H.; Clark, M. M.; Cockerham, R. S.; Ellsworth, W. L.; Lindh, A. G.; Prescott, W. H.; Shakal, A. F.; Spudich, P.

1984-01-01

31

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

32

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

USGS Publications Warehouse

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 region—an innovation over previous studies of the SFBR that considered only a small number of potential earthquakes of fixed magnitude.

Working Group on California Earthquake Probabilities

1999-01-01

33

Selection of minimum earthquake intensity in calculating pipe failure probabilities  

SciTech Connect

In a piping reliability analysis, it is sometimes necessary to specify a minimum ground motion intensity, usually the peak acceleration, below which the ground motions are not considered as earthquakes and, hence, are neglected. The calculated probability of failure of a piping system is dependent on this selected minimum earthquake intensity chosen for the analysis. A study was conducted to determine the effects of the minimum earthquake intensity on the probability of pipe failure. The results indicated that the probability of failure of the piping system is not very sensitive to the variations of the selected minimum peak ground acceleration. However, it does have significant effects on various scenarios that make up the system failure.

Lo, T.Y.

1985-01-01

34

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

USGS Publications Warehouse

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.

Michael, Andrew J.

2012-01-01

35

Earthquake preparedness levels amongst youth and adults in Oakland, California  

NASA Astrophysics Data System (ADS)

The San Francisco Bay Area has not experienced a large earthquake since 1989. However research shows that the Hayward fault is overdue for a tremor, based on paleo-seismic research. To analyze the level of earthquake preparedness in the Oakland area (close to the Hayward fault), we surveyed over 150 people to assess their understanding of earthquakes. Our research evaluates whether increased earthquake knowledge impacts people's preparedness and concern toward earthquake events. Data was collected using smart-phone technology and survey software in four sites across Oakland including; North Oakland, Downtown, East Oakland, and a summer school program in East Oakland, which has youth from throughout the city. Preliminary studies show that over 60% of interviewees have sufficient earthquake knowledge, but that over half of all interviewees are not prepared for a seismic event. Our study shows that in Oakland, California earthquake preparedness levels vary, which could mean we need to develop more ways to disseminate information on earthquake preparedness.

Burris, M.; Arroyo-Ruiz, D.; Crockett, C.; Dixon, G.; Jones, M.; Lei, P.; Phillips, B.; Romero, D.; Scott, M.; Spears, D.; Tate, L.; Whitlock, J.; Diaz, J.; Chagolla, R.

2011-12-01

36

High-Resolution Long-Term Earthquake Forecasts for California and Italy  

NASA Astrophysics Data System (ADS)

We present five-year and ten-year estimates of m > 5 earthquake probabilities in California and Italy. The forecasts will be tested independently and prospectively in the global Collaboratory for the Study of Earthquake Predictability (CSEP). Our long-term forecasts are calculated from smoothing declustered seismicity and assuming a tapered Gutenberg-Richter magnitude distribution. We carefully account for catalog completeness issues and optimize the amount of smoothing in retrospective tests. Confirming a previous finding, retrospective tests suggest that including small m > 2 earthquakes significantly improves the spatial forecast of m > 5 earthquakes. In contrast to other, relatively smooth models in CSEP, our forecasts have high spatial resolution - a feature apparently responsible for the model's current lead in the 19-model, five-year RELM experiment in California. We compare the Californian and Italian forecasts and evaluate the performance of the forecasts using the likelihood score.

Werner, M. J.; Helmstetter, A.; Jackson, D. D.; Kagan, Y. Y.

2009-04-01

37

Robust Distributed Earthquake Monitoring with CISN software in Northern California  

Microsoft Academic Search

Realtime earthquake monitoring in Northern California passed a milestone this June, when the original joint notification system operated by UC Berkeley's Seismological Laboratory and the USGS in Menlo Park was replaced by the CISN Earthquake Monitoring system. The database plays an integral part in this system, providing coordination for processing and publishing event information, as well as being the repository

D. S. Neuhauser; P. N. Lombard; L. D. Dietz; S. Zuzlewski; J. H. Luetgert; W. Kohler; M. Hellweg; D. H. Oppenheimer; B. A. Romanowicz

2009-01-01

38

Major improvements in progress for Southern California Earthquake Monitoring  

Microsoft Academic Search

Major improvements in seismic and strong-motion monitoring networks are being implemented in southern California to better meet the needs of emergency response personnel, structural engineers, and the research community in promoting earthquake hazard reduction. Known as the TriNet project, the improvements are being coordinated by the California Institute of Technology (Caltech), the U.S. Geological Survey (USGS), and the California Division

Jim Mori; Hiroo Kanamori; James Davis; Egill Hauksson; Robert Clayton; Thomas Heaton; Lucile Jones; Anthony Shakal; Ron Porcella

1998-01-01

39

Loma Prieta earthquake, October 17, 1989, Santa Cruz County, California  

SciTech Connect

On Tuesday, October 17, 1989 at 5:04 p.m. Pacific Daylight Time, a magnitude 7.1 earthquake occurred on the San Andreas fault 10 miles northeast of Santa Cruz. This earthquake was the largest earthquake to occur in the San Francisco Bay area since 1906, and the largest anywhere in California since 1952. The earthquake was responsible for 67 deaths and about 7 billion dollars worth of damage, making it the biggest dollar loss natural disaster in United States history. This article describes the seismological features of the earthquake, and briefly outlines a number of other geologic observations made during study of the earthquake, its aftershocks, and its effects. Much of the information in this article was provided by the U.S. Geological Survey (USGS).

McNutt, S.

1990-01-01

40

The Loma Prieta, California, Earthquake of October 17, 1989: Earthquake Occurrence  

USGS Publications Warehouse

Professional Paper 1550 seeks to understand the M6.9 Loma Prieta earthquake itself. It examines how the fault that generated the earthquake ruptured, searches for and evaluates precursors that may have indicated an earthquake was coming, reviews forecasts of the earthquake, and describes the geology of the earthquake area and the crustal forces that affect this geology. Some significant findings were: * Slip during the earthquake occurred on 35 km of fault at depths ranging from 7 to 20 km. Maximum slip was approximately 2.3 m. The earthquake may not have released all of the strain stored in rocks next to the fault and indicates a potential for another damaging earthquake in the Santa Cruz Mountains in the near future may still exist. * The earthquake involved a large amount of uplift on a dipping fault plane. Pre-earthquake conventional wisdom was that large earthquakes in the Bay area occurred as horizontal displacements on predominantly vertical faults. * The fault segment that ruptured approximately coincided with a fault segment identified in 1988 as having a 30% probability of generating a M7 earthquake in the next 30 years. This was one of more than 20 relevant earthquake forecasts made in the 83 years before the earthquake. * Calculations show that the Loma Prieta earthquake changed stresses on nearby faults in the Bay area. In particular, the earthquake reduced stresses on the Hayward Fault which decreased the frequency of small earthquakes on it. * Geological and geophysical mapping indicate that, although the San Andreas Fault can be mapped as a through going fault in the epicentral region, the southwest dipping Loma Prieta rupture surface is a separate fault strand and one of several along this part of the San Andreas that may be capable of generating earthquakes.

Coordinated by Bakun, William H.; Prescott, William H.

1993-01-01

41

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

NASA Astrophysics Data System (ADS)

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.

Hough, Susan E.

2008-07-01

42

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

USGS Publications Warehouse

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.

Mori, J.; Abercrombie, R. E.

1997-01-01

43

Are spontaneous earthquakes stationary in California?  

Microsoft Academic Search

Aftershocks and some main shocks are triggered, with timing controlled by preceding events. The remaining spontaneous earthquakes presumably respond to tectonic stresses. We consider whether triggered events can be reliably identified, whether the rest are stationary, and whether external phenomena control them. To all three questions, some studies of earthquake physics and hazard assume answers. Many suggest that stress changes

Qi Wang; David. D. Jackson; Jiancang Zhuang

2010-01-01

44

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

Microsoft Academic Search

Moderate-sized earthquakes (Richter magnitude ML 51\\/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.

W. H. Bakun; T. V. McEvilly

1979-01-01

45

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

USGS Publications Warehouse

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.

Edited by Simpson, Robert W.

1994-01-01

46

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

USGS Publications Warehouse

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.

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

1996-01-01

47

Long Period Earthquakes Beneath California's Young and Restless Volcanoes  

NASA Astrophysics Data System (ADS)

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 (~320 events), and Long Valley Caldera (~40 events). LP earthquakes are notably absent under Mount Shasta. With the exception of Long Valley Caldera where LP earthquakes occur at depths of ?5 km, hypocenters are generally between 15-25 km. The rates of LP occurrence over the last decade have been relatively steady within the study areas, except at Mammoth Mountain, where years of gradually declining LP activity abruptly increased after a swarm of unusually deep (20 km) VT earthquakes in October 2012. Epicenter locations relative to the sites of most recent volcanism vary across volcanic centers, but most LP earthquakes fall within 10 km of young vents. Source models for LP earthquakes often involve the resonance of fluid-filled cracks or nonlinear flow of fluids along irregular cracks (reviewed in Chouet and Matoza, 2013, JVGR). At mid-crustal depths the relevant fluids are likely to be low-viscosity basaltic melt and/or exsolved CO2-rich volatiles (Lassen, Clear Lake, Mammoth Mountain). In the shallow crust, however, hydrothermal waters/gases are likely involved in the generation of LP seismicity (Long Valley Caldera).

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

2013-12-01

48

Automatic 3D Moment tensor inversions for southern California earthquakes  

NASA Astrophysics Data System (ADS)

We present a new source mechanism (moment-tensor and depth) catalog for about 150 recent southern California earthquakes with Mw ? 3.5. We carefully select the initial solutions from a few available earthquake catalogs as well as our own preliminary 3D moment tensor inversion results. We pick useful data windows by assessing the quality of fits between the data and synthetics using an automatic windowing package FLEXWIN (Maggi et al 2008). We compute the source Fréchet derivatives of moment-tensor elements and depth for a recent 3D southern California velocity model inverted based upon finite-frequency event kernels calculated by the adjoint methods and a nonlinear conjugate gradient technique with subspace preconditioning (Tape et al 2008). We then invert for the source mechanisms and event depths based upon the techniques introduced by Liu et al 2005. We assess the quality of this new catalog, as well as the other existing ones, by computing the 3D synthetics for the updated 3D southern California model. We also plan to implement the moment-tensor inversion methods to automatically determine the source mechanisms for earthquakes with Mw ? 3.5 in southern California.

Liu, Q.; Tape, C.; Friberg, P.; Tromp, J.

2008-12-01

49

Deterministic Earthquake Hazard Assessment by Public Agencies in California  

NASA Astrophysics Data System (ADS)

Even in its short recorded history, California has experienced a number of damaging earthquakes that have resulted in new codes and other legislation for public safety. In particular, the 1971 San Fernando earthquake produced some of the most lasting results such as the Hospital Safety Act, the Strong Motion Instrumentation Program, the Alquist-Priolo Special Studies Zone Act, and the California Department of Transportation (Caltrans') fault-based deterministic seismic hazard (DSH) map. The latter product provides values for earthquake ground motions based on Maximum Credible Earthquakes (MCEs), defined as the largest earthquakes that can reasonably be expected on faults in the current tectonic regime. For surface fault rupture displacement hazards, detailed study of the same faults apply. Originally, hospital, dam, and other critical facilities used seismic design criteria based on deterministic seismic hazard analyses (DSHA). However, probabilistic methods grew and took hold by introducing earthquake design criteria based on time factors and quantifying "uncertainties", by procedures such as logic trees. These probabilistic seismic hazard analyses (PSHA) ignored the DSH approach. Some agencies were influenced to adopt only the PSHA method. However, deficiencies in the PSHA method are becoming recognized, and the use of the method is now becoming a focus of strong debate. Caltrans is in the process of producing the fourth edition of its DSH map. The reason for preferring the DSH method is that Caltrans believes it is more realistic than the probabilistic method for assessing earthquake hazards that may affect critical facilities, and is the best available method for insuring public safety. Its time-invariant values help to produce robust design criteria that are soundly based on physical evidence. And it is the method for which there is the least opportunity for unwelcome surprises.

Mualchin, L.

2005-12-01

50

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

USGS Publications Warehouse

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.

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

2004-01-01

51

New Earthquake Catalog for California, 1800 - 2006, Magnitude 4.7 and Above  

Microsoft Academic Search

To construct and test hypotheses of earthquake occurrence in California we are compiling a new catalog of California earthquakes, magnitude 4.7 and larger, from 1800 to 2006. Data come from other previously published or online catalogs, of which more than twenty have been identified. The catalog will cover all of California and will include aftershocks. All events will be labeled

Q. Wang; D. D. Jackson; Y. Y. Kagan

2006-01-01

52

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

NASA Astrophysics Data System (ADS)

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. The usable and realistic ground motion maps for urban areas are generated: - either from the assumption of a "reference earthquake" - or directly, showing values of macroseimic intensity generated by a damaging, real earthquake. In the study, applying deterministic approach, earthquake scenario in macroseismic intensity ("model" earthquake scenario) for the city of Sofia is generated. The deterministic "model" intensity scenario based on assumption of a "reference earthquake" is compared with a scenario based on observed macroseimic effects caused by the damaging 2012 earthquake (MW5.6). The difference between observed (Io) and predicted (Ip) intensities values is analyzed.

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

2014-05-01

53

MOHO ORIENTATION BENEATH CENTRAL CALIFORNIA FROM REGIONAL EARTHQUAKE TRAVEL TIMES.  

USGS Publications Warehouse

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.

Oppenheimer, David, H.; Eaton, Jerry, P.

1984-01-01

54

Estimates of long-term probabilities for future great earthquakes in the Aleutians  

Microsoft Academic Search

We compute probabilities for future great earthquakes in the Aleutian arc. Probability distributions are fitted to recurrence periods of great Aleutian evens (M\\/sub w\\/> or =7.8) since 1788. Given a probability distribution and data of the last grat earthquake in each arc segment, time-dependent conditional probabilities are determined for future periods of interest. We obtain for the next two decades

Klaus H. Jacob

1984-01-01

55

Nonlinear site response in medium magnitude earthquakes near Parkfield, California  

USGS Publications Warehouse

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).

Rubinstein, Justin L.

2011-01-01

56

Combining earthquakes and GPS data to estimate the probability of future earthquakes with magnitude Mw ? 6.0  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

57

Estimates of long-term probabilities for future great earthquakes in the Aleutians  

SciTech Connect

We compute probabilities for future great earthquakes in the Aleutian arc. Probability distributions are fitted to recurrence periods of great Aleutian evens (M/sub w/> or =7.8) since 1788. Given a probability distribution and data of the last grat earthquake in each arc segment, time-dependent conditional probabilities are determined for future periods of interest. We obtain for the next two decades high probabilities (99 to 30%) for great earthquakes in the Shumagin, Yakataga, Unalaska and Kommandorski seismic gaps. These probabilities are higher than for any other assessed region of the U.S. believed to be capable of great earthquakes. Low probabilities (17 to 9%) are found for segments that ruptured most recently in 1965, 1964 and 1957. Recurrence periods for great earthquakes measure on average about 80 years but vary substantially. Whether recurrence periods for great Aleutian earthquakes follow a normal, log-normal or any other probability distribution is not resolved because in most arc segments the known seismic record embraces at best one or two recurrences. The resulting uncertainty affects the magnitude of estimated probabilities, especially in seismic gaps that have not ruptured for a long time. In some instances a normal distribution yields a three times higher probability than the corresponding log-normal distribution.

Jacob, K.H.

1984-04-01

58

Earthquake Probability Map for San Francisco Bay Area (title provided or enhanced by cataloger)  

NSDL National Science Digital Library

This map displays earthquake probabilities for several faults in the San Francisco Bay Area. The probability values are for the occurrence of one or more major (magnitude greater than or equal to 6.7) earthquakes in the San Francisco Bay Region during the next thirty years. Each fault on the map is color-coded to indicate the relative probability, and numerical values are displayed in boxes. The site includes links to a fact sheet and full technical report that summarize the findings, indicating a 62 percent total probability of a major earthquake over the next thirty years. There are also links to planning scenario maps, a study on potential losses, a webcast on earthquake probability, and to a set of downloadable graphics (TIF or PDF files) used in the probability study.

59

Cascadia Earthquake and Tsunami Scenario for California's North Coast  

NASA Astrophysics Data System (ADS)

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 from 51 to 73 percent and knowing what the Cascadia subduction zone is from 16 to 42 percent. It is not surprising that the earlier surveys showed increases as several strong earthquakes occurred in the area between 1992 and 1995 and there was considerable media attention. But the 2001 survey, seven years after the last widely felt event, still shows significant increases in almost all preparedness indicators. The 1995 CDMG scenario was not the sole reason for the increased interest in earthquake and tsunami hazards in the area, but the scenario gave government recognition to an event that was previously only considered seriously in the scientific community and has acted as a catalyst for mitigation and planning efforts.

Dengler, L.

2006-12-01

60

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

USGS Publications Warehouse

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.

Edited by Keefer, David K.

1998-01-01

61

Earthquake!  

ERIC Educational Resources Information Center

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)

Hernandez, Hildo

2000-01-01

62

Short- and Long-Term Earthquake Forecasts for California and Nevada  

NASA Astrophysics Data System (ADS)

We present estimates of future earthquake rate density (probability per unit area, time, and magnitude) on a 0.1-degree grid for a region including California and Nevada, based only on data from past earthquakes. Our long-term forecast is not explicitly time-dependent, but it can be updated at any time to incorporate information from recent earthquakes. The present version, founded on several decades worth of data, is suitable for testing without updating over a five-year period as part of the experiment conducted by the Collaboratory for Study of Earthquake Predictability (CSEP). The short-term forecast is meant to be updated daily and tested against similar models by CSEP. The short-term forecast includes a fraction of our long-term one plus time-dependent contributions from all previous earthquakes. Those contributions decrease with time according to the Omori law: proportional to the reciprocal of the elapsed time. Both forecasts estimate rate density using a radially symmetric spatial smoothing kernel decreasing approximately as the reciprocal of the square of epicentral distance, weighted according to the magnitude of each past earthquake. We made two versions of both the long- and short-term forecasts, based on the Advanced National Seismic System (ANSS) and Preliminary Determinations of Epicenters (PDE) catalogs, respectively. The two versions are quite consistent, but for testing purposes we prefer those based on the ANSS catalog since it covers a longer time interval, is complete to a lower magnitude threshold and has more precise locations. Both forecasts apply to shallow earthquakes only (depth 25 km or less) and assume a tapered Gutenberg-Richter magnitude distribution extending to a lower threshold of 4.0.

Kagan, Y. Y.; Jackson, D. D.

2010-06-01

63

Southern California Earthquake Center Geologic Vertical Motion Database  

NASA Astrophysics Data System (ADS)

The Southern California Earthquake Center Geologic Vertical Motion Database (VMDB) integrates disparate sources of geologic uplift and subsidence data at 104- to 106-year time scales into a single resource for investigations of crustal deformation in southern California. Over 1800 vertical deformation rate data points in southern California and northern Baja California populate the database. Four mature data sets are now represented: marine terraces, incised river terraces, thermochronologic ages, and stratigraphic surfaces. An innovative architecture and interface of the VMDB exposes distinct data sets and reference frames, permitting user exploration of this complex data set and allowing user control over the assumptions applied to convert geologic and geochronologic information into absolute uplift rates. Online exploration and download tools are available through all common web browsers, allowing the distribution of vertical motion results as HTML tables, tab-delimited GIS-compatible text files, or via a map interface through the Google Maps™ web service. The VMDB represents a mature product for research of fault activity and elastic deformation of southern California.

Niemi, Nathan A.; Oskin, Michael; Rockwell, Thomas K.

2008-07-01

64

ERTS Applications in earthquake research and mineral exploration in California  

NASA Technical Reports Server (NTRS)

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.

Abdel-Gawad, M.; Silverstein, J.

1973-01-01

65

Earthquake epicenters and fault intersections in central and southern California  

NASA Technical Reports Server (NTRS)

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.

Abdel-Gawad, M. (principal investigator); Silverstein, J.

1972-01-01

66

Earthquake frequency statistics, and probabilistic seismic hazard in southern California and New Zealand  

NASA Astrophysics Data System (ADS)

Probabilistic Seismic Hazard Analysis (PSHA) is the subject of this dissertation. Chapters 1 to 4 address aspects of earthquake frequency statistics and fault mechanics, and investigate methods for evaluating PSH models. Chapter 5 incorporates the results of the earlier chapters to construct the first national PSH maps for New Zealand that consider both geological and seismological data. In Chapters 1, I examine whether the magnitude-frequency distributions for individual faults are described by the Gutenberg-Richter relationship log(n/yr)=a-bM (n/yr is the number of events per year of magnitude M), or the characteristic earthquake model, in which the recurrence rates of the largest earthquakes are greater than the rates predicted with the Gutenberg-Richter relationship. I find that the distributions are generally described by the characteristic earthquake model. In Chapter 2, I examine whether the discrepancy between the seismicity rates predicted from the Working Group on California Earthquake Probabilities PSH model for southern California and the historical seismicity rate is statistically significant, and find that it is not. In Chapter 3, I identify the factors that are responsible for the largest differences between recent PSH maps produced for southern California by different workers. They are; the proportion of predicted earthquakes that are distributed away from the mapped faults, the maximum magnitude defined for a fault, and whether geodetic data are used to predict earthquake rates. In Chapter 4, I contribute to the development of precarious rocks as a field criteria to test the predicted ground motions of PSH models, by examining whether or not the site conditions at precarious rocks are equivalent to the "engineering rock" site conditions assumed in the PSH models. I find that the site conditions are equivalent to "engineering rock" In Chapter 5, I undertake the first national PSHA of New Zealand that combines geologic and historical seismicity data. I identify a zone of high PSH that extends from the southwestern end of the country to the northeastern end, along the faults that accommodate most of the relative plate motion between the Australian and Pacific plates. Wellington city lies within this belt of high PSH.

Stirling, Mark Williamson

67

Spatial and Temporal Patterns of Regional Seismicity Preceding the 1992 Landers California Earthquake  

Microsoft Academic Search

We investigate regional seismicity patterns as a function of space, time and magnitude preceding the 1992 Landers California earthquake using both raw and declustered catalogs. In addition to the previously documented increase of intermediate earthquakes (and associated acceleration of seismic moment release), the occurrence of small earthquakes down to M=1.8 selected from the declustered catalog also accelerated before the Landers

Y. Chen; C. G. Sammis

2002-01-01

68

Comparison of Short-Term and Time-Independent Earthquake Forecast Models for Southern California  

Microsoft Academic Search

We have initially developed a time-independent forecast for southern California by smoothing the locations of magnitude 2 and larger earthquakes. We show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes. Our forecast outperforms other time-independent models (Kagan and Jackson, 1994; Frankel et al., 1997), mostly because it has higher spatial resolution. We have

Agnes Helmstetter; Yan Y. Kagan; David D. Jackson

2006-01-01

69

Full waveform earthquake location: Application to seismic streaks on the Calaveras Fault, California  

Microsoft Academic Search

We use a novel technique based upon source array analysis to locate three moderate earthquakes that occur at the edge of previously identified streaks of seismicity on the Calaveras Fault, California. Our method determines centroid locations for earthquakes, in addition to the hypocenters previously determined using first-break picks. Application of the method to smaller earthquakes indicates that the errors associated

Justin L. Rubinstein; Gregory C. Beroza

2007-01-01

70

Geometry and earthquake potential of the shoreline fault, central California  

USGS Publications Warehouse

The Shoreline fault is a vertical strike?slip fault running along the coastline near San Luis Obispo, California. Much is unknown about the Shoreline fault, including its slip rate and the details of its geometry. Here, I study the geometry of the Shoreline fault at seismogenic depth, as well as the adjacent section of the offshore Hosgri fault, using seismicity relocations and earthquake focal mechanisms. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm (Ouillon et al., 2008) is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty. The OADC results show that the Shoreline fault is a single continuous structure that connects to the Hosgri fault. Discontinuities smaller than about 1 km may be undetected, but would be too small to be barriers to earthquake rupture. The Hosgri fault dips steeply to the east, while the Shoreline fault is essentially vertical, so the Hosgri fault dips towards and under the Shoreline fault as the two faults approach their intersection. The focal mechanisms generally agree with pure right?lateral strike?slip on the OADC planes, but suggest a non?planar Hosgri fault or another structure underlying the northern Shoreline fault. The Shoreline fault most likely transfers strike?slip motion between the Hosgri fault and other faults of the Pacific–North America plate boundary system to the east. A hypothetical earthquake rupturing the entire known length of the Shoreline fault would have a moment magnitude of 6.4–6.8. A hypothetical earthquake rupturing the Shoreline fault and the section of the Hosgri fault north of the Hosgri–Shoreline junction would have a moment magnitude of 7.2–7.5.

Hardebeck, Jeanne L.

2013-01-01

71

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

USGS Publications Warehouse

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

Reimer, G. M.

1981-01-01

72

Subduction zone earthquake probably triggered submarine hydrocarbon seepage offshore Pakistan  

NASA Astrophysics Data System (ADS)

Seepage of methane-dominated hydrocarbons is heterogeneous in space and time, and trigger mechanisms of episodic seep events are not well constrained. It is generally found that free hydrocarbon gas entering the local gas hydrate stability field in marine sediments is sequestered in gas hydrates. In this manner, gas hydrates can act as a buffer for carbon transport from the sediment into the ocean. However, the efficiency of gas hydrate-bearing sediments for retaining hydrocarbons may be corrupted: Hypothesized mechanisms include critical gas/fluid pressures beneath gas hydrate-bearing sediments, implying that these are susceptible to mechanical failure and subsequent gas release. Although gas hydrates often occur in seismically active regions, e.g., subduction zones, the role of earthquakes as potential triggers of hydrocarbon transport through gas hydrate-bearing sediments has hardly been explored. Based on a recent publication (Fischer et al., 2013), we present geochemical and transport/reaction-modelling data suggesting a substantial increase in upward gas flux and hydrocarbon emission into the water column following a major earthquake that occurred near the study sites in 1945. Calculating the formation time of authigenic barite enrichments identified in two sediment cores obtained from an anticlinal structure called "Nascent Ridge", we find they formed 38-91 years before sampling, which corresponds well to the time elapsed since the earthquake (62 years). Furthermore, applying a numerical model, we show that the local sulfate/methane transition zone shifted upward by several meters due to the increased methane flux and simulated sulfate profiles very closely match measured ones in a comparable time frame of 50-70 years. We thus propose a causal relation between the earthquake and the amplified gas flux and present reflection seismic data supporting our hypothesis that co-seismic ground shaking induced mechanical fracturing of gas hydrate-bearing sediments creating pathways for free gas to migrate from a shallow reservoir within the gas hydrate stability zone into the water column. Our results imply that free hydrocarbon gas trapped beneath a local gas hydrate seal was mobilized through earthquake-induced mechanical failure and in that way circumvented carbon sequestration within the sediment. These findings lead to conclude that hydrocarbon seepage triggered by earthquakes can play a role for carbon budgets at other seismically active continental margins. The newly identified process presented in our study is conceivable to help interpret data from similar sites. Reference: Fischer, D., Mogollon, J.M., Strasser, M., Pape, T., Bohrmann, G., Fekete, N., Spieß, V. and Kasten, S., 2013. Subduction zone earthquake as potential trigger of submarine hydrocarbon seepage. Nature Geoscience 6: 647-651.

Fischer, David; José M., Mogollón; Michael, Strasser; Thomas, Pape; Gerhard, Bohrmann; Noemi, Fekete; Volkhard, Spiess; Sabine, Kasten

2014-05-01

73

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

USGS Publications Warehouse

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.

Hudnut, Ken; King, Nancy

2001-01-01

74

Aftershocks and triggered events of the Great 1906 California earthquake  

USGS Publications Warehouse

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 and an M ???5.0 event under or near Santa Monica Bay, 11.3 and 31.3 hr after the San Francisco mainshock, respectively. The western Arizona event is inferred to have been triggered dynamically. In general, the largest aftershocks occurred at the ends of the 1906 rupture or away from the rupture entirely; very few significant aftershocks occurred along the mainshock rupture itself. The total number of large aftershocks was less than predicted by a generic model based on typical California mainshock-aftershock statistics, and the 1906 sequence appears to have decayed more slowly than average California sequences. Similarities can be drawn between the 1906 aftershock sequence and that of the 1857 (Mw 7.9) San Andreas fault earthquake.

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

2003-01-01

75

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

USGS Publications Warehouse

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.

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

1996-01-01

76

Recalculated probability of M ??? 7 earthquakes beneath the Sea of Marmara, Turkey  

USGS Publications Warehouse

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. Copyright Published in 2004 by the American Geophysical Union.

Parsons, T.

2004-01-01

77

Bridge pier failure probabilities under combined hazard effects of scour, truck and earthquake. Part II: failure probabilities  

NASA Astrophysics Data System (ADS)

In many regions of the world, a bridge will experience multiple extreme hazards during its expected service life. The current American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) specifications are formulated based on failure probabilities, which are fully calibrated for dead load and non-extreme live loads. Design against earthquake load effect is established separately. Design against scour effect is also formulated separately by using the concept of capacity reduction (or increased scour depth). Furthermore, scour effect cannot be linked directly to an LRFD limit state equation because the latter is formulated using force-based analysis. This paper (in two parts) presents a probability-based procedure to estimate the combined hazard effects on bridges due to truck, earthquake and scour, by treating the effect of scour as an equivalent load effect so that it can be included in reliability-based failure calculations. In Part I of this series, the general principle for treating the scour depth as an equivalent load effect is presented. In Part II, the corresponding bridge failure probability, the occurrence of scour as well as simultaneously having both truck load and equivalent scour load effect are quantitatively discussed. The key formulae of the conditional partial failure probabilities and the necessary conditions are established. In order to illustrate the methodology, an example of dead, truck, earthquake and scour effects on a simple bridge pile foundation is represented.

Liang, Zach; Lee, George C.

2013-06-01

78

Bridge pier failure probabilities under combined hazard effects of scour, truck and earthquake. Part I: occurrence probabilities  

NASA Astrophysics Data System (ADS)

In many regions of the world, a bridge will experience multiple extreme hazards during its expected service life. The current American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) specifications are formulated based on failure probabilities, which are fully calibrated for dead load and nonextreme live loads. Design against earthquake loads is established separately. Design against scour effect is also formulated separately by using the concept of capacity reduction (or increased scour depth). Furthermore, scour effect cannot be linked directly to an LRFD limit state equation, because the latter is formulated using force-based analysis. This paper (in two parts) presents a probability-based procedure to estimate the combined hazard effects on bridges due to truck, earthquake and scour, by treating the effect of scour as an equivalent load effect so that it can be included in reliability-based bridge failure calculations. In Part I of this series, the general principle of treating the scour depth as an equivalent load effect is presented. The individual and combined partial failure probabilities due to truck, earthquake and scour effects are described. To explain the method of including non-force-based natural hazards effects, two types of common scour failures are considered. In Part II, the corresponding bridge failure probability, the occurrence of scour as well as simultaneously having both truck load and equivalent scour load are quantitatively discussed.

