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1

Change in the probability for earthquakes in Southern California due to the Landers magnitude 7.3 earthquake.  

PubMed

The Landers earthquake in June 1992 redistributed stress in southern California, shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions, up to the present. This earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter. This implies that the probabilistic estimate for future earthquakes in southern California changed because of the Landers earthquake. The location of the strongest increase in probability for large earthquakes in southern California was the volume that subsequently produced the largest slip in the magnitude 7.1 Hector Mine earthquake of October 1999. PMID:11082057

Wyss, M; Wiemer, S

2000-11-17

2

Southern California regional earthquake probability estimated from continuous GPS geodetic data  

Microsoft Academic Search

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

G. Anderson

2002-01-01

3

Probability of one or more M ???7 earthquakes in southern California in 30 years  

USGS Publications Warehouse

Eight earthquakes of magnitude greater than or equal to seven have occurred in southern California in the past 200 years. If one assumes that such events are the product of a Poisson process, the probability of one or more earthquakes of magnitude seven or larger in southern California within any 30 year interval is 67% ?? 23% (95% confidence interval). Because five of the eight M ??? 7 earthquakes in southern California in the last 200 years occurred away from the San Andreas fault system, the probability of one or more M ??? 7 earthquakes in southern California but not on the San Andreas fault system occurring within 30 years is 52% ?? 27% (95% confidence interval). -Author

Savage, J. C.

1994-01-01

4

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

5

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

USGS Publications Warehouse

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

Stein, Ross S.

2008-01-01

6

Forecasting southern California earthquakes  

Microsoft Academic Search

Since 1978 and 1979, California has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years. In the past such periods have also been associated with major desctructive earthquakes, of magnitude 7 or greater, and the annual probability of occurrence os such an event is now 13 percent in California. The increase in seismicity

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

1982-01-01

7

Forecasting Southern California Earthquakes  

Microsoft Academic Search

Since 1978 and 1979, California has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years. In the past such periods have also been associated with major destructive earthquakes, of magnitude 7 or greater, and the annual probability of occurrence of such an event is now 13 percent in California. The increase in seismicity

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

1982-01-01

8

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

9

Forecasting southern california earthquakes.  

PubMed

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

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

1982-09-17

10

Forecasting southern California earthquakes  

SciTech Connect

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

Raleigh, C.B. (Columbia Univ., New York, NY); Sieh, K.; Sykes, L.R.; Anderson, D.L.

1982-09-17

11

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

12

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).

13

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.

14

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

USGS Publications Warehouse

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

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

2002-01-01

15

Historic Earthquakes in Southern California  

NSDL National Science Digital Library

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

2011-04-06

16

Southern California earthquake data center  

Microsoft Academic Search

The Southern California Earthquake Center Data Center (SCECDC) is the component of SCEC that stores the seismological, geodetic, and strong-motion data collected in southern California. These data are to be integrated into a probabilistic seismic hazard analysis of southern California known locally as the ``master model.'' The SCECDC is located at Caltech in Pasadena, and has been on-line since January.

Katrin Douglass; Lisa Wald

1992-01-01

17

Probabilities of occurrence of large plate rupturing earthquakes for the San Andreas, San Jacinto, and Imperial faults, California, 1983--2003  

SciTech Connect

The San Andreas, San Jacinto, and Imperial faults in California are divided into 19 segments; conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake, i.e., an event that breaks the entire down-dip extent of the seismogenic zone, during the next 20 years. The sizes of such events, which account for most of the slip that occurs seismically, appear to vary greatly for different segments of these faults. Repeat time of large shocks, coseismic displacement, moment release, rupture length, and seismic magnitude appear to correlated with one another and to be a function of the tectonic style of different parts of those fault zones. Tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks. It is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size. Since repeat time varies, however, for a given segment of a fault, a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment, using as input the time of the last large shock, the average recurrence time, and the standard deviation of time intervals between events. Dates of the last large shocks are available for most of the segments investigated. Repeat times are estimated from times of historic and prehistoric events, tectonic similarity, and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup.

Sykes, L.R.; Nishenko, S.P.

1984-07-10

18

The Parkfield, California, Earthquake Experiment  

NSDL National Science Digital Library

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

19

Scientific Challenges in Developing the Next Uniform California Earthquake Rupture Forecast (UCERF3)  

Microsoft Academic Search

The Working Group on California Earthquake Probabilities (WGCEP) is in the process of developing the next-generation Uniform California Earthquake Rupture Forecast (UCERF version 3). The main goals for this future model, which is being developed jointly by the United States Geological Survey, California Geological Survey, and Southern California Earthquake Center, are to include multi-fault ruptures and spatial and temporal clustering.

E. H. Field

2009-01-01

20

How Do Scientists Determine Earthquake Probabilities?  

NSDL National Science Digital Library

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

21

Southern California Earthquake Center (SCEC)  

NSDL National Science Digital Library

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

22

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

23

Probability of derailment under earthquake conditions  

E-print Network

A quantitative assessment of the probability of derailment under earthquake conditions is presented. Two derailment modes are considered: by vibratory motion - during the ground motion - and by permanent track deformation ...

Guillaud, Lucile M. (Lucile Marie)

2006-01-01

24

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.

25

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.

26

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.

27

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.

28

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.

29

Earthquake probabilities: theoretical assessments and reality  

NASA Astrophysics Data System (ADS)

It is of common knowledge that earthquakes are complex phenomena which classification and sizing remain serious problems of the contemporary seismology. In general, their frequency-magnitude distribution exhibit power law scaling. This scaling differs significantly when different time and/or space domains are considered. At the scale of a particular earthquake rupture zone the frequency of similar size events is usually estimated to be about once in several hundred years. Evidently, contemporary seismology does not possess enough reported instrumental data for any reliable quantification of an earthquake probability at a given place of expected event. Regretfully, most of the state-of-the-art theoretical approaches to assess probability of seismic events are based on trivial (e.g. Poisson, periodic, etc) or, conversely, delicately-designed (e.g. STEP, ETAS, etc) models of earthquake sequences. Some of these models are evidently erroneous, some can be rejected by the existing statistics, and some are hardly testable in our life-time. Nevertheless such probabilistic counts including seismic hazard assessment and earthquake forecasting when used on practice eventually mislead to scientifically groundless advices communicated to decision makers and inappropriate decisions. As a result, the population of seismic regions continues facing unexpected risk and losses. The international project Global Earthquake Model (GEM) is on the wrong track, if it continues to base seismic risk estimates on the standard, mainly probabilistic, methodology to assess seismic hazard. It is generally accepted that earthquakes are infrequent, low-probability events. However, they keep occurring at earthquake-prone areas with 100% certainty. Given the expectation of seismic event once per hundred years, the daily probability of occurrence on a certain date may range from 0 to 100% depending on a choice of probability space (which is yet unknown and, therefore, made by a subjective lucky chance). How many days are needed to distinguish 0 from the average probability of 0.000027? Is it theoretically admissible to apply average when seismic events, including mega-earthquakes, are evidently clustered in time and space displaying behaviors that are far from independent? Is it possible to ignore possibly fractal, definitely, far from uniform distribution in space when mapping seismic probability density away from the empirical earthquake locus embedded onto the boundaries of the lithosphere blocks? These are simple questions to those who advocate the existing probabilistic products for seismic hazard assessment and forecasting. Fortunately, the situation is not hopeless due to deterministic pattern recognition approaches applied to available geological evidences, specifically, when intending to predict predictable, but not the exact size, site, date, and probability of a target event. Understanding by modeling the complexity of non-linear dynamics of hierarchically organized systems of blocks-and-faults has led already to methodologies of neo-deterministic seismic hazard analysis and intermediate-term middle- to narrow-range earthquake prediction algorithms tested in real-time applications over the last decades.

Kossobokov, V. G.

2013-12-01

30

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. PMID:21949355

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

2011-01-01

31

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

32

Prospective Tests of Southern California Earthquake Forecasts  

Microsoft Academic Search

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

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

2004-01-01

33

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

34

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

35

The southern California uplift and associated earthquakes  

Microsoft Academic Search

Southern California earthquakes >= M5.5 during the period 1955\\/01\\/01-1994\\/01\\/17, were concentrated along or adjacent to the south flank of the southern California uplift, as defined both at its culmination and following its partial collapse. Spatial clustering of these earthquakes within three more-or-less distinct groups suggests either gaps along the south flank that were previously filled or are yet to be

Robert O. Castle; Richard L. Bernknopf

1996-01-01

36

The southern California uplift and associated earthquakes  

Microsoft Academic Search

Southern California earthquakes ? M5.5 during the period 1955\\/01\\/01–1994\\/01\\/17 were concentrated along or adjacent to the south flank of the southern California uplift, as defined both at its culmination and following its partial collapse. Spatial clustering of these earthquakes within three more-or-less distinct groups suggests either gaps along the south flank that were previously filled or are yet to be

Robert O. Castle; Richard L. Bernknopf

1996-01-01

37

The southern California uplift and associated earthquakes  

USGS Publications Warehouse

Southern California earthquakes ??? M5.5 during the period 1955/01/01-1994/01/17 were concentrated along or adjacent to the south flank of the southern California uplift, as defined both at its culmination and following its partial collapse. Spatial clustering of these earthquakes within three more-or-less distinct groups suggests either gaps along the south flank that were previously filled or are yet to be filled. Nearly all of the indicated earthquakes accompanied or followed partial collapse of the uplift, and seismic activity within this regime seems to have been increasing through at least 1994/01/17. Copyright 1996 by the American Geophysical Union.

Castle, R. O.; Bernknopf, R. L.

1996-01-01

38

The parkfield, california, earthquake prediction experiment.  

PubMed

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

Bakun, W H; Lindh, A G

1985-08-16

39

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

SciTech Connect

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

Bea, R.G. [Univ. of California, Berkeley, CA (United States). Dept. of Civil Engineering

1996-12-31

40

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

USGS Publications Warehouse

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

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

1999-01-01

41

Accessing Data From the Southern California Earthquake Data Center  

Microsoft Academic Search

The Southern California Earthquake Data Center (SCEDC) archives and provides public access to earthquake parametric and waveform data gathered by the TriNet seismic network, southern California's earthquake monitoring network since January 1 2001. The parametric data includes earthquake locations, magnitudes, moment-tensor solutions (for some events), and phase picks. The waveform data consists of continuous recordings of 150 broadband stations, and

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

2001-01-01

42

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

43

Forecast of underwater earthquakes with a great degree of probability  

Microsoft Academic Search

The modes of the instant prognosis of earthquakes and tsunami with probability greater than 0.95 are offered. These modes are based on the principal idea of a simultaneous measurement of elastic and electromagnetic waves from the underground center of earthquakes. Electromagnetic waves with frequency from 1 Hz up to 1000 Hz transmit well on the surface of the Earth, bottom

G. P. Turmov; V. I. Korochentsev; E. V. Gorodetskaya; A. M. Mironenko; D. V. Kislitsin; O. A. Starodubtsev

2000-01-01

44

Comprehensive analysis of earthquake source spectra in southern California  

E-print Network

Comprehensive analysis of earthquake source spectra in southern California Peter M. Shearer,1 Germa of earthquake source spectra in southern California, J. Geophys. Res., 111, B06303, doi:10.1029/2005JB003979. 1 in southern California between 1989 and 2001 using a method that isolates source-, receiver-, and path

Shearer, Peter

45

Earthquake Alerting in California Prof. of Engineering Seismology  

E-print Network

Earthquake Alerting in California Tom Heaton Prof. of Engineering Seismology Caltech #12;Earthquake Alerting ... a different kind of prediction · What if earthquakes were really slow, like the weather? · We could recognize that an earthquake is beginning and then broadcast information on its development

Greer, Julia R.

46

The 1984 Morgan Hill, California, earthquake  

USGS Publications Warehouse

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

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

1984-01-01

47

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

USGS Publications Warehouse

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

1999-01-01

48

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

E-print Network

1957 Gobi-Altay, Mongolia, earthquake as a prototype for southern California's most devastating of earthquake hazards in the Los Angeles, California, area commonly fo- cus on two separate systems of faults (e slip on more than one fault, the possibility of both fault systems in southern California rupturing si

Mojzsis, Stephen J.

49

A new procedure modeling the probability distribution of earthquake size  

NASA Astrophysics Data System (ADS)

The probability distribution of earthquake size is needed as input data for some earthquake analyses. A common procedure is to calibrate the so-called b-value in the Gutenberg-Richter relationship and to use it as the best-estimate model parameter in an algorithm to simulate the observed earthquake-size distribution. This paper introduces a new procedure for such a simulation, on the basis of performing optimization to search for the optimum model parameter. The new option and an existing method are then both utilized to model the earthquake-size distribution around Taiwan since 1978. Owing to the nature and the power of optimization, three case studies presented in this paper all indicate that the new optimization procedure can indeed improve such a simulation over the existing procedure. Moreover, with a proper tool such as Excel Solver, practicing the new method to model the observed earthquake-size distribution is as effortless as using the existing procedure.

Wang, J. P.; Yun, X.; Chang, S. C.

2014-11-01

50

Earthquakes in Nevada triggered by the Landers, California earthquake, June 28, 1992  

SciTech Connect

Within 24 hours after the Landers earthquake, there were 11 magnitude 3.4+ events in the western Great Basin and northern Mojave Desert and a general increase in the rate of small events. Based on the previous 25 year combined catalog for northern and southern Nevada and eastern California, and using a quantitative model that assumes statistical independence of these regions, the probability of this happening by random changes is less than once in [approximately]10[sup 10] years. Therefore, it appears that these were triggered by the Landers event. The three events that define an upper bound to the magnitude of triggered events with distance were: Mina, 500 kilometers from Landers, M4.0, 36 minutes after Landers; Smith Valley, 590 kilometers from Landers, M3.4, 56 minutes after Landers; Little Skull Mountain, 280 kilometers from Landers, M5.6, 22.3 hours after Landers. These events are not associated with known volcanic activity or ongoing aftershock sequences. Earthquakes have been triggered in southern Nevada before, by nuclear testing and by filling of Lake Mead. Prior seismicity in the regions where triggering occurred was quite varied, and does not hold a clue about whether triggering is likely. The authors speculate that these events are triggered by the dynamic low-frequency stress associated with surface waves propagating from the Landers earthquake. A quantitative model for the strains, at the hypocentral depths of the triggered earthquakes, from significant prior events demonstrates that the Landers earthquake caused larger strains at low frequencies than other recent earthquakes of any magnitude and distance, but high frequency strains from some of the other recent earthquakes have had higher spectral amplitudes than what was expected from Landers. Prior events, including the Loma Prieta and Petrolia earthquakes, did not trigger any seismicity in the same region.

Anderson, J.G.; Louie, J.; Zeng, Y.; Yu, G.; Savage, M.; DePolo, D.; Brune, J.N. (Univ. of Nevada, Reno, NV (United States). Seismological Lab.)

1993-04-01

51

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

52

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

53

A Comprehensive Search for Tidal Triggering of Southern California Earthquakes  

Microsoft Academic Search

Tidal forces cause crustal stress changes that might be expected to trigger earthquakes but previous analyses searching for tidal periodicities in earthquake catalogs have yielded generally negative or inconclusive results. This study examines the Caltech\\/USGS southern California earthquake catalog from 1932 to 2003, which includes 429,886 events. We examine the data for any correlation between event occurrence and lunar phase

A. S. Wein; P. M. Shearer

2004-01-01

54

Southern California Earthquake Center (SCEC) Summer Internship Programs  

Microsoft Academic Search

For the eleventh consecutive year, the Southern California Earthquake Center (SCEC) coordinated undergraduate research experiences in summer 2004, allowing 35 students with a broad array of backgrounds and interests to work with the world's preeminent earthquake scientists and specialists. Students participate in interdisciplinary, system-level earthquake science and information technology research, and several group activities throughout the summer. Funding for student

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

2004-01-01

55

Changes in Seismic Stain Following the 1992 Landers California Earthquake  

Microsoft Academic Search

We examine spatio-temporal features of the strain pattern in relation to the large earthquake history of southern California in the last 20 years. Our analysis specifically focuses on the 1992 Landers and 1994 Northridge earthquakes. Recent studies disagree over whether or not maximum horizontal stress directions in the vicinity of these two earthquakes rotated in response to the events (e.g.

S. Levin; C. G. Sammis

2002-01-01

56

Earthquakes and faults in southern California (1970-2010)  

USGS Publications Warehouse

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

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

2012-01-01

57

Source Characterization and Ground Motion Modeling of the 1892 Vacaville-Winters Earthquake Sequence, California  

Microsoft Academic Search

We use a multidisciplinary approach that combines structural geologic analysis with geophysical modeling to evaluate the depth, geometry and segmentation of thrust faults that were the probable sources of the 1892 Winters-Vacaville earthquake sequence, which produced significant damage to towns in the southwestern Sacramento Valley, California. The largest event in this sequence occurred 19 April 1892 with a maximum Modified

D. R. O'Connell; J. Unruh; L. P. Block

2001-01-01

58

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

59

Two examples of earthquake- hazard reduction in southern California.  

USGS Publications Warehouse

Because California is seismically active, planners and decisionmakers must try to anticipate earthquake hazards there and, where possible, to reduce the hazards. Geologic and seismologic information provides the basis for the necessary plans and actions. Two examples of how such information is used are presented. The first involves assessing the impact of a major earthquake on critical facilities in southern California, and the second involves strengthening or removing unsafe masonry buildings in the Los Angeles area. -from Authors

Kockelman, W. J.; Campbell, C. C.

1983-01-01

60

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

61

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

Microsoft Academic Search

The Southern California Earthquake Data Center (SCEDC) archives and provides public access to earthquake parametric and waveform data gathered by the Southern California Seismic Network and since January 1, 2001, the TriNet seismic network, southern California's earthquake monitoring network. The parametric data in the archive includes earthquake locations, magnitudes, moment-tensor solutions and phase picks. The SCEDC waveform archive prior to

V. L. Appel

2002-01-01

62

The magnitude distribution of declustered earthquakes in Southern California  

PubMed Central

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

Knopoff, Leon

2000-01-01

63

The magnitude distribution of declustered earthquakes in Southern California.  

PubMed

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

Knopoff, L

2000-10-24

64

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

Microsoft Academic Search

Earthquake science is being communicated to and used by the 22 million residents of southern California to improve resiliency to future earthquakes through the Great Southern California ShakeOut. The ShakeOut began when the USGS partnered with the California Geological Survey, Southern California Earthquake Center and many other organizations to bring 300 scientists and engineers together to formulate a comprehensive description

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

2008-01-01

65

Probable Maximum Earthquake Magnitudes for the Cascadia Subduction  

NASA Astrophysics Data System (ADS)

The concept of maximum earthquake magnitude (mx) is widely used in seismic hazard and risk analysis. However, absolute mx lacks a precise definition and cannot be determined from a finite earthquake history. The surprising magnitudes of the 2004 Sumatra and the 2011 Tohoku earthquakes showed that most methods for estimating mx underestimate the true maximum if it exists. Thus, we introduced the alternate concept of mp(T), probable maximum magnitude within a time interval T. The mp(T) can be solved using theoretical magnitude-frequency distributions such as Tapered Gutenberg-Richter (TGR) distribution. The two TGR parameters, ?-value (which equals 2/3 b-value in the GR distribution) and corner magnitude (mc), can be obtained by applying maximum likelihood method to earthquake catalogs with additional constraint from tectonic moment rate. Here, we integrate the paleoseismic data in the Cascadia subduction zone to estimate mp. The Cascadia subduction zone has been seismically quiescent since at least 1900. Fortunately, turbidite studies have unearthed a 10,000 year record of great earthquakes along the subduction zone. We thoroughly investigate the earthquake magnitude-frequency distribution of the region by combining instrumental and paleoseismic data, and using the tectonic moment rate information. To use the paleoseismic data, we first estimate event magnitudes, which we achieve by using the time interval between events, rupture extent of the events, and turbidite thickness. We estimate three sets of TGR parameters: for the first two sets, we consider a geographically large Cascadia region that includes the subduction zone, and the Explorer, Juan de Fuca, and Gorda plates; for the third set, we consider a narrow geographic region straddling the subduction zone. In the first set, the ?-value is derived using the GCMT catalog. In the second and third sets, the ?-value is derived using both the GCMT and paleoseismic data. Next, we calculate the corresponding mc values for different ?-values. For magnitude larger than 8.5, the turbidite data are consistent with all three TGR models. For smaller magnitudes, the TGR models predict a higher rate than the paleoseismic data show. The discrepancy can be attributed to uncertainties in the paleoseismic magnitudes, the potential incompleteness of the paleoseismic record for smaller events, or temporal variations of the seismicity. Nevertheless, our results show that for this zone, earthquake of m 8.8×0.2 are expected over a 500-year period, m 9.0×0.2 are expected over a 1000-year period, and m 9.3×0.2 are expected over a 10,000-year period.

