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1

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

USGS Publications Warehouse

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

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

2003-01-01

2

Evaluating Short-Term Probability Forecasts of M4+ Earthquakes in California and Western Nevada Since 2001  

Microsoft Academic Search

Since 2001 we have made a number of forecasts of 10-day time periods of increased probability of earthquakes of M4 or greater (M4+) in California and Nevada. The forecasts are based on observations of non-Poissonian short-term clustering in the M4+ seismicity from 1968 to 2000 for Northern California\\/Western Nevada and from 1983 to 2000 for Southern California, and they assume

J. E. Ebel; A. L. Kafka

2004-01-01

3

Probabilities of large earthquakes in the San Francisco Bay region, California  

SciTech Connect

This book evaluates long-term probabilities of large earthquakes (magnitude 7 or greater) in the San Francisco Bay region by identifying fault segments expected to produce large earthquakes and then estimating the time to the next earthquake on each segment. The probability of one or more large earthquakes in the region in the coming 30 years is estimated at 67 percent. This report contains detailed, technical descriptions of the data and methods used to derive the estimates.

Not Available

1990-01-01

4

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

USGS Publications Warehouse

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

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

2008-01-01

5

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

6

Earthquake History of California  

NSDL National Science Digital Library

This article describes major earthquakes that have occurred in California since the colonial era, beginning with a 1769 earthquake experienced by a Spanish expedition near what is now Los Angeles, and ending with the July 1952 earthquake in Kern County. Each account provides observer's reports of injuries, fatalities, property damage, and ground effects (cracking, subsidence). More recent earthquake accounts include an estimated or measured magnitude.

7

The earthquake prediction experiment at Parkfield, California  

Microsoft Academic Search

Since 1985, a focused earthquake prediction experiment has been in progress along the San Andreas fault near the town of Parkfield in central California. Parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years, the most recent a magnitude of 6 event in 1966. The probability of another moderate earthquake soon appears high, but studies assigning

Evelyn Roeloffs; John Langbein

1994-01-01

8

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.

9

Parkfield, California, earthquake prediction experiment  

Microsoft Academic Search

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

W. H. Bakun; A. G. Lindh

1985-01-01

10

WGCEP Historical California Earthquake Catalog  

USGS Publications Warehouse

This appendix provides an earthquake catalog for California and the surrounding area. Our goal is to provide a listing for all known M > 5.5 earthquakes that occurred from 1850-1932 and all known M > 4.0 earthquakes that occurred from 1932-2006 within the region of 31.0 to 43.0 degrees North and -126.0 to -114.0 degrees West. Some pre-1932 earthquakes 4 5, before the Northern California network was online. Some earthquakes from 1900-1932, and particularly from 1910-1932 are also based on instrumental readings, but the quality of the instrumental record and the resulting analysis are much less precise than for later listings. A partial exception is for some of the largest earthquakes, such as the San Francisco earthquake of April 18, 1906, for which global teleseismic records (Wald et al. 1993) and geodetic measurements (Thatcher et al. 1906) have been used to help determine magnitudes.

Felzer, Karen R.; Cao, Tianqing

2008-01-01

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 Data Center  

NSDL National Science Digital Library

To say that there are a few earthquake research centers in Southern California is a bit like saying that Chicago sits on a lake of some size. It's a bit of an obvious remark, but given that there are a number of such projects, it's important to take a look at some of the more compelling ones out there. One such important resource is the Southern California Earthquake Data Center, sponsored by a host of organizations, including the California Institute of Technology and the United States Geological Survey. Visitors to the project site can peruse some of its recent work, which includes a clickable map of the region that features information on recent earthquakes in California and Nevada. Equally compelling is the clickable fault map of Southern California where visitors can learn about the local faults and recent activity along each fault. Another key element of the site is the historical earthquake database, which may be of interest to both the general public and those who are studying this area.

2005-11-03

13

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.

14

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.

15

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.

16

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.

17

Recent Earthquakes in California and Nevada  

NSDL National Science Digital Library

This site from the US Geological Survey provides information and updates about the recent earthquakes in California and Nevada. Data include magnitude, time, location, coordinates, and depth for each earthquake, and each data page points to additional sources of information for the given earthquake. Users can access information via a clickable map of California or specialty maps of Long Valley, Los Angeles, and San Francisco. Alternately, the site allows visitors to select an earthquake from a list of big earthquakes or a list of all earthquakes.

18

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

19

SCEC Earthquake Simulator Comparison Results for California  

NASA Astrophysics Data System (ADS)

This is our first report on comparisons of earthquake simulator results with one another and with actual earthquake data for all of California, excluding Cascadia. Earthquake simulators are computer programs that simulate long sequences of earthquakes and therefore allow study of a much longer earthquake history than is possible from instrumental, historical and paleoseismic data. The usefulness of simulated histories for anticipating the probabilities of future earthquakes and for contributing to public policy decisions depends on whether simulated earthquake catalogs properly represent actual earthquakes. Thus, we compare simulated histories generated by five different earthquake simulators with one another and with what is known about actual earthquake history in order to evaluate the usefulness of the simulator results. Although sharing common features, our simulators differ from one another in their details in many important ways. All simulators use the same fault geometry and the same ~15,000, 3x3 km elements to represent the strike-slip and thrust faults in California. The set of faults and the input slip rates on them are essentially those of the UCERF2 fault and deformation model; we will switch to the UCERF3 model once it is available. All simulators use the boundary element method to compute stress transfer between elements. Differences between the simulators include how they represent fault friction and what assumptions they make to promote rupture propagation from one element to another. The behavior of the simulators is encouragingly similar and the results are similar to what is known about real earthquakes, although some refinements are being made to some of the simulators to improve these comparisons as a result of our initial results. The frequency magnitude distributions of simulated events from M6 to M7.5 for a 30,000 year simulated history agree well with instrumental observations for all of California. Scaling relations, as seen on plots of slip vs. rupture length, magnitude vs. rupture area, and magnitude vs rupture length, are similar for the different simulators. On these plots, overlaying results from several studies characterizing actual earthquake scaling shows good agreement with the simulator results. Importantly, moment rates and event rates for M7+ events show variations by factors of 3 in 100-yr moving averages throughout the 30,000 year simulated histories, with event rates for M6+ events correlating with M7+ event rates and 200 year periods being too short to characterize the moment and event rates. This suggests that in California our observational instrumental and historical record is too short to characterize seismicity rates adequately. For fault sections where paleoseismic data exist to constrain interevent times, fault stress drops assumed by the simulators can be adjusted to agree with observations. Lacking constraining data the simulated interevent times may be off, perhaps by up to a factor of 2.

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

2011-12-01

20

Prospective Tests of Southern California Earthquake Forecasts  

NASA Astrophysics Data System (ADS)

We are testing earthquake forecast models prospectively using likelihood ratios. Several investigators have developed such models as part of the Southern California Earthquake Center's project called Regional Earthquake Likelihood Models (RELM). Various models are based on fault geometry and slip rates, seismicity, geodetic strain, and stress interactions. Here we describe the testing procedure and present preliminary results. Forecasts are expressed as the yearly rate of earthquakes within pre-specified bins of longitude, latitude, magnitude, and focal mechanism parameters. We test models against each other in pairs, which requires that both forecasts in a pair be defined over the same set of bins. For this reason we specify a standard "menu" of bins and ground rules to guide forecasters in using common descriptions. One menu category includes five-year forecasts of magnitude 5.0 and larger. Contributors will be requested to submit forecasts in the form of a vector of yearly earthquake rates on a 0.1 degree grid at the beginning of the test. Focal mechanism forecasts, when available, are also archived and used in the tests. Interim progress will be evaluated yearly, but final conclusions would be made on the basis of cumulative five-year performance. The second category includes forecasts of earthquakes above magnitude 4.0 on a 0.1 degree grid, evaluated and renewed daily. Final evaluation would be based on cumulative performance over five years. Other types of forecasts with different magnitude, space, and time sampling are welcome and will be tested against other models with shared characteristics. Tests are based on the log likelihood scores derived from the probability that future earthquakes would occur where they do if a given forecast were true [Kagan and Jackson, J. Geophys. Res.,100, 3,943-3,959, 1995]. For each pair of forecasts, we compute alpha, the probability that the first would be wrongly rejected in favor of the second, and beta, the probability that the second would be wrongly rejected in favor of the first. Computing alpha and beta requires knowing the theoretical distribution of likelihood scores under each hypothesis, which we estimate by simulations. In this scheme, each forecast is given equal status; there is no "null hypothesis" which would be accepted by default. Forecasts and test results will be archived and posted on the RELM web site. Major problems under discussion include how to treat aftershocks, which clearly violate the variable-rate Poissonian hypotheses that we employ, and how to deal with the temporal variations in catalog completeness that follow large earthquakes.

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

2004-12-01

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

An Investigation of Southern California Earthquakes  

NSDL National Science Digital Library

This site has directions for a classroom activity in which students plot locations of major Southern California earthquakes on a map. A table listing major earthquakes, when they occurred, their locations and their magnitudes is included. There is also a set of questions for the students to answer once they have plotted the earthquake data on their map. This site is in PDF format.

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

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

25

Building the Southern California Earthquake Center  

Microsoft Academic Search

Kei Aki was the founding director of the Southern California Earthquake Center (SCEC), a multi-institutional collaboration formed in 1991 as a Science and Technology Center (STC) under the National Science Foundation (NSF) and the U. S. Geological Survey (USGS). Aki and his colleagues articulated a system-level vision for the Center: investigations by disciplinary working groups would be woven together into

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

2004-01-01

26

California earthquakes: Why only shallow focus?  

USGS Publications Warehouse

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

Brace, W. F.; Byerlee, J. D.

1970-01-01

27

The Big Ten earthquake scenarios for Southern California  

NASA Astrophysics Data System (ADS)

The Big Ten project is generating a hierarchy of simulations for ten of the most probable large (M > 7) ruptures in Southern California, with the objective of understanding how source directivity, rupture complexity, and basin effects control ground motions. The ruptures and moment-magnitudes are selected from events with relatively high probability rates in the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF2) model. The event set is being used to coordinate multiple types of large-scale simulations (requiring high performance computing), as well as multiple groups of researchers around a common set of earthquake scenarios. The geoscience goals of the Big Ten project are to: (1) Understand the roles of source directivity, rupture complexity, and basin effects on ground motions, and evaluate how these factors control hazard curves from the CyberShake project; (2) Improve simulation capabilities by incorporating new codes that can model geologic complexities including topography, geologic discontinuities, and source complexities such as irregular, dipping, and offset faults; (3) Use dynamic rupture simulations to investigate the effects of realistic friction laws, geologic heterogeneities, and near-fault stress states on seismic radiation and thereby improve pseudo-dynamic rupture models of hazardous earthquakes; and (4) Use realistic earthquake simulations to evaluate static and dynamic stress transfer and assess their effects on strain accumulation, rupture nucleation, and stress release. Examples of some preliminary Big Ten simulations will be presented.

Ely, G.; Jordan, T. H.; Maechling, P. J.; Olsen, K. B.; Day, S. M.; Minster, J. H.; Graves, R. W.; Ma, S.; Beroza, G. C.; Bielak, J.; Taborda, R.; Cui, Y.; Urbanic, J.; Callaghan, S.

2009-12-01

28

Seafloor response for two southern California earthquakes  

SciTech Connect

A significant consideration in the design of offshore structures for seismically-active regions is their response to earthquakes. An appropriate design methodology would involve the synthesis of wave propagation/structural vibration models with in-situ soil/structural response measurements. A Seafloor Earthquake Measurement System (SEMS), designed and developed by Sandia National Laboratories, has been deployed in the Shell Oil Company Beta Field, offshore Long Beach, California. During July 1986, two significant earthquake events were simultaneously recorded by the SEMS unit and by accelerometers mounted on nearby offshore platforms. This paper describes the SEMS unit, presents SEMS data from these events, and contains a preliminary analysis of these data. The potential impact that this research will have in the design methodology of offshore structures is also indicated.

Sleefe, G.E.; Engi, D.

1987-01-01

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

Assigning probability gain for precursors of four large Chinese earthquakes  

SciTech Connect

We extend the concept of probability gain associated with a precursor (Aki, 1981) to a set of precursors which may be mutually dependent. Making use of a new formula, we derive a criterion for selecting precursors from a given data set in order to calculate the probability gain. The probabilities per unit time immediately before four large Chinese earthquakes are calculated. They are approximately 0.09, 0.09, 0.07 and 0.08 per day for 1975 Haicheng (M = 7.3), 1976 Tangshan (M = 7.8), 1976 Longling (M = 7.6), and Songpan (M = 7.2) earthquakes, respectively. These results are encouraging because they suggest that the investigated precursory phenomena may have included the complete information for earthquake prediction, at least for the above earthquakes. With this method, the step-by-step approach to prediction used in China may be quantified in terms of the probability of earthquake occurrence. The ln P versus t curve (where P is the probability of earthquake occurrence at time t) shows that ln P does not increase with t linearly but more rapidly as the time of earthquake approaches.

Cao, T.; Aki, K.

1983-03-10

31

Assigning probability gain for precursors of four large Chinese earthquakes  

NASA Astrophysics Data System (ADS)

We extend the concept of probability gain associated with a precursor (Aki, 1981) to a set of precursors which may be mutually dependent. Making use of a new formula, we derive a criterion for selecting precursors from a given data set in order to calculate the probability gain. The probabilities per unit time immediately before four large Chinese earthquakes are calculated. They are approximately 0.09, 0.09, 0.07 and 0.08 per day for 1975 Haicheng (M = 7.3), 1976 Tangshan (M = 7.8), 1976 Longling (M = 7.6), and Songpan (M - 7.2) earthquakes, respectively. These results are encouraging because they suggest that the investigated precursory phenomena may have included the complete information for earthquake prediction, at least for the above earthquakes. With this method, the step-by-step approach to prediction used in China may be quantified in terms of the probability of earthquake occurrence. The ln P versus t curve (where P is the probability of earthquake occurrence at time t) shows that ln P does not increase with t linearly but more rapidly as the time of earthquake approaches.

Cao, Tianqing; Aki, Keiiti

1983-03-01

32

Southern California Earthquake Center Geologic Vertical Motion Database  

Microsoft Academic Search

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

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

2008-01-01

33

Pattern recognition applied to earthquake epicenters in California  

Microsoft Academic Search

A pattern recognition procedure is explained which uses geological data and the earthquake history of a region, in this case California, and learns how to separate earthquake epicenters from other places. Sites of future earthquake epicenters are predicted as well as places where epicenters will not occur. The problem is formulated in several ways and control experiments are devised and

I. M. Gelfand; Sh. A. Guberman; V. I. Keilis-Borok; L. Knopoff; E. Ya. Ranzman; I. M. Rotwain; A. M. Sadovsky

1976-01-01

34

A probability method for local earthquake focal mechanisms  

SciTech Connect

The authors propose a method for obtaining focal mechanisms of earthquakes recorded on a local network. It is based on the non-linear estimation of the probability function for strike, dip and slip of the focal mechanisms from P polarizations and S/P amplitude ratios. The method is shown to be effective for the analysis of small earthquakes recorded by local networks. In particular, the S/P amplitude ratios bring strong constraints on fault parameters, even if large errors are present. An application to a small earthquake recorded at the volcanic zone of Campi Flegrei (Naples, Italy) during a seismic outburst is presented.

De Natale, G.; Virieux, J. (Univ. Paris 7 (France)); Ferraro, A.

1991-04-01

35

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

Microsoft Academic Search

We examine the initial subevent (ISE) of the M 6.7, 1994 Northridge, California, earthquake in order to discriminate between two end-member rupture initiation models: the ‘preslip’ and ‘cascade’ models. Final earthquake size may be predictable from an ISE's seismic signature in the preslip model but not in the cascade model. In the cascade model ISEs are simply small earthquakes that

D. Kilb; J. Gomberg

1999-01-01

36

Earthquake-resistant jacket installed off California  

SciTech Connect

In June 1984, Shell's Eureka platform jacket was loaded out aboard Heerema's 600 x 150-ft H-109 barge and began a 2-wk tow-out and installation phase in 700-ft water in the southern portion of the Beta field, approx. 9 miles off Huntington Beach, Calif. The jacket has 2 distinctions: it is the largest single-piece jacket yet constructed in California, and it is the first built in California with pre-installed curved conductors designed to precisely control angle and direction of wells to be drilled into the reservoir. The jacket is designed to withstand a 100-yr storm and meets API second-level criteria for earthquake survival for the category 2 earthquakes that can be expected in the Beta field. The 720 x 280 x 180-ft, 21,000-ton jacket's largest tubulars are 6 ft in diameter and have a 3.75-in. wall thickness. The structure is pinned to the seabed by twenty-four 5-ft-diameter piles driven 200 to 300 ft into the seabed through skirt pile sleeves.

Not Available

1984-01-01

37

Crustal Structure Near Coalinga, California Revisited: Implications for the Hypocentral Region of the 1983 ML 6.7 Earthquake  

Microsoft Academic Search

On May 2, 1983, a ML 6.7 earthquake occurred about 12 km northeast of the town of Coalinga, California on a previously unknown fault zone that underlies the boundary between the Coast Ranges and the Great Valley. Aftershock and focal mechanism studies have shown that the earthquake probably occurred on a southwest-dipping thrust fault at ca. 10 km depth. A

D. A. Popovich; K. C. Miller

2002-01-01

38

Toward earthquake early warning in northern California  

Microsoft Academic Search

Earthquake early warning systems are an approach to earthquake hazard mitigation which takes advantage of the rapid availability of earthquake information to quantify the hazard associated with an earthquake and issue a prediction of impending ground motion prior to its arrival in populated or otherwise sensitive areas. One such method, Earthquake Alarm Systems (ElarmS) has been under development in southern

Gilead Wurman; Richard M. Allen; Peter Lombard

2007-01-01

39

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

40

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

41

Recent Earthquakes in California and Nevada: Los Angeles Special Map  

NSDL National Science Digital Library

This map of the Los Angeles, California area displays earthquake locations for the latest week, day, and hour. The user can click on map symbols and get information on time, date, magnitude, location, and depth. Earthquake information is updated within 5 minutes of an actual event or otherwise once an hour. The information is from the U. S. Geological Survey-Caltech Seismic Net.

42

Automatic 3D Moment tensor inversions for southern California earthquakes  

Microsoft Academic Search

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

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

2008-01-01

43

Focal Depths of the 1966 Parkfield, California, Earthquakes.  

National Technical Information Service (NTIS)

Differences in arrival times of seismic phases at Berkeley, California (BRK), delta approximately 270 km, for the 0408 UT June 28 (M = 5.1), 0426 UT June 28 (M = 5.5), and 1953 UT June 29 (M = 5.0) 1966 Parkfield, California, earthquakes imply that focal ...

W. H. Bakun

1972-01-01

44

Influence of the 2008 Wenchuan earthquake (Mw 7.9) on the occurrence probability of future earthquakes on neighboring faults  

NASA Astrophysics Data System (ADS)

We calculate Coulomb stress change on Longquan–Shan and Huya faults after Wenchuan earthquake.The Longquan–Shan fault is closer to failure, but the Huya fault is in an inhibited state.The distribution of ML ? 1.5 earthquakes is consistent with Coulomb stress changes.Occurrence probability of earthquakes in the study regions for next decade is calculated.

Qian, Qi; Han, Zhu-Jun

2013-07-01

45

Significance of stress transfer in time-dependent earthquake probability calculations  

Microsoft Academic Search

A sudden change in stress is seen to modify earthquake rates, but should it also revise earthquake probability? Data used to derive input parameters permit an array of forecasts; so how large a static stress change is required to cause a statistically significant earthquake probability change? To answer that question, effects of parameter and philosophical choices are examined through all

Tom Parsons

2005-01-01

46

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

PubMed

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

Porter, Keith; Ramer, Kyle

2012-01-01

47

Earthquakes in the California-Nevada Map Area  

NSDL National Science Digital Library

This table provides information on all earthquakes in the California-Nevada area, as shown on the U.S. Geological Survey's real-time earthquake map. The table consists of all earthquakes cataloged in the last week (168 hours). The top three magnitude categories above magnitude 3 are in highlighted in red. Information provided includes magnitude, date and time, latitude and longitude, depth, and location. Each entry also has a link to a map showing the surface location of the event and a link to a written report.

48

Spectral Element Moment Tensor Inversions for Earthquakes in Southern California  

Microsoft Academic Search

We have developed and implemented a Centroid Moment-Tensor (CMT) inversion procedure to determine source parameters for southern California earthquakes. The method is based upon spectral-element simulations of regional seismic wave propagation in a recently developed three-dimensional southern California model. Sensitivity to source parameters is determined by numerically calculating the Fréchet derivatives required for the CMT inversion. We use a combination

Q. Liu; D. Komatitsch; J. Tromp

2003-01-01

49

Seafloor Response for Two Southern California Earthquakes.  

National Technical Information Service (NTIS)

A significant consideration in the design of offshore structures for seismically-active regions is their response to earthquakes. An appropriate design methodology would involve the synthesis of wave propagation/structural vibration models with in-situ so...

G. E. Sleefe D. Engi

1987-01-01

50

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

USGS Publications Warehouse

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

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

1989-01-01

51

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

USGS Publications Warehouse

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

Bakun, W. H.; Mcevilly, T. V.

1979-01-01

52

Seafloor response for two southern California earthquakes  

Microsoft Academic Search

A significant consideration in the design of offshore structures for seismically-active regions is their response to earthquakes. An appropriate design methodology would involve the synthesis of wave propagation\\/structural vibration models with in-situ soil\\/structural response measurements. A Seafloor Earthquake Measurement System (SEMS), designed and developed by Sandia National Laboratories, has been deployed in the Shell Oil Company Beta Field, offshore Long

G. E. Sleefe; D. Engi

1987-01-01

53

Very-long-period volcanic earthquakes beneath Mammoth Mountain, California  

USGS Publications Warehouse

Detection of three very-long-period (VLP) volcanic earthquakes beneath Mammoth Mountain emphasizes that magmatic processes continue to be active beneath this young, eastern California volcano. These VLP earthquakes, which occured in October 1996 and July and August 2000, appear as bell-shaped pulses with durations of one to two minutes on a nearby borehole dilatometer and on the displacement seismogram from a nearby broadband seismometer. They are accompanied by rapid-fire sequences of high-frequency (HF) earthquakes and several long- period (LP) volcanic earthquakes. The limited VLP data are consistent with a CLVD source at a depth of ???3 km beneath the summit, which we interpret as resulting from a slug of fluid (CO2- saturated magmatic brine or perhaps basaltic magma) moving into a crack.

Hill, D. P.; Dawson, P.; Johnston, M. J. S.; Pitt, A. M.; Biasi, G.; Smith, K.

2002-01-01

54

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

Microsoft Academic Search

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

C. Bayarsayhan; A. Bayasgalan; B. Enhtuvshin; R. A. Kurushin; Peter Molnar; M. Ölziybat

1996-01-01

55

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

SciTech Connect

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 concentrations returned to prequake levels either shortly before or after the earthquakes.

Reimer, G.M.

1981-05-01

56

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

57

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

58

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

59

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

60

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

61

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

62

United States Geological Survey, Earthquake Hazards Program-Northern California: Hazards & Preparedness  

NSDL National Science Digital Library

This page points to a number of reports and maps on earthquake hazards, prediction, and preparedness. The page is mainly about Northern California including the San Francisco Bay area, but also including some items on Southern California and Alaska, as well as general articles on the topics. Map types include seismic hazards maps, shaking hazards maps, and shaking intensity maps. Related programs are also referenced. Other links include, latest earthquake information, general earthquake information, and earthquake research.

63

Northridge, California earthquake of January 17, 1994: Performance of gas transmission pipelines. Technical report  

SciTech Connect

On January 17, 1994 at 4:31 a.m., a magnitude 6.6 earthquake struck the Los Angeles metropolitan area. Epicentered in the San Fernando Valley town of Northridge, California, the earthquake caused serious damage to buildings and sections of elevated freeways; ignited at least one hundred fires as it ruptured gas pipelines; and disrupted water supply systems. This reconnaissance report provides a performance analysis of gas transmission lines, both during this earthquake and during previous earthquakes, in Southern California.

O'Rourke, T.D.; Palmer, M.C.

1994-05-16

64

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.

65

Injury hospitalizations before and after the 1994 Northridge, California earthquake.  

PubMed

This study compared hospital-admitted injuries during the 14 days after the Northridge, California, earthquake of January 17, 1994, with hospital-admitted injuries during the preceding 16 days at the same facilities. Seventy-eight hospitals providing emergency care in Los Angeles County were screened; 16 were identified as having admitted at least one person for an earthquake-related injury. Retrospective chart reviews of hospitalized injuries for all of January 1994 were conducted at those facilities. The Northridge earthquake resulted in 138 injuries severe enough to require hospitalization. On the day of the earthquake, such injuries were 74% more frequent than usual overall. Some hospitals experienced as many as five times the number of injury admissions seen in the days preceding the event. The increase in caseload was short-lived, however; injury admissions tended to return to normal levels within two days after the quake. Previous reported estimates of the overall number of severe injuries caused by the Northridge earthquake appear to be exaggerated. PMID:10919519

McArthur, D L; Peek-Asa, C; Kraus, J F

2000-07-01

66

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

67

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

68

Testing Probabilistic Earthquake Forecast Hypotheses: Examples from California  

NASA Astrophysics Data System (ADS)

Several competing earthquake forecast models exist; however, there is no consensus on how to test the performance of these models against each other. The Regional Earthquake Likelihood Model (RELM) framework initiated by the Southern California Earthquake Center (SCEC) is dedicated to developing probabilistic forecast models and test them against each other with respect to future seismicity. We present our proposal for the grid-based likelihood ratio test for Poissonian earthquake forecast models. This test is based on expectations of future seismicity for every space/magnitude cell for the models. These expectations are generated through seismicity observations and/or additional information such as tectonic features or geodesy. Computing the likelihood of the observed seismicity with respect to the expectations per space/magnitude cell results in the likelihood ratio of both tested models. Additional simulations based on the expectations establish the significance of the result. A critical issue is the space and magnitude resolution of the testing grid. As an application, we present a test of two seismicity based forecast models for all of California. Both models assume the future seismicity to be proportional to the past (constant a-value of the frequency-magnitude distribution). The null hypothesis assumes the b-value (slope of the frequency-magnitude distribution) to be the regional average while the test hypothesis is using spatially varying b-values. To explore the behavior of our test, we test both models for all of California for various magnitude ranges and learning/testing periods. When testing the entire magnitude range from the magnitude of completeness up to M=7 on a 5km-spaced grid, we can reject the null hypothesis at a high significance level. Testing only higher magnitudes (M ( [4, 7]), we cannot reject the null hypothesis even though the test hypothesis is still performing better than the null hypothesis.

Schorlemmer, D.; Jackson, D.; Wiemer, S.; Field, N.; Giardini, D.

2003-04-01

69

TEMPORAL VARIATION OF SEISMICITY AND SPECTRUM OF SMALL EARTHQUAKES PRECEDING THE 1952 KERN COUNTY, CALIFORNIA, EARTHQUAKE  

Microsoft Academic Search

The spatio-temporal variation of seismicity in the epicentral area of the 1952 Kern County California, earthquake (Ms -- 7.7, 34°58.6'N; 119°02'W) was examined for the period prior to the main shock. Most of the events that occurred in the epicentral area were relocated by using the main shock as a master event. A large part of the fault plane of

MIZUHO ISHIDA; HIROO KANAMORI

1980-01-01

70

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

71

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

SciTech Connect

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

Sieh, K. (California Inst. of Tech., Pasadena (USA)); Stuiver, M. (Univ. of Washington, Seattle (USA)); Brillinger, D. (Univ. of California, Berkeley (USA))

1989-01-10

72

Variability of Near-Term Probability for the Next Great Earthquake on the Cascadia Subduction Zone  

Microsoft Academic Search

The threat of a great (M 9) earthquake along the Cascadia subduction zone is evidenced by both paleoseismology data and current strain accumulation along the fault. On the basis of recent information on the characteristics of this subduction system, we estimate the conditional probabilities of a great earthquake occurring within the next 50 years and their variabilities. The most important

Stephane Mazzotti; John Adams

2004-01-01

73

Liquefaction during the 1981 and previous earthquakes near Westmorland, California  

SciTech Connect

A 1981 earthquake generated liquefaction and other secondary ground effects at many localities within a 150 km/sup 2/ area north of Westmorland, California. Surface effects of liquefaction, including sand soils, fissures, slumps, lateral spreads, and ground settlement, spotted fields with sand and disrupted fields, roads, and canals with fissures and scarps. We specifically describe 22 localities where effects or damage were pronounced during the 1981 event. Similar effects were noted within or near this area after earthquakes in 1930, 1950, 1957, and 1979. The 1940 El Centro event also severely shook the area and could have produced ground effects that were unobserved or unreported. Secondary ground effects in this region have developed only in areas of late Holocene sedimentation, primarily areas inundated by 1905-1906 flooding from the New and Alamo Rivers and the concurrent rise of the Salton Sea. Sediment that liquefied during the 1930, 1950, 1957 and 1981 earthquakes are similar in mode of deposition and age to those that have been most susceptible to liquefaction in other parts of the world. All except one of the 1981 liquefaction sites were within a horizontal distance of 7 km from a surface projection of the estimated zone of seismic energy release. The one exception was slight rejuvenation of several sand boils that had previously erupted during the 1979 Imperial Valley earthquake. These sand boils were 12 km from the source zone. The distances agree well with similar distances measured in other parts of the world. 14 refs., 16 figs.