Liang, Zach; Lee, George C.

2013-06-01

79

Water level and strain changes preceding and following the August 4, 1985 Kettleman Hills, California, earthquake  

USGS Publications Warehouse

Two of the four wells monitored near Parkfield, California, during 1985 showed water level rises beginning three days before the M4 6.1 Kettleman Hills earthquake. In one of these wells, the 3.0 cm rise was nearly unique in five years of water level data. However, in the other well, which showed a 3.8 cm rise, many other changes of comparable size have been observed. Both wells that did not display pre-earthquake rises tap partially confined aquifers that cannot sustain pressure changes due to tectonic strain having periods longer than several days. We evaluate the effect of partial aquifer confinement on the ability of these four wells to display water level changes in response to aquifer strain. Although the vertical hydraulic diffusivities cannot be determined uniquely, we can find a value of diffusivity for each site that is consistent with the site's tidal and barometric responses as well as with the rate of partial recovery of the coseismic water level drops. Furthermore, the diffusivity for one well is high enough to explain why the preseismic rise could not have been detected there. For the fourth well, the diffusivity is high enough to have reduced the size of the preseismic signal as much as 50%, although it should still have been detectable. Imperfect confinement cannot explain the persistent water level changes in the two partially confined aquifers, but it does show that they were not due to volume strain. The pre-earthquake water level rises may have been precursors to the Kettleman Hills earthquake. If so, they probably were not caused by accelerating slip over the part of the fault plane that ruptured in that earthquake because they are of opposite sign to the observed coseismic water level drops.

Roeloffs, E.; Quilty, E.

1997-01-01

80

Coulomb static stress interactions between M>5 earthquakes and major active faults in Northern California  

NASA Astrophysics Data System (ADS)

We have calculated Coulomb stress changes between 1980-2006 in Northern California from fourteen events as well as from the major historic ruptures of 1865, 1868 and 1906. The seismic and fault geometry parameters are taken from the Working Group on California Earthquake Probabilities report (2008). We assess the static Coulomb stress hypothesis as a triggering mechanism for the aftershock sequences of these events using the high accuracy earthquake catalog of Waldhauser and Schaff (2008), which is based on waveform cross-correlation and double-difference methods. We examined the sensitivity of static Coulomb stress changes due to source parametrization by considering different rupture models and aftershock fault orientations for each event. To quantify the variability due to slip distribution, we used both a uniform and variable slip model. Source fault geometry corresponds to: (1) a fault plane suggested by the Global Centroid Moment Tensor (GCMT) and (2) the related mapped fault. In order to analyze the impact of the receiving fault geometry, we used: (1) geometry similar to the source and (2) optimally oriented fault planes for failure (King et al., 1994), taking into account the regional stress field derived in Hardebeck and Michael (2004) from focal mechanism analysis. The sensitivity of the calculations to different focal depths and apparent coefficients of friction (0.1-0.8) has been also investigated.

Segou, M.; Parsons, T.; Kalkan, E.

2011-12-01

81

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

82

Earthquake clusters in southern California I: Identification and stability  

NASA Astrophysics Data System (ADS)

We use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters. The method is based on nearest-neighbor distances of events in space-time-energy domain. The method is applied to a 1981-2011 relocated seismicity catalog of southern California having 111,981 events with magnitudes m ? 2 and corresponding synthetic catalogs produced by the Epidemic Type Aftershock Sequence (ETAS) model. Analysis of the ETAS model demonstrates that the cluster detection results are accurate and stable with respect to (1) three numerical parameters of the method, (2) variations of the minimal reported magnitude, (3) catalog incompleteness, and (4) location errors. Application of the method to the observed catalog separates the 111,981 examined earthquakes into 41,393 statistically significant clusters comprised of foreshocks, mainshocks, and aftershocks. The results reproduce the essential known statistical properties of earthquake clusters, which provide overall support for the proposed technique. In addition, systematic analysis with our method allows us to detect several new features of seismicity that include (1) existence of a significant population of single-event clusters, (2) existence of foreshock activity in natural seismicity that exceeds expectation based on the ETAS model, and (3) dependence of all cluster properties, except area, on the magnitude difference of events from mainshocks but not on their absolute values. The classification of detected clusters into several major types, generally corresponding to singles, burst-like and swarm-like sequences, and correlations between different cluster types and geographic locations is addressed in a companion paper.

Zaliapin, Ilya; Ben-Zion, Yehuda

2013-06-01

83

Nonlinear soil response as a natural passive isolation mechanism. Paper II. The 1933, Long Beach, California earthquake  

Microsoft Academic Search

The areas that experienced large strains and differential motions in the soil (indicated by breaks in the water and gas pipe distribution systems) and the areas with severely damaged buildings showed remarkable separation during the March 10, 1933, Long Beach, California earthquake. With analogous results for the 1994 Northridge, California earthquake [Soil Dynam. Earthquake Engng. 17 (1998) 41], the observations

M. D. Trifunac

2003-01-01

84

Tsunami Hazard in Crescent City, California from Kuril Islands earthquakes  

NASA Astrophysics Data System (ADS)

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 in a half meter difference in water heights. We also look at the contribution of fault segments along the Kuril subduction zone using the FACTS server to look at the potentially most damaging source regions for Crescent City. A similar-sized rupture as the November 15 event located further south along the Hokkaido - Honshu area of the subduction zone, is likely to produce a slightly larger amplitude signal with and even greater delay between the first wave arrivals and the largest waves.

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

2007-12-01

85

Community Response to Earthquake Threat in Southern California. Part Ten: Summary and Recommendations.  

National Technical Information Service (NTIS)

This volume summarizes findings and presents recommendations of a study investigating individual and community response to earthquake threat in southern California. The overall objective is to provide a basis for understanding community response to earthq...

B. S. Young D. H. Paz J. M. Nigg R. H. Turner

1981-01-01

86

Occurrence probability of moderate to large earthquakes in Italy based on new geophysical methods  

Microsoft Academic Search

We develop new approaches to calculating 30-year probabilities for occurrence of moderate-to-large earthquakes in Italy. Geodetic\\u000a techniques and finite-element modelling, aimed to reproduce a large amount of neotectonic data using thin-shell finite element,\\u000a are used to separately calculate the expected seismicity rates inside seismogenic areas (polygons containing mapped faults\\u000a and\\/or suspected or modelled faults). Thirty-year earthquake probabilities obtained from the two

Dario Slejko; Alessandro Caporali; Mark Stirling; Salvatore Barba

2010-01-01

87

Temporal variation in the attenuation of earthquake coda near Stone Canyon, California  

Microsoft Academic Search

We present evidence of a temporal trend in the attenuation properties of the high frequency coda of local earthquakes near Stone Canyon, central California. The trend appears as a systematic increase in the energy content of the coda of earthquakes with similar magnitudes and locations over a period of about a year. Present theoretical interpretations of the coda do not

Bernard Chouet

1979-01-01

88

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

ERIC Educational Resources Information Center

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…

California State Office of Emergency Services, Sacramento.

89

Characterization of earthquake forces for probability-based design of nuclear structures  

SciTech Connect

Research is underway to develop probability-based loading criteria for the design of safety-related steel and reinforced concrete nuclear plant structures. The random nature of earthquake loads and related structural response must be established before load criteria for design that include earthquake effects can be developed. This report provides a general statistical description of earthquake actions. Sources of uncertainty that might affect structural response are considered, including uncertainties in the peak ground motion at the site and in the structural response to prescribed ground motions. Power spectral density representations of earthquake ground motion needed for predicting response using random vibration analysis are examined and related to site conditions. The emphasis is on probabilistic models that are consistent with available data on seismicity and structural response.

Ellingwood, B.R.; Batts, M.E.

1982-09-01

90

Water-level changes induced by local and distant earthquakes at Long Valley caldera, California  

Microsoft Academic Search

Distant as well as local earthquakes have induced groundwater-level changes persisting for days to weeks at Long Valley caldera, California. Four wells open to formations as deep as 300 m have responded to 16 earthquakes, and responses to two earthquakes in the 3-km-deep Long Valley Exploratory Well (LVEW) show that these changes are not limited to weathered or unconsolidated near-surface

Evelyn Roeloffs; Michelle Sneed; Devin L Galloway; Michael L Sorey; Christopher D Farrar; James F Howle; Jennifer Hughes

2003-01-01

91

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

Microsoft Academic Search

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,

Zhuang Jiancang; Yosihiko Ogata

2006-01-01

92

Improved Data Access From the Northern California Earthquake Data Center  

NASA Astrophysics Data System (ADS)

The NCEDC is a joint project of the UC Berkeley Seismological Laboratory and the USGS Menlo Park to provide a long-term archive and distribution center for geophysical data for northern California. Most data are available via the Web at http://quake.geo.berkeley.edu and research accounts are available for access to specialized datasets. Current efforts continue to expand the available datasets, enhance distribution methods, and to provide rapid access to all datasets. The NCEDC archives continuous and event-based seismic and geophysical time-series data from the BDSN, the USGS NCSN, the UNR Seismic Network, the Parkfield HRSN, and the Calpine/Unocal Geysers network. In collaboration with the USGS, the NCEDC has archived a total of 887 channels from 139 sites of the "USGS low-frequency" geophysical network (UL), including data from strainmeters, creep meters, magnetometers, water well levels, and tiltmeters. There are 336 active continuous data channels that are updated at the NCEDC on a daily basis. Geodetic data from the BARD network of over 40 continuously recording GPS sites are archived at the NCEDC in both raw and RINEX format. The NCEDC is the primary archive for survey-mode GPS and other geodetic data collected in northern California by the USGS, universities, and other agencies. All of the BARD data and GPS data archived from USGS Menlo Park surveys are now available through the GPS Seamless Archive Centers (GSAC), and by FTP directly from the NCEDC. Virtually all time-series data at the NCEDC are now available in SEED with complete instrument responses. Assembling, verifying, and maintaining the response information for these networks is a huge task, and is accomplished through the collaborative efforts of the NCEDC and the contributing agencies. Until recently, the NCSN waveform data were available only through research accounts and special request methods due to incomplete instrument responses. In the last year, the USGS compiled the necessary descriptions for for both historic and current NCSN instrumentation. The NCEDC and USGS jointly developed a procedure to create and maintain the hardware attributes and instrument responses at the NCEDC for the 3500 NCSN channels. As a result, the NCSN waveform data can now be distributed in SEED format. 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 newly formed California Integrated Seismic Network, we are working with the SCEDC to provide unified access to California earthquake data.

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

2002-12-01

93

Recalculated probability of M ? 7 earthquakes beneath the Sea of Marmara, Turkey  

Microsoft Academic Search

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

Tom Parsons

2004-01-01

94

Recalculated probability of M >= 7 earthquakes beneath the Sea of Marmara, Turkey  

Microsoft Academic Search

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

Tom Parsons

2004-01-01

95

Northern California Earthquake Data Center Data Retrieval (title provided or enhanced by cataloger)  

NSDL National Science Digital Library

The Northern California Earthquake Data Center (NCEDC) offers various types of earthquake-related data. Most of the datasets are available on the WWW. A few require the establishment of a research account. Available information includes: earthquake catalogs and lists; seismic waveform data from the Berkeley Digital Seismic Network, the Northern California Seismic Network, the Parkfield High-Resolution Seismic Network, and the Calpine/Unocal Geysers Network; Global Positioning System data from continuous monitoring stations; and Berkeley Digital Seismic Network temperature, electromagnetic and strain data.

96

Persistent water level changes in a well near Parkfield, California, due to local and distant earthquakes  

USGS Publications Warehouse

Coseismic water level rises in the 30-m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes. Coseismic changes in static strain cannot explain these water level rises because (1) the well is insensitive to strain at tidal periods; (2) for the distant earthquakes, the expected coseismic static strain is extremely small; and (3) the water level response is of the incorrect sign for the local earthquakes. These water level changes must therefore be caused by seismic waves, but unlike seismic water level oscillations, they are monotonic, persist for days or weeks, and seem to be caused by waves with periods of several seconds rather than long-period surface waves. Other investigators have reported a similar phenomenon in Japan. Certain wells consistently exhibit this type of coseismic water level change, which is always in the same direction, regardless of the earthquake's azimuth or focal mechanism, and approximately proportional to the inverse square of hypocentral distance. To date, the coseismic water level rises in the BV well have never exceeded the seasonal water level maximum, although their sizes are relatively well correlated with earthquake magnitude and distance. The frequency independence of the well's response to barometric pressure in the frequency band 0.1 to 0.7 cpd implies that the aquifer is fairly well confined. High aquifer compressibility, probably due to a gas phase in the pore space, is the most likely reason why the well does not respond to Earth tides. The phase and amplitude relationships between the seasonal water level and precipitation cycles constrain the horizontal hydraulic diffusivity to within a factor of 4.5, bounding hypothetical earthquake-induced changes in aquifer hydraulic properties. Moreover, changes of hydraulic conductivity and/or diffusivity throughout the aquifer would not be expected to change the water level in the same direction at every time of the year. The first 2.5 days of a typical coseismic water level rise could be caused by a small coseismic discharge decrease at a point several tens of meters from the well. Alternatively, the entire coseismic water level signal could represent diffusion of an abrupt coseismic pore pressure increase within several meters of the well, produced by a mechanism akin to that of liquefaction. The coseismic water level changes in the BV well resemble, and may share a mechanism with, coseismic water level, stream discharge, and groundwater temperature changes at other locations where preearthquake changes have also been reported. No preearthquake changes have been observed at the BV well site, however.

Roeloffs, E. A.

1998-01-01

97

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

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.

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

2003-01-01

98

Error propagation in time-dependent probability of occurrence for characteristic earthquakes in Italy  

NASA Astrophysics Data System (ADS)

Time-dependent models for seismic hazard and earthquake probabilities are at the leading edge of research nowadays. In the framework of a 2-year national Italian project (2005-2007), we have applied the Brownian passage time (BPT) renewal model to the recently released Database of Individual Seismogenic Sources (DISS) to compute earthquake probability in the period 2007-2036. Observed interevent times on faults in Italy are absolutely insufficient to characterize the recurrence time. We, therefore, derived mean recurrence intervals indirectly. To estimate the uncertainty of the results, we resorted to the theory of error propagation with respect to the main parameters: magnitude and slip rate. The main issue concerned the high variability of slip rate, which could hardly be reduced by exploiting geodetic constraints. We did some validation tests, and interesting considerations were derived from seismic moment budgeting on the historical earthquake catalog. In a time-dependent perspective, i.e., when the date of the last event is known, only 10-15% of the 115 sources exhibit a probability of a characteristic earthquake in the next 30 years higher than the equivalent Poissonian probabilities. If we accept the Japanese conventional choice of probability threshold greater than 3% in 30 years to define “highly probable sources,” mainly intermediate earthquake faults with characteristic M < 6, having an elapsed time of 0.7-1.2 times the recurrence interval are the most “prone” sources. The number of highly probable sources rises by increasing the aperiodicity coefficient (from 14 sources in the case of variable ? ranging between 0.22 and 0.36 to 31 sources out of 115 in the case of an ? value fixed at 0.7). On the other hand, in stationary time-independent approaches, more than two thirds of all sources are considered probabilistically prone to an impending earthquake. The performed tests show the influence of the variability of the aperiodicity factor in the BPT renewal model on the absolute probability values. However, the influence on the relative ranking of sources is small. Future developments should give priority to a more accurate determination of the date of the last seismic event for a few seismogenic sources of the DISS catalog and to a careful check on the applicability of a purely characteristic model.

Peruzza, Laura; Pace, Bruno; Cavallini, Fabio

2010-01-01

99

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

NASA Astrophysics Data System (ADS)

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 for reliability and skill by retrospective testing, and the models should be under continuous prospective testing against long-term forecasts and alternative time-dependent models. (d) Short-term models used in operational forecasting should be consistent with the long-term forecasts used in probabilistic seismic hazard analysis. (e) Alert procedures should be standardized to facilitate decisions at different levels of government, based in part on objective analysis of costs and benefits. (f) In establishing alert protocols, consideration should also be given to the less tangible aspects of value-of-information, such as gains in psychological preparedness and resilience. Authoritative statements of increased risk, even when the absolute probability is low, can provide a psychological benefit to the public by filling information vacuums that lead to informal predictions and misinformation. Formal OEF procedures based on probabilistic forecasting appropriately separate hazard estimation by scientists from the decision-making role of civil protection authorities. The prosecution of seven Italian scientists on manslaughter charges stemming from their actions before the L'Aquila earthquake makes clear why this separation should be explicit in defining OEF protocols.

Jordan, T. H.; the International Commission on Earthquake Forecasting for Civil Protection

2011-12-01

100

Tilt precursors before earthquakes on the San Andreas fault, California  

USGS Publications Warehouse

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.

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

1974-01-01

101

The optimum Bayesian probability procedure and the prediction of strong earthquakes felt in Mexico city  

NASA Astrophysics Data System (ADS)

Bayes' theorem has possible application to earthquake prediction because it can be used to represent the dependence of the inter-arrival time ( T) of the next event on magnitude ( M) of the preceding earthquake ( Ferraes, 1975; Bufe et al., 1977; Shimazaki and Nakata, 1980; Sykes and Quittmeyer, 1981). First, we derive the basic formulas, assuming that the earthquake process behaves as a Poisson process. Under this assumption the likelihood probabilities are determined by the Poisson distribution ( Ferraes, 1985) after which we introduce the conjugate family of Gamma prior distributions. Finally, to maximize the posterior Bayesian probability P(?/M) we use calculus and introduce the analytical conditiond/{dtau }P(tau /M) = 0. Subsequently we estimate the occurrence of the next future large earthquake to be felt in Mexico City. Given the probabilistic model, the prediction is obtained from the data set that include all events with M?7.5 felt in Mexico City from 1900 to 1985. These earthquakes occur in the Middle-America trench, along Mexico, but are felt in Mexico City. To see the full significance of the analysis, we give the result using two models: (1) The Poisson-Gamma, and (2) The Poisson-Exponential (a special case of the Gamma). Using the Poisson-Gamma model, the next expected event will occur in the next time interval ?=2.564 years from the last event (occurred on September 19, 1985) or equivalently, the expected event will occur approximately in April, 1988. Using the Poisson-Exponential model, the next expected damaging earthquake will occur in the next time interval ?'=2.381 years from the last event, or equivalently in January, 1988. It should be noted that very strong agreement exists between the two predicted occurrence times, using both models.

Ferraes, Sergio G.

1988-12-01

102

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

USGS Publications Warehouse

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.

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

103

Collaborative Projects at the Northern California Earthquake Data Center (NCEDC)  

NASA Astrophysics Data System (ADS)

The NCEDC is a joint project of the UC Berkeley Seismological Laboratory and the USGS Menlo Park to provide a long-term archive and distribution center for geophysical data for northern California. Most data are available via the Web at http://quake.geo.berkeley.edu and research accounts are available for access to specialized datasets. Current efforts continue to expand the available datasets and to enhance distribution methods. The NCEDC currently archives continuous and event seismic waveform data from the BDSN and the USGS NCSN. Data from the BDSN are available in SEED and work is underway to make NCSN data available in this format. This massive project requires assembling and tracking the instrument responses from over 5000 current and historic NCSN data channels. Event waveforms from specialized networks, such as Geysers and Parkfield, are also available. In collaboration with the USGS, the NCEDC has archived a total of 887 channels from 139 sites of the "USGS low-frequency" geophysical network (UL), including data from strainmeters, creep meters, magnetometers, water well levels, and tiltmeters. There are 486 current data channels being updated at the NCEDC on a daily basis. All UL data are available in SEED. Data from the BARD network of over 40 continuously recording GPS sites are archived at the NCEDC in both raw and RINEX format. The NCEDC is now the primary archive for survey-mode GPS and other geodetic data collected in northern California by the USGS, universities, and other agencies. All of the BARD data and GPS data archived from USGS Menlo Park surveys are now available from the NCEDC via FTP. To support more portable and uniform data query programs among data centers, the NCEDC developed a set of Generic Data Center Views (GDVs) that incorporates the basic information that most datacenters maintain about data channels, instrument responses, and waveform inventory. We defined MSQL (Meta SeismiQuery Language), a query language based on the SQL SELECT command, to perform queries on the GDVs, and developed a program which converts the MSQL to an SQL request. MSQL2SQL converts the MSQL command into a parse tree, and defines an API allowing each datacenter to traverse the parse tree and revise it to produce a data center-specific SQL request. The NCEDC converted the IRIS SeismiQuery program to use the GDVs and MSQL, installed it at the NCEDC, and distributed the software to IRIS, SCEC-DC, and other interested parties. The resulting program should be much easier to install and support at other data centers. The NCEDC is also working on several data center integration projects in order to provide users with seamless access to data. The NCEDC is collaborating with IRIS on the NETDC project and with UNAVCO on the GPS Seamless Archive Centers initiative. Through the newly formed California Integrated Seismic Network, we are working with the SCEC-DC to provide unified access to California earthquake data.

Neuhauser, D.; Oppenheimer, D.; Zuzlewski, S.; Gee, L.; Murray, M.; Bassett, A.; Prescott, W.; Romanowicz, B.

2001-12-01

104

Foreshock probability in Southern California explained by clustering models  

Microsoft Academic Search

The foreshock is one of the most popular issues in the researches on seismicity and earthquake prediction, and even of public attentions. Up to now, there are still many problems on foreshocks under discussions. The first problem in foreshock studies is how to define foreshocks from other shocks. The second problem is whether a foreshock is a mainshock whose aftershocks

J. Zhuang; D. D. Jackson

2006-01-01

105

Dynamic Triggering of Earthquakes in the Salton Sea Region of Southern California from Large Regional and Teleseismic Earthquakes  

NASA Astrophysics Data System (ADS)

We perform a systematic survey of dynamically triggered earthquakes in the Salton Sea region of southern California using borehole seismic data recordings (2007 to present). We define triggered events as high-frequency seismic energy during large-amplitude seismic waves of distant earthquakes. Our mainshock database includes 26 teleseismic events (epicentral distances > 1000 km; Mw ? 7.5), and 8 regional events (epicentral distances 100 - 1000 km; Mw ? 5.5). Of these, 1 teleseismic and 7 regional events produce triggered seismic activity within our study region. The triggering mainshocks are not limited to specific azimuths. For example, triggering is observed following the 2008 Mw 6.0 Nevada earthquake to the north and the 2010 Mw7.2 Northern Baja California earthquake to the south. The peak ground velocities in our study region generated by the triggering mainshocks exceed 0.03 cm/s, which corresponds to a dynamic stress of ~2 kPa. This apparent triggering threshold is consistent with thresholds found in the Long Valley Caldera (Brodsky and Prejean, 2005), the Parkfield section of San Andreas Fault (Peng et al., 2009), and near the San Jacinto Fault (Kane et al., 2007). The triggered events occur almost instantaneously with the arrival of large amplitude seismic waves and appear to be modulated by the passing surface waves, similar to recent observations of triggered deep “non-volcanic” tremor along major plate boundary faults in California, Cascadia, Japan, and Taiwan (Peng and Gomberg, 2010). However, unlike these deep ‘tremor’ events, the triggered signals we find in this study have very short P- to S-arrival times, suggesting that they likely originate from brittle failure in the shallow crust. Confirming this, spectra of the triggered signals mimic spectra of typical shallow events in the region. Extending our observation time window to ~1 month following the mainshock event we find that for the 2010 Mw 7.2 Northern Baja California mainshock, triggered seismicity near the Salton Sea follows an Omori-law-type decay. In comparison, the seismicity rate at the nearby San Jacinto Fault (SJF) region remains continually high. These differences could be caused by the negative static Coulomb stress changes (i.e., stress shadows) near the Salton Sea and positive stress increases near the SJF. Alternatively, they may reflect differences in the mainshock generated dynamic stresses, background seismicity rates, earthquake detectability in these regions or some combinations of these various influences. We will be applying the recently developed matched filter technique to detect additional triggered earthquakes in these regions, allowing us to gain a better understanding of the physics of earthquake triggering in southern California.

Doran, A.; Meng, X.; Peng, Z.; Wu, C.; Kilb, D. L.

2010-12-01

106

Forecasting California's Earthquakes - What Can We Expect in the Next 30 Years?  

USGS Publications Warehouse

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.

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

2008-01-01

107

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)

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 age of this event overlaps with the 3.3-3.8 ka age of the penultimate (i.e. pre-1872) rupture on the Owens Valley fault. As yet, there are too few paleo-earthquake data from other faults north of the Garlock fault to test the possibility that the northern part of the ECSZ experienced a system wide cluster of earthquakes at ~3.5 ka.

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

2010-12-01

108

Cosmogenic Ages for Earthquake Recurrence Intervals and Debris Flow Fan Deposition, Owens Valley, California  

Microsoft Academic Search

Model exposure ages (beryllium-10, aluminum-26) of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 10Be:26Al years for a strand of the Owens Valley fault in California, which last ruptured in an earthquake of moment magnitude >7.5 in 1872. Cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern Sierra

Paul R. Bierman; Alan R. Gillespie; Marc W. Caffee

1995-01-01

109

Cosmogenic ages for earthquake recurrence intervals and debris flow fan deposition, Owens Valley, California  

Microsoft Academic Search

Model exposure ages (beryllium-10, aluminum-26) of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 ¹°Be:²⁶Al years for a strand of the Owens Valley fault in California, which last ruptured in an earthquake of moment magnitude>7.5 in 1872. Cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern Sierra Nevada

P. R. Bierman; A. R. Gillespie; M. W. Caffee

1995-01-01

110

Slip on the San Andreas Fault at Parkfield, California, over Two Earthquake Cycles, and the Implications for Seismic Hazard  

Microsoft Academic Search

Parkfield, California, which experienced M 6.0 earthquakes in 1934, 1966, and 2004, is one of the few locales for which geodetic observations span multiple earthquake cycles. We undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of ge- odetic data collected prior to the 1966 event. Through joint inversion of

Jessica Murray; John Langbein

2006-01-01

111

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

USGS Publications Warehouse

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

Gerstenberger, Matt; Wiemer, Stefan; Jones, Lucy

2004-01-01

112

Occurrence Probability of Characteristic Earthquakes Based on a Renewal Model and Stress Interaction Effect in Central and Southern Apennines, Italy  

NASA Astrophysics Data System (ADS)

We compute the effect of stress change due to previous historical earthquakes on the probability of occurrence of future earthquakes on neighboring faults, starting from the estimate of the probability of occurrence in the next 50 years for a characteristic earthquake through a time-dependent renewal model. Then, we apply a physical model for the Coulomb stress change caused by previous earthquakes on these structures. The influence of the stress change on the occurrence rate of characteristic earthquakes is computed taking into account both permanent (clock advance) and temporary (state-and-rate) perturbations. We apply this method to the computation of earthquake hazard for 35 seismogenic structures recognized in the Central and Southern Apennines region, for which both historical and paleoseismological data are available. This study provides the opportunity of reviewing the problems connected with the estimate of the parameters of a renewal model in case of characteristic earthquakes characterized by return times longer than the time spanned by the available catalogues, and the applicability of the concept of characteristic earthquake itself. An application of the decision tree approach has shown a wide variability of the probability of failure for all the characteristic sources in the next 50 years. The conclusion of this study is that the present status of both the methodology and the quality of input data for time-dependent earthquake hazard assessment in the study region are still at a premature stage for drawing results that can reliably substitute the time-independent Poisson hypothesis.

Console, R.; Falcone, G.; Murru, M.

2008-12-01

113

Space-time clustering of seismicity in California and the distance dependence of earthquake triggering  

NASA Astrophysics Data System (ADS)

Using two recent high-resolution earthquake catalogs, I examine clustering in California seismicity by plotting the average rate of earthquakes as a function of both space and time from target events ofM2 to 5. Comparisons between pre- and post-target event activity can be used to resolve earthquake-to-earthquake triggering associated with target events of different magnitudes. The results are more complicated than predicted by computer simulations of earthquake triggering that begin with background events occurring at random times. In particular, at least some of the temporal clustering of seismicity at short scales (0.1 to 5 km) does not appear to be caused by local earthquake triggering, but instead reflects an underlying physical process that temporarily increases the seismicity rate, such as is often hypothesized to drive earthquake swarms. Earthquake triggering forM < 4.5 earthquakes is only resolvable in average seismicity rates at times less than about one day and to distances of less than about 10 km, and its linear density decreases as r-1.5 to r-2.5, significantly steeper than some previous studies have found.

Shearer, P. M.

2012-10-01

114

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

USGS Publications Warehouse

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.

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

1992-01-01

115

Effects of Implementing Coulomb Stress Changes into Southern California Earthquake Forecasts  

NASA Astrophysics Data System (ADS)

Previous studies, such as those by Deng & Sykes (1997) and Stein (1997), retrospectively show that a majority of earthquakes tend to occur in areas of positive Coulomb stress change (?CFF). We confirm these results for recent seismicity in southern California, but also observe widespread areas with positive ?CFF where few earthquakes occur. In order to evaluate our hypothesis that ?CFF influences future earthquake locations, it is necessary to examine how seismically quiescent areas affect its reliability through pseudoprospective testing. Assuming uniform slip distribution and zero ?CFF just before the 1812 Wrightwood earthquake, we calculate ?CFF from seismic sources (Mw ? 5.8) and tectonic loading at just after the 1999 Hector Mine and the 2010 El Mayor earthquakes. We use the average ?CFF in 0.1x0.1° cells to calculate an arctangent index function, where earthquake rates increase monotonically with ?CFF, using maximum likelihood to obtain the optimal function width and median. Our target earthquake catalog includes 7379 Mw?2.8 events (Felzer, 2012) from after the Hector Mine earthquake to the present, which we divide into two time intervals: between the Hector Mine and El Mayor earthquakes, and after the El Mayor earthquake. We use uniform seismicity and smoothed seismicity (Hiemer, 2012) earthquake rates as null hypotheses to test against ?CFF earthquake rates during both time intervals. Our results indicate that, although it may potentially contribute to improved earthquake forecasts within a hybrid model, ?CFF alone is insufficient against other factors, such as fault and previous seismicity locations. Likelihood ratio tests show that ?CFF alone consistently outperforms uniform but not smoothed seismicity, and that a hybrid of ?CFF and smoothed seismicity is subject to bias from earthquake clustering. Because earthquake rates calculated from smoothed seismicity decay over a shorter distance than earthquake rates calculated from ?CFF, earthquake declustering methods play an important role in the forecasts' relative effectiveness. Additionally, introducing temporal dependence through combining ETAS (Zhuang, 2002) or rate- and state-friction (Dieterich, 1996 and Hainzl, 2010) with spatial earthquake density helps to account for aftershock effects and reduce variability in the forecasts' reliability.

Strader, A. E.; Jackson, D. D.