Rong, Y.; Jackson, D. D.; Magistrale, H.; Goldfinger, C.

2013-12-01

66

The magnitude distribution of earthquakes near Southern California faults  

USGS Publications Warehouse

We investigate seismicity near faults in the Southern California Earthquake Center Community Fault Model. We search for anomalously large events that might be signs of a characteristic earthquake distribution. We find that seismicity near major fault zones in Southern California is well modeled by a Gutenberg-Richter distribution, with no evidence of characteristic earthquakes within the resolution limits of the modern instrumental catalog. However, the b value of the locally observed magnitude distribution is found to depend on distance to the nearest mapped fault segment, which suggests that earthquakes nucleating near major faults are likely to have larger magnitudes relative to earthquakes nucleating far from major faults. Copyright 2011 by the American Geophysical Union.

Page, M. T.; Alderson, D.; Doyle, J.

2011-01-01

67

Major improvements in progress for Southern California Earthquake Monitoring  

Microsoft Academic Search

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

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

1998-01-01

68

EPiC: Earthquake Prediction in California  

E-print Network

Earthquake prediction has long been the holy grail for seismologists around the world. The various factors affecting earthquakes are far from being understood, and there exist no known correlations between largescale

Caroline Suen; David Lo; Frank Li

2010-01-01

69

Towards Practical, Real-Time Estimation of Spatial Aftershock Probabilities: A Feasibility Study in Earthquake Hazard  

Microsoft Academic Search

It is now widely accepted that the goal of deterministic earthquake prediction is unattainable in the short term and may even be forbidden by nonlinearity in the generating dynamics. This nonlinearity does not, however, preclude the estimation of earthquake probability and, in particular, how this probability might change in space and time; earthquake hazard estimation might be possible in the

P. Morrow; J. McCloskey; S. Steacy

2001-01-01

70

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

71

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

USGS Publications Warehouse

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

Jones, Lucile, M.

1985-01-01

72

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

SciTech Connect

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

Hough, Susan E. [U.S. Geological Survey, 525 South Wilson Avenue, Pasadena, California 91106 (United States)

2008-07-08

73

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

NASA Astrophysics Data System (ADS)

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

Hough, Susan E.

2008-07-01

74

IMPACT OF A LARGE SAN ANDREAS FAULT EARTHQUAKE ON TALL BUILDINGS IN SOUTHERN CALIFORNIA  

E-print Network

IMPACT OF A LARGE SAN ANDREAS FAULT EARTHQUAKE ON TALL BUILDINGS IN SOUTHERN CALIFORNIA Swaminathan the regional economy. Introduction The risk of earthquakes in southern California arises from two sources moderate earthquakes (moment magnitude 7). Fortunately, the urban areas of southern California have thus

Krishnan, Swaminathan

75

Southern California Earthquake Center Operates 1991 present, $3 -$5 million per year  

E-print Network

Southern California Earthquake Center · Operates 1991 ­ present, $3 - $5 million per year · NSF of transform boundaries; corner magnitude 8.1 #12;Southern California earthquakes, mostly located using precise faults Quake rates elsewhere Putting it all together ... Uniform California Earthquake Rupture Forecast

76

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

E-print Network

A model of earthquake triggering probabilities and application to dynamic deformations constrained) with the magnitude of and distance from the main shock fault to derive constraints on how the probability of a main triggering. Citation: Gomberg, J., and K. Felzer (2008), A model of earthquake triggering probabilities

Felzer, Karen

77

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

NASA Astrophysics Data System (ADS)

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

Mori, Jim; Abercrombie, Rachel E.

1997-07-01

78

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

USGS Publications Warehouse

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

Mori, J.; Abercrombie, R. E.

1997-01-01

79

Lithologic Control of the Depth of Earthquakes in Southern California  

PubMed

The depth distribution of southern California earthquakes indicates that areas underlain by schist basement rocks have a shallower (4 to 10 kilometers) maximum depth of earthquakes than do areas with other types of basement rocks. The predominant minerals in the schists become plastic at lower temperatures, and thus at shallower depths, than the minerals in the other basement rocks. The lateral variations in lithology will control the depth extent (and thus the magnitudes) of potential future earthquakes; these depths can be determined from the depth of the current background seismicity. PMID:8662553

Magistrale; Zhou

1996-08-01

80

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

NASA Astrophysics Data System (ADS)

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

Shedlock, Kaye M.

81

Refined Locations for Southern California Earthquakes from 1981 to 2005  

Microsoft Academic Search

We present results of a recent analysis of southern California waveform data from 1981 to 2005, which includes a new crustal 3-D velocity model and high-precision earthquake locations computed using waveform cross-correlation. This is a continuation of an ongoing Caltech\\/U.C. San Diego collaboration to develop new methods for analyzing the vast archive of seismograms recorded by the Southern California Seismic

P. Shearer; G. Lin; E. Hauksson

2006-01-01

82

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

83

An earthquake detection algorithm with pseudo-probabilities of multiple indicators  

NASA Astrophysics Data System (ADS)

We develop an automatic earthquake detection algorithm combining information from numerous indicator variables in a non-parametric framework. The method is shown to perform well with multiple ratios of moving short- and long-time averages having ranges of time intervals and frequency bands. The results from each indicator are transformed to a pseudo-probability time-series (PPTS) in the range [0, 1]. The various PPTS of the different indicators are multiplied to form a single joint PPTS that is used for detections. Since all information is combined, redundancy among the different indicators produces robust peaks in the output. This allows the trigger threshold applied to the joint PPTS to be significantly lower than for any one detector, leading to substantially more detected earthquakes. Application of the algorithm to a small data set recorded during a 7-d window by 13 stations near the San Jacinto fault zone detects 3.13 times as many earthquakes as listed in the Southern California Seismic Network catalogue. The method provides a convenient statistical platform for including other indicators, and may utilize different sets of indicators to detect other information such as specific seismic phases or tremor.

Ross, Z. E.; Ben-Zion, Y.

2014-04-01

84

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

85

Assessing Spatial Point Process Models for California Earthquakes Using Weighted  

E-print Network

Assessing Spatial Point Process Models for California Earthquakes Using Weighted K a weighted analogue of Ripley's K-function for assessing the fit of point process models. The advantage process and use it to assess the goodness-of-fit of two alternative point process models for the spatial

Schoenberg, Frederic Paik (Rick)

86

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

PubMed

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

Bakun, W H; McEvilly, T V

1979-09-28

87

Crustal anisotropy in southern California from local earthquake data  

Microsoft Academic Search

Shear wave splitting measurements were made for local earthquakes in southern California at incidence angles larger than the critical incidence angle. For the region of San Bernardino Mountains, the fast polarization directions vary strongly, but are consistently fast for directions roughly perpendicular to the ray paths. This observation is most readily explained by transverse isotropy with a vertical symmetry axis,

Hanneke Paulssen

2004-01-01

88

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

USGS Publications Warehouse

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

Simpson, Robert W.

1994-01-01

89

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

USGS Publications Warehouse

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

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

1996-01-01

90

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

NASA Astrophysics Data System (ADS)

Among the many kinds of natural and man-made disasters, earthquakes dominate with regard to their social and economical impact on the urban environment. Global seismic risk to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to effects of strong earthquakes. Additionally, the uncontrolled growth of mega cities in highly seismic areas around the world is often associated with the construction of seismically unsafe buildings and infrastructures, and undertaken with an insufficient knowledge of the regional seismicity peculiarities and seismic hazard. The assessment of seismic hazard and generation of earthquake scenarios is the first link in the prevention chain and the first step in the evaluation of the seismic risk. The earthquake scenarios are intended as a basic input for developing detailed earthquake damage scenarios for the cities and can be used in earthquake-safe town and infrastructure planning. The city of Sofia is the capital of Bulgaria. It is situated in the centre of the Sofia area that is the most populated (the population is of more than 1.2 mil. inhabitants), industrial and cultural region of Bulgaria that faces considerable earthquake risk. The available historical documents prove the occurrence of destructive earthquakes during the 15th-18th centuries in the Sofia zone. In 19th century the city of Sofia has experienced two strong earthquakes: the 1818 earthquake with epicentral intensity I0=8-9 MSK and the 1858 earthquake with I0=9-10 MSK. During the 20th century the strongest event occurred in the vicinity of the city of Sofia is the 1917 earthquake with MS=5.3 (I0=7-8 MSK). Almost a century later (95 years) an earthquake of moment magnitude 5.6 (I0=7-8 MSK) hit the city of Sofia, on May 22nd, 2012. In the present study as a deterministic scenario event is considered a damaging earthquake with higher probability of occurrence that could affect the city with intensity less than or equal to VIII. The usable and realistic ground motion maps for urban areas are generated: - either from the assumption of a "reference earthquake" - or directly, showing values of macroseimic intensity generated by a damaging, real earthquake. In the study, applying deterministic approach, earthquake scenario in macroseismic intensity ("model" earthquake scenario) for the city of Sofia is generated. The deterministic "model" intensity scenario based on assumption of a "reference earthquake" is compared with a scenario based on observed macroseimic effects caused by the damaging 2012 earthquake (MW5.6). The difference between observed (Io) and predicted (Ip) intensities values is analyzed.

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

2014-05-01

91

Distribution and Characteristics of Repeating Earthquakes in Northern California  

NASA Astrophysics Data System (ADS)

Repeating earthquakes are playing an increasingly important role in the study of fault processes and behavior, and have the potential to improve hazard assessment, earthquake forecast, and seismic monitoring capabilities. These events rupture the same fault patch repeatedly, generating virtually identical seismograms. In California, repeating earthquakes have been found predominately along the creeping section of the central San Andreas Fault, where they are believed to represent failing asperities on an otherwise creeping fault. Here, we use the northern California double-difference catalog of 450,000 precisely located events (1984-2009) and associated database of 2 billion waveform cross-correlation measurements to systematically search for repeating earthquakes across various tectonic regions. An initial search for pairs of earthquakes with high-correlation coefficients and similar magnitudes resulted in 4,610 clusters including a total of over 26,000 earthquakes. A subsequent double-difference re-analysis of these clusters resulted in 1,879 sequences (8,640 events) where a common rupture area can be resolved to the precision of a few tens of meters or less. These repeating earthquake sequences (RES) include between 3 and 24 events with magnitudes up to ML=4. We compute precise relative magnitudes between events in each sequence from differential amplitude measurements. Differences between these and standard coda-duration magnitudes have a standard deviation of 0.09. The RES occur throughout northern California, but RES with 10 or more events (6%) only occur along the central San Andreas and Calaveras faults. We are establishing baseline characteristics for each sequence, such as recurrence intervals and their coefficient of variation (CV), in order to compare them across tectonic regions. CVs for these clusters range from 0.002 to 2.6, indicating a range of behavior between periodic occurrence (CV~0), random occurrence, and temporal clustering. 10% of the RES show burst-like behavior with mean recurrence times smaller than one month. 5% of the RES have mean recurrence times greater than one year and include more than 10 earthquakes. Earthquakes in the 50 most periodic sequences (CV<0.2) do not appear to be predictable by either time- or slip-predictable models, consistent with previous findings. We demonstrate that changes in recurrence intervals of repeating earthquakes can be routinely monitored. This is especially important for sequences with CV~0, as they may indicate changes in the loading rate. We also present results from retrospective forecast experiments based on near-real time hazard functions.

Waldhauser, F.; Schaff, D. P.; Zechar, J. D.; Shaw, B. E.

2012-12-01

92

Long Period Earthquakes Beneath California's Young and Restless Volcanoes  

NASA Astrophysics Data System (ADS)

The newly established USGS California Volcano Observatory has the broad responsibility of monitoring and assessing hazards at California's potentially threatening volcanoes, most notably Mount Shasta, Medicine Lake, Clear Lake Volcanic Field, and Lassen Volcanic Center in northern California; and Long Valley Caldera, Mammoth Mountain, and Mono-Inyo Craters in east-central California. Volcanic eruptions occur in California about as frequently as the largest San Andreas Fault Zone earthquakes-more than ten eruptions have occurred in the last 1,000 years, most recently at Lassen Peak (1666 C.E. and 1914-1917 C.E.) and Mono-Inyo Craters (c. 1700 C.E.). The Long Valley region (Long Valley caldera and Mammoth Mountain) underwent several episodes of heightened unrest over the last three decades, including intense swarms of volcano-tectonic (VT) earthquakes, rapid caldera uplift, and hazardous CO2 emissions. Both Medicine Lake and Lassen are subsiding at appreciable rates, and along with Clear Lake, Long Valley Caldera, and Mammoth Mountain, sporadically experience long period (LP) earthquakes related to migration of magmatic or hydrothermal fluids. Worldwide, the last two decades have shown the importance of tracking LP earthquakes beneath young volcanic systems, as they often provide indication of impending unrest or eruption. Herein we document the occurrence of LP earthquakes at several of California's young volcanoes, updating a previous study published in Pitt et al., 2002, SRL. All events were detected and located using data from stations within the Northern California Seismic Network (NCSN). Event detection was spatially and temporally uneven across the NCSN in the 1980s and 1990s, but additional stations, adoption of the Earthworm processing system, and heightened vigilance by seismologists have improved the catalog over the last decade. LP earthquakes are now relatively well-recorded under Lassen (~150 events since 2000), Clear Lake (~60 events), Mammoth Mountain (~320 events), and Long Valley Caldera (~40 events). LP earthquakes are notably absent under Mount Shasta. With the exception of Long Valley Caldera where LP earthquakes occur at depths of ?5 km, hypocenters are generally between 15-25 km. The rates of LP occurrence over the last decade have been relatively steady within the study areas, except at Mammoth Mountain, where years of gradually declining LP activity abruptly increased after a swarm of unusually deep (20 km) VT earthquakes in October 2012. Epicenter locations relative to the sites of most recent volcanism vary across volcanic centers, but most LP earthquakes fall within 10 km of young vents. Source models for LP earthquakes often involve the resonance of fluid-filled cracks or nonlinear flow of fluids along irregular cracks (reviewed in Chouet and Matoza, 2013, JVGR). At mid-crustal depths the relevant fluids are likely to be low-viscosity basaltic melt and/or exsolved CO2-rich volatiles (Lassen, Clear Lake, Mammoth Mountain). In the shallow crust, however, hydrothermal waters/gases are likely involved in the generation of LP seismicity (Long Valley Caldera).

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

2013-12-01

93

Crustal deformation in great California earthquake cycles  

NASA Technical Reports Server (NTRS)

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

Li, Victor C.; Rice, James R.

1986-01-01

94

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

95

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, R.J., Jr.; Petersen, M.D.

2004-01-01

96

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

USGS Publications Warehouse

As part of the U.S. Geological Survey’s (USGS) multi-hazards project in the Long Valley Caldera-Mono Lake area, the California Geological Survey (CGS) developed several earthquake scenarios and evaluated potential seismic hazards, including ground shaking, surface fault rupture, liquefaction, and landslide hazards associated with these earthquake scenarios. The results of these analyses can be useful in estimating the extent of potential damage and economic losses because of potential earthquakes and in preparing emergency response plans. The Long Valley Caldera-Mono Lake area has numerous active faults. Five of these faults or fault zones are considered capable of producing magnitude ?6.7 earthquakes according to the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2) developed by the 2007 Working Group of California Earthquake Probabilities (WGCEP) and the USGS National Seismic Hazard Mapping (NSHM) Program. These five faults are the Fish Slough, Hartley Springs, Hilton Creek, Mono Lake, and Round Valley Faults. CGS developed earthquake scenarios for these five faults in the study area and for the White Mountains Fault to the east of the study area. Earthquake scenarios are intended to depict the potential consequences of significant earthquakes. They are not necessarily the largest or most damaging earthquakes possible. Earthquake scenarios are both large enough and likely enough that emergency planners should consider them in regional emergency response plans. Earthquake scenarios presented here are based on fault geometry and activity data developed by the WGCEP, and are consistent with the 2008 Update of the United States National Seismic Hazard Maps (NSHM).For the Hilton Creek Fault, two alternative scenarios were developed in addition to the NSHM scenario to account for different opinions in how far north the fault extends into the Long Valley Caldera. For each scenario, ground motions were calculated using the current standard practice: USGS deterministic seismic hazard analysis program and three Next Generation Ground Motion Attenuation (NGA) models. Ground motion calculations incorporated the potential amplification of seismic shaking by near-surface soils defined by a map of the average shear wave velocity in the uppermost 30 m (VS30) developed by CGS. In addition to ground shaking, earthquakes cause ground failure, which can cause severe damage to buildings and lifelines. Ground failure includes surface fault rupture, liquefaction, and seismically induced landslides. For each earthquake scenario, potential surface fault displacements are estimated using deterministic and probabilistic approaches. Liquefaction occurs when saturated sediments lose their strength because of ground shaking. Zones of potential liquefaction are mapped by incorporating areas where loose sandy sediments, shallow groundwater, and strong earthquake shaking coincide in the earthquake scenario. The process for defining zones of potential landslide and rockfall incorporates rock strength, surface slope, existing landslides, with ground motions caused by the earthquake scenario. Each scenario is illustrated with maps of seismic shaking potential and fault displacement, liquefaction, and landslide potential. Seismic shaking is depicted by the distribution of shaking intensity, peak ground acceleration, and 1.0-second spectral acceleration. One-second spectral acceleration correlates well with structural damage to surface facilities. Acceleration greater than 0.2 g is often associated with strong to violent perceived ground shaking and may cause moderate to heavy damage. The extent of strong shaking is influenced by subsurface fault dip and near surface materials. Strong shaking is more widespread in the hanging wall regions of a normal fault. Larger ground motions also occur where young alluvial sediments amplify the shaking. Both of these effects can lead to strong shaking that extends farther from the fault on the valley side than on the hill side. The effect of fault rupture displacements may be localized along the s

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

2014-01-01

97

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.

98

Finite Moment Tensors of Southern California Earthquakes  

Microsoft Academic Search

We have developed procedures for inverting broadband waveforms for the finite moment tensors (FMTs) of regional earthquakes. The FMT is defined in terms of second-order polynomial moments of the source space-time function and provides the lowest order representation of a finite fault rupture; it removes the fault-plane ambiguity of the centroid moment tensor (CMT) and yields several additional parameters of

T. H. Jordan; P. Chen; L. Zhao

2003-01-01

99

Images of crust beneath southern California will aid study of earthquakes and their effects  

Microsoft Academic Search

The Whittier Narrows earthquake of 1987 and the Northridge earthquake of 1991 highlighted the earthquake hazards associated with buried faults in the Los Angeles region. A more thorough knowledge of the subsurface structure of southern California is needed to reveal these and other buried faults and to aid us in understanding how the earthquake-producing machinery works in this region.

Gary S. Fuis; David A. Okaya; Robert W. Clayton; William J. Lutter; Trond Ryberg; Thomas M. Brocher; Thomas M. Henyey; Mark L. Benthien; Paul M. Davis; James Mori; Rufus D. Catchings; Uri S. ten Brink; Monica D. Kohler; Kim D. Klitgord; Robert G. Bohannon

1996-01-01

100

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

101

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

Microsoft Academic Search

The Southern California Earthquake Data Center (SCEDC) archives and provides public access to continuous and event-based earthquake parametric and waveform data gathered by the Southern California Seismic Network. The mission of the SCEDC is to maintain an easily-accessible, well-organized, high-quality, searchable archive of earthquake data for research in seismology and earthquake engineering. The SCEDC has compiled and converted all available

V. L. Appel; R. W. Clayton

2003-01-01

102

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

103

A geospatial analytical system for mapping global medium-term earthquake probabilities  

Microsoft Academic Search

The most widely used time interval for long-term earthquake forecast—the process of estimating the probability for a specific area to experience an earthquake of a given magnitude—is a 30-year time window. For earthquake hazards mitigation, it is desirable to shorten that time interval to a few years so that decision makers can allocate limited resources to high risk areas of

F. Benjamin Zhan; Zhongliang Cai; Yiqing Zhu; Jiangcun Zhou

2012-01-01

104

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

Microsoft Academic Search

The SCEDC archives continuous and triggered data from nearly 3000 data channels from 375 SCSN recorded stations. The SCSN and SCEDC process and archive an average of 12,000 earthquakes each year, contributing to the southern California earthquake catalog that spans from 1932 to present. The SCEDC provides public, searchable access to these earthquake parametric and waveform data through its website

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

2009-01-01

105

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

106

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.

Keefer, David K., (Edited By)

1998-01-01

107

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

108

Three-dimensional tomography of the 1992 southern California earthquake sequence: Constraints on dynamic earthquake rupture?  