Youd, T.L.; Wieczorek, G.F.

1984-01-01

74

Physical model for earthquakes, 2. Application to southern California  

SciTech Connect

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

Rundle, J.B.

1988-06-10

75

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

76

Aftershocks of the Coyote Lake, California, earthquake of August 6, 1979: A detailed study  

Microsoft Academic Search

Aftershock hypocenters and focal mechanism solutions for the Coyote Lake, California, earthquake reveal a geometrically complex fault structure, consisting of multiple slip surfaces. The faulting surface principally consists of two right stepping en echelon, northwest trending, partially overlapping, nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 Parkfield, California, earthquake. The overlap occurs

P. Reasenberg; W. L. Ellsworth

1982-01-01

77

Active Faults in the Los Angeles Metropolitan Region Southern California Earthquake Center Group C  

Microsoft Academic Search

Group C of the Southern California Earthquake Center was charged with an evaluation of earthquake fault sources in the Los Angeles Basin and nearby urbanized areas based on fault geology. The objective was to determine the location of active faults and their slip rates and earthquake recurrence intervals. This includes the location and dip of those faults reaching the surface

James F. Dolan; Eldon M. Gath; Lisa B. Grant; Mark Legg; Scott Lindvall; Karl Mueller; Michael Oskin; Daniel F. Ponti; Charles M. Rubin; Thomas K. Rockwell; Jerome A. Treiman; Chris Walls; Robert S. Yeats

78

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

79

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

Microsoft Academic Search

Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles\\u000a metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic\\u000a Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In\\u000a DSHA, seismic hazard in the event of the

Lalliana Mualchin

2011-01-01

80

Rupture directivity of moderate earthquakes in northern California  

USGS Publications Warehouse

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

Seekins, Linda C.; Boatwright, John

2010-01-01

81

Virtual California earthquake simulations: simple models and their application to an observed sequence of earthquakes  

NASA Astrophysics Data System (ADS)

Numerical simulations are routinely used for weather forecasting. It is clearly desirable to develop simulation models for regional seismicity. One model that has been developed for the purpose is the Virtual California (VC) simulation. In order to better understand the behaviour of seismicity simulations, we apply VC to three relatively simple problems involving a straight strike-slip fault. In problem I, we divide the fault into two segments with different mean earthquake interval times. In problem II, we add a central strong (asperity) segment and in problem III we change this to a weak central segment. In all cases we observe limit cycle behaviour with a wide range of periods. We also show that the historical sequence of 13 great earthquakes along the Nankai Trough, Japan, exhibits a limit-cycle behaviour very similar to our asperity model.

Y?k?lmaz, M. B.; Turcotte, D. L.; Yakovlev, G.; Rundle, J. B.; Kellogg, L. H.

2010-02-01

82

Comprehensive analysis of earthquake source spectra in southern California  

NASA Astrophysics Data System (ADS)

We compute and analyze P wave spectra from earthquakes in southern California between 1989 and 2001 using a method that isolates source-, receiver-, and path-dependent terms. We correct observed source spectra for attenuation using both fixed and spatially varying empirical Green's function methods. Estimated Brune-type stress drops for over 60,000 ML = 1.5 to 3.1 earthquakes range from 0.2 to 20 MPa with no dependence on moment or local b value. Median computed stress drop increases with depth in the upper crust, from about 0.6 MPa at the surface to about 2.2 MPa at 8 km, where it levels off and remains nearly constant in the midcrust down to about 20 km. However, the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop. Spatially coherent variations in median stress drop are observed, with generally low values for the Imperial Valley and Northridge aftershocks and higher values for the eastern Transverse ranges and the north end of the San Jacinto fault. We find no correlation between observed stress drop and distance from the San Andreas and other major faults. Significant along-strike variations in stress drop exist for aftershocks of the 1992 Landers earthquake, which may correlate with differences in main shock slip.

Shearer, Peter M.; Prieto, GermáN. A.; Hauksson, Egill

2006-06-01

83

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

84

Earthquake early warning in California: Evaluating Hardware and Software  

NASA Astrophysics Data System (ADS)

Three earthquake early warning (EEW) algorithms are currently being evaluated within the California Integrated Seismic Network (CISN) with support from the US Geological Survey. The evaluation encompasses two aspects: their operation using data from throughout the state under real time conditions, and assessment of their alerts at a web-accessible testing center. An EEW system rapidly detects the initiation of earthquakes and predicts their ground shaking. Its purpose is to provide warning of potentially damaging ground motion in a target region before the strong shaking arrives. One of the three algorithms implemented at the CISN data centers uses a single station, or 'On-site' approach (Caltech). The other two, 'ElarmS' (UC Berkeley) and 'Virtual Seismologist' (VS, Caltech/ETH), are network-based. Although single station alerts can be delivered more quickly than those from a network-based system, more of them tend to be false warnings. Network-based algorithms for EEW require that data be gathered at a central site for joint processing. The two network-based systems, ElarmS and VS, run 15 s behind real time in order to gather ~90% of station data before processing. The EEW alert testing center was developed by the Southern California Earthquake Center (SCEC). Results from the various algorithms are collected automatically. Automatically generated performance summaries allow the comparison of the EEW alerts with each other and with earthquakes within the region. Performance criteria include promptness of the alert, earthquake location and magnitude. Provisions have also been made to assess false alerts, ground motion predictions and uncertainties. In addition to evaluating the three algorithms in terms for separate and joint reliability, we review the needs of EEW with respect to instrumentation and data latency. Possible warning times will typically range from seconds to tens of seconds, and each second delay means a decrease in the available warning time. Minimal latency is therefore important to warning systems. As testing progresses, we are formulating specifications for geophysical networks that can provide real time data in a robust fashion.

Hellweg, M.; Allen, R.; Boese, M.; Brown, H.; Cua, G.; Given, D.; Hauksson, E.; Heaton, T.; Jordan, T.; Khainovski, O.; Maechling, P.; Neuhauser, D.; Oppenheimer, D.; Solanki, K.; Zeleznik, M.

2008-12-01

85

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

86

Time-dependent earthquake probability calculations for southern Kanto after the 2011 M9.0 Tohoku earthquake  

NASA Astrophysics Data System (ADS)

Seismicity in southern Kanto activated with the 2011 March 11 Tohoku earthquake of magnitude M9.0, but does this cause a significant difference in the probability of more earthquakes at the present or in the To? future answer this question, we examine the effect of a change in the seismicity rate on the probability of earthquakes. Our data set is from the Japan Meteorological Agency earthquake catalogue, downloaded on 2012 May 30. Our approach is based on time-dependent earthquake probabilistic calculations, often used for aftershock hazard assessment, and are based on two statistical laws: the Gutenberg-Richter (GR) frequency-magnitude law and the Omori-Utsu (OU) aftershock-decay law. We first confirm that the seismicity following a quake of M4 or larger is well modelled by the GR law with b ˜ 1. Then, there is good agreement with the OU law with p ˜ 0.5, which indicates that the slow decay was notably significant. Based on these results, we then calculate the most probable estimates of future M6-7-class events for various periods, all with a starting date of 2012 May 30. The estimates are higher than pre-quake levels if we consider a period of 3-yr duration or shorter. However, for statistics-based forecasting such as this, errors that arise from parameter estimation must be considered. Taking into account the contribution of these errors to the probability calculations, we conclude that any increase in the probability of earthquakes is insignificant. Although we try to avoid overstating the change in probability, our observations combined with results from previous studies support the likelihood that afterslip (fault creep) in southern Kanto will slowly relax a stress step caused by the Tohoku earthquake. This afterslip in turn reminds us of the potential for stress redistribution to the surrounding regions. We note the importance of varying hazards not only in time but also in space to improve the probabilistic seismic hazard assessment for southern Kanto.

Nanjo, K. Z.; Sakai, S.; Kato, A.; Tsuruoka, H.; Hirata, N.

2013-05-01

87

Assessment of active faults for maximum credible earthquakes of the southern California-northern Baja region  

SciTech Connect

Compilation of a data base is presented for maximum or maximum credible earthquakes that can be used to compute seismic hazard spectra at the San Onofre Nuclear Generating Stations (SONGS) in southern California. We also present our estimates of fault slip rate and estimated recurrence interval for analysis to determine b-values in the southern California - northern Baja California region. According to a direct relationship between the total fault length and the earthquake magnitude, we estimate the maximum earthquake magnitude, we estimate the maximum earthquake for the Offshore Zone of Deformation (OZD) to be of about 6.8 or 6.9 surface-wave magnitude (M/sub S/). Another empirical relationship relating the fractional fault length and earthquake magnitude for strike-slip faults results in an estimated maximum earthquake of about M/sub S/ = 6.8 for the OZD.

Slemmons, D.B.; O'Malley, P.; Whitney, R.A.; Chung, D.H.; Bernreuter, D.L.

1982-06-03

88

A New Earthquake Focal Mechanism Catalog for Southern California  

NASA Astrophysics Data System (ADS)

We present an earthquake focal mechanism catalog for southern California based on a new method for determining mechanisms from P-wave first-motion polarities. The catalog contains only mechanisms that are stable with respect to possible sources of error, so while there are fewer events than in other catalogs, the mechanisms are more robust. Our technique differs from previous methods in that it accounts for possible errors in the assumed earthquake location and seismic velocity model, as well as in the polarity observations. We find the set of acceptable focal mechanisms for each event, allowing for the expected errors in polarities and computed takeoff angles. Multiple trials are performed with different possible source locations and velocity models, and mechanisms with up to a specified fraction of misfit polarities are included in the set of acceptable mechanisms. Our preferred mechanism is given by the average of the set, and the uncertainty is represented by the distribution of acceptable mechanisms. The solution is considered adequately stable only if the set of acceptable mechanisms is tightly clustered around the preferred mechanism. We have compiled a new focal mechanism catalog for southern California using this technique and obtain well-constrained mechanisms for ~8000 events occurring between 1981 and 2000. The majority are part of aftershock sequences, but there are also many in areas of high background seismicity rate. Some regions feature clusters of closely-spaced events with very similar mechanisms. In other places, the seismicity is more diffuse, but the closer two events are spatially, the more similar their mechanisms tend to be. We will present examples from various regions of southern California.

Hardebeck, J. L.; Shearer, P. M.

2001-12-01

89

Spatial patterns of aftershocks of shallow focus earthquakes in California and implications for deep focus earthquakes  

USGS Publications Warehouse

Previous workers have pioneered statistical techniques to study the spatial distribution of aftershocks with respect to the focal mechanism of the main shock. Application of these techniques to deep focus earthquakes failed to show clustering of aftershocks near the nodal planes of the main shocks. To better understand the behaviour of these statistics, this study applies them to the aftershocks of six large shallow focus earthquakes in California (August 6, 1979, Coyote Lake; May 2, 1983, Coalinga; April 24, 1984, Morgan Hill; August 4, 1985, Kettleman Hills; July 8, 1986, North Palm Springs; and October 1, 1987, Whittier Narrows). The large number of aftershocks accurately located by dense local networks allows us to treat these aftershock sequences individually instead of combining them, as was done for the deep earthquakes. The results for individual sequences show significant clustering about the closest nodal plane and the strike direction for five of the sequences and about the presumed fault plane for all six sequences. This implies that the previously developed method does work properly. The reasons for the lack of clustering about main shock nodal planes for deep focus aftershocks are discussed. -from Author

Michael, A. J.

1989-01-01

90

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

91

Grid-Search for Accelerated Moment Release (AMR) Precursors to California Earthquakes  

NASA Astrophysics Data System (ADS)

Accelerated Moment Release (AMR) has been proposed as a potential medium to long-term predictor of large earthquakes. Previous studies have shown that earthquakes in California with magnitudes greater than 6.8 are preceded by an acceleration of intermediate-sized events. We define a false alarm as a period of accelerated regional seismicity that does not culminate in a large earthquake. For AMR to be useful as a predictive tool, acceleration must precede all large earthquakes and the false alarm rate must be small and known. Bowman et al. [1998] and Ikeda [2004] predicted AMR false alarm rates based on a synthetic earthquake catalogs. This study investigates the false alarm rate by using real earthquake catalogs to search for AMR signals across a broad region of California during a period of minimal earthquake activity. The AMR search is conducted on a grid covering the entire State of California. At each grid node a series of AMR calculations is performed to determine if AMR exists within circular regions over any temporal and spatial window. We construct false alarm rate curves base on the number of observed historical AMR sequences that did not culminate in a large earthquake. This provides a baseline for evaluating the utility of accelerating seismicity as a precursory signal before large earthquakes in California.

Reissman, J.; Bowman, D. D.

2005-12-01

92

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

93

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

94

CISN ShakeAlert: Delivering test warnings for California earthquakes  

NASA Astrophysics Data System (ADS)

The Earthquake Early Warning (EEW) project team within the California Integrated Seismic Network (CISN) has been developing a test earthquake alerting system for the past five years. The project is a collaboration between Caltech, UC Berkeley, ETH Zurich, USC/SCEC and the USGS, and is funded by the USGS. We use data from the recently upgraded academic- and government-operated geophysical networks across the state to rapidly detect earthquakes and assess the hazard. The test system is operational statewide and delivers warnings to project scientists and other interested scientists. Three event detection and hazard assessment algorithms are currently used: Virtual Seismologist, Onsite and ElarmS, but others may be added to the system. The algorithms provide hazard assessments to a DecisionModule that aggregates the information. It then generates a unified alert stream that is broadcast to certified users. The alerts are received via the UserDisplay, a pop-up computer application. When it opens, the UserDisplay shows a map with the event location and magnitude, and tracks the propagation of the P- and S-waves. It also shows a countdown to shaking at the user's location and an estimate of the expected peak shaking intensity. The algorithm and DecisionModule outputs are archived by the project testing center for independent performance evaluation. Over the coming year the project intends to release alerts to a small group of test users. Identification and engagement of possible project partners is already well underway. Individual project components presentations will provide additional detail.

Allen, R. M.; Boese, M.; Brown, H.; Caprio, M.; Cua, G. B.; Fischer, M.; Given, D. D.; Hauksson, E.; Heaton, T. H.; Hellweg, M.; Henson, I.; Liukis, M.; Maechling, P. J.; Meier, M. A.; Neuhauser, D. S.; Oppenheimer, D. H.; Solanki, K.

2011-12-01

95

Heightened odds of large earthquakes near Istanbul: An interaction-based probability calculation  

USGS Publications Warehouse

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

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

2000-01-01

96

Loma Prieta, California, Earthquake of October 17, 1989. Forecasts.  

National Technical Information Service (NTIS)

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 consiste...

R. A. Harris

1998-01-01

97

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

98

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

99

Times of increased probability of large earthquakes ( Ms ? 7.5) along the Mexican subduction zone  

NASA Astrophysics Data System (ADS)

Using the method of pattern recognition of infrequent events, we explore the possibility of identifying the times of increased probability (TIP) of occurrence of large earthquakes ( Ms ? 7.5) along the Mexican subduction zone. A TIP refers to a 5 year period within which a strong earthquake has a high probability of occurrence. We analyzed the seismicity for the regions of Chiapas-Eastern Oaxaca (91-97°W, Region 1), Western Oaxaca-Guerrero (97-102°W, Region 2), and Michoacan-Colima-Jalisco (102-106°W, Region 3) for the time interval 1970-1991 with the National Oceanic and Atmospheric Administration seismic catalog as the source data. The premonitory intermediate-term seismic activation to identify a TIP was measured using the algorithm M8. Three out of the five earthquakes of Ms ? 7.5 that occurred during the studied period are diagnosed by algorithm M8, and for the Region 3 segment a TIP is identified that will end between 1994 and 1996. We consider the area between the Western Colima gap and the Jalisco region (103.7-106.0°W) as the zone where the forecast earthquake has a higher than usual probability of occurrence. Our results by no means constitute a definitive earthquake prediction but suggest the need for detailed seismic analysis and the study of other geophysical precursors along the Colima-Jalisco segment.

Novelo-Casanova, David A.; Alvarez-Moctezuma, Jose

1995-01-01

100

CISN ShakeAlert - Towards a Prototype Earthquake Early Warning System for California  

Microsoft Academic Search

Over the past three years the California Integrated Seismic Network (CISN) has tested the real-time performance of three algorithms for providing earthquake early warnings in California: the single-sensor based tauc-Pd on-site and the network-based (2) ElarmS, and the (3) Virtual Seismologist (VS) algorithms. The algorithms have successfully detected many earthquakes and in some cases predicted the peak ground shaking a

M. Böse; R. M. Allen; H. Brown; G. B. Cua; D. Given; M. Fischer; E. Hauksson; T. H. Heaton; M. Hellweg; T. H. Jordan; O. Khainovski; P. J. Maechling; D. S. Neuhauser; D. H. Oppenheimer; K. Solanki

2009-01-01

101

Statistical analysis of an earthquake-induced landslide distribution — the 1989 Loma Prieta, California event  

Microsoft Academic Search

The 1989 Loma Prieta, California earthquake (moment magnitude, M=6.9) generated landslides throughout an area of about 15,000km2 in central California. Most of these landslides occurred in an area of about 2000km2 in the mountainous terrain around the epicenter, where they were mapped during field investigations immediately following the earthquake. The distribution of these landslides is investigated statistically, using regression and

David K Keefer

2000-01-01

102

Streamflow increase due to rupturing of hydrothermal reservoirs: Evidence from the 2003 San Simeon, California, Earthquake  

Microsoft Academic Search

Following the Mw = 6.5 San Simeon, California, earthquake on December 22, 2003, USGS stream gauges documented two consecutive increases in streamflow in the Salinas River and Lopez Creek in the central Coast Ranges. The first increase occurred within 15 minutes after the earthquake and lasted about an hour; the second one occurred a few hours later and lasted much

Chi-Yuen Wang; Michael Manga; Douglas Dreger; Alexander Wong

2004-01-01

103

Tsunami inundation at Crescent City, California generated by earthquakes along the Cascadia Subduction Zone  

Microsoft Academic Search

We model tsunami inundation and runup heights in Crescent City, California triggered by possible earthquakes on the Cascadia Subduction Zone (CSZ). The CSZ is believed capable of producing great earthquakes with magnitudes of M w ~ 9.0 or greater. We simulate plausible CSZ rupture scenarios and calculate inundation using MOST. We benchmark our CSZ inundation projections against mapped flooded areas

Burak Uslu; José C. Borrero; Lori A. Dengler; Costas E. Synolakis

2007-01-01

104

Tsunami inundation at Crescent City, California generated by earthquakes along the Cascadia Subduction Zone  

Microsoft Academic Search

We model tsunami inundation and runup heights in Crescent City, California triggered by possible earthquakes on the Cascadia Subduction Zone (CSZ). The CSZ is believed capable of producing great earthquakes with magnitudes of Mw ? 9.0 or greater. We simulate plausible CSZ rupture scenarios and calculate inundation using MOST. We benchmark our CSZ inundation projections against mapped flooded areas and

Burak Uslu; José C. Borrero; Lori A. Dengler; Costas E. Synolakis

2007-01-01

105

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.

106

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

Microsoft Academic Search

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

Evelyn A. Roelofts

1998-01-01

107

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

NASA Astrophysics Data System (ADS)

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

Parsons, Tom

2008-03-01

108

Earthquake prediction comes of age  

SciTech Connect

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

Lindth, A. (Geological Survey, Menlo Park, CA (USA). Office of Earthquakes, Volcanoes, and Engineering)

1990-02-01

109

Politics and Economics of Earthquake Hazard Mitigation. Unreinforced Masonry Buildings in Southern California. Program on Environment and Behavior.  

National Technical Information Service (NTIS)

Table of Contents: Earthquakes and Unreinforced Masonry Buildings: Introduction; Risks, Mitigation Techniques, and Costs; The Development, Enactment, and Implementation of Earthquake Hazard Mitigation Policies; Long Beach, California; Los Angeles, Califor...

D. J. Alesch W. J. Peak

1986-01-01

110

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

Microsoft Academic Search

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 deter- mine if ground motions at offshore sites are significantly different than those at onshore sites; if so, caution

David M. Boore; Charles E. Smith

1999-01-01

111

Times of increased probability of large earthquakes ( M s ? 7.5) along the Mexican subduction zone  

Microsoft Academic Search

Using the method of pattern recognition of infrequent events, we explore the possibility of identifying the times of increased probability (TIP) of occurrence of large earthquakes (Ms ? 7.5) along the Mexican subduction zone. A TIP refers to a 5 year period within which a strong earthquake has a high probability of occurrence. We analyzed the seismicity for the regions

David A. Novelo-Casanova; Jose Alvarez-Moctezuma

1995-01-01

112

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

113

Contrasts between source parameters of M [>=] 5. 5 earthquakes in northern Baja California and southern California  

SciTech Connect

Source parameters determined from the body waveform modeling of large (M [>=] 5.5) historic earthquakes occurring between 1915 and 1956 along the San Jacinto and Imperial fault zones of southern California and the Cerro Prieto, Tres Hermanas and San Miguel fault zones of Baja California have been combined with information from post-1960's events to study regional variations in source parameters. The results suggest that large earthquakes along the relatively young San Miguel and Tres Hermanas fault zones have complex rupture histories, small source dimensions (< 25 km), high stress drops (60 bar average), and a high incidence of foreshock activity. This may be a reflection of the rough, highly segmented nature of the young faults. In contrast, Imperial-Cerro Prieto events of similar magnitude have low stress drops (16 bar average) and longer rupture lengths (42 km average), reflecting rupture along older, smoother fault planes. Events along the San Jacinto fault zone appear to lie in between these two groups. These results suggest a relationship between the structural and seismological properties of strike-slip faults that should be considered during seismic risk studies.

Doser, D.I. (Univ. of Texas, El Paso, TX (United States). Dept. of Geological Sciences)

1993-04-01

114

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

Microsoft Academic Search

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

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

2003-01-01

115

GIS Mapping of Earthquake-Related Deaths and Hospital Admissions from the 1994 Northridge, California, Earthquake  

Microsoft Academic Search

PURPOSE: Earthquakes pose a persistent but unpredictable health threat. Although knowledge of geologic earthquake hazards for buildings has increased, spatial relations between injuries and seismic activity have not been explained.METHODS: Fatal and hospital-admitted earthquake injuries due to the 1994 Northridge Earthquake were identified. Geographical Information Systems software was used to map all injury locations. Injuries were analyzed with regard to

Corinne Peek-Asa; Marizen R Ramirez; Kim Shoaf; Hope Seligson; Jess F Kraus

2000-01-01

116

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

USGS Publications Warehouse

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

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

2005-01-01

117

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

118

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

119

Crustal Structure Near Coalinga, California Revisited: Implications for the Hypocentral Region of the 1983 ML 6.7 Earthquake  

NASA Astrophysics Data System (ADS)

On May 2, 1983, a ML 6.7 earthquake occurred about 12 km northeast of the town of Coalinga, California on a previously unknown fault zone that underlies the boundary between the Coast Ranges and the Great Valley. Aftershock and focal mechanism studies have shown that the earthquake probably occurred on a southwest-dipping thrust fault at ca. 10 km depth. A number of geophysical studies including acquisition and interpretation of seismic reflection and refraction data were conducted by the U. S. Geological Survey shortly after the earthquake in order to illuminate the hypocentral zone. These studies showed that the earthquake likely occurred within a wedge of Franciscan material that lies beneath folded sedimentary rocks of the Great Valley. We have revisited the U.S. Geological Survey data set along with COCORP reflection data and refraction data from the 1994 Southern Sierra Continental Dynamics experiment. First arrivals from the refraction data were used to develop a 3D velocity model for the region. This velocity model was then used to depth-convert the seismic reflection data . The results of this analysis suggest that Great Valley group sedimentary rocks occur to depths of 10 km in the vicinity of the Coalinga earthquake hypocenter. Previous analysis has put the base of Great Valley sedimentary rocks at 5 to 6 km depth. Our result implies that the Coalinga earthquake occurred at the interface between Great Valley and Franciscan rocks, rather than within a wedge of Franciscan material. This interface may represent a natural rheological boundary which focused slip during the earthquake.

Popovich, D. A.; Miller, K. C.

2002-12-01

120

Quantifying the remote triggering capabilities of large earthquakes using data from the ANZA Seismic Network catalog (southern California)  

Microsoft Academic Search

Various studies have examined remote earthquake triggering in geothermal areas, but few studies have investigated triggering in nongeothermal areas. We search the ANZA (southern California) network catalog for evidence of remote triggering. Using three statistical tests (binomial, Kolmogorov-Smirnov, and Wilcoxon rank sum), we determine the significance of the rates and timing of earthquakes in southern California following large teleseismic events.

Deborah L. Kane; Debi Kilb; Arthur S. Berg; Vladislav G. Martynov

2007-01-01

121

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

USGS Publications Warehouse

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

Working Group on Northern California Earthquake Potential

1996-01-01

122

Prediction of central California earthquakes from soil-gas helium fluctuations  

Microsoft Academic Search

The observations of short-term decreases in helium soil-gas concentrations along the San Andreas Fault in central California have been correlated with subsequent earthquake activity. The area of study is elliptical in shape with radii approximately 160×80 km, centered near San Benito, and with the major axis parallel to the Fault. For 83 percent of theM>4 earthquakes in this area a

G. M. Reimer

1984-01-01

123

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

Microsoft Academic Search

Two large strike-slip ruptures 11.4 hours apart occurred on intersecting, nearly orthogonal, vertical faults during the November 1987 Superstition Hills earthquake sequence in southern California. This sequence is the latest in a northwestward progression of earthquakes (1979, 1981, and 1987) rupturing a set of parallel left-lateral cross-faults that trend northeast between the Brawley seismic zone and Superstition Hills fault, a

K. W. Hudnut; L. Seeber; J. Pacheco

1989-01-01

124

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

125

Permeability changes associated with large earthquakes: An example from Loma Prieta, California  

SciTech Connect

The Loma Prieta (California) earthquake (October 17, 1989; M 7.1) caused significant changes in the hydrology of the San Lorenzo and Pescadero drainage basins, northwest of the epicenter. Streamflow increased at most gauging stations within 15 min after the earthquake. Ionic concentrations and the calcite saturation index of the stream water also increased. Streamflow and solute concentrations decayed significantly over a period of several months following the earthquake. Ground-water levels in the highland parts of the basins were locally lowered by as much as 21 m within weeks to months after the earthquake. The spatial and temporal character of the hydrologic response suggests that the earthquake increased rock permeability and temporarily enhanced ground-water flow rates in the region.

Rojstaczer, S. (Duke Univ., Durham, NC (United States)); Wolf, S. (Geological Survey, Menlo Park, CA (United States))

1992-03-01

126

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

127

Strong ground motion and source mechanism studies for earthquakes in the northern Baja California/southern California region  

SciTech Connect

Earthquake data sets collected from arrays of digital seismic event recorders and strong motion instruments operated in the northern Baja California/southern California region are analyzed. Complementing these near-source data sets with data from more distant seismic stations it was possible to begin to separate and understand the effects of stress drop, source size, sediment amplification, and physical attenuation on the variation of ground motion with distance. Surprisingly large ground accelerations, over 0.5g, were recorded for some relatively small (M/sub L/ < 5) earthquakes in the Victoria, Baja California earthquake swarm of March 1978. It was concluded that this is a result of relatively high stress drops (approx. 1 kilobar) and a relatively high sediment amplification factor of about 3.4. The ground motion from these earthquakes was relatively high frequency, which was somewhat surprising since the well-established depth of the events is about 10-12 km and the energy thus passed through the 5 km thick column of sediments of the Imperial and Mexicali Valleys, which might have been expected to produce severe attenuation. The primary factors which influence the results of studies with distant station data are geologic complexities, especially the boundary region between the Imperial Valley and the granitic batholith of the Peninsular Ranges.

