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1

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

2

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

USGS Publications Warehouse

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

Stein, Ross S.

2007-01-01

3

Earthquake History of California  

NSDL National Science Digital Library

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

4

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.

5

Intro Probability Rabbits Description Predictions Ontology of Earthquake Probability: Metaphor  

E-print Network

rather than knowledge: They amount to saying that earthquakes occur as if according to a casino game Earthquake probabilities are based on a metaphor · Earthquakes occur "as if" in a casino game whose rulesIntro Probability Rabbits Description Predictions Ontology of Earthquake Probability: Metaphor

Stark, Philip B.

6

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, R.J., II; Fumal, T.E.; Seitz, G.G.

2002-01-01

7

Next-Day Earthquake Forecasts for California  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

8

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.

9

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.

10

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

11

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.

12

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.

13

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.

14

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

15

Estimation of Future Earthquake Losses in California  

Microsoft Academic Search

Recent developments in earthquake hazards and damage modeling, computing, and data management and processing, have made it possible to develop estimates of the levels of damage from earthquakes that may be expected in the future in California. These developments have been mostly published in the open literature, and provide an opportunity to estimate the levels of earthquake damage Californians can

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

2003-01-01

16

An Investigation of Southern California Earthquakes  

NSDL National Science Digital Library

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

17

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

PubMed

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. PMID:15902254

Gerstenberger, Matthew C; Wiemer, Stefan; Jones, Lucile M; Reasenberg, Paul A

2005-05-19

18

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

19

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

20

Combining earthquake forecasts using differential probability gains  

NASA Astrophysics Data System (ADS)

We describe an iterative method to combine seismicity forecasts. With this method, we produce the next generation of a starting forecast by incorporating predictive skill from one or more input forecasts. For a single iteration, we use the differential probability gain of an input forecast relative to the starting forecast. At each point in space and time, the rate in the next-generation forecast is the product of the starting rate and the local differential probability gain. The main advantage of this method is that it can produce high forecast rates using all types of numerical forecast models, even those that are not rate-based. Naturally, a limitation of this method is that the input forecast must have some information not already contained in the starting forecast. We illustrate this method using the Every Earthquake a Precursor According to Scale (EEPAS) and Early Aftershocks Statistics (EAST) models, which are currently being evaluated at the US testing center of the Collaboratory for the Study of Earthquake Predictability. During a testing period from July 2009 to December 2011 (with 19 target earthquakes), the combined model we produce has better predictive performance - in terms of Molchan diagrams and likelihood - than the starting model (EEPAS) and the input model (EAST). Many of the target earthquakes occur in regions where the combined model has high forecast rates. Most importantly, the rates in these regions are substantially higher than if we had simply averaged the models.

Shebalin, Peter N.; Narteau, Clément; Zechar, Jeremy Douglas; Holschneider, Matthias

2014-12-01

21

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

22

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

23

California earthquakes: why only shallow focus?  

PubMed

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

Brace, W F; Byerlee, J D

1970-06-26

24

California earthquakes: Why only shallow focus?  

USGS Publications Warehouse

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

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

1970-01-01

25

Psychological distress following urban earthquakes in California.  

PubMed

During and following a disaster caused by a natural event, human populations are thought to be at greater risk of psychological morbidity and mortality directly attributable to increased, disaster-induced stress. Drawing both on the research of others and that conducted at the Center for Public Health and Disaster Relief of the University of California-Los Angeles (UCLA) following California earthquakes, this paper examines the extent to which research evidence supports these assumptions. Following a brief history of disaster research in the United States, the response of persons at the time of an earthquake was examined with particular attention to psychological morbidity; the number of deaths that can be attributed to cardiovascular events and suicides; and the extent to which and by whom, health services are used following an earthquake. The implications of research findings for practitioners in the field are discussed. PMID:12500731

Bourque, Linda B; Siegel, Judith M; Shoaf, Kimberley I

2002-01-01

26

Conditional Probabilities for Large Events Estimated by Small Earthquake Rate  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

27

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.

28

Infrasonic observations of the Northridge, California, earthquake  

SciTech Connect

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

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

1994-09-01

29

Earthquake probability based on multidisciplinary observations with correlations  

Microsoft Academic Search

A number of researchers have formulated earthquake probabilities based on precursory anomalies of multidisciplinary observations in which the underlying assumption is that the occurrence of one precursory anomaly is independent from those of other kinds of anomalies. Observations were classified into two groups, those events followed by an earthquake and those that were not, and the ratio of observed precursors

Masajiro Imoto

2006-01-01

30

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

USGS Publications Warehouse

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

Working Group on California Earthquake Probabilities

1999-01-01

31

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

32

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

33

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

Microsoft Academic Search

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

D. A. Popovich; K. C. Miller

2002-01-01

34

Detection of hydrothermal precursors to large northern california earthquakes.  

PubMed

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

Silver, P G; Valette-Silver, N J

1992-09-01

35

Are all major California cities seriously threatened by earthquakes?  

SciTech Connect

This report discusses the seismic hazards associated with living in various urban areas of California, particularly the Fresno area. According to this assessment and other studies, the Fresno metropolitan area is relatively safe from the threat of a large destructive earthquake, due to its location away from major earthquake-prone fault zones. Unlike other major metropolitan areas in California such as San Francisco and Los Angeles, the Fresno area has no known active faults that are capable of causing destructive tremors. Several maps are included which indicate the location of earthquake epicenters and magnitudes in California from 1769 to the present.

Suen, C.J. [California State Univ., Fresno, CA (United States)

1995-09-01

36

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

37

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

38

The magnitude distribution of declustered earthquakes in Southern California  

NASA Astrophysics Data System (ADS)

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.

Knopoff, Leon

2000-10-01

39

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

40

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

41

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

USGS Publications Warehouse

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

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

1993-01-01

42

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

43

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

USGS Publications Warehouse

We examine the difference between expected earthquake rates inferred from the historical earthquake catalog and the geologic data that was used to develop the consensus seismic source characterization for the state of California [California Department of Conservation, Division of Mines and Geology (CDMG) and U.S. Geological Survey (USGS) Petersen et al., 1996; Frankel et al., 1996]. On average the historic earthquake catalog and the seismic source model both indicate about one M 6 or greater earthquake per year in the state of California. However, the overall earthquake rates of earthquakes with magnitudes (M) between 6 and 7 in this seismic source model are higher, by at least a factor of 2, than the mean historic earthquake rates for both southern and northern California. The earthquake rate discrepancy results from a seismic source model that includes earthquakes with characteristic (maximum) magnitudes that are primarily between M 6.4 and 7.1. Many of these faults are interpreted to accommodate high strain rates from geologic and geodetic data but have not ruptured in large earthquakes during historic time. Our sensitivity study indicates that the rate differences between magnitudes 6 and 7 can be reduced by adjusting the magnitude-frequency distribution of the source model to reflect more characteristic behavior, by decreasing the moment rate available for seismogenic slip along faults, by increasing the maximum magnitude of the earthquake on a fault, or by decreasing the maximum magnitude of the background seismicity. However, no single parameter can be adjusted, consistent with scientific consensus, to eliminate the earthquake rate discrepancy. Applying a combination of these parametric adjustments yields an alternative earthquake source model that is more compatible with the historic data. The 475-year return period hazard for peak ground and 1-sec spectral acceleration resulting from this alternative source model differs from the hazard resulting from the standard CDMG-USGS model by less than 10% across most of California but is higher (generally about 10% to 30%) within 20 km from some faults.

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

2000-01-01

44

Triggering of repeating earthquakes in central California  

NASA Astrophysics Data System (ADS)

stresses carried by transient seismic waves have been found capable of triggering earthquakes instantly in various tectonic settings. Delayed triggering may be even more common, but the mechanisms are not well understood. Catalogs of repeating earthquakes, earthquakes that recur repeatedly at the same location, provide ideal data sets to test the effects of transient dynamic perturbations on the timing of earthquake occurrence. Here we employ a catalog of 165 families containing ~2500 total repeating earthquakes to test whether dynamic perturbations from local, regional, and teleseismic earthquakes change recurrence intervals. The distance to the earthquake generating the perturbing waves is a proxy for the relative potential contributions of static and dynamic deformations, because static deformations decay more rapidly with distance. Clear changes followed the nearby 2004 Mw6 Parkfield earthquake, so we study only repeaters prior to its origin time. We apply a Monte Carlo approach to compare the observed number of shortened recurrence intervals following dynamic perturbations with the distribution of this number estimated for randomized perturbation times. We examine the comparison for a series of dynamic stress peak amplitude and distance thresholds. The results suggest a weak correlation between dynamic perturbations in excess of ~20 kPa and shortened recurrence intervals, for both nearby and remote perturbations.

Wu, Chunquan; Gomberg, Joan; Ben-Naim, Eli; Johnson, Paul

2014-03-01

45

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

NASA Astrophysics Data System (ADS)

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. While there are broad range of challenges associated with the development, implementation, and use of this model, the intent of this presentation is to give an overview of some of the most pressing scientific issues. These questions can be distilled down as follows: 1) Does every small volume of space exhibit a Gutenberg Richter distribution of nucleations?; 2) What is the average slip distribution of large events, both down dip and along strike?; 3) How do we apply elastic rebound in an un-segmented fault model?; 4) How can we quantify fault-to-fault rupture probabilities, especially give uncertainties in fault endpoints?; 5) What constitutes “best available science” with respect to spatial and temporal clustering models?; and 6) What is the explanation for the apparent post-1906 seismicity-rate reduction? Each of these questions will be described and exemplified, together with our current plans for addressing them.

Field, E. H.

2009-12-01

46

Southern California Earthquake Center (SCEC) Community Fault Model (over 150 major faults of Southern California)  

NSDL National Science Digital Library

This is a movie made using the SCEC-VDO software showing a 3D animation of the SCEC Community Fault Model (over 150 major faults of Southern California). The movie highlights the San Andreas and Puente Hills faults. The Southern California Earthquake Center's Virtual Display of Objects (SCEC-VDO) is 3D visualization software that allows users to display, study and make movies of earthquakes as they occur globally. SCEC-VDO was developed by interns of SCEC Undergraduate Studies in Earthquake Information Technology (UseIT), under the supervision of Sue Perry and Tom Jordan.

47

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

48

Modified Mercalli intensities for some recent California earthquakes and historic San Francisco Bay Region earthquakes  

USGS Publications Warehouse

Modified Mercalli Intensity (MMI) data for recent California earthquakes were used by Bakun and Wentworth (1997) to develop a strategy for bounding the location and moment magnitude M of earthquakes from MMI observations only. Bakun (Bull. Seismol. Soc. Amer., submitted) used the Bakun and Wentworth (1997) strategy to analyze 19th century and early 20th century San Francisco Bay Region earthquakes. The MMI data and site corrections used in these studies are listed in this Open-file Report. This report is also accessible at http://quake.wr.usgs.gov/~bakun/.

Bakun, W.H.

1998-01-01

49

Search for seismic forerunners to earthquakes in central California  

USGS Publications Warehouse

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

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

1977-01-01

50

Assessing Spatial Point Process Models for California Earthquakes Using Weighted  

E-print Network

Assessing Spatial Point Process Models for California Earthquakes Using Weighted K Box 951554 Los Angeles, CA 90095-1554 U.S.A. veen@stat.ucla.edu 2 UCLA Department of Statistics 8125 Math Sciences Building Box 951554 Los Angeles, CA 90095-1554 U.S.A. frederic@stat.ucla.edu We propose

Schoenberg, Frederic Paik (Rick)

51

Modified Mercalli intensities for some California north-coast earthquakes  

USGS Publications Warehouse

Modified Mercalli Intensity (MMI) data are used by Bakun (in preparation) to estimate the location and moment magnitude M of California north-coast earthquakes from MMI observations only. The MMI data and site corrections used by Bakun (in preparation) are listed in this Open-file Report. This report is also accessible at http://quake.wr.usgs.gov/~bakun/.

Bakun, W.H.

1999-01-01

52

Spectral Discrimination between Quarry Blasts and Earthquakes in Southern California  

E-print Network

Short Note Spectral Discrimination between Quarry Blasts and Earthquakes in Southern California, with the goal of developing methods to discriminate between these events. We process the spectra using reliable explosion discriminant than the S-to-P am- plitude ratio and works for about 90% of the events

Shearer, Peter

53

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

54

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

55

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, USC · High profile seismic hazard reports from 1993 · Community data bases ­faults, earthquakes, 3-D faults Quake rates elsewhere Putting it all together ... Uniform California Earthquake Rupture Forecast

56

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

57

Southern California Earthquake Center (SCEC) Summer Internship Programs  

NASA Astrophysics Data System (ADS)

For the eleventh consecutive year, the Southern California Earthquake Center (SCEC) coordinated undergraduate research experiences in summer 2004, allowing 35 students with a broad array of backgrounds and interests to work with the world's preeminent earthquake scientists and specialists. Students participate in interdisciplinary, system-level earthquake science and information technology research, and several group activities throughout the summer. Funding for student stipends and activities is made possible by the NSF Research Experiences for Undergraduates (REU) program. SCEC coordinates two intern programs: The SCEC Summer Undergraduate Research Experience (SCEC/SURE) and the SCEC Undergraduate Summer in Earthquake Information Technology (SCEC/USEIT). SCEC/SURE interns work one-on-one with SCEC scientists at their institutions on a variety of earthquake science research projects. The goals of the program are to expand student participation in the earth sciences and related disciplines, encourage students to consider careers in research and education, and to increase diversity of students and researchers in the earth sciences. 13 students participated in this program in 2004. SCEC/USEIT is an NSF REU site that brings undergraduate students from across the country to the University of Southern California each summer. SCEC/USEIT interns interact in a team-oriented research environment and are mentored by some of the nation's most distinguished geoscience and computer science researchers. The goals of the program are to allow undergraduates to use advanced tools of information technology to solve problems in earthquake research; close the gap between computer science and geoscience; and engage non-geoscience majors in the application of earth science to the practical problems of reducing earthquake risk. SCEC/USEIT summer research goals are structured around a grand challenge problem in earthquake information technology. For the past three years the students have developed a new earthquake and fault visualization platform named "LA3D." 22 students participated in this program in 2004. SCEC Interns come together several times during the summer, beginning with a Communication Workshop that develops the student's oral and written communication skills. In mid-summer, a one-day SCEC Intern Colloquium is held, where student researchers present status reports on their research, followed by a three-day field trip of southern California geology and SCEC research locations. Finally, at the end of the summer each student presents a poster at the SCEC Annual Meeting.