Microsoft Academic Search

Tomographic inversion of P-wave arrival times from aftershocks of 1992 southern California earthquakes is used to produce three dimensional images of subsurface velocity. The preliminary 1992 data set, augmented by the 1986 M 5.9 North Palm Springs sequence, consists of 6458 high-quality events recorded by the permanent regional network---providing 76306 raypaths for inversion. The target area consisted of a 104

Jonathan M. Lees; Craig Nicholson

1993-01-01

109

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

110

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

111

Study of Near-Source Earthquake Ground Motions of Three California Earthquakes: North ridge, Whittier, and Landers.  

National Technical Information Service (NTIS)

Three datasets were analyzed and maps were prepared of near source ground motions associated with the Whittier, Northridge, and Landers earthquakes in southern California. Vertical motions were enhanced in the near source area of high angle thrust faults ...

D. J. Leeds

1998-01-01

112

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

Microsoft Academic Search

Interns in the program Southern California Earthquake Center\\/Undergraduate Studies in Earthquake Information Technology (SCEC\\/UseIT, an NSF Research Experience for Undergraduates Site) have designed, engineered, and distributed SCEC-VDO (Virtual Display of Objects), an interactive software used by earthquake scientists and educators to integrate and visualize global and regional, georeferenced datasets. SCEC-VDO is written in Java\\/Java3D with an extensible, scalable architecture. An

S. Perry; P. Maechling; T. Jordan

2006-01-01

113

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

Microsoft Academic Search

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

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

2010-01-01

114

Stress drops and radiated energies of aftershocks of the 1994 Northridge, California, earthquake  

Microsoft Academic Search

We study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern California earthquakes. We use empirical Green functions to obtain source time functions for 47 of the larger (M >= 4.0) aftershocks of the 1994 Northridge, California earthquake (M6.7). We estimate static and dynamic stress drops from the source time functions

Jim Mori; Rachel E. Abercrombie; Hiroo Kanamori

2003-01-01

115

Crustal earthquake bursts in California and Japan: Their patterns and relation to volcanoes  

E-print Network

Crustal earthquake bursts in California and Japan: Their patterns and relation to volcanoes John E; accepted 19 September 2006; published 26 October 2006. [1] We analyze 153 bursts of earthquakes in southern Cali- fornia and Japan. The burst patterns are similar in southern California and Japan; they fill

Shearer, Peter

116

UNIVERSITY OF SOUTHERN CALIFORNIA BUILDING PERIODS FOR USE IN EARTHQUAKE RESISTANT DESIGN  

E-print Network

UNIVERSITY OF SOUTHERN CALIFORNIA BUILDING PERIODS FOR USE IN EARTHQUAKE RESISTANT DESIGN CODES Investigator: Other contributors: Maria I. Todorovska M. D. Trifunac University of Southern California T.-Y Hao ­ EARTHQUAKE RESPONSE DATA COMPILATION AND ANALYSIS OF TIME AND AMPLITUDE VARIATIONS Final Project Report

Southern California, University of

117

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

E-print Network

Comprehensive analysis of earthquake source spectra and swarms in the Salton Trough, California X; published 23 September 2011. [1] We study earthquakes within California's Salton Trough from 1981 to 2009 with previous results indicating relatively high attenuation in the Salton Trough. Stress drops estimated from

Shearer, Peter

118

Southern California Earthquake Center Crustal Motion Map Version 3.0  

Microsoft Academic Search

To measure current deformation in southern California, the Southern California Earthquake Center (SCEC) has been collecting and analyzing geodetic data from a wide range of sources, and providing the results in the form of station velocities. These crustal motion results can be used to study tectonic processes and relate crustal deformation to earthquake potential. The most recent update (SCEC Crustal

Z. Shen; D. Agnew; Y. Bock; M v Domselaar; D. Dong; T. A. Herring; K. W. Hudnut; D. D. Jackson; R. W. King; S. McClusky; R. Nikolaidis; M. Wang

2001-01-01

119

Significance of stress transfer in time-dependent earthquake probability calculations  

USGS Publications Warehouse

A sudden change in stress is seen to modify earthquake rates, but should it also revise earthquake probability? Data used to derive input parameters permits an array of forecasts; so how large a static stress change is require to cause a statistically significant earthquake probability change? To answer that question, effects of parameter and philosophical choices are examined through all phases of sample calculations, Drawing at random from distributions of recurrence-aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs. Probability density funtions built from the recurrence-aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model. Consequences of choices made in stress transfer calculations, such as different slip models, fault rake, dip, and friction are, tracked. For interactions among large faults, calculated peak stress changes may be localized, with most of the receiving fault area changed less than the mean. Thus, to avoid overstating probability change on segments, stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean. Disparity resulting from interaction probability methodology is also examined. For a fault with a well-understood earthquake history, a minimum stress change to stressing rate ratio of 10:1 to 20:1 is required to significantly skew probabilities with >80-85% confidence. That ratio must be closer to 50:1 to exceed 90-95% confidence levels. Thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low.

Parsons, T.

2005-01-01

120

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.

Parsons, T.

2004-01-01

121

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

Microsoft Academic Search

Earthquake focal mechanisms from before and after the 1989 Loma Prieta, California earthquake are used to infer the coseismic stress change. Before the main shock, most earthquakes correspond to right lateral slip on planes sub-parallel to the San Andreas fault, and imply a generally N-S most compressional stress axis and a vertical intermediate stress axis. Aftershocks within the main shock

Andrew J. Michael; William L. Ellsworth; David H. Oppenheimer

1990-01-01

122

Evidence for Mogi doughnut behavior in seismicity preceding small earthquakes in southern California  

E-print Network

Evidence for Mogi doughnut behavior in seismicity preceding small earthquakes in southern preceding M 2­5 earthquakes in southern California from 1981 to 2005 using a high-resolution catalog and identify regions of enhanced activity in a 1-day period preceding larger earthquakes at distances

Lin, Guoqing

123

Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial Valley, California  

E-print Network

Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial; published 14 March 2013. [1] We investigate the finite rupture processes of two M > 5 earthquakes earthquakes in the 2012 Brawley swarm, Imperial Valley, California, Geophys. Res. Lett., 40, 847­852, doi:10

Martin, Alain

124

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

125

RESPONSE OF TALL STEEL BUILDINGS IN SOUTHERN CALIFORNIA TO THE MAGNITUDE 7.8 SHAKEOUT SCENARIO EARTHQUAKE  

E-print Network

in the Great Southern California Shakeout Scenario in 2008, a large-scale earthquake response exercise one striking southern California. Scenario Earthquake The scenario earthquake chosen is a magnitude 7RESPONSE OF TALL STEEL BUILDINGS IN SOUTHERN CALIFORNIA TO THE MAGNITUDE 7.8 SHAKEOUT SCENARIO

Krishnan, Swaminathan

126

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

NASA Astrophysics Data System (ADS)

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

Liang, Zach; Lee, George C.

2013-06-01

127

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

NASA Astrophysics Data System (ADS)

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

Liang, Zach; Lee, George C.

2013-06-01

128

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

129

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

USGS Publications Warehouse

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

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

1973-01-01

130

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

USGS Publications Warehouse

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

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

1973-01-01

131

Landslides triggered by the 1994 Northridge, California, earthquake  

USGS Publications Warehouse

The 17 January 1994 Northridge, California, earthquake (Mw, = 6.7) triggered more than 11,000 landslides over an area of about 10,000 km2. Most of the landslides were concentrated in a 1000-km2 area that included the Santa Susana Mountains and the mountains north of the Santa Clara River valley. We mapped landslides triggered by the earthquake in the field and from 1:60,000-nominal-scale aerial photography provided by the U.S. Air Force and taken the morning of the earthquake; these mapped landslides were subsequently digitized and plotted in a GIS-based format. Most of the triggered landslides were shallow (1- to 5-m thick), highly disrupted falls and slides within weakly cemented Tertiary to Pleistocene clastic sediment. Average volumes of these types of landslides were less than 1000 m3, but many had volumes exceeding 100,000 m3. The larger disrupted slides commonly had runout paths of more than 50 m, and a few traveled as far as 200 m from the bases of steep parent slopes. Deeper (>5-m thick) rotational slumps and block slides numbered in the tens to perhaps hundreds, a few of which exceeded 100,000 m3 in volume. Most of these were reactivations of previously existing landslides. The largest single landslide triggered by the earthquake was a rotational slump/block slide having a volume of 8 ?? 106 m3. Analysis of the mapped landslide distribution with respect to variations in (1) landslide susceptibility and (2) strong shaking recorded by hundreds of instruments will form the basis of a seismic landslide hazard analysis of the Los Angeles area.

Harp, E. L.; Jibson, R. W.

1996-01-01

132

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

133

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

Microsoft Academic Search

The Kobe earthquake struck at the edge of the densely populated Osaka-Kyoto corridor in southwest Japan. We investigate how the earthquake transferred stress to nearby faults, altering their proximity to failure and thus changing earthquake probabilities. We find that relative to the pre-Kobe seismicity, Kobe aftershocks were concentrated in regions of calculated Coulomb stress increase and less common in regions

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

1998-01-01

134

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

USGS Publications Warehouse

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

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

1973-01-01

135

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

136

Inventory of landslides triggered by the 1994 Northridge, California earthquake  

USGS Publications Warehouse

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

Harp, Edwin L.; Jibson, Randall W.

1995-01-01

137

Heightened Odds of Large Earthquakes Near Istanbul: An Interaction-Based Probability Calculation  

Microsoft Academic Search

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

Tom Parsons; Shinji Toda; Ross S. Stein; Aykut Barka; James H. Dieterich

2000-01-01

138

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

Microsoft Academic Search

Statistics of earthquakes in California show linear frequency-magnitude relationships in the range of M2.0 to M5.5 for various data sets. Assuming Gutenberg-Richter distributions, there is a systematic decrease in b value with increasing depth of earthquakes. We find consistent results for various data sets from northern and southern California that both include and exclude the larger aftershock sequences. We suggest

Jim Mori; Rachel E. Abercrombie

1997-01-01

139

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

PubMed

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

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

1974-06-21

140

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

Microsoft Academic Search

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

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

2003-01-01

141

Seismic Moment, Stress, and Source Dimensions for Earthquakes in the California-Nevada Region  

Microsoft Academic Search

The source mechanism of earthquakes in the California-Nevada region was studied using surface wave analyses, surface displacement observations in the source region, magnitude determinations, and accurate epicenter locations. Fourier analyses of surface waves from thirteen earthquakes in the Parkfield region have yielded the following relationship between seismic moment, Mo and Richter magnitude, M,: log Mo -- 1.4 M, n u

Max Wyss; James N. Brune

1968-01-01

142

Complex nonvolcanic tremor near Parkfield, California, triggered by the great 2004 Sumatra earthquake  

Microsoft Academic Search

In several instances, the passing surface waves from large earthquakes have ignited nonvolcanic tremor (NVT) on major faults. Still, the mechanism of tremor and its reaction to the dynamic stressing from various body and surface waves is poorly understood. We examine tremor near Parkfield, California, beneath the San Andreas fault triggered by the Mw 9.2, 2004 Sumatra earthquake. The prolonged

Abhijit Ghosh; John E. Vidale; Zhigang Peng; Kenneth C. Creager; Heidi Houston

2009-01-01

143

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.

144

Post-Earthquake Damage Evaluation and Reporting Procedures: A Guidebook for California Schools.  

ERIC Educational Resources Information Center

The California Office of the State Architect, Structural Safety Division (OSA/SSS) is responsible for evaluating public school structures after an earthquake. However, final authority on whether a building should be reoccupied after damage lies with the school district. This guidebook is designed to help school officials assess earthquake damage…

California State Office of Emergency Services, Sacramento.

145

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

Microsoft Academic Search

Methods designed to evaluate the chronology of earthquakes produced by the San Andreas fault in southern California are discussed. The date esimates obtained by various methods for the large 10 earthquakes recorded within the past 1800 years at Pallett Creek are presented and compared with new dates derived from radiocarbon analysis. It was found that old date ranges, although much

Kerry Sieh; Minze Stuiver; David Brillinger

1989-01-01

146

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

147

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

148

Simplifying Construction of Complex Workflows for Non-Expert Users of the Southern California Earthquake Center Community Modeling Environment  

E-print Network

90292, (3) Southern California Earthquake Center, USC, Los Angeles CA, 90089, USA, {Corresponding Author of the Community Modeling Environment developed by the Southern California Earthquake Center, these toolsSimplifying Construction of Complex Workflows for Non-Expert Users of the Southern California

Kim, Jihie

149

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

150

Southern California Earthquake Forecast Based on the Geodetic Strain Rate  

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

Z. Shen; D. D. Jackson

2005-01-01

151

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

152

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

NSDL National Science Digital Library

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

153

California takes earthquakes very seriously. The state straddles two major tectonic plates and is subject to relatively frequent, often major, potentially devastating quakes.  

E-print Network

on California and its San Andreas Fault. A team led by Southern California Earthquake Center (SCEC) director by Geoffrey Ely, University of Southern California. Jaguar OverviewEarthquake Simulation Rocks SouthernCalifornia takes earthquakes very seriously. The state straddles two major tectonic plates

154

Influence of static stress changes on earthquake locations in southern California  

USGS Publications Warehouse

EARTHQUAKES induce changes in static stress on neighbouring faults that may delay, hasten or even trigger subsequent earthquakes1-10. The length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment, but is presently unknown. Here we use an elastic half-space model11 to estimate the static stress changes generated by damaging (magnitude M???5) earthquakes in southern California over the past 26 years, and to investigate the influence of these changes on subsequent earthquake activity. We find that, in the 1.5-year period following a M???5 earthquake, any subsequent nearby M???5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake. After this period, damaging earthquakes are equally likely to rupture loaded and relaxed faults. Our results suggest that there is a short period of time following a damaging earthquake in southern California in which simple Coulomb failure stress models could be used to identify regions of increased seismic hazard. ?? 1995 Nature Publishing Group.

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

1995-01-01

155

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

NASA Astrophysics Data System (ADS)

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

Roeloffs, Evelyn A.

1998-01-01

156

The potential for earthquake early warning in southern California.  

PubMed

Earthquake mitigation efforts in the United States currently use long-term probabilistic hazard assessments and rapid post-earthquake notification to reduce the potential damage of earthquakes. Here we present the seismological design for and demonstrate the feasibility of a short-term hazard warning system. Using data from past earthquakes, we show that our Earthquake Alarm System (ElarmS) could, with current TriNet instrumentation, issue a warning a few to tens of seconds ahead of damaging ground motion. The system uses the frequency content of the P-wave arrival to determine earthquake magnitude, an approach that allows magnitude determination before any damaging ground motion occurs. PMID:12730599

Allen, Richard M; Kanamori, Hiroo

2003-05-01

157

Source Characterization and Ground Motion Modeling of the 1892 Vacaville-Winters Earthquake Sequence, California  

NASA Astrophysics Data System (ADS)

We use a multidisciplinary approach that combines structural geologic analysis with geophysical modeling to evaluate the depth, geometry and segmentation of thrust faults that were the probable sources of the 1892 Winters-Vacaville earthquake sequence, which produced significant damage to towns in the southwestern Sacramento Valley, California. The largest event in this sequence occurred 19 April 1892 with a maximum Modified Mercalli Intensity (Imm) of IX and was assigned M 6.5 based on felt area. Through crustal velocity modeling and analysis of seismic reflection data, we interpret that the epicentral region of the 1892 sequence is underlain by a system of blind, west-dipping thrust faults at a minimum depth of about 8 km. Quaternary uplift along the valley margin is a result of fault-propagation folding above the tips of the thrust faults. From analysis of seismic reflection data, we interpret that two geometrically distinct thrust-fault segments are separated by a right en echelon step at the latitude of the town of Winters. The "Gordon Valley" segment, which probably was the source of the 1892 main shock, is 18 +/- 2 km long and extends between the towns of Winters and Vacaville. The empirical peak horizontal acceleration- and velocity-Imm relationships of Wald et al. (1999) were used with synthetic ground motion modeling to demonstrate that rupture of the Gordon Valley segment reproduces the distribution of Imm >= VI intensities documented from anecdotal accounts of the 19 and 21 April 1892 earthquakes, including probable directivity effects east of the range front. Integrated structural analysis and ground motion modeling also were used to assess the role of the northern Gordon Valley segment boundary in arresting the 19 April 1892 earthquake rupture, and the subsequent occurrence of the 21 April 1892 aftershock. Our results support the inferences of previous workers (Wong and Ely, 1983; Eaton, 1986; Toppozada, 1987; Bennett, 1987; Unruh and Moores, 1992) that the 1983 Coalinga earthquake, which occurred on a blind thrust fault beneath the western San Joaquin Valley, is an analogue for the 1892 Winters-Vacaville sequence.

O'Connell, D. R.; Unruh, J.; Block, L. P.

2001-12-01

158

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

SciTech Connect

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

Stothers, R.B. (NASA, Goddard Space Flight Center, Greenbelt, MD (USA))

1990-10-01

159

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

NASA Technical Reports Server (NTRS)

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

Stothers, Richard B.

1990-01-01

160

Tilt precursors before earthquakes on the San Andreas fault, California  

USGS Publications Warehouse

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

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

1974-01-01

161

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

PubMed

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

Johnston, M J; Mortensen, C E

1974-12-13

162

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

NASA Astrophysics Data System (ADS)

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

Meng, L.; Shi, B.

2010-12-01

163

Earthquake cycle on a transform fault in the Gulf of California, Mexico.  

NASA Astrophysics Data System (ADS)

South of the San Andreas Fault system, ~90% of the North America/Pacific plate motion is accommodated along the Gulf of California. Here the plate boundary deformation is partitioned in deep basins formation, often resulting in production of new oceanic crust, connected by long transform faults. In the central part of the Gulf, one of these transform faults, the Ballenas fault, is localized in the Canal de Ballenas, a ~30 km wide channel between Isla Angel de la Garda and mainland Baja California in an area where full oceanic crust is still not generated. The presence of land on both the sides of this "quasi marine" transform fault give the unique opportunity to perform geodetic studies across its trace. On August 3rd 2009, a series of seismic strike slip events (including a M6.9) happened along this segment of plate boundary allowing a combined study of co- and inter-seismic deformation. Here we present the results from 5 years of EGPS along a transect perpendicular to the plate motion direction at approximately 29 degrees North. These surveys include at least 3 occupations before the seismic event and at least 2 occupations after the earthquake. The analysis of the inter-seismic data shows that ~46 mm/yr of relative motion is accommodated within the Canal de Ballenas. Co-seismic data show displacements up to 25 cm on the two sites closest to the event and a pattern compatible with the finite fault model computed by USGS (although the USGS location of the hypocenter is probably 100 km too much to the East). The geodetically estimated fault location is also compatible with multibeam bathymetry. The data collected after the earthquake show also the possibility to identify postseismic displacement from the campaign data. They also show the possibility that the postseismic behavior of the "marine" side is different from the one of the on land side.

Malservisi, Rocco; Hackl, Matthias; Plattner, Christina; Suarez Vidal, Francisco; Gonzales Garcia, Javier; Amelung, Falk

2010-05-01

164

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

165

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

166

Development of damage probability matrices based on Greek earthquake damage data  

NASA Astrophysics Data System (ADS)

A comprehensive study is presented for empirical seismic vulnerability assessment of typical structural types, representative of the building stock of Southern Europe, based on a large set of damage statistics. The observational database was obtained from post-earthquake surveys carried out in the area struck by the September 7, 1999 Athens earthquake. After analysis of the collected observational data, a unified damage database has been created which comprises 180,945 damaged buildings from/after the near-field area of the earthquake. The damaged buildings are classified in specific structural types, according to the materials, seismic codes and construction techniques in Southern Europe. The seismic demand is described in terms of both the regional macroseismic intensity and the ratio ? g/ a o, where ? g is the maximum peak ground acceleration (PGA) of the earthquake event and a o is the unique value PGA that characterizes each municipality shown on the Greek hazard map. The relative and cumulative frequencies of the different damage states for each structural type and each intensity level are computed in terms of damage ratio. Damage probability matrices (DPMs) and vulnerability curves are obtained for specific structural types. A comparison analysis is fulfilled between the produced and the existing vulnerability models.

Eleftheriadou, Anastasia K.; Karabinis, Athanasios I.

2011-03-01

167

Regression models for predicting the probability of near-fault earthquake ground motion pulses, and their period.  

E-print Network

Regression models for predicting the probability of near-fault earthquake ground motion pulses University, Stanford, CA, USA ABSTRACT: Near-fault earthquake ground motions containing large velocity pulses demonstrate the potential importance of quantitatively considering occurrence of near-fault pulses

Baker, Jack W.