Munguia-Orozco, L.

1983-01-01

128

Analysis of similar event clusters in aftershocks of the 1994 Northridge, California, earthquake  

Microsoft Academic Search

We perform waveform cross-correlation on over 14,000 aftershocks of the 1994 Northridge MW 6.7 earthquake in southern California as recorded by short-period stations of the Southern California Seismic Network (SCSN). Approximately 10–30% of the events belong to similar event clusters, depending upon the similarity criteria that are applied. We relocate events within 218 of these clusters to a relative location

Peter M. Shearer; Jeanne L. Hardebeck; Luciana Astiz; Keith B. Richards-Dinger

2003-01-01

129

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

Microsoft Academic Search

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

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

2009-01-01

130

Injuries as a result of California earthquakes in the past decade.  

PubMed

The devastating effects of earthquakes have been demonstrated repeatedly in the past decade, through moderate and major earthquakes such as the October 1987 Whittier Narrows earthquake (5.9 on the Richter scale), the October 1989 Loma Prieta earthquake (7.1) and the January 1994 Northridge earthquake (6.7). While 'official' tallies of injuries and deaths are reported for each event, the numbers vary from report to report. For Northridge, the number of injuries vary between 8,000 and 12,000; the number of deaths from 33 to 73 (Peek-Asa et al., 1997; Durkin, 1996). While official estimates are commonly reported following disasters, the study of actual numbers, types and causes of casualties has not developed. In this paper, we identify the numbers and risk factors for injuries within community-based samples across three earthquakes in urban California. We first report the numbers and types of injuries in each earthquake and then identify risk factors specifically associated with the Northridge earthquake. PMID:9753812

Shoaf, K I; Sareen, H R; Nguyen, L H; Bourque, L B

1998-09-01

131

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

132

Peak velocities and peak surface strains during Northridge, California, earthquake of 17 January 1994  

Microsoft Academic Search

We present contours of the largest horizontal and vertical recorded peak velocities of strong ground motion during the Northridge, California, earthquake. Above the fault, the horizontal peak velocities exceeded 100 cm\\/s. The vertical velocities were larger than 20 cm\\/s. We also present contours of peak horizontal and vertical strain factors. Through most of the San Fernando Valley and the Santa

M. D. Trifunac; M. I. Todorovska; S. S. Ivanovi?

1996-01-01

133

Coastal uplift associated with the 1992 Cape Mendocino earthquake, northern California  

Microsoft Academic Search

The April 25,1992, Cape Mendocino earthquake (Ms 7.1) uplifted ˜24 km of the northern California coast at the southern end of the Cascadia subduction zone, uplift which resulted in coastal emergence that caused extensive mortality of intertidal organisms between Cape Men docino and Punta Gorda. We estimated the amount of uplift by measuring the vertical extent of mortality of 14

G. A. Carver; A. S. Jayko; D. W. Valentine; W. H. Li

1994-01-01

134

Oceanside and Thirtymile Bank blind thrusts: Implications for earthquake hazards in coastal southern California  

Microsoft Academic Search

We define an active blind thrust system in offshore southern California that extends from Los Angeles south to the United States Mexico international border. These blind thrusts formed by tectonic inversion of Miocene extensional detachments. We attribute the 1986 Oceanside (ML 5.3) earthquake, local uplift of marine terraces, seafloor fold scarps, and observed geodetic convergence to motion on these faults.

Carlos Rivero; John H. Shaw; Karl Mueller

2000-01-01

135

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

136

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

137

Source parameters of the 1980 Mammoth Lakes, California earthquake sequence  

Microsoft Academic Search

From the more than 1500 Mammoth Lakes earthquakes recorded on three-component digital seismographs (Spudich et al., 1981), 150 were used in an analysis of the locations, mechanism, and source parameters. A composite fault plane solution of nine earthquakes 3.9?M?5.1 defines a right-lateral strike slip mechanism on a steeply dipping nearly east-west plane striking S75°E or left-lateral strike slip on a

Ralph J. Archuleta; Edward Cranswick; Charles Muller; Paul Spudich

1982-01-01

138

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.

139

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

USGS Publications Warehouse

The December 22, 2003, San Simeon, California, (M6.5) earthquake caused damage to houses, road surfaces, and underground utilities in Oceano, California. The community of Oceano is approximately 50 miles (80 km) from the earthquake epicenter. Damage at this distance from a M6.5 earthquake is unusual. To understand the causes of this damage, the U.S. Geological Survey conducted extensive subsurface exploration and monitoring of aftershocks in the months after the earthquake. The investigation included 37 seismic cone penetration tests, 5 soil borings, and aftershock monitoring from January 28 to March 7, 2004. The USGS investigation identified two earthquake hazards in Oceano that explain the San Simeon earthquake damage?site amplification and liquefaction. Site amplification is a phenomenon observed in many earthquakes where the strength of the shaking increases abnormally in areas where the seismic-wave velocity of shallow geologic layers is low. As a result, earthquake shaking is felt more strongly than in surrounding areas without similar geologic conditions. Site amplification in Oceano is indicated by the physical properties of the geologic layers beneath Oceano and was confirmed by monitoring aftershocks. Liquefaction, which is also commonly observed during earthquakes, is a phenomenon where saturated sands lose their strength during an earthquake and become fluid-like and mobile. As a result, the ground may undergo large permanent displacements that can damage underground utilities and well-built surface structures. The type of displacement of major concern associated with liquefaction is lateral spreading because it involves displacement of large blocks of ground down gentle slopes or towards stream channels. The USGS investigation indicates that the shallow geologic units beneath Oceano are very susceptible to liquefaction. They include young sand dunes and clean sandy artificial fill that was used to bury and convert marshes into developable lots. Most of the 2003 damage was caused by lateral spreading in two separate areas, one near Norswing Drive and the other near Juanita Avenue. The areas coincided with areas with the highest liquefaction potential found in Oceano. Areas with site amplification conditions similar to those in Oceano are particularly vulnerable to earthquakes. Site amplification may cause shaking from distant earthquakes, which normally would not cause damage, to increase locally to damaging levels. The vulnerability in Oceano is compounded by the widespread distribution of highly liquefiable soils that will reliquefy when ground shaking is amplified as it was during the San Simeon earthquake. The experience in Oceano can be expected to repeat because the region has many active faults capable of generating large earthquakes. In addition, liquefaction and lateral spreading will be more extensive for moderate-size earthquakes that are closer to Oceano than was the 2003 San Simeon earthquake. Site amplification and liquefaction can be mitigated. Shaking is typically mitigated in California by adopting and enforcing up-to-date building codes. Although not a guarantee of safety, application of these codes ensures that the best practice is used in construction. Building codes, however, do not always require the upgrading of older structures to new code requirements. Consequently, many older structures may not be as resistant to earthquake shaking as new ones. For older structures, retrofitting is required to bring them up to code. Seismic provisions in codes also generally do not apply to nonstructural elements such as drywall, heating systems, and shelving. Frequently, nonstructural damage dominates the earthquake loss. Mitigation of potential liquefaction in Oceano presently is voluntary for existing buildings, but required by San Luis Obispo County for new construction. Multiple mitigation procedures are available to individual property owners. These procedures typically involve either

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

2004-01-01

140

Numerical Simulations for Earthquake Physics (Virtual California): Recent Results and Current Plans  

NASA Astrophysics Data System (ADS)

Attention has recently been focused on the need for numerical simulations of interacting earthquake fault systems [1]. "Virtual California" is a topologically realistic model which has been used to simulate earthquakes on the San Andreas fault and its associated fault system. The Virtual California model includes elastic interactions among the faults in the model, driving at the correct plate tectonic rates, and frictional physics on the faults using the physics obtained from laboratory models with parameters consistent with the occurrence of historic earthquakes. An important consequence of the elastic interactions in the model is the appearance of correlations and space-time patterns of occurrence of events. Without the interactions, each fault element would behave independently; with the interactions, cooperative phenomena and patterns are observed. Previous numerical analysis of this simulation has focused on the distribution of recurrence times between large events. From this it is possible to compute the waiting times until the next great earthquake for California faults. Here we report on a variety of recent results. 1) We are investigating the stability of the numerical solutions and how these depend on the Greens function computations and other assumptions in the displacement discontinuity method; 2) We have developed a new method for generating and scoring a synthetic earthquake catalog utilizing Virtual California. The idea is to use paleoseismic data to identify intervals within the artificial data which most closely resemble the current seismic state of California; 3) We are working with collaborators to understand the interplay between fault system complexity and predictability. In this talk we summarize and discuss these issues, and indicate directions for the future.

Morein, G.; Aalsburg, J. V.; Rundle, P.; Donnellan, A.; Grant, L.; Rundle, J.; Turcotte, D.

2007-12-01

141

Prediction of central California earthquakes from soil-gas helium fluctuations  

NASA Astrophysics Data System (ADS)

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

Reimer, G. M.

1984-03-01

142

Distribution of intensity for the Westmorland, California, earthquake of April 26, 1981  

USGS Publications Warehouse

The maximum Modified Mercalli intensity of the April 26, 1981 earthquake located 5 km northwest of Westmorland, California is VII. Twelve buildings in Westmorland were severely damaged with an additional 30 sustaining minor damage. Two brick parapets fell in Calipatria, 14 km northeast of Westmorland and 10 km from the earthquake epicenter. Significant damage in rural areas was restricted to unreinforced, concrete-lined irrigation canals. Liquefaction effects and ground slumping were widespread in rural areas and were the primary causes of road cracking. Preliminary local government estimates of property loss range from one to three million dollars (Imperial Valley Press, 1981). The earthquake was felt over an area of approximately 160,000 km2; about the same felt area of the October 15, 1979 (Reagor and others, 1980), and May 18, 1940 (Ulrich, 1941) Imperial Valley earthquakes.

Barnhard, L. M.; Thenhaus, P. C.; Algermissen, Sylvester Theodore

1982-01-01

143

Prediction of central California earthquakes from soil-gas helium fluctuations  

USGS Publications Warehouse

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

Reimer, G. M.

1985-01-01

144

Precariously balanced rocks in Nevada and California: Implications for earthquake hazard in Nevada, particularly at Yucca Mtn  

SciTech Connect

In several localized areas of Nevada and California there are large numbers of precariously balanced rocks--rocks which could be knocked down by earthquake ground motion with peak accelerations of about 0.2 g or less. Brune and Whitney suggested that at Yucca Mountain, NV, these rocks could be used as paleoindicators of peak ground acceleration. In this study the locations of regions of precariously rocks are compared with probability maps for strong ground motion and intensity maps for known large earthquakes. Large numbers of precarious rocks have been found in the region around Yucca Mtn., site of the proposed high level nuclear waste repository. They have also been found near Lida, NV, 20 km southeast of the spectacular Holocene scarps in Fish Lake Valley; in the West Walter River Canyon 15 km south of Yerington, NV; 25 km north of the ground rupture in the 1932 M=7.4 Cedar Mtn. earthquake; the center of the Peninsular Ranges in southernmost CA; and in the center of the Sierra Nevada batholith. In CA these observations correlate well with published ground acceleration maps, but in NV there are significant discrepancies. The implication of these results for seismic hazard in NV and particularly at Yucca Mtn. are discussed. The observations suggest that for the last few thousand years peak ground accelerations at Yucca Mtn.have been limited to values considerably lower than those which have occurred recently in the neighborhood of the several historic earthquakes in northern NV. The ground accelerations necessary to topple particular precarious rocks can be estimated fairly accurately with stability calculations, numerical and physical modeling, force tests in the field, and artificially induced ground accelerations. Studies in areas of recent high ground acceleration, e.g. in the neighborhood of recent earthquakes and NTS explosions, further calibrate the method.

Brune, J.N. (Univ. of Nevada, Reno, NV (United States). Seismological Lab.)

1993-04-01

145

California Real Time Network: Test bed for earthquake early warning systems  

NASA Astrophysics Data System (ADS)

More than 80 CGPS stations in southern California have been upgraded to a 1 Hz sample rate, including stations from the SCIGN and PBO networks. The upgraded stations comprise the California Real Time Network and provide continuous 1 Hz (upgradable to 10-20 Hz at some stations) GPS displacement waveforms and troposphere delay estimates with a latency of less than 1 s. With funding from NASA, CRTN provides a test bed for developing advanced in situ-based observation systems within a modern data portal environment, which can be extended seamlessly to the entire PBO region and to other plate boundaries. We describe a prototype early warning system for earthquakes using CRTN, which is also being deployed at other plate boundaries. We demonstrate the elements of an earthquake early warning system by analyzing the 2003 Mw 8.3 Tokachi-Oki thrust earthquake off Hokkaido Island detected by the dense Japan national real-time CGPS network. The network has an approximately 20-km spacing with 1156 stations streaming 1 Hz data to a central facility. A Delaunay triangulation of the network is created every second and the 1 Hz displacements within triangular element are converted to principal components of strain to detect the event. The large spatial extent allows us to compute displacement waveforms relative to a station well away from the affected region through a real-time network adjustment algorithm. We then compute the earthquake hypocenter through a grid search and L2-norm minimization. The final earthquake source model is computed using the total displacement waveforms, the earthquake hypocenter and the predetermined fault structure in the inversion program Defnode. We finish by showing the method in action for the November, 2008 ShakeOut earthquake scenario using CRTN. We show that more accurate earthquake source parameters can be obtained by utilizing higher rate GPS up to 10-20 Hz.

Crowell, B. W.; Bock, Y.; Squibb, M.

2009-05-01

146

The Southern California Earthquake Data Center (SCEDC): Update for 2004  

Microsoft Academic Search

In 2004, the first deployment of the USArray transportable array (Big Foot) begins in Southern California. 40 stations of the Southern California Seismic Network (SCSN) will be used as the initial start. The 40 stations will be recorded by USArray as part of their archive, and they will also continue to contribute to the data archive at SCEDC to be

V. L. Appel; R. W. Clayton

2004-01-01

147

Earthquake potential along the northern hayward fault, california  

PubMed

The Hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace. Dislocation models of the surface deformation adjacent to the Hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at approximately 7 millimeters per year to the bottom of the seismogenic zone along a approximately 20-kilometer-long northern fault segment. Microearthquakes with the same waveform repeatedly occur at 4- to 10-kilometer depths and indicate deep creep at 5 to 7 millimeters per year. The difference between current creep rates and the long-term slip rate of approximately 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern Hayward fault adjacent to the locked 1868 earthquake rupture, which broke the southern 40 to 50 kilometers of the fault. The potential for a major independent earthquake of the northern Hayward fault might be less than previously thought. PMID:10947982

Burgmann; Schmidt; Nadeau; d'Alessio; Fielding; Manaker; McEvilly; Murray

2000-08-18

148

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

NASA Astrophysics Data System (ADS)

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 operational, and 165 entries are in the pipeline. When complete, information and resources for over 500 Earth science and engineering topics will be included, with connections to curricular materials useful for teaching Earth Science, engineering, physics and mathematics. To coordinate activities for the 10-year anniversary of the Northridge Earthquake in 2004 (and beyond), the "Earthquake Country Alliance" is being organized by SCEC CEO to present common messages, to share or promote existing resources, and to develop new activities and products jointly (such as a new version of Putting Down Roots in Earthquake Country). The group includes earthquake science and engineering researchers and practicing professionals, preparedness experts, response and recovery officials, news media representatives, and education specialists. A web portal, http://www.earthquakecountry.info, is being developed established with links to web pages and descriptions of other resources and services that the Alliance members provide. Another ongoing strength of SCEC is the Summer Intern program, which now has a year-round counterpart with students working on IT projects at USC. Since Fall 2002, over 32 students have participated in the program, including 7 students working with scientists throughout SCEC, 17 students involved in the USC "Earthquake Information Technology" intern program, and 7 students involved in CEO projects. These and other activities of the SCEC CEO program will be presented, along with lessons learned during program design and implementation.

Benthien, M. L.

2003-12-01

149

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

150

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

151

Earthquake Prediction and Forecasting  

NASA Astrophysics Data System (ADS)

Prospects for earthquake prediction and forecasting, and even their definitions, are actively debated. Here, "forecasting" means estimating the future earthquake rate as a function of location, time, and magnitude. Forecasting becomes "prediction" when we identify special conditions that make the immediate probability much higher than usual and high enough to justify exceptional action. Proposed precursors run from aeronomy to zoology, but no identified phenomenon consistently precedes earthquakes. The reported prediction of the 1975 Haicheng, China earthquake is often proclaimed as the most successful, but the success is questionable. An earthquake predicted to occur near Parkfield, California in 1988±5 years has not happened. Why is prediction so hard? Earthquakes start in a tiny volume deep within an opaque medium; we do not know their boundary conditions, initial conditions, or material properties well; and earthquake precursors, if any, hide amongst unrelated anomalies. Earthquakes cluster in space and time, and following a quake earthquake probability spikes. Aftershocks illustrate this clustering, and later earthquakes may even surpass earlier ones in size. However, the main shock in a cluster usually comes first and causes the most damage. Specific models help reveal the physics and allow intelligent disaster response. Modeling stresses from past earthquakes may improve forecasts, but this approach has not yet been validated prospectively. Reliable prediction of individual quakes is not realistic in the foreseeable future, but probabilistic forecasting provides valuable information for reducing risk. Recent studies are also leading to exciting discoveries about earthquakes.

Jackson, David D.

152

Identification and Reduction of Nonstructural Earthquake Hazards in California Schools.  

ERIC Educational Resources Information Center

|It is necessary to identify nonstructural hazards at the school site to reduce the possibly of injury in the event of an earthquake. Nonstructural hazards can occur in every part of a building and all of its contents with the exception of structure. In other words, nonstructural elements are everything but the columns, beams, floors, load-bearing…

Greene, Marjorie; And Others

153

Guide and Checklist for Nonstructural Earthquake Hazards in California Schools.  

ERIC Educational Resources Information Center

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

2003

154

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

155

Felt reports and intensity assignments for 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 strikeslip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the M 7.8 San Francisco earthquake, on 18 April 1906. This open-file report is a compilation of first-hand accounts (felt reports) describing aftershocks and triggered events of the 1906 earthquake, for the first twenty months of the aftershock sequence (through December 1907). The report includes a chronological catalog. For the larger events, Modified Mercalli intensities (MMIs) have been assigned based on the descriptions judged to be the most reliable.

Meltzner, Aron J.; Wald, David J.

2002-01-01

156

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

USGS Publications Warehouse

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

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

2013-01-01

157

Earthquakes.  

ERIC Educational Resources Information Center

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

Pakiser, Louis C.

158

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

159

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

NASA Astrophysics Data System (ADS)

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

Perry, S.; Jordan, T.

2006-12-01

160

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

161

Earthquakes  

MedlinePLUS

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

162

Earthquakes  

MedlinePLUS

... time. Before During After More Information Before an Earthquake The following are things you can do to ... most of the destruction during earthquakes. During an Earthquake Drop, cover and Hold On. Minimize your movements ...

163

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

USGS Publications Warehouse

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

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

1978-01-01

164

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

165

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

Microsoft Academic Search

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 39° 59°S, and trend about N84°E on the

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

1983-01-01

166

Damage distribution during the 1994 Northridge, California, earthquake relative to generalized categories of surficial geology  

Microsoft Academic Search

The spatial distributions of severely damaged buildings (red-tagged) and of breaks in the water distribution system following the 1994 Northridge, California, earthquake (ML = 6·4) are investigated relative to the local characteristics of surficial geology. The pipe breaks are used as an indicator of nonlinear soil response, and the red-tagged buildings as indicator of severe shaking. The surficial geology is

M. D. Trifunac; M. I. Todorovska

1998-01-01

167

Coseismic crustal deformations of 1994 Northridge, California, earthquake detected by interferometric JERS 1 synthetic aperture radar  

Microsoft Academic Search

Coseismic deformations of the January 17, 1994, Northridge, California earthquake are mapped using interferometric combination of synthetic aperture radar images acquired by the Japanese Earth Resource Satellite (JERS 1) on April 30, 1993, and June 14, 1994. We make an interferogram in a rectangular area with a size of 18.6 km (N-S) by 29.9 km (E-W). Although coherence is not

Makoto Murakami; Mikio Tobita; Satoshi Fujiwara; Takashi Saito; Hiroshi Masaharu

1996-01-01

168

Coseismic stress parameter of three California Earthquakes derived from the stochastic finite fault technique  

Microsoft Academic Search

Stochastic finite fault modeling is used to derive the coseismic stress parameter distribution on the fault surface of three\\u000a well-recorded California earthquakes: M7.0, 1989, Loma Prieta; M7.3, 1992, Landers; and M6.7, 1994, Northridge. Classical waveform inversion techniques are inherently more powerful than stochastic modeling as a\\u000a means of deriving detailed source parameters. However, the application of stochastic methods to the

Karen Assatourians; Gail M. Atkinson

2010-01-01

169

Earthquake early warning across California: Performance of ElarmS on the existing seismic networks  

NASA Astrophysics Data System (ADS)

The ElarmS methodology is designed to provide seconds of warning prior to damaging ground shaking in earthquakes. The algorithms are currently being tested as part of a state-wide effort to assess the likely accuracy and timeliness of warnings should the system be fully implemented. This is part of a collaborative study by the California Integrated Seismic Network (CISN) and funded by the USGS. The algorithms have been running in an automated but delayed fashion since February 2006 on all earthquakes with magnitude greater than 3.0 in northern California. The processing of this data shows the sensitivity of system performance to the density of stations in the region. In the greater Bay Area where station density is greatest the system performs very well, providing accurate locations, magnitude estimates and ground shaking predictions within 2 or 3 seconds of event detection. To the north of Santa Rosa and south of Hollister the station density is lower but still sufficient for ElarmS. The lower station density means that a few additional seconds are required to obtain good predictions. The station density in the Mendocino Triple Junction region and the Sierras is not sufficient to provide useful information about earthquakes in these regions. The ElarmS development team has been porting the algorithms to the realtime system in northern California. The system is now running in a test mode 15 seconds behind realtime. We will present the performance of the realtime system and comparisons with the automated system at the meeting.

Allen, R. M.; Wurman, G.; Hellweg, P.; Kireev, A.; Neuhauser, D.

2007-12-01

170

The Loma Prieta, California, Earthquake of October 17, 1989: Strong Ground Motion and Ground Failure  

USGS Publications Warehouse

Professional Paper 1551 describes the effects at the land surface caused by the Loma Prieta earthquake. These effects: include the pattern and characteristics of strong ground shaking, liquefaction of both floodplain deposits along the Pajaro and Salinas Rivers in the Monterey Bay region and sandy artificial fills along the margins of San Francisco Bay, landslides in the epicentral region, and increased stream flow. Some significant findings and their impacts were: * Strong shaking that was amplified by a factor of about two by soft soils caused damage at up to 100 kilometers (60 miles) from the epicenter. * Instrumental recordings of the ground shaking have been used to improve how building codes consider site amplification effects from soft soils. * Liquefaction at 134 locations caused $99.2 million of the total earthquake loss of $5.9 billion. Liquefaction of floodplain deposits and sandy artificial fills was similar in nature to that which occurred in the 1906 San Francisco earthquake and indicated that many areas remain susceptible to liquefaction damage in the San Francisco and Monterey Bay regions. * Landslides caused $30 million in earthquake losses, damaging at least 200 residences. Many landslides showed evidence of movement in previous earthquakes. * Recognition of the similarities between liquefaction and landslides in 1906 and 1989 and research in intervening years that established methodologies to map liquefaction and landslide hazards prompted the California legislature to pass in 1990 the Seismic Hazards Mapping Act that required the California Geological Survey to delineate regulatory zones of areas potentially susceptible to these hazards. * The earthquake caused the flow of many streams in the epicentral region to increase. Effects were noted up to 88 km from the epicenter. * Post-earthquake studies of the Marina District of San Francisco provide perhaps the most comprehensive case history of earthquake effects at a specific site developed for any earthquake. Soft soils beneath the Marina amplified ground shaking to damaging levels and caused liquefaction of sandy artificial fills. Liquefaction required 123 repairs of pipelines in the Municipal Water Supply System, more than three times the number of repairs elsewhere in the system. Approximately 13.6 km of gas-distribution lines were replaced, and more than 20% of the wastewater collection lines were repaired or replaced.

Coordinated by Holzer, Thomas L.

1992-01-01

171

Earthquakes.  

ERIC Educational Resources Information Center

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

Pakiser, Louis C.

172

Slip budget and potential for a M7 earthquake in central California  

NASA Astrophysics Data System (ADS)

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

Harris, Ruth A.; Archuleta, Ralph J.

1988-10-01

173

Living With Earthquakes in California: A Survivor's Guide  

NASA Astrophysics Data System (ADS)

I write this review from a California government building in a roomful of somber, frightened strangers with armed sheriffs guarding the door. We are prohibited from leaving. A state of emergency has been declared, the airports are closed, the burly man next to me is tearing up, and all I can think of is getting home to my loved ones. What are the odds of being trapped in a jury room with armed guards and a television set, watching the collapse of the World Trade Center Towers and the smoking Pentagon? What are the odds of being trapped in a building, thinking of loved ones, as the Earth shakes, the furniture dances, and the ceiling falls when the long-awaited ‘Big One’ finally hits California? The analogy is sobering.

Grant, Lisa B.

174

Extensive research on Loma Prieta improves understanding of earthquakes  

Microsoft Academic Search

Research on the 1989 Loma Prieta, California, earthquake, probably the most thoroughly documented in American history, has dramatically improved our understanding of the complexity of earthquakes and of how society can reduce risk and improve response in connection with large natural disasters. The magnitude 6.9 earthquake was the largest and most damaging to strike an American urban area since the

Thomas L. Holzer

1999-01-01

175

Space-Time Clustering and Correlations of Major Earthquakes  

SciTech Connect

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

Holliday, James R. [Center for Computational Science and Engineering, University of California, Davis, California 95616 (United States); Department of Physics, University of California, Davis, California 95616 (United States); Rundle, John B. [Center for Computational Science and Engineering, University of California, Davis, California 95616 (United States); Department of Physics, University of California, Davis, California 95616 (United States); Department of Geology, University of California, Davis, California 95616 (United States); Turcotte, Donald L. [Department of Geology, University of California, Davis, California 95616 (United States); Klein, William [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Tiampo, Kristy F. [Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B8 (Canada); Donnellan, Andrea [NASA Jet Propulsion Laboratory, Pasadena, California 91109 (United States)

2006-12-08

176

Earthquakes  

NSDL National Science Digital Library

Provided by the British Geological Survey, the Earthquakes Web site contains numerous educational topics for kids. Best suited for junior high school students and older, the site contains information on macroseismology (or the observable effects of earthquakes on people, buildings, and nature); seismic hazards; earthquake monitoring; recent and historical earthquakes; and more. Other links on the site include a Questions and Answers page, earthquake references, and additional educational links culminating in an informative and helpful source of online science learning. [JAB

177

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

178

Aftershock slip behavior of the 1989 Loma Prieta, California earthquake  

SciTech Connect

An analysis of 745 aftershocks of the M7.1 Loma Prieta earthquake of 17 October, 1989 reveals a wide variety of focal mechanisms. At the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the San Andreas fault. At the southeastern end the mechanisms exhibit right-lateral motion on near-vertical planes, suggesting that these aftershocks involve slip on the San Andreas fault. Few of the aftershock mechanisms in the central zone resemble the main shock mechanism (strike N130{degree}E, dip 70{degree}SW, rake 104{degree}), but instead exhibit reverse, right-lateral, left-lateral, and normal motion on planes subparallel to the main shock rupture plane. The dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter. However, the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane. This behavior is consistent with observations of aftershock sequences for other dip-slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic. If the stress drop for the main shock relieved most of the tectonic stress, the mechanisms could reflect the heterogeneity of the near-field stress redistribution. Alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane.