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

2004-12-01

58

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

59

San Andreas Fault, California, M 5.5 or greater Earthquakes 1800-2000  

Microsoft Academic Search

The San Andreas fault has been the most significant source of major California earthquakes since 1800. From 1812 to 1906 it generated four major earthquakes of M 7.2 or greater in two pairs on two major regions of the fault. A pair of major earthquakes occurred on the Central to Southern region, where the 1857 faulting overlapped the 1812 earthquake

T. Toppozada; D. Branum; M. Reichle; C. Hallstrom

2001-01-01

60

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

E-print Network

Recalculated probability of M !!!!!! 7 earthquakes beneath the Sea of Marmara, Turkey Tom Parsons U); KEYWORDS: earthquake probability, Sea of Marmara, seismic hazard, Turkey, stress interaction, North of Marmara, Turkey, J. Geophys. Res., 109, B05304, doi:10.1029/2003JB002667. 1. Introduction [2] The North

61

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

62

Earthquake Prediction  

NSDL National Science Digital Library

This video segment adapted from NOVA tells the tragic story of two Japanese seismologists who disagreed about the threat of earthquakes in the early twentieth century. Today, seismologists in California offer residents a probability of risk that an earthquake might occur.

2005-12-17

63

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

64

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

65

Accessing Data From the Southern California Earthquake Data Center  

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

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

2001-12-01

66

Earthquake Probabilities and Magnitude Distribution in 100a along the Haiyuan Fault, northwestern China  

NASA Astrophysics Data System (ADS)

The Haiyuan fault is a major seismogenic fault in north-central China. One of the most devastating great earthquake in 20th century occurred near Haiyuan in northwestern China in December 16, 1920. More than 220000 people were killed and thousands of towns and villages were destroyed during this devastating earthquake. A 230 km long left-lateral surface rupture zone formed along the Haiyuan fault during the earthquake with maximum left lateral displacement of 10 m. In recent years, some researchers have studied the paleoseismology along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on fault geometry, segmentation pattern, and paleoearthquake events along the Haiyuan fault we can identify three scales of earthquake rupture: rupture of one segment, cascade rupture of two segments, and cascade rupture of entire fault (three segments), and obtain the earthquake recurrence intervals of these scales of earthquake rupture. The earthquake probability and magnitude distribution in 100-year along the Haiyuan fault can be obtained through weighted computation, by applying these paleoseismological information mentioned above, using Possion and Brownian passage time model and considering different rupture patterns. The result shows that the earthquakes probability of is about 0.035 in 100-year along the Haiyuan fault.

Ran, H.

2004-12-01

67

Earthquake epicenters and fault intersections in central and southern California  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

68

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

E-print Network

not penetrate to depths where large earthquakes nucleate. Background seismicity in the Los Angeles basin occurs on the same fault [e.g., Hauksson, 1990, 2000]. Most recent earthquakes near Los Angeles occur as partAnalysis of similar event clusters in aftershocks of the 1994 Northridge, California, earthquake

Shearer, Peter

69

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

70

Geometry and earthquake potential of the shoreline fault, central California  

USGS Publications Warehouse

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

Hardebeck, Jeanne L.

2013-01-01

71

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

USGS Publications Warehouse

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

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

1996-01-01

72

Probability of a given-magnitude earthquake induced by a fluid injection  

NASA Astrophysics Data System (ADS)

Fluid injections in geothermic and hydrocarbon reservoirs induce small earthquakes (-3 < M < 2). Occasionally, however, earthquakes with larger magnitudes (M ~ 4) occur. We investigate magnitude distributions and show that for a constant injection pressure the probability to induce an earthquake with a magnitude larger than a given value increases with injection time corresponding to a bi-logarithmical law with a proportionality coefficient close to one. We find that the process of pressure diffusion in a poroelastic medium with randomly distributed sub-critical cracks obeying a Gutenberg-Richter relation well explains our observations. The magnitude distribution is mainly inherited from the statistics of pre-existing fracture systems. The number of earthquakes greater than a given magnitude also increases with the strength of the injection source and the tectonic activity of the injection site. Our formulation provides a way to estimate expected magnitudes of induced earthquakes. It can be used to avoid significant earthquakes by correspondingly planning fluid injections.

Shapiro, S. A.; Dinske, C.; Kummerow, J.

2007-11-01

73

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

74

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

75

Subduction zone earthquake probably triggered submarine hydrocarbon seepage offshore Pakistan  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

76

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

77

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

78

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

79

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

80

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

USGS Publications Warehouse

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

Parsons, T.

2008-01-01

81

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

USGS Publications Warehouse

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

Parsons, Tom

2008-01-01

82

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

83

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

Microsoft Academic Search

Four medium-sized earthquakes (Mw Global CMT project 5.5, 5.6, 5.9, 6.3; hereinafter named Topolobampo, Angel de la Guarda, San Lorenzo, and Loreto earthquakes, respectively) located in the Gulf of California Extensional Province were studied to obtain their kinematic rupture processes. A network of broadband seismic stations located around the Gulf of California recorded the events (Network of Autonomously Recording Seismographs–Baja

Héctor E. Rodríguez-Lozoya; Luis Quintanar; Roberto Ortega; Cecilio J. Rebollar; Yuji Yagi

2008-01-01

84

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

Microsoft Academic Search

Four medium-sized earthquakes (M w Global CMT project 5.5, 5.6, 5.9, 6.3; hereinafter named Topolobampo, Angel de la Guarda, San Lorenzo, and Loreto earthquakes, respectively) located in the Gulf of California Extensional Province were studied to obtain their kinematic rupture processes. A network of broadband seismic stations located around the Gulf of California recorded the events (Network of Autonomously Recording

Héctor E. Rodríguez-Lozoya; Luis Quintanar; Roberto Ortega; Cecilio J. Rebollar; Yuji Yagi

2008-01-01

85

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

Microsoft Academic Search

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

David K Keefer

2000-01-01

86

Variation of P-wave velocity before the Bear Valley, California, earthquake of 24 February 1972  

USGS Publications Warehouse

Residuals for P-wave traveltimes at a seismograph 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.

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

1974-01-01

87

A new and defective regulation in California for protecting critical buildings from earthquakes  

Microsoft Academic Search

The California Geological Survey issued a new regulatory directive specifying that critical buildings be designed for 50- and 100-year earthquakes obtained by probabilistic seismic hazard analysis (PSHA). PSHA incorporates serious uncertainties. Chiefly, they are: (1) PSHA smears earthquakes together to produce motions that are unrealistic for any specific earthquake-generating fault source, (2) PSHA assumes there is an essentially log–linear predictability

Lalliana Mualchin; Ellis L. Krinitzsky

2003-01-01

88

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

89

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

90

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.

91

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.

92

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

93

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

94

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

95

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

USGS Publications Warehouse

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

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

2003-01-01

96

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

NASA Astrophysics Data System (ADS)

Operational earthquake forecasting (OEF) is the dissemination of authoritative information about the time dependence of seismic hazards to help communities prepare for potentially destructive earthquakes. Most previous work on the public utility of OEF has anticipated that forecasts would deliver high probabilities of large earthquakes; i.e., deterministic predictions with low error rates (false alarms and failures-to-predict) would be possible. This expectation has not been realized. An alternative to deterministic prediction is probabilistic forecasting based on empirical statistical models of aftershock triggering and seismic clustering. During periods of high seismic activity, short-term earthquake forecasts can attain prospective probability gains in excess of 100 relative to long-term forecasts. The utility of such information is by no means clear, however, because even with hundredfold increases, the probabilities of large earthquakes typically remain small, rarely exceeding a few percent over forecasting intervals of days or weeks. Civil protection agencies have been understandably cautious in implementing OEF in this sort of "low-probability environment." The need to move more quickly has been underscored by recent seismic crises, such as the 2009 L'Aquila earthquake sequence, in which an anxious public was confused by informal and inaccurate earthquake predictions. After the L'Aquila earthquake, the Italian Department of Civil Protection appointed an International Commission on Earthquake Forecasting (ICEF), which I chaired, to recommend guidelines for OEF utilization. Our report (Ann. Geophys., 54, 4, 2011; doi: 10.4401/ag-5350) concludes: (a) Public sources of information on short-term probabilities should be authoritative, scientific, open, and timely, and need to convey epistemic uncertainties. (b) Earthquake probabilities should be based on operationally qualified, regularly updated forecasting systems. (c) All operational models should be evaluated for reliability and skill by retrospective testing, and the models should be under continuous prospective testing against long-term forecasts and alternative time-dependent models. (d) Short-term models used in operational forecasting should be consistent with the long-term forecasts used in probabilistic seismic hazard analysis. (e) Alert procedures should be standardized to facilitate decisions at different levels of government, based in part on objective analysis of costs and benefits. (f) In establishing alert protocols, consideration should also be given to the less tangible aspects of value-of-information, such as gains in psychological preparedness and resilience. Authoritative statements of increased risk, even when the absolute probability is low, can provide a psychological benefit to the public by filling information vacuums that lead to informal predictions and misinformation. Formal OEF procedures based on probabilistic forecasting appropriately separate hazard estimation by scientists from the decision-making role of civil protection authorities. The prosecution of seven Italian scientists on manslaughter charges stemming from their actions before the L'Aquila earthquake makes clear why this separation should be explicit in defining OEF protocols.

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

2011-12-01

97

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

98

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

99

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

100

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

101

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

USGS Publications Warehouse

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

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

2008-01-01

102

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

103

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

104

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 calibrated regression models to predict the occurrence of velocity pulses in future ground motions, as well

Baker, Jack W.

105

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

106

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

Microsoft Academic Search

In 1999 the Southern California Earthquake Center initiated an effort to expand its reach to multiple target audiences through the development of an interpretive trail on the San Andreas fault at Wallace Creek and an earthquake exhibit at Fingerprints Youth Museum in Hemet. These projects and involvement with the San Bernardino County Museum in Redlands beginning in 2007 led to

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

2009-01-01

107

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

108

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

109

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

110

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

Microsoft Academic Search

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

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

2000-01-01

111

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

112

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

113

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

114

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

USGS Publications Warehouse

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

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

2004-01-01

115

Local earthquake travel times and spatial variations of crustal velocity in southern California  

NASA Astrophysics Data System (ADS)

Measurements of P-wave arrival times from local earthquakes contain information about differences in crustal velocity within a region. Using 32,000 arrival times recorded by a seismic array in southern California, these spatial variations in velocity were estimated. A statistical model of the behavior of travel time residuals derived from a laterally homogeneous velocity model accounts for the major sources of error in the recording and hypocenter location processes, and leads to a set of editing procedures to remove aberrant data. Edited data were inverted under a variety of assumptions to estimate a laterally varying veocity model using a variation on a method originally developed for teleseismic data. The improvement in the residuals due to the new velocity models is statistically significant. The inversion method appears to underestimate the size of the velocity contrasts, but the results are generally consistent with those obtained using other types of data. A major result is that the Peninsular Ranges have substantially higher average velocity than nearby regions, probably due to differences in crustal tickness and composition.

Ergas, R. A.

116

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

117

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

118

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

119

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

120

Instability model for recurring large and great earthquakes in southern California  

NASA Astrophysics Data System (ADS)

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

Stuart, William D.

1984-11-01

121

Diagnosis of time of increased probability of volcanic earthquakes at Mt. Vesuvius zone  

E-print Network

The possibility of intermediate-term earthquake prediction at Mt. Vesuvius by means of the algorithm CN is explored. CN was originally designed to identify the Times of Increased Probability (TIPs) for the occurrence of strong tectonic earthquakes, with magnitude M >= M sub 0 , within a region a priori delimited. Here the algorithm CN is applied, for the first time, to the analysis of volcanic seismicity. The earthquakes recorded at Mt. Vesuvius, during the period from February 1972 to October 2002, are considered and the magnitude threshold M sub 0 , selecting the events to be predicted, is varied within the range: 3.0 - 3.3. Satisfactory prediction results are obtained, by retrospective analysis, when a time scaling is introduced. In particular, when the length of the time windows is reduced by a factor 2.5 - 3, with respect to the standard version of CN algorithm, more than 90% of the events with M >= M sub 0 occur within the TIP intervals, with TIPs occupying about 30% of the total time considered. The co...

Rotwain, I; Kuznetsov, I V; Panza, G F; Peresan, A

2003-01-01

122

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

USGS Publications Warehouse

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

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

2012-01-01

123

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

124

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

NASA Astrophysics Data System (ADS)

Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In DSHA, seismic hazard in the event of the Maximum Credible Earthquake (MCE) magnitude from each of the known seismogenic faults within and near the state are assessed. The likely occurrence of the MCE has been assumed qualitatively by using late Quaternary and younger faults that are presumed to be seismogenic, but not when or within what time intervals MCE may occur. MCE is the largest or upper-bound potential earthquake in moment magnitude, and it supersedes and automatically considers all other possible earthquakes on that fault. That moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships, and for calculating ground motions as in neo-DSHA (Z uccolo et al., 2008). The first deterministic California earthquake hazard map was published in 1974 by the California Division of Mines and Geology (CDMG) which has been called the California Geological Survey (CGS) since 2002, using the best available fault information and ground motion attenuation relationships at that time. The California Department of Transportation (Caltrans) later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists, seismologists, and engineers for many years. Some engineers involved in the siting process of large important projects, for example, dams and nuclear power plants, continued to challenge the map(s). The second edition map was completed in 1985 incorporating more faults, improving MCE's estimation method, and using new ground motion attenuation relationships from the latest published results at that time. CDMG eventually published the second edition map in 1992 following the Governor's Board of Inquiry on the 1989 Loma Prieta earthquake and at the demand of Caltrans. The third edition map was published by Caltrans in 1996 utilizing GIS technology to manage data that includes a simplified three-dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map. The spatial relationship of fault hazards with highways, bridges or any other attribute can be efficiently managed and analyzed now in GIS at Caltrans. There has been great confidence in using DSHA in bridge engineering and other applications in California, and it can be confidently applied in any other earthquake-prone region. Earthquake hazards defined by DSHA are: (1) transparent and stable with robust MCE moment magnitudes; (2) flexible in their application to design considerations; (3) can easily incorporate advances in ground motion simulations; and (4) economical. DSHA and neo-DSHA have the same approach and applicability. The accuracy of DSHA has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment. In the final analysis, DSHA is a reality-check for public safety and PSHA results. Although PSHA has been acclaimed as a better approach for seismic hazard assessment, it is DSHA, not PSHA, that has actually been used in seismic hazard assessment for building and bridge engineering, particularly in California.