168

Earthquake-Induced Landslide Probability Derived From Four Different Methods and Result Comparison  

NASA Astrophysics Data System (ADS)

This study analyzed landslides induced by the 1999 Chi-Chi, Taiwan earthquake at a test site in Central Taiwan, called Kuohsing, and landslide spatial probability maps for the test site were made. Landslides induced by the earthquake were extracted from SPOT imageries, Landslide potential factors, which include slope, slope aspect, terrain roughness, total curvature and slope height were derived from a 40m resolution DEM. Lithology and structural data were obtained from a 1 to 50 thousand scaled geological map. Earthquake strong-motion data were used to calculate Arias intensity and others. The state-of-the-art methods, which include two multivariate approach - discriminant analysis and logistic regression, an artificial neural network approach, and the Newmark's method, were used in the analyses. In the discriminant analysis, the output discriminant scores are used to develop landslide susceptibility index (LSI). In the logistic regression, an output probability is used as a LSI directly. In the artificial neural network approach, a fuzzy set concept for landslide and non-landslide was incorporated into the analysis so that the network can output a continuous spectrum for landslide and non-landslide membership, and a defuzzifier was used to obtain a nonfuzzy value for LSI. In the Newmark's method, the output value is a Newmark displacement (Dn). All LSIs and Dns are compared with the landslide inventory and then calculate the landslide ratio or probability of failure for each LSI or Dn interval. These were used to develop the probability of failure functions against LSIs or Dn. Landslide probability maps were then drawn by using the probability of failure functions. All the four methods obtain good result in predicting landslides. Four landslide probability maps show similar probability level and distribution pattern. Among the four methods, discriminant analysis and logistic regression are both stable and good in predicting landslides. The artificial neural network method is good also, but it revealed over-trained phenomenon at the hilly terrain in our test area. The performance of the Newmark's method is not so good as the other methods.

Lee, C.

2005-12-01

169

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

PubMed

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

1990-01-19

170

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

171

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

USGS Publications Warehouse

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

Field, Edward H.; Milner, Kevin R.

2008-01-01

172

Coseismic folding, earthquake recurrence, and the 1987 source mechanism at Whittier Narrows, Los Angeles Basin, California  

Microsoft Academic Search

Static deformation associated with the October 1, 1987, Whittier Narrows, California, M=6.0 earthquake was detected by geodetic elevation changes. The earthquake uplifted a 1.5-km-high Quaternary fold (the Santa Monica Mountains anticlinorium) by 50 mm but caused no fault rupture at the ground surface. This suggests that folding and faulting of the Los Angeles basin sediments are coincident and continuing. After

Jian Lin; Ross S. Stein

1989-01-01

173

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

NASA Technical Reports Server (NTRS)

The source parameters of 19 earthquakes in the Gulf of California were determined from an inversion of long-period P and SH waveforms. The inversion procedure is described and the estimated precision of the derived source parameters is examined, with particular attention given to source complexity, the resolution of slip vector azimuth, and the resolution of centroid depth. The implications of these earthquake source characteristics for the tectonic evolution of the gulf are discussed.

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

1987-01-01

174

Spatio-temporal Patterns of Inelastic Strain Produced by Southern California Earthquakes  

Microsoft Academic Search

We analyze spatial and temporal features of co-seismic in-elastic deformation in the southern California crust. At present we examine results associated with approximately 100,000 earthquakes occurring between 1981 and 2000, and are in the process of expanding the research to include earlier events. Locations and fault plane solutions for the earthquakes are determined using the HYPOINVERSE and FPFIT computer codes.

S. Levin; Y. Ben-Zion; J. Sheridan

2001-01-01

175

Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California - Implications for earthquake scaling  

Microsoft Academic Search

A 2.5-km deep triaxial seismometer at Cajon Pass in southern California has recorded several hundred earthquakes less than M(L)4.0 occurring within the San Andreas fault system. At 2.5-km seismic background noise is below amplifier sensitivity, and the 2-250 Hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs. Compared with downhole recorded

Rachel Abercrombie; Peter Leary

1993-01-01

176

Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California: Implications for earthquake scaling  

Microsoft Academic Search

A 2.5 km deep triaxial seismometer at Cajon Pass in southern California has recorded several hundred earthquakes

Rachel Abercrombie; Peter Leary

1993-01-01

177

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

Microsoft Academic Search

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

Jessica Murray; John Langbein

2006-01-01

178

The June, 2005 Anza/Yucaipa Southern California Earthquake Sequence: Distant Triggering by Moderate Mainshocks On June 12, 2005, a MW  

E-print Network

The June, 2005 Anza/Yucaipa Southern California Earthquake Sequence: Distant Triggering by Moderate-2005) there have been only 8 M > 4.9 earthquakes in Southern California. Is it plausible that a M 5.2 earthquake of Anza and was felt throughout Southern California. Two subsequent events appeared unusual. The first

Felzer, Karen

179

FACTORS AFFECTING DETECTION PROBABILITY OF CALIFORNIA BLACK RAILS  

E-print Network

of Reclamation, P.O. Box 61470, Boulder City, NV 89005-1470, USA Abstract: Optimal survey methods for estimating, Laterallus jamaicensis coturniculus, marshlands, monitoring, observer bias, population declines, survey methods, tape playback, vocalizations, western United States, wetlands. 360 California black rails

Conway, Courtney J.

180

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

181

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

PubMed

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

Jaumé, S C; Sykes, L R

1992-11-20

182

Probability assessment on the recurring Meishan earthquake in central Taiwan with a new non-stationary analysis  

NASA Astrophysics Data System (ADS)

From theory to experience, earthquake probability should be increasing with time as far as the same fault is concerned, rather than being a stationary process or independent of the date of the last occurrence. With a new non-stationary model, we evaluated the earthquake probability associated with the Meishan fault in central Taiwan, a growing concern to the local community given a relatively short return period reported (i.e., around 160 years). The analysis shows that on the condition that the earthquake has not recurred by the end of year 2014, the earthquake probability in the next 50 years could be around 0.3 (mean value), with a 95% confidence interval from 0.26 to 0.36.

Wang, J. P.; Yun, X.

2014-07-01

183

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

SciTech Connect

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

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

2006-04-15

184

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

185

Potential earthquake faults offshore Southern California, from the eastern Santa Barbara Channel south to Dana Point  

USGS Publications Warehouse

Urban areas in Southern California are at risk from major earthquakes, not only quakes generated by long-recognized onshore faults but also ones that occur along poorly understood offshore faults. We summarize recent research findings concerning these lesser known faults. Research by the U.S. Geological Survey during the past five years indicates that these faults from the eastern Santa Barbara Channel south to Dana Point pose a potential earthquake threat. Historical seismicity in this area indicates that, in general, offshore faults can unleash earthquakes having at least moderate (M 5-6) magnitude. Estimating the earthquake hazard in Southern California is complicated by strain partitioning and by inheritance of structures from early tectonic episodes. The three main episodes are Mesozoic through early Miocene subduction, early Miocene crustal extension coeval with rotation of the Western Transverse Ranges, and Pliocene and younger transpression related to plate-boundary motion along the San Andreas Fault. Additional complication in the analysis of earthquake hazards derives from the partitioning of tectonic strain into strike-slip and thrust components along separate but kinematically related faults. The eastern Santa Barbara Basin is deformed by large active reverse and thrust faults, and this area appears to be underlain regionally by the north-dipping Channel Islands thrust fault. These faults could produce moderate to strong earthquakes and destructive tsunamis. On the Malibu coast, earthquakes along offshore faults could have left-lateral-oblique focal mechanisms, and the Santa Monica Mountains thrust fault, which underlies the oblique faults, could give rise to large (M ??7) earthquakes. Offshore faults near Santa Monica Bay and the San Pedro shelf are likely to produce both strike-slip and thrust earthquakes along northwest-striking faults. In all areas, transverse structures, such as lateral ramps and tear faults, which crosscut the main faults, could segment earthquake rupture zones. ?? 2009 The Geological Society of America.

Fisher, M. A.; Sorlien, C. C.; Sliter, R. W.

2009-01-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

187

FORECAST MODEL FOR MODERATE EARTHQUAKES NEAR PARKFIELD, CALIFORNIA.  

USGS Publications Warehouse

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

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

1985-01-01

188

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

USGS Publications Warehouse

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

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

2010-01-01

189

Stress drops and radiated energies of aftershocks of the 1994 Northridge, California, earthquake  

NASA Astrophysics Data System (ADS)

We study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern California earthquakes. We use empirical Green functions to obtain source time functions for 47 of the larger (M ? 4.0) aftershocks of the 1994 Northridge, California earthquake (M6.7). We estimate static and dynamic stress drops from the source time functions and compare them to well-calibrated estimates of the radiated energy. Our measurements of radiated energy are relatively low compared to the static stress drops, indicating that the static and dynamic stress drops are of similar magnitude. This is confirmed by our direct estimates of the dynamic stress drops. Combining our results for the Northridge aftershocks with data from other southern California earthquakes appears to show an increase in the ratio of radiated energy to moment, with increasing moment. There is no corresponding increase in the static stress drop. This systematic change in earthquake scaling from smaller to larger (M3 to M7) earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults.

Mori, Jim; Abercrombie, Rachel E.; Kanamori, Hiroo

2003-11-01

190

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.

Harris, Ruth A.

1998-01-01

191

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.

192

Complexity of energy release during the Imperial Valley, California, earthquake of 1940  

Microsoft Academic Search

The pattern of energy release during the Imperial Valley, California, earth- quake of 1940 is studied by analyzing the El Centro strong motion seismograph record and records from the Tinemaha seismograph station, 546 km from the epicenter. The earthquake was a multiple event sequence with at least 4 events recorded at El Centro in the first 25 seconds, followed by

M. D. Trifunac; JAMES N. BRUNE

1970-01-01

193

Earthquake Locations and Three-Dimensional Crustal Structure in the Coyote Lake Area, Central California  

Microsoft Academic Search

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

Clifford H. Thurber

1983-01-01

194

Response of desert pavement to seismic shaking, Hector Mine earthquake, California, 1999  

Microsoft Academic Search

The October 1999 Mw 7.1 Hector Mine earthquake in the Mojave Desert, California, generated characteristic surface disturbances on nearby desert pavements. These disturbances included (1) zones of wholesale gravel displacement interspersed with zones of intact pavement, (2) displaced and rotated cobbles, (3) moats around loosened, embedded boulders, (4) filling of abandoned cobble sockets, boulder moats, and other depressions with gravel,

P. K. Haff

2005-01-01

195

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

E-print Network

a bootstrap resampling method. We define 37 bursts with sm 0.8 as the migration group, and 32 bursts with smSpatial migration of earthquakes within seismic clusters in Southern California: Evidence for fluid to migrate slowly with time, which may reflect event triggering due to slow fault slip or fluid flow. We

Abercrombie, Rachel E.

196

Response of desert pavement to seismic shaking, Hector Mine earthquake, California, 1999  

E-print Network

Response of desert pavement to seismic shaking, Hector Mine earthquake, California, 1999 P. K. Haff characteristic surface disturbances on nearby desert pavements. These disturbances included (1) zones of wholesale gravel displacement interspersed with zones of intact pavement, (2) displaced and rotated cobbles

Ahmad, Sajjad

197

Stress drops and radiated energies of aftershocks of the 1994 Northridge, California, earthquake  

E-print Network

Stress drops and radiated energies of aftershocks of the 1994 Northridge, California, earthquake December 2000; revised 11 May 2003; accepted 25 June 2003; published 28 November 2003. [1] We study stress estimate static and dynamic stress drops from the source time functions and compare them to well

Abercrombie, Rachel E.

198

Near-Field Observations and Source Parameters of Central California Earthquakes.  

National Technical Information Service (NTIS)

In 1966-67 the San Andreas Geophysical Observatory (SAGO) was established on the San Andreas fault zone in central California some 5 miles south of Hollister. This study is an investigation of near-field radiation from local earthquakes recorded on broadb...

L. R. Johnson, T. V. McEvilly

1973-01-01

199

Locations of Small Earthquakes Near the Trifurcation Of the San Jacinto Fault Southeast of Anza, California.  

National Technical Information Service (NTIS)

About 100 small earthquakes (M approximately equal to 1/2 to 2) which occurred near the trifurcation of the San Jacinto fault southeast of Anza, California, have been accurately located using five- and six-station arrays with dimensions of about 10 km. Th...

W. J. Arabasz, J. N. Brune, G. R. Engen

1969-01-01

200

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

Microsoft Academic Search

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

J. E. Ebel; A. L. Kafka

2003-01-01

201

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

Microsoft Academic Search

The Southern California Earthquake Center's Fault Information System (FIS) provides a single point of access to fault-related data and models from multiple databases and datasets. The FIS is built of computer code, metadata and Web interfaces based on Web services technology, which enables queries and data interchange irrespective of computer software or platform. Currently we have working prototypes of programmatic

S. Perry

2003-01-01

202

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

USGS Publications Warehouse

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

Wesson, R.L.; Nicholson, C.

1988-01-01

203

Implication of the Central Gulf of California (MX) Earthquake cycle in understanding continental plate boundary rheology  

NASA Astrophysics Data System (ADS)

The Gulf of California is characterized by the development of a highly oblique plate boundary that rifted the Baja California Peninsula from mainland North America through a series of long transform faults and deep basins. Within the central part of Gulf of California 90 % of the relative motion between North America and Pacific plate is localized in a very narrow region between the Baja California peninsula and a chain of islands (in particular Angel de la Guarda and San Lorenzo). In August 2009 and April 2012, two earthquakes (Mw~7) struck the region. The collection of campaign GPS data since 2004 and after the two seismic events, allows an evaluation of the surface deformation during the full earthquake cycle. Here we focus on the surface deformation relative to a rigid Baja California motion (defined by GPS observations along the Peninsula) during the interseismic period before the two seismic events, and the co- and post-seismic period of each earthquake. In particular, we explore the implications of the post-seismic surface deformation in understanding the rheological and mechanical properties underneath the seismogenic layer in a region characterized by a developing plate boundary. a) Interseismic velocity field in a Baja fixed reference frame. b-c) cosesimic displacement fro the 2009 and 2012 seismic events (focal mechanisms from Global CMT web page) Relative position with respect to the first observation of the two stations closest to the coast up to July 1st 2012.

Malservisi, R.; Plattner, C.; Hackl, M.; Suarez Vidal, F.

2012-12-01

204

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

205

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

USGS Publications Warehouse

The Kobe earthquake struck at the edge of the densely populated Osaka-Kyoto corridor in southwest Japan. We investigate how the earthquake transferred stress to nearby faults, altering their proximity to failure and thus changing earthquake probabilities. We find that relative to the pre-Kobe seismicity, Kobe aftershocks were concentrated in regions of calculated Coulomb stress increase and less common in regions of stress decrease. We quantify this relationship by forming the spatial correlation between the seismicity rate change and the Coulomb stress change. The correlation is significant for stress changes greater than 0.2-1.0 bars (0.02-0.1 MPa), and the nonlinear dependence of seismicity rate change on stress change is compatible with a state- and rate-dependent formulation for earthquake occurrence. We extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of Kobe and calculating the change in probability caused by these stress changes. Transient effects of the stress changes are incorporated by the state-dependent constitutive relation, which amplifies the permanent stress changes during the aftershock period. Earthquake probability framed in this manner is highly time-dependent, much more so than is assumed in current practice. Because the probabilities depend on several poorly known parameters of the major faults, we estimate uncertainties of the probabilities by Monte Carlo simulation. This enables us to include uncertainties on the elapsed time since the last earthquake, the repeat time and its variability, and the period of aftershock decay. We estimate that a calculated 3-bar (0.3-MPa) stress increase on the eastern section of the Arima-Takatsuki Tectonic Line (ATTL) near Kyoto causes fivefold increase in the 30-year probability of a subsequent large earthquake near Kyoto; a 2-bar (0.2-MPa) stress decrease on the western section of the ATTL results in a reduction in probability by a factor of 140 to 2000. The probability of a Mw = 6.9 earthquake within 50 km of Osaka during 1997-2007 is estimated to have risen from 5-6% before the Kobe earthquake to 7-11% afterward; during 1997-2027, it is estimated to have risen from 14-16% before Kobe to 16-22%.

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

1998-01-01

206

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

USGS Publications Warehouse

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

Julian, B. R.

1983-01-01

207

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

USGS Publications Warehouse

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

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

1998-01-01

208

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

PubMed

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

Nadeau, Robert M; Guilhem, Aurélie

2009-07-10

209

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

210

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

PubMed

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

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

1978-09-01

211

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

USGS Publications Warehouse

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

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

1978-01-01

212

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

213

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

214

Instability model for recurring large and great earthquakes in southern California  

USGS Publications Warehouse

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

Stuart, W. D.

1985-01-01

215

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

NASA Astrophysics Data System (ADS)

The SCEDC archives continuous and triggered data from nearly 3000 data channels from 375 SCSN recorded stations. The SCSN and SCEDC process and archive an average of 12,000 earthquakes each year, contributing to the southern California earthquake catalog that spans from 1932 to present. The SCEDC provides public, searchable access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP, NETDC and DHI. New data products: ? The SCEDC is distributing synthetic waveform data from the 2008 ShakeOut scenario (Jones et al., USGS Open File Rep., 2008-1150) and (Graves et al. 2008; Geophys. Res. Lett.) This is a M 7.8 earthquake on the southern San Andreas fault. Users will be able to download 40 sps velocity waveforms in SAC format from the SCEDC website. The SCEDC is also distributing synthetic GPS data (Crowell et al., 2009; Seismo. Res. Letters.) for this scenario as well. ? The SCEDC has added a new web page to show the latest tomographic model of Southern California. This model is based on Tape et al., 2009 Science. New data services: ? The SCEDC is exporting data in QuakeML format. This is an xml format that has been adopted by the Advanced National Seismic System (ANSS). This data will also be available as a web service. ? The SCEDC is exporting data in StationXML format. This is an xml format created by the SCEDC and adopted by ANSS to fully describe station metadata. This data will also be available as a web service. ? The stp 1.6 client can now access both the SCEDC and the Northern California Earthquake Data Center (NCEDC) earthquake and waveform archives. In progress - SCEDC to distribute 1 sps GPS data in miniSEED format: ? As part of a NASA Advanced Information Systems Technology project in collaboration with Jet Propulsion Laboratory and Scripps Institution of Oceanography, the SCEDC will receive real time 1 sps streams of GPS displacement solutions from the California Real Time Network (http://sopac.ucsd.edu/projects/realtime; Genrich and Bock, 2006, J. Geophys. Res.). These channels will be archived at the SCEDC as miniSEED waveforms, which then can be distributed to the user community via applications such as STP.

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

2009-12-01

216

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

217

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

218

Great earthquakes and great asperities, San Andreas fault, southern California  

Microsoft Academic Search

The big bend region of the southern San Andreas fault consists of two great asperities that rupture infrequently in great earthquakes. The eastern knot near San Gorgonio Pass, which has not ruptured historically in a large event, is the main locus of plate motion, appears to break in great events every few hundred years, and is more advanced in the

Lynn R. Sykes; Leonardo Seeber

1985-01-01

219

IMAGING OF EARTHQUAKE SOURCES IN LONG VALLEY CALDERA, CALIFORNIA, 1983  

Microsoft Academic Search

A finite difference technique by which an earthquake wave field recorded at the Earth's surface could be extrapolated backward in time to produce an image of the source was presented by McMechan (1982). The resulting image is dynamic and reveals the temporal and spatial configuration of the acoustic equivalent of the source. The method was successfully tested on synthetic data,

GEORGE A. MCMECHAN; J. H. LUETGERT; W. D. MOONEY

1985-01-01

220

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

Microsoft Academic Search

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

M. L. Benthien

2003-01-01

221

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

USGS Publications Warehouse

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

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

2011-01-01

222

Superficial simplicity of the 2010 El Mayor-Cucapah earthquake of Baja California in Mexico  

NASA Astrophysics Data System (ADS)

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

Wei, Shengji; Fielding, Eric; Leprince, Sebastien; Sladen, Anthony; Avouac, Jean-Philippe; Helmberger, Don; Hauksson, Egill; Chu, Risheng; Simons, Mark; Hudnut, Kenneth; Herring, Thomas; Briggs, Richard

2011-09-01

223

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

224

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

USGS Publications Warehouse

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

Ward, Peter L.; Page, Robert A.

1990-01-01

225

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

226

Regional Estimates of Radiated Seismic Energy for Four Moderate (4.6 <= M <= 5.2) Southern California Earthquakes  

Microsoft Academic Search

We apply a direct spectral technique to estimate radiated energy E_s from recordings of four moderate Southern California earthquakes. Each of these earthquakes, the M4.6 2002 Yorba Linda, the M5.0 2003 Big Bear City, and the M5.1 2001 and M5.2 2005 Anza earthquakes produced ~ 200 recordings at distances r = 0.25 Hz and a connection distance of ro ?