2012-12-01

116

Conversion of Historic Seismic Data at the Southern California Earthquake Data Center (SCEDC)  

NASA Astrophysics Data System (ADS)

The Southern California Earthquake Data Center (SCEDC) archives and provides public access to continuous and event-based earthquake parametric and waveform data gathered by the Southern California Seismic Network. The mission of the SCEDC is to maintain an easily-accessible, well-organized, high-quality, searchable archive of earthquake data for research in seismology and earthquake engineering. The SCEDC has compiled and converted all available historic seismic data to create a single source of southern California earthquake data from 1932-present. The 1932-1976 era of seismic data was key-punched from the original phase cards into CUSP-format on a VAX system. The data was then imported into the SCEDC Oracle database, so phase and epicenter data is available for direct retrieval by users via STP. A problematic four-year span of CEDAR data from 1977-1980 is currently not accessible, but has been converted and is being processed to include magnitude information. The parametric data from 1981 to present has been loaded into the Oracle 9i database system and the waveforms for that time period have been converted to mSEED format and are accessible through the STP interface. Quality control of 1981-2000 historic parametric and waveform data has progressed using a detailed reverse-chronological examination and verification of magnitudes. Current efforts at the SCEDC are focused on continuing to expand the available seismic datasets, enhancing and expanding distribution methods, and providing rapid access to all datasets, historic and modern. Through the California Integrated Seismic Network, the SCEDC is working with the NCEDC to provide unified access to California earthquake data.

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

2003-12-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

118

FORECAST MODEL FOR MODERATE EARTHQUAKES NEAR PARKFIELD, CALIFORNIA.  

USGS Publications Warehouse

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.

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

1985-01-01

119

Spatial Variation of Short-Term M4+ Earthquake Clusters in Southern California  

Microsoft Academic Search

The M4+ seismicity in Southern California from 1932 to 2000 (declustered of foreshocks and aftershocks) is temporally clustered over time periods of a few days at a rate that is greater than expected from a Poisson process. An analysis of this same data set was carried out to search for those areas where M4+ earthquakes are most often followed by

J. E. Ebel; A. L. Kafka

2003-01-01

120

A DOCUMENTARY STUDY OF THE FELT EFFECTS OF THE GREAT CALIFORNIA EARTHQUAKE OF 1857  

Microsoft Academic Search

We have collected over 60 hitherto unpublished accounts of the California earthquake of January 9,1857. We have used them, together with those already known, to estimate felt intensities and prepare an isoseismal map which roughly indicates the level of short-period ground motion experienced during this earth­ quake. Modified Mercalli intensities of VI to VII occurred in the modern metro­ politan

DUNCAN CARR AGNEW; KERRY E. SIEH

121

Earthquake Source Mechanisms and Transform Fault Tectonics in the Gulf of California (Abstract Only),  

National Technical Information Service (NTIS)

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 Nor...

J. A. Goff E. A. Bergman S. C. Solomon

1987-01-01

122

What Parts of PTSD Are Normal: Intrusion, Avoidance, or Arousal? Data from the Northridge, California, Earthquake  

Microsoft Academic Search

The incidence and comorbidity of posttraumatic stress disorder (PTSD) are addressed in a study of 130 Northridge, California, earthquake survivors interviewed 3 months postdisaster. Only 13% of the sample met full PTSD criteria, but 48% met both the reexperiencing and the arousal symptom criteria, without meeting the avoidance and numbing symptom criterion. Psychiatric comorbidity was associated mostly with avoidance and

J. Curtis McMillen; Carol S. North; Elizabeth M. Smith

2000-01-01

123

Initial investigation of the Landers, California, earthquake of 28 June 1992 using TERRAscope  

Microsoft Academic Search

The TERRAscope system by Kanamori et al. (1991) is employed in six stations in southern California to study the June 28, 1992 earthquake. Data from the TERRAscope system include low-gain channels for recording strong ground motions and surface waves, and estimates of peak accelerations and velocities. Source parameters are determined by inverting teleseismic P and S waves, and attention is

Hiroo Kanamori; Hong-Kie Thio; Doug Dreger; Egill Hauksson; Tom Heaton

1992-01-01

124

Moment tensor inversions of M ~ 3 earthquakes in the Geysers geothermal fields, California  

NASA Astrophysics Data System (ADS)

have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields, hydrofracturing, and CO2 sequestration sites. Characterizing and understanding the faulting process of induced earthquakes, which is generally achieved through moment tensor inversion, could both help in risk prediction and in reservoir development monitoring. However, this is a challenging task because of their lower signal-to-noise ratio at frequencies typically used in earthquake source analyses. Therefore, higher-resolution velocity models and modeling of seismic waves at higher frequencies are required. In this study, we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions. We utilize a short-period seismic network located in the Geysers geothermal field in northern California and limit our study to that which would be achieved by industry in a typical reservoir environment. We obtain full moment tensor solutions of M ~ 3 earthquakes using waveform modeling and first-motion inversions. We find that these two data sets give complimentary but yet different solutions. Some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially. This illuminates the presence of fluids at depth and their role for the generation of these small-magnitude earthquakes. Finally, since first motions are routinely obtained for all magnitude earthquakes, our approach could be extended to small earthquakes where noise level and complex Green's functions prohibit using waveforms in moment tensor inversions.

Guilhem, A.; Hutchings, L.; Dreger, D. S.; Johnson, L. R.

2014-03-01

125

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

USGS Publications Warehouse

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.

Edited by Harris, Ruth A.

1998-01-01

126

The October 17, 1989, Loma Prieta, California, Earthquake: Selected Photographs  

NSDL National Science Digital Library

This collection of images is the online version of a CD-ROM publication containing 103 digitized color 35-mm photos of the 1989 Loma Prieta earthquake. The images are accompanied by an index map showing the localities where they were taken. They are browsable by location, by thumbnail, or by screen-resolution image. A PDF version and slideshow is also available. Links to additional information on the Loma Prieta earthquake and to ordering information for the CD-ROM are provided.

127

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

USGS Publications Warehouse

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.

Wesson, R. L.; Nicholson, C.

1988-01-01

128

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

SciTech Connect

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.

Zhuang Jiancang; Ogata, Yosihiko [Institute of Statistical Mathematics, Research Organization of Information and Systems, 4-6-7 Minami Azabu, Minato-Ku, Tokyo 106-8659 (Japan)

2006-04-15

129

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

USGS Publications Warehouse

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.

Julian, B. R.

1983-01-01

130

Observation of the seismic nucleation phase in the Ridgecrest, California, earthquake sequence  

USGS Publications Warehouse

Near-source observations of five M 3.8-5.2 earthquakes near Ridgecrest, California are consistent with the presence of a seismic nucleation phase. These earthquakes start abruptly, but then slow or stop before rapidly growing again toward their maximum rate of moment release. Deconvolution of instrument and path effects by empirical Green's functions demonstrates that the initial complexity at the start of the earthquake is a source effect. The rapid growth of the P-wave arrival at the start of the seismic nucleation phase supports the conclusion of Mori and Kanamori [1996] that these earthquakes begin without a magnitude-scaled slow initial phase of the type observed by Iio [1992, 1995].

Ellsworth, W. L.; Beroza, G. C.

1998-01-01

131

Instability model for recurring large and great earthquakes in southern California  

USGS Publications Warehouse

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.

Stuart, W. D.

1985-01-01

132

Instability model for recurring large and great earthquakes in southern California  

NASA Astrophysics Data System (ADS)

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.

Stuart, William D.

1984-11-01

133

On the reported ionospheric precursor of the Hector Mine, California earthquake  

USGS Publications Warehouse

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 identified as being 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.

Thomas, J. N.; Love, J. J.; Komjathy, A.; Verkhoglyadova, O. P.; Butala, M.; Rivera, N.

2012-01-01

134

Probability  

NSDL National Science Digital Library

Probability Guess the Probability Do you know the probability? Take an educated guess. Probability - Guess the next card What's the next card? Is it higher or lower? Probability knowledge will help. Fish Tank Probability Fish Tank Probability. Do you know what you'll catch next? Ball Probability Predict the probability red and blue balls will be chosen. ...

Clark, Mr

2012-10-31

135

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

NASA Astrophysics Data System (ADS)

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 results at that time. CDMG eventually published the second edition map in 1992 following the Governor's Board of Inquiry on the 1989 Loma Prieta earthquake and at the demand of Caltrans. The third edition map was published by Caltrans in 1996 utilizing GIS technology to manage data that includes a simplified three-dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map. The spatial relationship of fault hazards with highways, bridges or any other attribute can be efficiently managed and analyzed now in GIS at Caltrans. There has been great confidence in using DSHA in bridge engineering and other applications in California, and it can be confidently applied in any other earthquake-prone region. Earthquake hazards defined by DSHA are: (1) transparent and stable with robust MCE moment magnitudes; (2) flexible in their application to design considerations; (3) can easily incorporate advances in ground motion simulations; and (4) economical. DSHA and neo-DSHA have the same approach and applicability. The accuracy of DSHA has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment. In the final analysis, DSHA is a reality-check for public safety and PSHA results. Although PSHA has been acclaimed as a better approach for seismic hazard assessment, it is DSHA, not PSHA, that has actually been used in seismic hazard assessment for building and bridge engineering, particularly in California.

Mualchin, Lalliana

2011-03-01

136

Southern California Earthquake Center (SCEC) Communication, Education and Outreach Program  

Microsoft Academic Search

The SCEC Communication, Education, and Outreach Program (CEO) offers student research experiences, web-based education tools, classroom curricula, museum displays, public information brochures, online newsletters, and technical workshops and publications. This year, much progress has been made on the development of the Electronic Encyclopedia of Earthquakes (E3), a collaborative project with CUREE and IRIS. The E3 development system is now fully

M. L. Benthien

2003-01-01

137

Real-time earthquake detection and hazard assessment by ElarmS across California  

NASA Astrophysics Data System (ADS)

ElarmS is a network-based methodology for rapid earthquake detection, location and hazard assessment in the form of magnitude estimation and peak ground motion prediction. The methodology is currently being tested as part of the real-time seismic system in California leveraging the resources of the California Integrated Seismic Network (CISN) and the Advanced National Seismic System. A total of 603 velocity and acceleration sensors at 383 sites across the state stream waveform data to ElarmS processing modules at three network processing centers where waveforms are reduced to a few parameters. These parameters are then collected and processed at UC Berkeley to provide a single statewide prediction of future ground shaking that is updated every second. The system successfully detected the Mw 5.4 Alum Rock earthquake in northern California for which it generated an accurate hazard prediction before peak shaking began in San Francisco. It also detected the Mw 5.4 Chino Hills earthquake in southern California. The median system latency is currently 11.8 sec; the median waveform data latency is 6.5 sec.

Allen, Richard M.; Brown, Holly; Hellweg, Margaret; Khainovski, Oleg; Lombard, Peter; Neuhauser, Douglas

2009-03-01

138

Trends in the probability of twins and males in California, 1983-2003.  

PubMed

This study examines the probability of twins by birth year, maternal race-ethnicity, age, and parity and the influences of these demographic factors on the probability of male in twins and singletons in a large, racially diverse population. Recent publications note steep increases in twin births while the probability of male births has been reported to vary by parental race-ethnicity and age and birth order. Probability of male stratified by plurality has not been investigated in California prior to this study. Cubic spline estimates and Poisson regression techniques were employed to describe trends in twins and males using California vital statistics birth and fetal death records over the period from 1983-2003. This study includes 127,787 twin pair and 11,025,106 singleton births. The probability of twins varied by birth year, maternal race-ethnicity, age, and parity. The probability of twins increased by 10.1% from 1983-1992 and increased by 20.1% from 1993-2003, nearly doubling the previous increase. All maternal race-ethnicity groups showed increases in probability of twins with increasing maternal age. Parous women compared to nulliparous women had larger increases in the probability of twins. The probability of males in twins decreased from 1983-1992 and increased from 1993-2003; while in singletons the probability appeared unchanged. These findings show increases in the probability of twins in California from 1983-2003 and identify maternal age, race-ethnicity, and parity groups most likely to conceive twins. The cause of the increase in twins is unknown but coincides with trends towards delayed childbearing and increased use of subfertility treatments. PMID:19210184

Hardin, Jill; Carmichael, Suzan L; Selvin, Steve; Shaw, Gary M

2009-02-01

139

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

USGS Publications Warehouse

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 2000. The probability of a Mw = 6.9 earthquake within 50 km of Osaka during 1997-2007 is estimated to have risen from 5-6% before the Kobe earthquake to 7-11% afterward; during 1997-2027, it is estimated to have risen from 14-16% before Kobe to 16-22%.

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

1998-01-01

140

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

NASA Astrophysics Data System (ADS)

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 2000. The probability of a Mw = 6.9 earthquake within 50 km of Osaka during 1997-2007 is estimated to have risen from 5-6% before the Kobe earthquake to 7-11% afterward; during 1997-2027, it is estimated to have risen from 14-16% before Kobe to 16-22%.

Toda, Shinji; Stein, Ross S.; Reasenberg, Paul A.; Dieterich, James H.; Yoshida, Akio

1998-10-01

141

Lg and Rg waves on the California regional networks from the December 23, 1985 Nahanni earthquake  

USGS Publications Warehouse

Investigates Lg and Rg propagation in California using the central and southern California regional networks. The waveforms recorded from the December 23, 1985, Nahanni, Canada, earthquake are used to construct three profiles along the propagation path (almost N-S) and three perpendicular to the propagation path (almost E-W) to look at the nature of propagation of these two types of surface waves. Groups of records from stations in various geological and tectonic provinces in California are also examined in order to establish regional characteristics of the surface waves, it is found that the propagation characteristics of Lg differ from those of Rg across California; Lg waves are apparently more sensitive to crustal heterogeneities. The most striking observations are the similarity of coda for both the Lg and the Rg waves within geologic provinces and the marked difference in coda between regions. -from Authors

Wald, L. A.; Heaton, T. H.

1991-01-01

142

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

USGS Publications Warehouse

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.

Hardebeck, Jeanne L.

2012-01-01

143

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

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.

Ward, Peter L.; Page, Robert A.

1990-01-01

144

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

SciTech Connect

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.

Roquemore, G.R. (Irvine Valley College, Irvine, CA (United States). Dept. of Geosciences); Simila, G.A. (California State Univ., Northridge, CA (United States). Dept. of Geological Sciences)

1993-04-01

145

Triggering of 1812 Santa Barbara earthquake by a great San Andreas shock: Implications for future seismic hazards in southern California  

Microsoft Academic Search

We study the evolution of the stress field over the last 200 years in southern California using the stress buildup associated with major faults and stress drops associated with great earthquakes. In this report we calculate the change in the Coulomb Failure Function (DeltaCFF) associated with the great Wrightwood earthquake of Dec. 8, 1812 on the San Andreas fault for

Jishu Deng; Lynn R. Sykes

1996-01-01

146

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

USGS Publications Warehouse

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.

Yashinsky, Mark

1998-01-01

147

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

NASA Astrophysics Data System (ADS)

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 of such a search includes letters, approximately eight pictures useful in structure-damage analysis. Over 170 newspapers were published during 1857 throughout California, Nevada, and New Mexico Territory, encompassing the area of Arizona and New Mexico today. Historical information regarding the settlement of areas also proved useful. Although earlier scholars knew of LDS settlement missions in San Bernardino, California and Las Vegas, Nevada, only brief information was located. Preliminary results include increasing the felt area to include Las Vegas, Nevada; support for a Mercalli Index of IX or even X for San Bernardino; VIII or greater for sites NE of Sacramento, a northwest to southeast rupture pattern, and reports of electromagnetic disturbances. Based on these results, we suggest that the 1857 Ft. Tejon earthquake be felt over a wider area, and in places created greater ground shaking, than previously documented.

Martindale, D.; Evans, J. P.

2002-12-01

148

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

NASA Astrophysics Data System (ADS)

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 awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist concerns about tsunami hazard signs. Over the thirteen 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 from 51 to 73 percent and knowing what the Cascadia subduction zone is from 16 to 42 percent.

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

2008-12-01

149

Focal mechanisms of Southern California offshore earthquakes: the effects of incomplete geographical data coverage on understanding rupture patterns  

NASA Astrophysics Data System (ADS)

Calculating accurate focal mechanisms for offshore seismic events is difficult due to a lack of nearby seismic stations, limited azimuthal coverage, and uncertain velocity structure. We conducted an experiment to determine what effect data from island seismic stations in Southern California (San Miguel, Santa Rosa, Santa Cruz, Santa Barbara, San Nicolas, Santa Catalina, and San Clemente Islands), and ocean bottom seismometers (OBSs) have on constraining focal mechanisms for earthquakes in the California Borderland with a local magnitude greater than three. Thirty-four OBSs were deployed in August of 2010 with the ALBACORE project to collect data for over a year before being recovered in September of 2011. Waveform data from those stations as well as the Southern California Seismic Network were analyzed to determine P-wave first-motion polarities for twenty-nine earthquakes with an acceptable signal-to-noise ratio. These data were then used to calculate focal mechanisms with and without the offshore stations using HASH v.1.2 [Hardebeck and Shearer, 2002], an algorithm that accounts for errors in earthquake location, velocity model, and polarity observations. Comparisons of these results show that including offshore stations improves the errors in fault plane uncertainty and solution probability due to the increased azimuthal coverage and smaller source-receiver distance. Plots of these solutions on maps of the offshore region indicate that the San Clemente fault, San Diego Trough fault, Palos Verdes fault, and additional unmapped faults are currently active. These observations agree with maps of more comprehensive seismicity patterns from the past twenty years. Additionally, the focal mechanisms show that the San Clemente fault, San Diego Trough fault, and a region south of San Nicolas Island all exhibit right lateral movement. The Palos Verdes fault exhibits reverse faulting and a region west of the northern Channel Islands exhibits normal faulting. These observations provide evidence that offshore faults are not purely strike-slip, but have normal and reverse slip, and present the possibility of producing tsunamis that could threaten the highly populated areas of Southern California.

Brunner, K.; Kohler, M. D.; Weeraratne, D. S.

2011-12-01

150

Uncertainties in Earthquake Loss Analysis: A Case Study From Southern California  

NASA Astrophysics Data System (ADS)

Probabilistic earthquake hazard and loss analyses play important roles in many areas of risk management, including earthquake related public policy and insurance ratemaking. Rigorous loss estimation for portfolios of properties is difficult since there are various types of uncertainties in all aspects of modeling and analysis. It is the objective of this study to investigate the sensitivity of earthquake loss estimation to uncertainties in regional seismicity, earthquake source parameters, ground motions, and sites' spatial correlation on typical property portfolios in Southern California. Southern California is an attractive region for such a study because it has a large population concentration exposed to significant levels of seismic hazard. During the last decade, there have been several comprehensive studies of most regional faults and seismogenic sources. There have also been detailed studies on regional ground motion attenuations and regional and local site responses to ground motions. This information has been used by engineering seismologists to conduct regional seismic hazard and risk analysis on a routine basis. However, one of the more difficult tasks in such studies is the proper incorporation of uncertainties in the analysis. From the hazard side, there are uncertainties in the magnitudes, rates and mechanisms of the seismic sources and local site conditions and ground motion site amplifications. From the vulnerability side, there are considerable uncertainties in estimating the state of damage of buildings under different earthquake ground motions. From an analytical side, there are challenges in capturing the spatial correlation of ground motions and building damage, and integrating thousands of loss distribution curves with different degrees of correlation. In this paper we propose to address some of these issues by conducting loss analyses of a typical small portfolio in southern California, taking into consideration various source and ground motion uncertainties. The approach is designed to integrate loss distribution functions with different degrees of correlation for portfolio analysis. The analysis is based on USGS 2002 regional seismicity model.

Mahdyiar, M.; Guin, J.

2005-12-01

151

Transient Stress-Coupling Between the 1992 Landers and 1999 Hector Mine, California, Earthquakes  

Microsoft Academic Search

A three-dimensional finite-element model (FEM) of the Mojave block region in southern California is constructed to investigate transient stress-coupling between the 1992 Landers and 1999 Hector Mine earthquakes. The FEM simulates a poroelastic upper-crust layer coupled to a viscoelastic lower-crust layer, which is decoupled from the upper mantle. FEM predictions of the transient mechanical be- havior of the crust are

Timothy Masterlark; Herbert F. Wang

2002-01-01

152

Determination of earthquake early warning parameters, ?c and Pd, for southern California  

NASA Astrophysics Data System (ADS)

We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter ?c and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from ?c and the peak ground-motion velocity (PGV) from Pd. The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P-wave trigger is constantly monitored. When a trigger occurs, ?c and Pd are computed. We found the relationship between ?c and magnitude (M) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds.

Wu, Yih-Min; Kanamori, Hiroo; Allen, Richard M.; Hauksson, Egill

2007-08-01

153

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

USGS Publications Warehouse

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

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

1982-01-01

154

San Andreas fault earthquake chronology and Lake Cahuilla history at Coachella, California  

USGS Publications Warehouse

The southernmost ~100 km of the San Andreas fault has not ruptured historically. It is imperative to determine its rupture history to better predict its future behavior. This paleoseismic investigation in Coachella, California, establishes a chronology of at least five and up to seven major earthquakes during the past ~1100 yr. This chronology yields a range of average recurrence intervals between 116 and 221 yr, depending on assumptions, with a best-estimate average recurrence interval of 180 yr. The most recent earthquake occurred c.1690, more than 300 yr ago, suggesting that this stretch of the fault has accumulated a large amount of tectonic stress and is likely to rupture in the near future, assuming the fault follows a stress renewal model. This study also establishes the timing of the past 5-6 highstands of ancient Lake Cahuilla since A.D. 800.We found that earthquakes do not tend to occur at any particular stage in the lake cycle.

Philibosian, B.; Fumal, T.; Weldon, R.

2011-01-01

155

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

USGS Publications Warehouse

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.

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

1985-01-01

156

Coseismic stress changes induced by the 1989 Loma Prieta, California earthquake  

SciTech Connect

Earthquake focal mechanisms from before and after the 1989 Loma Prieta, California earthquake are used to infer the coseismic stress change. Before the main shock, most earthquakes correspond to right lateral slip on planes sub-parallel to the San Andreas fault, and imply a generally N-S most compressional stress axis and a vertical intermediate stress axis. Aftershocks within the main shock rupture zone, however, display almost every style and orientation of faulting, implying an extremely heterogeneous stress field. This suggests that the main shock relieved most, if not all, of the shear stress acting on its fault plane. Aftershocks that lie on the perimeter of the rupture agree with spatially uniform stress states, but only when considered in three groups: north, south, and above the main shock rupture area. In each of these areas the stress state may reflect stress transfer by the main shock.

Michael, A.J.; Ellsworth, W.L.; Oppenheimer, D.H. (Geological Survey, Menlo Park, CA (USA))

1990-08-01

157

Probability of chance correlations of earthquakes with predictions in areas of heterogeneous seismicity rate: The VAN Case  

NASA Astrophysics Data System (ADS)

Evaluations of 22 claims of successful earthquake predictions in Greece by Varotsos and Lazaridou [1991] were performed using the Ms (surface wave) as well as the ML (local) magnitude scales. If we assume that the predicted magnitudes were Ms (the scale was not specified in the prediction telegrams), and use the Preliminary Determinations of Epicenters (PDE) to estimate the seismicity rate expected at random, we find that 74% were false (they did not correlate with an earthquake as specified), 9% correlated by chance (probability, p, of one or more earthquakes at random >.50), and 17% are uncertain (0.15 < p < 0.40). There were no successes above the 85% confidence level. If we assume that the magnitude scale for predictions and seismicity rate was M(VAN)=ML(ATH)+0.5, and use the Monthly Bulletin of the Seismological Institute, National Observatory Athens (SI-NOA), for estimating the seismicity rate, we find that 12 of 23 claims were false and that the rest, except for one, most likely correlated by chance with earthquakes. The missed earthquakes eligible for prediction numbered 35 and 456, respectively, using the two data sets. The probability that the observed correlation of predictions with earthquakes (6 and 11 respectively, out of 23 attempts) was due to chance is estimated as 69% and 96%, respectively, by summing the products of the individual probabilities for success and all the permutations of m successes out of n attempts. The probabilities of individual predictions to be fulfilled by chance were estimated based on the declustered catalogs for each prediction area separately, except for predictions during aftershock periods. For these the average seismicity rate during one month after the mainshock was used. We conclude that the various hypotheses of Varotsos et al. [1981a,b,c, 1982a,b, 1983, 1993a,b, 1996] and Varotsos and Lazaridou [1991] (these references will be referred to as VAN) relating seismic electrical signals (SES) to earthquakes, are invalid.

Wyss, M.; Allmann, A.

158

New Continuous Timeseries Data at the Northern California Earthquake Data Center  

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

159

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

USGS Publications Warehouse

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.

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

1999-01-01

160

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

USGS Publications Warehouse

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.

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

1999-01-01

161

Water-level changes induced by local and distant earthquakes at Long Valley caldera, California  

USGS Publications Warehouse

Distant as well as local earthquakes have induced groundwater-level changes persisting for days to weeks at Long Valley caldera, California. Four wells open to formations as deep as 300 m have responded to 16 earthquakes, and responses to two earthquakes in the 3-km-deep Long Valley Exploratory Well (LVEW) show that these changes are not limited to weathered or unconsolidated near-surface rocks. All five wells exhibit water-level variations in response to earth tides, indicating they can be used as low-resolution strainmeters. Earthquakes induce gradual water-level changes that increase in amplitude for as long as 30 days, then return more slowly to pre-earthquake levels. The gradual water-level changes are always drops at wells LKT, LVEW, and CH-10B, and always rises at well CW-3. At a dilatometer just outside the caldera, earthquake-induced strain responses consist of either a step followed by a contractional strain-rate increase, or a transient contractional signal that reaches a maximum in about seven days and then returns toward the pre-earthquake value. The sizes of the gradual water-level changes generally increase with earthquake magnitude and decrease with hypocentral distance. Local earthquakes in Long Valley produce coseismic water-level steps; otherwise the responses to local earthquakes and distant earthquakes are indistinguishable. In particular, water-level and strain changes in Long Valley following the 1992 M7.3 Landers earthquake, 450 km distant, closely resemble those initiated by a M4.9 local earthquake on November 22, 1997, during a seismic swarm with features indicative of fluid involvement. At the LKT well, many of the response time histories are identical for 20 days after each earthquake, and can be matched by a theoretical solution giving the pore pressure as a function of time due to diffusion of a nearby, instantaneous, pressure drop. Such pressure drops could be produced by accelerated inflation of the resurgent dome by amounts too small to be detected by the two-color electronic distance-measuring network. Opening-mode displacement in the south moat, inferred to have followed a M4.9 earthquake on November 22, 1997, could also create extensional strain on the dome and lead to water-level changes similar to those following dome inflation. Contractional strain that could account for earthquake-induced water-level rises at the CW-3 well is inconsistent with geodetic observations. We instead attribute these water-level rises to diffusion of elevated fluid pressure localized in the south moat thermal aquifer. For hydraulic diffusivities appropriate to the upper few hundred meters at Long Valley, an influx of material at temperatures of 300??C can thermally generate pressure of 6 m of water or more, an order of magnitude larger than needed to account for the CW-3 water-level rises. If magma or hot aqueous fluid rises to within 1 km of the surface in the eastern part of the south moat, then hydraulic diffusivities are high enough to allow fluid pressure to propagate to CW-3 on the time scale observed. The data indicate that seismic waves from large distant earthquakes can stimulate upward movement of fluid in the hydrothermal system at Long Valley. ?? 2003 Elsevier B.V. All rights reserved.

Roeloffs, E.; Sneed, M.; Galloway, D. L.; Sorey, M. L.; Farrar, C. D.; Howle, J. F.; Hughes, J.

2003-01-01

162

Probability  

NSDL National Science Digital Library

This is introduction into probability. This project allows students to explore with probability, the days following gives students a further look into probability. Today, you are going to experiment with probability. Go to the site An introduction into probability and read the first three sections, the last sections is the one with the picture of the coins. After you have read a little bit about probability, you now get to explore probability through some games. Start ...

Thompson, Ms.

2008-12-01

163

CISN ShakeAlert: Progress Toward Using Early Warnings for Earthquakes in California  

NASA Astrophysics Data System (ADS)

In California, the California Integrated Seismic Network (CISN) is now developing and implementing components of a prototype system for earthquake early warning, the ShakeAlert system. As this processing system is implemented, we invite a suite of perspective users from critical industries and institutions throughout California to partner with us in developing useful ShakeAlert procedures and products. At the same time, we will support their efforts to determine and implement appropriate responses to alerts of expected earthquake shaking. In Northern California, our partnership with the Bay Area Rapid Transit District (BART) has progressed farthest, although we have initiated discussions with the Red Cross of Alameda County and various agencies in the City of San Francisco. Our collaboration with BART has begun with a basic system transmitting realtime ground shaking information from more than 150 seismic stations operating in the San Francisco Bay Area to BART's operation center, where they are displayed. BART engineers are developing a way to interface this information with the train operating system, so that the trains can automatically slow and stop if the shaking is strong. We will continue this collaboration to include more sophisticated information from the prototype CISN ShakeAlert system.

Hellweg, M.; Allen, R. M.; Brown, H.; Neuhauser, D. S.; Khainovsky, O.; Cisn Earthquake Early Warning Team

2010-12-01

164

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

USGS Publications Warehouse

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 generating destructive tsunamis in the southern California offshore. In order to evaluate the strain associated with the offshore structures, the initial results from the field mapping under this project will be used to identify possible sites for deployment of acoustic geodetic instruments to monitor strain in the offshore region. A major goal of mapping under this project is to provide detailed geologic and geophysical information in GIS data bases that build on the earlier studies and use the new data to precisely locate active faults and to map recent submarine landslide deposits.

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

1999-01-01

165

WHITTIER NARROWS, CALIFORNIA EARTHQUAKE OF OCTOBER 1, 1987-PRELIMINARY ASSESSMENT OF STRONG GROUND MOTION RECORDS.  

USGS Publications Warehouse

More than 250 strong-motion accelerograph stations were triggered by the Whittier Narrows, California earthquake of 1 October 1987. Considering the number of multichannel structural stations in the area of strong shaking, this set of records is one of the more significant in history. Three networks, operated by the U. S. Geological Survey, the California Division of Mines and Geology, and the University of Southern California produced the majority of the records. The excellent performance of the instruments in these and the smaller arrays is attributable to the quality of the maintenance programs. Readiness for a magnitude 8 event is directly related to these maintenance programs. Prior to computer analysis of the analog film records, a number of important structural resonant modes can be identified, and frequencies and simple mode shapes have been scaled.

Brady, A. G.; Etheredge, E. C.; Porcella, R. L.

1988-01-01

166

Earthquake.  

PubMed

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

Cowen, A R; Denney, J P

1994-04-01

167

Spatial and temporal synthesized probability gain for middle and long-term earthquake forecast and its preliminary application  

Microsoft Academic Search

The principle of middle and long-term earthquake forecast model of spatial and temporal synthesized probability gain and the\\u000a evaluation of forecast efficiency (R-values) of various forecast methods are introduced in this paper. The R-value method, developed by Xu (1989), is further developed here, and can be applied to more complicated cases. Probability\\u000a gains in spatial and\\/or temporal domains and the

Xiao-Qing Wang; Zheng-Xiang Fu; Li-Ren Zhang; Sheng-Ping Su; Xiang Ding

2000-01-01

168

Probability  

NSDL National Science Digital Library

Using different probabilities Help cybersquad clean up the buggy mess. Which bugs will Probability show up? Try out all the probability Possibilities. Find the answers to these Ratio activities. Practice Ratios and Proportions. ...