Mualchin, Lalliana

2011-03-01

125

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

126

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

127

Earthquakes.  

ERIC Educational Resources Information Center

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

Pakiser, Louis C.

128

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

129

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 ...

130

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

131

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

132

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

133

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

Microsoft Academic Search

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

Timothy Masterlark; Herbert F. Wang

2002-01-01

134

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

USGS Publications Warehouse

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

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

1999-01-01

135

Earthquake Recurrence on Continental Transform Faults: Alpine Fault, New Zealand and San Andreas Fault, California Compared  

NASA Astrophysics Data System (ADS)

The Alpine fault in South Island, New Zealand, and the San Andreas fault in California are high slip-rate continental transform faults that are so similar as to be studied as analogs of each other. Both slip in the range of 2-3 cm/yr and have hundreds of km of total accumulated slip. New results from the Hokuri Creek site on the southern on-land part of the Alpine fault allow us to extend that comparison to study the recurrence behavior of large earthquakes. Paleoseismic study at Hokuri Creek using natural geologic exposures, radiocarbon dating, and paleo-ecological markers has yielded a record of 22 cycles of sediments created by meter scale reverse components of large ruptures on this dominantly strike-slip fault. Radiocarbon dating at a nearby paleoseismic site confirmed the youngest Hokuri Creek event and provides evidence for two additional post-Hokuri events. The result is an 8000-year record with 24 large earthquakes, the most recent of which occurred in A.D. 1717. The fault slip rate is 23+-2 mm/yr, so the average displacement among these ruptures is expected to be in the range of 7-8 meters. Field evidence for slip in the most recent event and the sum of the most recent three events are all consistent with this average. Earthquake recurrence on the southern Alpine fault has been relatively regular, with a coefficient of variation (COV) of 0.33 for the complete record. This relatively regular pattern of occurrence is in some contrast with paleoseismic records on the San Andreas fault. While still time dependent, the COVs of 0.7 and 0.6 for San Andreas records at Wrightwood (29 events) and Pallett Creek (10 events), respectively, are significantly less regular. Shorter paleoseismic records from elsewhere along the San Andreas yield less certain bounds on variability, but all are consistent with a COV higher than the southern Alpine fault. Slip per event data for the San Andreas fault are limited, but at Wrightwood and Pallett Creek, slip appears to be much more variable than for the Alpine fault. Conditional probability estimates using parameters for lognormal, Brownian Passage Time, and empirical recurrence models reflect the time-dependent hazard variation. Currently both models put the 50-year hazard of a large southern Alpine fault event near 27%, compared to a time-independent hazard of 15%. These estimates are relatively robust to plausible alternative interpretations of the record. Because of the larger COV, conditional probabilities between time-dependent and time-independent models are more similar for the San Andreas fault. The emerging picture is that the southern Alpine fault is simpler in its slip characteristics than the San Andreas fault. This may reflect the simpler geometry of the southern Alpine fault and greater number of interacting fault components in the San Andreas system.

Biasi, G. P.; Berryman, K. R.; Cochran, U. A.; Clark, K.; Langridge, R. M.; Villamor, P.

2012-12-01

136

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

137

New Continuous Timeseries Data at the Northern California Earthquake Data Center  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

138

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

139

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

USGS Publications Warehouse

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

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

1999-01-01

140

Earthquakes  

NSDL National Science Digital Library

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

Pamela Gore

141

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

142

Earthquakes  

NSDL National Science Digital Library

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

Hemedinger, Mrs.

2007-11-26

143

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.

144

Tom Parsons, U.S. Geological Survey, 345 Middlefield Rd. Menlo Park, CA, 94025 Earthquake probability calculated from paleoseismic  

E-print Network

the mean 30-year probability (2010-2040) is 17.9%. Taking account of coseismic and post-seismic stress similar, and relatively high mean 30-year results (17.9% and 19.4%). Thus expedient retrofitting transfer and post-seismic viscoelastic relaxation from the 1906 great San Francisco earthquake. 179

145

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

146

Earthquakes  

ERIC Educational Resources Information Center

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

Roper, Paul J.; Roper, Jere Gerard

1974-01-01

147

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

148

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

149

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

150

Modelling aftershock migration and afterslip of the San Juan Bautista, California, earthquake of October 3, 1972  

USGS Publications Warehouse

The San Juan Bautista earthquake of October 3, 1972 (ML = 4.8), located along the San Andreas fault in central California, initiated an aftershock sequence characterized by a subtle, but perceptible, tendency for aftershocks to spread to the northwest and southeast along the fault zone. The apparent dimension of the aftershock zone along strike increased from about 7-10 km within a few days of the earthquake, to about 20 km eight months later. In addition, the mainshock initiated a period of accelerated fault creep, which was observed at 2 creep meters situated astride the trace of the San Andreas fault within about 15 km of the epicenter of the mainshock. The creep rate gradually returned to the preearthquake rate after about 3 yrs. Both the spreading of the aftershocks and the rapid surface creep are interpreted as reflecting a period of rapid creep in the fault zone representing the readjustment of stress and displacement following the failure of a "stuck" patch or asperity during the San Juan Bautista earthquake. Numerical calculations suggest that the behavior of the fault zone is consistent with that of a material characterized by a viscosity of about 3.6??1014 P, although the real rheology is likely to be more complicated. In this model, the mainshock represents the failure of an asperity that slips only during earthquakes. Aftershocks represent the failure of second-order asperities which are dragged along by the creeping fault zone. ?? 1987.

Wesson, R.L.

1987-01-01

151

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

USGS Publications Warehouse

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

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

2000-01-01

152

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

153

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

154

Deformation and seismicity triggered beneath Mammoth Mountain, California, by surface waves from the M7.9 Denali fault, Alaska, earthquake of 3 November 2002  

Microsoft Academic Search

The November 3, 2002, MW 7.9 Denali Fault earthquake triggered deformational offsets and microseismicity in Long Valley Caldera, California some 3200 km from the earthquake. Such strain offsets and microseismicity were not recorded at other borehole strain sites along the San Andreas fault system in California. The Long Valley offsets were recorded on borehole strainmeter and tiltmeters at three sites

M. J. S. Johnston; D. P. Hill; A. M. Pitt

2002-01-01

155

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

NASA Astrophysics Data System (ADS)

Currently the SCEDC archives continuous and triggered data from nearly 5000 data channels from 425 SCSN recorded stations, processing and archiving an average of 12,000 earthquakes each year. The SCEDC provides public access to these earthquake parametric and waveform data through its website www.data.scec.org and through client applications such as STP and DHI. This poster will describe the most significant developments at the SCEDC in the past year. Updated hardware: ? The SCEDC has more than doubled its waveform file storage capacity by migrating to 2 TB disks. New data holdings: ? Waveform data: Beginning Jan 1, 2010 the SCEDC began continuously archiving all high-sample-rate strong-motion channels. All seismic channels recorded by SCSN are now continuously archived and available at SCEDC. ? Portable data from El Mayor Cucapah 7.2 sequence: Seismic waveforms from portable stations installed by researchers (contributed by Elizabeth Cochran, Jamie Steidl, and Octavio Lazaro-Mancilla) have been added to the archive and are accessible through STP either as continuous data or associated with events in the SCEDC earthquake catalog. This additional data will help SCSN analysts and researchers improve event locations from the sequence. ? Real time GPS solutions from El Mayor Cucapah 7.2 event: Three component 1Hz seismograms of California Real Time Network (CRTN) GPS stations, from the April 4, 2010, magnitude 7.2 El Mayor-Cucapah earthquake are available in SAC format at the SCEDC. These time series were created by Brendan Crowell, Yehuda Bock, the project PI, and Mindy Squibb at SOPAC using data from the CRTN. The El Mayor-Cucapah earthquake demonstrated definitively the power of real-time high-rate GPS data: they measure dynamic displacements directly, they do not clip and they are also able to detect the permanent (coseismic) surface deformation. ? Triggered data from the Quake Catcher Network (QCN) and Community Seismic Network (CSN): The SCEDC in cooperation with QCN and CSN is exploring ways to archive and distribute data from high density low cost networks. As a starting point the SCEDC will store a dataset from QCN and CSN and distribute it through a separate STP client. New archival methods: ? The SCEDC is exploring the feasibility of archiving and distributing waveform data using cloud computing such as Google Apps. A month of continuous data from the SCEDC archive will be stored in Google Apps and a client developed to access it in a manner similar to STP. XML formats: ? The SCEDC is now distributing earthquake parameter data through web services in QuakeML format. ? The SCEDC in collaboration with the Northern California Earthquake Data Center (NCEDC) and USGS Golden has reviewed and revised the StationXML format to produce version 2.0. The new version includes a rules on extending the schema, use of named complex types, and greater consistency in naming conventions. Based on this work we plan to develop readers and writers of the StationXML format.

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

2010-12-01

156

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

Microsoft Academic Search

We examine remotely triggered microearthquakes and tectonic tremor in central California following the 2010 Mw 8.8 Chile earthquake. Several microearthquakes near the Coso Geothermal Field were apparently triggered, with the largest earthquake (Ml 3.5) occurring during the large-amplitude Love surface waves. The Chile mainshock also triggered numerous tremor bursts near the Parkfield-Cholame section of the San Andreas Fault (SAF). The

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

2010-01-01

157

4.10 Earthquake Hydrology M. Manga and C.-Y. Wang, University of California Berkeley, Berkeley, CA, USA  

E-print Network

4.10 Earthquake Hydrology M. Manga and C.-Y. Wang, University of California Berkeley, Berkeley, CA, USA ª 2007 Elsevier B.V. All rights reserved. 4.10.1 Introduction 293 4.10.2 Hydrologic Response.10.3.3 Mud Volcanoes 310 4.10.3.4 Geysers 311 4.10.4 Feedback between Earthquakes and Hydrology 312 4

Manga, Michael

158

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

159

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

USGS Publications Warehouse

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

Boore, D.M.

1999-01-01

160

Coulomb static stress interactions between simulated M>7 earthquakes and major faults in Southern California  

NASA Astrophysics Data System (ADS)

We calculate the Coulomb stress changes imparted to major Southern California faults by thirteen simulated worst-case-scenario earthquakes for the region, including the “Big Ten” scenarios (Ely et al, in progress). The source models for the earthquakes are variable-slip simulations from the SCEC CyberShake project (Graves et al, 2010). We find strong stress interactions between the San Andreas and subparallel right-lateral faults, thrust faults under the Los Angeles basin, and the left-lateral Garlock Fault. M>7 earthquakes rupturing sections of the southern San Andreas generally decrease Coulomb stress on the San Jacinto and Elsinore faults and impart localized stress increases and decreases to the Garlock, San Cayetano, Puente Hills and Sierra Madre faults. A M=7.55 quake rupturing the San Andreas between Lake Hughes and San Gorgonio Pass increases Coulomb stress on the eastern San Cayetano fault, consistent with Deng and Sykes (1996). M>7 earthquakes rupturing the San Jacinto, Elsinore, Newport-Inglewood and Palos Verdes faults decrease stress on parallel right-lateral faults. A M=7.35 quake on the San Cayetano Fault decreases stress on the Garlock and imparts localized stress increases and decreases to the San Andreas. A M=7.15 quake on the Puente Hills Fault increases stress on the San Andreas and San Jacinto faults, decreases stress on the Sierra Madre Fault and imparts localized stress increases and decreases to the Newport-Inglewood and Palos Verdes faults. A M=7.25 shock on the Sierra Madre Fault increases stress on the San Andreas and decreases stress on the Puente Hills Fault. These findings may be useful for hazard assessment, paleoseismology, and comparison with dynamic stress interactions featuring the same set of earthquakes.

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

2010-12-01

161

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

162

Anomalous early aftershock decay rate of the 2004 Mw6.0 Parkfield, California, earthquake  

NASA Astrophysics Data System (ADS)

We analyze the seismicity rate immediately after the 2004 Mw6.0 Parkfield, California, earthquake from near-source seismograms. By scrutinizing high-frequency signals, we can distinguish mainshock coda from early aftershocks occurring as soon as 30 s after the mainshock. We find, as expected, that a significant fraction of aftershocks in the first few hours after the main shock are missing in the Northern California Seismic Network catalog. We observe a steady rate of aftershocks in the first 130 s, followed by a power-law decay of aftershock activity. Thus, there appears to be a distinct early stage of aftershock activity that does not fit the Omori's law with a constant p value, a phenomenon that we refer to as Early Aftershock Deficiency (EAD). Our observation suggests that mainshock rupture and aftershocks are distinct processes, not described by a single Omori's law. Several physical models of aftershocks can explain the EAD.