J. Boatwright; L. C. Seekins

2006-01-01

227

Fault structure and kinematics of the Long Valley Caldera region, California, revealed by high-accuracy earthquake hypocenters and  

E-print Network

-accuracy earthquake hypocenters and focal mechanism stress inversions Stephanie Prejean,1,3 William Ellsworth,2 Mark seismicity, we performed stress inversions using focal mechanisms with 50 or more first motions Caldera region, California, revealed by high-accuracy earthquake hypocenters and focal mechanism stress

Waldhauser, Felix

228

The 1999 (Mw 7.1) Hector Mine, California Earthquake: Near-Field Postseismic Deformation from ERS Interferometry  

E-print Network

in the near-fault postseismic deformation are consistent with a characteristic time scale of 135 +42/-25 daysThe 1999 (Mw 7.1) Hector Mine, California Earthquake: Near-Field Postseismic Deformation from ERS La Jolla, CA 92093-0225 Submitted to: BSSA Special Issue on Hector Mine Earthquake October 16, 2000

Vernon, Frank

229

U.S.Geological Survey Grant No. 01HQGR0018 EARTHQUAKE POTENTIAL OF MAJOR FAULTS OFFSHORE SOUTHERN CALIFORNIA  

E-print Network

U.S.Geological Survey Grant No. 01HQGR0018 EARTHQUAKE POTENTIAL OF MAJOR FAULTS OFFSHORE SOUTHERN;U.S.Geological Survey Grant No. 01HQGR0018 EARTHQUAKE POTENTIAL OF MAJOR FAULTS OFFSHORE SOUTHERN Major active faults offshore southern California are poorly known with respect to slip-rates and seismic

Goldfinger, Chris

230

Use of dependence probabilities to detect near-fault bias in earthquake triggering  

Microsoft Academic Search

Models of triggered seismicty, such as ETAS, do a good job of predicting observed earthquake patterns in time and space, excepting the largest events. However, these models are typically spatially isotropic and so far do not incorporate the fault structure that controls earthquake distribution. We have demonstrated that the average rate of small earthquakes decays with distance from strike-slip faults

P. M. Powers; T. H. Jordan

2007-01-01

231

Hospital compliance with a state unfunded mandate: the case of California's Earthquake Safety Law.  

PubMed

Abstract In recent years, community hospitals have experienced heightened regulation with many unfunded mandates. The authors assessed the market, organizational, operational, and financial characteristics of general acute care hospitals in California that have a main acute care hospital building that is noncompliant with state requirements and at risk of major structural collapse from earthquakes. Using California hospital data from 2007 to 2009, and employing logistic regression analysis, the authors found that hospitals having buildings that are at the highest risk of collapse are located in larger population markets, possess smaller market share, have a higher percentage of Medicaid patients, and have less liquidity. PMID:23216262

McCue, Michael J; Thompson, Jon M

2012-01-01

232

Probability  

NSDL National Science Digital Library

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

Marsh, Mrs.

2006-11-16

233

Crustal imaging in southern California using earthquake sequences  

Microsoft Academic Search

An inexpensive means to further understand the geometry of active faults in southern California arises from the use of aftershock recordings to image crustal structures. The advent of regional seismic networks that record digital seismograms from hundreds of stations makes this crustal reflectivity profiling possible even in the absence of conventional active-source seismic data. We show that it is feasible

Sergio Chávez-Pérez; John N. Louie

1998-01-01

234

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

235

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

NASA Astrophysics Data System (ADS)

Humboldt County has the longest coastline in California and is one of the most seismically active areas of the state. It is at risk from earthquakes located on and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ), other regional fault systems, and from distant sources elsewhere in the Pacific. In 1995 the California Division of Mines and Geology published the first earthquake scenario to include both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of representatives from government agencies, tribes, service groups, academia and the private sector from the three northern coastal California counties, was formed in 1996 to coordinate and promote earthquake and tsunami hazard awareness and mitigation. The RCTWG and its member agencies have sponsored a variety of projects including education/outreach products and programs, tsunami hazard mapping, signage and siren planning, and has sponsored an Earthquake - Tsunami Education Room at the Humboldt County fair for the past eleven years. Three editions of Living on Shaky Ground an earthquake-tsunami preparedness magazine for California's North Coast, have been published since 1993 and a fourth is due to be published in fall 2008. In 2007, Humboldt County was the first region in the country to participate in a tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD and the first area in California to conduct a full-scale tsunami evacuation drill. The County has conducted numerous multi-agency, multi-discipline coordinated exercises using county-wide tsunami response plan. Two Humboldt County communities were recognized as TsunamiReady by the National Weather Service in 2007. Over 300 tsunami hazard zone signs have been posted in Humboldt County since March 2008. Six assessment surveys from 1993 to 2006 have tracked preparedness actions and personal awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist concerns about tsunami hazard signs. Over the thirteen year period covered by the surveys, the percent with houses secured to foundations has increased from 58 to 80 percent, respondents aware of a local tsunami hazard increased from 51 to 73 percent and knowing what the Cascadia subduction zone is from 16 to 42 percent.

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

2008-12-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

237

Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California - Implications for earthquake scaling  

NASA Astrophysics Data System (ADS)

A 2.5-km deep triaxial seismometer at Cajon Pass in southern California has recorded several hundred earthquakes less than M(L)4.0 occurring within the San Andreas fault system. At 2.5-km seismic background noise is below amplifier sensitivity, and the 2-250 Hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs. Compared with downhole recorded motion, seismic amplitudes at the surface are amplified below 10 Hz and severely attenuated above 30 Hz. We estimate that Q(S) is at least 1000 for wave motion at 2.5 km and below and Q(P) is over 2000. The range of source dimensions in the downhole recorded catalog is about 10 m to about 70 m (M(L) about -2.0, M(0) about 10 exp 8 Nm to M(L) about 2.7, M(0) about 10 exp 13 Nm). The plot of log(source-radius) vs. log(moment) has a straight line trend compatible with earthquake scaling at constant stress drop; inferred stress drops are scattered between 1 and 500 bars. There is no evidence in the catalog for the proposed minimum source dimension at about 100 m. When the Cajon Pass borehole catalog, containing some of the smallest recorded natural earthquakes, is combined with 800 larger events from previous studies, the moment-radius trend suggests that natural earthquakes are self-similar over a magnitude range M about -2 to about 8. We suggest that inferences of minimum source dimension are more likely due to bias in band-limited individual catalogs than to properties of the seismic crust.

Abercrombie, Rachel; Leary, Peter

1993-07-01

238

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

SciTech Connect

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

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

1990-08-01

239

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

USGS Publications Warehouse

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

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

2011-01-01

240

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 ...

241

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

Microsoft Academic Search

Enigmatic structures, possibly generated by large earthquakes, are common in Pleistocene shelf deposit exposed in sea cliffs south of San Francisco, California. The shelf deposits, consisting of very fine sandstone and sandy siltstone, lie within a 1,750-m-thick succession part of the Merced Formation. The structures described here are restricted to the siltstone, where they occupy stratigraphic intervals centimeters to decimeters

H. Edward Clifton

1990-01-01

242

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

SciTech Connect

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

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

1993-10-01

243

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

244

Probability  

NSDL National Science Digital Library

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

2011-01-18

245

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

USGS Publications Warehouse

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

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

2003-01-01

246

The 2011 M = 9.0 Tohoku oki earthquake more than doubled the probability of large shocks beneath Tokyo  

NASA Astrophysics Data System (ADS)

The Kanto seismic corridor surrounding Tokyo has hosted four to five M ? 7 earthquakes in the past 400 years. Immediately after the Tohoku earthquake, the seismicity rate in the corridor jumped 10-fold, while the rate of normal focal mechanisms dropped in half. The seismicity rate decayed for 6-12 months, after which it steadied at three times the pre-Tohoku rate. The seismicity rate jump and decay to a new rate, as well as the focal mechanism change, can be explained by the static stress imparted by the Tohoku rupture and postseismic creep to Kanto faults. We therefore fit the seismicity observations to a rate/state Coulomb model, which we use to forecast the time-dependent probability of large earthquakes in the Kanto seismic corridor. We estimate a 17% probability of a M ? 7.0 shock over the 5 year prospective period 11 March 2013 to 10 March 2018, two-and-a-half times the probability had the Tohoku earthquake not struck.

Toda, Shinji; Stein, Ross S.

2013-06-01

247

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

248

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

USGS Publications Warehouse

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

Frankel, Arthur; Mueller, Charles

2008-01-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

250

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

251

Do earthquakes exhibit self-organized criticality?  

PubMed

If earthquakes are phenomena of self-organized criticality (SOC), statistical characteristics of the earthquake time series should be invariant after the sequence of events in an earthquake catalog are randomly rearranged. In this Letter we argue that earthquakes are unlikely phenomena of SOC because our analysis of the Southern California Earthquake Catalog shows that the first-return-time probability PM(T) is apparently changed after the time series is rearranged. This suggests that the SOC theory should not be used to oppose the efforts of earthquake prediction. PMID:15245263

Yang, Xiaosong; Du, Shuming; Ma, Jin

2004-06-01

252

Upgrading the Southern California Seismic Network Along the Southern San Andreas Fault for Near-Source Ground Motions and Earthquake Early Warning  

NASA Astrophysics Data System (ADS)

The Southern San Andreas Fault (SoSAF) has the highest probability of producing a significant earthquake ( M 6.7) of any fault in California (Field, et al, 2007). Potentially affecting more than 20 million inhabitants, this fault presents the greatest urban earthquake risk in the United States. The Southern California Seismic Network (SCSN) has embarked on a multi-year project to enhance its ability to monitor the SoSAF by installing 11 new and upgrading 6 existing seismic stations along the fault trace from Bombay Beach to Wrightwood. This is made possible by funding from the USGS's Multihazards Demonstration Project. The plan is to achieve a station spacing of less than 20km along strike within 5km of the fault trace. The stations are state-of-the-art and include broad-band and strong ground motion sensors and "smart" data loggers. Continuous, real-time data from these stations will be integrated with the current SCSN operations in Pasadena, CA. SCSN is operated collaboratively by USGS and Caltech. It is part of the California Integrated Seismic Network (CISN) which is a region of the Advanced National Seismic System (ANSS). These new stations will provide several scientific, engineering and practical benefits. They will produce better and faster recording of background seismicity and strong ground motions in the region. When a large SoSAF event does occur they will record on-scale, near-field ground motions; such records are rare and will be of immense scientific and engineering value. Finally, these near-fault stations will pave the way for an earthquake early warning system in southern California. The USGS and ANSS have stated their intent to pursue earthquake early warning (EEW) in California. Currently they are supporting the development and testing of several EEW algorithms in California (Allan, et al, 2008). In addition to robust algorithms there are two main technical requirements for an operational EEW system in California: sufficient station density in source areas and small data delays. The SoSAF project addresses both requirements. First, the 20km target station spacing has been demonstrated to be sufficient for EEW in algorithm tests. Second, the new and upgraded stations will include ruggedized, low power computers capable of running EEW algorithms in the field, thus eliminating whole-waveform transmission delays. We believe this project provides a model for how existing regional seismic networks can evolve into multipurpose, operational EEW systems.

Given, D.; Hauksson, E.; Bhadha, R.; Lydeen, S.; Cone, G.; Curtis, W.; Yip, R.; Watkins, M.; Solanki, K.; Koesterer, C.

2008-12-01

253

Estimating locations and magnitudes of earthquakes in southern California from modified Mercalli intensities  

USGS Publications Warehouse

Modified Mercalli intensity (MMI) assignments, instrumental moment magnitudes M, and epicenter locations of thirteen 5.6 ??? M ??? 7.1 "training-set" events in southern California were used to obtain the attenuation relation MMI = 1.64 + 1.41M - 0.00526 * ??h - 2.63 * log ??h, where ??h is the hypocentral distance in kilometers and M is moment magnitude. Intensity magnitudes MI and locations for five 5.9 ??? M ??? 7.3 independent test events were consistent with the instrumental source parameters. Fourteen "historical" earthquakes between 1890 and 1927 were then analyzed. Of particular interest are the MI 7.2 9 February 1890 and MI 6.6 28 May 1892 earthquakes, which were previously assumed to have occurred near the southern San Jacinto fault; a more likely location is in the Eastern California Shear Zone (ECSZ). These events, and the 1992 M 7.3 Landers and 1999 M 7.1 Hector Mine events, suggest that the ECSZ has been seismically active since at least the end of the nineteenth century. The earthquake catalog completeness level in the ECSZ is ???M 6.5 at least until the early twentieth century.

Bakun, W. H.

2006-01-01

254

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

USGS Publications Warehouse

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

Hough, S.E.; Kanamori, H.

2002-01-01

255

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

PubMed Central

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

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

2002-01-01

256

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

USGS Publications Warehouse

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

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

2009-01-01

257

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

PubMed

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

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

2002-12-24

258

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.

259

Non-Poissonian Earthquake Clustering and the Hidden Markov Model as Bases for Earthquake Forecasting in California  

E-print Network

The quest to find successful methods to forecast future earthquakes has proven to be very challenging. Useful earthquake forecasts require detailed specification of a number of variables, namely the epicenter, depth, time and magnitude of the coming earthquake. While forecasting the times of strong aftershocks within the rupture zone of a strong earthquake has been developed with

John E. Ebel; Daniel W. Chambers; Alan L. Kafka; Jenny A. Baglivo

260

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

NASA Astrophysics Data System (ADS)

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

Hardy, S.; Konter, B.

2013-12-01

261

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

NASA Astrophysics Data System (ADS)

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

Field, Michael E.; Hall, Robert K.

1982-09-01

262

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

USGS Publications Warehouse

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

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

1996-01-01

263

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

NASA Astrophysics Data System (ADS)

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

Li, X.; Ji, C.

2013-12-01

264

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

265

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

266

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

NASA Technical Reports Server (NTRS)

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

Granat, Robert; Donnellan, Andrea

2011-01-01

267

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

Microsoft Academic Search

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

JAMES H. LUETGERT; WALTER D. MOONEY

1985-01-01

268

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

269

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

270

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

NASA Astrophysics Data System (ADS)

The Southern California Earthquake Data Center (SCEDC) archives and provides public access to earthquake parametric and waveform data gathered by the Southern California Seismic Network and since January 1, 2001, the TriNet seismic network, southern California's earthquake monitoring network. The parametric data in the archive includes earthquake locations, magnitudes, moment-tensor solutions and phase picks. The SCEDC waveform archive prior to TriNet consists primarily of short-period, 100-samples-per-second waveforms from the SCSN. The addition of the TriNet array added continuous recordings of 155 broadband stations (20 samples per second or less), and triggered seismograms from 200 accelerometers and 200 short-period instruments. Since the Data Center and TriNet use the same Oracle database system, new earthquake data are available to the seismological community in near real-time. Primary access to the database and waveforms is through the Seismogram Transfer Program (STP) interface. The interface enables users to search the database for earthquake information, phase picks, and continuous and triggered waveform data. Output is available in SAC, miniSEED, and other formats. Both the raw counts format (V0) and the gain-corrected format (V1) of COSMOS (Consortium of Organizations for Strong-Motion Observation Systems) are now supported by STP. EQQuest is an interface to prepackaged waveform data sets for select earthquakes in Southern California stored at the SCEDC. Waveform data for large-magnitude events have been prepared and new data sets will be available for download in near real-time following major events. The parametric data from 1981 to present has been loaded into the Oracle 9.2.0.1 database system and the waveforms for that time period have been converted to mSEED format and are accessible through the STP interface. The DISC optical-disk system (the "jukebox") that currently serves as the mass-storage for the SCEDC is in the process of being replaced with a series of inexpensive high-capacity (1.6 Tbyte) magnetic-disk RAIDs. These systems are built with PC-technology components, using 16 120-Gbyte IDE disks, hot-swappable disk trays, two RAID controllers, dual redundant power supplies and a Linux operating system. The system is configured over a private gigabit network that connects to the two Data Center servers and spans between the Seismological Lab and the USGS. To ensure data integrity, each RAID disk system constantly checks itself against its twin and verifies file integrity using 128-bit MD5 file checksums that are stored separate from the system. The final level of data protection is a Sony AIT-3 tape backup of the files. The primary advantage of the magnetic-disk approach is faster data access because magnetic disk drives have almost no latency. This means that the SCEDC can provide better "on-demand" interactive delivery of the seismograms in the archive.

Appel, V. L.

2002-12-01

271

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

272

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

NASA Astrophysics Data System (ADS)

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

Zaliapin, Ilya; Ben-Zion, Yehuda

2013-06-01

273

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

274

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

USGS Publications Warehouse

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

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

2004-01-01

275

Earthquake locations using single-station deep borehole recordings: Implications for microseismicity on the San Andreas fault in southern California  

NASA Astrophysics Data System (ADS)

We have located and estimated source parameters of 109 earthquakes (0 to 5 M) using seismograms recorded at 2.5 km depth in the Cajon Pass borehole, southern California. The borehole is about 4 km from the San Andreas fault, at the boundary between the locked, almost aseismic Mojave and San Bernardino segments, where the San Jacinto fault approaches the San Andreas. This area is of interest both on account of its tectonic complexity and its high potential seismic hazard. The clear, relatively unattenuated downhole recordings are rotated to determine the incoming azimuth of the P wave, and the delay time between the P and S arrivals is used to estimate the hypocentral distance. The difference between the hypocenters located this way and the Southern California Seismic Network (SCSN) locations of the same earthquakes increases with hypocentral distance from the borehole. Of the earthquakes within 20 km of the borehole, 95% are within 1-2 km of the SCSN epicenters and all are within 5 km of the SCSN depths. All but three of the 58 earthquakes located here which the SCSN did not record were within 20 km of the borehole and so the location errors are similar to those of SCSN A and B quality events. Most of the small earthquakes occurred within the relatively active San Jacinto fault zone, but at least eight are located close to or within the San Andreas fault zone. The stress drops for these events range from 0.1 to 18 MPa. These earthquakes appear similar to the other events in this study suggesting that the San Andreas fault is similar to other faults at the scale of these small earthquakes. The variation in stress drop and slip orientation of these small earthquakes suggests that larger scale heterogeneity continues to these small scales. Also, the location of these small earthquakes in major established fault zones implies that earthquake source dimensions are not geometrically controlled by fault zone width.

Abercrombie, Rachel E.

1995-12-01

276

Capture probability of released males of two Bactrocera species (Diptera: Tephritidae) in detection traps in California.  

PubMed

The genus Bactrocera (Diptera: Tephritidae) includes approximately 70 polyphagous species that are major pests of fruit and vegetable crops. Most Bactrocera species have limited geographic distributions, but several species are invasive, and many countries operate continuous trapping programs to detect infestations. In the United States, California maintains approximately 25,000 traps (baited with male lures) specifically for Bactrocera detection distributed over an area of approximately 6,400 km2 (2,500 miles2) in the Los Angeles area. Although prior studies have used male lures to describe movement of Bactrocera males, they do not explicitly relate capture probability with fly distance from lure-baited traps; consequently, they do not address the relative effectiveness of male lures in detecting incipient populations of Bactrocera species. The objective of this study was to measure the distance-dependent capture probability of marked, released males of Bactrocera dorsalis (Hendel) and Bactrocera cucurbitae (Coquillett) (methyl eugenol- and cue lure-responding species, respectively) within the detection trapping grid operating in southern California. These data were then used to compute simple probability estimates for detecting populations of different sizes of the two species. Methyl eugenol was the more powerful attractant, and based on the mark-recapture data, we estimated that B. dorsalis populations with as few as approximately 50 males would always (>99.9%) be detected using the current trap density of five methyl eugenol-baited traps per 2.6 km2 (1 mile2). By contrast, we estimated that certain detection of B. cucurbitae populations would not occur until these contained approximately 350 males. The implications of the results for the California trapping system are discussed, and the findings are compared with mark-release-recapture data obtained for the same two species in Hawaii. PMID:21309224

Shelly, T; Nishimoto, J; Diaz, A; Leathers, J; War, M; Shoemaker, R; Al-Zubaidy, M; Joseph, D

2010-12-01

277

The magnitude-frequency distribution of earthquakes recorded with deep seismometers at Cajon Pass, southern California  

NASA Astrophysics Data System (ADS)

The cumulative b-value (the slope of the Gutenberg-Richter relationship between earthquake occurrence rate and magnitude) is commonly found to be constant (˜1). Network catalogues, however, reveal a decrease at small magnitudes (<3). Some recent studies have suggested that this decrease in b-value is not just an artifact of catalogue incompleteness, but that small earthquakes are really not as numerous as a constant b-value extrapolated from larger events would predict. In the Cajon Pass area, southern California, the b-value of seismicity recorded by the local network (SCSN) appears to decrease below about ML 1.6. In order to investigate whether this decrease is real or simply represents the network detection threshold, we use seismicity recorded by the deep (1.5 and 2.5 km) seismometers deployed in the Cajon Pass Scientific Drillhole between April 1992 and October 1994. The maximum amplitudes recorded downhole are compared to SCSN magnitudes for events recorded by the network, to determine the relationship between amplitude and ML as a function of hypocentral distance from the borehole. Magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole. Magnitude-frequency curves are calculated for those events within 18 km of the borehole, and a constant b-value is observed to ML 0.5.