Oppenheimer, D.H. (Geological Survey, Menlo Park, CA (USA))

1990-07-01

179

In Search for Thermal Precursors to Earthquakes in California Using MODIS Land Surface Temperature Data  

NASA Astrophysics Data System (ADS)

We test claims that earthquakes are preceded by thermal anomalies by analyzing daily nighttime land surface temperatures (LSTs) derived from data collected by the MODIS (Moderate Resolution Imaging Spectroradiometer) instruments mounted on the Terra and Aqua satellites. Terra precedes Aqua by ~3 hours, so the LST difference between the two satellites provides an estimate of nighttime cooling/warming rates. The MODIS LST data used cover the period between 2000 and 2006 and are with ~1 km spatial resolution. They cover a 10°x10° tile including most of California, parts of neighboring Nevada and Arizona, and northern Mexico. Our focus is on quantifying various factors influencing the background variability of LSTs and estimating the uniqueness and statistical significance of any apparent LST anomalies. For this purpose, the LSTs and their Aqua-Terra differences are used to calculate parameters similar to the Robust Estimator of Thermal Infrared Anomalies (RETIRA) index, first described by Tramutoli (1998) and subsequently reported to show anomalously high values preceding a number of earthquakes (e.g., Tramutoli et al., 2005; Corrado et al., 2005; Genzano et al, 2007). We develop the RETIRA concept further in order to account better for meteorological and other effects on the LSTs. In particular, we quantify cloud edge effects and the effects of topography. The RETIRA index is computed for Terra LSTs, Aqua LSTs, and Aqua-Terra LST differences. We examine the relationship between M>4.5 earthquakes and anomalous RETIRA by generating movies of RETIRA time evolution. We also compare and test for statistical significance of the differences among four types of combined time periods - pre-seismic, during seismic clusters, post-seismic and seismically quiet periods. Although some statistically significant differences are established, they do not involve uniquely the pre-seismic periods and anomalies appear too ubiquitous during all types of periods to be useful for earthquake prediction. We will be further testing smaller areas around "hot spots" (Holliday and Rundle, 2005) and past earthquakes in California.

Adams, D. A.; Eneva, M.

2007-12-01

180

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

181

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

Microsoft Academic Search

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

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

1993-01-01

182

Earthquakes  

NSDL National Science Digital Library

This lesson on earthquakes is based on naturalist John Muir's experiences with two significant earthquakes, the 1872 earthquake on the east side of the Sierra Nevada Mountains, and the Great San Francisco Earthquake of 1906. Students will learn to explain that earthquakes are sudden motions along breaks in the crust called faults, and list the major geologic events including earthquakes, volcanic eruptions and mountain building, which are the result of crustal plate motions. A downloadable, printable version (PDF) of the lesson plan is available.

183

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

184

Earthquake-by-earthquake fold growth above the Puente Hills blind thrust fault, Los Angeles, California: Implications for fold kinematics and seismic hazard  

Microsoft Academic Search

Boreholes and high-resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the Puente Hills thrust fault (PHT) beneath Los Angeles, California, provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault. These data document fold growth within a discrete kink band that narrows upward from ?460 m

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

2007-01-01

185

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

186

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

187

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

188

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

189

The 1989 Ms 7.1 Loma Prieta, California, Magnetic Earthquake Precursor Revisited  

NASA Astrophysics Data System (ADS)

Repeatable prediction of individual large earthquakes on the basis of quantitative geophysical data has proven to be frustratingly difficult and fraught with controversy. Still, some claims of success have been published, and among these are reports of identifiable precursory changes in magnetic-field activity as measured by ground- based magnetometers. By far the most prominent of such claims is that of Fraser-Smith et al., GRL, 17, 1465- 1468, 1990 who identified changes in Ultra Low Frequency (ULF, 0.01-10 Hz) magnetic noise prior to the 18 October 1989 Ms 7.1 Loma Prieta, California earthquake. The Fraser-Smith et al. result has been frequently cited in the literature, and it has been a major motivational influence for new research programs involving large arrays of ground-based instruments and even some satellite-based systems. We re-examine the data of the reported precursor, comparing them against independent data collected by magnetometers located in Japan and in the United States at the time of the Loma Prieta earthquake. From our analysis we infer that the key components of the precursory signal identified by Fraser-Smith et al. can be explained by minor corruption of the data in the form of a gain enhancement and time-stamp missassignment, possibly due to digital processing errors or inadvertent post-acquisitional treatment. We conclude that the reported magnetic anomaly is not related to the Loma Prieta earthquake.

Thomas, J. N.; Love, J. J.; Johnston, M. J.

2007-12-01

190

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

NASA Astrophysics Data System (ADS)

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

Provost, Ann-Sophie; Houston, Heidi

2003-10-01

191

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

192

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

193

Lessons learned from high-resolution earthquake locations in southern California (Invited)  

NASA Astrophysics Data System (ADS)

For a number of years, we have been working to improve earthquake locations in southern California using a variety of methods. To improve absolute event locations, we apply 3D ray tracing through a crustal tomography model. To improve relative event locations, we compute differential times using waveform cross-correlation. This has yielded a catalog of over 400,000 events from 1981 to 2005 with estimated absolute location errors of less than 1 km and estimated relative location errors at fine scales of less than 100 m. Our results show a dramatic sharpening of seismicity features and improved resolution of fine-scale fault structures. In general, seismicity in southern California is complicated and does not form obvious linear seismicity features along major faults (e.g., as is seen along the San Andreas Fault (SAF) in central California). Although seismicity at large scales is organized into northwest-southeast trends, conjugate faults are common at fine scales. For example, the Brawley seismic zone in the Salton Trough has numerous parallel southwest-northeast trending faults. Major earthquakes produce aftershocks in which the bulk of the events are not on the mainshock rupture plane itself but within damage zones several kilometers wide. Seismicity along most of the SAF is sparse, but in two regions near the southern SAF it appears to align on dipping faults. In situ Vp/Vs ratios estimated from differential times for 142 similar event clusters have a median value of 1.67, which suggests the presence of water-filled cracks with several percent porosity within these earthquake source regions.

Shearer, P. M.; Lin, G.; Hauksson, E.

2010-12-01

194

Localization of intermediate-term earthquake prediction  

Microsoft Academic Search

Relative seismic quiescence within a region which has already been diagnosed as having entered a Time of Increased Probability (TIP) for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur. A simple algorithm with parameters fitted from the data in Northern California preceding the 1980 magnitude 7.0

V. G. Kossobokov; V. I. Keilis-Borok; S. W. Smith

1990-01-01

195

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

USGS Publications Warehouse

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

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

2002-01-01

196

Stress/strain changes and triggered seismicity following the Mw 7.3 Landers, California earthquake  

NASA Astrophysics Data System (ADS)

Calculations of dynamic stresses and strains, constrained by broadband seismograms, are used to investigate their role in generating the remotely triggered seismicity that followed the June 28, 1992 Mw7.3 Landers, California earthquake. I compare straingrams and dynamic Coulomb failure functions calculated for the Landers earthquake at sites that did experience triggered seismicity with those at sites that did not. Bounds on triggering thresholds are obtained from analysis of dynamic strain spectra calculated for the Landers and Mw6.1 Joshua Tree, California earthquakes at various sites, combined with results of static strain investigations by others. I interpret three principal results of this study with those of a companion study by Gomberg and Davis [this issue]. First, the dynamic elastic stress changes themselves cannot explain the spatial distribution of triggered seismicity, particularly the lack of triggered activity along the San Andreas fault system. In addition to the requirement to exceed a Coulomb failure stress level, this result implies the need to invoke and satisfy the requirements of appropriate slip instability theory. Second, results of this study are consistent with the existence of frequency- or rate-dependent stress/strain triggering thresholds, inferred from the companion study and interpreted in terms of earthquake initiation involving a competition of processes, one promoting failure and the other inhibiting it. Such competition is also part of relevant instability theories. Third, the triggering threshold must vary from site to site, suggesting that the potential for triggering strongly depends on site characteristics and response. The lack of triggering along the San Andreas fault system may be correlated with the advanced maturity of its fault gouge zone; the strains from the Landers earthquake were either insufficient to exceed its larger critical slip distance or some other critical failure parameter; or the faults failed stably as aseismic creep events. Variations in the triggering threshold at sites of triggered seismicity may be attributed to variations in gouge zone development and properties. Finally, these interpretations provide ready explanations for the time delays between the Landers earthquake and the triggered events.

Gomberg, Joan

1996-01-01

197

Stress/strain changes and triggered seismicity following the MW7.3 Landers, California, earthquake  

USGS Publications Warehouse

Calculations of dynamic stresses and strains, constrained by broadband seismograms, are used to investigate their role in generating the remotely triggered seismicity that followed the June 28, 1992, MW7.3 Landers, California earthquake. I compare straingrams and dynamic Coulomb failure functions calculated for the Landers earthquake at sites that did experience triggered seismicity with those at sites that did not. Bounds on triggering thresholds are obtained from analysis of dynamic strain spectra calculated for the Landers and MW,6.1 Joshua Tree, California, earthquakes at various sites, combined with results of static strain investigations by others. I interpret three principal results of this study with those of a companion study by Gomberg and Davis [this issue]. First, the dynamic elastic stress changes themselves cannot explain the spatial distribution of triggered seismicity, particularly the lack of triggered activity along the San Andreas fault system. In addition to the requirement to exceed a Coulomb failure stress level, this result implies the need to invoke and satisfy the requirements of appropriate slip instability theory. Second, results of this study are consistent with the existence of frequency- or rate-dependent stress/strain triggering thresholds, inferred from the companion study and interpreted in terms of earthquake initiation involving a competition of processes, one promoting failure and the other inhibiting it. Such competition is also part of relevant instability theories. Third, the triggering threshold must vary from site to site, suggesting that the potential for triggering strongly depends on site characteristics and response. The lack of triggering along the San Andreas fault system may be correlated with the advanced maturity of its fault gouge zone; the strains from the Landers earthquake were either insufficient to exceed its larger critical slip distance or some other critical failure parameter; or the faults failed stably as aseismic creep events. Variations in the triggering threshold at sites of triggered seismicity may be attributed to variations in gouge zone development and properties. Finally, these interpretations provide ready explanations for the time delays between the Landers earthquake and the triggered events.

Gomberg, J.

1996-01-01

198

A Strong Stress Shadow Effect from the 1992 M=7.3 Landers, California, Earthquake  

NASA Astrophysics Data System (ADS)

Both dynamic and static stress have the potential to trigger earthquakes within several rupture dimensions of a mainshock. It has, however, proven extraordinarily difficult to disentangle their contribution to aftershocks and subsequent mainshocks. There are nevertheless ways to discriminate between the two: Only dynamic stress can trigger quakes in the far field (tens of rupture dimensions from the source), and only static stress has an identified physical mechanism to produce stress shadows, areas where the stress is calculated to have dropped. The seismicity rate would be expected to drop in the stress shadows, and so they provide a key falsification test of the static stress hypothesis, and thus have been subject to intensive investigation and debate. Here we show that where the April 1992 Mw=6.1 Joshua Tree, California, aftershock zone was subjected to a static stress increase from the June 1992 Mw=7.3 Landers earthquake, the rate of aftershocks jumped, and where the aftershock zone was subjected to a static stress decrease on the likely earthquake nodal planes, seismicity abruptly shut down. This stress shadow interaction was first noted by Zanzerkia (Stanford Univ. Ph.D. thesis, 2003), and was subsequently investigated by Marsan and Nalbant (PAGEOPH, 2005); we have deepened these analyses by carrying out a systematic search of the source, receiver, and focal mechanism diversity, and a time and space study of catalog completeness. The sudden arrest of seismicity in the Joshua Tree aftershock zone upon the Landers earthquake demonstrates that static stress is a requisite—but not necessarily exclusive—element of earthquake triggering.

Toda, S.; Stein, R. S.; Beroza, G. C.

2010-12-01

199

Preseismic and coseismic magnetic field measurements near the Coyote Lake, California, earthquake of August 6, 1979  

SciTech Connect

The epicenter of the Coyote Lake earthquake (M/sub L/ = 5.9 +- 0.2) of August 6, 1979, is located within an array of recording magnetometers which has been in operation since 1974. The nearest instrument, COY, was within 5 km of the epicenter. It was installed in October 1978 and is located on sedimentary rock, although volcanic and ultramafic rocks with magnetizations of up to 1 A/m outcrop 2 km to the west. A second recording magnetometer was operated for 18 days, beginning 4 days after the main event, to record the latter stages of the aftershock activity. Although longer-term magnetic field variations were recorded at station COY early in 1979 relative to other sites in the area, no anomalous changes within the two months prior to the earthquake were obeserved outside the present measurement uncertainty of 0.8 nT for hourly average differences. During the late aftershock stage, no magnetic field change greater than 0.25 nT occurred for more than a day. We conclude that in contrast to the 2-nT change observed before a previous M = 5.2 earthquake near Hollister, California, no demonstrable preseismic, coseismic, or postseismic tectonomagnetic effect was detected. A reasonable seismomagnetic model of the earthquake indicates that station COY was poorly located to detect stress-generated magnetic perturbations from this earthquake. Using a magnetization distribution indicated by modeling the aeromagnetic data over the area, we have calculated that homogeneous shear stress changes of about 5 MPa or greater would have been necessary to produce any observable effect at COY. This change is stress is precluded by geodetic data from over the area. However, COY is ideally situated for detection of electrokinetically generated magnetic anomalies. This initial null observation indicates that the assumptions used in the calculation of electrokinetic effects have, in this case, not been satisfied.

Johnston, M.J.S.; Mueller, R.J.; Keller, V.

1981-02-10

200

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

NASA Astrophysics Data System (ADS)

The Virtual Seismologist (VS) method is a regional network-based approach to earthquake early warning that estimates earthquake magnitude and location based on the available envelopes of ground motion amplitudes from the seismic network monitoring a given region, predefined prior information, and appropriate attenuation relationships. Bayes' theorem allows for the introduction of prior information (possibilities include network topology or station health status, regional hazard maps, earthquake forecasts, the Gutenberg- Richter magnitude-frequency relationship) into the source estimation process. Peak ground motion amplitudes (PGA and PGV) are then predicted throughout the region of interest using the estimated magnitude and location and the appropriate attenuation relationships. Implementation of the VS algorithm in California and Switzerland is funded by the Seismic Early Warning for Europe (SAFER) project. The VS algorithm is one of three early warning algorithms whose real-time performance on California datasets is being evaluated as part of the California Integrated Seismic Network (CISN) early warning effort funded by the United States Geological Survey (USGS). Real-time operation of the VS codes at the Southern California Seismic Network (SCSN) began in July 2008, and will be extended to Northern California in the following months. In Switzerland, the VS codes have been run on offline waveform data from over 125 earthquakes recorded by the Swiss Digital Seismic Network (SDSN) and the Swiss Strong Motion Network (SSMN). We discuss the performance of the VS codes on these datasets in terms of available warning time and accuracy of magnitude and location estimates.

Cua, G. B.; Fischer, M.; Heaton, T. H.; Wiemer, S.; Giardini, D.

2008-12-01

201

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

USGS Publications Warehouse

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

Boore, D. M.

1999-01-01

202

Paleoseismic features as indicators of earthquake hazards in North Coastal, San Diego County, California, USA  

Microsoft Academic Search

New road cut and mass-grading excavations in the north coastal area of San Diego County, California expose heretofore generally unrecognized, probable late Holocene tsunami deposits and paleoseismically deformed sediments. Remnant tsunami deposits occur up to 100+ m in elevation around the margins of modern coastal lagoons and estuaries and, combined with local mima mounds of possible sand blow origin, provide

Gerald G. Kuhn

2005-01-01

203

Coseismic stress parameter of three California Earthquakes derived from the stochastic finite fault technique  

NASA Astrophysics Data System (ADS)

Stochastic finite fault modeling is used to derive the coseismic stress parameter distribution on the fault surface of three well-recorded California earthquakes: M7.0, 1989, Loma Prieta; M7.3, 1992, Landers; and M6.7, 1994, Northridge. Classical waveform inversion techniques are inherently more powerful than stochastic modeling as a means of deriving detailed source parameters. However, the application of stochastic methods to the source modeling problem is useful to: (1) explore and calibrate the limitations and boundaries of stochastic modeling, (2) understand its relationship to more deterministically based techniques, and (3) provide a view of the source radiation not available from deterministic modeling. The stress parameter distribution for the M7.0 1989 Loma Prieta earthquake fault shows a concentration of stress in the lower part of the northwest side of the fault and another concentration in the upper southeast side of the fault, with an average stress parameter of 80 bars over the fault surface. The stress parameter distribution for the M7.3 1992 Landers earthquake fault shows a gradual increase of stress starting from the southeast side of the fault, close to the hypocenter, towards the center. The maximum stress occurs in the lower central part of the modeled fault surface. The average stress parameter is 70 bars for the Landers earthquake. The stress parameter distribution of the M6.7 1994 Northridge earthquake shows a concentration at the lower southeast end of the fault surface, extending toward the center of the fault surface and stretching to the northwest end. The average stress parameter is 80 bars for Northridge earthquake. The stress parameter distributions derived in this study by stochastic finite-fault modeling of high-frequency motions show considerable similarity to many of the slip distributions provided by different research groups for the same earthquakes, suggesting that the derivation of stress parameter distribution on a fault surface by the method applied in this study is reliable and closely tied to slip on the fault.

Assatourians, Karen; Atkinson, Gail M.

2010-07-01

204

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

Microsoft Academic Search

An ecological data base for the San Jacinto Mountains, California, USA, was used to construct a probability model of wildland\\u000a fire occurrence. The model incorporates both environmental and human factors, including vegetation, temperature, precipitation,\\u000a human structures, and transportation. Spatial autocorrelation was examined for both fire activity and vegetation to determine\\u000a the specification of neighborhood effects in the model. Parameters were

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

1993-01-01

205

Estimated Ground Motion From the 1994 Northridge, California, Earthquake at the Site of the Interstate 10 and La Cienega Boulevard Bridge Collapse, West Los Angeles, California  

Microsoft Academic Search

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

David M. Boore; James F. Gibbs; William B. Joyner; John C. Tinsley; Daniel J. Ponti

2003-01-01

206

Reply to “Comment on “Should Memphis build for California's earthquakes?” From A.D. Frankel”  

NASA Astrophysics Data System (ADS)

Carl Sagan observed that “extraordinary claims require extraordinary evidence.” In our view, A.D. Frankel's arguments (see accompanying Comment piece) do not reach the level required to demonstrate the counter-intuitive propositions that the earthquake hazard in the New Madrid Seismic Zone (NMSZ) is comparable to that in coastal California, and that buildings should be built to similar standards.This interchange is the latest in an ongoing debate beginning with Newman et al.'s [1999a] recommendation, based on analysis of Global Positioning System and earthquake data, that Frankel et al.'s [1996] estimate of California-level seismic hazard for the NMSZ should be reduced. Most points at issue, except for those related to the costs and benefits of the proposed new International Building Code 2000, have already been argued at length by both sides in the literature [e.g.,Schweig et al., 1999; Newman et al., 1999b, 2001; Cramer, 2001]. Hence,rather than rehash these points, we will try here to provide readers not enmeshed in this morass with an overview of the primary differences between our view and that of Frankel.

Stein, Seth; Tomasello, Joseph; Newman, Andrew

207

Earthquake locations and three-dimensional crustal structure in the Coyote Lake Area, central California  

NASA Astrophysics Data System (ADS)

Previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure. Approximate ray tracing and parameter separation are important elements of the improved method. Application of the method to P wave arrival time data recorded by stations of the U.S. Geological Survey Central California Network yields a three-dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the Coyote Lake earthquake of August 1979. Very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed. Improved estimates of the locations of earthquakes in the study area are also determined. The relocation of explosions indicates epicentral accuracies of the order of a kilometer or better. Based on the revised hypocentral locations, it is concluded that the San Andreas fault is vertical in this area, with no actual offset between the epicenters and the fault trace. In contrast, the Calaveras has two (or more) active fault surfaces, one nearly vertical and another dipping 75° to the northeast.

Thurber, Clifford H.

1983-10-01

208

Seismic slip, aseismic slip, and the mechanics of repeating earthquakes on the Calaveras fault, california  

NASA Astrophysics Data System (ADS)

The 1969-1984 history of seismic slip on the Calaveras fault in central California can be used to examine how slip is distributed in time and is partitioned between different deformation processes. Nowhere is there evidence that brittle deformation is the predominant failure mode over the entire depth range for which small earthquakes can be located (between about 2 and 15 km). The closest approach to completely brittle strain release occurs only for a more limited range of depths in a part of the region that ruptured during the 1984 Morgan Hill earthquake. Elsewhere aseismic deformation appears to contribute substantially to the total deformation. Except for the Hollister Valley, it is not known whether creep occurs on the fault, or in the surrounding media. In the Hollister Valley, creepmeter data suggest that fault creep can entirely accommodate the slip. Previous work indicates that rupture on the Calaveras fault, in both the Coyote Lake and Morgan Hill earthquakes, initiated and terminated at bends or offsets. Mechanisms invoking purely brittle and elastic behavior have been offered to explain observations of this type. The results that we present suggest that creep, as well as elastic-brittle processes, must play an important role in the micro-mechanics of these regions.

Bakun, William H.; King, Geoffrey C. P.; Cockerham, Robert S.

209

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

SciTech Connect

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

Hudnut, K.W.; Pacheco, J. (Lamont-Doherty Geological Observatory, Palisades, NY (USA) Columbia University, New York, NY (USA)); Seeber, L. (Lamont-Doherty Geological Observatory, Palisades, NY (USA))

1989-02-01

210

Turbidity anomaly and probability of slope failure following the 2011 Great Tohoku Earthquake  

NASA Astrophysics Data System (ADS)

Turbidity anomaly at seafloor is often observed immediately after earthquakes (Thunnell et al., 1999: Mikada et al., 2006). Such turbidity anomaly at deepsea is thought to be results of the seismically induced landslides at trench slopes. Turbidity distribution was observed using turbidity meter (Seapoint Sensors Inc.) at the mainshock area of the 2011 off the Pacific coast Tohoku earthquake (Mw 9.0) one month after the event. Turbidity anomalies, in which the turbidity increased with depth, were observed near the seafloor at all four sites. The thickness of the anomalous zones increased with water depth; the thickness at station B, the deepest measurement site, was about 1300 m above the seafloor and the average particle concentration which is equivalent to turbidity in the zone was 1.5 mg/L. We analyzed the mineral composition and grain size distribution of the suspended particle collected one month after the earthquake and shallow sediment core collected before the earthquake at the mainshock area. The grain size of the suspended particles was ranged from 1 to 300?m, and XRD analysis confirmed the presence of chlorite, illite, quartz, and albite in the particles. These characteristics are similar to the subsurface sediment material. Earlier studies (Prior, 1984) have introduced a mathematical model for analysis of submarine slope stability that include the effect of vertical and horizontal seismic accelerations caused by the earthquake. We analyzed slope instability on the basis of their model using the physical properties (density and shear strength) of the shallow sediment core materials and the acceleration of 2011 off the Pacific coast Tohoku earthquake. Our results show that a submarine landslide can be induced by a very large ground acceleration, as high as 3 m/s2, even if the sediment layer on the sliding surface is not very thick. We interpret the high turbidity observed one month after the Tohoku earthquake as the result of thin submarine landsliding. Reference Mikada, H. K. Mitsuzawa, H. Matsumoto, T. Watanabe, S. Morita, R. Otsuka, H. Sugioka, T. Baba, E. Araki, K. Suyehiro, (2006), New discoveries in dynamics of an M8 earthquake-phenomena and their implications from the 2003 Tokachi-oki earthquake using a long term monitoring cabled observatory, Tectonophysics, 426, 95-105. Prior, D. B. (1984), Methods of stability analysis, in Slope Instability, Edited by Brunsden, D. and D. B. Prior, pp. 419-455, Wiley, New York. Thunnell, R., E. Tappa, R. Varela, M. Llano, Y. Astor, F. Muller-Karger, and R. Bohrer (1999), Increased marine sediment suspension and fluxes following an earthquake. Nature, 398, 233-236.

Noguchi, T.; Tanikawa, W.; Hirose, T.; Lin, W.; Kawagucci, S.; Yoshida, Y.; Honda, M. C.; Takai, K.; Kitazato, H.; Okamura, K.

2011-12-01

211

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

212

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

USGS Publications Warehouse

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

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

2003-01-01

213

Probability  

NSDL National Science Digital Library

This lesson is designed to develop students' understanding of probability in real life situations. Students will also be introduced to running experiments, experimental probability, and theoretical probability. This lesson provides links to discussions and activities related to probability as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one.

2010-01-01

214

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

215

Earthquakes!  

NSDL National Science Digital Library

A strong earthquake struck Istanbul, Turkey on Monday, only weeks after a major quake in the same area claimed more than 15,500 lives. This site, from The Why Files (see the August 9, 1996 Scout Report), offers background information on the science of earthquakes, with particular emphasis on the recent tectonic activity in Turkey.

216

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

SciTech Connect

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

Prentice, C.S.

1989-01-01

217

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

218

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

219

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.

220

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

221

Probability  

NSDL National Science Digital Library

What are the chances? What is probability? Math Glossary What are the chances that you will get a baby brother or a baby sister? Boy or Girl? If you flip more than one coin, what are the combinations you could get? What are the chances you will get each combination? Probability in Flipping Coins ...

Banks, Ms.

2005-05-11

222

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

223

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

224

Earthquakes  

NSDL National Science Digital Library

To understand P and S waves, to observe some videos of earthquakes, and to find out where and when the last earthquake in Utah was. Print out this worksheet for the questions to accompany the following websites. Worksheet Go to The Earth Layers The Earth's Layers and read the information. Answer the following 4 questions on a separate paper. Name the four layers of the Earth in order from the outside to the center of the Earth. What causes ...

Clemons, Mrs.

2010-11-02

225

Slow rupture in Andaman during 2004 Sumatra-Andaman earthquake: a probable consequence of subduction of 90°E ridge  

NASA Astrophysics Data System (ADS)

One of the most enigmatic features of the 2004 Sumatra-Andaman earthquake was the slow rupture speed and low slip on the northern part of the rupture under the Andaman region. We propose that the aseismic 90°E Ridge (NER) on the Indian Plate obliquely subducts under the Andaman frontal arc region. Though other possibilities also exist, we hypothesized that this ridge probably acted as a structural barrier influencing rupture characteristics of the earthquake. Here we present several features of the Andaman region that favour NER subduction under the region, which include (i) comparatively shallow bathymetry and trench depth, (ii) low seismicity, (iii) significant variation in the azimuths of coseismic horizontal offsets due to the 2004 Sumatra-Andaman earthquake, (iv) lack of post-seismic afterslip on the coseismic rupture in the Andaman frontal arc region, (v) low P wave with only small decrease in S wave speed from tomographic studies, (vi) gravity anomalies on the Indian Plate indicating continuation of the ridge under the Andaman frontal arc and (vii) lack of back arc volcanoes in the Andaman region.

Gahalaut, V. K.; Subrahmanyam, C.; Kundu, B.; Catherine, J. K.; Ambikapathy, A.

2010-03-01

226

What parts of PTSD are normal: intrusion, avoidance, or arousal? Data from the Northridge, California, earthquake.  

PubMed

The incidence and comorbidity of posttraumatic stress disorder (PTSD) are addressed in a study of 130 Northridge, California, earthquake survivors interviewed 3 months post-disaster. Only 13% of the sample met full PTSD criteria, but 48% met both the re-experiencing and the arousal symptom criteria, without meeting the avoidance and numbing symptom criterion. Psychiatric comorbidity was associated mostly with avoidance and numbing symptoms. For moderately severe traumatic events, re-experiencing and arousal symptoms may be the most "normal," and survivors with a history of psychiatric problems may be those most likely to develop full PTSD. A system that considers people who meet all three symptom criteria to have a psychiatric disorder yet recognizes the distress of other symptomatic survivors may best serve traumatized populations. PMID:10761174

McMillen, J C; North, C S; Smith, E M

2000-01-01

227

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

SciTech Connect

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

Cruikshank, K.M. [Portland State Univ., OR (United States). Dept. of Geology; Johnson, A.M. [Purdue Univ., West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences; Fleming, R.W. [Geological Survey, Denver, CO (United States); Jones, R.L. [City of Los Angeles, CA (United States). Dept. of Public Works

1996-12-31

228

Aftershocks of the Coyote Lake, California, earthquake of August 6, 1979: A detailed study  

NASA Astrophysics Data System (ADS)

Aftershock hypocenters and focal mechanism solutions for the Coyote Lake, California, earthquake reveal a geometrically complex fault structure, consisting of multiple slip surfaces. The faulting surface principally consists of two right stepping en echelon, northwest trending, partially overlapping, nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 Parkfield, California, earthquake. The overlap occurs near a prominent bend in the surface trace of the Calaveras fault at San Felipe Lake. Slip during the main rupture, as inferred from the distribution of early aftershocks, appears to have been confined to a 14-km portion of the northeastern sheet between 4- and 10-km depth. Focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex, with left stepping imbricate structure. Seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock. Aftershocks in this zone define a single vertical plane 8 km long between 3- and 7-km depth. Within the overlap zone between the two main slip surfaces, the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone, in close agreement with the stress perturbations predicted by crack interaction models. Aftershock activity in the overlap zone is not associated with a simple dislocation surface. Space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone. This alternation is consistent with local stress perturbations predicted by crack interaction models. We conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which, in turn, control the displacements. Table 5 is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J82-006; $1.00. Payment must accompany order.