Marsh, Mrs.

2006-11-16

169

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

NASA Astrophysics Data System (ADS)

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 data can be accessed through the above web services and through special NCEDC web pages.

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

2012-12-01

170

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)

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 collaboration, and lessons learned from interacting with free-choice learning institutions.

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

2009-12-01

171

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

USGS Publications Warehouse

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.

Rymer, M. J.; Tinsley, III, J. C.; 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

172

Probability  

NSDL National Science Digital Library

This application demomstrates simple probability concepts by having student rank the probability of an event on a probability line (from impossible to certain). After several trials the application then allows students to complete a simulation and collect data based on the probability task (retrieving balls from a machine). Several guiding questions are provided throughout the activity to encourage student dialogue.

2011-01-18

173

CISN ShakeAlert: Using early warnings for earthquakes in California  

NASA Astrophysics Data System (ADS)

As part of a USGS-funded project, the California Integrated Seismic Network (CISN) is now implementing and testing a prototype, end-to-end system for earthquake early warning, the ShakeAlert system. Having an alert of shaking just before it starts can improve resilience if the recipient of the alert has developed plans for responding to it and acts on them. We are working with a suite of perspective users from critical industries and institutions throughout California, such as the Bay Area Rapid Transit District, to identify information necessary for ShakeAlert users, as well as delivery mechanisms, procedures and products. At the same time, we will support their efforts to determine and implement appropriate responses to alerts of expected earthquake shaking, and to assess possible uses and especially benefits to themselves and to society. Thus, a detailed introduction to the CISN ShakeAlert system is an integral part of our interaction with the users, as are regular opportunities for feedback and support. In a final workshop, users will be surveyed for evaluations of perspective uses for early warning in their organizations as well as expected improvements in their response to earthquakes due to the early warning and their expected savings in terms of lives, damage and resilience.

Hellweg, M.; Vinci, M.; CISN-EEW Project Team

2011-12-01

174

How do "ghost transients" from past earthquakes affect GPS slip rate estimates on southern California faults?  

NASA Astrophysics Data System (ADS)

In this study, we investigate the extent to which viscoelastic velocity perturbations (or "ghost transients") from individual fault segments can affect elastic block model-based inferences of fault slip rates from GPS velocity fields. We focus on the southern California GPS velocity field, exploring the effects of known, large earthquakes for two end-member rheological structures. Our approach is to compute, at each GPS site, the velocity perturbation relative to a cycle average for earthquake cycles on particular fault segments. We then correct the SCEC CMM4.0 velocity field for this perturbation and invert the corrected field for fault slip rates. We find that if asthenosphere viscosities are low (3 × 1018 Pa s), the current GPS velocity field is significantly perturbed by viscoelastic earthquake cycle effects associated with the San Andreas Fault segment that last ruptured in 1857 (Mw = 7.9). Correcting the GPS velocity field for this perturbation (or "ghost transient") adds about 5 mm/a to the SAF slip rate along the Mojave and San Bernardino segments. The GPS velocity perturbations due to large earthquakes on the Garlock Fault (most recently, events in the early 1600s) and the White Wolf Fault (most recently, the Mw = 7.3 1952 Kern County earthquake) are smaller and do not influence block-model inverted fault slip rates. This suggests that either the large discrepancy between geodetic and geologic slip rates for the Garlock Fault is not due to a ghost transient or that un-modeled transients from recent Mojave earthquakes may influence the GPS velocity field.

Hearn, E. H.; Pollitz, F. F.; Thatcher, W. R.; Onishi, C. T.

2013-04-01

175

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

USGS Publications Warehouse

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.

Hough, S. E.; Kanamori, H.

2002-01-01

176

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

USGS Publications Warehouse

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.

Love, Jeffrey J.

2012-01-01

177

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

NASA Astrophysics Data System (ADS)

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 ?. Under transformations that stabilize data and model-parameter variances, the most likely Poisson-event occurrence rate, k/?, 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/?)(k-z/2)2,(k+z/2)2, where z is a parameter that specifies the width, z = 1 (z = 2) corresponding to 1?, 68.3% (2?, 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.

Love, Jeffrey J.

2012-05-01

178

Earthquake Propagation Observations and Ambient Noise Cross-Correlation from Dense Long Beach, California Seismic Array  

NASA Astrophysics Data System (ADS)

In January 2012, a 3D seismic array was deployed in Long Beach, California by Signal Hill Petroleum, Inc. The array consists of about 2400 vertical-component geophones, with an average station spacing of 330 m. Data are being continuously recorded (24 hours/day) over a span of four months, making the resulting data ideal for earthquake research and exploration seismology. Here we provide results related to both fields. We present waveforms recorded from earthquakes both near (less than 15 km) and far (greater than 250 km) from the array. For some events, we applied low-pass filters to accentuate the incoming waveforms. In order to retrieve Green's functions between receivers, we perform cross-correlation of recorded ambient noise that has been band-passed for low frequencies. We observe that the resulting wavefronts preferably travel toward the northeast, suggesting that noise at low frequencies is primarily generated by the Pacific Ocean.

Chang, J. P.; de Ridder, S.; Levin, S. A.; Biondi, B. C.

2012-12-01

179

Cosmogenic ages for earthquake recurrence intervals and debris flow fan deposition, Owens Valley, California  

SciTech Connect

Model exposure ages (beryllium-10, aluminum-26) of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 {sup 10}Be:{sup 26}Al years for a strand of the Owens Valley fault in California, which last ruptured in an earthquake of moment magnitude>7.5 in 1872. Cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern Sierra Nevada are consistent with stratigraphic relations and suggest that these surfaces were abandoned after 1000, 8000, and 21,000 {sup 10}Be:{sup 26}Al years ago. The wide scatter and nonconcordance of {sup 10}Be:{sup 26}Al ages on an older fan surface suggest that boulder erosion and lowering of the fan surface there have influenced apparent exposure ages. 15 refs., 3 figs., 1 tab.

Bierman, P.R. [Univ. of Vermont, Burlington, VT (United States); Gillespie, A.R. [Univ. of Washington, Seattle, WA (United States); Caffee, M.W. [Lawrence Livermore National Laboratory, CA (United States)

1995-10-20

180

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

NASA Astrophysics Data System (ADS)

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 well predicted; additional parameter adjustments are needed to improve these. Alternatively, both tide gauge and GPS data show a better short-term than long-term correlation; oceanographic and possibly groundwater effects could be responsible for these differences.

Hardy, S.; Konter, B.

2013-12-01

181

Rupture process of the 29 May 2013 Mw 4.8 Isla Vista, California earthquake and its tectonic implication  

NASA Astrophysics Data System (ADS)

The Santa Barbara Channel is one of the most seismically active regions in southern California as the result of roughly north-south compressive deformation associating with the Western Transverse Range. On 29 May 2013, a Mw 4.8 earthquake occurred at a depth of 10 km beneath the north Santa Barbara Channel, about 5 km west offshore of the Isla Vista, California. This Isla Vista earthquake is the largest earthquake in the Santa Barbara region after the 1978 ML 5.1 (Mw 5.9) Santa Barbara earthquake. The large historic earthquake also includes the catastrophic 1925 ML 6.8 Santa Barbara earthquake. However, the causative fault planes of these two earthquakes are still debated, presumably due to their limited observations. The analysis to the Isla Vista earthquake then shall shed light on the potential large-magnitude thrust earthquakes in this region. The CISN focal mechanism and the distribution of relocated aftershocks suggest that the 2013 Isla Vista earthquake is a pure thrust failure on a north dipping low angle (~30°) fault plane orienting N287°E, consistent with the local tectonic setting. The Isla Vista earthquake is well recorded by CISN and CGS strong motion stations. Eight of them locating within 20 km away from the epicenter. The observed peak ground acceleration is 0.265 g. A finite fault analysis with this dataset is being conducted to constrain its slip distribution. The preliminary analysis using just local P wave observations reveals a compact slip distribution on a low angle fault plane with a slightly larger fault dip of 37°.

Li, X.; Ji, C.

2013-12-01

182

Mapping probability of fire occurrence in San Jacinto Mountains, California, USA  

NASA Astrophysics Data System (ADS)

An ecological data base for the San Jacinto Mountains, California, USA, was used to construct a probability model of wildland fire occurrence. The model incorporates both environmental and human factors, including vegetation, temperature, precipitation, human structures, and transportation. Spatial autocorrelation was examined for both fire activity and vegetation to determine the specification of neighborhood effects in the model. Parameters were estimated using stepwise logistic regressions. Among the explanatory variables, the variable that represents the neighborhood effects of spatial processes is shown to be of great importance in the distribution of wildland fires. An important implication of this result is that the management of wildland fires must take into consideration neighborhood effects in addition to environmental and human factors. The distribution of fire occurrence probability is more accurately mapped when the model incorporates the spatial term of neighborhood effects. The map of fire occurrence probability is useful for designing large-scale management strategies of wildfire prevention.

Chou, Yue Hong; Minnich, Richard A.; Chase, Richard A.

1993-01-01

183

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

NASA Astrophysics Data System (ADS)

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 with a series of inexpensive high-capacity (1.6 Tbyte) magnetic-disk RAIDs. These systems are built with PC-technology components, using 16 120-Gbyte IDE disks, hot-swappable disk trays, two RAID controllers, dual redundant power supplies and a Linux operating system. The system is configured over a private gigabit network that connects to the two Data Center servers and spans between the Seismological Lab and the USGS. To ensure data integrity, each RAID disk system constantly checks itself against its twin and verifies file integrity using 128-bit MD5 file checksums that are stored separate from the system. The final level of data protection is a Sony AIT-3 tape backup of the files. The primary advantage of the magnetic-disk approach is faster data access because magnetic disk drives have almost no latency. This means that the SCEDC can provide better "on-demand" interactive delivery of the seismograms in the archive.

Appel, V. L.

2002-12-01

184

Earthquake clusters in southern California II: Classification and relation to physical properties of the crust  

NASA Astrophysics Data System (ADS)

This is a second paper in a study of statistical identification and classification of earthquake clusters using a relocated catalog of 1981-2011 seismicity in southern California and synthetic catalogs produced by the Epidemic Type Aftershock Sequence model. Here we focus on classification of event families—statistically significant clusters composed of foreshocks, mainshocks, and aftershocks—that are detected with the methodology discussed in part I of the study. The families are analyzed using their representation as time oriented tree graphs. The results (1) demonstrate that the clustering associated with the largest earthquakes, m > 7, is statistically different from that of small-to-medium earthquakes; (2) establish the existence of two dominant types of small-to-medium magnitude earthquake families—burst-like and swarm-like sequences—and a variety of intermediate cluster forms obtained as a mixture of the two dominant types; (3) suggest a simple new quantitative measure for identifying the cluster type based on its topological structure; (4) demonstrate systematic spatial variability of the cluster characteristics on a scale of tens of kilometers in relation to heat flow and other properties governing the effective viscosity of a region; and (5) establish correlation between the family topological structure and a dozen of metric properties traditionally considered in the literature (number of aftershocks, duration, spatial properties, b-value, parameters of Omori-Utsu and Båth law, etc.). The burst-like clusters likely reflect highly brittle failures in relatively cold regions, while the swarm-like clusters are likely associated with mixed brittle-ductile failures in regions with relatively high temperature and/or fluid content. The results of this and paper I may be used to develop improved region-specific hazard estimates and earthquake forecasts.

Zaliapin, Ilya; Ben-Zion, Yehuda

2013-06-01

185

Earthquakes  

NSDL National Science Digital Library

This outline of basic information on earthquakes starts with an explanation of an earthquake, including the forces acting on rock, (tension, compression, and shear) and plastic and elastic deformation of rock. Next, the principle of the seismograph, seismometer, and seismogram along with the three types of seismic waves are discussed. Information is then presented to help the student distinguish between the focus and epicenter of an earthquake, describe the world-wide distribution pattern of earthquake activity, and explain the earthquake magnitude (Richter) scale and the Modified Mercalli scale of earthquake intensity. This site also includes an explanation of how the epicenter of an earthquake can be located. There is a discussion of some past earthquakes along with a description of the effects of earthquake activity.

Gore, Pamela

186

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

USGS Publications Warehouse

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 faults is equivocal, because age dates on deformed or offset sediment are lacking.

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

2004-01-01

187

Earthquakes  

NSDL National Science Digital Library

Students will participate in a virtual earthquake lab where they will locate an epicenter and measure Richter Scale magnitude. They will also plot the positions of earthquakes that occurred that day. 1) Go to Virtual Earthquake website and follow instructions to complete the online lab assignment. 2) Go to the USGS earthquake site. Take a few minutes to explore the earthquakes displayed on the world map. Click on \\"M2.5/4+ Earthquake List\\". Use the world map provided by your teacher to plot the locations ...

Hemedinger, Mrs.

2007-11-26

188

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

NASA Astrophysics Data System (ADS)

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 sessions. Economic losses are estimated using the ShakeMap scenario ground motions (Saffar, 2007). The calibration tasks necessary in generating these scenarios (developing Vs30 maps, attenuation relationships) complement the on-going efforts of the Puerto Rico Seismic Network to generate ShakeMaps in real-time.

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

2007-12-01

189

Earthquakes  

MedlinePLUS

... for Pet Owners Frequently Asked Questions Additional Information Tornadoes Preparing for a Tornado (Part 1 of 2) ... Severe Weather Earthquakes Extreme Heat Floods Hurricanes Landslides Tornadoes Tsunamis Volcanoes Wildfires Winter Weather Earthquakes Language: English ...

190

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

NASA Astrophysics Data System (ADS)

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.

Prejean, Stephanie; Stork, Anna; Ellsworth, William; Hill, David; Julian, Bruce

2003-12-01

191

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

NASA Astrophysics Data System (ADS)

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 an 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.

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

1996-03-01

192

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

USGS Publications Warehouse

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.

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

1996-01-01

193

The Salton Seismic Imaging Project: Investigating Earthquake Hazards in the Salton Trough, Southern California  

NASA Astrophysics Data System (ADS)

The Salton Seismic Imaging Project (SSIP) is a collaborative effort between academia and the U.S. Geological Survey to provide detailed, subsurface 3-D images of the Salton Trough of southern California and northern Mexico. From both active- and passive-source seismic data that were acquired both onshore and offshore (Salton Sea), the resulting images will provide insights into earthquake hazards, rift processes, and rift-transform interaction at the southern end of the San Andreas Fault system. The southernmost San Andreas Fault (SAF) is considered to be at high-risk of producing a large damaging earthquake, yet the structure of this and other regional faults and that of adjacent sedimentary basins is not currently well understood. Seismic data were acquired from 2 to 18 March 2011. One hundred and twenty-six borehole explosions (10-1400 kg yield) were detonated along seven profiles in the Salton Trough region, extending from area of Palm Springs, California, to the southwestern tip of Arizona. Airguns (1500 and 3500 cc) were fired along two profiles in the Salton Sea and at points in a 2-D array in the southern Salton Sea. Approximately 2800 seismometers were deployed at over 4200 locations throughout the Salton Trough region, and 48 ocean-bottom seismometers were deployed at 78 locations beneath the Salton Sea. Many of the onshore explosions were energetic enough to be recorded and located by the Southern California Seismograph Network. The geometry of the SAF has important implications for energy radiation in the next major rupture. Prior potential field, seismicity, and InSAR data indicate that the SAF may dip moderately to the northeast from the Salton Sea to Cajon Pass in the Transverse Ranges. Much of SSIP was designed to test models of this geometry.

Fuis, G. S.; Goldman, M.; Sickler, R. R.; Catchings, R. D.; Rymer, M. J.; Rose, E. J.; Murphy, J. M.; Butcher, L. A.; Cotton, J. A.; Criley, C. J.; Croker, D. S.; Emmons, I.; Ferguson, A. J.; Gardner, M. A.; Jensen, E. G.; McClearn, R.; Loughran, C. L.; Slayday-Criley, C. J.; Svitek, J. F.; Hole, J. A.; Stock, J. M.; Skinner, S. M.; Driscoll, N. W.; Harding, A. J.; Babcock, J. M.; Kent, G.; Kell, A. M.; Harder, S. H.

2011-12-01

194

Source processes of industrially-induced earthquakes at The Geysers geothermal area, California  

SciTech Connect

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 V{sub p} and V{sub p}/V{sub s} 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 not 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 {approximately}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.

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

1999-12-01

195

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

USGS Publications Warehouse

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

Macgregor-Scott, N.; Walter, A.

1988-01-01

196

Earthquakes  

NSDL National Science Digital Library

In this lesson, students explore the causes of earthquakes and their impact on the geology of an area and on human societies. They begin by looking at the role tectonic plates play in creating the forces that cause earthquakes, to help them understand why earthquakes occur when and where they do. Hands-on activities illustrate how rocks can withstand a certain amount of stress, but that every material has its breaking point. When rocks break underground, an earthquake occurs. In the last section, students explore the impact earthquakes have on humans and look at the efforts scientists are making to better understand and predict these sometimes deadly events.

2006-01-01

197

Probable Earthquake Archaeological Effects in the ancient pyramids of Quetzalcóatl and Sun in Teotihuacán (Central Mexico)  

NASA Astrophysics Data System (ADS)

Teotihuacán was one of the blooming and greater cities of the Prehispanic cultural period within the central valley of México and one of the best archaeological findings of the Earth. During the period of splendour (Middle-Late Classic Period, 350-650 AD), almost 125.000 inhabitants lived in a vast city with more than 2000 stucco and block buildings, including the great religious and ceremonial pyramids: the Great Sun Pyramid, built between 1- 150 AD, the Moon Pyramid, built during a large time span (1-650 AD) and the outstanding Quetzalcóatl Pyramid (Feathered Snake Temple), built in two phases: the first original edifice built before 350 AD and the second one mainly are repairs of the west side and dated post-350 AD. The Quetzalcóatl Pyramid (Q- pyramid) shows a quadrangular base of ca. 3500 m2 with an extraordinary decoration of feathered snakes (attributed to the God Quetzalcóatl) and lizards. The second phase of construction consisted in a townhouse façade covering the west side of the pyramid (post 350AD), up to now with no evidence to justify such annexed wrapper of this west side. This ceremonial building was built within the Citadel, a complex area of Teotihuacán with residential and common zones as well (i.e. market). A detailed view of the steps of the west side stairs, displays different patterns of deformation affecting the blocks of the stair. The original and ancient stair exhibits rotated, overturned and displaced blocks, being stronger this deformation at the base of the pyramid. Moreover, the upper corners of the blocks appear broken in a similar form than the seismic-related feature defined as dipping broken corners or chipped corners. However, the horizontal disposition of the blocks suggests lateral vibration between them from horizontal shaking propagation. Besides, this feature appears lesser evident affecting the lower blocks of the annexed west façade, the only originally preserved ones. We have carried out a systematic measurement of this feature across the original west stairs of the Q- pyramid and the first stair level of the Sun pyramid. Furthermore, these horizontal dipping broken corners were also described affecting the new stairs of the annexed façade of the Q- pyramid. This suggests that seismic shaking could produce that deformation with a relative date of 350 AD post-quem. More data are necessary to properly test the earthquake occurrence and to bracket a probable intensity value.

Perez-Lopez, Raul; Rodríguez-Pascua, Miguel Angel; Garduño-Monroy, Victor Hugo; Oliveros, Arturo; Giner-Robles, Jorge L.; Silva, Pablo G.

2010-05-01

198

Preliminary Analysis of Remote Triggered Seismicity in Northern Baja California Generated by the 2011, Tohoku-Oki, Japan Earthquake  

NASA Astrophysics Data System (ADS)

We analyze possible variations of seismicity in the northern Baja California due to the passage of seismic waves from the 2011, M9.0, Tohoku-Oki, Japan earthquake. The northwestern area of Baja California is characterized by a mountain range composed of crystalline rocks. These Peninsular Ranges of Baja California exhibits high microseismic activity and moderate size earthquakes. In the eastern region of Baja California shearing between the Pacific and the North American plates takes place and the Imperial and Cerro-Prieto faults generate most of the seismicity. The seismicity in these regions is monitored by the seismic network RESNOM operated by the Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE). This network consists of 13 three-component seismic stations. We use the seismic catalog of RESNOM to search for changes in local seismic rates occurred after the passing of surface waves generated by the Tohoku-Oki, Japan earthquake. When we compare one month of seismicity before and after the M9.0 earthquake, the preliminary analysis shows absence of triggered seismicity in the northern Peninsular Ranges and an increase of seismicity south of the Mexicali valley where the Imperial fault jumps southwest and the Cerro Prieto fault continues.

Wong-Ortega, V.; Castro, R. R.; Gonzalez-Huizar, H.; Velasco, A. A.

2013-05-01

199

The Effect of Shallow San Francisco Bay Sediments on Waveforms Recorded during the MW 4.6 Bolinas, California, Earthquake  

Microsoft Academic Search

To investigate the effect of the shallow, low-velocity sediments on the seismic wave field in the northern San Francisco Bay, we modeled tangential com- ponent displacement seismograms recorded during the 18 August 1999 MW 4.6 Bol- inas, California, earthquake. The modeling indicates that the velocity structure of Pleistocene horizons in the San Francisco Bay is important for simulations of weak

Laurie G. Baise; Douglas S. Dreger; Steven D. Glaser

2003-01-01

200

The 1992 M=7 Cape Mendocino, California, earthquake: Coseismic deformation at the south end of the Cascadia megathrust  

Microsoft Academic Search

We invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the April 25, 1992, M=7 Cape Mendocino, California, earthquake. The orientation of the model slip vector, which nearly parallels North America-Juan de Fuca relative plate convergence, and the location and orientation of the model fault relative to the offshore Cascadia megathrust, suggest that the 1992 Cape

Mark H. Murray; Grant A. Marshall; Michael Lisowski; Ross S. Stein

1996-01-01

201

The 1992 M =7 Cape Mendocino, California, earthquake: Coseismic deformation at the south end of the Cascadia megathrust  

Microsoft Academic Search

We invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the April 25, 1992, M=7 Cape Mendocino, California, earthquake. The orientation of the model slip vector, which nearly parallels North America-Juan de Fuca relative plate convergence, and the location and orientation of the model fault relative to the offshore Cascadia megathrust, suggest that the 1992 Cape

Mark H. Murray; Grant A. Marshall; Michael Lisowski; Ross S. Stein

1996-01-01

202

A Public Health Issue Related To Collateral Seismic Hazards: The Valley Fever Outbreak Triggered By The 1994 Northridge, California Earthquake  

NASA Astrophysics Data System (ADS)

Following the 17 January 1994 Northridge, California earthquake (M = 6.7), Ventura County, California, experienced a major outbreak ofcoccidioidomycosis (CM), commonly known as valley fever, a respiratory disease contracted byinhaling airborne fungal spores. In the 8 weeks following the earthquake (24 Januarythrough 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 Valleyproduced many highly disrupted, dust-generating landslides during the earthquake andits aftershocks. Winds after the earthquake were from the North East, which transporteddust 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.

Jibson, Randall W.

203

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

USGS Publications Warehouse

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.

Jibson, R. W.

2002-01-01

204

Robust features of the source process for the 2004 Parkfield, California, earthquake from strong-motion seismograms  

NASA Astrophysics Data System (ADS)

We explore a recently developed procedure for kinematic inversion based on an elliptical subfault approximation. In this method, the slip is modelled by a small set of elliptical patches, each ellipse having a Gaussian distribution of slip. We invert near-field strong ground motion for the 2004 September 28 Mw 6.0 Parkfield, California, earthquake. The data set consists of 10 digital three-component 18-s long displacement seismograms. The best model gives a moment of 1.21 × 1018 N m, with slip on two distinct ellipses, one with a high-slip amplitude of 0.91 m located 20 km northwest of the hypocentre. The average rupture speed of the rupture process is ˜2.7 km s-1. We find no slip in the top 5 km. At this depth, a lineation of small aftershocks marks the transition from creeping above to locked below, in the interseismic period. The high-slip patch coincides spatially with the hypocentre of the 1966 Mw6.0 Parkfield, California, earthquake. The larger earthquakes prior to the 2004 Parkfield earthquake and the aftershocks of the 2004 earthquake (Mw > 3) also lie around this high-slip patch, where our model images a sharp slip gradient. This observation suggests the presence of a permanent asperity that breaks during large earthquakes, and has important implications for the slip deficit observed on the Parkfield segment, which is necessary for reliable seismic hazard assessment.

Twardzik, C.; Madariaga, R.; Das, S.; Custódio, S.

2012-12-01

205

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

USGS Publications Warehouse

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 M6.5–7 earthquake rates and also includes types of multifault ruptures seen in nature. Although UCERF3 fits the data better than UCERF2 overall, there may be areas that warrant further site-specific investigation. Supporting products may be of general interest, and we list key assumptions and avenues for future model improvements.

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

206

Long-term changes of earthquake inter-event times and low-frequency earthquake recurrence in central California  

NASA Astrophysics Data System (ADS)

The temporal evolution of earthquake inter-event time (IET) may provide important clues for the timing of future events and underlying physical mechanisms of earthquake interaction. In this study, we examine ~12 yr of local earthquake and low-frequency earthquake (LFE) activity near Parkfield, CA from catalogs of ~50,000 earthquakes and ~730,000 LFEs. We focus on the long-term evolution of IETs after the 2003 Mw6.5 San Simeon and 2004 Mw6.0 Parkfield earthquakes. The IETs of local earthquakes along and to the southwest of the San Andreas fault show clear decreases of several orders of magnitude after the Parkfield and San Simeon earthquakes, followed by recoveries with time scales of ~3 yr and >8 yr, respectively. We also observe decreases in recurrence times in some of LFE families, followed by long-term recoveries with time scales of ~4 months to several years. The long-term recovery of the earthquake IET is a manifestation of the aftershock decay of the Parkfield and San Simeon earthquakes, and the different recovery time scales likely reflect the different tectonic loading rates in the two regions. The drop in the recurrence times of LFEs after the Parkfield earthquake is likely caused by static and dynamic stresses induced by the Parkfield earthquake, and the long-term recovery in LFE recurrence time could be due to post-seismic relaxation or gradual recovery of fault zone material properties. The recovery time scales for general earthquake IET and LFE recurrence following the Parkfield earthquake are similar to those estimated for repeating earthquake recurrence identified in previous studies, indicating that they could be controlled by similar mechanisms.

Wu, Chunquan; Shelly, David R.; Gomberg, Joan; Peng, Zhigang; Johnson, Paul

2013-04-01

207

Rapid Determination of Event Source Parameters in Southern California for earthquake early warning  

NASA Astrophysics Data System (ADS)

The rapid increase in the number of seismic stations in earthquake prone regions, combined with the implementation of near real time data transmission technologies, provides the potential for earthquake early warning. In the absence of earthquake prediction methodologies in the foreseeable future, the rapid detection and analysis of a seismic event on its initiation, allowing the issuance of a ground motion warning of the order of seconds, is appealing. We present our efforts to design and implement such a system in southern California. The early warning systems currently operating in Mexico and Taiwan rely on significant distances (> 100 km) between the source and populated regions. In this scenario an early warning system can wait for several stations to detect an event, allowing the application of standard location and magnitude determination algorithms (a process that may take tens of seconds), and still issue a warning tens of seconds in advance of associated ground motion. The close proximity of fault zones to metropolitan areas in southern California precludes such an approach. Instead, we develop a system more similar to the UrEDAS warning system in Japan. The two event parameters needed are location and magnitude. The high density of seismic stations in southern California ( ~25 km spacing in populated areas) allows for an adequate location of events based solely on the first station to detect a P-arrival. The classical use of amplitude to determine magnitude is problematic due to its relatively high sensitivity to epicentral distance close to the source. Instead, we utilize the frequency dependence of the P-arrival to magnitude, which is less sensitive to epicentral distance. With this approach we estimate event magnitude with an accuracy of +/-1 magnitude unit using the P-arrival at one station only. As the P-arrival is recorded at additional stations, we average the magnitude estimates, which reduces the uncertainty. The event location and magnitude may then be used to estimate ground motion throughout the region using attenuation relations. Using the current TriNet infrastructure we expect to be able to reduce data transmission and analysis time sufficiently to be able to give zero to a few seconds warning prior to the onset of peak, damaging ground motion in the epicentral region. The warning time improves for locations further from the epicenter and, as the time-since-event initiation increases, the uncertainty in ground motion predictions decreases and warning messages can be updated.

Allen, R. M.; Kanamori, H.

2001-12-01

208

Probability  

NSDL National Science Digital Library

This series of videos, created by Salman Khan of the Khan Academics, introduces students to basic probability. Anyone using these videos should a reasonable grounding in basic algebra before viewing. This collection features seventeen different videos covering a broad array of topics within the discipline. Overall, this should serve as a solid introduction to this field.

Khan, Salman

2010-12-16

209

Compilation of Slip in Last Earthquake Data for High-Slip Rate Faults in California for Input into Slip Dependent Rupture Forecast  

NASA Astrophysics Data System (ADS)

Slip in the last earthquake along a fault, in conjunction with the application of appropriate recurrence models, can be used to estimate the timing and size of future ground-rupturing earthquakes. Surface slip measurements are relatively easy to acquire along highly active faults because offsets from the last event are usually well preserved by geomorphic features in the landscape. We present a comprehensive database of slip measurements for high slip rate strike-slip and dip-slip faults in California for input into the slip-dependent 2011 Uniform California Earthquake Rupture Forecast (UCERF 3). Our database includes historic, paleoseismic, and geomorphic data on the slip in the last event and multi-event offsets. Faults were prioritized by highest slip rates and longest time since the last event relative to average recurrence interval. Slip rate, timing of the last event, and recurrence interval were obtained from past reports by the Working Group on California Earthquake Probabilities, unless more recently published data were available. A literature search determined the availability of offset data for the highest priority faults. We contacted authors of published slip studies to ascertain whether additional data exist in unpublished archives, gray literature, or publications in preparation. The lack of consistency in existing schemes to rate offset quality led us to develop a new semi-quantitative method to asses feature quality and tectonic quality for new and existing data. Recent analyses of newly available, high-resolution LiDAR topography for micro-geomorphic offsets have substantially increased the number of slip measurements available for our compilation. For faults with LiDAR coverage, but limited, poor, or unavailable offset data, we identified reaches with a high potential to preserve geomorphic offsets and calculated slip measurements. The methodology for our geomorphic analyses has been developed and implemented successfully in recent studies along the central San Jacinto Fault and 1857 earthquake reach of the San Andreas Fault. Last, we compiled data collected from our literature search and LiDAR analysis into a geodatabase. Our database contains multiple measurements for the same features using different techniques, making it a powerful tool to test the repeatability of slip measurements. Our compilation reveals that despite local variation, slip values tend to cluster around a reach averaged mean, and slip can be similar at a point over multiple events.

Arrowsmith, R.; Madden, C.; Haddad, D. E.; Salisbury, J. B.; Weldon, R. J.