Abercrombie, Rachel E.

1996-08-01

278

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

279

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

280

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

NASA Technical Reports Server (NTRS)

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

Rundle, John B.

1988-01-01

281

Increased probability of large earthquakes near aftershock regions with relative quiescence  

Microsoft Academic Search

It is shown that after a large earthquake of M6 class or over has taken place, another event of similar size or larger is relatively more likely (in the sense of rate per unit area) to occur in the near field than in the far field. In particular, we show that the aftershock activity of the first event provides useful

Yosihiko Ogata

2001-01-01

282

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

283

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

284

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

USGS Publications Warehouse

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

Macgregor-Scott, N.; Walter, A.

1988-01-01

285

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

286

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

287

Slip Rate on the San Diego Trough Fault Zone, Inner California Borderland, and the 1986 Oceanside Earthquake  

E-print Network

Slip Rate on the San Diego Trough Fault Zone, Inner California Borderland, and the 1986 Oceanside Earthquake Swarm Revisited by H. F. Ryan, J. E. Conrad, C. K. Paull, and M. McGann Abstract The San Diego.g., Field, 2007). The focus of this study is on the San Diego trough fault zone (SDTFZ), one of several

288

VARIABILITY IN GROUND MOTIONS: ROOT MEAN SQUARE ACCELERATION AND PEAK ACCELERATION FOR THE 1971 SAN FERNANDO, CALIFORNIA, EARTHQUAKE  

Microsoft Academic Search

Data from the 1971 San Fernando, California, earthquake provided the op- portunity to study the variation of ground motions on a local scale. The uncer- tainty in ground motion was analyzed by studying the residuals about a regres- sion with distance and by utilizing the network of strong-motion instruments in three local geographic regions in the Los Angeles area. Our

MARTIN W. MCCANN; DAVID M. BOORE

1983-01-01

289

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.

290

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

291

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

USGS Publications Warehouse

In this report we present the time-independent component of the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), which provides authoritative estimates of the magnitude, location, and time-averaged frequency of potentially damaging earthquakes in California. The primary achievements have been to relax fault segmentation assumptions and to include multifault ruptures, both limitations of the previous model (UCERF2). The rates of all earthquakes are solved for simultaneously, and from a broader range of data, using a system-level "grand inversion" that is both conceptually simple and extensible. The inverse problem is large and underdetermined, so a range of models is sampled using an efficient simulated annealing algorithm. The approach is more derivative than prescriptive (for example, magnitude-frequency distributions are no longer assumed), so new analysis tools were developed for exploring solutions. Epistemic uncertainties were also accounted for using 1,440 alternative logic tree branches, necessitating access to supercomputers. The most influential uncertainties include alternative deformation models (fault slip rates), a new smoothed seismicity algorithm, alternative values for the total rate of M?5 events, and different scaling relationships, virtually all of which are new. As a notable first, three deformation models are based on kinematically consistent inversions of geodetic and geologic data, also providing slip-rate constraints on faults previously excluded because of lack of geologic data. The grand inversion constitutes a system-level framework for testing hypotheses and balancing the influence of different experts. For example, we demonstrate serious challenges with the Gutenberg-Richter hypothesis for individual faults. UCERF3 is still an approximation of the system, however, and the range of models is limited (for example, constrained to stay close to UCERF2). Nevertheless, UCERF3 removes the apparent UCERF2 overprediction of M6.5–7 earthquake rates and also includes types of multifault ruptures seen in nature. Although UCERF3 fits the data better than UCERF2 overall, there may be areas that warrant further site-specific investigation. Supporting products may be of general interest, and we list key assumptions and avenues for future model improvements.

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

2013-01-01

292

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

USGS Publications Warehouse

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

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

1999-01-01

293

Earthquake  

MedlinePLUS

... during an earthquake, even if there is no fire. If You Are Outside When the Shaking Starts... Find a clear spot (away from buildings, power lines, trees, streetlights) and drop to the ground. Stay there ...

294

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

295

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

USGS Publications Warehouse

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

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

2004-01-01

296

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

USGS Publications Warehouse

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

Waldhauser, F.; Ellsworth, W. L.

2000-01-01

297

Earthquake cycle on the Ballenas Fault, Central Gulf of California, MX  

NASA Astrophysics Data System (ADS)

South of the San Andreas Fault system, ~90% of the North America/Pacific plate motion is accommodate along the Gulf of California. Here the plate boundary deformation is partitioned in deep basins, often resulting in formation of new oceanic crust, connected by long transform faults. In the central part of the Gulf, one of these transform fault, the Ballenas fault, is localized in the Canales de Ballenas, a ~30 km wide channel between Isla Angel de la Garda and mainland Baja California. The presence of land on both the sides of this marine transform fault give the unique opportunity to perform geodetic study across its trace. On August 3rd 2009, a series of seismic strike slip events (including a M6.9) happened along this segment of plate boundary allowing a combined study of co- and inter- seismic deformation. Here we present the results from 5 years of EGPS along two transects perpendicular to the plate motion direction at 29 and 28 degrees North. These surveys include at least 3 occupations before the seismic event and at least 1 occupation after the earthquake. The analysis of the inter-seismic data shows that ~46 mm/yr is accommodated within the Canales de Ballenas. Co-seismic data are being collected at the time of the deadline for this abstract and will be presented at the meeting in combination with InSar signal.

Malservisi, R.; Plattner, C.; Hackl, M.; Gonzalez-Garcia, J. J.; Suarez Vidal, F.; Amelung, F.; Dixon, T. H.

2009-12-01

298

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

299

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

300

Southern California Earthquake Center - SCEC1: Final Report Summary Alternative Earthquake Source Characterization for the Los Angeles Region  

Microsoft Academic Search

The objective my research has been to synthesize current understanding of the tectonics and faults of the Los Angeles Basin and surrounding region to quantify uncertainty in the characterization of earthquake sources used for geologically- and geodetically-based regional earthquake likelihood models. This work has focused on capturing epistemic uncertainty; i.e. uncertainty stemming from ignorance of the true characteristics of the

Foxall

2003-01-01

301

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

302

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

USGS Publications Warehouse

Paleoseismic investigations across the Mission Creek strand of the San Andreas fault at Thousand Palms Oasis indicate that four and probably five surface-rupturing earthquakes occurred during the past 1200 years. Calendar age estimates for these earthquakes are based on a chronological model that incorporates radio-carbon dates from 18 in situ burn layers and stratigraphic ordering constraints. These five earthquakes occurred in about A.D. 825 (770-890) (mean, 95% range), A.D. 982 (840-1150), A.D. 1231 (1170-1290), A.D. 1502 (1450-1555), and after a date in the range of A.D. 1520-1680. The most recent surface-rupturing earthquake at Thousand Palms is likely the same as the A.D. 1676 ?? 35 event at Indio reported by Sieh and Williams (1990). Each of the past five earthquakes recorded on the San Andreas fault in the Coachella Valley strongly overlaps in time with an event at the Wrightwood paleoseismic site, about 120 km northwest of Thousand Palms Oasis. Correlation of events between these two sites suggests that at least the southernmost 200 km of the San Andreas fault zone may have ruptured in each earthquake. The average repeat time for surface-rupturing earthquakes on the San Andreas fault in the Coachella Valley is 215 ?? 25 years, whereas the elapsed time since the most recent event is 326 ?? 35 years. This suggests the southernmost San Andreas fault zone likely is very near failure. The Thousand Palms Oasis site is underlain by a series of six channels cut and filled since about A.D. 800 that cross the fault at high angles. A channel margin about 900 years old is offset right laterally 2.0 ?? 0.5 m, indicating a slip rate of 4 ?? 2 mm/yr. This slip rate is low relative to geodetic and other geologic slip rate estimates (26 ?? 2 mm/yr and about 23-35 mm/yr, respectively) on the southernmost San Andreas fault zone, possibly because (1) the site is located in a small step-over in the fault trace and so the rate is not be representative of the Mission Creek fault, (2) slip is partitioned northward from the San Andreas fault and into the eastern California shear zone, and/or (3) slip is partitioned onto the Banning strand of the San Andreas fault zone.

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

2002-01-01

303

Quantifying properties of seismic spectra: an examination of 100's of spectra from southern California earthquakes recorded by the ANZA seismic network  

Microsoft Academic Search

Unraveling earthquake source properties from seismic spectra requires an understanding of the inherent uncertainties that can be introduced from site and path effects. Here, we quantify properties of hundreds of earthquake spectra, and the associated uncertainties, from ~0earthquakes in southern California recorded by the ANZA seismic network. From the spectrum that meet our data-quality and data-fit requirements we: (1)

D. Kilb; G. Biasi; J. Brune; J. Anderson; F. L. Vernon

2003-01-01

304

Bulletin of the Seismological Society of America, Vol. 92, No. 4, pp. 14331442, May 2002 The 1999 (Mw 7.1) Hector Mine, California, Earthquake: Near-Field  

E-print Network

. The temporal variations in the near-fault postseismic deformation are consistent with a characteristic time The 1999 (Mw 7.1) Hector Mine, California, Earthquake: Near-Field Postseismic Deformation from ERS synthetic aperture radar (InSAR) data over the area of the Hector Mine earthquake (Mw 7.1, 16 October 1999

Fialko, Yuri

305

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

306

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

USGS Publications Warehouse

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

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

2008-01-01

307

Coseismic and postseismic vertical movements associated with the 1940 M7.1 Imperial Valley, California, earthquake  

NASA Technical Reports Server (NTRS)

Leveling surveys conducted along two routes that cross the Imperial fault in southern California indicate spatially coherent elevation changes attributable to coseismic and postseismic effects of the 1940, M7.1 Imperial Valley earthquake. The 1931-1941 elevation changes are consistent with theoretical models of vertical deformation of an elastic half space for a finite length strike-slip fault, using fault parameters that are consistent with the observed surface offsets following the 1940 earthquake. The elevation changes suggest an earthquake scenario consisting of a large coeismic slip in the southern half of the fault which transferred stress to the northern part as well as to the Brawley fault to the northeast.

Reilinger, R.

1984-01-01

308

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

309

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

310

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

311

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

Microsoft Academic Search

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

S. Perry; T. Jordan

2006-01-01

312

The coseismic slip distributions of the 1940 and 1979 Imperial Valley, California, earthquakes and their implications  

NASA Astrophysics Data System (ADS)

Geodetic arrays observed by the U.S. Coast and Geodetic Survey span the Imperial fault in southern California. For the 1940 M 7.1 Imperial Valley earthquake, a 1934-1941 triangulation network has sufficient resolution to allow inversion for the coseismic slip distribution on fault segments 5 to 25 km long extending from the surface to a depth of 9 km. The estimated right-lateral slip is 0.8 to 1.7 m on the northern 30 km of the main trace of the Imperial fault, 4.8±0.2 m on a 10-km-long segment straddling the United States - Mexico border, and 1.3±0.4 m on a southern 25-km-long segment in Mexico. Fixing this strike-slip model and inverting 1940 leveling data only for dip slip yields 0.1 m of east-side-down dip slip. The seismic moment for this model is M0 = (3.2±0.3) ×1019 N m. The 1979 geodetic data set, mostly elevation changes from leveling routes, has insufficient resolution for inversion. However, it is possible to use this geodetic data set and results published by others to infer that the 1940 and 1979 earthquakes may be similar on the rupture zone common to both events. Our preferred 1940 model is similar to the 1979 geodetic results of Crook [1984] on the segments where both networks have good resolution. Elevation changes from 1940 and 1979 leveling data are very similar. Thus the geodetic data corroborate the surface slip evidence of Sharp [1982b] that the 1940 and 1979 slip distributions are examples of "characteristic slip" on the northern Imperial fault.

King, N. E.; Thatcher, W.

1998-08-01

313

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

NASA Astrophysics Data System (ADS)

Last October 21st marked the 140th anniversary of the M6.8 1868 Hayward Earthquake, the last damaging earthquake on the southern Hayward Fault. This anniversary was used to help publicize the seismic hazards associated with the fault because: (1) the past five such earthquakes on the Hayward Fault occurred about 140 years apart on average, and (2) the Hayward-Rodgers Creek Fault system is the most likely (with a 31 percent probability) fault in the Bay Area to produce a M6.7 or greater earthquake in the next 30 years. To promote earthquake awareness and preparedness, over 140 public and private agencies and companies and many individual joined the public-private nonprofit 1868 Hayward Earthquake Alliance (1868alliance.org). The Alliance sponsored many activities including a public commemoration at Mission San Jose in Fremont, which survived the 1868 earthquake. This event was followed by an earthquake drill at Bay Area schools involving more than 70,000 students. The anniversary prompted the Silver Sentinel, an earthquake response exercise based on the scenario of an earthquake on the Hayward Fault conducted by Bay Area County Offices of Emergency Services. 60 other public and private agencies also participated in this exercise. The California Seismic Safety Commission and KPIX (CBS affiliate) produced professional videos designed forschool classrooms promoting Drop, Cover, and Hold On. Starting in October 2007, the Alliance and the U.S. Geological Survey held a sequence of press conferences to announce the release of new research on the Hayward Fault as well as new loss estimates for a Hayward Fault earthquake. These included: (1) a ShakeMap for the 1868 Hayward earthquake, (2) a report by the U. S. Bureau of Labor Statistics forecasting the number of employees, employers, and wages predicted to be within areas most strongly shaken by a Hayward Fault earthquake, (3) new estimates of the losses associated with a Hayward Fault earthquake, (4) new ground motion simulations of a Hayward Fault earthquake, (5) a new USGS Fact Sheet about the earthquake and the Hayward Fault, (6) a virtual tour of the 1868 earthquake, and (7) a new online field trip guide to the Hayward Fault using locations accessible by car and public transit. Finally, the California Geological Survey and many other Alliance members sponsored the Third Conference on Earthquake Hazards in the East Bay at CSU East Bay in Hayward for the three days following the 140th anniversary. The 1868 Alliance hopes to commemorate the anniversary of the 1868 Hayward Earthquake every year to maintain and increase public awareness of this fault, the hazards it and other East Bay Faults pose, and the ongoing need for earthquake preparedness and mitigation.

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

2008-12-01

314

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)  

Microsoft Academic Search

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

S. Y. Martosudarmo; A. M. Johnson; R. W. Fleming

1997-01-01

315

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.

316

The California Academy of Sciences, Grove Karl Gilbert, and Photographs of the 1906 Earthquake, mostly from the Archives of the Academy  

Microsoft Academic Search

In the early morning hours of 18 April 1906, a catastrophic earthquake struck the San Francisco region of central California. Buildings were severely damaged, trans- portation systems disrupted, water mains broken. When fires broke out in the down- town area, firefighters had no means to control them. The California Academy of Sciences museum building lay in the path of advancing

Alan E. Leviton; Michele L. Aldrich; Karren Elsbernd

317

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

318

179EARTHQUAKE CONTROL OF HOLOCENE TURBIDITE FREQUENCY, NORTHERN CALIFORNIA CONTINENTAL MARGINS EARTHQUAKE CONTROL OF HOLOCENE TURBIDITE FREQUENCY CONFIRMED  

E-print Network

intervals have been studied along the continental margins of the Cascadia Subduction Zone and northern San California margin. This difference in frequency of turbidites in a subduction zone compared to a transform ON THE CASCADIA AND NORTHERN CALIFORNIA ACTIVE CONTINENTAL MARGINS JULIA GUTIERREZ-PASTOR AND C. HANS NELSON

Goldfinger, Chris

319

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

USGS Publications Warehouse

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

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

1981-01-01

320

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

PubMed

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

Fram, Miranda S; Belitz, Kenneth

2011-02-15

321

Observations of earthquake source parameters at 2 km depth in the Long Valley Caldera, eastern California  

USGS Publications Warehouse

To investigate seismic source parameter scaling and seismic efficiency in the Long Valley caldera, California, we measured source parameters for 41 earthquakes (M 0.5 to M 5) recorded at 2 km depth in the Long Valley Exploratory Well. Borehole recordings provide a wide frequency bandwidth, typically 1 to 200–300 Hz, and greatly reduce seismic noise and path effects compared to surface recordings. We calculated source parameters in both the time and frequency domains for P and S waves. At frequencies above the corner frequency, spectra decay faster than ?3, indicating that attenuation plays an important role in shaping the spectra (path averaged Qp = 100–400, Qs = 200–800). Source parameters are corrected for attenuation and radiation pattern. Both static stress drops and apparent stresses range from approximately 0.01 to 30 MPa. Although static stress drops do not vary with seismic moment for these data, our analyses are consistent with apparent stress increasing with increasing moment. To estimate tectonic driving stress and seismic efficiencies in the region, we combined source parameter measurements with knowledge of the stress field and a Coulomb failure criterion to infer a driving stress of 40–70 MPa. Subsequent seismic efficiencies are consistent with McGarr's (1999) hypothesis of a maximum seismic efficiency of 6%.

Prejean, Stephanie G.; Ellsworth, William L.

2001-01-01

322

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

323

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

USGS Publications Warehouse

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

Gomberg, J.; Felzer, K.

2008-01-01

324

Seismicity remotely triggered by the magnitude 7.3 Landers, California, earthquake  

Microsoft Academic Search

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

D. P. Hill; P. A. Reasenberg; A. Michael; W. J. Arabaz; G. Beroza; D. Brumbaugh; J. N. Brune; R. Castro; S. Davis; D. Depolo; R. B. Smith; L. Munguia; A. Vidal; V. Wong; J. Gomberg; S. Harmsen; L. House; S. M. Jackson; L. Jones; R. Keller; S. Malone; A. Sanford; S. Walter; J. Zollweg

1993-01-01

325

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

Microsoft Academic Search

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

R. M. Allen; H. Kanamori

2001-01-01

326

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

USGS Publications Warehouse

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

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

2005-01-01

327

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

328

Santa Barbara Earthquake History  

NSDL National Science Digital Library

This resource provides eyewitness accounts and historical photographs from notable damaging earthquakes that have occurred in or near Santa Barbara County, California. It also contains a catalog of all earthquakes that have been felt in the greater Santa Barbara region between 1800 and 1960. Major earthquakes covered include the 1812 Santa Barbara Earthquake, the 1857 Fort Tejon Earthquake, the 1902 Los Alamos Earthquakes, the 1925 Santa Barbara Earthquake, the 1927 Lompoc Earthquake, and the 1978 Goleta Earthquake. For each earthquake there is a brief description and a map showing the location. Some have other details and photographs.

329

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

330

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

USGS Publications Warehouse

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

Sherrouse, Benson C.; Hester, David J.

2008-01-01

331

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

332

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

333

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

334

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

SciTech Connect

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

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

1990-05-01

335

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

USGS Publications Warehouse

The U.S. Geological Survey (USGS), as part of an ongoing program to acquire seismic velocity and geologic data at locations that recorded strong-ground motions during earthquakes, has investigated five sites in the Fortuna, California region (Figure 1). We selected drill sites at strong-motion stations that recorded high accelerations (Table 1) from the Cape Mendocino earthquake (M 7.0) of 25 April 1992 (Oppenheimer et al., 1993). The boreholes were drilled to a nominal depth of 95 meters (310 ft) and cased with schedule 80 pvc-casing grouted in place at each location. S-wave and P-wave data were acquired at each site using a surface source and a borehole three-component geophone. This report contains the velocity models interpreted from the borehole data and gives reference to locations and peak accelerations at the selected strong-motion stations.

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

2002-01-01

336

Evidence for aseismic deformation rate changes prior to earthquakes  

USGS Publications Warehouse

For ten earthquakes in nonmagmatic settings, there are credible published accounts of pre-earthquake deformation-rate changes lasting hundreds of seconds to more than a decade. Although most M > 7.5 earthquakes have occurred without detectable pre-earthquake deformation, the detection threshold for aseismic deformation remains high, in that aseismic slip with moment equivalent to an M5 earthquake would in most (although not all) cases have been missed. Interseismic deformation rates vary without being followed by earthquakes, and a strain-rate change prior to the 1989 Mw6.9 Loma Prieta, California, earthquake is shown to be similar in size to many other rate changes that have occurred since that time. Most examples of pre-earthquake aseismic deformation lasting hundreds of seconds or more probably originate adjacent to, or downdip of, the seismic rupture plane, rather than within the zone that undergoes seismic failure. Copyright ?? 2006 by Annual Reviews. All rights reserved.