Peng, Zhigang; Vidale, John E.; Houston, Heidi

2006-09-01

163

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

164

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

NASA Astrophysics Data System (ADS)

The SCSN is the modern digital ground motion seismic network in Southern California and performs the following tasks: 1) Operates remote seismic stations and the central data processing systems in Pasadena; 2) Generates and reports real-time products including location, magnitude, ShakeMap, aftershock probabilities and others; 3) Responds to FEMA, CalOES, media, and public inquiries about earthquakes; 4) Manages the production, archival, and distribution of waveforms, phase picks, and other data at the SCEDC; 5) Contributes to development and implementation of the demonstration EEW system called CISN ShakeAlert. Initially, the ShakeAlert project was funded through the US Geological Survey (USGS) and in early 2012, the Gordon and Betty Moore Foundation provided three years of new funding for EEW research and development for the US west coast. Recently, we have also received some Urban Areas Security Initiative (UASI) funding to enhance the EEW capabilities for the local UASI region by making our system overall faster, more reliable and redundant than the existing system. The additional and upgraded stations will be capable of decreasing latency and ensuring data delivery by using more reliable and redundant telemetry pathways. Overall, this will enhance the reliability of the earthquake early warnings by providing denser station coverage and more resilient data centers than before. * Seismic Datalogger upgrade: replaces existing dataloggers with modern equipment capable of sending one-second uncompressed packets and utilizing redundant Ethernet telemetry. * GPS upgrade: replaces the existing GPS receivers and antennas, especially at "zipper array" sites near the major faults, with receivers that perform on-board precise point positioning to calculate position and velocity in real time and stream continuous data for use in EEW calculations. * New co-located seismic/GPS stations: increases station density and reduces early warning delays that are incurred by travel time of the seismic waves to the nearest station and will increase the reliability of the early warning with multiple measurements from more than one reporting station. * New server hardware: will allow for separate software development, testing/integration of algorithms and production systems capable of testing with current as well as playback of historical data. Also the new systems will be used to develop and test new EEW algorithms like slip detection (GPSlip) and Finite-Fault Rupture Detection (FinDer). * Standardization and Security: the new systems will allow us to standardize on hardware installation and configuration procedures. It will also enable us to implement the latest computer and network security measures to secure the data and internal processing from malicious threats. * System architecture: the new hardware will allow us to port existing EEW algorithms from Solaris to Linux. The new equipment will also allow us to experiment with different system architecture configurations like redundant servers with fail-over capabilities for the production EEW system. When installed the new and upgraded seismic dataloggers and GPS stations as well as the new server hardware will greatly improve the EEW capabilities of the SCSN network and the CISN ShakeAlert system in general providing more resilience, robustness and redundancy in the system.

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

2013-12-01

165

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

USGS Publications Warehouse

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

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

2003-01-01

166

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

NASA Astrophysics Data System (ADS)

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

Stein, Seth; Tomasello, Joseph; Newman, Andrew

167

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.

168

High-resolution earthquake catalogs for southern California and Hawaii from waveform cross-correlation  

NASA Astrophysics Data System (ADS)

For many years, seismologists have known that earthquake location accuracy can be dramatically improved in an absolute sense by using 3D velocity models and in a relative sense among nearby events by exploiting correlated travel-time residuals and using waveform cross-correlation to improve phase pick consistency. However, most earthquakes are still located using 1D velocity models without taking advantage of these improvements. This is partly due to a desire to maintain consistency in earthquake catalogs, but also reflects difficulties in implementing methods originally developed as research projects for limited numbers of events to large-scale network processing in near-real-time. However, continued increases in computer speed and cheaper online storage options have made routine production of high-resolution catalogs more practical. We have recently produced such catalogs for southern California and Hawaii, after computing tens of millions of P and S differential times from waveform cross-correlation. These catalogs show a dramatic sharpening of seismicity features, permitting better identification of faults and volcanic structures. A key part of these projects is maintaining an online archive of seismograms from previous events that facilitates random and rapid retrieval of records for cross-correlation calculations. This waveform archive can be used for other purposes, such as computing spectra for comprehensive stress drop estimates and using P and S amplitudes to improve focal mechanisms.

Shearer, P. M.; Matoza, R. S.; Hauksson, E.; Wolfe, C. J.; Okubo, P.; Lin, G.

2012-12-01

169

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

170

Probability  

NSDL National Science Digital Library

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

Thompson, Ms.

2008-12-01

171

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

172

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

173

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

174

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

175

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

177

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

USGS Publications Warehouse

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

Jibson, R.W.

2002-01-01

178

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

179

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

California takes earthquakes very seriously. The state straddles two major tectonic plates the Pacific and North American tectonic plates. The Pacific Plate includes a sliver of California and Baja California, as well as Hawaii and most of the Pacific Ocean, while the North American Plate includes

180

Earthquakes  

MedlinePLUS

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

181

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

USGS Publications Warehouse

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

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

2013-01-01

182

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

183

Application of a Gravity Green's Function Method Using a Stress-evolution Earthquake Simulation of California  

NASA Astrophysics Data System (ADS)

Using a stress-evolution time-dependent model, simulated slip histories were created for the San Andreas Fault network in California. From the slip histories created, and through the use of gravity Green's functions, we generated a time-dependent model of the gravity evolution over the San Andreas Fault network. The model includes gravity effects from the underlying tectonic plate loading, as well as the gravity chnages from the sudden strain release during seismic events. Moreover, the method is general enough to include effects from faults with arbitrary dip and orientation in the fault network. The complex fault geometry contributes significantly to the spatial distribution of the various gravity signals observed while the signal magnitude is constrained by the amount slip modeled. The gravity signal over long periods exhibit highly complex signals; potentially highlighting directly observable regions of seismic susceptibilty prior to large earthquakes.

Hayes, T.; Tiampo, K.; Rundle, J. B.

2005-12-01

184

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

USGS Publications Warehouse

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

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

1985-01-01

185

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

NASA Astrophysics Data System (ADS)

The Southern California Earthquake Center's Fault Information System (FIS) provides a single point of access to fault-related data and models from multiple databases and datasets. The FIS is built of computer code, metadata and Web interfaces based on Web services technology, which enables queries and data interchange irrespective of computer software or platform. Currently we have working prototypes of programmatic and browser-based access. The first generation FIS may be searched and downloaded live, by automated processes, as well as interactively, by humans using a browser. Users get ascii data in plain text or encoded in XML. Via the Earthquake Information Technology (EIT) Interns (Juve and others, this meeting), we are also testing the effectiveness of querying multiple databases using a fault database ontology. For more than a decade, the California Geological Survey (CGS), SCEC, and the U. S. Geological Survey (USGS) have put considerable, shared resources into compiling and assessing published fault data, then providing the data on the Web. Several databases now exist, with different formats, datasets, purposes, and users, in various stages of completion. When fault databases were first envisioned, the full power of today's internet was not yet recognized, and the databases became the Web equivalents of review papers, where one could read an overview summation of a fault, then copy and paste pertinent data. Today, numerous researchers also require rapid queries and downloads of data. Consequently, the first components of the FIS are MySQL databases that deliver numeric values from earlier, text-based databases. Another essential service provided by the FIS is visualizations of fault representations such as those in SCEC's Community Fault Model. The long term goal is to provide a standardized, open-source, platform-independent visualization technique. Currently, the FIS makes available fault model viewing software for users with access to Matlab or Java3D. The latter is the interactive LA3D software of the SCEC EIT intern team, which will be demonstrated at this session.

Perry, S.

2003-12-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

188

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

189

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

190

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

191

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

192

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

193

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

194

Revised earthquake hazard of the Hat Creek fault, northern California: A case example of a normal fault dissecting variable-age basaltic lavas  

E-print Network

Revised earthquake hazard of the Hat Creek fault, northern California: A case example of a normal ABSTRACT Normal faults in basalt have distinctive surface-trace morphologies and earthquake evidence be applied to any normal-faulted basalt envi- ronment. Applied to the Hat Creek fault, we estimate

Kattenhorn, Simon

195

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.

196

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

197

Probability  

NSDL National Science Digital Library

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

Banks, Ms.

2005-05-11

198

Full Moment Tensor Variations and Isotropic Characteristics of Earthquakes in the Gulf of California Transform Fault System  

NASA Astrophysics Data System (ADS)

The full moment tensor is a mathematical expression of six independent variables; however, on a routine basis, it is a common practice to reduce them to five assuming that the isotropic component is zero. This constraint is valid in most tectonic regimes where slip occurs entirely at the fault surface (e.g. subduction zones); however, we found that full moment tensors are best represented in transform fault systems. Here we present a method to analyze source complexity of earthquakes of different sizes using a simple formulation that relates the elastic constants obtained from independent studies with the angle between the slip and the fault normal vector, referred to as angle ; this angle is obtained from the full moment tensors. The angle , the proportion of volume change and the constant volume (shear) component are numerical indicators of complexity of the source; earthquakes are more complex as deviates from or as T and k deviate from zero as well. These parameters are obtained from the eigensolution of the full moment tensor. We analyzed earthquakes in the Gulf of California that exhibit a clear isotropic component and we observed that the constant volume parameter T is independent of scalar moments, suggesting that big and small earthquakes are equally complex. In addition, simple models of one single fault are not sufficient to describe physically all the combinations of in a source type plot. We also found that the principal direction of the strike of the Transform Fault System in the Gulf of California is following the first order approximation of the normal surface of the full moment tensor solution, whereas for deviatoric moment tensors the principal direction does not coincide with the strike of the Transform Fault System. Our observations that small and large earthquakes are equally complex are in agreement with recent studies of strike-slip earthquakes.

Ortega, Roberto; Quintanar, Luis; Rivera, Luis

2014-10-01

199

Stability and uncertainty of finite-fault slip inversions: Application to the 2004 Parkfield, California, earthquake  

USGS Publications Warehouse

The 2004 Parkfield, California, earthquake is used to investigate stability and uncertainty aspects of the finite-fault slip inversion problem with different a priori model assumptions. We utilize records from 54 strong ground motion stations and 13 continuous, 1-Hz sampled, geodetic instruments. Two inversion procedures are compared: a linear least-squares subfault-based methodology and a nonlinear global search algorithm. These two methods encompass a wide range of the different approaches that have been used to solve the finite-fault slip inversion problem. For the Parkfield earthquake and the inversion of velocity or displacement waveforms, near-surface related site response (top 100 m, frequencies above 1 Hz) is shown to not significantly affect the solution. Results are also insensitive to selection of slip rate functions with similar duration and to subfault size if proper stabilizing constraints are used. The linear and nonlinear formulations yield consistent results when the same limitations in model parameters are in place and the same inversion norm is used. However, the solution is sensitive to the choice of inversion norm, the bounds on model parameters, such as rake and rupture velocity, and the size of the model fault plane. The geodetic data set for Parkfield gives a slip distribution different from that of the strong-motion data, which may be due to the spatial limitation of the geodetic stations and the bandlimited nature of the strong-motion data. Cross validation and the bootstrap method are used to set limits on the upper bound for rupture velocity and to derive mean slip models and standard deviations in model parameters. This analysis shows that slip on the northwestern half of the Parkfield rupture plane from the inversion of strong-motion data is model dependent and has a greater uncertainty than slip near the hypocenter.

Hartzell, S.; Liu, P.; Mendoza, C.; Ji, C.; Larson, K.M.

2007-01-01

200

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

USGS Publications Warehouse

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

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

2010-01-01

201

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

NASA Astrophysics Data System (ADS)

The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) originally formulated by Cua and Heaton (2007). Implementation of VS into real-time EEW codes has been an on-going effort of the Swiss Seismological Service at ETH Zürich since 2006, with support from ETH Zürich, various European projects, and the United States Geological Survey (USGS). VS is one of three EEW algorithms - the other two being ElarmS (Allen and Kanamori, 2003) and On-Site (Wu and Kanamori, 2005; Boese et al., 2008) algorithms - that form the basis of the California Integrated Seismic Network (CISN) ShakeAlert system, a USGS-funded prototype end-to-end EEW system that could potentially be implemented in California. In Europe, VS is currently operating as a real-time test system in Switzerland. As part of the on-going EU project REAKT (Strategies and Tools for Real-Time Earthquake Risk Reduction), VS will be installed and tested at other European networks. VS has been running in real-time on stations of the Southern California Seismic Network (SCSN) since July 2008, and on stations of the Berkeley Digital Seismic Network (BDSN) and the USGS Menlo Park strong motion network in northern California since February 2009. In Switzerland, VS has been running in real-time on stations monitored by the Swiss Seismological Service (including stations from Austria, France, Germany, and Italy) since 2010. We present summaries of the real-time performance of VS in Switzerland and California over the past two and three years respectively. The empirical relationships used by VS to estimate magnitudes and ground motion, originally derived from southern California data, are demonstrated to perform well in northern California and Switzerland. Implementation in real-time and off-line testing in Europe will potentially be extended to southern Italy, western Greece, Istanbul, Romania, and Iceland. Integration of the VS algorithm into both the CISN Advanced Quake Monitoring System (AQMS) and the SeisComP3 real-time earthquake monitoring systems is underway. VS operation in California will eventually be fully transitioned to the CISN AQMS system. European installations of VS will most likely be based on the SeisComP3 platform.

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

2012-12-01

202

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

203

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

USGS Publications Warehouse

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

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

2003-01-01

204

Low Velocity Zones along the San Jacinto Fault, Southern California, inferred from Local Earthquakes  

NASA Astrophysics Data System (ADS)

Natural fault zones have regions of brittle damage leading to a low-velocity zone (LVZ) in the immediate vicinity of the main fault interface. The LVZ may amplify ground motion, modify rupture propagation, and impact derivation of earthquke properties. Here we image low-velocity fault zone structures along the San Jacinto Fault (SJF), southern California, using waveforms of local earthquakes that are recorded at several dense arrays across the SJFZ. We use generalized ray theory to compute synthetic travel times to track the direct and FZ-reflected waves bouncing from the FZ boundaries. This method can effectively reduce the trade-off between FZ width and velocity reduction relative to the host rock. Our preliminary results from travel time modeling show the clear signature of LVZs along the SJF, including the segment of the Anza seismic gap. At the southern part near the trifrication area, the LVZ of the Clark Valley branch (array JF) has a width of ~200 m with ~55% reduction in Vp and Vs. This is consistent with what have been suggested from previous studies. In comparison, we find that the velocity reduction relative to the host rock across the Anza seismic gap (array RA) is ~50% for both Vp and Vs, nearly as prominent as that on the southern branches. The width of the LVZ is ~230 m. In addition, the LVZ across the Anza gap appears to locate in the northeast side of the RA array, implying potential preferred propagation direction of past ruptures.