Reasenberg, P.; Ellsworth, W. L.

1982-12-01

229

Aftershocks of the Coyote Lake, California, earthquake of August 6, 1979: A detailed study  

SciTech Connect

Aftershock hypocenters and focal mechanism solutions for the Coyote Lake, California, earthquake reveal a geometrically complex fault structure, consisting of multiple slip surfaces. The faulting surface principally consists of two right stepping en echelon, northwest trending, partially overlapping, nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 Parkfield, California, earthquake. The overlap occurs near a prominent bend in the surface trace of the Calaveras fault at San Felipe Lake. Slip during the main rupture, as inferred from the distribution of early aftershocks, appears to have been confined to a 14-km portion of the northeastern sheet between 4- and 10-km depth. Focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex, with left stepping imbricate structure. Seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock. Aftershocks in this zone define a single vertical plane 8 km long between 3- and 7-km depth. Within the overlap zone between the two main slip surfaces, the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone, in close agreement with the stress perturbations predicted by crack interaction models. Aftershock activity in the overlap zone is not associated with a simple dislocation surface. Space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone. This alternation is consistent with local stress perturbations predicted by crack interaction models. We conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which, in turn, control the displacements.

Reasenberg, P.; Ellsworth, W.L.

1982-12-10

230

Surficial slip distribution on the central Emerson fault during the June 28, 1992, Landers earthquake, California  

NASA Astrophysics Data System (ADS)

We present the results of our mapping of a 5.6-km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right-lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right-lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left-lateral or thrust displacement. The maximum net vertical displacement was 175 cm, east-side-up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike-slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as 1 m or more over distances ranging from 1-2 km to a few tens of meters, suggesting that strains of the order of 10-1 may have occurred locally within the surficial sediments. The long-wavelength (kilometer-scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.

McGill, Sally F.; Rubin, Charles M.

1999-03-01

231

Spatial and temporal stress drop variations in small earthquakes near Parkfield, California  

NASA Astrophysics Data System (ADS)

We estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the Parkfield segment of the San Andreas Fault in central California. We use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed P wave source spectra with a spatially varying empirical Green's function (EGF). Our Brune-type stress drop estimates vary from 0.1 to over 100 MPa with a median value of 6.75 MPa, which is nearly constant with moment, implying self-similarity over the ML = 0.5 to 3.0 range of our data. The corner frequency decreases for earthquakes at shallower depths, consistent with slower rupture velocities and reduced shear wave velocities in local velocity models. The estimated median stress drops show significant lateral variations: we find lower stress drops in the Middle Mountain asperity and along the creeping fault section, and higher stress drops in the hypocentral region of the 2004 M6.0 Parkfield earthquake. The main shock did not alter the overall pattern of high and low stress drop regions. However, a statistical test reveals areas with significant changes in computed stress drops after the main shock, which we compare to estimated absolute shear stress changes from a main shock slip model. By calculating ?t* from the spectral EGF ratio, we also identify areas with increased attenuation after the main shock, and we are able to distinguish source effects and near-source attenuation effects in the spectral analysis. These results are confirmed independently from spectral ratios of repeating microearthquake clusters.

Allmann, Bettina P.; Shearer, Peter M.

2007-04-01

232

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

NASA Astrophysics Data System (ADS)

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 39° 59°S, and trend about N84°E 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 × 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.

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

1983-05-01

233

Faulting processes of the 1956 San Miguel, Baja California, earthquake sequence  

NASA Astrophysics Data System (ADS)

Body waveform modeling is used to determine the source processes of three large earthquakes (magnitude 6.8, 6.4, 6.3) occurring between February 9 and 15, 1956 along the San Miguel fault in northern Baja California, Mexico. Results of the modeling suggest that the mainshock on February 9 was responsible for the 20 km of surface faulting observed during the sequence. Although previous researchers have suggested a complex rupture history for the mainshock, uncertainty estimates of source-time function shape indicate single or double source models fit the observed waveforms equally well. The February 15 aftershock, however, appears to have consisted of two events. Locations and focal mechanisms obtained for the three events suggest that the rupture process may have been controlled by cross faults to the main trace of the San Miguel fault. The good correlation between source parameter information and the surficial geology/geometry of the San Miguel fault zone demonstrates the usefulness of waveform modeling studies in unravelling the complexities of historic multi-event earthquake sequences.

Doser, Diane I.

1992-03-01

234

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

USGS Publications Warehouse

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

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

1998-01-01

235

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

USGS Publications Warehouse

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

Luetgert, James, H.; Mooney, Walter, D.

1985-01-01

236

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

SciTech Connect

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

Stevenson, J.D. [Stevenson and Associates, Cleveland, OH (United States)

1995-11-01

237

Trees and herbs killed by an earthquake ˜300 yr ago at Humboldt Bay, California  

NASA Astrophysics Data System (ADS)

Evidence of rapid seismic-induced subsidence at Humboldt Bay, California, is produced by analyses of annual growth rings of relict Sitka spruce [Picea sitchensis (Bong.) Carr.] roots and entombed herbaceous plants. These results add to previously reported evidence that an earthquake caused subsidence ˜300 yr ago at Mad River slough, California. Both types of remains are rooted in buried soils that stood at or above the high-tide level until the area subsided at least 0.5 m into the intertidal zone. Burial by intertidal muds took place quickly enough to preserve the herbs in the growth position. Analysis of the annual growth rings of the tree roots shows that all died within four growing seasons, but the time of root death varies even among roots of the same tree. With no central nervous system, tree cells do not die simultaneously throughout the organism. The 0.5 to 1.5 m of subsidence, as evidenced by stratigraphy and sedimentology, was not enough to kill all the trees even in one season. Although such gradual death could be due to rapid aseismic subsidence, the tree deaths and preserved herbs are much better explained by sudden coseismic subsidence.

Jacoby, Gordon; Carver, Gary; Wagner, Wendy

1995-01-01

238

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

239

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

240

Soil radon concentration changes preceding and following four magnitude 4. 2--4. 7 earthquakes on the San Jacinto fault in southern California  

Microsoft Academic Search

Radon concentrations in soil gas measured in shallow holes by plastic Track Etch detectors show variations which may be associated with four magnitude 4.2 to 4.7 earthquakes on the San Jacinto Fault in southern California. A simple sinusoidal correction for the annual soil temperature cycle removes most of the variability in radon concentration that cannot be correlated with earthquakes. The

G. F. Birchard; W. F. Libby

1980-01-01

241

Earthquakes  

Microsoft Academic Search

Regression method has been applied to design multidimensional nonlinear statistical model of seismic energy flow release by local earthquakes using the data of integrated geophysical monitoring in the Transcarpathian seismogenic zone, Ukraine, as input. It has been shown that to obtain adequate model it is necessary to utilize temporal series of geophysical parameters that are not less than 730 days

Taras Verbytskyj; Yurij Verbytskyj

1889-01-01

242

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.

243

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

USGS Publications Warehouse

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

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

1999-01-01

244

Potency-magnitude scaling relations for southern California earthquakes with 1.0 < M L < 7.0  

Microsoft Academic Search

Linear and quadratic scaling relations between potency P 0 and local magnitude M L for southern California earthquakes are derived using observed data of small events (1.0 < M L < 3.5) recorded in the Cajon Pass borehole and moderate events (3.5 < M L < 6.0) recorded by the broad-band TERRAscope\\/TriNet network. The derived relations are extended to M

Yehuda Ben-Zion; Lupei Zhu

2002-01-01

245

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

SciTech Connect

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

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

1993-04-01

246

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

SciTech Connect

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

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

1993-04-01

247

Directional Topographic Site Response at Tarzana Observed in Aftershocks of the 1994 Northridge, California, Earthquake: Implications for Mainshock Motions  

Microsoft Academic Search

The Northridge earthquake caused 1.78 g acceleration in the east-west direction at a site in Tarzana, California, located about 6 km south of the mainshock epicenter. The accelerograph was located atop a hill about 15-m high, 500-m long, and 130-m wide, striking about N78°E. During the aftershock sequence, a temporary array of 21 three-component geophones was deployed in six radial

Paul Spudich; Margaret Hellweg; W. H. K. Lee

1996-01-01

248

Stochastic Finite-Fault Modeling of Ground Motions from the 1994 Northridge, California, Earthquake. I. Validation on Rock Sites  

Microsoft Academic Search

The stochastic method of simulating ground motions from finite faults is validated against strong-motion data from the M 6.7 1994 Northridge, California, earthquake. The finite-fault plane is subdivided into elements, each element is as- signed a stochastic o92 spectrum, and the delayed contributions from all subfaults are summed in the time domain. Simulated horizontal acceleration time histories and Fourier spectra

Igor A. Beresnev; Gall M. Atkinson

1998-01-01

249

Assessment of Creep Events as Potential Earthquake Precursors: Application to the Creeping Section of the San Andreas Fault, California  

NASA Astrophysics Data System (ADS)

We report the analysis of over 16 years of fault creep and seismicity data from part of the creeping section of the San Andreas fault to examine and assess the temporal association between creep events and subsequent earthquakes. The goal is to make a long-term evaluation of creep events as a potential earthquake precursor. We constructed a catalog of creep events from available digital creepmeter data and compared it to a declustered seismicity catalog for the area between San Juan Bautista and San Benito, California, for 1980 to 1996. For magnitude thresholds of 3.8 and above and time windows of 5 to 10 days, we find relatively high success rates (40% to 55% 'hits') but also very high false alarm rates (generally above 90%). These success rates are statistically significant (0.0007 < P < 0.04). We also tested the actual creep event catalog against two different types of synthetic seismicity catalogs, and found that creep events are followed closely in time by earthquakes from the real catalog far more frequently than the average for the synthetic catalogs, generally by more than two standard deviations. We find no identifiable spatial pattern between the creep events and earthquakes that are hit or missed. We conclude that there is a significant temporal correlation between creep events and subsequent small to moderate earthquakes, however that additional information (such as from other potential precursory phenomena) is required to reduce the false alarm rate to an acceptable level.

Thurber, C.; Sessions, R.

250

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

USGS Publications Warehouse

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

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

2010-01-01

251

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

SciTech Connect

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

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

1986-12-01

252

"Ghost transients" in the southern California GPS velocity field: An investigation using finite-fault earthquake cycle models  

NASA Astrophysics Data System (ADS)

Elastic block models are generally used to infer slip rates on fault segments in tectonically complex areas, such as southern California (e.g. McCaffrey, 2005; Meade et al., 2005). These models implicitly assume steady-state deformation. However, owing to viscoelastic effects of past large earthquakes, deformation rates and patterns around major faults are expected to vary with time. Where viscoelasticity has been incorporated into block models, differences in inferred slip rates have resulted (Johnson et al., 2007). Here, we investigate the extent to which viscoelastic velocity perturbations (or "ghost transients") from individual earthquakes 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 end-member rheological structures. For selected faults, an idealized earthquake history is constructed, consisting of a sequence of periodic, identical repeating slip events. For each earthquake, we first calculate average velocities and time-dependent perturbations relative to this average at all GPS sites in the neighborhood of an earthquake. (We deal with perturbations because to recover the velocities, we would have to compute and sum cycle-average velocities and perturbations for all fault segments in the region.) Next, we invert two GPS velocity fields for slip rates using a block modeling approach: one field that has been corrected for the perturbation, and one which has not, and we compare the resulting slip rates. For now, the viscoelastic models are simple (layers with linear rheologies), and locking depth is fixed in the block models. We find that if asthenosphere viscosities are low enough (3 x 10**18 Pa-s) the current GPS velocity field is significantly perturbed by the 1857 M 7.9 San Andreas Fault (SAF) earthquake sequence; that is, current strain rates around the SAF are lower than their average values. Correcting the GPS velocity field for this perturbation adds up to about 5 mm/yr to the SAF slip rate along the Mojave and San Bernardino segments, consistent with the results of Johnson et al. (2007). The GPS velocity perturbation due to the most recent, large Garlock Fault earthquake (assumed to be an M 7.5 event in 1640) is smaller. In this case, inversions of the corrected and uncorrected GPS velocity fields yield near-identical slip rates for all of the faults in our block model. This suggests that the discrepancy between geodetic and geologic slip rates for the Garlock Fault is not due to a ghost transient.

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

2011-12-01

253

Arrest and recovery of frictional creep on the southern Hayward fault triggered by the 1989 Loma Prieta, California, earthquake and implications for future earthquakes  

NASA Astrophysics Data System (ADS)

Theodolite measurements across the right-lateral Hayward fault, San Francisco Bay, California, show a dramatic reduction in surface creep rate from 5 to 10 mm/yr before the 1989 Loma Prieta earthquake to nearly zero creep rate after the earthquake. A ˜6 year period of nearly zero surface creep was followed by sudden fault creep that accumulated about 20-25 mm of right-lateral displacement followed by an eventual return to a steady creep by year ˜2000. This creep behavior can be explained as a result of a sudden shear stress reduction on the fault and is consistent with model predictions for a fault imbedded in an elastic medium with slip governed by laboratory-derived friction laws. We infer friction parameters on the fault using a spring-slider model and a boundary element model with the rate- and state-dependent friction laws. The state (healing) term in the friction law is critical for reproducing the observed evolution of surface creep; a popular simplified rate-dependent friction law is insufficient. Results suggest that the creep event extended to a depth of ˜4-7.5 km. The inferred critical slip distance, dc, is 1-2 orders of magnitude larger than lab values, and inferred a? values imply low effective fault-normal stresses of 5-30 MPa. This range of effective normal stress and inversion results for (a - b)? imply very small values for a - b of 10-5 to 10-3, suggesting the fault has nearly velocity-neutral frictional properties. Earthquake simulations with such small a - b values show that creeping areas on the Hayward fault may be capable of rupturing during earthquakes.

Kanu, Chinaemerem; Johnson, Kaj

2011-04-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

255

Public Education for Household Mitigation and Preparedness for Earthquakes in California: The Research Base and Program Innovations  

NASA Astrophysics Data System (ADS)

This presentation summarizes the findings from previous research in the social sciences regarding the factors and processes that enhance the effectivenss of public education efforts for household mitigation and preparedness actions for earthquakes. The conclusions from this research base include that the most effective efforts are those that are designed as an ongoing process with multiple channels and types of public communications. Second, an anticipated survey to measure household mitigation and preparedness actions in the State of California is sumarized. This survey will measure actual household mitigation and preparedness actions taken, knowledge, perceived risk, and other factors that previous research suggests impact these actions and perceptions; each of these factors are reviewed. The presentation then illustrates how knowledge from previous research will be blended with the information obtained from the planned survey in order to desgin a state-of-the-art public education campaign in California that maximizes household mitigation and preparedness for earthquakes and mega-earthquakes. Among other things, this requires that government agencies, NGOs, and provate sector organizations cooperate to coordinate their efforts to maximize program effectivenss. Finally, how this program might be evaluated to inform program refinements over time is discussed.

Mileti, D. S.

2007-05-01

256

Comprehensive analysis of earthquake source spectra and swarms in the Salton Trough, California  

NASA Astrophysics Data System (ADS)

We study earthquakes within California's Salton Trough from 1981 to 2009 from a precisely relocated catalog. We process the seismic waveforms to isolate source spectra, station spectra and travel-time dependent spectra. The results suggest an average P wave Q of 340, agreeing with previous results indicating relatively high attenuation in the Salton Trough. Stress drops estimated from the source spectra using an empirical Green's function (EGF) method reveal large scatter among individual events but a low median stress drop of 0.56 MPa for the region. The distribution of stress drop after applying a spatial-median filter indicates lower stress drops near geothermal sites. We explore the relationships between seismicity, stress drops and geothermal injection activities. Seismicity within the Salton Trough shows strong spatial clustering, with 20 distinct earthquake swarms with at least 50 events. They can be separated into early-Mmax and late-Mmax groups based on the normalized occurrence time of their largest event. These swarms generally have a low skew value of moment release history, ranging from -9 to 3.0. The major temporal difference between the two groups is the excess of seismicity and an inverse power law increase of seismicity before the largest event for the late-Mmax group. All swarms exhibit spatial migration of seismicity at a statistical significance greater than 85%. A weighted L1-norm inversion of linear migration parameters yields migration velocities from 0.008 to 0.8 km/hour. To explore the influence of fluid injection in geothermal sites, we also model the migration behavior with the diffusion equation, and obtain a hydraulic diffusion coefficient of approximately 0.25 m2/s for the Salton Sea geothermal site, which is within the range of expected values for a typical geothermal reservoir. The swarms with migration velocities over 0.1 km/hour cannot be explained by the diffusion curve, rather, their velocity is consistent with the propagation velocity of creep and slow slip events. These variations in migration behavior allow us to distinguish among different driving processes.

Chen, X.; Shearer, P. M.

2011-09-01

257

Earthquake-cycle models of the Pacific-North America plate boundary at Point Reyes, California  

NASA Astrophysics Data System (ADS)

At Point Reyes, California, about 36 mm/yr of Pacific-North America relative plate motion is accommodated by (from west to east) the San Andreas, Rodgers Creek, Napa and Green Valley faults. We have developed a suite of viscoelastic earthquake cycle models which take into account the timing and recurrence intervals of large earthquakes on these faults, and are calibrated to the current GPS velocity field. We infer a locking depth of about 12 km for all four faults, consistent with previous analyses of local hypocenter depths (e.g., d'Alessio et al, 2005). Low-viscosity viscous shear zones appear to be required for our models to fit the GPS velocities. In order to fit the high surface velocity gradient across this set of faults, the effective viscosity for the lower crust and mantle must exceed 10^20 Pa s. A modest contrast in effective viscosity of the lower crust and upper mantle across the San Andreas Fault, with higher viscosity values (at least 5 x 10^20 Pa s) to the east, is also indicated. In the region between the Rodgers Creek Fault and the Green Valley Fault, GPS data indicate a higher strain rate than our models can explain. Even after shifting the entire Green Valley Fault slip rate (9 mm/yr) westward to the Napa Fault, the misfit is not eliminated. Double-difference hypocenter data (Waldhauser and Schaff, 2008) suggest the presence of another fault zone between the Napa Fault and the Green Valley Fault, and that all three of these faults dip toward the west. This offsets their deep, creeping extensions several km from their surface traces. A preliminary model with a suitably offset, deep Green Valley Fault extension cuts the WRSS misfit to GPS site velocities by over a factor of two. Since non-vertical fault dips are often missed in seismic studies (e.g. Fuis et al., 2008), creeping shear zones at depth may routinely be offset by several kilometers from their surface traces, unless alternate evidence of their position at depth is available (e.g. Shelly et al., 2009). This may lead to incorrect inferences of material asymmetry, or errors in the attribution of slip rates to closely spaced, active faults.

Vaghri, A.; Hearn, E. H.

2011-12-01

258

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

SciTech Connect

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

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

2012-01-23

259

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

USGS Publications Warehouse

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

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

2009-01-01

260

Potential Effects of a Scenario Earthquake on the Economy of Southern California: Labor Market Exposure and Sensitivity Analysis to a Magnitude 7.8 Earthquake  

USGS Publications Warehouse

The Multi-Hazards Demonstration Project (MHDP) is a collaboration between the U.S. Geological Survey (USGS) and various partners from the public and private sectors and academia, meant to improve Southern California's resiliency to natural hazards (Jones and others, 2007). In support of the MHDP objectives, the ShakeOut Scenario was developed. It describes a magnitude 7.8 (M7.8) earthquake along the southernmost 300 kilometers (200 miles) of the San Andreas Fault, identified by geoscientists as a plausible event that will cause moderate to strong shaking over much of the eight-county (Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura) Southern California region. This report contains an exposure and sensitivity analysis of economic Super Sectors in terms of labor and employment statistics. Exposure is measured as the absolute counts of labor market variables anticipated to experience each level of Instrumental Intensity (a proxy measure of damage). Sensitivity is the percentage of the exposure of each Super Sector to each Instrumental Intensity level. The analysis concerns the direct effect of the scenario earthquake on economic sectors and provides a baseline for the indirect and interactive analysis of an input-output model of the regional economy. The analysis is inspired by the Bureau of Labor Statistics (BLS) report that analyzed the labor market losses (exposure) of a M6.9 earthquake on the Hayward fault by overlaying geocoded labor market data on Instrumental Intensity values. The method used here is influenced by the ZIP-code-level data provided by the California Employment Development Department (CA EDD), which requires the assignment of Instrumental Intensities to ZIP codes. The ZIP-code-level labor market data includes the number of business establishments, employees, and quarterly payroll categorized by the North American Industry Classification System. According to the analysis results, nearly 225,000 business establishments, or 44 percent of all establishments, would experience Instrumental Intensities between VII (7) and X (10). This represents more than 4 million employees earning over $45 billion in quarterly payroll. Over 57,000 of these establishments, employing over 1 million employees earning over $10 billion in quarterly payroll, would experience Instrumental Intensities of IX (9) or X (10). Based upon absolute counts and percentages, the Trade, Transportation, and Utilities Super Sector and the Manufacturing Super Sector are estimated to have the greatest exposure and sensitivity respectively. The Information and the Natural Resources and Mining Super Sectors are estimated to be the least impacted. Areas estimated to experience an Instrumental Intensity of X (10) account for approximately 3 percent of the region's labor market.

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

2008-01-01

261

Development of Earthquake Early Warning System in Southern California Using Real Time GPS and Seismic Data  

NASA Astrophysics Data System (ADS)

We discuss the fusion of low-latency (1 s) high-rate (1 Hz or greater) CGPS total displacement waveforms and traditional seismic data, in order to extend the frequency range and timeliness of surface displacement data already available at lower frequencies from space borne InSAR and (typically daily) CGPS coordinate time series. The goal of our NASA AIST project is to develop components of early warning systems for mitigation of geological hazards (direct seismic damage, tsunamis, landslides, volcanoes). The advantage of the GPS data is that it is a direct measurement of ground displacement. With seismic data, this type of measure has to be obtained by deconvolution of the instrument response and integration of the broadband (velocity) measurements, or a double integration of the strong motion (acceleration) measurements. Due to the bandwidth and the dynamic range limits of seismometers the accuracy of absolute displacements so derived is poor. This problem is not present in the high-sample rate GPS data. We have developed a multi-rate Kalman filter that can combine in real time the complementary GPS and seismic data for use in an earthquake early warning (EEW) system, which results in an improved determination of total displacement waveforms by taking advantage of the strong points of each data type. While the seismic measurement provides a powerful constraint on the much noisier GPS measurements, unlike the seismometer, the GPS receiver never clips. We have identified about 25 “co-located” real-time GPS and broadband seismic stations (STS-1, STS-2, and CMG-3T instruments) in southern California. We are currently addressing issues related to data formats and metadata exchange, which will allow us to efficiently combine the two data types in the multi-rate Kalman filter. We describe the elements of the EEW system for southern California, discuss issues of detection and characterization of signals, and consider minimization of false alarms. We show an example of the how the system works using the Mw=7.8 ShakeOut simulation in November, 2008.

Squibb, M. B.; Bock, Y.; Crowell, B. W.; Jamason, P.; Fang, P.; Yu, E.; Clayton, R. W.; Kedar, S.; Webb, F.; Bar-Sever, Y.; Miller, K. J.

2009-12-01

262

CISN ShakeAlert: Three Years of Comparative Real-Time Earthquake Early Warning Testing in California  

NASA Astrophysics Data System (ADS)

The California Integrated Seismic Network (CISN) recently concluded a three-year project (August 2006-July 2009) aimed at the implementation, real-time testing, and comparative performance evaluation of three participating earthquake early warning (EEW) algorithms: 1) the Tau-C/P-d onsite algorithm developed by the California Institute of Technology, 2) the ElarmS algorithm developed by UC Berkeley, and 3) the Virtual Seismologist (VS) algorithm developed by the Swiss Seismological Service at ETH Zurich. These 3 EEW algorithms were installed and tested, and continue to run in real-time, at the Southern California Seismic Network, the Berkeley Digital Seismic Network, and the USGS Menlo Park network. The OnSite algorithm provides single-station magnitude estimates and estimates peak ground velocity at a given station. ElarmS and VS both provide magnitude and location estimates, as well as estimates of the geographic distribution of peak ground shaking. Over the last three years, these EEW algorithms submitted real-time and automatic non-interactive offline event reports to the Southern California Earthquake Center (SCEC) EEW Testing Center, which independently evaluated algorithm performance relative to the ANSS earthquake catalogue and observed ground motion datasets. We quantify the performance of these participating algorithms in terms of the accuracy of magnitude, location, and peak ground motion estimation, as well as the speed at which the algorithms provide information. Based on the derived performance characteristics, we infer how a prototype system based on the three algorithms might operate given alternative conditions, such as shorter telemetry delays, faster processing times, or higher station densities. The 2006-2009 CISN-EEW project demonstrated the feasibility and potential benefits of EEW in California. A new USGS-funded effort is underway to develop key components of CISN ShakeAlert, a prototype EEW system that could potentially be implemented in California. These key components include: 1) integration of the three algorithms into a single processing thread capable of providing alerts, 2) development of partnerships with key test users, and 3) development of protocols and procedures in collaboration with the test users that will govern the form and release of EEW information, if such a system is built.

Cua, G. B.; Allen, R. M.; Boese, M.; Brown, H.; Given, D.; Fischer, M.; Hauksson, E.; Heaton, T. H.; Hellweg, M.; Jordan, T. H.; Khainovski, O.; Maechling, P. J.; Neuhauser, D. S.; Oppenheimer, D. H.; Solanki, K.

2009-12-01

263

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

Microsoft Academic Search

Currently the SCEDC archives continuous and triggered data from nearly 5000 data channels from 425 SCSN recorded stations, processing and archiving an average of 12,000 earthquakes each year. The SCEDC provides public access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP and DHI. This poster will describe the most significant

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

2010-01-01

264

Plotting Earthquakes  

NSDL National Science Digital Library

In this activity, learners discover how to plot earthquakes on a map by exploring recent earthquake activity in California and Nevada. Within this activity, learners also practice using latitudinal and longitudinal lines and make predictions. This detailed lesson plan includes key vocabulary words, background information for educators, extension ideas, and resources.

Sciences, California A.

2012-06-26

265

Earthquake-by-earthquake fold growth above the Puente Hills blind thrust fault, Los Angeles, California: Implications for fold kinematics and seismic hazard  

NASA Astrophysics Data System (ADS)

Boreholes and high-resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the Puente Hills thrust fault (PHT) beneath Los Angeles, California, provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault. These data document fold growth within a discrete kink band that narrows upward from ˜460 m at the base of the Quaternary section (200-250 m depth) to <150 m at 2.5 m depth, with most growth during the most recent folding event occurring within a zone only ˜60 m wide. These observations, coupled with evidence from petroleum industry seismic reflection data, demonstrate that most (>82% at 250 m depth) folding and uplift occur within discrete kink bands, thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault. The borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site. We interpret the intervals of growth as occurring after the formation of now-buried paleofold scarps during three large PHT earthquakes in the past 8 kyr. The intervening intervals of no growth record periods of structural quiescence and deposition at the regional, near-horizontal stream gradient at the study site. Minimum uplift in each of the scarp-forming events, which occurred at 0.2-2.2 ka (event Y), 3.0-6.3 ka (event X), and 6.6-8.1 ka (event W), ranged from ˜1.1 to ˜1.6 m, indicating minimum thrust displacements of ?2.5 to 4.5 m. Such large displacements are consistent with the occurrence of large-magnitude earthquakes (Mw > 7). Cumulative, minimum uplift in the past three events was 3.3 to 4.7 m, suggesting cumulative thrust displacement of ?7 to 10.5 m. These values yield a minimum Holocene slip rate for the PHT of ?0.9 to 1.6 mm/yr. The borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally, such that older strata that have been deformed by more earthquakes dip more steeply than younger strata. Specifically, strata dip 0.4° at 4 m depth, 0.7° at 20 m depth, 8° at 90 m, 16° at 110 m, and 17° at 200 m. Moreover, structural restorations of the borehole data show that the locus of active folding (the anticlinal active axial surface) does not extend to the surface in exactly the same location from earthquake to earthquake. Rather, that the axial surfaces migrate from earthquake to earthquake, reflecting a component of fold growth by kink band migration. The incremental acquisition of bed dip in the growth triangle may reflect some combination of fold growth by limb rotation in addition to kink band migration, possibly through a component of trishear or shear fault bend folding. Alternatively, the component of limb rotation may result from curved hinge fault bend folding, and/or the mechanical response of loosely consolidated granular sediments in the shallow subsurface to folding at depth.