Roeloffs, E. A.

2006-01-01

337

Instrumental intensity distribution for the Hector Mine, California, and the Chi-Chi, Taiwan, earthquakes: Comparison of two methods  

USGS Publications Warehouse

We compare two methods of seismic-intensity estimation from ground-motion records for the two recent strong earthquakes: the 1999 (M 7.1) Hector Mine, California, and the 1999 (M 7.6) Chi-Chi, Taiwan. The first technique utilizes the peak ground acceleration (PGA) and velocity (PGV), and it is used for rapid generation of the instrumental intensity map in California. The other method is based on the revised relationships between intensity and Fourier amplitude spectrum (FAS). The results of using the methods are compared with independently observed data and between the estimations from the records. For the case of the Hector Mine earthquake, the calculated intensities in general agree with the observed values. For the case of the Chi-Chi earthquake, the areas of maximum calculated intensity correspond to the areas of the greatest damage and highest number of fatalities. However, the FAS method producees higher-intensity values than those of the peak amplitude method. The specific features of ground-motion excitation during the large, shallow, thrust earthquake may be considered a reason for the discrepancy. The use of PGA and PGV is simple; however, the use of FAS provides a natural consideration of site amplification by means of generalized or site-specific spectral ratios. Because the calculation of seismic-intensity maps requires rapid processing of data from a large network, it is very practical to generate a "first-order" map from the recorded peak motions. Then, a "second-order" map may be compiled using an amplitude-spectra method on the basis of available records and numerical modeling of the site-dependent spectra for the regions of sparse station spacing.

Sokolov, V.; Wald, D. J.

2002-01-01

338

Localization of intermediate-term earthquake prediction  

SciTech Connect

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 earthquake offshore from Eureka depicts relative quiescence within the region of a TIP. The procedure was tested, without readaptation of parameter, on 17 other strong earthquake occurrences in North America, Japan, and Eurasia, most of which were in regions for which a TIP had been previously diagnosed. The localizing algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes. The area of prediction in each case was reduced significantly, ranging between 7% and 25% of the total area covered by the TIP.

Kossobokov, V.G.; Keilis-Borok, V.I. (International Inst. of Earthquake Prediction Theory and Mathematical Geophysics, Moscow (USSR)); Smith, S.W. (Univ. of Washington, Seattle (USA))

1990-11-10

339

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

USGS Publications Warehouse

Boreholes and high-resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the Puente Hills thrust fault (PHT) beneath Los Angeles, California, provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault. These data document fold growth within a discrete kink band that narrows upward from ???460 m at the base of the Quaternary section (200-250 m depth) to 82% at 250 m depth) folding and uplift occur within discrete kink bands, thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault. The borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site. We interpret the intervals of growth as occurring after the formation of now-buried paleofold scarps during three large PHT earthquakes in the past 8 kyr. The intervening intervals of no growth record periods of structural quiescence and deposition at the regional, near-horizontal stream gradient at the study site. Minimum uplift in each of the scarp-forming events, which occurred at 0.2-2.2 ka (event Y), 3.0-6.3 ka (event X), and 6.6-8.1 ka (event W), ranged from ???1.1 to ???1.6 m, indicating minimum thrust displacements of ???2.5 to 4.5 m. Such large displacements are consistent with the occurrence of large-magnitude earthquakes (Mw > 7). Cumulative, minimum uplift in the past three events was 3.3 to 4.7 m, suggesting cumulative thrust displacement of ???7 to 10.5 m. These values yield a minimum Holocene slip rate for the PHT of ???0.9 to 1.6 mm/yr. The borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally, such that older strata that have been deformed by more earthquakes dip more steeply than younger 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. Copyright 2007 by the American Geophysical Union.

Leon, L. A.; Christofferson, S. A.; Dolan, J. F.; Shaw, J. H.; Pratt, T. L.

2007-01-01

340

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

USGS Publications Warehouse

We seek to restore the integrity of the geodetic network in the San Fernando, Simi, Santa Clarita Valleys and in the northern Los Angeles Basin by remeasurement of the network and identification of BMs which experienced non-tectonic displacements associated with the Northridge earthquake. We then use the observed displacement of BMs in the network to portray or predict the permanent vertical and horizontal deformation associated with the 1994 Northridge earthquake throughout the area, including sites where we lack geodetic measurements. To accomplish this, we find the fault geometry and earthquake slip that are most compatible with the geodetic and independent seismic observations of the earthquake. We then use that fault model to predict the deformation everywhere at the earth's surface, both at locations where geodetic observations exist and also where they are absent. We compare displacements predicted for a large number of numerical models of the earthquake faulting to the coseismic displacements, treating the earthquake fault as a cut or discontinuity embedded in a stiff elastic solid. This comparison is made after non-tectonic deformation has been removed from the measured elevation changes. The fault slip produces strain in the medium and deforms the ground surface. The model compatible with seismic observations that best fits the geodetic data within their uncertainties is selected. The acceptable model fault bisects the mainshock focus, and the earthquake size , magnitude, is compatible with the earthquake size measured seismically. Our fault model was used to identify geodetic monuments on engineered structures that were anomalously displaced by the earthquake.

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

1996-01-01

341

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

342

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

USGS Publications Warehouse

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

Moyle, W. R., Jr.

1980-01-01

343

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.

Johnston, Malcolm J. S., (Edited By)

1993-01-01

344

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

Microsoft Academic Search

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

Lisa B. Grant; Kerry Sieh

1994-01-01

345

Earthquake locations and seismic velocity structure in the Los Angeles Area, Southern California  

SciTech Connect

To determine to the extent possible the three dimensional velocity structure of the Los Angeles basin, and to make use of that in the relocation of earthquakes, a study was undertaken to invert for that velocity structure, making use of existing earthquake data and incorporating a ray tracing routine which allowed use of the program for the larger area of the current study.

Piper, K.A.

1985-01-01

346

Three-Dimensional Seismic Velocity Structure and Precise Earthquake Relocations in the Salton Trough, Southern California  

E-print Network

Three-Dimensional Seismic Velocity Structure and Precise Earthquake Relocations in the Salton-precision earthquake relocations between 1981 and 2010 near the Salton Trough and the San Jacinto fault zone. The simul.7) in the middle crust except for the Salton Trough and the Imperial Valley. The newly resolved model is used

Lin, Guoqing

347

Postearthquake relaxation and aftershock accumulation linearly related after the 2003 M 6.5 Chengkung, Taiwan, and the 2004 M 6.0 Parkfield, California, earthquakes  

USGS Publications Warehouse

We treat both the number of earthquakes and the deformation following a mainshock as the superposition of a steady background accumulation and the post-earthquake process. The preseismic displacement and seismicity rates ru and rE are used as estimates of the background rates. Let t be the time after the mainshock, u(t) + u0 the postseismic displacement less the background accumulation rut, and ??N(t) the observed cumulative number of postseismic earthquakes less the background accumulation rE t. For the first 160 days (duration limited by the occurrence of another nearby earthquake) following the Chengkung (M 6.5, 10 December 2003, eastern Taiwan) and the first 560 days following the Parkfield (M 6.0, 28 September 2004, central California) earthquakes u(t) + u0 is a linear function of ??N(t). The aftershock accumulation ??N(t) for both earthquakes is described by the modified Omori Law d??N/dt ?? (1 + t/??)-p with p = 0.96 and ?? = 0.03 days. Although the Chengkung earthquake involved sinistral, reverse slip on a moderately dipping fault and the Parkfield earthquake right-lateral slip on a near-vertical fault, the earthquakes share an unusual feature: both occurred on faults exhibiting interseismic fault creep at the surface. The source of the observed postseismic deformation appears to be afterslip on the coseismic rupture. The linear relation between u(t) + u0 and N(t) suggests that this afterslip also generates the aftershocks. The linear relation between u(t) + u0 and ??N(t) obtains after neither the 1999 M 7.1 Hector Mine (southern California) nor the 1999 M 7.6 Chi-Chi (central Taiwan) earthquakes, neither of which occurred on fault segments exhibiting fault creep.

Savage, J. C.; Yu, S. -B.

2007-01-01

348

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

USGS Publications Warehouse

Where the San Andreas fault passes along the southwestern margin of the Mojave desert, it exhibits a large change in trend, and the deformation associated with the Pacific/North American plate boundary is distributed broadly over a complex shear zone. The importance of understanding the partitioning of strain across this region, especially to the east of the Mojave segment of the San Andreas in a region known as the eastern California shear zone (ECSZ), was highlighted by the occurrence (on 28 June 1992) of the magnitude 7.3 Landers earthquake in this zone. Here we use geodetic observations in the central Mojave desert to obtain new estimates for the rate and distribution of strain across a segment of the ECSZ, and to determine a coseismic strain drop of ~770 ??rad for the Landers earthquake. From these results we infer a strain energy recharge time of 3,500-5,000 yr for a Landers-type earthquake and a slip rate of ~12 mm yr-1 across the faults of the central Mojave. The latter estimate implies that a greater fraction of plate motion than heretofore inferred from geodetic data is accommodated across the ECSZ.

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

1994-01-01

349

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

350

Staying Safe in Earthquake Country  

E-print Network

the most frequent large earthquakes. In southern California, the most recent earthquake on the San Andreas in earthquake country. Seismic hazards in California are sort of a good news/bad news deal. The bad news! The Bad News When most southern Californians think of earthquakes, their minds leap immediately to the San

de Lijser, Peter

351

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

USGS Publications Warehouse

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

Rymer, M.J.

2000-01-01

352

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.

Holzer, Thomas L.

1998-01-01

353

Lower crustal earthquake swarms beneath Mammoth Mountain, California - evidence for the magmatic roots to the Mammoth Mountain mafic volcanic field?  

NASA Astrophysics Data System (ADS)

Mammoth Mountain is a cluster of dacitic domes erupted ~ 68 ka. It stands on the SW topographic rim of Long Valley caldera in eastern CA. Structurally, it is outboard of the caldera ring-fracture system and its magmatic system is genetically distinct from that of the caldera. It resides within a field of mafic (basaltic) vents that erupted between 190 - 8 ka. A series of phreatic explosions from the north flank of the mountain some 700 ybp attest to the infusion of heat to shallow depths shortly prior to the 600 ybp eruptions of the Inyo Domes 6 to 12 km north of the Mountain. Unrest beneath Mammoth Mountain since 1980 has included 1) swarms of brittle-failure earthquakes in the upper 10 km of the crust that define concentric elliptical ring-like patterns centered beneath the summit, 2) mid-crustal (depths 10 to 20 km) long-period volcanic earthquakes, 3) the onset of diffuse CO2 degassing in 1990 following an 11-month-long swarm of shallow (<10 km), brittle-failure earthquakes in 1989, 4) occasional very-long-period earthquakes at depths of ~ 3 km, and 5) brief swarms of lower-crustal, brittle-failure earthquakes at depths of 20 to 30 km, including sizable episodes June 16-17, 2006 and September 29-30, 2009. Seismic waveform correlation analysis at multiple stations reveals that these lower-crustal, brittle-failure swarms consist of tens to hundreds of repeated similar events and also serves to identify many events not included in the Northern California Seismic Network (NCSN) catalog. In the case of the 2009 episode, an evolution in waveform is clearly discernible over the sequence, suggesting a corresponding evolution in source location or mechanism. Work is ongoing to take advantage of the waveform similarity to estimate precise hypocentral locations of these events in order to distinguish between these possibilities.We suggest that the brittle-failure earthquakes at depths of 20 to 30 km are occurring within the more mafic mid- to lower-crust, which can remain in the brittle domain to temperatures as high as ~700o C. Above these deep events are two distinct shallower zones of seismicity. The mid-crustal long-period earthquakes between 10 and 20 km are presumably occurring within the silicic crust, but below the rheological transition from brittle to plastic behavior, expected to occur at temperatures of ~350 to 400o C. Above this transition are shallow brittle-failure earthquakes, in the upper 8 kilometers of the silicic crust. These lower crustal brittle-failure earthquakes are similar in depth and tectonic setting to those that occurred beneath the Sierra Nevada crest in the vicinity of Lake Tahoe in late 2003, which Smith et al. (Science, 2004) concluded were associated with a magmatic intrusion in the lower crust. The Mammoth sequences, however, are much shorter in duration (1-2 days compared with several months) and have no detectable accompanying geodetic signal. Thus, there is no clear evidence for a significant intrusion associated with these deep swarms of brittle-failure earthquakes beneath Mammoth Mountain.

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

2010-12-01

354

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

355

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

USGS Publications Warehouse

Several approaches are used to assess the performance of the built environment following an earthquake -- preliminary damage surveys conducted by professionals, detailed studies of individual structures, and statistical analyses of groups of structures. Reports of damage that are issued by many organizations immediately following an earthquake play a key role in directing subsequent detailed investigations. Detailed studies of individual structures and statistical analyses of groups of structures may be motivated by particularly good or bad performance during an earthquake. Beyond this, practicing engineers typically perform stress analyses to assess the performance of a particular structure to vibrational levels experienced during an earthquake. The levels may be determined from recorded or estimated ground motions; actual levels usually differ from design levels. If a structure has seismic instrumentation to record response data, the estimated and recorded response and behavior of the structure can be compared.

Celebi, Mehmet

1998-01-01

356

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

357

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

USGS Publications Warehouse

To the general public who had their televisions tuned to watch the World Series, the 1989 Loma Prieta earthquake was a lifelines earthquake. It was the images seen around the world of the collapsed Cypress Street viaduct, with the frantic and heroic efforts to pull survivors from the structure that was billowing smoke; the collapsed section of the San Francisco-Oakland Bay Bridge and subsequent home video of a car plunging off the open span; and the spectacular fire in the Marina District of San Francisco fed by a broken gasline. To many of the residents of the San Francisco Bay region, the relation of lifelines to the earthquake was characterized by sitting in the dark because of power outage, the inability to make telephone calls because of network congestion, and the slow and snarled traffic. Had the public been aware of the actions of the engineers and tradespeople working for the utilities and other lifeline organizations on the emergency response and restoration of lifelines, the lifeline characteristics of this earthquake would have been even more significant. Unobserved by the public were the warlike devastation in several electrical-power substations, the 13 miles of gas-distribution lines that had to be replaced in several communities, and the more than 1,200 leaks and breaks in water mains and service connections that had to be excavated and repaired. Like the 1971 San Fernando, Calif., earthquake, which was a seminal event for activity to improve the earthquake performance of lifelines, the 1989 Loma Prieta earthquake demonstrated that the tasks of preparing lifelines in 'earthquake country' were incomplete-indeed, new lessons had to be learned.

Schiff, Anshel J., (Edited By)

1998-01-01

358

Earthquake deformation cycle on the San Andreas Fault near Parkfield, California  

Microsoft Academic Search

Six moderate earthquakes are thought to have ruptured the Parkfield segment of the San Andreas fault since 1857. The similar characteristics of the three seismically recorded events, together with the quasi-regular 22-year recurrence interval, have led to the forecast of a similar event in 1988+\\/-5 years. In this study the potential for the hypothesized earthquake is assessed by estimating the

Paul Segall; Ruth Harris

1987-01-01

359

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)] [California Institute of Technology, Pasadena, CA (United States)

1994-04-01

360

Strong-motion earthquake accelerograms at Brawley, California: January 25, 1975  

Microsoft Academic Search

During the Brawley earthquake swarm of January, February, 1975, a single strong-motion accelerograph installed after the swarm began recorded 27 positively identified earthquakes in 14 hr, at hypocentral distances of approximately 5 km. Eight of these had magnitudes (M\\/sub L\\/) greater than or equal to 3.5, and several had M\\/sub L\\/ less than 2.5; the instrument independently triggered 18 times.

D. A. Johnson; T. C. Hanks

1976-01-01

361

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

NASA Astrophysics Data System (ADS)

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, Lisa B.; Sieh, Kerry

1994-04-01

362

Satellite radar interferometric map of the coseismic deformation field of the M=6.1 Eureka Valley, California earthquake of May 17, 1993  

Microsoft Academic Search

Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS-1 satellite before and after the Eureka Valley, California earthquake of May 17, 1993 maps the coseismic deformation field. The fringes corresponding to contours of equal change in satellite-to-ground distance can be enhanced by forming the sum of two of such interferograms with altitudes of ambiguity roughly

Didier Massonnet; Kurt L. Feigl

1995-01-01

363

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

364

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.

Reasenberg, Paul A., (Edited By)

1997-01-01

365

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

SciTech Connect

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

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

1987-01-01

366

Probability Probability  

E-print Network

(x,y,z) Marginal Probabilities #15;We can "sum out" part of a joint distribution to get the marginal distribution;ne random variables and sample spaces carefully: e.g. Prisoner's paradox Entropy #15; Measures H(p) = 0. #15; Maximal value when p is uniform. #15; Tells you the expected "cost" if each event

Roweis, Sam

367

Is earthquake triggering driven by small earthquakes?  

PubMed

Using a catalog of seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this relation and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that seismicity triggering is driven by the smallest earthquakes, which trigger fewer events than larger earthquakes, but which are much more numerous. We propose that the nontrivial scaling of the number of triggered earthquakes emerges from the fractal spatial distribution of seismicity. PMID:12906641

Helmstetter, Agnès

2003-08-01

368

UNIVERSITY OF CALIFORNIA, SAN DIEGO Geodetic Imaging of the Earthquake Cycle  

E-print Network

and electronically: Chair University of California, San Diego 2013 iii #12;DEDICATION To Professor David T. Sandwell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Andreas fault . . . . . . . . . . . . . . . . . . . 5 1.3 GPS basics

Sandwell, David T.

369

USGS Earthquake Hazards Program  

NSDL National Science Digital Library

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

370

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.

O'Rourke, Thomas D., (Edited By)

1992-01-01

371

Geodetic measurement of deformation in the Loma Prieta, California earthquake with Very Long Baseline Interferometry (VLBI)  

SciTech Connect

Following the Loma Prieta earthquake, two mobile Very Long Baseline Interferometry (VLBI) systems operated by the NASA Crustal Dynamics Project and the NOAA National Geodetic Survey were deployed at three previously established VLBI sites in the earthquake area: Fort Ord (near Monterey), the Presidio (in San Francisco) and Point Reyes. From repeated VLBI occupations of these sites since 1983, the pre-earthquake rates of deformation have been determined with respect to a North American reference frame with 1{sigma} formal standard errors of {approximately}1 mm/yr. The VLBI measurements immediately following the earthquake showed that the Fort Ord site was displaced 49 {plus minus} 4 mm at an azimuth of 11 {plus minus} 4{degree} and that the Presidio site was displaced 12 {plus minus} 5 mm at an azimuth of 148 {plus minus} 13{degree}. No anomalous change was detected at Point Reyes with 1{sigma} uncertainty of 4 mm. The estimated displacements at Fort Ord and the Presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment is shallower than slip on the more northern segment of the fault rupture. The authors also give the Cartesian positions at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the vicinity of the earthquake.

Clark, T.A.; Ma, C.; Sauber, J.M.; Ryan, J.W. (NASA Goddard Space Flight Center, Greenbelt, MD (USA)); Gordon, D.; Caprette, D.S. (STX, Lanham, MD (USA)); Shaffer, D.B.; Vandenberg, N.R. (Interferometrics Inc., Vienna, VA (USA))

1990-07-01

372

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

373

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

USGS Publications Warehouse

Medicine Lake volcano has had 4 eruptive episodes in its postglacial history (since 13,000 years ago) comprising 16 eruptions. Time intervals between events within the episodes are relatively short, whereas time intervals between the episodes are much longer. An updated radiocarbon chronology for these eruptions is presented that uses paleomagnetic data to constrain the choice of calibrated ages. This chronology is used with exponential, Weibull, and mixed-exponential probability distributions to model the data for time intervals between eruptions. The mixed exponential distribution is the best match to the data and provides estimates for the conditional probability of a future eruption given the time since the last eruption. The probability of an eruption at Medicine Lake volcano in the next year from today is 0.00028.