2011-12-01

210

EFFECTS OF THE 1983 COALINGA, CALIFORNIA, EARTHQUAKE ONCREEP ALONG THE SAN ADREAS FAULT.  

USGS Publications Warehouse

The M//L approximately equals 6. 5 earthquake that occurred near Coalinga, California, on May 2, 1983 induced changes in near-surface fault slip along the San Andreas fault. Coseismic steps were observed by creepmeters along a 200-km section of the San Andreas. some of the larger aftershocks induced additional steps, both right-lateral and left-lateral, and in general the sequence disrupted observed creep at several sites from preseismic long-term patterns. Static dislocation models can approximately explain the magnitudes and distribution of the larger coseismic steps on May 2. The smaller, more distant steps appear to be the abrupt release of accumulated slip, triggered by the coseismic strain changes, but independent of the strain change amplitudes.

Mavko, Gerald, M.; Schulz, Sandra; Brown, Beth, D.

1985-01-01

211

Triggered reverse fault and earthquake due to crustal unloading, northwest Transverse Ranges, California.  

USGS Publications Warehouse

A reverse-right-oblique surface rupture, associated with a ML 2.5 earthquake, formed in a diatomite quarry near Lompoc, California, in the northwesternmost Transverse Ranges on April 7, 1981. The 575-m-long narrow zone of ruptures formed in clay interbeds in diatomite and diatomaceous shale of the Neogene Monterey Formation. The ruptures parallel bedding, dip 39o-59oS, and trend about N84oE on the north limb of an open symmetrical syncline. Maximum net slip was 25 cm; maximum reverse dip slip was 23 cm, maximum right-lateral strike slip was about 9 cm, and average net slip was about 12 cm. The seismic moment of the earthquake is estimated at 1 to 2 X 1018 dyne/cm and the static stress drop at about 3 bar. The removal of an average of about 44 m of diatomite resulted in an average load reduction of about 5 bar, which decreased the normal stress by about 3.5 bar and increased the shear stress on the tilted bedding plane by about 2 bar. The April 7, 1981, event was a very shallow bedding-plane rupture, apparently triggered by crustal unloading. -Authors

Yerkes, R. F.; Ellsworth, W. L.; Tinsley, J. C.

1983-01-01

212

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

USGS Publications Warehouse

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.

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

2006-01-01

213

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

USGS Publications Warehouse

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.

Waldhauser, F.; Ellsworth, W. L.

2000-01-01

214

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

NASA Astrophysics Data System (ADS)

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-specific investigation. Supporting products may be of general interest, and we list key assumptions and avenues for future model improvements.

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

215

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

USGS Publications Warehouse

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 waveforms are available, we find that fewer than 6.5% of the earthquakes can be classified as repeating earthquakes, events that rupture the same fault patch more than one time. These most commonly are located in the shallow creeping part of the fault, or within the streaks at greater depth. The slow repeat rate of 2-3 times within the 15-year observation period for events with magnitudes around M = 1.5 is indicative of a low slip rate or a high stress drop. The absence of microearthquakes over large, contiguous areas of the northern Hayward Fault plane in the depth interval from ???5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large-magnitude earthquakes.

Waldhauser, F.; Ellsworth, W. L.

2002-01-01

216

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

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) slip is partitioned northward from the San Andreas fault and into the eastern California shear zone, and/or (3) slip is partitioned onto the Banning strand of the San Andreas fault zone.

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

2002-01-01

217

Southern California permanent GPS geodetic array: Spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 Landers earthquake  

Microsoft Academic Search

The June 28, 1992 (MW=7.3) Landers, California, earthquake was the first earthquake to be surveyed by a continuously operating Global Positioning System (GPS) array. The coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake. We employ a new spatial filtering technique that removes common-mode errors

Shimon Wdowinkski; Yehuda Bock; Jie Zhang; Peng Fang; Joachim Genrich

1997-01-01

218

Earthquakes  

MedlinePLUS

... earthquake is the sudden, rapid shaking of the earth, caused by the breaking and shifting of subterranean ... the forces of plate tectonics have shaped the earth, as the huge plates that form the earth’s ...

219

Earthquakes  

USGS Publications Warehouse

One of the most frightening and destructive phenomena of nature is a severe earthquake and its terrible aftereffects. An earthquake is a sudden movement of the Earth, caused by the abrupt release of strain that has accumulated over a long time. For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that form the Earth's surface slowly move over, under, and past each other. Sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free. If the earthquake occurs in a populated area, it may cause many deaths and injuries and extensive property damage. Today we are challenging the assumption that earthquakes must present an uncontrollable and unpredictable hazard to life and property. Scientists have begun to estimate the locations and likelihoods of future damaging earthquakes. Sites of greatest hazard are being identified, and definite progress is being made in designing structures that will withstand the effects of earthquakes.

Shedlock, Kaye M.; Pakiser, Louis Charles

1998-01-01

220

Anomalous geomagnetic variations associated with Parkfield (Ms=6.0, 28-SEP-2004, California, USA) earthquake  

NASA Astrophysics Data System (ADS)

Analysis of geomagnetic and telluric data, measured at the station PRK (Parkfield, ULF flux-gate 3-axial magnetometer) 1 week before (including) the day of the major EQ (EarthQuake, Ms=6.0, 28-SEP-2004, 17:15:24) near Parkfield, California, USA, are presented. Spectral analysis reveal the ULF geomagnetic disturbances observed the day before the event, Sep 27, at 15:00- 20:00 by UT, and at the day of the EQ, Sep 28, at 11:00-19:00. Filtering in the corresponding frequency band f = 0.25-0.5 Hz gives the following estimations of the amplitudes of the signals: up to 20 pT for the magnetic channels and 1.5 mkV/km for the telluric ones. Observed phenomena occurs under quiet geomagnetic conditions (|Dst|<20 nT); revision of the referent stations data situated far away from the EQ epicenter (330 km) does not reveal any similar effect. Moreover, the Quake Finder research group (http:www.quakefinder.com) received very similar results (ELF range instrument, placed about 50 km from the EQ epicenter) for the day of the EQ. Mentioned above suggests the localized character of the source, possibly of the ionosphere or tectonic origin rather than of magnetosphere. Comparative analysis of the mentioned 2 stations show that we observed the lower-frequency part of the ULF- ELF burst, localized in the frequency range 0.25-1 Hz, generated 9 hours before the earthquake. Acknowledgements. The authors are grateful to Malcolm Johnston for providing us with the geomagnetic data.

Kotsarenko, A. A.; Pilinets, S. A.; Perez Enriquez, R.; Lopez Cruz Abeyro, J. A.

2007-05-01

221

Crustal structure beneath the eastern part of the Coast Ranges (Diablo Range) of central California from explosion seismic and near earthquake data  

Microsoft Academic Search

Seismic refraction and near earthquake data of the U.S. Geological Survey for central California have been compiled into record sections along profiles and interpreted in terms of crustal structure. The profiles are located northeast of the San Andreas fault of central California and run parallel to the general structures. For the explosion seismic line through the centre of the Diablo

P. Blümbling; C. Prodehl

1983-01-01

222

From the Testing Center of Regional Earthquake Likelihood Models to the Collaboratory for the Study of Earthquake Predictability  

Microsoft Academic Search

The Regional Earthquake Likelihood Models (RELM) project aims to produce and evaluate alternate models of earthquake potential (probability per unit volume, magnitude, and time) for California. Based on differing assumptions, these models are produced to test the validity of their assumptions and to explore which models should be incorporated in seismic hazard and risk evaluation. During the years of the

D. Schorlemmer; M. Gerstenberger; T. Jordan; E. Field; S. Wiemer; L. Jones; D. D. Jackson

223

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

NASA Astrophysics Data System (ADS)

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.

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

2009-07-01

224

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

NASA Astrophysics Data System (ADS)

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 Quake Monitoring System (AQMS) and the SeisComP3 real-time earthquake monitoring systems is underway. VS operation in California will eventually be fully transitioned to the CISN AQMS system. European installations of VS will most likely be based on the SeisComP3 platform.

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

2012-12-01

225

Earthquakes  

NSDL National Science Digital Library

This is an online lesson that can be transferred into a classroom instructional activity by the teacher. This lesson simplifies the concepts while pushing the the higher order thinking concepts with scaffolding all concepts of the layers of the earth, plate tectonics, P and S waves, creating a model of an earthquake. Students enjoy this lesson and have been able to improve on assessment after completing the Earthquake lesson. Teachers will enjoy the online printable worksheets that correlate to the lesson/data sheets and the variety of choices while using the interactive tool for whole group instruction. There are many choices for formative assessment as well as summamtive assessment.

U.S. Geological Survey Joy Lopez, M.A., teacher Scott Hassler, Ph.D. Geologist

2011-10-14

226

Probability of detecting perchlorate under natural conditions in deep groundwater in California and the southwestern United States.  

PubMed

We use data from 1626 groundwater samples collected in California, primarily from public drinking water supply wells, to investigate the distribution of perchlorate in deep groundwater under natural conditions. The wells were sampled for the California Groundwater Ambient Monitoring and Assessment Priority Basin Project. We develop a logistic regression model for predicting probabilities of detecting perchlorate at concentrations greater than multiple threshold concentrations as a function of climate (represented by an aridity index) and potential anthropogenic contributions of perchlorate (quantified as an anthropogenic score, AS). AS is a composite categorical variable including terms for nitrate, pesticides, and volatile organic compounds. Incorporating water-quality parameters in AS permits identification of perturbation of natural occurrence patterns by flushing of natural perchlorate salts from unsaturated zones by irrigation recharge as well as addition of perchlorate from industrial and agricultural sources. The data and model results indicate low concentrations (0.1-0.5 ?g/L) of perchlorate occur under natural conditions in groundwater across a wide range of climates, beyond the arid to semiarid climates in which they mostly have been previously reported. The probability of detecting perchlorate at concentrations greater than 0.1 ?g/L under natural conditions ranges from 50-70% in semiarid to arid regions of California and the Southwestern United States to 5-15% in the wettest regions sampled (the Northern California coast). The probability of concentrations above 1 ?g/L under natural conditions is low (generally <3%). PMID:21247209

Fram, Miranda S; Belitz, Kenneth

2011-02-15

227

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

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)

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

1981-01-01

228

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

USGS Publications Warehouse

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.

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

2003-01-01

229

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

NASA Technical Reports Server (NTRS)

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.

Merifield, P. M.; Lamar, D. L. (principal investigators)

1974-01-01

230

Earthquake Myths  

NSDL National Science Digital Library

This site serves to belie several popular myths about earthquakes. Students will learn that most earthquakes do not occur in the early morning and one cannot be swallowed up by an earthquake. In addition, there is no such thing as earthquake weather and California is not falling into the ocean. On the more practical side, students can learn that good building codes do not insure good buildings, it is safer under a table than in a doorway during an earthquake, and most people do not panic during an earthquake.

231

Earthquakes  

Microsoft Academic Search

I HAVE observed, in several recent numbers of NATURE, various notices of earthquakes, so frequent as to suggest the idea to me (perhaps incorrect) that for several months past they have been more numerous than usual. Since my arrival in West Java I have experienced several severe shocks. On March 28, between 7 and 8 P.M., I was startled by

Henry O. Forbes

1879-01-01

232

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

Microsoft Academic Search

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

Susan E. Hough; Susan E

2008-01-01

233

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

USGS Publications Warehouse

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.

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

2005-01-01

234

Coulomb stress changes imparted by simulated M>7 earthquakes to major fault surfaces in Southern California  

NASA Astrophysics Data System (ADS)

To study static stress interactions between faults in southern California and identify cases where one large earthquake could trigger another, we select fourteen M>7 events simulated by the SCEC/CME CyberShake project and calculate the Coulomb stress changes those events impart to major fault surfaces in the UCERF2 fault model for the region. CyberShake simulates between 6 and 32 slip distributions for each event at a slip sampling resolution of 1 km, and we calculate stress changes on fault surfaces at the same resolution, a level of detail which is unprecedented in studies of stress transfer and which allows us to study the way that variabilities in slip on the source can affect imparted stress changes. We find that earthquakes rupturing the southern San Andreas fault generally decrease Coulomb stress on right-lateral faults in the Los Angeles basin, while M>7 events on the San Jacinto, Elsinore, Newport-Inglewood and Palos Verdes faults generally decrease stress on parallel right-lateral faults but increase Coulomb stress on the Mojave or San Bernardino sections of the San Andreas. Stress interactions between strike-slip and thrust faults and between the San Andreas and Garlock faults depend on the rupture area of the source. Coulomb stress changes imparted by simulated SAF events to locations on the San Jacinto and Garlock faults within ~8 km of the San Andreas appear to be influenced more by the nearby distribution of high and low slip on the San Andreas than by the overall slip distribution across the entire rupture. Using a simplified model, we calculate that an area of no slip surrounded by high slip on a rupture imparts strong Coulomb stress increases ?7 km to either side of the source fault, possibly explaining the apparent ~8-km range of influence of local slip on the San Andreas. Additionally, we devise a method for evaluating uncertainty values in Coulomb stress changes caused by uncertainties in the strike, dip and rake of the receiver fault. These findings may be useful in understanding stress interactions between faults of different orientations and rakes, stress transfer and variability at short distances from the source fault, and applications of uncertainty values to Coulomb stress changes.

Rollins, J. C.; Ely, G. P.; Jordan, T. H.

2011-12-01

235

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)

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 earthquakes in the Foothills Cluster are occurring in response to the downward pull of an attached piece of dense ultramafic batholith residue and the events in the Yosemite Cluster are related to post-delamination crustal magmatic processes.

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

2008-12-01

236

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

USGS Publications Warehouse

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.

Sherrouse, Benson C.; Hester, David J.

2008-01-01

237

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

USGS Publications Warehouse

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.

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

1985-01-01

238

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

USGS Publications Warehouse

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.

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

2002-01-01

239

Spatial migration of earthquakes within seismic clusters in Southern California: Evidence for fluid diffusion  

NASA Astrophysics Data System (ADS)

Seismicity within many earthquake swarms is observed to migrate slowly with time, which may reflect event triggering due to slow fault slip or fluid flow. We search for this behavior in Southern California by applying a weighted least squares method to quantify event migration within 69 previously observed seismicity bursts. We obtain best-fitting migration directions and velocities, and compute a statistical migration significancesm for each burst using a bootstrap resampling method. We define 37 bursts with sm ? 0.8 as the migration group, and 32 bursts with sm < 0.8 as the non-migration group. To explore differences between the two groups, for each burst we compute effective stress drop (??quasi, the ratio between total moment and radius), the skew of the moment release time series (?), the timing of the largest event (tmax), and the distance separation between the first half and second half of the sequence (ds). As expected, the migration group features larger ds and lower ??quasi, consistent with higher migration significance. It also features lower ? and higher tmax, similar to observations from swarms in the Salton Trough, while the non-migration group is more similar to main shock-aftershock sequences. To explore possible fluid involvement, we model the migration behavior with the fluid diffusion equation, and identify 18 bursts with diffusion coefficients ranging from 0.01 to 0.8 m2/s, with the majority below 0.16 m2/s. The obtained diffusion coefficients and migration behavior are similar to the Reservoir-induced seismicity beneath the Açu reservoir in Brazil. The majority of normal faulting events are associated with these 18 bursts, while the non-migration group has the most reverse faulting events, indicating a possible link between sequence type and focal mechanism.

Chen, X.; Shearer, P. M.; Abercrombie, R. E.

2012-04-01

240

Deformational structures of possible earthquake origin in Pleistocene shelf siltstone, San Francisco, California  

SciTech Connect

Enigmatic structures, possibly generated by large earthquakes, are common in Pleistocene shelf deposit exposed in sea cliffs south of San Francisco, California. The shelf deposits, consisting of very fine sandstone and sandy siltstone, lie within a 1,750-m-thick succession part of the Merced Formation. The structures described here are restricted to the siltstone, where they occupy stratigraphic intervals centimeters to decimeters thick of closely spaced, anastomosing thin laminae, of silt and sand. In some beds, the concentrations of sand take the form of flattened rods, 1-2 mm high, 3-4 mm across, and a few centimeters long. Many of the disarticulated bivalve shells and shell fragment and small pieces of wood within these intervals stand upright and, on bedding-plane exposures, are visually aligned parallel to the long axes of the rods of sand in the same interval. Small sand-filled fractures, parallel to the rods and the vertical shells, extend downward from 1 cm to several centimeters from the base of individual silt laminae, particularly where they are bowed into small anticlinal structures. The intervals have sharp lower contacts and less well defined upper contacts. Balls of sand and silt with deformed internal lamination attest to a deformational origin for the anastomosing laminae, and the aligned sand rods, vertical shells, and fractures. Some of the intervals are penetrated by tubular burrows, suggesting that they formed no more than a few tens of centimeters below the sea floor. The intervals occur in clusters of three to five within 1-2 m of section and are separated by 2-4 m of section in which the structure is absent. The combination of features within the intervals can be explained by alternating extension and compression of the sediment accompanied by rapid dewatering.

Clifton, H.E. (Geological Survey, Menlo Park, CA (USA))

1990-05-01

241

Modeling the Mechanical Behavior and Slip Distribution of Faults Involved in the 1992 Landers Earthquake in Southern California  

NASA Astrophysics Data System (ADS)

Multi-fault, strike-slip earthquakes can be more powerful than earthquakes involving one fault, and the complexity of multi-fault systems makes it difficult to determine the probability of multi-fault earthquakes. Modeling the mechanical behaviors of such fault systems may give insight into these complex events. The project involves the 1992 Landers earthquake, focusing on (1) organizing data from the earthquake, and (2) using a simple model to determine how certain rock properties influence slip on a fault in an earthquake. For (1), previously obtained field measurements of lateral and vertical slip were labeled on a map of the region, and given a coordinate system, we digitized the locations and values of the slip measurements. For (2), a software program called Poly3D was used to simulate faults and their surrounding rock. The program allows the user to input parameters called elastic moduli that constrain how the rock responds to stress. To simulate an earthquake, a stress is applied to the system and the program displays the simulation results, usually showing that the fault surface has slipped in response to the stress. Using a simple model of a 20-km rectangular fault, we performed four sets of runs; in each set, one parameter is varied while others are kept constant. The maximum right-lateral slip that occurs was recorded for each run, and then the maximum slip was graphed versus the variable parameter. This way, the relation of each parameter to the maximum slip that occurs in the simulation could be determined. Knowing these relationships helps improve the models to match the field measurements compiled in part (1) of our work. The next step is to compare more complex models to the field data. Results for one model are shown as an example of how this comparison will be done.

He, J.; Madden, B. H.

2010-12-01

242

Monitoring Local and Teleseismic Earthquakes Off--Shore San Diego(California) During an OBSIP Test Deployment  

NASA Astrophysics Data System (ADS)

The Scripps OBS (Ocean Bottom Seismometer) team is one of three groups that provide instrumentation for the US National OBS Instrument Pool (OBSIP). The compact active source LC2000 instruments are being used successfully in numerous experiments, with excellent data quality and return rates. A set of five new passive seismic instruments was test--deployed from November 6th, 2003 through January 8th, 2004 in the San Diego Trough, about 1km below the sea surface, about 40km off--shore San Diego, California. These instruments are equipped with a Nanometrics Trillium 40s 3--component seismometer and a Cox--Webb differential pressure gauge. We recorded more than 30 teleseismic earthquakes suitable for a long-period surface wave study. The vertical--component seismometer recordings are of excellent quality and are often superior to those from similar sensors on land (Guralp CMG-40T). The signal--to--noise ratio on the DPGs depend strongly on the water depth and was expected to be low for the test deployment. Nevertheless, the December 22, 2003 San Simeon/ California earthquake was recorded with high fidelity and non--seismogenic signals are extremely coherent down to very long periods. We also recorded numerous local earthquakes. Many of these occurred off-shore and the OBSs were the closest stations by many tens of kilometers. For example, a magnitude 3.0 earthquake on the Coronado Banks Fault was recorded at station SOL in La Jolla at about 30km distance, with a signal-to-noise ratio too poor to pick the first arrival. The next closest stations were 60km and 80km away, while one of the OBSs was only 20km away. The co-deployment of DPGs allowed us to observe the first P arrival very clearly. We also recorded numerous events that were not recorded on land. About six months later, on June 15, 2004 the greater San Diego area was struck by a magnitude 5.2 earthquake on the San Clemente Fault, about 40km southwest of the OBS test deployment. Though no structural damage was reported, intensity 4 shaking occurred throughout the city, which prompted Amtrak and Sea World to shut down operations for inspections. These events are continous reminders that significant seismic hazard is caused by activity along the only poorly understood, off-shore faults in the California Borderland. Realtime seismic monitoring using cabled or moored seismic observatories is clearly needed.

Laske, G.; Babcock, J.; Hollinshead, C.; Georgieff, P.; Allmann, B.; Orcutt, J.

2004-12-01

243

The magnitude 6.7 Northridge, California, earthquake of 17 January 1994  

USGS Publications Warehouse

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.

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

244

Damage and restoration of geodetic infrastructure caused by the 1994 Northridge, California, earthquake  

USGS Publications Warehouse

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.

Hodgkinson, Kathleen M.; Stein, Ross S.; Hudnut, Kenneth W.; Satalich, Jay; Richards, John H.

1996-01-01

245

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)

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 showed similar increases in 30 minute averaged energy excursions, but the 30 minute averages had a disadvantage in that they reduced the signal to noise ratio over the individual pulse counting method. In other electromagnetic monitoring methods, air conductivity instrumentation showed major changes in positive air-borne ions observed near the Alum Rock and Tacna sites, peaking during the 24 hours prior to the earthquake. The use of GOES (geosynchronous) satellite infra red (IR) data showed that an unusual apparent “night time heating” occurred in an extended area within 40+ km. of the Alum Rock site, and this IR signature peaked around the time of the magnetic pulse count peak. The combination of these 3 indicators (magnetic pulse counts, air conductivity, and IR night time heating) may be the start in determining the time (within 1-2 weeks), location (within 20-40km) and magnitude (within +/- 1 increment of Richter magnitude) of earthquake greater than M5.4

Bleier, T. E.; Dunson, C.; Roth, S.; Heraud, J.; Freund, F. T.; Dahlgren, R.; Bryant, N.; Bambery, R.; Lira, A.

2010-12-01

246

Paleoseismology of the southern Panamint Valley fault: Implications for regional earthquake occurrence and seismic hazard in southern California  

NASA Astrophysics Data System (ADS)

data from the southern Panamint Valley fault (PVF) reveal evidence of at least four surface ruptures during late Holocene time (0.33-0.48 ka, 0.9-3.0 ka, 3.3-3.6 ka, and >4.1 ka). These paleo-earthquake ages indicate that the southern PVF has ruptured at least once and possibly twice during the ongoing (?1.5 ka) seismic cluster in the Mojave section of the eastern California shear zone (ECSZ). The most recent event (MRE) on the PVF is also similar in age to the 1872 Owens Valley earthquake and the geomorphically youthful MRE on the Death Valley fault. The timing of the three oldest events at our site shows that the PVF ruptured at least once and possibly thrice during the well-defined 2-5 ka seismic lull in the Mojave section of the ECSZ. Interestingly, the 3.3-3.6 ka age of Event 3 overlaps with the 3.3-3.8 ka age of the penultimate (i.e., pre-1872) rupture on the central Owens Valley fault. These new PVF data support the notion that earthquake occurrence in the ECSZ may be spatially and temporally complex, with earthquake clusters occurring in different regions at different times. Coulomb failure function modeling of the Panamint Valley and Garlock faults reveals significant stress interactions between these two faults that may influence future earthquake occurrence. Specifically, our models suggest a possible rupture sequence whereby an event on the southern Panamint Valley fault can lead to the potential triggering of an event on the Garlock fault, which in turn could trigger the Mojave section of the San Andreas Fault.

McAuliffe, Lee J.; Dolan, James F.; Kirby, Eric; Rollins, Chris; Haravitch, Ben; Alm, Steve; Rittenour, Tammy M.

2013-09-01

247

Ground-water-level monitoring for earthquake prediction; a progress report based on data collected in Southern California, 1976-79  

USGS Publications Warehouse

The U.S. Geological Survey is conducting a research program to determine if groundwater-level measurements can be used for earthquake prediction. Earlier studies suggest that water levels in wells may be responsive to small strains on the order of 10 to the minus 8th power to 10 to the minus 10th power (dimensionless). Water-level data being collected in the area of the southern California uplift show response to earthquakes and other natural and manmade effects. The data are presently (1979) being made ready for computer analysis. The completed analysis may indicate the presence of precursory earthquake information. (USGS)

Moyle, W. R., Jr.

1980-01-01

248

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

Microsoft Academic Search

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

J. Woessner; S. Wiemer; D. Giardini

2002-01-01

249

The Loma Prieta, California, Earthquake of October 17, 1989: Performance of the Built Environment  

USGS Publications Warehouse

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).

Coordinated by Holzer, Thomas L.

1998-01-01

250

Chapter C. The Loma Prieta, California, Earthquake of October 17, 1989 - Preseismic Observations  

USGS Publications Warehouse

The October 17, 1989, Loma Prieta, Calif., Ms=7.1 earthquake provided the first opportunity in the history of fault monitoring in the United States to gather multidisciplinary preearthquake data in the near field of an M=7 earthquake. The data obtained include observations on seismicity, continuous strain, long-term ground displacement, magnetic field, and hydrology. The papers in this chapter describe these data, their implications for fault-failure mechanisms, the scale of prerupture nucleation, and earthquake prediction in general. Of the 10 papers presented here, about half identify preearthquake anomalies in the data, but some of these results are equivocal. Seismicity in the Loma Prieta region during the 20 years leading up to the earthquake was unremarkable. In retrospect, however, it is apparent that the principal southwest-dipping segment of the subsequent Loma Prieta rupture was virtually aseismic during this period. Two M=5 earthquakes did occur near Lake Elsman near the junction of the Sargent and San Andreas faults within 2.5 and 15 months of, and 10 km to the north of, the Loma Prieta epicenter. Although these earthquakes were not on the subsequent rupture plane of the Loma Prieta earthquake and other M=5 earthquakes occurred in the preceding 25 years, it is now generally accepted that these events were, in some way, foreshocks to the main event.

Edited by Johnston, Malcolm J. S.

1993-01-01

251

The Cape Mendocino, California, earthquakes of April 1992 - Subduction at the Triple Junction  

Microsoft Academic Search

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

D. Oppenheimer; G. Beroza; G. Carver; L. Dengler; J. Eaton; L. Gee; F. Gonzalez; A. Jayko; W. H. Li; M. Lisowski; R. McPherson; B. Romanowicz; K. Satake; P. Somerville; D. Valentine

1993-01-01

252

Seismotectonics of the 2010 El Mayor Cucapah - Indiviso Earthquake and its Relation to Seismic Hazard in Southern California  

NASA Astrophysics Data System (ADS)

The April 4th, 2010 Mw 7.2 earthquake was the largest earthquake in over 100 years of known historical seismicity in the Salton Trough region. It was a relatively benign earthquake, with only two deaths related to its occurrence. It produced, however, profound agricultural and ecological changes at the southern section of the Mexicali Valley, where a new fault called the Indiviso fault, is shown to have ruptured by analysis of ALOS PALSAR and Landsat imagery. The Indiviso fault connects the ridge-transform and continental transform tectonic regimes with a straight linkage, as revealed by this earthquake, but this event also simultaneously involved oblique normal faulting and cross-faulting. The earthquake was complex, with at least three distinct slip pulses. It originated as a normal rupture along the ~18 km long, N-S striking El Mayor-Hardy fault along the east margin of the Sierra El Mayor. After 10 seconds, two large bursts of energy were released, one to the NW and one to the SE, producing the total moment release equivalent to Mw 7.25. The NW ruptures reactivated portions of the Pescadores, Borrego and Paso Superior faults with minor slip along the Laguna Salada and several other faults. This section had a dominant right lateral strike slip sense of motion with the NE side down. To the SE of the epicenter, disruption occurred along the dominantly strike-slip Indiviso fault, with a SW side down component of dip slip. The epicentral aftershock area, including its main aftershock to the NW, is >120 km in length; the surficial faulting occurs along ~110 km with 6-9 km of splaying to the N-NE at the NW end and to the S-SW at the SE end. The El Mayor Cucapah - Indiviso event follows nine M>6.5 earthquakes along the San Andreas fault system in the past 80 years between the head of the Gulf of California and the Transverse Ranges. Long, straight fault segments capable of larger earthquakes, and that have not ruptured historically, include portions of the San Jacinto and Elsinore faults, and the entire southern San Andreas Fault.

Gonzalez-Garcia, J. J.; Gonzalez Ortega, A.; Bock, Y.; Fialko, Y.; Fielding, E. J.; Fletcher, J. M.; Galetzka, J. E.; Hudnut, K. W.; Munguia, L.; Nelson, S. M.; Rockwell, T. K.; Sandwell, D. T.; Stock, J.

2010-12-01

253

Real-time Testing of On-site Earthquake Early Warning within the California Integrated Seismic Network (CISN) Using Statewide Distributed and On-site Processing  

Microsoft Academic Search

Currently, the real-time performance of three algorithms for earthquake early warning is being tested within the California Integrated Seismic Network (CISN). We report on the implementation and performance of the tauc-Pd on-site warning algorithm in California and describe recent improvements of the software. These include: (1) the development of a new tauc-Pd based trigger criterion to reduce the number of

M. Böse; E. Hauksson; K. Solanki; H. Kanamori; T. H. Heaton; Y. Wu

2008-01-01

254

New Technology to Help Measurement and Study of Earthquakes  

NSF Publications Database

... movements of earthquake faults throughout southern California. This information should help ... in decades," says Tom Henyey, director of the Southern California Earthquake Center (SCEC) in Los ...

255

Estimating Earthquake Hazards in the San Pedro Shelf Region, Southern California  

NASA Astrophysics Data System (ADS)

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 basement, where observed, is approx. 1.7 km. beneath the base then shallows to approx. 1 km at the top of the SPS. This corresponds to the results obtained by Fisher et al. (in press) and Wright (1991). The pattern of faulting changes from southwest to the northeast. West of CF, faulting is confined to the pelagic and older units. Closely spaced faulting (~0.75 km) is prominent between CF and Avalon Knoll (AV), while generally more widely spaced faults (~5 km) with localized fracture zones is observed from AV to the SPS. The SPS is dominated by major faults such as the Cabrillo, Palos Verdes, THUMS Huntington Beach and Newport-Inglewood fault zones. The Cabrillo and Palos Verdes fault are major stratigraphic discontinuity with laminar beds (~30 cm) adjacent to gently folded sediments (wavelength ~1.5 km). There is evidence of recent displacement on the Cabrillo fault.

Baher, S.; Fuis, G.; Normark, W. R.; Sliter, R.