Li, Z.; Yang, H.; Peng, Z.; Ben-Zion, Y.; Vernon, F.

2013-12-01

205

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

206

Virtual Earthquake  

NSDL National Science Digital Library

Virtual Earthquake was created by California State University, Los Angeles, as part of the Electronic Desktop Project. This virtual simulation allows students to locate the epicenter of an earthquake and determine its magnitude on the Richter scale. Students can choose from four geographic areas for their simulation. Virtual Earthquake carefully guides the student through the steps required to calculate the epicenter and to determine the magnitude of a simulated earthquake. The actual epicenter is provided along with the epicenter determined by the user. The user can then determine the magnitude of the earthquake as measured on the Richter scale.

1997-01-01

207

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

208

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

209

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

NASA Astrophysics Data System (ADS)

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

Chen, X.; Shearer, P. M.

2011-09-01

210

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

NASA Astrophysics Data System (ADS)

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

Vaghri, A.; Hearn, E. H.

2011-12-01

211

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

212

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

USGS Publications Warehouse

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

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

2008-01-01

213

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

USGS Publications Warehouse

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

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

2009-01-01

214

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

215

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

SciTech Connect

The objective my research has been to synthesize current understanding of the tectonics and faults of the Los Angeles Basin and surrounding region to quantify uncertainty in the characterization of earthquake sources used for geologically- and geodetically-based regional earthquake likelihood models. This work has focused on capturing epistemic uncertainty; i.e. uncertainty stemming from ignorance of the true characteristics of the active faults in the region and of the tectonic forces that drive them. In the present context, epistemic uncertainty has two components: First, the uncertainty in source geometrical and occurrence rate parameters deduced from the limited geological, geophysical and geodetic observations available; and second. uncertainties that result from fundamentally different interpretations of regional tectonic deformation and faulting. Characterization of the large number of active and potentially active faults that need to be included in estimating earthquake occurrence likelihoods for the Los Angeles region requires synthesis and evaluation of large amounts of data and numerous interpretations. This was accomplished primarily through a series of carefully facilitated workshops, smaller meetings involving key researchers, and email groups. The workshops and meetings were made possible by the unique logistical and financial resources available through SCEC, and proved to be extremely effective forums for the exchange and critical debate of data and interpretations that are essential in constructing fully representative source models. The main products from this work are a complete source model that characterizes all know or potentially active faults in the greater Los Angeles region. which includes the continental borderland as far south as San Diego, the Ventura Basin, and the Santa Barbara Channel. The model constitutes a series of maps and representative cross-sections that define alternative fault geometries, a table containing rault geometrical and slip-rate parameters, including full uncertainty distributions, and a set of logic trees that define alternative source characterizations, particularly for sets of fault systems having inter-dependent geometries and kinematics resulting from potential intersection and interaction in the sub-surface. All of these products exist in a form suitable for input to earthquake likelihood and seismic hazard analyses. In addition, moment-balanced Poissonian earthquake rates for the alternative multi-segment characterizations of each fault system have been estimated. Finally, this work has served an important integrative function in that the exchange and debate of data, results and ideas that it has engendered has helped to focus SCEC research over the past six years on to key issues in tectonic deformation and faulting.

Foxall, B

2003-02-26

216

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.

California Academy of Sciences

2012-06-26

217

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

SciTech Connect

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

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

2007-07-09

218

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

PubMed

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

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

1994-09-01

219

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

PubMed

The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes. PMID:17816681

1994-10-21

220

Point Mugu, California, earthquake of 21 February 1973 and its aftershocks  

USGS Publications Warehouse

Seismological investigations show that the Point Mugu earthquake involved north-south crustal shortening deep within the complex fault zone that marks the southern front of the Transverse Ranges province. This earthquake sequence results from the same stress system responsible for the deformation in this province in the Pliocene through Holocene and draws attention to the significant earthquake hazard that the southern frontal fault system poses to the Los Angeles metropolitan area.

Ellsworth, W.L.; Campbell, R.H.; Hill, D.P.; Page, R.A.; Alewine, R. W., III; Hanks, T.C.; Heaton, T.H.; Hileman, J.A.; Kanamori, H.; Minster, B.; Whitcomb, J.H.

1973-01-01

221

Earthquake-induced structures in sediments of Van Norman Lake, San Fernando, California  

USGS Publications Warehouse

The 9 February 1971 earthquake in the San Fernando Valley damaged the Lower Van Norman Dam severely enough to warrant draining the reservoir. In March 1972 the sediment deposited on the reservoir floor was examined to determine whether the 1971 earthquake had induced sediment deformation and, if so, what types. A zone of deformational structures characterized by small-scale loads and slightly recumbent folds associated with the 1971 earthquake was discovered, in addition to two older zones of load structures. Each of the zones has been tentatively correlated with an historic earthquake.

Sims, J.D.

1973-01-01

222

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

223

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

USGS Publications Warehouse

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

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

2004-01-01

224

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

225

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

NASA Technical Reports Server (NTRS)

The most damaging earthquake in the United States since 1906 struck northern Los Angeles on January 17.1994. The magnitude 6.7 Northridge earthquake produced a maximum of more than 3 meters of reverse (up-dip) slip on a south-dipping thrust fault rooted under the San Fernando Valley and projecting north under the Santa Susana Mountains.

Donnellan, A.

1994-01-01

226

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

227

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

E-print Network

transform faults separated by the Salton Sea transten- sional domain (see Fig. 1). The southernmost SAF 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

Lin, Guoqing

228

Fault length, multi-fault rupture, and relations to earthquakes in California  

Microsoft Academic Search

Fault length is used to estimate the rupture length of future earthquakes. However, fault length is often poorly defined, and rupture often breaks beyond the mapped faults. Furthermore, multiple faults often rupture together in a single earthquake. In this work I quantify how to use fault length to infer future rupture length. I used observations of previous ruptures breaking multiple

Natanya Maureen Black

2008-01-01

229

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

Microsoft Academic Search

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

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

1990-01-01

230

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

USGS Publications Warehouse

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%).

Fram, Miranda S.; Belitz, Kenneth

2011-01-01

231

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

232

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

SciTech Connect

As a result of the October 17, 1989, Loma Prieta (Santa Cruz Mountains, California) earthquake, liquefaction of the fluvial, estuarine, eolian, and beach sediments under a sand spit destroyed the Moss Landing Marine Laboratories and damaged other structures and utilities. Initial studies suggested that the liquefaction was a local phenomenon. More detailed offshore investigations, however, indicate that it occurred over a large area (maximum 8 km{sup 2}) during or shortly after the earthquake with movement of unconsolidated sediment toward and into the head of Monterey submarine canyon. This conclusion is supported by side-scan sonographs, high-resolution seismic-reflection and bathymetric profiles, onshore and sea-floor photographs, and underwater video tapes. Many distinct lobate features were identified on the shallow shelf. These features almost certainly were the result of the October 17 earthquake; they were subsequently destroyed by winter storms. In addition, fresh slump scars and recently dislodged mud debris were found on the upper, southern wall of Monterey submarine canyon.

Greene, H.G.; Chase, T.E.; Hicks, K.R. (Geological Survey, Menlo Park, CA (United States)); Gardner-Taggart, J.; Ledbetter, M.T.; Barminski, R. (Moss Landing Marine Labs., CA (United States)); Baxter, C. (Monterey Bay Aquarium Research Inst., CA (United States))

1991-09-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

234

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).

235

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

USGS Publications Warehouse

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

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

1993-01-01

236

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

237

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

238

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

239

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

240

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

241

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

USGS Publications Warehouse

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

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

2003-01-01

242

School Site Preparedness for the Safety of California's Children K-12. Official Report of the Northridge Earthquake Task Force on Education.  

ERIC Educational Resources Information Center

This report asserts that disaster preparedness at all school sites must become a major and immediate priority. Should a disaster equaling the magnitude of the Northridge earthquake occur, the current varying levels of site preparedness may not adequately protect California's children. The report describes why the state's children are not safe and…

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

243

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

244

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

USGS Publications Warehouse

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

Campbell, K.W.

1989-01-01

245

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

NASA Astrophysics Data System (ADS)

The Northern California counties of Del Norte, Humboldt, and Mendocino account for over 30% of California's coastline and is one of the most seismically active areas of the contiguous 48 states. The region is at risk from earthquakes located on- and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ) and from distant sources elsewhere in the Pacific. In 1995 the California Geological Survey (CGS) published a scenario for a CSZ earthquake that included both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of government agencies, tribes, service groups, academia and the private sector, was formed to coordinate and promote earthquake and tsunami hazard awareness and mitigation in the three-county region. The RCTWG and its member agencies projects include education/outreach products and programs, tsunami hazard mapping, signage and siren planning. Since 2008, RCTWG has worked with the California Emergency Management Agency (Cal EMA) in conducting tsunami warning communications tests on the North Coast. In 2007, RCTWG members helped develop and carry out the first tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD. The RCTWG has facilitated numerous multi-agency, multi-discipline coordinated exercises, and RCTWG county tsunami response plans have been a model for other regions of the state and country. Eight North Coast communities have been recognized as TsunamiReady by the National Weather Service, including the first National Park the first State Park and only tribe in California to be so recognized. Over 500 tsunami hazard zone signs have been posted in the RCTWG region since 2008. Eight assessment surveys from 1993 to 2010 have tracked preparedness actions and personal awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist concerns about tsunami hazard signs. Over the seventeen-year period covered by the surveys, the percent with houses secured to foundations has increased from 58 to 84 percent, respondents aware of a local tsunami hazard increased from 51 to 89 percent and knowing what the Cascadia subduction zone is from 16 to 57 percent. In 2009, the RCTWG was recognized by the Western States Seismic Policy Council (WSSPC) with an award for innovation and in 2010, the RCTWG-sponsored class "Living on Shaky Ground" was awarded WSSPC's overall Award in Excellence. The RCTWG works closely with CGS and Cal EMA on a number of projects including tsunami mapping, evacuation zone planning, siren policy, tsunami safety for boaters, and public education messaging. Current projects include working with CGS to develop a "playbook" tsunami mapping product to illustrate the expected effects from a range of tsunami source events and assist local governments in focusing future response actions to reflect the range expected impacts from distant source events. Preparedness efforts paid off on March 11, 2011 when a tsunami warning was issued for the region and significant damage occurred in harbor regions of Del Norte County and Mendocino County. Full-scale evacuations were carried out in a coordinated manner and the majority of the commercial fishing fleet in Crescent City was able to exit the harbor before the tsunami arrived.

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

2012-12-01

246

Earthquake Photo Collections  

NSDL National Science Digital Library

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

247

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

248

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

249

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

250

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

251

Source inversion of the 1988 Upland, California, earthquake: determination of a fault plane for a small event  

USGS Publications Warehouse

We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4,6) earthquake near Upland, California. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 ?? 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. -from Authors

Mori, J.; Hartzell, S.

1990-01-01

252

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

USGS Publications Warehouse

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

Hill, D.P.

1990-01-01

253

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

2007-01-01

254

Continuous GPS observations of postseismic deformation following the 16 October 1999 Hector Mine, California, earthquake (Mw 7.1)  

USGS Publications Warehouse

Rapid field deployment of a new type of continuously operating Global Positioning System (GPS) network and data from Southern California Integrated GPS Network (SCIGN) stations that had recently begun operating in the area allow unique observations of the postseismic deformation associated with the 1999 Hector Mine earthquake. Innovative solutions in fieldcraft, devised for the 11 new GPS stations, provide high-quality observations with 1-year time histories on stable monuments at remote sites. We report on our results from processing the postseismic GPS data available from these sites, as well as 8 other SCIGN stations within 80 km of the event (a total of 19 sites). From these data, we analyze the temporal character and spatial pattern of the postseismic transients. Data from some sites display statistically significant time variation in their velocities. Although this is less certain, the spatial pattern of change in the postseismic velocity field also appears to have changed. The pattern now is similar to the pre-Landers (pre-1992) secular field, but laterally shifted and locally at twice the rate. We speculate that a 30 km ?? 50 km portion of crust (near Twentynine Palms), which was moving at nearly the North American plate rate (to within 3.5 mm/yr of that rate) prior to the 1992 Landers sequence, now is moving along with the crust to the west of it, as though it has been entrained in flow along with the Pacific Plate as a result of the Landers and Hector Mine earthquake sequence. The inboard axis of right-lateral shear deformation (at lower crustal to upper mantle depth) may have jumped 30 km farther into the continental crust at this fault junction that comprises the southern end of the eastern California shear zone.

Hudnutt, K.W.; King, N.E.; Galetzka, J.E.; Stark, K.F.; Behr, J.A.; Aspiotes, A.; van, Wyk S.; Moffitt, R.; Dockter, S.; Wyatt, F.

2002-01-01

255

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

256

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

257

Earthquake precursors: activation or quiescence?  