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

2007-01-01

374

Acceleration and volumetric strain generated by the Parkfield 2004 earthquake on the GEOS strong-motion array near Parkfield, California  

USGS Publications Warehouse

An integrated array of 11 General Earthquake Observation System (GEOS) stations installed near Parkfield, CA provided on scale broad-band, wide-dynamic measurements of acceleration and volumetric strain of the Parkfield earthquake (M 6.0) of September 28, 2004. Three component measurements of acceleration were obtained at each of the stations. Measurements of collocated acceleration and volumetric strain were obtained at four of the stations. Measurements of velocity at most sites were on scale only for the initial P-wave arrival. When considered in the context of the extensive set of strong-motion recordings obtained on more than 40 analog stations by the California Strong-Motion Instrumentation Program (Shakal, et al., 2004 http://www.quake.ca.gov/cisn-edc) and those on the dense array of Spudich, et al, (1988), these recordings provide an unprecedented document of the nature of the near source strong motion generated by a M 6.0 earthquake. The data set reported herein provides the most extensive set of near field broad band wide dynamic range measurements of acceleration and volumetric strain for an earthquake as large as M 6 of which the authors are aware. As a result considerable interest has been expressed in these data. This report is intended to describe the data and facilitate its use to resolve a number of scientific and engineering questions concerning earthquake rupture processes and resultant near field motions and strains. This report provides a description of the array, its scientific objectives and the strong-motion recordings obtained of the main shock. The report provides copies of the uncorrected and corrected data. Copies of the inferred velocities, displacements, and Psuedo velocity response spectra are provided. Digital versions of these recordings are accessible with information available through the internet at several locations: the National Strong-Motion Program web site (http://agram.wr.usgs.gov/), the COSMOS Virtual Data Center Web site (http://www.cosmos-eq.org), and the CISN Engineering and Berkeley data centers (http://www.quake.ca.gov/cisn-edc). They are also accessible together with recordings on the GEOS Strong-motion Array near Parkfield, CA since its installation in 1987 through the USGS GEOS web site ( http://nsmp.wr.usgs.gov/GEOS).

Borcherdt, Rodger D.; Johnston, Malcolm J.S.; Dietel, Christopher; Glassmoyer, Gary; Myren, Doug; Stephens, Christopher

2004-01-01

375

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

376

Geodetic measurement of deformation in the Loma Prieta, California earthquake with very long baseline interferometry  

NASA Technical Reports Server (NTRS)

VLBI measurements were conducted immediately after the Loma Prieta earthquake and compared with VLBI gathered at Monterey, San Francisco, and Point Reyes since 1983 to obtain preearthquake deformation rates with respect to a North American reference frame. The estimated displacements at Monterey and San Francisco are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the northern segment of the fault rupture. Cartesian positions are presented at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the earthquake's vicinity.

Clark, T. A.; Ma, C.; Sauber, J. M.; Ryan, J. W.; Gordon, D.; Shaffer, D. B.; Carprette, D. S.; Vandenberg, N. R.

1990-01-01

377

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

USGS Publications Warehouse

Although some scientists considered the Ms=7.1 Loma Prieta, Calif., earthquake of 1989 to be an anticipated event, some aspects of the earthquake were surprising. It occurred 17 km beneath the Santa Cruz Mountains along a left-stepping restraining bend in the San Andreas fault system. Rupture on the southwest-dipping fault plane consisted of subequal amounts of right-lateral and reverse motion but did not reach the surface. In the area of maximum uplift, severe shaking and numerous ground cracks occurred along Summit Road and Skyland Ridge, several kilometers south of the main trace of the San Andreas fault. The relatively deep focus of the earthquake, the distribution of ground failure, the absence of throughgoing surface rupture on the San Andreas fault, and the large component of uplift raised several questions about the relation of the 1989 Loma Prieta earthquake to the San Andreas fault: Did the earthquake actually occur on the San Andreas fault? Where exactly is the San Andreas fault in the heavily forested Santa Cruz Mountains, and how does the fault relate to ground ruptures that occurred there in 1989 and 1906? What is the geometry of the San Andreas fault system at depth, and how does it relate to the major crustal blocks identified by geologic mapping? Subsequent geophysical and geologic investigations of crustal structure in the Loma Prieta region have addressed these and other questions about the relation of the earthquake to geologic structures observed in the southern Santa Cruz Mountains. The diverse papers in this chapter cover several topics: geologic mapping of the region, potential- field and electromagnetic modeling of crustal structure, and the velocity structure of the crust and mantle in and below the source region for the earthquake. Although these papers were mostly completed between 1992 and 1997, they provide critical documentation of the crustal structure of the Loma Prieta region. Together, they present a remarkably coherent, three-dimensional picture of the earthquake source region--a geologically complex volume of crust with a long history of both right-lateral faulting and fault-normal compression, thrusting, and uplift.

Wells, Ray E.

2004-01-01

378

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.

Borcherdt, Roger D.

1994-01-01

379

Interaction of the San Jacinto and San Andreas Fault Zones, Southern California: Triggered Earthquake Migration and Coupled Recurrence Intervals  

Microsoft Academic Search

Two lines of evidence suggest that large earthquakes that occur on either the San Jacinto fault zone (SJFZ) or the San Andreas fault zone (SAFZ) may be triggered by large earthquakes that occur on the other. First, the great 1857 Fort Tejon earthquake in the SAFZ seems to have triggered a progressive sequence of earthquakes in the SJFZ. These earthquakes

Christopher O. Sanders

1993-01-01

380

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

381

Spatial Separation of Large Earthquakes, Aftershocks, and Background Seismicity: Analysis of Interseismic and Coseismic Seismicity Patterns in Southern California  

NASA Astrophysics Data System (ADS)

We associate waveform-relocated background seismicity and aftershocks with the 3-D shapes of late Quaternary fault zones in southern California. Major earthquakes that can slip more than several meters, aftershocks, and near-fault background seismicity mostly rupture different surfaces within these fault zones. Major earthquakes rupture along the mapped traces of the late Quaternary faults, called the principal slip zones (PSZs). Aftershocks occur either on or in the immediate vicinity of the PSZs, typically within zones that are ±2-km wide. In contrast, the near-fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces, and forms spatially decaying distributions extending out to distances of ±10 km from the PSZs. We call the regions where the enhanced rate of background seismicity occurs, the seismic damage zones. One possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the PSZs. The seismic damage zones mature and reach their finite width early in the history of a fault, during the first few kilometers of cumulative offset. Alternatively, the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength, although the amount of cumulative offset varies widely. It may also depend on the strength of the fault zone, the time since the last major earthquake as well as other parameters. In addition, the seismic productivity appears to be influenced by the crustal structure and heat flow, with more extensive fault networks in regions of thin crust and high heat flow.

Hauksson, Egill

2010-08-01

382

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

USGS Publications Warehouse

The southern California Permanent GPS Geodetic Array (PGGA) was established in 1990 across the Pacific-North America plate boundary to continuously monitor crustal deformation. We describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19-month period between the June 28, 1992 (Mw=7.3), Landers and January 17, 1994 (Mw=6.7), Northridge earthquakes. We compare displacement rates at four site locations with those reported by Feigl et al. [1993], which were derived from an independent set of Global Positioning System (GPS) and very long baseline interferometry (VLBI) measurements collected over nearly a decade prior to the Landers earthquake. The velocity differences for three sites 65-100 km from the earthquake's epicenter are of order of 3-5 mm/yr and are systematically coupled with the corresponding directions of coseismic displacement. The fourth site, 300 km from the epicenter, shows no significant velocity difference. These observations suggest large-scale postseismic deformation with a relaxation time of at least 800 days. The statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets; two possible noise models fit the PGGA data equally well as described in the companion paper by Zhang et al. [this issue]; the pre-Landers data are too sparse and heterogeneous to derive a reliable noise model. Under a fractal white noise model for the PGGA data we find that the velocity differences for all three sites are statistically different at the 99% significance level. A white noise plus flicker noise model results in significance levels of only 94%, 43%, and 88%. Additional investigations of the pre-Landers data, and analysis of longer spans of PGGA data, could have an important effect on the significance of these results and will be addressed in future work. Copyright 1997 by the American Geophysical Union.

Bock, Y.; Wdowinski, S.; Fang, P.; Zhang, J.; Williams, S.; Johnson, H.; Behr, J.; Genrich, J.; Dean, J.; Van Domselaar, M.; Agnew, D.; Wyatt, F.; Stark, K.; Oral, B.; Hudnut, K.; King, R.; Herring, T.; Dinardo, S.; Young, W.; Jackson, D.; Gurtner, W.

1997-01-01

383

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

384

Site response, shallow shear-wave velocity, and damage in Los Gatos, California, from the 1989 Loma Prieta earthquake  

USGS Publications Warehouse

Aftershock records of the 1989 Loma Prieta earthquake are used to calculate site response in the frequency band of 0.5-10 Hz at 24 locations in Los Gatos, California, on the edge of the Santa Clara Valley. Two different methods are used: spectral ratios relative to a reference site on rock and a source/site spectral inversion method. These two methods complement each other and give consistent results. Site amplification factors are compared with surficial geology, thickness of alluvium, shallow shear-wave velocity measurements, and ground deformation and structural damage resulting from the Loma Prieta earthquake. Higher values of site amplification are seen on Quaternary alluvium compared with older Miocene and Cretaceous units of Monterey and Franciscan Formation. However, other more detailed correlations with surficial geology are not evident. A complex pattern of alluvial sediment thickness, caused by crosscutting thrust faults, is interpreted as contributing to the variability in site response and the presence of spectral resonance peaks between 2 and 7 Hz at some sites. Within the range of our field measurements, there is a correlation between lower average shear-wave velocity of the top 30 m and 50% higher values of site amplification. An area of residential homes thrown from their foundations correlates with high site response. This damage may also have been aggravated by local ground deformation. Severe damage to commercial buildings in the business district, however, is attributed to poor masonry construction.

Hartzell, S.; Carver, D.; Williams, R. A.

2001-01-01

385

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

386

Late Holocene slip rate and recurrence of great earthquakes on the San Andreas fault in northern California  

SciTech Connect

The slip rate of the San Andreas fault 45 km north of San Francisco at Olema, California, is determined by matching offset segments of a buried late Holocene stream channel. Stream deposits from 1,800 {plus minus} 78 yr B.P. are offset 42.5 {plus minus} 3.5 m across the active (1906) fault trace for a minimum late Holocene slip rate of 24 {plus minus} 3 mm/yr. When local maximum coseismic displacements of 4.9 to 5.5 m from the 1906 earthquake are considered with this slip rate, the recurrence of 1906-type earthquakes on the North Coast segment of the San Andreas fault falls within the interval of 221 {plus minus} 40 yr. Both comparable coseismic slip in 1906 and similar late Holocene geologic slip rates at the Olema site and a site 145 km northwest at Point Arena (Prentice, 1989) suggest that the North Coast segment behaves as a coherent rupture unit.

Niemi, T.M. (Stanford Univ., CA (United States) Earth Sciences Associates, Palo Alto, CA (United States)); Hall, N.T. (Geomatrix Consultants, San Francisco, CA (United States))

1992-03-01

387

Superficial simplicity of the 2010 El Mayor-Cucapah earthquake of Baja California in Mexico  

E-print Network

The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures. The fault system that runs from southern California ...

Herring, Thomas A.

388

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras fault, California  

Microsoft Academic Search

We present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet, or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates. We compute differences in arrival times between seismograms recorded at the same station in the frequency domain by cross correlation

G. Poupinet; V. L. Ellsworth; J. Frechet

1984-01-01

389

Geodetic estimate of coseismic slip during the 1989 Loma Prieta, California, earthquake  

Microsoft Academic Search

Offsets in the relative positions of geodetic stations resulting from the Loma Prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the San Andreas fault, dipping 70° to the SW, and extending from a depth of about 5 to 17.5 km. Assuming uniform slip

M. Lisowski; W. H. Prescott; J. C. Savage; M. J. Johnston

1990-01-01

390

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.'

Bolton, Patricia A., (Edited By)

1993-01-01

391

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.

Rojstaczer, Stuart A., (Edited By)

1994-01-01

392

The Northern California Earthquake Management System: A Unified System From Realtime Monitoring to Data Distribution  

Microsoft Academic Search

The longstanding cooperation between the USGS Menlo Park and UC Berkeley's Seismological Laboratory for monitoring earthquakes and providing data to the research community is achieving a new level of integration. While station support and data collection for each network (NC, BK, BP) remain the responsibilities of the host institution, picks, codas and amplitudes will be produced and shared between the

D. Neuhauser; L. Dietz; P. Lombard; F. Klein; S. Zuzlewski; W. Kohler; M. Hellweg; J. Luetgert; D. Oppenheimer; B. Romanowicz

2006-01-01

393

Time-Reversal to Estimate Focal Depth for Local, Shallow Earthquakes in Southern California  

Microsoft Academic Search

Current approaches for focal depth estimation are typically based on travel times and result in large uncertainties primarily due to poor data coverage and inaccurate travel time picks. We propose an alternative method based on an adaptation of time-reversed acoustics (TRA). In the context of TRA theory, the autocorrelation of an earthquake recording can be thought of as the convolution

F. Pearce; R. Lu; N. Toksoz

2007-01-01

394

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

395

Paleoearthquakes on the southern San Andreas Fault, Wrightwood, California, 3000 to 1500 B.C.: A new method for evaluating paleoseismic evidence and earthquake horizons  

USGS Publications Warehouse

We present evidence of 11-14 earthquakes that occurred between 3000 and 1500 B.C. on the San Andreas fault at the Wrightwood paleoseismic site. Earthquake evidence is presented in a novel form in which we rank (high, moderate, poor, or low) the quality of all evidence of ground deformation, which are called "event indicators." Event indicator quality reflects our confidence that the morphologic and sedimentologic evidence can be attributable to a ground-deforming earthquake and that the earthquake horizon is accurately identified by the morphology of the feature. In four vertical meters of section exposed in ten trenches, we document 316 event indicators attributable to 32 separate stratigraphic horizons. Each stratigraphic horizon is evaluated based on the sum of rank (Rs), maximum rank (Rm), average rank (Ra), number of observations (Obs), and sum of higher-quality event indicators (Rs>1). Of the 32 stratigraphic horizons, 14 contain 83% of the event indicators and are qualified based on the number and quality of event indicators; the remaining 18 do not have satisfactory evidence for further consideration. Eleven of the 14 stratigraphic horizons have sufficient number and quality of event indicators to be qualified as "probable" to "very likely" earthquakes; the remaining three stratigraphic horizons are associated with somewhat ambiguous features and are qualified as "possible" earthquakes. Although no single measurement defines an obvious threshold for designation as an earthquake horizon, Rs, Rm, and Rs>1 correlate best with the interpreted earthquake quality. Earthquake age distributions are determined from radio-carbon ages of peat samples using a Bayesian approach to layer dating. The average recurrence interval for the 10 consecutive and highest-quality earthquakes is 111 (93-131) years and individual intervals are ??50% of the average. With comparison with the previously published 14-15 earthquake record between A.D. 500 and present, we find no evidence to suggest significant variations in the average recurrence rate at Wrightwood during the past 5000 years.

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

2007-01-01

396

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

397

Seven: Southern California Survey  

E-print Network

Report. ” Southern California Earthquake Data Center.the Southern California region has about 10,000 earthquakes,Southern California residents have confidence in their local government’s ability to respond quickly and effectively in the aftermath of a major earthquake.

Haselhoff, Kim; Ong, Paul

2006-01-01

398

Local Public Health System Response to the Tsunami Threat in Coastal California following the T?hoku Earthquake  

PubMed Central

Background On Friday March 11, 2011 a 9.0 magnitude earthquake triggered a tsunami off the eastern coast of Japan, resulting in thousands of lives lost and billions of dollars in damage around the Pacific Rim. The tsunami first reached the California coast on Friday, March 11th, causing more than $70 million in damage and at least one death. While the tsunami’s impact on California pales in comparison to the destruction caused in Japan and other areas of the Pacific, the event tested emergency responders’ ability to rapidly communicate and coordinate a response to a potential threat. Methods To evaluate the local public health system emergency response to the tsunami threat in California, we surveyed all local public health, emergency medical services (EMS), and emergency management agencies in coastal or floodplain counties about several domains related to the tsunami threat in California, including: (1) the extent to which their community was affected by the tsunami, (2) when and how they received notification of the event, (3) which public health response activities were carried out to address the tsunami threat in their community, and (4) which organizations contributed to the response. Public health activities were characterized using the Centers for Disease Control and Prevention (CDC) Public Health Preparedness Capabilities (PHEP) framework. Findings The tsunami's impact on coastal communities in California ranged widely, both in terms of the economic consequences and the response activities. Based on estimates from the National Oceanic and Atmospheric Administration (NOAA), ten jurisdictions in California reported tsunami-related damage, which ranged from $15,000 to $35 million. Respondents first became aware of the tsunami threat in California between the hours of 10:00pm Pacific Standard Time (PST) on Thursday March 10th and 2:00pm PST on Friday March 11th, a range of 16 hours, with notification occurring through both formal and informal channels. In response to this threat, the activities most commonly reported by the local government agencies included in this study were: emergency public information and warning, emergency operations coordination, and inter-organizational information sharing, which were reported by 86%, 75%, and 65% of all respondents, respectively. When looking at the distribution of responsibility, emergency management agencies were the most likely to report assuming a lead role in these common activities as well as those related to evacuation and community recovery. While activated less frequently, public health agencies carried out emergency response functions related to surveillance and epidemiology, environmental health, and mental health/psychological support. Both local public health and EMS agencies took part in mass care and medical material management activities. A large network of organizations contributed to response activities, with emergency management, law enforcement, fire, public health, public works, EMS, and media cited by more than half of respondents. Conclusions In response to the tsunami threat in California, we found that emergency management agencies assumed a lead role in the local response efforts. While public health and medical agencies played a supporting role in the response, they uniquely contributed to a number of specific activities. If the response to the recent tsunami is any indication, these support activities can be anticipated in planning for future events with similar characteristics to the tsunami threat. Additionally, we found that many respondents first learned of the tsunami through the media, rather than through rapid notification systems, which suggests that government agencies must continue to develop and maintain the ability to rapidly aggregate and analyze information in order to provide accurate assessments and guidance to a potentially well-informed public. Citation: Hunter JC, Crawley AW, Petrie M, Yang JE, Aragón TJ. Local Public Health System Response to the Tsunami Threat in Coastal California following the T?hok

Hunter, Jennifer C.; Crawley, Adam W.; Petrie, Michael; Yang, Jane E.; Aragon, Tomas J.

2012-01-01

399

Stress Drop and Its Uncertainty for Central California Earthquakes M 3.8-5.5  

NASA Astrophysics Data System (ADS)

In studies where stress drop (tau) is estimated from the displacement spectrum of body waves (Brune, 1970,1971), the standard deviation of tau (std-tau) is around a factor of four (Cotton et al., 2013). The std-tau is primarily due to uncertainty in the corner frequency (fc) because tau is proportional to fc^3. An alternative approach is to compute tau based on the acceleration spectrum, using the root-mean-square amplitude (A-rms) for frequencies greater than fc (Hanks, 1979). To compare these two methods we use borehole recordings at the Hollister downhole array (Steidl, 2006); earthquakes have M>3.8 to ensure a good signal to noise. The recordings at depth remove the near surface attenuation. However, the whole path attenuation must still be accounted for. To date we have analyzed 5 earthquakes (M 3.8-4.5) at hypocentral distance 8-17 km and 6 earthquakes (M 3.9-5.5) at hypocentral distance 26-76 km. We find that it is critically important to correct the spectrum for attenuation. For these earthquakes we used Q=Qo x f^0.6. We find an average t* (=travel time/Qo) near 5.5 for 8 of the earthquakes. After correcting for Q, the spectrum has an ?^2 shape for frequencies up to 70 Hz for the close distances and up to 40 Hz for the far distances. This bandwidth allows for a stable estimate of the rms acceleration. With the corrected spectrum we estimated fc, the low-frequency asymptote (to determine seismic moment) and the rms acceleration. Using the A-rms method we find nearly the same mean value of tau: 1.3 MPa and 1.0 MPa for close and far distances, with an uncertainty of a factor of 1.9 and 2.1, respectively. Whereas the same spectra produce a Brune tau of 1.1 MPa and 0.3 MPa for close and far distances, with an uncertainty of a factor of 3.5 and 3.4, respectively. Our analysis suggests that we can use the A-rms method for estimating tau for distances as large as 76 km provided we correct the spectrum for whole path attenuation. This analysis suggests that the intrinsic variability in earthquake stress drop is around a factor of 2.

Ding, L.; Crempien, J.; Archuleta, R. J.

2013-12-01

400

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

401

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

402

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

USGS Publications Warehouse

Examination of main shock and microearthquake data from the Calaveras Fault during the last 20 years reveals that main shock hypocenters occur at depths of 8-9 km near the base of the zone of microearthquakes. Microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones. Estimates of the fault regions which slipped during the Coyote Lake and Morgan Hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic. We propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes. From the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the Calaveras Fault. -from Authors

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

1990-01-01