2003-12-01

256

A search for evidence of secondary static stress triggering during the 1992 Mw7.3 Landers, California, earthquake sequence  

NASA Astrophysics Data System (ADS)

Secondary triggering of aftershocks is widely observed and often ascribed to secondary static stress transfer. However, small to moderate earthquakes are generally disregarded in estimates of Coulomb stress changes (?CFS), either because of source parameter uncertainties or a perceived lack of importance. We use recently published high-quality focal mechanisms and hypocenters to reassess the role of small to moderate earthquakes for static stress triggering of aftershocks during the 1992 Mw7.3 Landers, California, earthquake sequence. We compare the ?CFS imparted by aftershocks (2?M?6) onto subsequent aftershocks with the total ?CFS induced by the M>6 main shocks. We find that incremental stress changes between aftershock pairs are potentially more often positive than expected over intermediate distances. Cumulative aftershock stress changes are not reliable for receivers with nearby aftershock stress sources because we exclude unrealistic aftershock stress shadows that result from uniform slip models. Nonetheless, 27% of aftershocks receive greater positive stress from aftershocks than from the main shocks. Overall, 85% of aftershocks are encouraged by the main shocks, while adding secondary stress encourages only 79%. We infer that source parameter uncertainties of small aftershocks remain too large to convincingly demonstrate (or rule out) that secondary stress transfer induces aftershocks. An important exception concerns aftershocks in main shock stress shadows: well-resolved secondary stress from detected aftershocks rarely compensates negative main shock stress; these aftershocks require a different triggering mechanism.

Meier, M.-A.; Werner, M. J.; Woessner, J.; Wiemer, S.

2014-04-01

257

Comments on baseline correction of digital strong-motion data: Examples from the 1999 Hector Mine, California, earthquake  

USGS Publications Warehouse

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.

Boore, D. M.; Stephens, C. D.; Joyner, W. B.

2002-01-01

258

Geodetic slip rate for the eastern California shear zone and the recurrence time of Mojave desert earthquakes  

USGS Publications Warehouse

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.

Sauber, J.; Thatcher, W.; Solomon, S. C.; Lisowski, M.

1994-01-01

259

Rupture process and energy budget of the 29 July 2008 Mw 5.4 Chino Hills, California, earthquake  

NASA Astrophysics Data System (ADS)

The source model of the 2008 Mw 5.4 Chino Hills, California, earthquake is constrained using near-field seismic body waves recorded by the California Integrated Seismic Network (CISN). Finite fault inversions are preformed for the two fault models based on the nodal planes derived from the CISN moment tensor solution. The northeast dipping plane (strike = 289°; dip = 62°), which has a similar strike as the nearby Whittier fault, is chosen as the causative fault because it fits the data significantly better. Our inversion result indicates that the majority of the Chino Hills earthquake rupture occurred in a compact area. In particular, 48% of the total seismic moment (1.6 × 1017 Nm) was released by the failure of a 1.8 km2 asperity located east of the hypocenter in a short time window from 0.4 to 0.8 s after the rupture initiation. The average slip is approximately 0.5 m but the maximum slip is 1.8 m. The average rupture velocity is 1.9 km/s. The static stress drop calculated using the slip model is up to 80 MPa and the average stress drop changes from 19 to 38 MPa, depending on the average schemes. The weighted average slip velocity is 6.5 m/s for entire rupture and is 11 m/s for the east asperity. The inferred available energy and radiated energy are 8 × 1013 J and 2.5 × 1013 J, respectively. Radiation efficiency is then 0.31, which is moderately low compared with previous earthquakes but consistent with the inferred high average fracture energy density, ranging from 6.5 to 14.8 MJ/m2.

Shao, Guangfu; Ji, Chen; Hauksson, Egill

2012-07-01

260

Triggered surface slips in the Coachella Valley area associated with the 1992 Joshua Tree and Landers, California, Earthquakes  

USGS Publications Warehouse

The Coachella Valley area was strongly shaken by the 1992 Joshua Tree (23 April) and Landers (28 June) earthquakes, and both events caused triggered slip on active faults within the area. Triggered slip associated with the Joshua Tree earthquake was on a newly recognized fault, the East Wide Canyon fault, near the southwestern edge of the Little San Bernardino Mountains. Slip associated with the Landers earthquake formed along the San Andreas fault in the southeastern Coachella Valley. Surface fractures formed along the East Wide Canyon fault in association with the Joshua Tree earthquake. The fractures extended discontinuously over a 1.5-km stretch of the fault, near its southern end. Sense of slip was consistently right-oblique, west side down, similar to the long-term style of faulting. Measured offset values were small, with right-lateral and vertical components of slip ranging from 1 to 6 mm and 1 to 4 mm, respectively. This is the first documented historic slip on the East Wide Canyon fault, which was first mapped only months before the Joshua Tree earthquake. Surface slip associated with the Joshua Tree earthquake most likely developed as triggered slip given its 5 km distance from the Joshua Tree epicenter and aftershocks. As revealed in a trench investigation, slip formed in an area with only a thin (<3 m thick) veneer of alluvium in contrast to earlier documented triggered slip events in this region, all in the deep basins of the Salton Trough. A paleoseismic trench study in an area of 1992 surface slip revealed evidence of two and possibly three surface faulting events on the East Wide Canyon fault during the late Quaternary, probably latest Pleistocene (first event) and mid- to late Holocene (second two events). About two months after the Joshua Tree earthquake, the Landers earthquake then triggered slip on many faults, including the San Andreas fault in the southeastern Coachella Valley. Surface fractures associated with this event formed discontinuous breaks over a 54-km-long stretch of the fault, from the Indio Hills southeastward to Durmid Hill. Sense of slip was right-lateral; only locally was there a minor (~1 mm) vertical component of slip. Measured dextral displacement values ranged from 1 to 20 mm, with the largest amounts found in the Mecca Hills where large slip values have been measured following past triggered-slip events.

Rymer, M. J.

2000-01-01

261

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

USGS Publications Warehouse

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.

Edited by Holzer, Thomas L.

1998-01-01

262

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)

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 in the brittle domain to temperatures as high as ~700o C. Above these deep events are two distinct shallower zones of seismicity. The mid-crustal long-period earthquakes between 10 and 20 km are presumably occurring within the silicic crust, but below the rheological transition from brittle to plastic behavior, expected to occur at temperatures of ~350 to 400o C. Above this transition are shallow brittle-failure earthquakes, in the upper 8 kilometers of the silicic crust. These lower crustal brittle-failure earthquakes are similar in depth and tectonic setting to those that occurred beneath the Sierra Nevada crest in the vicinity of Lake Tahoe in late 2003, which Smith et al. (Science, 2004) concluded were associated with a magmatic intrusion in the lower crust. The Mammoth sequences, however, are much shorter in duration (1-2 days compared with several months) and have no detectable accompanying geodetic signal. Thus, there is no clear evidence for a significant intrusion associated with these deep swarms of brittle-failure earthquakes beneath Mammoth Mountain.

Hill, D. P.; Shelly, D. R.

2010-12-01

263

The 2010 M w 7.2 El Mayor-Cucapah Earthquake Sequence, Baja California, Mexico and Southernmost California, USA: Active Seismotectonics along the Mexican Pacific Margin  

NASA Astrophysics Data System (ADS)

The El Mayor-Cucapah earthquake sequence started with a few foreshocks in March 2010, and a second sequence of 15 foreshocks of M > 2 (up to M4.4) that occurred during the 24 h preceding the mainshock. The foreshocks occurred along a north-south trend near the mainshock epicenter. The M w 7.2 mainshock on April 4 exhibited complex faulting, possibly starting with a ~M6 normal faulting event, followed ~15 s later by the main event, which included simultaneous normal and right-lateral strike-slip faulting. The aftershock zone extends for 120 km from the south end of the Elsinore fault zone north of the US-Mexico border almost to the northern tip of the Gulf of California. The waveform-relocated aftershocks form two abutting clusters, each about 50 km long, as well as a 10 km north-south aftershock zone just north of the epicenter of the mainshock. Even though the Baja California data are included, the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border. The spatial distribution of large aftershocks is asymmetric with five M5+ aftershocks located to the south of the mainshock, and only one M5.7 aftershock, but numerous smaller aftershocks to the north. Further, the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes. Thus, the aftershocks also express a complex pattern of stress release along strike. The overall rate of decay of the aftershocks is similar to the rate of decay of a generic California aftershock sequence. In addition, some triggered seismicity was recorded along the Elsinore and San Jacinto faults to the north, but significant northward migration of aftershocks has not occurred. The synthesis of the El Mayor-Cucapah sequence reveals transtensional regional tectonics, including the westward growth of the Mexicali Valley and the transfer of Pacific-North America plate motion from the Gulf of California in the south into the southernmost San Andreas fault system to the north. We propose that the location of the 2010 El Mayor-Cucapah, as well as the 1992 Landers and 1999 Hector Mine earthquakes, may have been controlled by the bends in the plate boundary.

Hauksson, Egill; Stock, Joann; Hutton, Kate; Yang, Wenzheng; Vidal-Villegas, J. Antonio; Kanamori, Hiroo

2011-08-01

264

Why earthquakes correlate weakly with the solid Earth tides: Effects of periodic stress on the rate and probability of earthquake occurrence  

USGS Publications Warehouse

We provide an explanation why earthquake occurrence does not correlate well with the daily solid Earth tides. The explanation is derived from analysis of laboratory experiments in which faults are loaded to quasiperiodic failure by the combined action of a constant stressing rate, intended to simulate tectonic loading, and a small sinusoidal stress, analogous to the Earth tides. Event populations whose failure times correlate with the oscillating stress show two modes of response; the response mode depends on the stressing frequency. Correlation that is consistent with stress threshold failure models, e.g., Coulomb failure, results when the period of stress oscillation exceeds a characteristic time tn; the degree of correlation between failure time and the phase of the driving stress depends on the amplitude and frequency of the stress oscillation and on the stressing rate. When the period of the oscillating stress is less than tn, the correlation is not consistent with threshold failure models, and much higher stress amplitudes are required to induce detectable correlation with the oscillating stress. The physical interpretation of tn is the duration of failure nucleation. Behavior at the higher frequencies is consistent with a second-order dependence of the fault strength on sliding rate which determines the duration of nucleation and damps the response to stress change at frequencies greater than 1/tn. Simple extrapolation of these results to the Earth suggests a very weak correlation of earthquakes with the daily Earth tides, one that would require >13,000 earthquakes to detect. On the basis of our experiments and analysis, the absence of definitive daily triggering of earthquakes by the Earth tides requires that for earthquakes, tn exceeds the daily tidal period. The experiments suggest that the minimum typical duration of earthquake nucleation on the San Andreas fault system is ???1 year.

Beeler, N. M.; Lockner, D. A.

2003-01-01

265

Early Tertiary magmatism and probable Mesozoic fabrics in the Black Mountains, Death Valley, California  

NASA Astrophysics Data System (ADS)

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.

Miller, Martin G.; Friedman, Richard M.

1999-01-01

266

Probing the mechanical properties of seismically active crust with space geodesy: Study of the coseismic deformation due to the 1992 Mw7.3 Landers (southern California) earthquake  

Microsoft Academic Search

The coseismic deformation due to the 1992 Mw7.3 Landers earthquake, southern California, is investigated using synthetic aperture radar (SAR) and Global Positioning System (GPS) measurements. The ERS-1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components (east, north, up) of the coseismic surface displacement field. The coseismic displacement field exhibits symmetries

Yuri Fialko

2004-01-01

267

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

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…

California State Legislature, Sacramento. Senate Select Committee on the Northridge Earthquake.

268

Chapter C. The Loma Prieta, California, Earthquake of October 17, 1989 - Building Structures  

USGS Publications Warehouse

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.

Edited by Celebi, Mehmet

1998-01-01

269

Seismicity remotely triggered by the magnitude 7.3 landers, california, earthquake  

USGS Publications Warehouse

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).

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, 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.

1993-01-01

270

Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Lifelines  

USGS Publications Warehouse

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.

Edited by Schiff, Anshel J.

1998-01-01

271

Broadband Records of Earthquakes in Deep Gold Mines and a Comparison with Results from SAFOD, California  

Microsoft Academic Search

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 de- termining source and ground-motion parameters for the mining-induced earthquakes within and adjacent to our network. Four earthquakes with magnitudes close to 2 were

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

2009-01-01

272

Near-field postseismic deformation associated with the 1992 Landers and 1999 Hector Mine, California, earthquakes  

USGS Publications Warehouse

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.

Savage, J. C.; Svarc, J. L.; Prescott, W. H.

2003-01-01

273

Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Aftershocks and Postseismic Effects  

USGS Publications Warehouse

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.

Edited by Reasenberg, Paul A.

1997-01-01

274

Earthquake location data for the southern Great Basin of Nevada and California: 1984 through 1986  

SciTech Connect

This report presents data in map and table form for earthquake parameters such as hypocentral coordinates and magnitudes for earthquakes located by the southern Great Basin Seismic network for the time period January 1, 1984, through December 31, 1986. These maps show concentrations of earthquakes in regions previously noted to be seismically active, including the Pahranagat Shear Zone, Pahroc Mountains, southern Nevada Test Site, Timber Mountain, Black Mountain, Gold Mountain, Montezuma Range, and Grapevine Mountains. A concentration of earthquake activity in the Reveille Range was observed in 1986, in a previously inactive area. The northern Nevada Test Site had fewer earthquakes than a comparable area of the southern Nevada Test Site, indicating that the low-yield nuclear testing program is not currently triggering significant numbers of aftershocks. Eight microearthquakes occurred at Yucca Mountain during the 1984-1986 monitoring period. Depths of focus for well-located earthquakes continue to indicate a bimodal distribution, with peaks at 1 to 2 and 8 to 9 km below sea-level and a local minimum at 4 to 5 km. Focal mechanisms range from strike slip to normal slip. No dependence of slip mode on depth or magnitude is evident. 8 refs., 46 figs., 5 tabs.

Harmsen, S.C.; Rogers, A.M.

1987-01-01

275

Using Logistic Regression to Predict the Probability of Debris Flows in Areas Burned by Wildfires, Southern California, 2003-2006  

USGS Publications Warehouse

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 southern California. This study demonstrates that logistic regression is a valuable tool for developing models that predict the probability of debris flows occurring in recently burned landscapes.

Rupert, Michael G.; Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Helsel, Dennis R.

2008-01-01

276

The Redwood Coast Tsunami Work Group: a unique organization promoting earthquake and tsunami resilience on California's North Coast  

NASA Astrophysics Data System (ADS)

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 concerns about tsunami hazard signs. Over the seventeen-year period covered by the surveys, the percent with houses secured to foundations has increased from 58 to 84 percent, respondents aware of a local tsunami hazard increased from 51 to 89 percent and knowing what the Cascadia subduction zone is from 16 to 57 percent. In 2009, the RCTWG was recognized by the Western States Seismic Policy Council (WSSPC) with an award for innovation and in 2010, the RCTWG-sponsored class "Living on Shaky Ground" was awarded WSSPC's overall Award in Excellence. The RCTWG works closely with CGS and Cal EMA on a number of projects including tsunami mapping, evacuation zone planning, siren policy, tsunami safety for boaters, and public education messaging. Current projects include working with CGS to develop a "playbook" tsunami mapping product to illustrate the expected effects from a range of tsunami source events and assist local governments in focusing future response actions to reflect the range expected impacts from distant source events. Preparedness efforts paid off on March 11, 2011 when a tsunami warning was issued for the region and significant damage occurred in harbor regions of Del Norte County and Mendocino County. Full-scale evacuations were carried out in a coordinated manner and the majority of the commercial fishing fleet in Crescent City was able to exit the harbor before the tsunami arrived.

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

2012-12-01

277

Retardations in fault creep rates before local moderate earthquakes along the San Andreas fault system, central California  

USGS Publications Warehouse

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 the past 5 years. Retardations with durations of 21 and 19 months also occurred at Shore Road before the 1974 and 1984 earthquakes of ML=5.2 and ML=6.2, respectively. Although creep retardation remains poorly understood, several possible explanations have been discussed previously. (1) Certain onsets of apparent creep retardation may be explained as abrupt terminations of afterslip generated from previous moderate-mainshock sequences. (2) Retardations may be related to significant decreases in the rate of seismic and/or aseismic slip occurring within or beneath the underlying seismogenic zone. Such decreases may be caused by changes in local conditions related to growth of asperities, strain hardening, or dilatancy, or perhaps by passage of stress-waves or other fluctuations in driving stresses. (3) Finally, creep rates may be lowered (or increased) by stresses imposed on the fault by seismic or aseismic slip on neighboring faults. In addition to causing creep-rate increases or retardations, such fault interactions occasionally may trigger earthquakes. Regardless of the actual mechanisms involved and the current lack of understanding of creep retardation, it appears that shallow fault creep is sensitive to local and regional effects that promote or accompany intermediate-term preparation stages leading to moderate earthquakes. A strategy for more complete monitoring of fault creep, wherever it is known to occur, therefore should be assigned a higher priority in our continuing efforts to test various hypotheses concerning the mechanical relations between seismic and aseismic slip. ?? 1988 Birkha??user Verlag.

Burford, R. O.

1988-01-01

278

Chapter F. The Loma Prieta, California, Earthquake of October 17, 1989 - Marina District  

USGS Publications Warehouse

During the earthquake, a total land area of about 4,300 km2 was shaken with seismic intensities that can cause significant damage to structures. The area of the Marina District of San Francisco is only 4.0 km2--less than 0.1 percent of the area most strongly affected by the earthquake--but its significance with respect to engineering, seismology, and planning far outstrips its proportion of shaken terrain and makes it a centerpiece for lessons learned from the earthquake. The Marina District provides perhaps the most comprehensive case history of seismic effects at a specific site developed for any earthquake. The reports assembled in this chapter, which provide an account of these seismic effects, constitute a unique collection of studies on site, as well as infrastructure and societal, response that cover virtually all aspects of the earthquake, ranging from incoming ground waves to the outgoing airwaves used for emergency communication. The Marina District encompasses the area bounded by San Francisco Bay on the north, the Presidio on the west, and Lombard Street and Van Ness Avenue on the south and east, respectively. Nearly all of the earthquake damage in the Marina District, however, occurred within a considerably smaller area of about 0.75 km2, bounded by San Francisco Bay and Baker, Chestnut, and Buchanan Streets. At least five major aspects of earthquake response in the Marina District are covered by the reports in this chapter: (1) dynamic site response, (2) soil liquefaction, (3) lifeline performance, (4) building performance, and (5) emergency services.

Edited by O'Rourke, Thomas D.

1992-01-01

279

Chronology of Postglacial Eruptive Activity and Calculation of Eruption Probabilities for Medicine Lake Volcano, Northern California  

USGS Publications Warehouse

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.

Nathenson, Manuel; Donnelly-Nolan, Julie M.; Champion, Duane E.; Lowenstern, Jacob B.

2007-01-01

280

Deformation following the 1994 Northridge earthquake (M=6.7), southern California  

USGS Publications Warehouse

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.

Savage, J. C.; Svarc, J. L.; Prescott, W. H.; Hudnut, K. W.

1998-01-01

281

USGS Earthquake Hazards Program  

NSDL National Science Digital Library

This is the homepage of the Earthquake Hazards Program (EHP) of the United States Geological Survey (USGS). This page points to information on earthquakes in Northern California, the United States, and the world. Topics include reports on recent large earthquakes, real-time earthquake maps, real-time shaking maps, real-time seismograms, earthquake network reports and updates, recent and significant earthquakes, and earthquake news releases. Users will be able to view maps and click on them. The EHP is part of the National Earthquake Hazards Reduction Program (NEHRP) lead by the Federal Emergency Management Agency (FEMA).

282

The SAFRR Tsunami Scenario: Improving Resilience for California from a Plausible M9 Earthquake near the Alaska Peninsula  

NASA Astrophysics Data System (ADS)

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 mini?m of two days due to strong currents. Inundation of dry land in the ports would result in 100 million damages to cargo and additional downtime. The direct exposure of port trade value totals over 1.2 billion, while associated business interruption losses in the California economy could more than triple that value. Other estimated damages include 1.8 billion of property damage and 85 million for highway and railroad repairs. In total, we have estimated repair and replacement costs of almost 3 billion to California marinas, coastal properties and the POLA/LB. These damages could cause $6 billion of business interruption losses in the California economy, but that could be reduced by 80-90% with the implementation of business continuity or resilience strategies. This scenario provides the basis for improving preparedness, mitigation, and continuity planning for tsunamis, which can reduce damage and economic impacts and enhance recovery efforts. Two positive outcomes have already resulted from the SAFRR Tsunami Scenario. Emergency managers in areas where the scenario inundation exceeds the State's maximum inundation zone have been notified and evacuation plans have been updated appropriately. The State has also worked with NOAA's West Coast and Alaska Tsunami Warning Center to modify future message protocols to facilitate effective evacuations in California. While our specific results pertain to California, the lessons learned and our scenario approach can be applied to other regions.

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

283

Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Strong Ground Motion  

USGS Publications Warehouse

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 (artificial fill and bay mud). These exceptional ground-motion data are used by the authors of the papers in this chapter to infer radiation characteristics of the earthquake source, identify dominant propagation characteristics of the Earth?s crust, quantify amplification characteristics of near-surface geologic deposits, develop general amplification factors for site-dependent building-code provisions, and revise earthquake-hazard assessments for the San Francisco Bay region. Interpretations of additional data recorded in well-instrumented buildings, dams, and freeway overpasses are provided in other chapters of this report.

Edited by Borcherdt, Roger D.

1994-01-01

284

Chapter E. The Loma Prieta, California, Earthquake of October 17, 1989 - Geologic Setting and Crustal Structure  

USGS Publications Warehouse

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-dimensional picture of the earthquake source region--a geologically complex volume of crust with a long history of both right-lateral faulting and fault-normal compression, thrusting, and uplift.

Edited by Wells, Ray E.

2004-01-01

285

Comment on "Revisiting the 1872 owens valley, California, earthquake" by Susan E. Hough and Kate Hutton  

USGS Publications Warehouse

Bakun (2009) argues that the conclusions of Hough and Hutton (2008) are wrong because the study failed to take into account the Sierra Nevada attenuation model of Bakun (2006). In particular, Bakun (2009) argues that propagation effects can explain the relatively high intensities generated by the 1872 Owens Valley earthquake. Using an intensity attenuation model that attempts to account for attenuation through the Sierra Nevada, Bakun (2006) infers the magnitude estimate (Mw 7.4–7.5) that is currently accepted by National Earthquake Information Center (NEIC).

Bakun, W. H.

2009-01-01

286

Displacement Patterns of Cemetery Monuments in Ferndale, CA, During the MW 6.5 Offshore Northern California Earthquake of January 10, 2010  

NASA Astrophysics Data System (ADS)

Displaced and toppled monuments in a cemetery are an effective means of assessing local ground motion during an earthquake. The MW 6.5 Offshore Northern California earthquake of January 10, 2010, was felt throughout northwestern California and caused moderate damage in coastal communities between Petrolia and Eureka. The earthquake was generated by left-lateral strike slip on a NE-trending fault within the subducting Gorda plate. Peak horizontal ground accelerations of -0.440g (E) and 0.279g (N) and vertical ground acceleration of -0.122g (up) were recorded in Ferndale, CA, on the North American plate 37km east southeast of the epicenter. We measured displaced and toppled monuments in the Ferndale cemetery as a means of assessing ground motion during the January 10, 2010 Offshore Northern California earthquake. The cemetery occupies a hillside that slopes gently to the northwest, and a dormant landslide underlies the cemetery. Approximately 30% of the monuments were displaced during the earthquake. Affects included toppled columns and urns; headstones, columns and large tomb covers that slid and rotated and relative to monument bases; tilted retaining walls and headstones; and liquefaction-related settling (or, less commonly, uplift) of monuments. We measured translation and rotation of 79 monuments displaced from their bases during the earthquake. Toppled monuments do not display a preferred orientation. Seven of the 18 toppled monuments fell to the southeast, but toppling occurred in all directions. For monuments that were displaced but not toppled, 1-10 cm of northwestward translation and 3-8° of clockwise rotation were most common; however, virtually all directions of translation and both clockwise and counterclockwise rotations and were recorded. Damage was not evenly distributed geographically. In general, damage was concentrated in the northern, topographically lower, part of the cemetery. Counterclockwise rotation of monuments occurred mainly along the northeastern margin of the cemetery. Twelve of the measured monuments consist of three of more segments that rotated in different directions and/or slid different distances than adjacent segments. Our measurements therefore record the cumulative displacement of each monument segment, but many values are undoubtedly less than the maximum offset experienced during earthquake shaking. We infer that a combination of direct ground shaking from seismic waves, local liquefaction, and possibly earthquake-induced remobilization of the dormant landslide underlying the cemetery, all influenced displacement of monuments during the earthquake. One outcome of our data analysis will be insight on the patterns of movement that earthquakes produce in dormant landslide topography.

French, K. S.; Cashman, S. M.; Structural Geology Class Spring 2010

2010-12-01

287

Formation of left-lateral fractures within the Summit Ridge shear zone, 1989 Loma Prieta, California, earthquake  

SciTech Connect

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.

Johnson, A.M.; Fleming, R.W. [Purdue Univ., West Lafayette, IN (United States)]|[Geological Survey, Denver, CO (United States)

1993-12-01

288

Southern California Permanent GPS Geodetic Array: Continuous measurements of regional crustal deformation between the 1992 Landers and 1994 Northridge earthquakes  

NASA Astrophysics Data System (ADS)

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.

Bock, Y.; Wdowinski, S.; Fang, P.; Zhang, J.; 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.

1997-08-01

289

Southern California Permanent GPS Geodetic Array: Continuous measurements of regional crustal deformation between the 1992 Landers and 1994 Northridge earthquakes  

USGS Publications Warehouse

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.

Bock, Y.; Wdowinski, S.; Fang, P.; Zhang, J.; 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

290

Late Quaternary history of the Owens Valley fault zone, eastern California, and surface rupture associated with the 1872 earthquake  

SciTech Connect

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.

Beanland, S. (Inst. of Geological and Nuclear Sciences, Ltd., Lower Hutt (New Zealand). Earth Deformation Section); Clark, M.M. (Geological Survey, Menlo Park, CA (United States))

1993-04-01

291

Alaska Earthquake Source for the SAFRR Tsunami Scenario. California Geological Survey Special Report 229.  

National Technical Information Service (NTIS)

Tsunami modeling has shown that tsunami sources located along the Alaska Peninsula segment of the Aleutian-Alaska subduction zone have the greatest impacts on southern California shorelines by raising the highest tsunami waves for a given source seismic m...

D. Scholl R. von Huene R. Wells S. Kirby

2013-01-01

292

Present-day loading rate of faults in southern California and northern Baja California, Mexico, and post-seismic deformation following the M7.2 April 4, 2010, El Mayor-Cucapah earthquake from GPS Geodesy  

NASA Astrophysics Data System (ADS)

We use 142 GPS velocity estimates from the SCEC Crustal Motion Map 4 and 59 GPS velocity estimates from additional sites to model the crustal velocity field of southern California, USA, and northern Baja California, Mexico, prior to the 2010 April 4 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. The EMC earthquake is the largest event to occur along the southern San Andreas fault system in nearly two decades. In the year following the EMC earthquake, the EarthScope Plate Boundary Observatory (PBO) constructed eight new continuous GPS sites in northern Baja California, Mexico. We used our velocity model, which represents the period before the EMC earthquake, to assess postseismic velocity changes at the new PBO sites. Time series from the new PBO sites, which were constructed 4-18 months following the earthquake do not exhibit obvious exponential or logarithmic decay, showing instead fairly secular trends through the period of our analysis (2010.8-2012.5). The weighted RMS misfit to secular rates, accounting for periodic site motions is typically around 1.7 mm/yr, indicating high positioning precision and fairly linear site motion. Results of our research include new fault slip rate estimates for the greater San Andreas fault system, including model faults representing the Cerro Prieto (39.0±0.1 mm/yr), Imperial (35.7±0.1 mm/yr), and southernmost San Andreas (24.7±0.1 mm/yr), generally consistent with previous geodetic studies within the region. Velocity changes at the new PBO sites associated with the EMC earthquake are in the range 1.7±0.3 to 9.2±2.6 mm/yr. The maximum rate difference is found in Mexicali Valley, close to the rupture. Rate changes decay systematically with distance from the EMC epicenter and velocity orientations exhibit a butterfly pattern as expected from a strike slip earthquake. Sites to the south and southwest of the Baja California shear zone are moving more rapidly to the northwest relative to their motions prior to the earthquake. Sites to the west of the Laguna Salada fault zone are moving more westerly. Sites to the east of the EMC rupture move more southerly than prior to the EMC earthquake. Continued monitoring of these velocity changes will allow us to differentiate between lower crustal and upper mantle relaxation processes.

Spinler, J. C.; Bennett, R. A.

2012-12-01

293

Simulation studies on the differences between spontaneous and triggered seismicity and on foreshock probabilities  

Microsoft Academic Search

In this study we investigate the foreshock probabilities calculated from earthquake catalogs from Japan, Southern California and New Zealand. Unlike conventional studies on foreshocks, we use a probability-based declustering method to separate each catalog into stochastic versions of family trees, such that each event is classified as either having been triggered by a preceding event, or being a spontaneous event.

J. Zhuang; D. Vere-Jones; Y. Ogata; A. Christophersen; M. K. Savage; D. D. Jackson

2008-01-01

294

Direct and indirect evidence for earthquakes; an example from the Lake Tahoe Basin, California-Nevada  

NASA Astrophysics Data System (ADS)

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.

Maloney, J. M.; Noble, P. J.; Driscoll, N. W.; Kent, G.; Schmauder, G. C.

2012-12-01

295

Chapter E. The Loma Prieta, California, Earthquake of October 17, 1989 - Hydrologic Disturbances  

USGS Publications Warehouse

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.

Edited by Rojstaczer, Stuart A.

1994-01-01

296

Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Public Response  

USGS Publications Warehouse

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.'

Edited by Bolton, Patricia A.

1993-01-01

297

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

Microsoft Academic Search

We develop a forecast model to reproduce the distribution of main shocks, aftershocks and surrounding seismicity observed during 1986–2003 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

Shinji Toda; Ross S. Stein; Keith Richards-Dinger; Serkan B. Bozkurt

2005-01-01

298

Migrating swarms of brittle-failure earthquakes in the lower crust beneath Mammoth Mountain, California  

NASA Astrophysics Data System (ADS)

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. When they occur, these earthquakes provide a unique opportunity to constrain volcanic processes in the lower crust, such as fluid injection and migration. Here, we examine recent brief earthquakes swarms occurring deep beneath Mammoth Mountain, located on the southwestern margin of Long Valley Caldera. Brief lower-crustal swarms were observed beneath Mammoth in 2006, 2008, and 2009. These brittle-failure earthquakes at depths of 19 to 30 km are likely occurring within the more mafic mid- to lower crust, which can remain in the brittle domain to temperatures as high as ~700 degrees C. Above these deep events are two distinct shallower zones of seismicity. Mid-crustal, long-period earthquakes between 10 and 19 km are presumably occurring within the silicic crust, but below the rheological transition from brittle to plastic behavior, which is expected to occur at temperatures of ~350 to 400 degrees C. Above this transition shallow, brittle-failure earthquakes occur in the upper 8 kilometers of the silicic crust. We focus primarily on a deep swarm that occurred September 29-30, 2009, which is the best recorded of the recent lower-crustal swarms. To maximally illuminate the spatial-temporal progression of seismicity, we supplement the earthquake catalog by identifying 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. We also observe substantial diversity in the pattern of P-wave first motions, where events with very similar hypocenters and origin times exhibit nearly opposite patterns of compressional and dilational first motions at network seismometers. These lower-crustal, brittle-failure earthquakes are similar in many respects to those that occurred beneath the Sierra Nevada crest in the vicinity of Lake Tahoe in late 2003, which Smith et al. (Science, 2004) concluded were associated with a magmatic intrusion into the lower crust. The 2009 Mammoth sequence, however, is much shorter in duration (1-2 days compared with several months), faster migrating, and has no detectible accompanying geodetic signal. This suggests that the events may be triggered by upward diffusion of a lower viscosity fluid. CO2 is a likely candidate, given its abundant release in the area at the surface. Thus our preferred hypothesis is that this earthquake swarm is a symptom of ascending high-pressure CO2, perhaps reflecting slip induced on pre-existing fractures by reducing the effective normal stress. Indeed, the concentration of earthquakes with similar epicenters at a wide range of depths beneath Mammoth Mountain suggests that this may be a preferred pathway for CO2, and occasionally melt, to travel upward through the crust.