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

2007-03-01

266

The magnitude 6.7 northridge, california, earthquake of 17 january 1994.  

PubMed

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. PMID:17816681

1994-10-21

267

Stress triggering of the 1994 m = 6.7 northridge, california, earthquake by its predecessors.  

PubMed

A model of stress transfer implies that earthquakes in 1933 and 1952 increased the Coulomb stress toward failure at the site of the 1971 San Fernando earthquake. The 1971 earthquake in turn raised stress and produced aftershocks at the site of the 1987 Whittier Narrows and 1994 Northridge ruptures. The Northridge main shock raised stress in areas where its aftershocks and surface faulting occurred. Together, the earthquakes with moment magnitude M >/= 6 near Los Angeles since 1933 have stressed parts of the Oak Ridge, Sierra Madre, Santa Monica Mountains, Elysian Park, and Newport-lnglewood faults by more than 1 bar. Although too small to cause earthquakes, these stress changes can trigger events if the crust is already near failure or advance future earthquake occurrence if it is not. PMID:17833817

Stein, R S; King, G C; Lin, J

1994-09-01

268

Cross-sections and maps showing double-difference relocated earthquakes from 1984-2000 along the Hayward and Calaveras faults, California  

USGS Publications Warehouse

We present cross-section and map views of earthquakes that occurred from 1984 to 2000 in the vicinity of the Hayward and Calaveras faults in the San Francisco Bay region, California. These earthquakes came from a catalog of events relocated using the double-difference technique, which provides superior relative locations of nearby events. As a result, structures such as fault surfaces and alignments of events along these surfaces are more sharply defined than in previous catalogs.

Simpson, Robert W.; Graymer, Russell W.; Jachens, Robert C.; Ponce, David A.; Wentworth, Carl M.

2004-01-01

269

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

270

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

271

Earthquake Hazard and Segmented Fault Evolution, Hat Creek Fault, Northern California  

NASA Astrophysics Data System (ADS)

Precise insight into surface rupture and the evolution and mechanical interaction of segmented normal fault systems is critical for assessing the potential seismic hazard. The Hat Creek fault is a ~35 km long, NNW trending segmented normal fault system located on the western boundary of the Modoc Plateau and within the extending backarc basin of the Cascadia subduction zone in northern California. The Hat Creek fault has a prominent surface rupture showing evidence of multiple events in the past 15 ka, although there have been no historic earthquakes. In response to interactions with volcanic activity, the fault system has progressively migrated several km westward, causing older scarps to become seemingly inactive, and producing three distinct, semi-parallel scarps with different ages. The oldest scarp, designated the “Rim”, is the farthest west and has up to 352 m of throw. The relatively younger “Pali” scarp has up to 174 m of throw. The young “Active” scarp has a maximum throw of 65 m in the 24±6 ka Hat Creek basalt, with 20 m of throw in ~15 ka glacial gravels (i.e., a Holocene slip rate of ~1.3 mm/yr). Changes in the geometry and kinematics of the separate scarps during the faulting history imply the orientation of the stress field has rotated clockwise, now inducing oblique right-lateral motion. Previous studies suggested that the Active scarp consists of 7 left-stepping segments with a cumulative length of 23.5 km. We advocate that the Active scarp is actually composed of 8 or 9 segments and extends 4 km longer than previous estimates. This addition to the active portion of the fault is based on detailed mapping of a young surface rupture in the northern portion of the fault system. This ~30 m high young scarp offsets lavas that erupted from Cinder Butte, a low shield volcano, but has a similar geometry and properties as the Active scarp in the Hat Creek basalt. At its northern end, the Active scarp terminates at Cinder Butte. Our mapping indicates that surface rupture undergoes a 4.5 km right-step from the Active scarp west to the Rim, perhaps due to the fault responding to localized volcanic activity at Cinder Butte. The newly mapped segment ruptured repeatedly along the pre-existing Rim, creating a cumulative throw of up to 150 m. The addition of this segment increases the seismic risk in this area. Previous studies suggest that a surface breaking rupture along the Hat Creek fault could produce an earthquake magnitude of at least M 6.0. However, with the increase in rupture length, the fault system has the potential to produce at least a M 6.5. Finally, we consider the importance of deformation within segment overlap zones (relay ramps), which contribute to the distribution of fault throw, and can create inaccurate anomalies in throw profiles if not properly accounted for. Relay ramps tilt either toward the front fault segment or toward the back fault segment. We measure the change in elevation across relay ramps perpendicular to the fault strike to quantify the ramp contribution to fault throw, then incorporate this data into throw profiles to eliminate anomalous peaks or lows where segments overlap. More accurate throw profiles lead to better slip rate estimates for the fault system.

Blakeslee, M. W.; Kattenhorn, S. A.

2010-12-01

272

Mechanics of nonplanar faults at extensional steps with application to the 1992 M 7.3 Landers, California, earthquake  

NASA Astrophysics Data System (ADS)

that rupture across steps between faults can be larger than those predicted from individual fault lengths, making understanding multifault events critical to assessing earthquake hazard. Empirical data from earthquake surface ruptures suggest that the distances between faults that rupture together can range from <1 to 5 km. Dynamic and quasi-static models of planar faults determine similar distances. However, studies of interactions between realistic, 3-D nonplanar faults are few. A general comparison of quasi-static stress perturbations and triggering potentials with mechanical models incorporating either planar or nonplanar faults highlights the sensitivity of planar fault models to model parameters and reveals no clear relationship between mean fault slip and triggering potential. More specifically, planar fault models predict triggering across a 3 km extensional step, while models incorporating nonplanar faults indicate that a connecting fault is necessary to transfer slip through a 3 km step along the 1992 Landers, California earthquake rupture. The mechanical approach taken captures the stress changes as well as the total stress following fault slip, improving the criterion used to determine triggered failure potential. This underscores the need for additional constraint on fault strength and cohesion. The focus on complex fault geometry restricts analyses to the quasi-static realm, limiting the results to fault interactions over the short distances and slow rupture velocities for which the quasi-static stress field is relevant or approximates the dynamic stress field.

Madden, Elizabeth H.; Maerten, Frantz; Pollard, David D.

2013-06-01

273

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

274

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

275

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

276

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

277

The M7 October 21, 1868 Hayward Earthquake, Northern California-140 Years Later  

NASA Astrophysics Data System (ADS)

October 21, 2008 marks the 140th anniversary of the M7 1868 Hayward earthquake. This large earthquake, which occurred slightly before 8 AM, caused extensive damage to San Francisco Bay Area and remains the nation's 12th most lethal earthquake. Property loss was extensive and about 30 people were killed. This earthquake culminated a decade-long series of earthquakes in the Bay Area which started with an M~6 earthquake in the southern Peninsula in 1856, followed by a series of four M5.8 to M6.1 sized earthquakes along the northern Calaveras fault, and ended with a M~6.5 earthquake in the Santa Cruz Mountains in 1865. Despite this flurry of quakes, the shaking from the 1868 earthquake was the strongest that the new towns and growing cities of the Bay Area had ever experienced. The effect on the brick buildings of the time was devastating: walls collapsed in San Francisco, Oakland, and San Jose, and buildings cracked as far away as Napa, Santa Rosa, and Hollister. The area that was strongly shaken (at Modified Mercalli Intensity VII or higher) encompassed about 2,300 km2. Aftershocks continued into November 1868. Surface cracking of the ground along the southern end of the Hayward Fault was traced from Warm Springs in Fremont northward 32 km to San Leandro. As Lawson (1908) reports, "the evidence to the northward of San Leandro is not very satisfactory. The country was then unsettled, and the information consisted of reports of cow- boys riding on the range". Analysis of historical triangulation data suggest that the fault moved as far north as Berkeley, and from these data the average slip along the fault is inferred to be about 1.9 ± 0.4 meters. The paleoseismic record from the southern end of the Hayward Fault provides evidence for 10 earthquakes before 1868. The average interval between these earthquakes is 170 ± 80 years, but the last five earthquakes have had an average interval of only 140 ± 50 years. The 1868 Hayward earthquake and more recent analogs such as the 1995 Kobe earthquake are stark reminders of the awesome energy waiting to be released from below the east side of the San Francisco Bay along the Hayward Fault. The population at risk from a Hayward Fault earthquake is now 100 times larger than in 1868. The infrastructure in the San Francisco Bay Area has been tested only by the relatively remote 1989 M6.9 Loma Prieta earthquake. To help focus public attention on these hazards, the 1868 Hayward Earthquake Alliance has been formed, consisting of public and private sector agencies and corporations (see their website www.1868alliance.org). The Alliance is planning a series of activities leading up to the 140th anniversary on October 21, 2008. These include public forums, conferences, commemoration events, publications, websites, videos, and public service announcements.

Brocher, T. M.; Boatwright, J.; Lienkaemper, J. J.; Schwartz, D. P.; Garcia, S.

2007-12-01

278

Implications of Geodetic Strain Rate for Future Earthquakes, with a Five-Year Forecast of M5 Earthquakes in Southern California  

Microsoft Academic Search

We construct an earthquake likelihood model based on the hypothesis that earthquake frequency and magnitude distribution are related to geodetic strain rate in two ways: a) seismicity rate is steady and proportional to the average horizontal maximum shear strain rate during interseismic time period between large earthquakes; and b) earthquake magnitude distribution is spatially invariant except for an amplitude constant

Zheng-Kang Shen; David D. Jackson; Yan Y. Kagan

2007-01-01

279

Birth of a fault: Connecting the Kern County and Walker Pass, California, earthquakes  

USGS Publications Warehouse

A band of seismicity transects the southern Sierra Nevada range between the northeastern end of the site of the 1952 MW (moment magnitude) 7.3 Kern County earthquake and the site of the 1946 MW 6.1 Walker Pass earthquake. Relocated earthquakes in this band, which lacks a surface expression, better delineate the northeast-trending seismic lineament and resolve complex structure near the Walker Pass mainshock. Left-lateral earthquake focal planes are rotated counterclockwise from the strike of the seismic lineament, consistent with slip on shear fractures such as those observed in the early stages of fault development in laboratory experiments. We interpret this seismic lineament as a previously unrecognized, incipient, currently blind, strike-slip fault, a unique example of a newly forming structure.

Bawden, G. W.; Michael, A. J.; Kellogg, L. H.

1999-01-01

280

Evaluation of Bridge Damage Data from the Loma Prieta and Northridge, California Earthquakes.  

National Technical Information Service (NTIS)

The overall overall objective of this task was to correlate observed bridge damage resulting from the 1989 Loma Prieta and 1994 Northridge earthquake to the local ground motions, bridge structural characteristics, and repair costs and time. Damage states ...

A. S. Kiremidjian N. Basoez

1998-01-01

281

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

282

A seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the 17 January, 1994 Northridge, California earthquake  

Microsoft Academic Search

One of the most significant effects of the 17 January, 1994 Northridge, California earthquake (M=6.7) was the triggering of thousands of landslides over a broad area. Some of these landslides damaged and destroyed homes and other structures, blocked roads, disrupted pipelines, and caused other serious damage. Analysis of the distribution and characteristics of these landslides is important in understanding what

Mario Parise; Randall W. Jibson

2000-01-01

283

Comparisons of Ground Motions from Five Aftershocks of the 1999 Chi-Chi, Taiwan, Earthquake with Empirical Predictions Largely Based on Data from California  

Microsoft Academic Search

The observed ground motions from five large aftershocks of the 1999 Chi-Chi, Taiwan, earthquake are compared with predictions from four equations based primarily on data from California. The four equations for active tectonic re- gions are those developed by Abrahamson and Silva (1997), Boore et al. (1997), Campbell (1997, 2001), and Sadigh et al. (1997). Comparisons are made for horizontal-component

Guo-Quan Wang; David M. Boore; Heiner Igel; Xi-Yuan Zhou

2004-01-01

284

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

285

The Magnitude 6.7 Northridge, California, Earthquake of 17 January 1994  

Microsoft Academic Search

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

1994-01-01

286

Paleoseismic evidence of clustered earthquakes on the San Andreas fault in the Carrizo Plain, California  

SciTech Connect

Exposures we have excavated across the San Andreas fault contradict the hypothesis that part of the fault in the Carrizo Plain is unusually strong and experiences relatively infrequent rupture. The exposures record evidence of at least seven surface-rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in-situ plants. Five large earthquakes have occurred since 1218 A.D. The most recent earthquake, event A, was the 1857 Fort Tejon earthquake, which we have associated with 6.6-10 m of dextral slip along the main fault trace. The penultimate earthquake, event B, most likely occurred within the period A.D. 1405-1510. Slip from either events B and C combined or from event B alone, totals 7-11 m. Three earthquakes, events C, D, and E, occurred in a temporal cluster prior to event B and after approximately A.D. 1218. The average recurrence interval within this cluster is 73-116 years, depending on assumptions. Events F and G occurred after 200 years B.C. A depositional hiatus between events E and F may hide evidence of additional earthquakes. Events B and D within the Carrizo cluster of A.D. 1218-1510 may correlate with events T (A.D. 1329-1363) and V (A.D. 1465-1495) at Pallett Creek on the Mojave `segment` of the fault. This suggests two fault ruptures similar in length to that of 1857. Events C and E apparently did not rupture the Mojave section, which suggests that the Carrizo segment has ruptured independently or in combination with segments to the north. Irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic `supercycles.`

Grant, L.B.; Sieh, K. [California Institute of Technology, Pasadena, CA (United States)

1994-04-01

287

Surface Displacement of the 17 May 1993 Eureka Valley, California, Earthquake Observed by SAR Interferometry  

Microsoft Academic Search

Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The ±3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification

Gilles Peltzer; Paul Rosen

1995-01-01

288

The dependence of peak horizontal acceleration on magnitude, distance, and site effects for small-magnitude earthquakes in California and eastern North America  

USGS Publications Warehouse

One-hundred and ninety free-field accelerograms recorded on deep soil (>10 m deep) were used to study the near-source scaling characteristics of peak horizontal acceleration for 91 earthquakes (2.5 ??? ML ??? 5.0) located primarily in California. An analysis of residuals based on an additional 171 near-source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower acclerations, and that free-field accelerograms recorded on shallow soil (???10 m deep) have 82 per cent higher accelerations than free-field accelerograms recorded on deep soil. An analysis of residuals based on 27 selected strong-motion recordings from 19 earthquakes in Eastern North America indicated that near-source accelerations associated with frequencies less than about 25 Hz are consistent with predictions based on attenuation relationships derived from California. -from Author

Campbell, K. W.

1989-01-01

289

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

290

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

SciTech Connect

Examination of main shock and microearthquake data from the Calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8-9 km near the base of the zone of microearthquakes. The spatial pattern of pre-main shock microseismicity surrounding the Coyote Lake and Morgan Hill hypocenters is similar to the pattern of the post-main shock microseismicity. Microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones. Estimates of the fault regions which slipped during the Coyote Lake Morgan Hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic. The authors propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes. From the pattern of microearthquake locations they recognize six aseismic zones where they expect future main shocks will rupture the Calaveras fault. From an analysis of historic seismic data they establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next M > 5 earthquakes. The first zone is located near Gilroy and was last ruptured by a M5.2 earthquake in 1949. The second zone is located south of Calaveras Reservoir and north of the 1988 M5.1 Alum Rock earthquake. It has not slipped seismically since at least 1903, and the size of the aseismic region is sufficiently large to sustain a M5.5 earthquake.

Oppenheimer, D.H.; Bakun, W.H.; Lindh, A.G. (Geological Survey, Menlo Park, CA (United States))

1990-06-10

291

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

NASA Astrophysics Data System (ADS)

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 M L =5.3 and M L =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 M L =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 M L =5.2 and M L =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.

Burford, Robert O.

1988-06-01

292

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

293

Statistical analysis of the induced Basel 2006 earthquake sequence: introducing a probability-based monitoring approach for Enhanced Geothermal Systems  

NASA Astrophysics Data System (ADS)

Geothermal energy is becoming an important clean energy source, however, the stimulation of a reservoir for an Enhanced Geothermal System (EGS) is associated with seismic risk due to induced seismicity. Seismicity occurring due to the water injection at depth have to be well recorded and monitored. To mitigate the seismic risk of a damaging event, an appropriate alarm system needs to be in place for each individual experiment. In recent experiments, the so-called traffic-light alarm system, based on public response, local magnitude and peak ground velocity, was used. We aim to improve the pre-defined alarm system by introducing a probability-based approach; we retrospectively model the ongoing seismicity in real time with multiple statistical forecast models and then translate the forecast to seismic hazard in terms of probabilities of exceeding a ground motion intensity level. One class of models accounts for the water injection rate, the main parameter that can be controlled by the operators during an experiment. By translating the models into time-varying probabilities of exceeding various intensity levels, we provide tools which are well understood by the decision makers and can be used to determine thresholds non-exceedance during a reservoir stimulation; this, however, remains an entrepreneurial or political decision of the responsible project coordinators. We introduce forecast models based on the data set of an EGS experiment in the city of Basel. Between 2006 December 2 and 8, approximately 11 500 m3 of water was injected into a 5-km-deep well at high pressures. A six-sensor borehole array, was installed by the company Geothermal Explorers Limited (GEL) at depths between 300 and 2700 m around the well to monitor the induced seismicity. The network recorded approximately 11 200 events during the injection phase, more than 3500 of which were located. With the traffic-light system, actions where implemented after an ML 2.7 event, the water injection was reduced and then stopped after another ML 2.5 event. A few hours later, an earthquake with ML 3.4, felt within the city, occurred, which led to bleed-off of the well. A risk study was later issued with the outcome that the experiment could not be resumed. We analyse the statistical features of the sequence and show that the sequence is well modelled with the Omori-Utsu law following the termination of water injection. Based on this model, the sequence will last 31+29/-14 years to reach the background level. We introduce statistical models based on Reasenberg and Jones and Epidemic Type Aftershock Sequence (ETAS) models, commonly used to model aftershock sequences. We compare and test different model setups to simulate the sequences, varying the number of fixed and free parameters. For one class of the ETAS models, we account for the flow rate at the injection borehole. We test the models against the observed data with standard likelihood tests and find the ETAS model accounting for the on flow rate to perform best. Such a model may in future serve as a valuable tool for designing probabilistic alarm systems for EGS experiments.

Bachmann, C. E.; Wiemer, S.; Woessner, J.; Hainzl, S.

2011-08-01

294

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

295

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

296

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

SciTech Connect

As part of the contract with the US Department of Energy, Nevada Operations Office (DOE/NV), URS/John A. Blume & Associates, Engineers (URS/Blume) maintained a network of seismographs to monitor the ground motion generated by the underground nuclear explosions (UNEs) at the Nevada Test Site (NTS). The seismographs were located in the communities surrounding the NTS and the Las Vegas valley. When these seismographs were not used for monitoring the UNE generated motions, a limited number of seismographs were maintained for monitoring motion generated by other than UNEs (e.g. motion generated by earthquakes, wind, blast). Scotty`s Castle was one of the selected earthquake monitoring station. During the period from 1982 through 1993, numerous earthquakes with varied in magnitudes and distances were recorded at Scotty`s Castle. The records from 24 earthquakes were processed and included in this report. Tables 1 and 2 lists the processed earthquakes in chronological order and in the order of epicentral distances, respectively. Figure 1 shows these epicenters and magnitudes. Due to the potential benefit of these data for the scientific community, DOE/NV and the National Park Service authorize the release of these records.

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

1993-10-01

297

Preseismic and coseismic deformation associated with the Coyote Lake, California, earthquake.  

USGS Publications Warehouse

The Coyote Lake earthquake (ML=5.9; August 6, 1979; epicenter c100 km SE of San Francisco) occurred on the Calaveras fault within a geodetic network that had been surveyed annually since 1972 to monitor strain accumulation. The rupture surface as defined by aftershocks is a vertical rectangle 20 km in length extending from a depth of 4 km to c12 km. The observed deformation of the geodetic network constrains the average slip to be 0.33 + or - 0.05m right lateral. Although the geodetic data furnished an exceptionally detailed picture of the pre-earthquake deformation, no significant premonitory anomaly associated with the Coyote Lake earthquake can be identified.-Authors

King, N. E.; Savage, J. C.; Lisowski, M.; Prescott, W. H.

1981-01-01

298

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

299

The 1989 earthquake swarm beneath Mammoth Mountain, California: an initial look at the 4 May through 30 September activity  

USGS Publications Warehouse

Mammoth Mountain is a 50 000- to 200 000-yr-old cumulovolcano standing on the southwestern rim of Long Valley in eastern California. On 4 May 1989, two M=1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months. In addition to its longevity, noteworthy aspects of this persistent swarm are described. These aspects of the swarm, together with its location along the southern extension of the youthful Mono-Inyo volcanic chain, which last erupted 500 to 600 yr ago, point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath Mammoth Mountain. -from Authors

Hill, D. P.

1990-01-01

300

Low stress-drop earthquakes in the light of new data from the Anza, California telemetered digital array  

NASA Astrophysics Data System (ADS)

Recent data from the Anza, California array (10 station 3-component 16 bit 250 samples per second, digitally telemetered array) offer the opportunity to test explanations of one of the earliest observations of high resolution spectral analysis of small earthquakes, namely the existence of small low stress drop events intermixed with events with stress drops comparable to expected effective stresses. Preliminary analysis of the Anza data suggests that the partial stress drop model of Brune (1970) may be an explanation for these events, but the results are somewhat confused by unknown attenuation effects, site effects, and possible contamination of spectra (for smaller events). It is suggested that very high stress drop events (>300 bars) may represent a third type of event where high stresses are caused by rapid quasi-static strain buildup.

Brune, James N.; Fletcher, Joe; Vernon, Frank; Haar, Linda; Hanks, Tom; Berger, Jon

301

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

302

Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day Earthquake, Hollister, California  

NASA Astrophysics Data System (ADS)

Seven weeks prior to the M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, an anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods of reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three, of the six stations analysed. Such changes have not been seen either previously or subsequently. The largest variation occurred at the two stations closest to the earthquake, but a change also occurred at a station 44 km to the south.

Davis, Paul M.; Jackson, David D.; Johnston, Malcolm J. S.

1980-07-01

303

Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day earthquake, Hollister, California  

SciTech Connect

Seven weeks prior to he M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, and anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods or reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three of the six stations analysed. Such changes have not been seen either previously or subsequently. The largest variation occurred at the two stations closest to the earthquake, but a change also occurred at a station 44 km to the south.

Davis, P.M.; Jackson, D.D.; Johnston, M.J.S.

1980-07-01

304

Viscoelastic flow in the lower crust after the 1992 landers, california, earthquake  

PubMed

Space geodesy showed that broad-scale postseismic deformation occurred after the 1992 Landers earthquake. Three-dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation, whereas viscoelastic flow can explain the horizontal and near-vertical displacements. The viscosity of a weak, about 10-km-thick layer, in the lower crust beneath the rupture zone that controls the rebound is about 10(18) pascal seconds. The viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the Basin and Range province and it may be used for the analysis of earthquake hazard. PMID:9831556

Deng; Gurnis; Kanamori; Hauksson

1998-11-27

305

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

306

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

307

Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day earthquake, Hollister, California  

Microsoft Academic Search

Seven weeks prior to he M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, and anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods or reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three of

Paul M. Davis; David D. Jackson; Malcolm J. S. Johnston

1980-01-01

308

Nonlinear soil response as a natural passive isolation mechanism—the 1994 Northridge, California, earthquake  

Microsoft Academic Search

The spatial relationship between areas with severely damaged (red-tagged) buildings and areas with large strains in the soil (indicated by reported breaks in the water distribution system), observed during the 1994 Northridge earthquake, is analysed. It is shown that these areas can be separated almost everywhere. Minimal overlapping is observed only in the regions with very large amplitudes of shaking

M. D. Trifunac; M. I. Todorovska

1998-01-01

309

The 1994 Northridge earthquake sequence in California: Seismological and tectonic aspects  

Microsoft Academic Search

The Mw 6.7 Northridge earthquake occurred on January 17, 1994, beneath the San Fernando Valley. Two seismicity clusters, located 25 km to the south and 35 km to the north-northwest, preceded the mainshock by 7 days and 16 hours, respectively. The mainshock hypocenter was relatively deep, at 19 km depth in the lower crust. It had a thrust faulting focal

Egill Hauksson; Lucile M. Jones; Kate Hutton

1995-01-01

310

Linearized inversion for fault rupture behavior: Application to the 1984 Morgan Hill, California, earthquake  

Microsoft Academic Search

We present a technique to infer the rupture history of an earthquake from near-source records of ground motion. Unlike most previous studies, each point on the fault is assumed to slip only once, when the rupture front passes, with a spatially variable slip intensity. In this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture

Gregory C. Beroza; Paul Spudich

1988-01-01

311

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

312

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

313

Probability of chance correlations of earthquakes with predictions in areas of heterogeneous seismicity rate: the VAN case  

Microsoft Academic Search

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

M. Wyss; A. Allmann

1996-01-01

314

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

315

Triggered Fault Slip in Southern California Associated with the 2010 Sierra El Mayor-Cucapah, Baja California, Mexico, Earthquake  

NASA Astrophysics Data System (ADS)

Surface fracturing (triggered slip) occurred in the central Salton Trough and to the southwest, in the Yuha Desert area—all in association with the 4 April 2010 (M7.2) El Mayor-Cucapah earthquake and its aftershocks. Triggered slip in the central Salton Trough occurred on the ‘frequent movers’: the southern San Andreas, Coyote Creek, Superstition Hills, and Imperial Faults, all of which have slipped in previous moderate to large, local and regional earthquakes in the past five decades. Other faults in the central Salton Trough that also slipped in 2010 include the Wienert Fault (southeastern section of the Superstition Hills Fault), the Kalin Fault (in the Brawley Seismic Zone), and the Brawley Fault Zone; triggered slip had not been reported on these faults in the past. Geologic measures of slip on faults in the central Salton Trough ranged from 1 to 18 mm, and everywhere was located where previous primary (tectonic) or triggered slip has occurred. Triggered slip in the Yuha Desert area occurred along at least two dozen faults, only some of which were known before the 4 April 2010 El Mayor-Cucapah earthquake. From east to northwest, slip occurred in seven general areas; 1) in the Northern Centinela Fault Zone (newly named), 2) along unnamed faults south of Pinto Wash, 3) along the Yuha Fault (newly named), 4) along both east and west branches of the Laguna Salada Fault, 5) along the Yuha Well Fault Zone (newly revised name), 6) along the Ocotillo Fault (newly named), and 7) along the southeastern-most section of the Elsinore Fault. Faults that slipped in the Yuha Desert area include northwest-trending right-lateral faults, northeast-trending left-lateral faults, and north-south faults, some of which had dominantly vertical slip. Triggered slip along the Ocotillo and Elsinore Faults occurred only in association with the 14 June 2010 (M5.7) aftershock, which also initiated slip along other faults near the town of Ocotillo. Triggered slip on faults in the Yuha Desert area was most commonly less than 20 mm, but two significant exceptions are slip of about 50-60 mm on the Yuha Fault and of about 80 mm on the Ocotillo Fault. All triggered slips in the Yuha Desert area occurred along pre-existing faults, whether previously recognized or not.

Rymer, M. J.; Treiman, J. A.; Kendrick, K. J.; Lienkaemper, J. J.; Wei, M.; Weldon, R. J.; Bilham, R. G.; Fielding, E. J.