NASA Astrophysics Data System (ADS)

We discuss the long-standing question of whether the probability for large earthquake occurrence (magnitudes m > 6.0) is highest during time periods of smaller event activation, or highest during time periods of smaller event quiescence. The physics of the activation model are based on an idea from the theory of nucleation, that a small magnitude earthquake has a finite probability of growing into a large earthquake. The physics of the quiescence model is based on the idea that the occurrence of smaller earthquakes (here considered as magnitudes m > 3.5) may be due to a mechanism such as critical slowing down, in which fluctuations in systems with long-range interactions tend to be suppressed prior to large nucleation events. To illuminate this question, we construct two end-member forecast models illustrating, respectively, activation and quiescence. The activation model assumes only that activation can occur, either via aftershock nucleation or triggering, but expresses no choice as to which mechanism is preferred. Both of these models are in fact a means of filtering the seismicity time-series to compute probabilities. Using 25 yr of data from the California-Nevada catalogue of earthquakes, we show that of the two models, activation and quiescence, the latter appears to be the better model, as judged by backtesting (by a slight but not significant margin). We then examine simulation data from a topologically realistic earthquake model for California seismicity, Virtual California. This model includes not only earthquakes produced from increases in stress on the fault system, but also background and off-fault seismicity produced by a BASS-ETAS driving mechanism. Applying the activation and quiescence forecast models to the simulated data, we come to the opposite conclusion. Here, the activation forecast model is preferred to the quiescence model, presumably due to the fact that the BASS component of the model is essentially a model for activated seismicity. These results lead to the (weak) conclusion that California seismicity may be characterized more by quiescence than by activation, and that BASS-ETAS models may not be robustly applicable to the real data.

Rundle, John B.; Holliday, James R.; Yoder, Mark; Sachs, Michael K.; Donnellan, Andrea; Turcotte, Donald L.; Tiampo, Kristy F.; Klein, William; Kellogg, Louise H.

2011-10-01

258

Stability and Uncertainty of Finite-Fault Slip Inversions: Application to the 2004 Parkfield, California, Earthquake  

E-print Network

aspects of the finite-fault slip inversion problem with different a priori model assumptions. We utilize used to solve the finite-fault slip inversion problem. For the Parkfield earthquake and the inversionStability and Uncertainty of Finite-Fault Slip Inversions: Application to the 2004 Parkfield

Larson, Kristine

259

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

260

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

261

Three dimensional images of geothermal systems: local earthquake P-wave velocity tomography at the Hengill and Krafla geothermal areas, Iceland, and The Geysers, California  

USGS Publications Warehouse

Local earthquake tomography - the use of earthquake signals to form a 3-dimensional structural image - is now a mature geophysical analysis method, particularly suited to the study of geothermal reservoirs, which are often seismically active and severely laterally inhomogeneous. Studies have been conducted of the Hengill (Iceland), Krafla (Iceland) and The Geysers (California) geothermal areas. All three systems are exploited for electricity and/or heat production, and all are highly seismically active. Tomographic studies of volumes a few km in dimension were conducted for each area using the method of Thurber (1983).

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

1993-01-01

262

Rupture process of the 4 April 2010 Baja California Earthquake estimated from high-rate GPS data  

NASA Astrophysics Data System (ADS)

The 4 April 2010 El Mayor Earthquake (Mw7.2) occurred in Baja California, Mexico. Its source region is located close to the plate boundary and there are several active faults in its vicinity. In association with this earthquake, surface rupture appears. Rupture is considered to propagate from southeast to northwest. Some high rate GPS’s are located close to the source fault. They are 56 stations with 5Hz sampling and 34 stations with 1Hz operated by UNAVCO. With these data, we did a precise point positioning analysis to detect temporal variations in displacement. The high-rate time series of coordinates of CGPS site are capable to deal with both dynamic and static displacements, but not suitable for the analysis with shorter period than its sampling period (usually 1sec). We used the GPS software GpsTools developed by Takasu and Kasai(2005). First, we estimated 1-Hz clock-biases of GPS satellites by using 1-Hz data of worldwide 70 stations from IGS. Next, with these estimated satellites clock, we did precise point positioning for GPS data during the earthquake. Comparing with average data for ten seconds before and after the earthquake, we recognized the maximum static displacement of 22cm at CRRS 99km from the epicenter which is near the Salton Sea. We suspect that this large displacement is attributed to its soil condition. We inverted displacement waveforms to compute a fault slip distribution with horizontal waveforms from several sites. We assumed a fault plate that is 100km long and 20km wide in the direction of N319W with a dip angle of 82 deg. We divide this fault plane into 80 subfaults with 5km*5km one. Green function was calculated with the Frequency-Wavenumber method (Zhu and Rivera, 2002) using the Hadley-Kanamori velocity model (Hadley and Kanamori, 1977). We calculated both dynamic and static displacement by this Green function with the duration and rise time of 6s and 1s, respectively. Rupture velocity was assumed to be 3.0km/s. The preliminary result shows that a normal fault component with a down warping of the eastern side is dominant in the southern part, while a right lateral with significant east down slip is prevailing in the northwestern part. Max fault slip is found to be 4m at northwest part. Acknowledgement: We’d like to thank UNAVCO for providing GPS data.

Nakamura, Y.; Hashimoto, M.

2010-12-01

263

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

SciTech Connect

Radon concentrations in soil gas measured in shallow holes by plastic Track Etch detectors show variations which may be associated with four magnitude 4.2 to 4.7 earthquakes on the San Jacinto Fault in southern California. A simple sinusoidal correction for the annual soil temperature cycle removes most of the variability in radon concentration that cannot be correlated with earthquakes. The two earthquakes located approximately 4 and 5.5 km away from the array of detectors showed spatially coherent responses with the largest radon concentration changes occurring closes to the earthquake. The two earthquakes 10--15 km distant from the closest site showed changes apparent when all sites were averaged together. The two nearby earthquakes were right lateral strike-slip events which had quadrants of seismic compression and dilation which correlate with radon concentration increases and decreases, respectively. Radon increases occur when the upward velocity of soil gas increases, since a sharp radon concentration gradient exists in the top few meters of soil. Gas outflow may occur in regions of compression and inflow in areas of dilation, thus producing the observed radon concentration changes.

Birchard, G.F.; Libby, W.F.

1980-06-10

264

The 1987 Whittier Narrows earthquake in the Los Angeles metropolitan area, California  

USGS Publications Warehouse

The Whittier Narrows earthquake sequence (local magnitude, ML=5.9), which caused over $358-million damage, indicates that assessments of earthquake hazards in the Los Angeles metropolitan area may be underestimated. The sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east-west length of the northern margin of the Los Angeles basin. Peak horizontal accelerations from the main shock, which were measured at ground level and in structures, were as high as 0.6g (where g is the acceleration of gravity at sea level) within 50 kilometers of the epicenter. The distribution of the modified Mercalli intensity VII reflects a broad north-south elongated zone of damage that is approximately centered on the main shock epicenter.

Hauksson, E.; Jones, L.M.; Davis, T.L.; Hutton, L.K.; Brady, A.G.; Reasenberg, P.A.; Michael, A.J.; Yerkes, R.F.; Williams, P.; Reagor, G.; Stover, C.W.; Bent, A.L.; Shakal, A.K.; Etheredge, E.; Porcella, R.L.; Bufe, C.G.; Johnston, M.J.S.; Cranswick, E.

1988-01-01

265

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

PubMed

Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The +/-3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event. These observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west-dipping, north-northeast fault plane, reactivating the largest escarpment in the Saline Range. PMID:17778980

Peltzer, G; Rosen, P

1995-06-01

266

Bulletin of the Seismological Society of America, Vol. 86, No. 1B, pp. $49-$70, February 1996 The Slip History of the 1994 Northridge, California, EarthquakeDetermined  

E-print Network

the largest ground motions ever recorded in an urban environment and caused the greatest damage in the United val- ues were among the largest ever recordedin any earthquake, and the large number of strong The Slip History of the 1994 Northridge, California, EarthquakeDetermined from Strong-Motion, Teleseismic

Greer, Julia R.

267

A STUDY OF THE STRONG GROUND MOTION OF THE BORREGO MOUNTAIN CALIFORNIA EARTHQUAKE  

Microsoft Academic Search

ABSTRACT Several synthetic models are constructed to fit the first 40 sec of the transversely polarized displacement, as recorded at El Centro, of the April 9, 1968 Borrego Mountain earthquake. The modeling is done in the time domain using the response computed,for a distributed set of point shear dislocations embedded,in a layered half-space. The beginning 10 sec of the observed,record

Thomas H. Heaton; Donald V. Helmberger

268

A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California  

Microsoft Academic Search

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 solu- tion is found

Felix Waldhauser; William L. Ellsworth

2000-01-01

269

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

USGS Publications Warehouse

Based on OpenSHA and HAZUS-MH, we present loss estimates for an earthquake rupture on the recently identified Puente Hills blind-thrust fault beneath Los Angeles. Given a range of possible magnitudes and ground motion models, and presuming a full fault rupture, we estimate the total economic loss to be between $82 and $252 billion. This range is not only considerably higher than a previous estimate of $69 billion, but also implies the event would be the costliest disaster in U.S. history. The analysis has also provided the following predictions: 3,000-18,000 fatalities, 142,000-735,000 displaced households, 42,000-211,000 in need of short-term public shelter, and 30,000-99,000 tons of debris generated. Finally, we show that the choice of ground motion model can be more influential than the earthquake magnitude, and that reducing this epistemic uncertainty (e.g., via model improvement and/or rejection) could reduce the uncertainty of the loss estimates by up to a factor of two. We note that a full Puente Hills fault rupture is a rare event (once every ???3,000 years), and that other seismic sources pose significant risk as well. ?? 2005, Earthquake Engineering Research Institute.

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

2005-01-01

270

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

NASA Astrophysics Data System (ADS)

Along creeping sections of the San Andreas and other faults, small asperities in the fault zone load and fail in characteristic repeating earthquake sequences which can be used as subsurface creepmeters. Here, we use these virtual creepmeters to examine and compare slip rates on both the northwestern end of the creeping section of the San Andreas Fault near San Juan Bautista and on the nearby sub-parallel Sargent Fault, previously observed to have ~3mm/year of right-lateral creep. While creep on the San Andreas increases dramatically in response to the 1989 Loma Prieta earthquake and takes about ten years to resume interseismic rates, the Sargent shows little immediate response. The Sargent rather exhibits a very gradual increase of activity after the Loma Prieta earthquake, consistent with its generally lower interseismic slip rate and with static stress change models that show only a minor increase in the stress along the Sargent. When the SAF resumes its interseismic rate, it begins creeping coherently in time with the Sargent, indicating a mutual driving force in the system. Background seismicity in gray points, newly discovered repeaters in black circles (inset). Boxes show study area. Stars show epicenters of 1989 Loma Prieta EQ, 1998 San Juan Bautista EQ, and 2004 Parkfield EQ.

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

2012-12-01

271

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

USGS Publications Warehouse

Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. Where they occur, these earthquakes provide a rare opportunity to observe volcanic processes in the lower crust, such as fluid injection and migration, which may induce brittle faulting under these conditions. Here, we examine recent short-duration earthquake swarms deep beneath the southwestern margin of Long Valley Caldera, near Mammoth Mountain. We focus in particular on a swarm that occurred September 29-30, 2009. To maximally illuminate the spatial-temporal progression, we supplement catalog events by detecting additional small events with similar waveforms in the continuous data, achieving up to a 10-fold increase in the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the 2009 swarm exhibits systematically decelerating upward migration, with hypocenters shallowing from 21 to 19 km depth over approximately 12 hours. This relatively high migration rate, combined with a modest maximum magnitude of 1.4 in this swarm, suggests the trigger might be ascending CO2 released from underlying magma.

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

2011-01-01

272

Faulting apparently related to the 1994 Northridge, California, earthquake and possible co-seismic origin of surface cracks in Potrero Canyon, Los Angeles County, California  

USGS Publications Warehouse

Apparent southward-dipping, reverse-fault zones are imaged to depths of about 1.5 km beneath Potrero Canyon, Los Angeles County, California. Based on their orientation and projection to the surface, we suggest that the imaged fault zones are extensions of the Oak Ridge fault. Geologic mapping by others and correlations with seismicity studies suggest that the Oak Ridge fault is the causative fault of the 17 January 1994 Northridge earthquake (Northridge fault). Our seismically imaged faults may be among several faults that collectively comprise the Northridge thrust fault system. Unusually strong shaking in Potrero Canyon during the Northridge earthquake may have resulted from focusing of seismic energy or co-seismic movement along existing, related shallow-depth faults. The strong shaking produced ground-surface cracks and sand blows distributed along the length of the canyon. Seismic reflection and refraction images show that shallow-depth faults may underlie some of the observed surface cracks. The relationship between observed surface cracks and imaged faults indicates that some of the surface cracks may have developed from nontectonic alluvial movement, but others may be fault related. Immediately beneath the surface cracks, P-wave velocities are unusually low (<400 m/sec), and there are velocity anomalies consistent with a seismic reflection image of shallow faulting to depths of at least 100 m. On the basis of velocity data, we suggest that unconsolidated soils (<800 m/sec) extend to depths of about 15 to 20 m beneath our datum (<25 m below ground surface). The underlying rocks range in velocity from about 1000 to 5000 m/sec in the upper 100 m. This study illustrates the utility of high-resolution seismic imaging in assessing local and regional seismic hazards.

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

1998-01-01

273

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

Microsoft Academic Search

The clu:onology of M>7 palcoearthquakes 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 thne of 350 years. Repeat times for individual segments vary by a factor of 2, and range from about 1200 to 2600

J. P. McCalpin; S. P. Nishenko

1996-01-01

274

Estimating the probability of occurrence of earthquakes (M>6) in the Western part of the Corinth rift using fault-based and classical seismotectonic approaches.  