Shelly, D. R.; Hill, D. P.

2011-12-01

299

Earthquake hazards of active blind-thrust faults under the central Los Angeles basin, California  

NASA Astrophysics Data System (ADS)

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.

Shaw, John H.; Suppe, John

1996-04-01

300

Ages of Late Holocene earthquakes on the central Garlock fault near El Paso Peaks, California  

NASA Astrophysics Data System (ADS)

A trench across the central Garlock fault within a small playa adjacent to El Paso Mountains revealed buried fissures and fault scarps that provide strong evidence for five surface rupturing earthquakes within the past 5 kyr. Weaker evidence suggested the possibility of three additional events within this same time period. These observations indicate an average recurrence interval of 700 to 1200 years. Nearly all 28 radiocarbon dates on samples of detrital charcoal, wood and shell are in correct stratigraphic order. These dates constrain the ages of the individual faulting events and indicate that the recurrence interval is not periodic but is quite irregular. Individual recurrence intervals range from 190 to 1545 years (if all eight events are actual earthquakes) or from 190 to 3405 years (if only the five well-documented events represent earthquakes). The two most recent earthquakes occurred within the past 550 years, with preferred ages of about A.D. 1790 and A.D. 1600. The A.D. 1790 event ruptured a narrower width of the fault zone, and may have been a smaller earthquake than the others. The radiocarbon dates from the trench also indicate that the sedimentation rate on the playa has fluctuated within the past 5 kyr. Low sedimentation rates (0.1 to 0.35 mm/yr) and infrequent floods (?1 per century) prevailed from about 2000 B.C. to A.D. 100 and from A.D. 500 to 1300. During the remaining intervals within the past 5 kyr, the sedimentation rate averaged 1.0 to 1.7 mm/yr and major floods occurred two to four times per century. The changes in sedimentation rate and flood frequency may reflect climatic changes, or they may simply reflect changes in drainage patterns.

McGill, Sally; Rockwell, Tom

1998-04-01

301

Preliminary analysis of strong-motion recordings from the 28 September 2004 Parkfield, California earthquake  

USGS Publications Warehouse

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.

Shakal, A.; Graizer, V.; Huang, M.; Borcherdt, R.; Haddadi, H.; Lin, K. -W.; Stephens, C.; Roffers, P.

2005-01-01

302

Forecasting the Next Great San Francisco Earthquake  

NASA Astrophysics Data System (ADS)

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.

Rundle, P.; Rundle, J. B.; Turcotte, D. L.; Donnellan, A.; Yakovlev, G.; Tiampo, K. F.

2005-12-01

303

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

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 to suggest significant variations in the average recurrence rate at Wrightwood during the past 5000 years.

Scharer, K. M.; Weldon, II, R. J.; Fumal, T. E.; Biasi, G. P.

2007-01-01

304

The 2010 Mw7.2 El Mayor-Cucapah Earthquake Sequence, Baja California, Mexico and Southernmost California, USA: Active Seismotectonics Along the Mexican Pacific Margin  

NASA Astrophysics Data System (ADS)

The El Mayor-Cucapah earthquake sequence started with preshocks in March 2010, and a sequence of 15 foreshocks of M>2 (up to M4.4) that occurred during the 24 hours preceding the mainshock. The foreshocks occurred along a north-south trend near the mainshock epicenter. The Mw7.2 mainshock that occurred on the 4th of April exhibited complex faulting, possibly starting with a ~M6 normal faulting event, followed ~15 sec later by the main event, which included simultaneous normal and right-lateral strike-slip faulting. The aftershock zone extends for 120 km from the south end of the Elsinore fault zone at the US-Mexico border almost to the northern tip of the Gulf of California. The waveform-relocated aftershocks form two abutting clusters, of about equal length of 50 km each, as well as a 10 km north-south aftershock zone just north of the epicenter of the mainshock. Even though the Baja California data are included, the magnitude of completeness and the hypocentral errors increase gradually with distance to the south of the international border. The spatial distribution of large aftershocks is asymmetric with five M5+ aftershocks located to the south of the mainshock, and only one M5.7 aftershock but numerous smaller aftershocks to the north. Further, the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes. Thus the aftershocks also express a complex pattern of stress release along strike. The overall rate of decay of the aftershocks is similar to the rate of decay of a generic California aftershock sequence. In addition, some triggered seismicity was recorded along the Elsinore and San Jacinto faults to the north but significant northward migration of aftershocks has not occurred. The synthesis of the El Mayor-Cucapah sequence reveals transtensional regional tectonics, including the westward growth of the Mexicali Valley as well as how Pacific North America plate motion is transferred from the Gulf of California in the south into the southernmost San Andreas fault system to the north.

Hauksson, E.; Stock, J.; Hutton, K.; Yang, W.; Vidal-Villegas, A.; Kanamori, H.

2010-12-01

305

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

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).

Julian, B. R.; Prisk, A.; Foulger, G. R.; Evans, J. R.

1993-01-01

306

Earthquake Photo Collections  

NSDL National Science Digital Library

This collection of earthquake photos, published by the United States Geological Survey (USGS), contains links to photos for specific earthquakes, as well as links to other USGS image collections and non-USGS collections. Highlights include photos from the 1906 San Francisco earthquake, the 1989 Loma Prieta earthquake, and the 1994 earthquake in Northridge, California. There is also a link to the USGS photo library (general geologic topics), and links to collections published by universities, museums, other government organizations, and professional organizations.

2011-06-21

307

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

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.

Catchings, R. D.; Goldman, M. R.; Lee, W. H. K.; Rymer, M. J.; Ponti, D. J.

1998-01-01

308

Activity remotely triggered in volcanic and geothermal centers in California and Washington by the 3 November 2002 Mw=7.9 Alaska earthquake  

NASA Astrophysics Data System (ADS)

The M=7.9 Alaska earthquake of 3 November 2002 was followed by bursts of remotely triggered earthquakes at several volcanic and geothermal areas across the western United States at epicentral distances of 2,500 to 3,660 km. Husen et al. (this session) describe the triggered response for Yellowstone caldera, Wyoming. Here we highlight the triggered response for the Geysers geothermal field in northern California, Mammoth Mountain and Long Valley caldera in eastern California, the Coso geothermal field in southeastern California, and Mount Rainier in central Washington. The onset of triggered seismicity at each of these areas began 15 to 17 minutes after the Alaska earthquake during the S-wave coda and the early phases of the Love and Raleigh waves with periods of 5 to 40 seconds and dynamic strains of a few microstrain. In each case, the seismicity was characterized by spasmodic bursts of small (M<2 ), brittle-failure earthquakes. The activity persisted for just a few minutes at Mount Rainier and Mammoth Mountain and roughly 30 minutes at the Geysers and Coso geothermal fields. Many of the triggered earthquakes at all three sites were too small for reliable locations (magnitudes M<1), although their small S-P times indicate hypocentral locations within a few km of the nearest seismic station. Borehole dilatometers in vicinity of Mammoth Mountain recorded strain offsets on the order of 0.1 microstrain coincident in time with the triggered seismicity (Johnston et al. this session), and water level in the 3-km-deep LVEW well in the center of Long Valley caldera dropped by ~13 cm during passage of the seismic wave train from the Alaska earthquake followed by a gradual recovery. The Geysers, Coso, and Mount Rainier have no continuous, high-resolution strain instrumentation. A larger earthquake swarm that began 23.5 hours later (21:38 UT on the 4th) in the south moat of Long Valley caldera and included nine M>2 and one M=3.0 earthquake may represent a delayed response to the Alaska earthquake.

Hill, D. P.; Prejean, S.; Oppenheimer, D.; Pitt, A. M.; S. D. Malone; Richards-Dinger, K.

2002-12-01

309

In-situ Seafloor Sediment Characterization From Background Noise and Earthquakes Recorded in the Gulf of California  

NASA Astrophysics Data System (ADS)

We present an in-situ evaluation of the response of the Gulf of California (GoC) seafloor sediments to passive dynamic loads. Horizontal-to-vertical (H/V) spectral ratios are used to characterize the local seafloor sediment response in terms of the distribution of ground motions with their respective resonant frequencies. Ambient noise, local and regional earthquakes are used as passive dynamic loads. An analysis and description of the GoC seafloor background noise is also presented. The data was recorded by fourteen stations with three-component broadband sensors and a differential pressure gauge (Ocean Bottom Seismograph, OBS) of the Sea of Cortez Ocean-Bottom Array (SCoOBA) seismic experiment. Earthquakes and other natural seismic signals were recorded for nearly 12 months between October 2005 and October 2006. High frequency local events with impulsive onset arrivals as well as emergent onset arrivals are frequent on all stations. Earthquakes from regional and teleseismic distances are abundant and well defined on several stations simultaneously. The background noise clearly shows changes of the noise levels at intervals of approximately 6 hours in long period signals. Two sub-arrays were centered within the Alarcon and Guaymas basins, ~20 km spacing, and four additional instruments were deployed at ~100 km spacing. The array successfully recorded micro- seismic activity, dozens of local events, M > 3.5, and two large (M ~ 6) events with numerous foreshocks and aftershocks. The H/V spectral ratio technique offers a fast and inexpensive means to obtain information of the preferential vibration modes of soft sediment systems. This information is useful for the design of marine structures because makes use of background noise and earthquake signals. The main advantage is that there is no need for active sources to conduct the study. The method is also well suited for modeling shallow sediments, which usually cover most of the seafloor. H/V spectral ratios were computed for all signals and compared between each other to characterize the effect of the seafloor marine sediments on the seismic records.

Huerta, C. I.; Castro, R. R.; Gaherty, J. B.; Collins, J. A.; Contreras, R. S.

2008-12-01

310

Non-shear focal mechanisms of earthquakes at The Geysers, California and Hengill, Iceland, geothermal areas  

USGS Publications Warehouse

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.

Julian, B. R.; Miller, A. D.; Foulger, G. R.

1993-01-01

311

Slip partitioning of the Calaveras Fault, California, and prospects for future earthquakes  

USGS Publications Warehouse

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. 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 and Morgan Hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic. We propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes. From the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the Calaveras Fault. -from Authors

Oppenheimer, D. H.; Bakun, W. H.; Lindh, A. G.

1990-01-01

312

The Cape Mendocino, California, earthquakes of April 1992: Subduction at the triple junction  

USGS Publications Warehouse

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.

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

313

Dynamic modeling of the 2004 Mw 6.0 Parkfield, California, earthquake  

Microsoft Academic Search

We present two spontaneous rupture models of the 2004 Mw 6.0 Parkfield earthquake constrained by near-source ground motions. We start with a stress drop distribution calculated from a kinematic slip distribution. Using a linear slip-weakening friction law, we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records.

Shuo Ma; Susana Custódio; Ralph J. Archuleta; Pengcheng Liu

2008-01-01

314

Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Loss Estimation and Procedures  

USGS Publications Warehouse

This Professional Paper includes a collection of papers on subjects ranging from evaluation of building safety, to human injuries, to correlation of ground deformation with building damage. What these papers share is a common goal to improve the tools available to the research community to measure the nature, extent, and causes of damage and losses due to earthquakes. These measurement tools are critical to reducing future loss.

Edited by Tubbesing, Susan K.

1994-01-01

315

Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Recovery, Mitigation, and Reconstruction  

USGS Publications Warehouse

The papers in this chapter reflect the broad spectrum of issues that arise following a major damaging urban earthquake-the regional economic consequences, rehousing problems, reconstruction strategies and policies, and opportunities for mitigation before the next major seismic event. While some of these papers deal with structural or physical science topics, their significant social and policy implications make them relevant for improving our understanding of the processes and dynamics that take place during the recovery period.

Edited by Nigg, Joanne M.

1998-01-01

316

Loss estimates for a Puente Hills blind-thrust earthquake in Los Angeles, California  

USGS Publications Warehouse

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.

Field, E. H.; Seligson, H. A.; Gupta, N.; Gupta, V.; Jordan, T. H.; Campbell, K. W.

2005-01-01

317

Creep Transients and Fault Interaction from Repeating Earthquakes Near San Juan Bautista, California  

NASA Astrophysics Data System (ADS)

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.

Turner, R. C.; Nadeau, R. M.; Burgmann, R.

2012-12-01

318

Migrating swarms of brittle-failure earthquakes in the lower crust beneath Mammoth Mountain, California  

USGS Publications Warehouse

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.

Shelly, D. R.; Hill, D. P.

2011-01-01

319

Chapter A. The Loma Prieta, California, Earthquake of October 17, 1989 - Main Shock Characteristics  

USGS Publications Warehouse

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.

Edited by Spudich, Paul

1996-01-01

320

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)

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-SISCOR Working Group. On the basis of this consensual logic tree, median probability of occurrences of M>=6 events were computed for the region of study. Time-dependent models (Brownian Passage time and Weibull probability distributions) were also explored. The probability of a M>=6.0 event is found to be greater in the western region compared to the eastern part of the Corinth rift, whether a fault-based or a classical seismotectonic approach is used. Percentile probability estimates are also provided to represent the range of uncertainties in the results. The percentile results show that, in general, probability estimates following the classical approach (based on the definition of seismotectonic source zones), cover the median values estimated following the fault-based approach. On the contrary, the fault-based approach in this region is still affected by a high degree of uncertainty, because of the poor constraints on the 3D geometries of the faults and the high uncertainties in their slip rates.

Boiselet, Aurelien; Scotti, Oona; Lyon-Caen, Hélène

2014-05-01

321

Triggered surface slips in southern California associated with the 2010 El Mayor-Cucapah, Baja California, Mexico, earthquake  

USGS Publications Warehouse

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.

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

322

Slip rates and interseismic locking depths of southern California faults inferred from viscoelastic earthquake cycle models  

Microsoft Academic Search

Estimates of fault slip rates and interseismic fault locking in southern California are important for seismic hazard assessments. However, some model estimates of slip rates from geodetic data are lower than geologic rates on the Garlock Fault and Mojave and San Bernadino segment of the San Andreas Fault, and locking depth, which varies along the strike, is poorly resolved. We

R. Y. Chuang; K. M. Johnson

2009-01-01

323

Coseismic and Initial Postseismic Deformation from the 2004 Parkfield, California, Earthquake, Observed by Global Positioning System, Electronic Distance Meter, Creepmeters, and Borehole Strainmeters  

Microsoft Academic Search

Global Positioning System (GPS), electronic distance meter, creepmeter, and strainmeter measurements spanning the M 6.0 Parkfield, California, earthquake are examined. Using these data from 100 sec through 9 months following the main- shock, the Omori's law, with rate inversely related to time, 1\\/tp and p ranging be- tween 0.7 and 1.3, characterizes the time-dependent deformation during the post- seismic period;

J. Langbein; J. R. Murray; H. A. Snyder

2006-01-01

324

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

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.

Langenheim, V. E.; Schmidt, K. M.; Jachens, R. C.

1997-01-01

325

Testing time-predictable earthquake recurrence by direct measurement of strain accumulation and release  

NASA Astrophysics Data System (ADS)

Probabilistic estimates of earthquake hazard use various models for the temporal distribution of earthquakes, including the `time-predictable' recurrence model formulated by Shimazaki and Nakata (which incorporates the concept of elastic rebound described as early as 1910 by H. F. Reid). This model states that an earthquake occurs when the fault recovers the stress relieved in the most recent earthquake. Unlike time-independent models (for example, Poisson probability), the time-predictable model is thought to encompass some of the physics behind the earthquake cycle, in that earthquake probability increases with time. The time-predictable model is therefore often preferred when adequate data are available, and it is incorporated in hazard predictions for many earthquake-prone regions, including northern California, southern California, New Zealand and Japan. Here we show that the model fails in what should be an ideal locale for its application - Parkfield, California. We estimate rigorous bounds on the predicted recurrence time of the magnitude ~6 1966 Parkfield earthquake through inversion of geodetic measurements and we show that, according to the time-predictable model, another earthquake should have occurred by 1987. The model's poor performance in a relatively simple tectonic setting does not bode well for its successful application to the many areas of the world characterized by complex fault interactions.

Murray, Jessica; Segall, Paul

2002-09-01

326

Testing time-predictable earthquake recurrence by direct measurement of strain accumulation and release.  

PubMed

Probabilistic estimates of earthquake hazard use various models for the temporal distribution of earthquakes, including the 'time-predictable' recurrence model formulated by Shimazaki and Nakata (which incorporates the concept of elastic rebound described as early as 1910 by H. F. Reid). This model states that an earthquake occurs when the fault recovers the stress relieved in the most recent earthquake. Unlike time-independent models (for example, Poisson probability), the time-predictable model is thought to encompass some of the physics behind the earthquake cycle, in that earthquake probability increases with time. The time-predictable model is therefore often preferred when adequate data are available, and it is incorporated in hazard predictions for many earthquake-prone regions, including northern California, southern California, New Zealand and Japan. Here we show that the model fails in what should be an ideal locale for its application -- Parkfield, California. We estimate rigorous bounds on the predicted recurrence time of the magnitude approximately 6 1966 Parkfield earthquake through inversion of geodetic measurements and we show that, according to the time-predictable model, another earthquake should have occurred by 1987. The model's poor performance in a relatively simple tectonic setting does not bode well for its successful application to the many areas of the world characterized by complex fault interactions. PMID:12239564

Murray, Jessica; Segall, Paul

2002-09-19

327

Triggered surface slips in the Salton Trough associated with the 1999 Hector Mine, California, earthquake  

USGS Publications Warehouse

Surface fracturing occurred along the southern San Andreas, Superstition Hills, and Imperial faults in association with the 16 October 1999 (Mw 7.1) Hector Mine earthquake, making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the Salton Trough. Fractures associated with the event formed discontinuous breaks over a 39-km-long stretch of the San Andreas fault, from the Mecca Hills southeastward to Salt Creek and Durmid Hill, a distance from the epicenter of 107 to 139 km. Sense of slip was right lateral; only locally was there a minor (~1 mm) vertical component of slip. Dextral slip ranged from 1 to 13 mm. Maximum slip values in 1999 and earlier triggered slips are most common in the central Mecca Hills. Field evidence indicates a transient opening as the Hector Mine seismic waves passed the southern San Andreas fault. Comparison of nearby strong-motion records indicates several periods of relative opening with passage of the Hector Mine seismic wave-a similar process may have contributed to the field evidence of a transient opening. Slip on the Superstition Hills fault extended at least 9 km, at a distance from the Hector Mine epicenter of about 188 to 196 km. This length of slip is a minimum value, because we saw fresh surface breakage extending farther northwest than our measurement sites. Sense of slip was right lateral; locally there was a minor (~1 mm) vertical component of slip. Dextral slip ranged from 1 to 18 mm, with the largest amounts found distributed (or skewed) away from the Hector Mine earthquake source. Slip triggered on the Superstition Hills fault commonly is skewed away from the earthquake source, most notably in 1968, 1979, and 1999. Surface slip on the Imperial fault and within the Imperial Valley extended about 22 km, representing a distance from the Hector Mine epicenter of about 204 to 226 km. Sense of slip dominantly was right lateral; the right-lateral component of slip ranged from 1 to 19 mm. Locally there was a minor (~1-2 mm) vertical component of slip; larger proportions of vertical slip (up to 10 mm) occurred in Mesquite basin, where scarps indicate long-term oblique-slip motion for this part of the Imperial fault. Slip triggered on the Imperial fault appears randomly distributed relative to location along the fault and source direction. Multiple surface slips, both primary and triggered slip, indicate that slip repeatedly is small at locations of structural complexity.

Rymer, M. J.; Boatwright, J.; Seekins, L. C.; Yule, J. D.; Liu, J.

2002-01-01

328

Structural Constraints and Earthquake Recurrence Estimates for the West Tahoe-Dollar Point Fault, Lake Tahoe Basin, California  

NASA Astrophysics Data System (ADS)

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 floor, but offset increases down-section to ~14 m and ~8 m at the acoustic basement. Studying the style and timing of earthquake deformation in Fallen Leaf Lake, Cascade Lake, Emerald Bay and Lake Tahoe will help us to understand how strain is partitioned between adjacent segments and the potential rupture magnitude.

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

329

Geodetic evidence for creep along the Rodgers Creek and Maacama fault zones, northern California  

Microsoft Academic Search

The `North Bay' region, north of San Francisco, is poorly covered by existing geodetic measurements, yet is home to the fault currently considered most dangerous in northern California by the 2008 Working Group on California Earthquake Probabilities, the Rodgers Creek fault. Previous studies using the PS-InSAR technique suggest that creep may occur on the Rodgers Creek fault around the city

M. A. Floyd; G. J. Funning; B. Lipovsky

2009-01-01

330

Variability in nonlinear sediment response during the 1994 Northridge, California, earthquake  

USGS Publications Warehouse

Spectral ratios between sediment sites and rock sites for strong and weak ground motion are compared to infer the extent of nonlinear sediment response in the Los Angeles area during the 1994 Northridge earthquake. Northridge mainshock records form the strong-motion database and aftershock records form the weak-motion database. The degree of nonlinearity is evaluated at 25 locations in and around the San Fernando and Los angeles Basins based on the ratio of weak-to-strong spectral amplification factors (WSAF). Values of WSAF vary greatly from site to site and, for a given site, from one frequency band to another over the range from 0.75 to 20 Hz. This complexity is attributed to differences in several factors: materials properties under the sites and the amplitude and frequency content of the input ground motions. Given these observations, it is not possible to assign an acceleration or velocity level at which nonlinearity initiates for all the stiff soil sites analyzed. However, no nonlinearity is seen below a peak acceleration of about 200 to 300 cm/sec2 or peak velocity of 20 to 30 cm/sec. Nonlinearity is seen at all sites in or near the San Fernando Valley. Nonlinearity in the Los Angeles Basin is limited to a few isolated sites. For the Northridge earthquake, even sites with strong nonlinearity still show amplification levels greater than 1.0 relative to rock sites for frequencies below 10 Hz.

Hartzell, S.

1998-01-01

331

The 130-km-long Green Valley Fault Zone of Northern California: Discontinuities Regulate Its Earthquake Recurrence  

NASA Astrophysics Data System (ADS)

The Green Valley fault (GVF), a branch of the dextral strike-slip San Andreas fault system, connects the Northern Calaveras fault (NCF) to the Bartlett Springs fault (BSF) to the north. Although, the GVF may occasionally rupture along its entire length to produce M7 earthquakes, 2-3 km discontinuities in its trace appear to modulate the length and frequency of ruptures. The global historical earthquake record suggests that ruptures tend to stop at such fault discontinuities (1-4 km steps) about half the time (Wesnousky and Biasi, 2011). The GVF has three sections: the 77-km-long southern GVF (SGVF), the 25-km Berryessa (BF), and the 30-km Hunting Creek (HCF). The SGVF itself could produce large (M6.7) events, and the BF and HCF somewhat smaller events (M6.3-6.6). The BF is centered on a compressional pop-up structure. It is separated to the north from the HCF by a ~2.5-3 km extensional stepover and to the south from the SGVF by a ~2.5-3 km extensional bend. At its south end, the GVF is separated from the NCF by the 5-km Alamo stepover, which is likely to stop all ruptures; and at its north end the GVF (HCF section) makes a 2.5 km right step to the BSF at Wilson Valley. The HCF apparently forms a significant transition between the BSF and the GVF. The overall trend of the GVF bends ~17° through the HCF and emerges on the BSF trend. Thus, this bend, along with the Wilson Valley step-over, would tend to inhibit ruptures between BSF and sections of the GVF. Creep rates along most of the GVF (SGVF, HCF) range from 1 to 4 mm/yr. No creep is known for the BF section, but its microseismicity levels are similar to creeping parts of the GVF and BSF, so we assume that the BF may creep too. We estimate slip rate on the GVF is 6±2 mm/yr by interpolating rates on the BSF and the NCF. Lienkaemper and Brown (2009) estimated ~6.5 mm/yr for the average deep loading rate on the BSF using a rigid block model of the USGS-GPS site velocities observed in the central BSF. This rate is comparable to the 6 mm/yr Holocene slip rate observed on the NCF (Kelson et al., 1996). Microearthquakes on the GVF reach a depth of ~14 km. Using methods of Savage and Lisowski (1993) for the GVF suggests that creep may on average extend to depths of ~7.5 km, leaving a width of ~6.5 km of locked fault zone below. Trenching on the SGVF indicates 400 (±50) years have elapsed since the most recent large earthquake (MRE) in 1610±50 yr CE. Previous earthquake recurrence intervals (RI) in the past millennium indicate a mean RI of 200±80 yr (?±?) for the SGVF, which is much shorter than the 400-yr open interval. Preliminary evidence from trenching on the BF gives a MRE of 1630±100 yr CE, which may thus coincide with of the MRE on the SGVF. If the MRE on the BF and SGVF sections is the same earthquake, then its expected larger size (M~6.9-7.0 vs 6.7) and greater fault complexity may have produced a large stress drop, which would possibly help explain the current long open interval. The SGVF paleoseismic recurrence model is consistent with a simple probabilistic rupture model (i.e., 50%-probable rupture across 1-4 km steps) and with a Brownian Passage Time recurrence model with a mean RI of 250 yr, CV (coefficient of variation, ?/?) of 0.6, and a 30-yr rupture probability of 20-25%.

Lienkaemper, J. J.

2012-12-01

332

Reply to “Probability of earthquake occurrence in Greece with special reference to the VAN predictions,” by Y. Honkura and N. Tanaka  

NASA Astrophysics Data System (ADS)

The calculation of Honkura and Tanaka [1996] and that of Aceves et al. [1996], provide important tools for the clarification of the main question of this issue, i.e., whether or not the VAN predictions can be ascribed to chance. Honkura and Tanaka's [1996] calculation showed that, in a circular area with a radius of 120 km and for the time window of 22 days, the probability P of occurrence of an earthquake (EQ) with Ms ? 5.0 in Greece is less than 0.25, and even smaller for a time window of 11 days. For larger magnitude thresholds, i.e., Ms ? 5.5 or Ms ? 5.8 (and in view of Gutenberg-Richter relation), their P-value has to be drastically smaller. A simple comparison of these P-values with the Tables of Mulargia and Gasperini [1992, 1996a] immediately reveals that VAN-predictions cannot be ascribed to chance. Note that an inspection of the latter Tables leads to (i) the VAN success rate is 40?45% (when considering correlations with earthquakes having MEQ ? 5.0 only), and (ii) the VAN alarm rates increase with the (earthquake) magnitude threshold, reaching to values of 50% and 60%, for MEQ ? 5.5 and MEQ ? 5.8 respectively. Another important point, which emerges from the calculation of Honkura and Tanaka [1996], is that “aftershocks must be treated carefully.” This strengthenes our remarks in Principles 4 and 5 of Varotsos et al. [1996a] that the inappropriate treatment of aftershocks in Mulargia and Gasperini’s [1992] calculation (which was based on Poisson distribution): (i) changed drastically the values of the significance level and (ii) turned a true “forward time correlation,” between predictions and earthquakes, to a “backward time association.” The latter point is also separately checked by Honkura and Tanaka [1996] who conclude that: “… with the backwards time correlation in mind … we could not find cases in which a high probability arises for the occurrence of an EQ of Ms ? 5.0 in the target area.” In this Reply we also proceed to some necessary clarifications, concerning the calculation of the “success rate” and “alarm rate” when a prediction method has, as expected, an experimental error in the magnitude determination.

Varotsos, P.; Lazaridou, M.

333

Primary surface rupture associated with the Mw 7.1 16 October 1999 Hector Mine earthquake, San Bernardino County, California  

USGS Publications Warehouse

The Mw 7.1 Hector Mine earthquake occurred within the Mojave Desert portion of the eastern California shear zone and was accompanied by 48 km of dextral surface rupture. Complex northward rupture began on two branches of the Lavic Lake fault in the northern Bullion Mountains and also propagated southward onto the Bullion fault. Lesser amounts of rupture occurred across two right steps to the south. Surface rupture was mapped using postearthquake, 1:10,000-scale aerial photography. Field mapping provided additional detail and more than 400 fault-rupture observations; of these, approximately 300 measurements were used to characterize the slip distribution. En echelon surface rupture predominated in areas of thick alluvium, whereas in the bedrock areas, rupture was more continuous and focused within a narrower zone. Measured dextral offsets were relatively symmetrical about the epicentral region, with a maximum displacement of 5.25 ?? 0.85 m. Vertical slip was a secondary component and was variable, with minor west-side-down displacements predominat.ing in the Bullion Mountains. Field and aerial photographic evidence indicates that most of the faults that ruptured in 1999 had had prior late-Quaternary displacement, although only limited sections of the rupture show evidence for prior Holocene displacement.

Treiman, J. A.; Kendrick, K. J.; Bryant, W. A.; Rockwell, T. K.; McGill, S. F.

2002-01-01

334

Imaging the source region of the 2003 San Simeon earthquake within the weak Franciscan subduction complex, central California  

USGS Publications Warehouse

Data collected from the 2003 Mw6.5 San Simeon earthquake sequence in central California and a 1986 seismic refraction experiment demonstrate that the weak Franciscan subduction complex suffered brittle failure in a region without significant velocity contrast across a slip plane. Relocated hypocenters suggest a spatial relationship between the seismicity and the Oceanic fault, although blind faulting on a nearby, unknown fault is an equally plausible alternative. The aftershock volume is sandwiched between the Nacimiento and Oceanic faults and is characterized by rocks of low compressional velocity (Vp) abutted to the east and west by rocks of higher Vp. This volume of inferred Franciscan rocks is embedded within the larger Santa Lucia anticline. Pore fluids, whose presence is implied by elevated Vp/Vs values, may locally decrease normal stress and limit the aftershock depth distribution between 3 to 10 km within the hanging wall. The paucity of aftershocks along the mainshock rupture surface may reflect either the absence of a damage zone or an almost complete stress drop within the low Vp or weak rock matrix surrounding the mainshock rupture. Copyright 2004 by the American Geophysical Union.

Hauksson, E.; Oppenheimer, D.; Brocher, T. M.