2010-12-01

316

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

317

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

318

Long Return Periods for Earthquakes in San Gorgonio Pass and Implications for Large Ruptures of the San Andreas Fault in Southern California  

NASA Astrophysics Data System (ADS)

The largest discontinuity in the surface trace of the San Andreas fault occurs in southern California at San Gorgonio Pass. Here, San Andreas motion moves through a 20 km-wide compressive stepover on the dextral-oblique-slip thrust system known as the San Gorgonio Pass fault zone. This thrust-dominated system is thought to rupture during very large San Andreas events that also involve strike-slip fault segments north and south of the Pass region. A wealth of paleoseismic data document that the San Andreas fault segments on either side of the Pass, in the San Bernardino/Mojave Desert and Coachella Valley regions, rupture on average every ~100 yrs and ~200 yrs, respectively. In contrast, we report here a notably longer return period for ruptures of the San Gorgonio Pass fault zone. For example, features exposed in trenches at the Cabezon site reveal that the most recent earthquake occurred 600-700 yrs ago (this and other ages reported here are constrained by C-14 calibrated ages from charcoal). The rupture at Cabezon broke a 10 m-wide zone of east-west striking thrusts and produced a >2 m-high scarp. Slip during this event is estimated to be >4.5 m. Evidence for a penultimate event was not uncovered but presumably lies beneath ~1000 yr-old strata at the base of the trenches. In Millard Canyon, 5 km to the west of Cabezon, the San Gorgonio Pass fault zone splits into two splays. The northern splay is expressed by 2.5 ± 0.7 m and 5.0 ± 0.7 m scarps in alluvial terraces constrained to be ~1300 and ~2500 yrs old, respectively. The scarp on the younger, low terrace postdates terrace abandonment ~1300 yrs ago and probably correlates with the 600-700 yr-old event at Cabezon, though we cannot rule out that a different event produced the northern Millard scarp. Trenches excavated in the low terrace reveal growth folding and secondary faulting and clear evidence for a penultimate event ~1350-1450 yrs ago, during alluvial deposition prior to the abandonment of the low terrace. Subtle evidence for a third event is poorly constrained by age data to have occurred between 1600 and 2500 yrs ago. The southern splay at Millard Canyon forms a 1.5 ± 0.1 m scarp in an alluvial terrace that is inset into the lowest terrace at the northern Millard site, and therefore must be < ~1300 yrs old. Slip on this fault probably occurred during the most recent rupture in the Pass. In summary, we think that the most recent earthquake occurred 600-700 yrs ago and generated ~6 m of slip on the San Gorgonio Pass fault zone. The evidence for two older earthquakes is less complete but suggests that they are similar in style and magnitude to the most recent event. The available data therefore suggest that the San Gorgonio Pass fault zone has produced three large (~6 m) events in the last ~2000 yrs, a return period of ~700 yrs assuming that the next rupture is imminent. We prefer a model whereby a majority of San Andreas fault ruptures end as they approach the Pass region from the north or the south (like the Wrightwood event of A.D. 1812 and possibly the Coachella Valley event of ~A.D. 1680). Relatively rare (once-per-millennia?), through-going San Andreas events break the San Gorgonio Pass fault zone and produce the region's largest earthquakes.

Yule, J.; McBurnett, P.; Ramzan, S.

2011-12-01

319

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

320

Earthquake response  

NASA Astrophysics Data System (ADS)

The Loma Prieta earthquake in northern California gave geophysicists an unexpected chance to mobilize a team to take portable seismographs to an earthquake region. The magnitude-7.1 earthquake occurred Tuesday, October 17 at 5:04 P.M. Pacific Daylight Time. Less than 48 hours after the main shock, IRIS consortium seismologists from Lamont-Doherty Geological Observatory in Palisades, N.Y., were setting up new, portable equipment around San Francisco.The ability to move quickly to the earthquake area was an unanticipated bonus of two National Science Foundation programs: IRIS, the Incorporated Research Institutions for Seismology in Arlington, Va., and NCEER, the National Center for Earthquake Engineering Research in Buffalo, N.Y.

Simpson, David; Hough, Susan; Lerner-Lam, Arthur; Phinney, Robert

321

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

322

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

323

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

324

Triggered slip on the Calaveras Fault during the magnitude 7.1 Loma Prieta, California, Earthquake  

NASA Astrophysics Data System (ADS)

After the magnitude (M) 7.1 Loma Prieta earthquake on the San Andreas fault we inspected selected sites along the Calaveras fault for evidence of recent surface displacement. In two areas along the Calaveras fault we documented recent right-lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep. The areas are in the city of Hollister and at Highway 152 near San Felipe Lake, located approximately 25 km southeast and 18 km northeast, respectively, of the nearest part of the San Andreas rupture zone. On the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the Loma Prieta mainshock. We conclude that this earthquake on the San Andreas fault triggered surface rupture along at least a 17-km-long segment of the Calaveras fault. These geologic observations extend evidence of triggered slip from instrument stations within this zone of Calaveras fault rupture.

McClellan, P. H.; Hay, E. A.

325

Seismicity in the twenty years preceding the Loma Prieta, California earthquake  

SciTech Connect

Persistent seismicity occurred at a low rate during at least the twenty years before the Loma Prieta earthquake along the 60 km-long rupture zone. The depth distribution of this seismicity forms a broad U-shape that delineates the previously locked rupture zone. Relocations of seismicity during the ten years before the earthquake relative to the Loma Prieta aftershocks show that this U-shaped distribution can be partitioned lengthwise into activity on two adjacent subparallel structures: a vertical fault beneath the San Andreas fault trace and an eastward-dipping blind fault beneath the Sargent fault trace. The 11-18 km deep, southwest-dipping part of the Loma Prieta rupture was not active during at least the preceding ten years. The slip geometry of intersecting fault structures in this zone could contribute to both the preparation process and the complexity of the rupture.

Olson, J.A. (Geological Survey, Menlo Park, CA (USA))

1990-08-01

326

Triggered slip on the Calaveras fault during the magnitude 7. 1 Loma Prieta, California, earthquake  

SciTech Connect

After the magnitude (M) 7.1 Loma Prieta earthquake on the San Andreas fault the authors inspected selected sites along the Calaveras fault for evidence of recent surface displacement. In two areas along the Calaveras fault they documented recent right-lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep. The areas are in the city of Hollister and at Highway 152 near San Felipe Lake, located approximately 25 km southeast and 18 km northeast, respectively, of the nearest part of the San Andreas rupture zone. On the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the Loma Prieta mainshock. They conclude that this earthquake on the San Andreas fault triggered surface rupture along at least a 17-km-long segment of the Calaveras fault. These geologic observations extend evidence of triggered slip from instrument stations within this zone of Calaveras fault rupture.

McClellan, P.H.; Hay, E.A.

1990-07-01

327

Fault-plane solutions for microearthquakes preceding the Thanksgiving Day, 1974, earthquake at Hollister, California  

Microsoft Academic Search

Fault-plane solutions were obtained for 80 microearthquakes in a 900-km2 area centered on the Busch fault during a 1-year period preceding the Thanksgiving Day, 1974, Hollister, Calif., earthquake. Strike-slip motion occurred in 64 of these quakes, mainly at active points on the Sargent, Castro, Busch, and Calaveras faults. Eleven of the solutions are thrust type, and five are normal. No

David H. Warren

1979-01-01

328

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

Microsoft Academic Search

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

Stephen Hartzell; Pengcheng Liu; Carlos Mendoza

1996-01-01

329

Postseismic relaxation following the 1994 Mw6.7 Northridge earthquake, southern California  

NASA Astrophysics Data System (ADS)

We have reexamined the postearthquake deformation of a 65 km long linear array of 11 geodetic monuments extending north-south across the rupture (reverse slip on a blind thrust dipping 40°S-20°W) associated with the 1994 Mw6.7 Northridge earthquake. That array was surveyed frequently in the interval from 4 to 2650 days after the earthquake. The velocity of each of the monuments over the interval 100-2650 days postearthquake appears to be constant. Moreover, the profile of those velocities along the length of the array is very similar to a preearthquake velocity profile for a nearby, similarly oriented array. We take this to indicate that significant postseismic relaxation is evident only in the first 100 days postseismic and that the subsequent linear trend is typical of the interseismic interval. The postseismic relaxation (postseismic displacement less displacement that would have occurred at the preseismic velocity) is found to be almost wholly parallel (N70°W) to the nearby (40 km) San Andreas Fault with only negligible relaxation in the direction of coseismic slip (N20°E) on the Northridge rupture. We suggest that the N70°W relaxation is caused by aseismic, right-lateral slip at depth on the San Andreas Fault, excess slip presumably triggered by the Northridge rupture. Finally, using the Dieterich (1994) stress-seismicity relation, we show that return to the preseismic deformation rate within 100 days following the earthquake could be consistent with the cumulative number of M > 2.5 earthquakes observed following the main shock.

Savage, J. C.; Svarc, J. L.

2010-12-01

330

Magmatic resurgence in Long Valley caldera, California: Possible cause of the 1980 Mammoth Lakes earthquakes  

USGS Publications Warehouse

Changes in elevation between 1975 and October 1980 along a leveling line across the Long Valley caldera indicate a broad (half-width, 15 kilometers) uplift (maximum, 0.25 meter) centered on the old resurgent dome. This uplift is consistent with reinflation of a magma reservoir at a depth of about 10 kilometers. Stresses generated by this magmatic resurgence may have caused the sequence of four magnitude 6 earthquakes near Mammoth Lakes in May 1980. Copyright ?? 1982 AAAS.

Savage, J. C.; Clark, M. M.

1982-01-01

331

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

332

The use of geologic and seismologic information to reduce earthquake Hazards in California  

NASA Astrophysics Data System (ADS)

Five examples illustrate how geologic and seismologic information can be used to reduce the effects of earthquakes Included are procedures for anticipating damage to critical facilities, preparing, adopting, or implementing seismic safety studies, plans, and programs, retrofitting highway bridges, regulating development in areas subject to fault-rupture, and strengthening or removing unreinforced masonry buildings. The collective effect of these procedures is to improve the public safety, health, and welfare of individuals and their communities.

Kockelman, William J.; Campbell, Catherine C.

1984-06-01

333

Three-dimensional imaging of active structures using earthquake aftershocks: the Northridge thrust, California  

Microsoft Academic Search

Aftershocks of the 1994 Northridge earthquake (M6.8) allow us to image the structure beneath the San Fernando Valley in northwestern Los Angeles in three dimensions. We combine aftershocks and geological data to build an image of the three-dimensional (3-D) geometry of the previously unrecognized, north-vergent Northridge blind thrust to a depth of 21km. The most striking feature of the imaged

S. Carena; J. Suppe

2002-01-01

334

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

335

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. 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, David R.; Hill, David P.

2011-10-01

336

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

337

Toward petascale earthquake simulations  

Microsoft Academic Search

Earthquakes are among the most complex terrestrial phenomena, and modeling of earthquake dynamics is one of the most challenging\\u000a computational problems in science. Computational capabilities have advanced to a state where we can perform wavefield simulations\\u000a for realistic three-dimensional earth models, and gain more insights into the earthquakes that threaten California and many\\u000a areas of the world. The Southern California

Yifeng Cui; Reagan Moore; Kim Olsen; Amit Chourasia; Philip Maechling; Bernard Minster; Steven Day; Yuanfang Hu; Jing Zhu; Thomas Jordan

2009-01-01

338

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

339

The Prediction of Damage to Buildings by Earthquake in the Residential Zones of Colima, México, From the Damage Probability Matrix and its Test by the 2003 Mw 7.5 Earthquake  

NASA Astrophysics Data System (ADS)

The damage probability matrix was calculated for the Colima, México masonry (Zobin and Ventura-Ramírez, 1999) for three residential zones and for the earthquakes of intensity MM of VI to IX (Mercalli Modify Scale). The Mw 7.5 earthquake of 21 January 2003 that occurred within the Mexican subduction zone had tested this prediction. The macroseismic investigation of damage produced by the earthquake in Colima city was realized for 3,332 constructions within the area of study representing about 20 per cent of the total city area and covered with the different type of constructions. The 7-grade scale of damage was used to describe the damage distribution. The damage matrix, constructed for the area, showed that the damage distribution varied from 63 per cent for constructions with relatively slight damages (grades 1 to 3) for 29 per cent to constructions that had significant damages (grades 4 to 5) and 8 per cent for completely destructed or demolished masonry. The damage matrix, constructed for 12 subzones of the area of study, reflected two tendencies in the damage distributions: the predominance of slight damage to the recent constructions situated in the northern and eastern parts of the area and the predominance of significant damage to the older constructions in the southern and western parts of the area. It was observed a significant dependence of damage index upon the age of constructions and the type of masonry. The observed damage matrix was in a good accordance with the 1999 damage probability matrix (MM VII) for two zones of three where the prediction was done.

Zobin, V. M.

2007-05-01

340

Processed seismic motion records from Desert Hot Springs, California earthquake of April 22, 1992, recorded at seismic stations in southern Nevada  

SciTech Connect

The 8mm data tape contains the processed seismic data of the Desert Hot Springs, California earthquake of April 22nd, 1992. The seismic data were recorded by 19 seismographs maintained by the DOE/NV in Southern Nevada. Four files were generated from each seismic recorder. They are ``Uncorrected acceleration time histories, 2. corrected acceleration, velocity and displacement time histories, 3. pseudo response velocity spectra and 4. Fourier amplitude spectra of acceleration.

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

1993-04-01

341

Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake  

Microsoft Academic Search

Results of two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, are presented. Both surveys were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (ML=5.3, epicenter 1.5km west from the building site) and its early aftershocks. The first survey was conducted on 4 and 5 February 1994, and

S. s. Ivanovic; M. d. Trifunac; E. i. Novikova; A. a. Gladkov; M. i. Todorovska

2000-01-01

342

Stochastic Finite-Fault Modeling of Ground Motions from the 1994 Northridge, California, Earthquake. II. Widespread Nonlinear Response at Soil Sites  

Microsoft Academic Search

On average, soil sites behaved nonlinearly during the M 6.7 1994 North- ridge, California, earthquake. This conclusion follows from an analysis that combines elements of two independent lines of investigation. First, we apply the stochastic finite-fault simulation method, calibrated with 28 rock-site recordings of the North- ridge mainshock, to the simulation of the input motions to the soil sites that

Igor A. Beresnev; Gail M. Atkinson; Paul A. Johnson; Edward H. Field

1998-01-01

343

Coseismic deformation field of the M=6.7 Northridge, California earthquake of January 17, 1994 recorded by two radar satellites using interferometry  

Microsoft Academic Search

Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS-1 and JERS-1 satellites before and after the Northridge, California earthquake of January 17, 1994 provide two maps of the coseismic deformation field. The fringes corresponding to contours of equal change in satellite-to-ground distance show the coseismic displacement of the mainshock. The fringe patterns remain clear for

Didier Massonnet; Kurt L. Feigl; Hélène Vadon; Marc Rossi

1996-01-01

344

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

345

Survey of strong motion earthquake effects on thermal power plants in California with emphasis on piping systems. Volume 1, Main report  

SciTech Connect

Since 1982, there has been a major effort expended to evaluate the susceptibility of nuclear Power plant equipment to failure and significant damage during seismic events. This was done by making use of data on the performance of electrical and mechanical equipment in conventional power plants and other similar industrial facilities during strong motion earthquakes. This report is intended as an extension of the seismic experience data collection effort and a compilation of experience data specific to power plant piping and supports designed and constructed US power piping code requirements which have experienced strong motion earthquakes. Eight damaging (Richter Magnitude 7.7 to 5.5) California earthquakes and their effects on 8 power generating facilities in use natural gas and California were reviewed. All of these facilities were visited and evaluated. Seven fossel-fueled (dual use natural gas and oil) and one nuclear fueled plants consisting of a total of 36 individual boiler or reactor units were investigated. Peak horizontal ground accelerations that either had been recorded on site at these facilities or were considered applicable to these power plants on the basis of nearby recordings ranged between 0.20g and 0.5lg with strong motion durations which varied from 3.5 to 15 seconds. Most US nuclear power plants are designed for a safe shutdown earthquake peak ground acceleration equal to 0.20g or less with strong motion durations which vary from 10 to 15 seconds.

Stevenson, J.D. [Stevenson and Associates, Cleveland, OH (United States)

1995-11-01

346

Northridge, California, earthquake of 1994: density of pipe breaks and surface strains  

Microsoft Academic Search

Empirical scaling equations are presented which relate the average number of water pipe breaks per km2, n, with the peak strain in the soil or intensity of shaking at the site. These equations are based on contour maps of peak surface strain evaluated from strong motion recordings, and observations of intensity of ground shaking and damage following the Northridge, California,

M. D. Trifunac; M. I. Todorovska

1997-01-01

347

Near-fault measurement of postseismic slip associated with the 1989 Loma Prieta, California, earthquake  

SciTech Connect

Five small-aperture (0.5 to 7.7 m) quadrilaterals were installed across the San Andreas fault and newly formed extensional cracks shortly after the October 17, 1989 Loma Prieta M7.1 earthquake. Two quadrilaterals were installed across the San Andreas fault near the southeast and northwest ends of the 1989 rupture, and three were installed across dominantly extensional cracks in the Summit Road area near the main-shock epicenter and off the San Andreas fault. Measurements of line-length changes from as early as 4 d up to 184 d after the earthquake in the nail quadrilaterals indicate a small amount of right-lateral postseismic slip on the San Andreas fault. The site near the southeast end of the 1989 aftershock zone on the San Andreas fault showed about 5{plus minus}2 mm of postseismic right-lateral component of slip in addition to 23 mm of right-lateral coseismic movement. The site near the northwest end of aftershocks likewise showed about 5{plus minus}2 mm of postseismic slip, but after only 5 mm of coseismic slip. Measurements at sites across extensional cracks indicate possible minor left-lateral postseismic slips, and possible extensional/contractional motion. No measurements were made of possible vertical movements. Sites on extensional cracks showed similarly small amounts of possible postseismic lateral slip, from {approximately}2 to 10 mm, even though coseismic lateral slips were much greater (up to 410 mm) than on the surface trace of the San Andreas fault. The small slip values, in spite of uncertainties, clearly show that the lack of coseismic surface slip associated with the earthquake was not followed by large postseismic slip.

Rymer, M.J. (Geological Survey, Menlo Park, CA (USA))

1990-09-01

348

Earthquake stress drops and inferred fault strength on the Hayward Fault, east San Francisco Bay, California  

USGS Publications Warehouse

We study variations in earthquake stress drop with respect to depth, faulting regime, creeping versus locked fault behavior, and wall-rock geology. We use the P-wave displacement spectra from borehole seismic recordings of M 1.0-4.2 earthquakes in the east San Francisco Bay to estimate stress drop using a stack-and-invert empirical Green's function method. The median stress drop is 8.7 MPa, and most stress drops are in the range between 0.4 and 130 MPa. An apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4-55 Hz. There is a trend of increasing stress drop with depth, with a median stress drop of ~5 MPa for 1-7 km depth, ~10 MPa for 7-13 km depth, and ~50 MPa deeper than 13 km. We use S=P amplitude ratios measured from the borehole records to better constrain the first-motion focal mechanisms. High stress drops are observed for a deep cluster of thrust-faulting earthquakes. The correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress. We compare the spatial distribution of stress drops on the Hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near Oakland. This also suggests a connection between stress drop and applied shear stress, as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher-strength material. The stress drops do not directly correlate with the strength of the proposed wall-rock geology at depth, suggesting that the relationship between fault strength and the strength of the wall rock is complex.

Hardebeck, J. L.; Aron, A.

2009-01-01

349

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

350

Earthquakes, Segments, Bends, and Fault-Face Geology: Correlations Within the San Andreas System, California  

NASA Astrophysics Data System (ADS)

Three-dimensional geologic maps of regions surrounding parts of the San Andreas Fault system reveal correlations between fault face geology and both short- and long-term behavior of the faults. The Loma Prieta fault segment that ruptured during the 1989 M6.9 earthquake, as defined by its aftershocks, closely corresponds to the subsurface reach (80 km long) where a large body of Logan gabbro is truncated at the fault, as defined by its magnetic anomaly. This Jurassic ophiolitic gabbro and its related rocks occupy an unusual fault-bounded basement block within Salinaa, a largely Cretaceous granitic terrane SW of the San Andreas Fault. The along-fault reach of the Logan gabbro also coincides with essentially the entire Santa Cruz Mountains left-bend in the San Andreas Fault. Rejecting a chance coincidence, the position of the Logan gabbro with respect to the left bend implies that the bend is fixed relative to Salinia and that the block NE of the San Andreas Fault has been forced to negotiate around the bend as the blocks moved past each other. Thus the basement rocks of the Logan block appear to define (control?) the Loma Prieta segment in terms both of short-term behavior (earthquakes) and long-term behavior (restraining bend fault geometry). The Parkfield segment of the San Andreas Fault also closely corresponds to a characteristic geologic unit in the NE face of the fault, the greenstone-rich Permanente terrane of the Franciscan Complex. The along-fault subsurface extent of the Permanente terrane at the fault face, as inferred from a recent 3D tomographic wavespeed model, corresponds to the reach filled by the aftershocks of the 2004 Parkfield earthquake. Furthermore, the 2004 co-seismic slip inferred from geodetic observations also coincides with the Permanente terrane at the fault face. To test whether these observations are directly related to the presence of the Permanente terrane along the fault face, we looked at fault behavior at the location of its offset counterpart, which truncates at the Calaveras Fault near Hollister 175 km to the NW. Here, the along-fault subsurface extent of the Permanente terrane, as defined by its gravity and magnetic anomalies, corresponds to the aftershock distribution of the 1979 Coyote Lake earthquake, giving support to the idea that fault-face geology can influence fault behavior and control fault segmentation.

Jachens, R. C.; Simpson, R. W.; Thurber, C. H.; Murray, J. R.

2006-12-01

351

Analecta of structures formed during the 28 June 1992 Landers-Big Bear, California earthquake sequence (including maps of shear zones, belts of shear zones, tectonic ridge, duplex en echelon fault, fault elements, and thrusts in restraining steps).  

National Technical Information Service (NTIS)

The June 28, 1992, M(sub s) 7.5 earthquake at Landers, California, which occurred about 10 km north of the community of Yucca Valley, California, produced spectacular ground rupturing more than 80 km in length (Hough and others, 1993). The ground rupturin...

A. M. Johnson N. A. Johnson K. M. Johnson W. Wei R. W. Fleming

1997-01-01

352

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

USGS Publications Warehouse

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 Mendocino earthquake is the first well-recorded event to relieve strain associated with the Cascadia subduction zone. We use data from three geodetic techniques: (1) the horizontal and vertical displacements of 13 monuments surveyed with the Global Positioning System, corrected for observed horizontal interseismic strain accumulation, (2) 88 section-elevation differences between leveling monuments, and (3) the uplift of 12 coastal sites observed from the die-off of intertidal marine organisms. Maximum observed displacements are 0.4 m of horizontal movement and 1.5 m of uplift along the coast. We use Monte Carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties. The optimal model using all the data resolves 4.9 m of slip on a 14 by 15 km fault that dips 28?? SE. The fault extends from 1.5 to 8.7 km in depth and the main-shock hypocenter is close to the downdip projection of the fault. The shallowly dipping fault plane is consistent with the observed aftershock locations, and the estimated geodetic moment is 3.1??1019 N m, 70% of the seismic moment. Other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry. If the earthquake is characteristic for this segment, the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years, with a 95% confidence range of 100-670 years. The coseismic uplift occurred in a region that also has high Quaternary uplift rates determined from marine terrace studies. If repeated ruptures of this southernmost segment of the Cascadia megathrust are responsible for the Quaternary uplift, a comparison of the coseismic uplift with coastal uplift rates suggests a recurrence interval of 200-400 years. Thus comparing horizontal and vertical coseismic to long-term deformation suggests a recurrence interval of about 100-300 years for M=7 events at the south end of the Cascadia megathrust.

Murray, M. H.; Marshall, G. A.; Lisowski, M.; Stein, R. S.

1996-01-01

353

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

354

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.

355

The 1992 Landers earthquake sequence - Earthquake occurrence and structural heterogeneities  

NASA Astrophysics Data System (ADS)

The June 28, 1992, Mw 7.3 Landers earthquake occurred in the southeastern Mojave Desert, California. Over 10,000 aftershocks of the earthquake were recorded by the Caltech-USGS Southern California Seismic Network (SCSN) in 1992. To investigate the relationship between complexities in the crustal structure and variations in seismicity, we have used a tomographic method to invert 145,098 P wave arrival times from 3740 Landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary SCSN stations. We determined a detailed P wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3D velocity model. The results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities. The higher velocity areas are considered to be strong and brittle parts of the fault zone, which are apt to generate earthquakes. In contrast, low velocity areas are probably more ductile and weaker, allowing aseismic slippage.

Zhao, Dapeng; Kanamori, Hiroo

1993-06-01

356

Implications of Site Effects in the Mexico City Earthquake of September 19, 1985 for Earthquake-Resistant Design Criteria in the San Francisco Bay Area of California.  

National Technical Information Service (NTIS)

One of the most dramatic aspects of the earthquake effects in the Mexico City earthquake of September 19, 1985 was the enormous differences in intensities of shaking and associated building damage in different parts of the city. The report examines the fa...

H. B. Seed J. I. Sun

1989-01-01

357

Late Quaternary uplift and earthquake potential of the San Joaquin Hills, southern Los Angeles basin, California  

Microsoft Academic Search

Analysis of emergent marine terraces in the San Joaquin Hills, California, and 230Th dating of solitary corals from the lowest terraces reveal that the San Joaquin Hills have risen at a rate of 0.21 0.27 m\\/k.y. during the past 122 k.y. Movement on a blind thrust fault in the southern Los Angeles basin has uplifted the San Joaquin Hills and

Lisa B. Grant; Karl J. Mueller; Eldon M. Gath; Hai Cheng; R. Lawrence Edwards; Rosalind Munro; George L. Kennedy

1999-01-01

358

Late Quaternary uplift and earthquake potential of the San Joaquin Hills, southern Los Angeles basin, California  

Microsoft Academic Search

Analysis of emergent marine terraces in the San Joaquin Hills, California, and 230Th dating of solitary corals from the lowest terraces reveal that the San Joaquin Hills have risen at a rate of 0.21-0.27 m\\/k.y. during the past 122 k.y. Movement on a blind thrust fault in the southern Los Angeles basin has uplifted the San Joaquin Hills and has

Lisa B. Grant; Karl J. Mueller; Eldon M. Gath; Hai Cheng; R. Lawrence Edwards; Rosalind Munro; George L. Kennedy

1999-01-01

359

Probability of earthquake occurrence and magnitude estimation in the post shut-in phase of geothermal projects  

NASA Astrophysics Data System (ADS)

Induced seismicity in geothermal projects is observed to continue after shut-in of the fluid injection. Recent experiments show that the largest events tend to occur after the termination of injection. We use a probabilistic approach based on Omori's law and the Gutenberg-Richter magnitude-frequency distribution to demonstrate that the probability of exceeding a certain maximum magnitude still increases after shut-in. This increase is governed by the exponent of Omori's law q and the Gutenberg-Richter b value. For a reduced b value in the post-injection phase, the probability of occurrence directly after shut-in can be even higher than the corresponding probability for an ongoing injection. For the reference case of q = 2 and a 10% probability at shut-in time t S to exceed a given maximum magnitude, we obtain an increase to 14.6% for t = 2t S at a constant Gutenberg-Richter b value after shut-in. A reduction of the b value by one quarter leads to a probability of 20.5%. If we consider a constant probability level of occurrence for an event larger than a given magnitude at shut-in time, this maximum magnitude increases by 0.12 units for t = 2t S (0.26 units for a reduced b value). For the Soultz-sous-Forêts (France) injection experiment in 2000, recent studies reveal q = 9.5 and a b value reduction by 14%. A magnitude 2.3 event 9 h after shut-in falls in the phase with a probability higher than for the continued injection. The probability of exceeding the magnitude of this post-injection event is determined to 97.1%.

Barth, Andreas; Wenzel, Friedemann; Langenbruch, Cornelius

2011-12-01

360

Probability of earthquake occurrence and magnitude estimation in the post shut-in phase of geothermal projects  

NASA Astrophysics Data System (ADS)

Induced seismicity in geothermal projects is observed to continue after shut-in of the fluid injection. Recent experiments show that the largest events tend to occur after the termination of injection. We use a probabilistic approach based on Omori's law and the Gutenberg-Richter magnitude-frequency distribution to demonstrate that the probability of exceeding a certain maximum magnitude still increases after shut-in. This increase is governed by the exponent of Omori's law q and the Gutenberg-Richter b value. For a reduced b value in the post-injection phase, the probability of occurrence directly after shut-in can be even higher than the corresponding probability for an ongoing injection. For the reference case of q = 2 and a 10% probability at shut-in time t S to exceed a given maximum magnitude, we obtain an increase to 14.6% for t = 2 t S at a constant Gutenberg-Richter b value after shut-in. A reduction of the b value by one quarter leads to a probability of 20.5%. If we consider a constant probability level of occurrence for an event larger than a given magnitude at shut-in time, this maximum magnitude increases by 0.12 units for t = 2 t S (0.26 units for a reduced b value). For the Soultz-sous-Forêts (France) injection experiment in 2000, recent studies reveal q = 9.5 and a b value reduction by 14%. A magnitude 2.3 event 9 h after shut-in falls in the phase with a probability higher than for the continued injection. The probability of exceeding the magnitude of this post-injection event is determined to 97.1%.