NASA Astrophysics Data System (ADS)

The Corinth rift, Greece, is one of the regions with highest strain rates in the Euro-Mediterranean area and as such it has long been identified as a site of major importance for earthquake studies in Europe (20 years of research by the Corinth Rift Laboratory and 4 years of in-depth studies by the ANR-SISCOR project). This enhanced knowledge, acquired in particular, in the western part of the Gulf of Corinth, an area about 50 by 40 km, between the city of Patras to the west and the city of Aigion to the east, provides an excellent opportunity to compare fault-based and classical seismotectonic approaches currently used in seismic hazard assessment studies. A homogeneous earthquake catalogue was first constructed for the Greek territory based on two existing earthquake catalogues available for Greece (National Observatory of Athens and Thessaloniki). In spite of numerous documented damaging earthquakes, only a limited amount of macroseismic intensity data points are available in the existing databases for the damaging earthquakes affecting the west Corinth rift region. A re-interpretation of the macroseismic intensity field for numerous events was thus conducted, following an in-depth analysis of existing and newly found documentation (for details see Rovida et al. EGU2014-6346). In parallel, the construction of a comprehensive database of all relevant geological, geodetical and geophysical information (available in the literature and recently collected within the ANR-SISCOR project), allowed proposing rupture geometries for the different fault-systems identified in the study region. The combination of the new earthquake parameters and the newly defined fault geometries, together with the existing published paleoseismic data, allowed proposing a suite of rupture scenarios including the activation of multiple fault segments. The methodology used to achieve this goal consisted in setting up a logic tree that reflected the opinion of all the members of the ANR-SISCOR Working Group. On the basis of this consensual logic tree, median probability of occurrences of M>=6 events were computed for the region of study. Time-dependent models (Brownian Passage time and Weibull probability distributions) were also explored. The probability of a M>=6.0 event is found to be greater in the western region compared to the eastern part of the Corinth rift, whether a fault-based or a classical seismotectonic approach is used. Percentile probability estimates are also provided to represent the range of uncertainties in the results. The percentile results show that, in general, probability estimates following the classical approach (based on the definition of seismotectonic source zones), cover the median values estimated following the fault-based approach. On the contrary, the fault-based approach in this region is still affected by a high degree of uncertainty, because of the poor constraints on the 3D geometries of the faults and the high uncertainties in their slip rates.

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

2014-05-01

275

Forecasting damaging earthquakes in the central and eastern United States  

USGS Publications Warehouse

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

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

1990-01-01

276

Situated Preparedness: The Negotiation of a Future Catastrophic Earthquake in a California University  

ERIC Educational Resources Information Center

This dissertation examines disaster preparedness as engaged at a large university in southern California using inductive research and grounded theory data collection and analysis methods. The thesis consists of three parts, all addressing the problem of disaster preparedness as enacted in this at-risk context. I use in-depth interviews, archival…

Baker, Natalie Danielle

2013-01-01

277

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

Microsoft Academic Search

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

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

2006-01-01

278

INVERSION OF STRONG GROUND MOTION AND TELESEISMIC WAVEFORM DATA FOR THE FAULT RUPTURE HISTORY OF THE 1979 IMPERIAL VALLEY, CALIFORNIA, EARTHQUAKE  

Microsoft Academic Search

A least-squares point-by-point inversion of strong ground motion and tele- seismic body waves is used to infer the fault rupture history of the 1979 Imperial Valley, California, earthquake. The Imperial fault is represented by a plane embedded in a half-space where the elastic properties vary with depth. The inversion yields both the spatial and temporal variations in dislocation on the

STEPHEN H. HARTZELL; THOMAS H. HEATON

1983-01-01

279

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

SciTech Connect

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

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

1995-11-01

280

Interseismic Strain Accumulation in the Imperial Valley and Implications for Triggering of Large Earthquakes in Southern California  

NASA Astrophysics Data System (ADS)

From February, 2008 to March, 2009, we performed three rapid-static Global Positioning System (GPS) surveys of 115 geodetic monuments stretching from the United States-Mexico border into the Coachella Valley using the method of instantaneous positioning. The monuments are located in key areas near the Imperial, Superstition Hills, San Jacinto, San Andreas and Brawley Faults with nominal baselines generally less than 10 km. We perform a bicubic spline interpolation on the crustal motion vectors from the campaign measurements and 1005 continuous GPS monuments in western North America and solve for the velocity gradient tensor to look at the maximum shear strain, dilatation and rotation rates in the Imperial Valley. We then compare our computed strain field to that computed using the Southern California Earthquake Center Crustal Motion Map 3.0, which extends through 2003 and includes 840 measurements. We show that there is an interseismic strain transient that corresponds to an increase in the maximum shear strain rate of 0.7 ?strain/yr near Obsidian Buttes since 2003 along a fault referred to as the Obsidian Buttes Fault (OBF). A strong subsidence signal of 27 mm/yr and a left-lateral increase of 10 mm/yr are centered along the OBF. Changes in the dilatation and rotation rates confirm the increase in left-lateral motion, as well as infer a strong increase in spreading rate in the southern Salton Sea. The increase in spreading rate has caused an accelerated slip rate along the southern San Andreas near Durmid Hill as evidenced by continuous GPS, which has the potential for earthquake triggering.

Crowell, B. W.; Bock, Y.; Sandwell, D. T.

2009-12-01

281

Probable Middle Holocene geomagnetic excursion at the Red Rock archaeological site, California  

Microsoft Academic Search

Paleomagnetic data from three sedimentary sections at a locality in western California (U.S.A.) is reported. Natural rema- nent magnetization directions obtained from 61 oriented cores showed a magnetic component different from the present geomag- netic field. The characteristic remanent magnetizations (ChRM) show oblique normal, oblique reverse and reverse polarities during the Middle Holocene. The transitional VGP resembles those registered during

Hugo G. Nami

1999-01-01

282

Avian Flu / Earthquake Prediction  

NSDL National Science Digital Library

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

283

Foreshock occurrence before large earthquakes  

USGS Publications Warehouse

Rates of foreshock occurrence involving shallow M ??? 6 and M ??? 7 mainshocks and M ??? 5 foreshocks were measured in two worldwide catalogs over ???20-year intervals. The overall rates observed are similar to ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span. The observed worldwide rates were compared to a generic model of earthquake clustering based on patterns of small and moderate aftershocks in California. The aftershock model was extended to the case of moderate foreshocks preceding large mainshocks. Overall, the observed worldwide foreshock rates exceed the extended California generic model by a factor of ???2. Significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region, with the rate before thrust events higher and the rate before strike-slip events lower than the worldwide average. Among the thrust events, a large majority, composed of events located in shallow subduction zones, had a high foreshock rate, while a minority, located in continental thrust belts, had a low rate. These differences may explain why previous surveys have found low foreshock rates among thrust events in California (especially southern California), while the worldwide observations suggests the opposite: California, lacking an active subduction zone in most of its territory, and including a region of mountain-building thrusts in the south, reflects the low rate apparently typical for continental thrusts, while the worldwide observations, dominated by shallow subduction zone events, are foreshock-rich. If this is so, then the California generic model may significantly underestimate the conditional probability for a very large (M ??? 8) earthquake following a potential (M ??? 7) foreshock in Cascadia. The magnitude differences among the identified foreshock-mainshock pairs in the Harvard catalog are consistent with a uniform distribution over the range of observation.

Reasenberg, P.A.

1999-01-01

284

History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland  

USGS Publications Warehouse

During the past several years, devastating tsunamis were generated along subduction zones in Indonesia, Chile, and most recently Japan. Both the Chile and Japan tsunamis traveled across the Pacific Ocean and caused localized damage at several coastal areas in California. The question remains as to whether coastal California, in particular the California Continental Borderland, is vulnerable to more extensive damage from a far-field tsunami sourced along a Pacific subduction zone. Assuming that the coast of California is at risk from a far-field tsunami, its coastline is most exposed to a trans-Pacific tsunami generated along the eastern Aleutian-Alaska subduction zone. We present the background geologic constraints that could control a possible giant (Mw ~9) earthquake sourced along the eastern Aleutian-Alaska megathrust. Previous great earthquakes (Mw ~8) in 1788, 1938, and 1946 ruptured single segments of the eastern Aleutian-Alaska megathrust. However, in order to generate a giant earthquake, it is necessary to rupture through multiple segments of the megathrust. Potential barriers to a throughgoing rupture, such as high-relief fracture zones or ridges, are absent on the subducting Pacific Plate between the Fox and Semidi Islands. Possible asperities (areas on the megathrust that are locked and therefore subject to infrequent but large slip) are identified by patches of high moment release observed in the historical earthquake record, geodetic studies, and the location of forearc basin gravity lows. Global Positioning System (GPS) data indicate that some areas of the eastern Aleutian-Alaska megathrust, such as that beneath Sanak Island, are weakly coupled. We suggest that although these areas will have reduced slip during a giant earthquake, they are not really large enough to form a barrier to rupture. A key aspect in defining an earthquake source for tsunami generation is determining the possibility of significant slip on the updip end of the megathrust near the trench. Large slip on the updip part of the eastern Aleutian-Alaska megathrust is a viable possibility owing to the small frontal accretionary prism and the presence of arc basement relatively close to the trench along most of the megathrust.

Ryan, Holly F.; von Huene, Roland; Wells, Ray E.; Scholl, David W.; Kirby, Stephen; Draut, Amy E.

2012-01-01

285

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

286

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

USGS Publications Warehouse

Following the earthquake of April 18, 1906, it was discovered that a brick forebay and other parts of the reservoir outlet system were in the slip zone of the San Andreas fault. The original outlet through which water was directed to San Francisco consisted of two tunnels joined at the brick forebay; one tunnel extends 2,820 ft to the east under Bald Hill on Buri Buri Ridge, and the other tunnel intersects the lake bottom about 250 ft west of the forebay. In 1897 a second intake was added to the system, also joining the original forebay. During the present study the accessible parts of this original outlet system were examined with the hope of learning how the system had been affected by fault slip in 1906.

Pampeyan, Earl H.

1986-01-01

287

Research Spotlight: Spooky action at a distance, for earthquakes  

NASA Astrophysics Data System (ADS)

On 27 February 2010 a magnitude 8.8 earthquake rocked millions of Chileans from their slumber, but the South American people weren't the only ones so affected. New research by Peng et al. suggests that the trembling off the Chilean coast could have triggered a swarm of shallow earthquakes nearly 10,000 kilometers away in central California. The team identified four earthquakes with magnitudes of 2 or higher, with the largest of the group being a M 3.5 quake that rattled the Coso geothermal field. The affected region is plagued by small earthquakes, but when the authors calculated the chance of a swarm so neatly following the Chilean earthquake, they inferred that the two seismic events were probably connected. The authors also saw a cluster of deep, low-frequency earthquakes along the Parkfield-Cholame section of the San Andreas Fault that also appeared to be influenced by the Chilean event. The researchers suggest that the timing of the California earthquakes was affected by the arrival of Love waves—horizontal surface movement that would have traveled out from the epicenter of the Chilean earthquake, pushing already stressed faults over the edge. (Geophysical Research Letters, doi:10.1029/2010GL045462, 2010)

Schultz, Colin

2011-02-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

289

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

SciTech Connect

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

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

1987-01-01

290

Earthquake Clusters over Multi-dimensional Space, Visualization of E 2347 Earthquake Clusters over  

E-print Network

Earthquake Clusters over Multi-dimensional Space, Visualization of E 2347 E Earthquake Clusters of Southern California, Los Angeles, USA 4 Department of Computer Science, University of Colorado, Boulder, USA Article Outline Glossary Definition of the Subject Introduction Earthquakes Clustering

Ben-Zion, Yehuda

291

Analysis of Injection-Induced Micro-Earthquakes in a Geothermal Steam Reservoir, The Geysers Geothermal Field, California  

SciTech Connect

In this study we analyze relative contributions to the cause and mechanism of injection-induced micro-earthquakes (MEQs) at The Geysers geothermal field, California. We estimated the potential for inducing seismicity by coupled thermal-hydrological-mechanical analysis of the geothermal steam production and cold water injection to calculate changes in stress (in time and space) and investigated if those changes could induce a rock mechanical failure and associated MEQs. An important aspect of the analysis is the concept of a rock mass that is critically stressed for shear failure. This means that shear stress in the region is near the rock-mass frictional strength, and therefore very small perturbations of the stress field can trigger an MEQ. Our analysis shows that the most important cause for injection-induced MEQs at The Geysers is cooling and associated thermal-elastic shrinkage of the rock around the injected fluid that changes the stress state in such a way that mechanical failure and seismicity can be induced. Specifically, the cooling shrinkage results in unloading and associated loss of shear strength in critically shear-stressed fractures, which are then reactivated. Thus, our analysis shows that cooling-induced shear slip along fractures is the dominant mechanism of injection-induced MEQs at The Geysers.

Rutqvist, Jonny; Rutqvist, J.; Oldenburg, C.M.

2008-05-15

292

Moment-tensor solutions for the 24 November 1987 Superstition Hills, California, earthquakes  

USGS Publications Warehouse

The teleseismic long-period waveforms recorded by the Global Digital Seismograph Network from the two largest Superstition Hills earthquakes are inverted using an algorithm based on optimal filter theory. These solutions differ slightly from those published in the Preliminary Determination of Epicenters Monthly Listing because a somewhat different, improved data set was used in the inversions and a time-dependent moment-tensor algorithm was used to investigate the complexity of the main shock. The foreshock (origin time 01:54:14.5, mb 5.7, Ms6.2) had a scalar moment of 2.3 ?? 1025 dyne-cm, a depth of 8km, and a mechanism of strike 217??, dip 79??, rake 4??. The main shock (origin time 13:15:56.4, mb 6.0, Ms6.6) was a complex event, consisting of at least two subevents, with a combined scalar moment of 1.0 ?? 1026 dyne-cm, a depth of 10km, and a mechanism of strike 303??, dip 89??, rake -180??. -Authors

Sipkin, S.A.