2004-01-01

335

Rupture directivity and slip distribution of the M 4.3 foreshock to the 1992 Joshua Tree earthquake, Southern California  

USGS Publications Warehouse

Details of the M 4.3 foreshock to the Joshua Tree earthquake were studied using P waves recorded on the Southern California Seismic Network and the Anza network. Deconvolution, using an M 2.4 event as an empirical Green's function, corrected for complicated path and site effects in the seismograms and produced simple far-field displacement pulses that were inverted for a slip distribution. Both possible fault planes, north-south and east-west, for the focal mechanism were tested by a least-squares inversion procedure with a range of rupture velocities. The results showed that the foreshock ruptured the north-south plane, similar to the mainshock. The foreshock initiated a few hundred meters south of the mainshock and ruptured to the north, toward the mainshock hypocenter. The mainshock (M 6.1) initiated near the northern edge of the foreshock rupture 2 hr later. The foreshock had a high stress drop (320 to 800 bars) and broke a small portion of the fault adjacent to the mainshock but was not able to immediately initiate the mainshock rupture.

Mori, J.

1996-01-01

336

EFFECTS OF THE 1906 EARTHQUAKE ON THE BALD HILL OUTLET SYSTEM, SAN MATEO COUNTY, CALIFORNIA.  

USGS Publications Warehouse

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.

Pampeyan, Earl, H.

1986-01-01

337

Electrical structure in a region of the Transverse Ranges, southern California. [for earthquake prediction  

NASA Technical Reports Server (NTRS)

Magnetotelluric sounding at a site in the Transverse Ranges province in southern California indicates a low-resistivity region in the lower crust and possibly also the upper mantle. A two-dimensional model fit to the data indicates that the resistivity of this region is between 1 and 10 ohm-meters. The depth to the top surface of this zone is between 15 and 20 km. The lateral extent of this feature, which strikes N65 deg W, appears to be confined to the Transverse Ranges province. The petrological characteristics of this region cannot be deduced unambiguously from the magnetotelluric sounding alone.

Reddy, I. K.; Phillips, R. J.; Whitcomb, J. H.; Rankin, D.

1977-01-01

338

Evidence for large Holocene earthquakes on the Compton thrust fault, Los Angeles, California  

NASA Astrophysics Data System (ADS)

We demonstrate that the Compton blind thrust fault is active and has generated at least six large-magnitude earthquakes (Mw 7.0-7.4) during the past 14,000 years. This large, concealed fault underlies the Los Angeles metropolitan area and thus poses one of the largest deterministic seismic risk in the United States. We employ a methodology that uses a combination of high-resolution seismic reflection profiles and borehole excavations to link blind faulting at seismogenic depths directly to near-surface fault-related folding. Deformed Holocene strata record recent activity on the Compton thrust and are marked by discrete sequences that thicken repeatedly across a series of buried fold scarps. We interpret the intervals of growth as occurring after the formation of now-buried paleofold scarps that formed during uplift events on the underlying Compton thrust ramp. Minimum uplift in each of the scarp-forming events, which occurred at 0.7-1.75 ka (event 1), 0.7-3.4 ka or 1.9-3.4 (event 2), 5.6-7.2 ka (event 3), 5.4-8.4 ka (event 4), 10.3-12.5 ka (event 5), and 10.3-13.7 ka (event 6), ranged from ˜0.6 to ˜1.9 m, indicating minimum thrust displacements of ?1.3 to 4.2 m. Such large displacements are consistent with the occurrence of large-magnitude earthquakes (Mw ? 7). This multidisciplinary methodology provides a means of defining the recent seismic behavior, and therefore the hazard, for blind thrust faults that underlie other major metropolitan regions around the world.

Leon, Lorraine A.; Dolan, James F.; Shaw, John H.; Pratt, Thomas L.

2009-12-01

339

Surface slip associated with the 2004 Parkfield, California, earthquake measured on alinement arrays  

USGS Publications Warehouse

Although still continuing, surface slip from the 2004 Parkfield earth-quake as measured on alinement arrays appears to be approaching about 30-35 cm between Parkfield and Gold Hill. This includes slip along the main trace and the Southwest Fracture Zone (SWFZ). Slip here was higher in 1966 at about 40 cm. The distribution of 2004 slip appears to have a shape similar to that of the 1966 event, but final slip is expected to be lower in 2004 by about 3-15 cm, even when continuing slip is accounted for. Proportionately, this difference is most notable at the south end at Highway 46, where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm. Continuous Global Positioning System and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the SWFZ and perhaps on Middle Mountain (the latter possibly caused by shaking) (Langbein et al., 2005). Creepmeters indicate only minor (<0.2 cm) surface coseismic slip occurred on the main trace between Parkfield and Gold Hill. We infer that 3-6 cm slip accumulated across our arrays in the first 24 hr. At Highway 46, slip appears complete, whereas the remaining sites are expected to take 2-6 years to reach their background creep rates. Following the 1966 event, afterslip at one site persisted as much as 5-10 years. The much longer recurrence intervals between the past two Parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the Parkfield segment.

Lienkaemper, J. J.; Baker, B.; McFarland, F. S.

2006-01-01

340

Forecasting damaging earthquakes in the central and eastern United States  

USGS Publications Warehouse

Analysis of seismograph network data, earthquake catalogs from 1727 to 1982, and paleoseismic data for the central and eastern United States indicate that the Poisson probability of a damaging earthquake (magnitude ??? 6.0) occurring during the next 30 years is at a moderate to high level (0.4 to 0.6). When differences in seismic wave attenuation are taken into account, the central and eastern United States has approximately two-thirds the likelihood of California to produce an earthquake with comparable damage area and societal impact within the next 30 years.

Nishenko, S. P.; Bollinger, G. A.

1990-01-01

341

A probable mechanism of the water level subsidence in wells as a precursor of an earthquake event  

NASA Astrophysics Data System (ADS)

Case histories of water level subsidence in bore-holes as a precursor of earthquakes are given here. Based on the examples, a testable quantitative theory for causative mechanism of the precursor—“draining-injecting water model with variable discharge” is proposed (abbreviated to DIW model). Through analysing the constitution law of which the deformation changes in the porous, water-saturated media under the effect of exterior stress, as first step of all, the authors suggested first a simple “drainage-natural restoration model” (abbreviated to DNR model), calculated and gave a group of theoretical precursor curve by using DNR model, compared the theoretical precursor curves of DNR model with the observational curves, found out the differences of the two curves, studied the causative physical factors that caused the differences then, revised the DNR model, and finally, the theory on “draining-injecting water model with variable discharge” in the paper was obtained. The authors deduced general equation of the two dimensions “draining-injecting water linear source drawdown field” in the paper, suggested and developed the concept on “domain”. DIW model can also give a possible explanation for both regularity and complexity of this precursor. DIW theory can quantitatively divide the seismogenic process of the foci on the short-term and impending process into several phases, and by inversing the discharge function q(?) curve, the time values by which the phases are divided were obtained. They will be helpful to predicting the occurrence time of earthquake and judging the DD and IPE model of the seismogenesis.

Wang, Liu-Qiao; Li, Shan-Yin

1993-08-01

342

Vertical crustal deformation associated with the 1979 M = 6.6 Imperial Valley, California Earthquake: Implications for fault behavior  

NASA Astrophysics Data System (ADS)

Elevation changes in the Imperial Valley, California, derived from repeated leveling surveys for the time period including the 1979 M = 6.6 earthquake, provide some constraints on fault geometry and slip distribution associated with this event. Many of the first-order features of the observed vertical movements are well matched by simple models consisting of variable slip on planar faults in an elastic half-space using fault offsets inferred from strong ground motion observations (Archuleta, 1984) and measured afterslip. The geodetic and seismic observations suggest that significant slip is confined to depths above 13 km with maximum right-lateral offset reaching about 1.5 m on the Imperial fault. Dip slip occurs predominantly in the sediments on the upper 5 km of the Imperial fault and on the Brawley fault. Right-lateral afterslip is confined to the upper 5 km of the Imperial fault and reaches about 30 cm for the period 1979-1981. In contrast, observed elevation changes near the 1979 hypocenter (on southern end of Imperial fault) and in the Brawley Seismic Zone show significant deviations from those predicted by models of fault slip inferred from strong ground motion measurements. Specifically, the geodetic data suggest that slip on the Imperial fault is significantly lower in the vicinity of the earthquake hypocenter than along the central and northern sections of the fault. In addition, there is marginal evidence that the dip of the Imperial fault changes along strike from approximately vertical just north of the U.S.-Mexico border to between 70° and 80° near the northernmost extent of the 1979 surface break. This change in dip may be related to a change in local strike along the fault. Large elevation changes (>15 cm) also occur within the Brawley Seismic Zone well north of the primary surface faulting. While these movements are consistent with a number of possible fault models, our prefered interpretation based on geodetic and seismic observations (aftershock locations and focal mechanisms) involves right-lateral, aseismic slip on a northwest striking fault along the east side of the Brawley Seismic Zone and conjugate left-lateral faulting on a northeast striking fault (possibly associated with an M = 5.8 aftershock). Buried creep on this same right-lateral fault in the Brawley Seismic Zone can also account for vertical deformation during the postseismic period of the 1940, M = 7.1 Imperial Valley earthquake as well as deformation during the interseismic period between the 1940 and 1979 events. Substantial right-lateral slip in the Brawley Seismic Zone suggests that a significant part of the shear strain released during and following the 1940 and 1979 earthquakes on the Imperial fault is transferred through the Brawley Seismic Zone to the southern end of the San Andreas fault.

Reilinger, Robert; Larsen, Shawn

1986-12-01

343

The 2007 M5.4 Alum Rock, California, earthquake: Implications for future earthquakes on the central and southern Calaveras Fault  

NASA Astrophysics Data System (ADS)

The similarity of seismograms recorded by two seismic stations demonstrate that the 31 October 2007 moment magnitude M5.4 Alum Rock earthquake is a repeat of a 1955 ML5.5 earthquake. Both occurred on Oppenheimer et al.'s (1990) Zone V "stuck patch" on the central Calaveras fault, providing new support for their model of Calaveras fault earthquake activity. We suggest that Zone V fails only in a family of recurring M ˜ 5.4-5.5 earthquakes. The 1955 and 2007 earthquakes are the penultimate and ultimate Zone V events. Earthquakes in 1891 and 1864 are possible earlier Zone V events. The next Zone V event is not expected in the next few decades, assuming a time-dependent recurrence model: the mean forecast date is 2064 (2035-2104, 95% confidence range). We further suggest that Zones I, II, III, and IV fail in recurring M ˜ 5.1-5.3, M ˜ 5.6-5.8, M ˜ 6.1-6.3, and M ˜ 4.9-5.0 earthquakes, respectively. If our earthquake recurrence model is correct, the next Zone I event is overdue and could occur anytime, and M5-6 earthquakes should not occur on Zones II, III, and IV before 2014, 2012, and 2026, respectively. We cannot rule out the possibility that Zone VI, which lies at the southern end of the Mission Seismic Trend, where the southern Hayward and central Calaveras faults appear to connect at depth, fails aseismically or in large events on the southern Hayward fault, such as last occurred in 1868, or in large events on the adjoining northern Calaveras fault segment.

Oppenheimer, David H.; Bakun, William H.; Parsons, Tom; Simpson, Robert W.; Boatwright, John; Uhrhammer, Robert A.

2010-08-01

344

Avian Flu / Earthquake Prediction  

NSDL National Science Digital Library

This radio broadcast includes a discussion of the avian flu spreading though Southeast Asia, Russia and parts of Europe. Topics include whether the outbreak is a pandemic in the making, and what preparations might be made to control the outbreak. The next segment of the broadcast discusses earthquake prediction, in light of the 2005 earthquake in Pakistan. Two seismologists discuss what was learned in the Parkfield project, an experiment in earthquake prediction conducted in California. Other topics include the distribution of large versus small earthquakes; how poor construction magnifies earthquake devastation; and the relationship of plate tectonics to the Pakistan earthquake.

345

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)

A long paleoseismic record at Hog Lake on the central San Jacinto fault (SJF) in southern California documents evidence for 18 surface ruptures in the past 3.8-4 ka. This yields a long-term recurrence interval of about 210 years, consistent with its slip rate of ~16 mm/yr and field observations of 3-4 m of displacement per event. However, during the past 3800 years, the fault has switched from a quasi-periodic mode of earthquake production, during which the recurrence interval is similar to the long-term average, to clustered behavior with the inter-event periods as short as a few decades. There are also some periods as long as 450 years during which there were no surface ruptures, and these periods are commonly followed by one to several closely-timed ruptures. The coefficient of variation (CV) for the timing of these earthquakes is about 0.6 for the past 4000 years (17 intervals). Similar behavior has been observed on the San Andreas Fault (SAF) south of the Transverse Ranges where clusters of earthquakes have been followed by periods of lower seismic production, and the CV is as high as 0.7 for some portions of the fault. In contrast, the central North Anatolian Fault (NAF) in Turkey, which ruptured in 1944, appears to have produced ruptures with similar displacement at fairly regular intervals for the past 1600 years. With a CV of 0.16 for timing, and close to 0.1 for displacement, the 1944 rupture segment near Gerede appears to have been both periodic and characteristic. The SJF and SAF are part of a broad plate boundary system with multiple parallel strands with significant slip rates. Additional faults lay to the east (Eastern California shear zone) and west (faults of the LA basin and southern California Borderland), which makes the southern SAF system a complex and broad plate boundary zone. In comparison, the 1944 rupture section of the NAF is simple, straight and highly localized, which contrasts with the complex system of parallel faults in southern California. These observations suggest that the complexity of the southern California fault network is partly responsible for the apparent increase in “noise” and non-periodic behavior, perhaps resulting from stress transfer to adjacent faults after a large earthquake on one fault. The simplicity of the central NAF may account for its relatively simple behavior. If correct, the study of simple plate boundary faults may provide new insights into the constitutive elements of fault zones, and may aid in identifying those components that are critical for better forecasting future seismicity in complex systems.

Rockwell, T. K.

2010-12-01

346

Paleoseismic Event Dating and the Conditional Probability of Large Earthquakes on the Southern San Andreas Fault, California  

Microsoft Academic Search

We introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the Wrightwood and Pallett Creek sites on the southern San Andreas fault. We illustrate how stratigraphic ordering, sedimentolog- ical, and historical data can be used quantitatively in the process of estimating earth- quake ages. Calibrated radiocarbon age distributions are used directly from layer dating through

Glenn P. Biasi; Ray J. Weldon II; Thomas E. Fumal; Gordon G. Seitz

2002-01-01

347

Southern California Earthquake Center\\/Undergraduate Studies in Earthquake Information Technology (SCEC\\/UseIT): Towards the Next Generation of Internship  

Microsoft Academic Search

The SCEC\\/UseIT internship program is training the next generation of earthquake scientist, with methods that can be adapted to other disciplines. UseIT interns work collaboratively, in multi-disciplinary teams, conducting computer science research that is needed by earthquake scientists. Since 2002, the UseIT program has welcomed 64 students, in some two dozen majors, at all class levels, from schools around the

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

2005-01-01

348

Correlation of ground motion and intensity for the 17 January 1994 Northridge, California, earthquake  

USGS Publications Warehouse

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.

Boatwright, J.; Thywissen, K.; Seekins, L. C.

2001-01-01

349

Static-stress impact of the 1992 Landers earthquake sequence on nucleation and slip at the site of the 1999 M=7.1 Hector Mine earthquake, southern California  

USGS Publications Warehouse

The proximity in time (?7 years) and space (?20 km) between the 1992 M=7.3 Landers earthquake and the 1999 M=7.1 Hector Mine event suggests a possible link between the quakes. We thus calculated the static stress changes following the 1992 Joshua Tree/Landers/Big Bear earthquake sequence on the 1999 M=7.1 Hector Mine rupture plane in southern California. Resolving the stress tensor into rake-parallel and fault-normal components and comparing with changes in the post-Landers seismicity rate allows us to estimate a coefficient of friction on the Hector Mine plane. Seismicity following the 1992 sequence increased at Hector Mine where the fault was unclamped. This increase occurred despite a calculated reduction in right-lateral shear stress. The dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction (µ?0.8). We calculated the Coulomb stress change using µ=0.8 and found that the Hector Mine hypocenter was mildly encouraged (0.5 bars) by the 1992 earthquake sequence. In addition, the region of peak slip during the Hector Mine quake occurred where Coulomb stress is calculated to have increased by 0.5–1.5 bars. In general, slip was more limited where Coulomb stress was reduced, though there was some slip where the strongest stress decrease was calculated. Interestingly, many smaller earthquakes nucleated at or near the 1999 Hector Mine hypocenter after 1992, but only in 1999 did an event spread to become a M=7.1 earthquake.

Parsons, Tom; Dreger, Douglas S.

2000-01-01

350

Comment on "Self-similar earthquake triggering, Båth's law, and foreshock/aftershock magnitudes: Simulations, theory, and results for southern California" by P. M. Shearer  

NASA Astrophysics Data System (ADS)

Shearer [2012] finds three differences of the seismicity clustering in southern California compared to self-similar triggering models: (i) a significantly lower b-value for the aftershocks, (ii) a too large aftershock number, and (iii) a too large foreshock-aftershock ratio to be consistent with the Båth law. Based on these observations, the author concluded that the observed seismicity is not in agreement with self-similarity triggering and/or the observed clustering is not primarily caused by earthquake-to-earthquake triggering. However, I show that the observed lower b-value is likely related to incomplete recordings after mainshocks and that the apparently too large aftershock number does not disprove the self-similarity. Thus, only the enhanced foreshock-to-aftershock ratio seems to indicate some discrepancy to self-similar triggering.

Hainzl, Sebastian

2013-03-01

351

Moment Tensors and their Uncertainties for M3 Earthquakes in the Geysers, California, from Waveform Modeling and First Motions  

NASA Astrophysics Data System (ADS)

We investigate moment tensor solutions and their uncertainties for magnitude (M) ~3 earthquakes located in the northwest Geysers geothermal field, California. We are exploiting an unusual opportunity where data for M~3 events have been recorded by three different networks and have moment tensor solutions calculated by three different methods. We solve for both deviatoric and full moment tensor solutions. The data sets include local short-period instruments (4.5 Hz) of the 30 stations of the Lawrence Berkeley National Laboratory (LBNL), with which we obtain waveform inversion solutions at relatively high frequencies (i.e., up to 2.5 Hz), and regionally distributed broadband stations operated by the Berkeley Seismological Laboratory (BSL), with which are used to provide waveform inversion solutions with data filtered at longer periods (i.e., > 10 sec). We also utilize the LBNL data to obtain moment tensor solutions by fitting the P-wave first motions. The USGS, LBNL, and BSL obtain different event locations, utilize different velocity models, and analyze different frequency bands and wave types (i.e., body waves for LBNL method and primarily surface waves for the BSL analysis). Preliminary results indicate that the BSL and LBNL waveform modeling analyses give similar results in terms of nodal plane characteristics, moment magnitude, and moment tensor decomposition. Analysis of the P-wave first motions recorded by LBNL stations can illuminate complexities in the source processes when compared to waveform moment tensor solutions. We discuss uncertainties in the source inversions that use broadband and/or short-period waveform modeling, and in the source inversions from first motions only. We also combine the different datasets and compare their individual importance as they can help illustrate the complex source processes happening in the Geysers. This study introduces the possibility to interpret the seismic sources as complex processes in which both shear and tensile processes can occur simultaneously or sequentially.

Guilhem, A.; Dreger, D. S.; Hutchings, L. J.; Johnson, L.

2012-12-01

352

The 1994 Northridge, California, earthquake: Investigation of rupture velocity, risetime, and high-frequency radiation  

USGS Publications Warehouse

A hybrid global search algorithm is used to solve the nonlinear problem of calculating slip amplitude, rake, risetime, and rupture time on a finite fault. Thirty-five strong motion velocity records are inverted by this method over the frequency band from 0.1 to 1.0 Hz for the Northridge earthquake. Four regions of larger-amplitude slip are identified: one near the hypocenter at a depth of 17 km, a second west of the hypocenter at about the same depth, a third updip from the hypocenter at a depth of 10 km, and a fourth updip from the hypocenter and to the northwest. The results further show an initial fast rupture with a velocity of 2.8 to 3.0 km/s followed by a slow termination of the rupture with velocities of 2.0 to 2.5 km/s. The initial energetic rupture phase lasts for 3 s, extending out 10 km from the hypocenter. Slip near the hypocenter has a short risetime of 0.5 s, which increases to 1.5 s for the major slip areas removed from the hypocentral region. The energetic rupture phase is also shown to be the primary source of high-frequency radiation (1-15 Hz) by an inversion of acceleration envelopes. The same global search algorithm is used in the envelope inversion to calculate high-frequency radiation intensity on the fault and rupture time. The rupture timing from the low- and high-frequency inversions is similar, indicating that the high frequencies are produced primarily at the mainshock rupture front. Two major sources of high-frequency radiation are identified within the energetic rupture phase, one at the hypocenter and another deep source to the west of the hypocenter. The source at the hypocenter is associated with the initiation of rupture and the breaking of a high-stress-drop asperity and the second is associated with stopping of the rupture in a westerly direction.

Hartzell, S.; Liu, P.; Mendoza, C.

1996-01-01

353

The 1998 earthquake sequence south of Long Valley Caldera, California: Hints of magmatic involvement  

USGS Publications Warehouse

A significant episode of seismic and geodetic unrest took place at Long Valley Caldera, California, beginning in the summer of 1997. Activity through late May of 1998 was concentrated in and around the south moat and the south margin of the resurgent dome. The Sierran Nevada block (SNB) region to the south/southeast remained relatively quiet until a M 5.1 event occurred there on 9 June 1998 (UT). A second M 5.1 event followed on 15 July (UT); both events were followed by appreciable aftershock sequences. An additional, distinct burst of activity began on 1 August 1998. The number of events in the August sequence (over the first week or two) was similar to the aftershock sequence of the 15 July 1998 M 5.1 event, but the later sequence was not associated with any events larger than M 4.3. All of the summer 1998 SNB activity was considered tectonic rather than magmatic; in general the SNB is considered an unlikely location for future eruptions. However, the August sequence-an 'aftershock sequence without a mainshock'-is suggestive of a strain event larger than the cumulative seismotectonic strain release. Moreover, a careful examination of waveforms from the August sequence reveals a small handful of events whose spectral signature is strikingly harmonic. We investigate the waveforms of these events using spectral, autocorrelation, and empirical Green's function techniques and conclude that they were most likely associated with a fluid-controlled source. Our observations suggest that there may have been some degree of magma or magma-derived fluid involvement in the 1998 SNB sequence.

Hough, S. E.; Dollar, R. S.; Johnson, P.

2000-01-01

354

Predicting catastrophic earthquakes  

NSDL National Science Digital Library

This resource provides an abstract. This article discusses a method based on the magnitude-frequency distribution of previous earthquakes in a region. It is used to examine the probability of a small earthquake growing into a catastrophic one. When a small earthquake is detected in a region where a catastrophic one is expected, early warning systems can be modified to determine the probability that this earthquake will grow in magnitude. It was found that if the observed earthquake magnitude reaches 6.5, the estimated probability that the final magnitude will reach 7.5 is between 25 and 41 percent.

Al., Iwata E.; Agu

355

Dynamic stress drop and rupture dynamics of the October 15, 1979 Imperial Valley, California, earthquake  

NASA Astrophysics Data System (ADS)

A dynamic faulting model is constructed to determine the dynamic stress drop and relative strength distribution for the October 15, 1989 Imperial Valley earthquake, and to study the dynamics of rupture propagation for this event. Reproduction of the kinematic quantities of the strike-slip rate, strike-slip final offset, rupture time, and rupture duration, bu varying the dynamic parameters of dynamic stress drop and yield strength, is attempted. The fault plane is discretized in 1.5 km square grids. The model incorporates first-order corrections for the effect of the free surface and material property heterogeneity on the calculation of rupture at depth. The strike-slip particle velocities, final offsets, and rupture durations of the kinematic model are matched within about 40% everywhere below about 5 km, except in the hypocentral region and in a high displacement region 20 km north of the epicenter. The strike-slip rate of the dynamic model is half and rupture duration double those of the kinematic model in the epicentral region. The rupture durations and strike-slip final offsets are two thirds those of the kinematic model in a high-stress drop region beneath the El Centro crossing array. Two slip concentrations correspond to stress drop concentrations, one of about 80 bar at 20 km from the epicenter and at 8 km depth, and the other of about 70 bar at 30 km from the epicenter and 10 km depth. Most of the dynamic stress drop occurs between the depths of 9 and 11 km, averaging about 60 bar. Stress drops in the 7-9 km range vary between 25 and 35 bar, while stress drops in the 5-7 km depth range vary between 10 and 15 bar. This depth dependence of stress drop was a consistent feature across nearly 20 km of the fault. Stress drop appeared to be well correlated with rock type; negative stress drop was found in the sediment regions and the regions at depth, while positive stress drop was found in the metasediment regions between the depths of 5 and 11 km. Yield strength and rupture velocity are inversely related; high yield strength is found in regions of low rupture velocity and vice versa. Rupture was found to terminate at the northern end of the fault by collision with a high strength barrier. A region of supersonic rupture velocity was found to occur in a region of high stress drop and low fracture strength. The kinematic rupture velocity at the northern end of the fault was found to be unreasonably low; results show that this region reaches its peak stress before the kinematic break time. Yield strength increased with depth in the seismogenetic zone until the base of the zone was reached, below which it tapered off slightly

Quin, H.

1990-03-01

356

Full-3D waveform tomography of Southern California crustal structure by using earthquake recordings and ambient noise Green's functions based on adjoint and scattering-integral methods  

NASA Astrophysics Data System (ADS)

We apply a unified methodology for seismic waveform analysis and inversions to Southern California. To automate the waveform selection processes, we developed a semi-automatic seismic waveform analysis algorithm for full-wave earthquake source parameters and tomographic inversions. The algorithm is based on continuous wavelet transforms, a topological watershed method, and a set of user-adjustable criteria to select usable waveform windows for full-wave inversions. The algorithm takes advantages of time-frequency representations of seismograms and is able to separate seismic phases in both time and frequency domains. The selected wave packet pairs between observed and synthetic waveforms are then used for extracting frequency-dependent phase and amplitude misfit measurements, which are used in our seismic source and structural inversions. Our full-wave waveform tomography uses the 3D SCEC Community Velocity Model Version 4.0 as initial model, a staggered-grid finite-difference code to simulate seismic wave propagations. The sensitivity (Fréchet) kernels are calculated based on the scattering integral and adjoint methods to iteratively improve the model. We use both earthquake recordings and ambient noise Green's functions, stacking of station-to-station correlations of ambient seismic noise, in our full-3D waveform tomographic inversions. To reduce errors of earthquake sources, the epicenters and source parameters of earthquakes used in our tomographic inversion are inverted by our full-wave CMT inversion method. Our current model shows many features that relate to the geological structures at shallow depth and contrasting velocity values across faults. The velocity perturbations could up to 45% with respect to the initial model in some regions and relate to some structures that do not exist in the initial model, such as southern Great Valley. The earthquake waveform misfits reduce over 70% and the ambient noise Green's function group velocity delay time variance reduce over 90% when compared with that at the initial stage.

Lee, E.; Chen, P.; Jordan, T. H.; Maechling, P. J.; Denolle, M.; Beroza, G. C.

2013-12-01

357

Evidence for large earthquakes on the San Andreas fault at the Wrightwood, California paleoseismic site: A.D. 500 to present  

USGS Publications Warehouse

We present structural and stratigraphic evidence from a paleoseismic site near Wrightwood, California, for 14 large earthquakes that occurred on the southern San Andreas fault during the past 1500 years. In a network of 38 trenches and creek-bank exposures, we have exposed a composite section of interbedded debris flow deposits and thin peat layers more than 24 m thick; fluvial deposits occur along the northern margin of the site. The site is a 150-m-wide zone of deformation bounded on the surface by a main fault zone along the northwest margin and a secondary fault zone to the southwest. Evidence for most of the 14 earthquakes occurs along structures within both zones. We identify paleoearthquake horizons using infilled fissures, scarps, multiple rupture terminations, and widespread folding and tilting of beds. Ages of stratigraphic units and earthquakes are constrained by historic data and 72 14C ages, mostly from samples of peat and some from plant fibers, wood, pine cones, and charcoal. Comparison of the long, well-resolved paleoseimic record at Wrightwood with records at other sites along the fault indicates that rupture lengths of past earthquakes were at least 100 km long. Paleoseismic records at sites in the Coachella Valley suggest that each of the past five large earthquakes recorded there ruptured the fault at least as far northwest as Wrightwood. Comparisons with event chronologies at Pallett Creek and sites to the northwest suggests that approximately the same part of the fault that ruptured in 1857 may also have failed in the early to mid-sixteenth century and several other times during the past 1200 years. Records at Pallett Creek and Pitman Canyon suggest that, in addition to the 14 earthquakes we document, one and possibly two other large earthquakes ruptured the part of the fault including Wrightwood since about A.D. 500. These observations and elapsed times that are significantly longer than mean recurrence intervals at Wrightwood and sites to the southeast suggest that at least the southermost 200 km of the San Andreas fault is near failure.

Fumal, T. E.; Weldon, R. J.; Biasi, G. P.; Dawson, T. E.; Seitz, G. G.; Frost, W. T.; Schwartz, D. P.

2002-01-01

358

Southern California Earthquake Center/Undergraduate Studies in Earthquake Information Technology (SCEC/UseIT): Towards the Next Generation of Internship  

NASA Astrophysics Data System (ADS)

The SCEC/UseIT internship program is training the next generation of earthquake scientist, with methods that can be adapted to other disciplines. UseIT interns work collaboratively, in multi-disciplinary teams, conducting computer science research that is needed by earthquake scientists. Since 2002, the UseIT program has welcomed 64 students, in some two dozen majors, at all class levels, from schools around the nation. Each summer''s work is posed as a ``Grand Challenge.'' The students then organize themselves into project teams, decide how to proceed, and pool their diverse talents and backgrounds. They have traditional mentors, who provide advice and encouragement, but they also mentor one another, and this has proved to be a powerful relationship. Most begin with fear that their Grand Challenge is impossible, and end with excitement and pride about what they have accomplished. The 22 UseIT interns in summer, 2005, were primarily computer science and engineering majors, with others in geology, mathematics, English, digital media design, physics, history, and cinema. The 2005 Grand Challenge was to "build an earthquake monitoring system" to aid scientists who must visualize rapidly evolving earthquake sequences and convey information to emergency personnel and the public. Most UseIT interns were engaged in software engineering, bringing new datasets and functionality to SCEC-VDO (Virtual Display of Objects), a 3D visualization software that was prototyped by interns last year, using Java3D and an extensible, plug-in architecture based on the Eclipse Integrated Development Environment. Other UseIT interns used SCEC-VDO to make animated movies, and experimented with imagery in order to communicate concepts and events in earthquake science. One movie-making project included the creation of an assessment to test the effectiveness of the movie''s educational message. Finally, one intern created an interactive, multimedia presentation of the UseIT program.

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

2005-12-01