Barth, Andreas; Wenzel, Friedemann; Langenbruch, Cornelius

2013-01-01

361

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

362

Postseismic deformation associated with the 1992 M ?=7.3 Landers earthquake, southern California  

NASA Astrophysics Data System (ADS)

Following the 1992 M?=7.3 Landers earthquake, a linear array of 10 geodetic monuments at roughly 5-km spacing was established across the Emerson fault segment of the Landers rupture. The array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it. The array was surveyed by Global Positioning System 0.034, 0.048, 0.381, 1.27, 1.88, 2.60, and 3.42 years after the Landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation. The temporal behavior is described roughly by a short-term (decay time 84±23 days) exponential relaxation superimposed upon an apparently linear trend. Because the linear trend represents motions much more rapid than the observed preseismic motions, we attribute that trend to a slower (decay time greater than 5 years) postseismic relaxation, the curvature of which cannot be resolved in the short run (3.4 years) of postseismic data. About 100 mm of right-lateral displacement and 50 mm of fault-normal displacement accumulated across the geodetic array in the 3.4-year interval covered by the postseismic surveys. Those displacements are attributed to postseismic, right-lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace. The right-lateral slip amounted to about 1 m directly beneath the geodetic array, and the fault-normal displacement is apparently primarily a consequence of the curvature of the rupture. These conclusions are based upon dislocation models fit to the observed deformation. However, no dislocation model was found with rms residuals as small as the expected observational error.

Savage, J. C.; Svarc, J. L.

1997-04-01

363

Deep Structure Of Long Valley, California, Based On Deep Reflections From Earthquakes  

SciTech Connect

Knowledge of the deep structure of Long Valley comes primarily from seismic studies. Most of these efforts have focused on delimiting the top of the inferred magma chamber. We present evidence for the location of the bottom of the low velocity layer (LVL). Two other studies have provided similar information. Steeples and Iyer (1976) inferred from teleseismic P-wave delays that low-velocity material extends from 7 km depth to 25 to 40 km, depending on the velocities assumed. Luetgert and Mooney (1985) have examined seismic refraction data from earthquake sources and have identified a reflection that appears to be from the lower boundary of a magma chamber. They detected the reflection with a linear array of single component stations, and assuming it traveled in a vertical plane, matched the travel time and apparent velocity (6.3 km/sec) to deduce that it was a P-P reflection from within a LVL. We recorded a similar phase with a 2-dimensional array of three-component stations, and carried out a similar analysis, but utilized additional information about the travel path, particle motions and amplitudes to constrain our interpretation. Our data comes from a passive seismic refraction experiment conducted during August 1982. Fourteen portable seismograph stations were deployed in a network with approximately 5 km station spacing in the Mono Craters region north of Long Valley (Figure 1). The network recorded earthquakes located south of Long Valley and in the south moat. Three components of motion were recorded at all sites. The data represent one of the few times that three-component data has been collected for raypaths through a magma chamber in the Long Valley area.

Zucca, J. J.; Kasameyer, P. W.

1987-01-01

364

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

365

An Empirical Interpretation of the Effects of Topography on Ground Motion of the San Fernando, California, Earthquake, 9 February 1971.  

National Technical Information Service (NTIS)

This study attempts to determine site effects on earthquake ground motion and the correlation between acceleration and/or velocity generated during the San Fernando Earthquake and topography of the San Gabriel Mountain range. It was found that the contour...

F. K. Chang

1976-01-01

366

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  

NASA Astrophysics Data System (ADS)

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.

367

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

368

Postearthquake relaxation after the 2004 M6 Parkfield, California, earthquake and rate-and-state friction  

USGS Publications Warehouse

An unusually complete set of measurements (including rapid rate GPS over the first 10 days) of postseismic deformation is available at 12 continuous GPS stations located close to the epicenter of the 2004 M6.0 Parkfield earthquake. The principal component modes for the relaxation of the ensemble of those 12 GPS stations were determined. The first mode alone furnishes an adequate approximation to the data. Thus, the relaxation at all stations can be represented by the product of a common temporal function and distinct amplitudes for each component (north or east) of relaxation at each station. The distribution in space of the amplitudes indicates that the relaxation is dominantly strike slip. The temporal function, which spans times from about 5 min to 900 days postearthquake, can be fit by a superposition of three creep terms, each of the form ??l loge(1 + t/??l), with characteristic times ??, = 4.06, 0.11, and 0.0001 days. It seems likely that what is actually involved is a broad spectrum of characteristic times, the individual components of which arise from afterslip on different fault patches. Perfettini and Avouac (2004) have shown that an individual creep term can be explained by the spring-slider model with rate-dependent (no state variable) friction. The observed temporal function can also be explained using a single spring-slider model (i.e., single fault patch) that includes rate-and-state-dependent friction, a single-state variable, and either of the two commonly used (aging and slip) state evolution laws. In the latter fits, the rate-and-state friction parameter b is negative.

Savage, J. C.; Langbein, J.

2008-01-01

369

Spatial organization of foreshocks as a tool to forecast large earthquakes  

PubMed Central

An increase in the number of smaller magnitude events, retrospectively named foreshocks, is often observed before large earthquakes. We show that the linear density probability of earthquakes occurring before and after small or intermediate mainshocks displays a symmetrical behavior, indicating that the size of the area fractured during the mainshock is encoded in the foreshock spatial organization. This observation can be used to discriminate spatial clustering due to foreshocks from the one induced by aftershocks and is implemented in an alarm-based model to forecast m > 6 earthquakes. A retrospective study of the last 19 years Southern California catalog shows that the daily occurrence probability presents isolated peaks closely located in time and space to the epicenters of five of the six m > 6 earthquakes. We find daily probabilities as high as 25% (in cells of size 0.04 × 0.04deg2), with significant probability gains with respect to standard models.

Lippiello, E.; Marzocchi, W.; de Arcangelis, L.; Godano, C.

2012-01-01

370

Comparison of Repeating Magnitude 2 Earthquakes Near the SAFOD Site, California, With Similar-Magnitude Mining-Induced Earthquakes in South Africa  

NASA Astrophysics Data System (ADS)

A small patch of the San Andreas fault at a depth of about 2.7 km near the site of SAFOD (San Andreas Fault Observatory at Depth) produces magnitude 2 earthquakes that repeat at intervals of 2.89 years (Nadeau and Johnson, Bull. Seism. Soc. Am., 1998; Dreger et al., Geophys. Res. Lett., 2007). A repeat occurred on 20 October 2003 and was recorded by the SAFOD Pilot Hole Array, a vertical network of 3- component seismometers at 32 levels extending from 856 to 2096 m below the local ground surface (Imanishi and Ellsworth, AGU Geophysical Monograph 170, 2006). The ground velocity signals from this repeating earthquake, recorded in the Pilot Hole at hypocentral distances of several km, are remarkably similar to those recorded using a four-station network of IRIS/PASSCAL broadband recording units with accelerometers, deployed underground at depths between 2 and 3.5 km, within two of the deepest and most seismically active mines in South Africa. During our one-week deployment, four earthquakes, of seismic moment and hypocentral depth much the same as those of the repeating earthquakes near SAFOD, were recorded and analyzed to investigate their source processes. In addition to determining the traditional source parameters, including seismic moment, we used distance-corrected peak ground velocities to estimate maximum seismic slips within the four rupture zones, ranging from 4 to 27 mm. (Although our method of doing this involves several model assumptions, underground observations of maximum slip due to mining-induced earthquakes indicate that our approach yields realistic estimates.) These maximum slips, in conjunction with data from laboratory stick-slip friction experiments, were used to estimate maximum slip rates that fell in the range 2 to 7 m/s, typical for earthquakes in the continental crust. Applying the same methods to the 20 October 2003 earthquake data, as recorded in the Pilot Hole, revealed a maximum slip of about 17 mm and a maximum slip rate of 4.7 m/s. That is, our analysis has not indicated any aspect of this repeating earthquake that is out of the ordinary for crustal earthquakes of the same magnitude (McGarr and Fletcher, Bull. Seism. Soc. Am., 2003, 2007).

McGarr, A.; Fletcher, J. B.; Boettcher, M.; Ellsworth, W.

2008-12-01

371

Source characteristics of the Loma Prieta, California, earthquake of October 18, 1989 from global digital seismic data  

SciTech Connect

Displacement, velocity and acceleration records of P and SH body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the Loma Prieta, California earthquake of October 18, 1989 (m{sub b} 6.6, M{sub s} 7.1). Three distinct bursts of energy corresponding to three subevents can be recognized in most records. The displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents. The second and third subevents are located north and south of the initial nucleation. A fourth small subevent needed to model later features of the P waveforms suggests that slow slip continued after the major releases of energy occurred. The waveforms are fit with a fault plane solution having strike 130{degree}, dip 65{degree} and slip 140{degree} for all the subevents. The focal depths of the two major subevents are 16 and 12 km, and their asperity radii are 4.0 and 6.0 km, respectively. The seismic moment, M{sub o}, is 2.2{times}10{sup 26} dyne-cm. From spectral analysis of teleseismic velocity, the radiated energy, E{sub s}, is estimated to be 1.1{times}10{sup 22} dyne-cm, implying an apparent stress of 15 bars. From the high-frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km{sup 2}, the authors derive a dynamic stress drop of 51 bars.

Choy, G.L. (Geological Survey, Denver, CO (USA)); Boatwright, J. (Geological Survey, Menlo Park, CA (USA))

1990-07-01

372

Precursory Activation and Quiescence Prior to Major Earthquakes  

NASA Astrophysics Data System (ADS)

Many years ago, Gardner and Knopoff (1974) asked the question: “Is the sequence of large earthquakes, with aftershocks removed, Poissonian?”. The one-word abstract was “Yes”. They came to this answer by removing earthquakes from the Southern California catalog until the remaining event occurrences were consistent with Poisson statistics. Since that time, there has been a vigorous debate as to whether the probability for earthquake occurrence is highest during periods of smaller-event activation, or highest during periods of smaller-event quiescence. The physics of the activation model are based on an idea from the theory of nucleation --that a small event has a finite probability of growing into a large earthquake, so that more small events imply a larger probability for occurrence of a large earthquake. An objection to this model has been stated as: “the greatest probability for a large earthquake is the moment after it occurs”. Examples of this type of model are the ETAS and STEP models, which are statistical models utilizing the Omori and Gutenberg-Richter laws. The physics of the quiescence model is based on the idea that the occurrence of smaller earthquakes may be due to a mechanism such as critical slowing down, in which fluctuations in systems with long range interactions tend to be suppressed prior to large nucleation events. An example of such a model is the seismic gap model. Other models include both, such as the Pattern Informatics model which looks only for deviations (activation or quiescence) and weights both equally. In this talk we use this background to discuss both previous and new models that illustrate these points. We also discuss the question of whether time since the last large earthquake should play a role in earthquake probabilities (such as in the elastic rebound model).

Rundle, J. B.; Holliday, J. R.; Turcotte, D. L.; Tiampo, K. F.; Klein, W.; Graves, W.

2010-12-01

373

Location of Moderate-Sized Earthquakes Recorded by the NARS-Baja Array in the Gulf of California Region Between 2002 and 2006  

NASA Astrophysics Data System (ADS)

We relocated the hypocentral coordinates of small to moderate-sized earthquakes reported by the National Earthquake Information Center (NEIC) between April 2002 and August 2006 in the Gulf of California region and recorded by the broadband stations of the network of autonomously recording seismographs (NARS-Baja array). The NARS-Baja array consists of 19 stations installed in the Baja California peninsula, Sonora and Sinaloa, Mexico. The events reported by the preliminary determinations of epicenters (PDE) catalog within the period of interest have moment magnitudes ( M w) ranging between 1.1 and 6.7. We estimated the hypocentral location of these events using P and S wave arrivals recorded by the regional broadband stations of the NARS-Baja and the RESBAN ( Red Sismológica de Banda Ancha) arrays and using a standard location procedure with the HYPOCENTER code ( Lienert and Havskov in Seism Res Lett 66:26-36, 1995) as a preliminary step. To refine the location of the initial hypocenters, we used the shrinking box source-specific station term method of Lin and Shearer (J Geophys Res 110, B04304, 2005). We found that most of the seismicity is distributed in the NW-SE direction along the axis of the Gulf of California, following a linear trend that, from north to south, steps southward near the main basins (Wagner, Delfin, Guaymas, Carmen, Farallon, Pescadero and Alarcon) and spreading centers. We compared the epicentral locations reported in the PDE with the locations obtained using regional arrival times, and we found that earthquakes with magnitudes in the range 3.2-5.0 mb differ on the average by as much as 43 km. For the M w magnitude range between 5 and 6.7 the discrepancy is less, differing on the average by about 25 km. We found that the relocated epicenters correlate well with the main bathymetric features of the Gulf.

Castro, Raul R.; Perez-Vertti, Arturo; Mendez, Ignacio; Mendoza, Antonio; Inzunza, Luis

2011-08-01

374

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

375

The effects of attenuation on the scaling of source parameters for earthquakes at Anza, California  

NASA Astrophysics Data System (ADS)

Source radii for Anza earthquakes calculated from spectral corner frequencies are surprisingly constant over 4 orders of magnitude in moment. This apparent constancy leads to a strong dependence of stress drop on moment: the largest events (1021 dyne-cm) have stress drops of about 100 bars, whereas events with moment of 1018 dyne-cm or less have stress drops of a bar or less. However, displacement spectra used for corner frequency picks were not corrected for attenuation. In this paper we explore two arguments which suggest that an attenuation correction would alter, but not eliminate the small stress drops. Spectral ratios calculated for three events strongly support a linear frequency-dependent Q. The dependence Q = 12.9 + 11.8 f was obtained from one ratio for which the effect of (f ? 60 Hz) site resonances appeared to be at a minimum. Above 60 Hz the spectra would require an exponentially increasing Q. Alternatively, this could be due to their being contaminated by excessive noise above 60 Hz. The high Q/low attenuation at higher frequencies suggests that corner frequencies would not change drastically as a result of this attenuation correction. This method, however, does not differentiate where along the ray path attenuation is occurring or attenuation that may be common to all of the recording sites. f max, the intercept of the level part of acceleration spectra with high-frequency decay, can be interpreted as a site-specific attenuation parameter. Anza stations to the north and east tend to have a high fmax (? 30 Hz) compared to stations near the trifurcation of the San Jacinto-Buck Ridge-Coyote Creek faults, and to the southwest. Most of the corner frequencies at a specific station will tend to be lower than the fmax for that station, thus attenuation does limit the upper range of corner frequencies. Source radii were recomputed using data only from just those stations with fmax ? 20 Hz and again from those with fmax ? 30 Hz. Recomputed source radii for some events did shift to smaller values, but the overall range of stress drops stayed about the same. We conclude that some events with high corner frequencies were affected by attenuation at the low fmax sites, but that on the average, this is not a severe effect.

Fletcher, J. B.; Haar, L. C.; Vernon, F. L.; Brune, J. N.; Hanks, T. C.; Berger, J.

376

Risk Factors Associated with Moderate and Serious Injuries Attributable to the 1994 Northridge Earthquake, Los Angeles, California  

Microsoft Academic Search

PURPOSE: The purpose of this study was to use emergency department data to estimate levels of morbidity and risk factors due to earthquake-related mechanisms of injury subsequent to an urban night-time earthquake.METHODS: Data were abstracted from 4190 medical records for the month of January, 1994. Injuries attributable to the earthquake were identified through emergency department and medical records. These injuries

Maya Mahue-Giangreco; Wendy Mack; Hope Seligson; Linda B Bourque

2001-01-01

377

The Distribution of Earthquakes: Where Do Large Earthquakes Occur?  

NSDL National Science Digital Library

In this activity, students investigate the distribution of large earthquakes (magnitude greater than 6) in Southern California. Using online maps of earthquake epicenters in Southern California and the Los Angeles Basin, they will compare these distributions with historic distributions (1932-1996), and with respect to the locations of major fault traces.

Marquis, John

378

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

379

ULF Pulsations, Air Conductivity Changes, and Infrared (IR) Radiation Signatures Observed Prior to the 2008 Alum Rock (California) M5.4 Earthquake  

NASA Astrophysics Data System (ADS)

A collaboration between QuakeFinder (Palo Alto) and NASA JPL utilized both ground and space instruments to observe a series of electromagnetic (EM) signals detected up to 2 weeks prior to the Oct 30, 2007 Alum Rock, California, M5.4 earthquake. These signals included Ultra Low Frequency (ULF: 0.01 to 12 Hz) pulsations that were detected with a 3 axis induction magnetometer located 2 km from the epicenter. The 1- 12 sec wide pulsations were 10-50 times more intense than 2 year normal background noise levels, and the pulsations occurred 10-30 times more frequently in the 2 weeks prior to the quake than the average pulse count for the 1.8 years prior. The air conductivity sensor at the same site saturated for much of the evening prior to the quake. The conductivity levels were compared to the previous year's average conductivity patterns at the site, and determined not to be caused by moisture contamination. The GOES-West weather satellite typically observes the west coast of California, and during October of 2007, detected an area almost 100km around the quake that changed the usual night time cooling rate (a 4 year average negative temperature slope) to a positive slope during the night time for much of the 2 weeks prior to the quake. These EM signals were then compared against predictions based on several earthquake theories postulated during recent years.

Bleier, T. E.; Dunson, C.; Maniscalco, M.; Bryant, N.; Bambery, R.

2008-12-01

380

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

NASA Astrophysics Data System (ADS)

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 ?c-Pd on-site warning algorithm in California and describe recent improvements of the software. These include: (1) the development of a new ?c-Pd based trigger criterion to reduce the number of false triggers and the scattering in magnitude estimates for small and moderate earthquakes; (2) the integration of additional broadband stations, including the ANZA network and stations with older dataloggers that provide waveform data with highest sampling rate of 80 sps; and (3) the implementation of leap-second capabilities in the real-time software used within CISN. At present, we are working on the implementation of the remote processing sites for the BK and NP, NC networks operated by UC Berkeley and USGS Menlo Park. These processing sites will analyze available local waveform data and provide ?c-Pd values as well as Mw and PGV estimates. The new processing sites will provide more data for algorithm testing and improved data analysis for earthquakes located in northern California. We are also implementing the ?c-Pd algorithm software on SLATE Field Processors to eliminate telemetry delays associated with waveform data. On-site the SLATE receives data from a Q330 datalogger and provides ?c-Pd estimates from the first 3 seconds of P-waveforms. These ?c-Pd values along with station-specific Mw and PGV values are transmitted to the central site as a short notification message. In the future, such station processors can also transmit warnings to local users directly. The ?c-Pd algorithm software performed well during the recent July 29 2008 Mw5.4 Chino Hills earthquake. A total of 36 stations provided real-time estimates of ?c-Pd values and derived Mw and PGV values. The current CISN network configuration would have provided a 6 second warning at Los Angles City Hall, which is located 50 km to the west-southwest of the mainshock epicenter.

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

2008-12-01

381

Comparisons of ground motions from the 1999 Chi-Chi, earthquake with empirical predictions largely based on data from California  

USGS Publications Warehouse

This article has the modest goal of comparing the ground motions recorded during the 1999 Chi-Chi, Taiwan, mainshock with predictions from four empirical-based equations commonly used for western North America; these empirical predictions are largely based on data from California. Comparisons are made for peak acceleration and 5%-damped response spectra at periods between 0.1 and 4 sec. The general finding is that the Chi-Chi ground motions are smaller than those predicted from the empirically based equations for periods less than about 1 sec by factors averaging about 0.4 but as small as 0.26 (depending on period, on which equation is used, and on whether the sites are assumed to be rock or soil). There is a trend for the observed motions to approach or even exceed the predicted motions for longer periods. Motions at similar distances (30-60 km) to the east and to the west of the fault differ dramatically at periods between about 2 and 20 sec: Long-duration wave trains are present on the motions to the west, and when normalized to similar amplitudes at short periods, the response spectra of the motions at the western stations are as much as five times larger than those of motions from eastern stations. The explanation for the difference is probably related to site and propagation effects; the western stations are on the Coastal Plain, whereas the eastern stations are at the foot of young and steep mountains, either in the relatively narrow Longitudinal Valley or along the eastern coast-the sediments underlying the eastern stations are probably shallower and have higher velocity than those under the western stations.

Boore, D. M.

2001-01-01

382

Offshore and onshore liquefaction at Moss Landing spit, central California, - result of the October 17, 1989, Loma Prieta earthquake  

USGS Publications Warehouse

As a result of the October 17, 1989, Loma Prieta earthquake, liquefaction of the fluvial, estuarine, eolian, and beach sediments under a sand spit destroyed the Moss Landing Marine Laboratories and damaged other structures and utilities. Detailed offshore investigations indicate that liquefaction occurred over a large area (max. 8 km2) during or shortly after the earthquake with movement of unconsolidated sediment toward and into the head of Monterey submarine canyon. Many distinct lobate features were identified on the shallow shelf. These features almost certainly were the result of the October 17 earthquake; they were subsequently destroyed by winter storms. -from Authors

Greene, H. G.

1991-01-01

383

Comparisons of ground motions from five aftershocks of the 1999 Chi-Chi, Taiwan, earthquake with empirical predictions largely based on data from California  

USGS Publications Warehouse

The observed ground motions from five large aftershocks of the 1999 Chi-Chi, Taiwan, earthquake are compared with predictions from four equations based primarily on data from California. The four equations for active tectonic regions are those developed by Abrahamson and Silva (1997), Boore et al. (1997), Campbell (1997, 2001), and Sadigh et al. (1997). Comparisons are made for horizontal-component peak ground accelerations and 5%-damped pseudoacceleration response spectra at periods between 0.02 sec and 5 sec. The observed motions are in reasonable agreement with the predictions, particularly for distances from 10 to 30 km. This is in marked contrast to the motions from the Chi-Chi mainshock, which are much lower than the predicted motions for periods less than about 1 sec. The results indicate that the low motions in the mainshock are not due to unusual, localized absorption of seismic energy, because waves from the mainshock and the aftershocks generally traverse the same section of the crust and are recorded at the same stations. The aftershock motions at distances of 30-60 km are somewhat lower than the predictions (but not nearly by as small a factor as those for the mainshock), suggesting that the ground motion attenuates more rapidly in this region of Taiwan than it does in the areas we compare with it. We provide equations for the regional attenuation of response spectra, which show increasing decay of motion with distance for decreasing oscillator periods. This observational study also demonstrates that ground motions have large earthquake-location-dependent variability for a specific site. This variability reduces the accuracy with which an earthquake-specific prediction of site response can be predicted. Online Material: PGAs and PSAs from the 1999 Chi-Chi earthquake and five aftershocks.

Wang, G. -Q.; Boore, D. M.; Igel, H.; Zhou, X. -Y.

2004-01-01

384

Earthquake Engineering Research at Berkeley, 1992.  

National Technical Information Service (NTIS)

Twenty-five papers by faculty participants and research personnel associated with the Earthquake Engineering Research Center of the University of California at Berkeley were presented at the Tenth World Conference on Earthquake Engineering held in Madrid,...

1992-01-01

385

Earthquake Engineering Abstracts (EERC)  

NSDL National Science Digital Library

The University of California Berkeley's well known Earthquake Engineering Research Center has recently added a searchable-only version of Earthquake Engineering Abstracts, a database that currently contains over 55,000 citations. Users can search by author, title, subject and year. The search engine supports Boolean operators, as well as stem and phrase searching. For authors, phonetic searching is also available. EEA joins EqIIS (Earthquake Image Information System), the giant searchable image base of the Karl V. Steinbrugge Collection of "slides and photographs of historical earthquake damage," as major resources of the EERC.

386

Ground fracturing at the southern end of Summit Ridge caused by October 17, 1989 Loma Prieta, California, earthquake sequence (maps of Summit Ridge Shear Zones, en echelon tension cracks, complex and compound fractures, and small faults that formed coactively with the earthquake sequence)  

SciTech Connect

The Loma Prieta earthquake of 17 October 1989 was the first of three large earthquakes that occurred in California in less than 5 years. The main shock of the Loma Prieta earthquake was deep-seated, the rupture zones of the main shock did not reach the surface, and the earthquake produced enigmatic surface ruptures along the frontal faults of the Coast Range and in the epicentral area that were explained in several quite different ways. The Landers earthquake of 28 June 1992 was near surface and produced more than 80 km of spectacular surface rupture of many different kinematic expressions. Detailed study of fractures at Landers has provided a basis for re-evaluating earlier work on fractures produced by the Loma Prieta earthquake. This paper is a description of some of the fractures produced by the Loma Prieta earthquake and a discussion of their causes. Detailed mapping (scale of 1:250) in an area on either side of Summit Road and between Morrell Cutoff Road in the northwest and the intersection of Summit Road and San Jose-Soquel Road in the southeast has provided documentation of fracture orientations and differential displacements required to decipher the ground deformation in that area during the Loma Prieta earthquake.

Martosudarmo, S.Y. [BPP Technologi, Jakarta (Indonesia); Johnson, A.M. [Purdue Univ., West Lafayette, IN (United States). Harry Fielding Reid Earthquake Research Lab.; Fleming, R.W. [Geological Survey, Denver, CO (United States)

1997-12-31

387

The Southern California Fault Activity Database  

Microsoft Academic Search

The Southern California Fault Activity Database (SCFAD) will supply WEB-accessible data about active faults throughout southern California, an essential resource for basic research and earthquake hazard mitigation. The SCFAD is funded by the Southern California Earthquake Center (SCEC) to compile and summarize published data pertaining to each fault's slip rate, recurrence interval, slip per event, and known damaging earthquakes, as

S. C. Perry; M. P. Silva

2001-01-01

388

Comparison of characteristic and Gutenberg-Richter models for time-dependent M ? 7.9 earthquake probability in the Nankai-Tokai subduction zone, Japan  

NASA Astrophysics Data System (ADS)

Earthquake forecasts are usually underinformed, and can be plagued by uncertainty in terms of the most appropriate model, and parameter values used in that model. In this paper, we explore the application of two different models to the same seismogenic area. The first is a renewal model based on the characteristic earthquake hypothesis that uses historical/palaeoseismic recurrence times, and fixed rupture geometries. The hazard rate is modified by the Coulomb static stress change caused by nearby earthquakes that occurred since the latest characteristic earthquake. The second model is a very simple earthquake simulator based on plate-motion, or fault-slip rates and adoption of a Gutenberg-Richter magnitude-frequency distribution. This information is commonly available even if historical and palaeoseismic recurrence data are lacking. The intention is to develop and assess a simulator that has a very limited parameter set that could be used to calculate earthquake rates in settings that are not as rich with observations of large-earthquake recurrence behaviour as the Nankai trough. We find that the use of convergence rate as a primary constraint allows the simulator to replicate much of the spatial distribution of observed segmented rupture rates along the Nankai, Tonankai and Tokai subduction zones. Although we note rate differences between the two forecast methods in the Tokai zone, we also see enough similarities between simulations and observations to suggest that very simple earthquake rupture simulations based on empirical data and fundamental earthquake laws could be useful forecast tools in information-poor settings.

Parsons, Tom; Console, Rodolfo; Falcone, Giuseppe; Murru, Maura; Yamashina, Ken'ichiro

2012-09-01

389

Strong-Motion Earthquake Accelerograms. Digitized and Plotted Data. Volume I. Uncorrected Accelerograms. Part C. Accelerograms IC041 through IC055. Accelerograms from the San Fernando, California, Earthquake of Feb ruary 9, 1971.  

National Technical Information Service (NTIS)

Contents: Instrument characteristics for the San Fernando Earthquake; Earthquake data and references; Reproduction of the Pacoima Dam strong motion accelerogram; Print-out of accelerograms; Plots of accelerograms.

1971-01-01

390

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

SciTech Connect

As part of the contract with the US Department of Energy, Nevada Field office (DOE/NV), URS/John A. Blume & Associates, Engineers (URS/Blume) maintains a network of seismographs in southern Nevada to monitor the ground motion generated by the underground nuclear explosions (UNEs) at the Nevada Test Site (NTS). The seismographs are located in the communities surrounding the NTS and the Las Vegas valley. When these seismographs are not used for monitoring the UNE generated motions, a limited number of seismographs are maintained for monitoring motion generated by other than UNEs (e.g. motion generated by earthquakes, wind, blast). During the subject earthquake of June 28, 1992, a total of 15 of these systems recorded the earthquake motions. This report contains the recorded data.

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

1993-04-01

391