1989-01-01

293

Study of triggered non-volcanic tremor and local earthquakes near the Anza segment of the San Jacinto fault, southern California  

NASA Astrophysics Data System (ADS)

Non-volcanic tremor (NVT) occurring in the deep extension of the fault has been widely observed in subduction zones, but has not been observed extensively along strike-slip faults. We aim to understand whether there are different stress levels required for triggering between crustal NVT and earthquakes. We will examine the spatial and temporal occurrences of triggered tremor and earthquakes along the Anza segment of the San Jacinto Fault. The Anza section of the San Jacinto Fault (SJF) is an ideal region for more detailed observation of tremor since there is a densely spaced seismic network, including borehole stations. We used continuous waveform data, collected by 16 broadband stations of Southern California Seismic Network (SCSN) along with borehole stations from Plate Boundary Observatory (PBO) to search for NVT triggered by teleseismic surface waves. We examine teleseismic surface arrivals of large earthquakes (Mw >= 7.5 and distances > 2000 km) that occurred between 2001 and 2009 to identify triggered tremor and earthquakes. Preliminary observations suggest that only the Mw 7.8, 2002 Denali earthquake triggered detectable NVT, but more than half show local earthquakes occurring within the teleseismic surface wave arrivals. We determine, by comparing to background seismicity rates, if the local earthquakes are likely triggered by the teleseismic arrivals. In addition, we locate the NVTs observed near Anza, California using precise phase arrivals determined by waveform template matching. We use moving windows to cross-correlate tremor waveforms recorded at different stations, in order to identify identical LFEs within the tremor series. We identify template pairs with correlation coefficient with a correlation threshold over 4 times the mean absolute deviation (MAD) and matching pairs are grouped into template families of NVTs. These templates help us better define the arrival times of tremor bursts within the triggered NVT episode. We will locate the triggered NVT hypocenters using the cross-correlated arrivals and the SCEC Community Velocity Model. These NVT families can then be used to explore the spatial and temporal pattern of triggered non-volcanic tremor near the Anza segment of the San Jacinto fault.

Wang, T.; Cochran, E. S.

2010-12-01

294

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

USGS Publications Warehouse

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

Savage, J.C.; Langbein, J.

2008-01-01

295

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

USGS Publications Warehouse

We analyze the correlations between intensity and a set of groundmotion parameters obtained from 66 free-field stations in Los Angeles County that recorded the 1994 Northridge earthquake. We use the tagging intensities from Thywissen and Boatwright (1998) because these intensities are determined independently on census tracts, rather than interpolated from zip codes, as are the modified Mercalli isoseismals from Dewey et al. (1995). The ground-motion parameters we consider are the peak ground acceleration (PGA), the peak ground velocity (PGV), the 5% damped pseudovelocity response spectral (PSV) ordinates at 14 periods from 0.1 to 7.5 sec, and the rms average of these spectral ordinates from 0.3 to 3 sec. Visual comparisons of the distribution of tagging intensity with contours of PGA, PGV, and the average PSV suggest that PGV and the average PSV are better correlated with the intensity than PGA. The correlation coefficients between the intensity and the ground-motion parameters bear this out: r = 0.75 for PGA, 0.85 for PGV, and 0.85 for the average PSV. Correlations between the intensity and the PSV ordinates, as a function of period, are strongest at 1.5 sec (r = 0.83) and weakest at 0.2 sec (r = 0.66). Regressing the intensity on the logarithms of these ground-motion parameters yields relations I ?? mlog?? with 3.0 ??? m ??? 5.2 for the parameters analyzed, where m = 4.4 ?? 0.7 for PGA, 3.4 ?? 0.4 for PGV, and 3.6 ?? 0.5 for the average PSV.

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

2001-01-01

296

Earthquakes Living Lab: Geology and the 1906 San Francisco Earthquake  

NSDL National Science Digital Library

Students examine the effects of geology on earthquake magnitudes and how engineers anticipate and prepare for these effects. Using information provided through the Earthquakes Living Lab interface, students investigate how geology, specifically soil type, can amplify the magnitude of earthquakes and their consequences. Students look in-depth at the historical 1906 San Francisco earthquake and its destruction thorough photographs and data. They compare the 1906 California earthquake to another historical earthquake in Kobe, Japan, looking at the geological differences and impacts in the two regions, and learning how engineers, geologists and seismologists work to predict earthquakes and minimize calamity. A worksheet serves as a student guide for the activity.

Civil And Environmental Engineering Department

297

The Mw 6.5 offshore Northern California earthquake of 10 January 2010: Ordinary stress drop on a high-strength fault  

NASA Astrophysics Data System (ADS)

10 January 2010 Mw 6.5 earthquake offshore Northern California is one of the first intraplate earthquakes in oceanic lithosphere to be well captured by a GPS network. It presents an opportunity to evaluate rupture mechanics on a high-strength fault. Static inversion of the coseismic displacements shows that the slip peaks at the same depth as the expected strength envelope, where the differential stresses can be as high as 600 MPa. Laboratory experiments on peridotite predict dramatic dynamic weakening at these conditions. The observed ordinary stress drop, 2-20 MPa, may indicate that the lithosphere is much weaker than strength envelope predicts or that the failure mechanisms seen in the laboratory are not occurring during the rupture. The GPS observations show very little postseismic signal indicating that if a shear zone exists beneath the coseismic rupture, it operates at significantly greater stress levels than the coseismic stress change.

Wei, Meng; McGuire, Jeffrey J.

2014-09-01

298

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

USGS Publications Warehouse

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

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

1996-01-01

299

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

300

Operational earthquake forecasting can enhance earthquake preparedness  

USGS Publications Warehouse

We cannot yet predict large earthquakes in the short term with much reliability and skill, but the strong clustering exhibited in seismic sequences tells us that earthquake probabilities are not constant in time; they generally rise and fall over periods of days to years in correlation with nearby seismic activity. Operational earthquake forecasting (OEF) is the dissemination of authoritative information about these time?dependent probabilities to help communities prepare for potentially destructive earthquakes. The goal of OEF is to inform the decisions that people and organizations must continually make to mitigate seismic risk and prepare for potentially destructive earthquakes on time scales from days to decades. To fulfill this role, OEF must provide a complete description of the seismic hazard—ground?motion exceedance probabilities as well as short?term rupture probabilities—in concert with the long?term forecasts of probabilistic seismic?hazard analysis (PSHA).

Jordan, T.H.; Marzocchi, W.; Michael, A.J.; Gerstenberger, M.C.

2014-01-01

301

Space-time model for repeating earthquakes and analysis of recurrence intervals on the San Andreas Fault near Parkfield, California  

NASA Astrophysics Data System (ADS)

propose a stochastic model for characteristically repeating earthquake sequences to estimate the spatiotemporal change in static stress loading rate. These earthquakes recur by a cyclic mechanism where stress at a hypocenter is accumulated by tectonic forces until an earthquake occurs that releases the accumulated stress to a basal level. Renewal processes are frequently used to describe this repeating earthquake mechanism. Variations in the rate of tectonic loading due to large earthquakes and aseismic slip transients, however, introduce nonstationary effects into the repeating mechanism that result in nonstationary trends in interevent times, particularly for smaller-magnitude repeating events which have shorter interevent times. These trends are also similar among repeating earthquake sites having similar hypocenters. Therefore, we incorporate space-time structure represented by cubic B-spline functions into the renewal model and estimate their coefficient parameters by maximizing the integrated likelihood in a Bayesian framework. We apply our model to 31 repeating earthquake sequences including 824 events on the Parkfield segment of the San Andreas Fault and estimate the spatiotemporal transition of the loading rate on this segment. The result gives us details of the change in tectonic loading caused by an aseismic slip transient in 1993, the 2004 Parkfield M6 earthquake, and other nearby or remote seismic activities. The degree of periodicity of repeating event recurrence intervals also shows spatial trends that are preserved in time even after the 2004 Parkfield earthquake when time scales are normalized with respect to the estimated loading rate.

Nomura, Shunichi; Ogata, Yosihiko; Nadeau, Robert M.

2014-09-01

302

Predicting Earthquakes  

NSDL National Science Digital Library

Five moderate-to-strong earthquakes struck California in June 2005. Could the cluster of quakes be a harbinger of the Big One? Another earthquake-prone area, New Madrid, near Memphis, Tennessee, has had more than its share of impressive quakes and strain is building along its fault lines. This radio broadcast discusses these two seismic zones, the new data based on years of GPS (Global Positioning System) measurements that may give scientists more information, and how the Earth generates the stress which leads to earthquakes. There is also discussion of the danger of tsunamis in the Virgin Islands and the need for a worldwide tsunami warning network. The broadcast is 18 minutes in length.

303

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

304

The Distribution of Earthquakes: Where Do Large Earthquakes Occur?  

NSDL National Science Digital Library

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

Marquis, John

305

2004), Importance of small earthquakes for stress transfers and earthquake  

E-print Network

Abstract. We estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering, assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension D. This model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as ? 10 Dm/2. The stronger the spatial clustering, the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering. If earthquake magnitudes follow the Gutenberg-Richter law with b> D/2, small earthquakes collectively dominate stress transfer and earthquake triggering, because their greater frequency overcomes their smaller individual triggering potential. Using a Southern-California catalog, we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 ?m, where ? = 1.00 ± 0.05. We also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake’s magnitude m. When ? ? b, small earthquakes are roughly as important to earthquake triggering as larger ones. We evaluate the fractal correlation

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

306

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

307

Development of the ElarmS methodology for earthquake early warning: Realtime application in California and offline testing in Japan  

E-print Network

Development of the ElarmS methodology for earthquake early warning: Realtime application. Here we discuss the history, methodology, and performance of one of the algorithms, ElarmS. Earthquake the state. We outline the methodology as currently implemented, present several example events from

Allen, Richard M.

308

Staying Safe in Earthquake Country  

E-print Network

two of the largest earthquakes in the history of the State of California, including the famous event; some of the intervals between geologically recorded earthquakes are as short as 30 years, while othersStaying Safe in Earthquake Country David Bowman On July 29 of this year, Mother Nature sent Cal

de Lijser, Peter

309

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

USGS Publications Warehouse

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

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

2002-01-01

310

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

USGS Publications Warehouse

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

Boore, D.M.

2001-01-01

311

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

USGS Publications Warehouse

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

Greene, H. Gary

1991-01-01

312

Downscaling of slip distribution for strong earthquakes  

NASA Astrophysics Data System (ADS)

We intend to develop a downscaling model to enhance the earthquake slip distribution resolution. Slip distributions have been obtained by other researchers using various inversion methods. As a downscaling model, we are discussing fractal models that include mono-fractal models (fractional Brownian motion, fBm; fractional Lévy motion, fLm) and multi-fractal models as candidates. Log - log-linearity of k (wave number) versus E (k) (power spectrum) is the necessary condition for fractality: the slip distribution is expected to satisfy log - log-linearity described above if we can apply fractal model to a slip distribution as a downscaling model. Therefore, we conducted spectrum analyses using slip distributions of 11 earthquakes as explained below. 1) Spectrum analyses using one-dimensional slip distributions (strike direction) were conducted. 2) Averaging of some results of power spectrum (dip direction) was conducted. Results show that, from the viewpoint of log - log-linearity, applying a fractal model to slip distributions can be inferred as valid. We adopt the filtering method after Lavallée (2008) to generate fBm/ fLm. In that method, generated white noises (random numbers) are filtered using a power law type filter (log - log-linearity of the spectrum). Lavallée (2008) described that Lévy white noise that generates fLm is more appropriate than the Gaussian white noise which generates fBm. In addition, if the 'alpha' parameter of the Lévy law, which governs the degree of attenuation of tails of the probability distribution, is 2.0, then the Lévy distribution is equivalent to the Gauss distribution. We analyzed slip distributions of 11 earthquakes: the Tohoku earthquake (Wei et al., 2011), Haiti earthquake (Sladen, 2010), Simeulue earthquake (Sladen, 2008), eastern Sichuan earthquake (Sladen, 2008), Peru earthquake (Konca, 2007), Tocopilla earthquake (Sladen, 2007), Kuril earthquake (Sladen, 2007), Benkulu earthquake (Konca, 2007), and southern Java earthquake (Konca, 2006)). We obtained the following results. 1) Log - log-linearity (slope of the linear relationship is ' - ?') of k versus E(k) holds for all earthquakes. 2) For example, ? = 3.70 and ? = 1.96 for the Tohoku earthquake (2011) and ? = 4.16 and ? = 2.00 for the Haiti earthquake (2010). For these cases, the Gauss' law is appropriate because alpha is almost 2.00. 3) However, ? = 5.25 and ? = 1.25 for the Peru earthquake (2007) and ? = 2.24 and ? = 1.57 for the Simeulue earthquake (2008). For these earthquakes, the Lévy law is more appropriate because ? is far from 2.0. 4) Although Lavallée (2003, 2008) concluded that the Lévy law is more appropriate than the Gauss' law for white noise, which is later filtered, our results show that the Gauss law is appropriate for some earthquakes. Lavallée and Archuleta, 2003, Stochastic modeling of slip spatial complexities for the 1979 Imperial Valley, California, earthquake, GEOPHYSICAL RESEARCH LETTERS, 30(5). Lavallée, 2008, On the random nature of earthquake source and ground motion: A unified theory, ADVANCES IN GEOPHYSICS, 50, Chap 16.

Yoshida, T.; Oya, S.; Kuzuha, Y.

2013-12-01

313

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

USGS Publications Warehouse

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

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

2004-01-01

314

Eruption probabilities for the Lassen Volcanic Center and regional volcanism, northern California, and probabilities for large explosive eruptions in the Cascade Range  

USGS Publications Warehouse

Chronologies for eruptive activity of the Lassen Volcanic Center and for eruptions from the regional mafic vents in the surrounding area of the Lassen segment of the Cascade Range are here used to estimate probabilities of future eruptions. For the regional mafic volcanism, the ages of many vents are known only within broad ranges, and two models are developed that should bracket the actual eruptive ages. These chronologies are used with exponential, Weibull, and mixed-exponential probability distributions to match the data for time intervals between eruptions. For the Lassen Volcanic Center, the probability of an eruption in the next year is 1.4x10-4 for the exponential distribution and 2.3x10-4 for the mixed exponential distribution. For the regional mafic vents, the exponential distribution gives a probability of an eruption in the next year of 6.5x10-4, but the mixed exponential distribution indicates that the current probability, 12,000 years after the last event, could be significantly lower. For the exponential distribution, the highest probability is for an eruption from a regional mafic vent. Data on areas and volumes of lava flows and domes of the Lassen Volcanic Center and of eruptions from the regional mafic vents provide constraints on the probable sizes of future eruptions. Probabilities of lava-flow coverage are similar for the Lassen Volcanic Center and for regional mafic vents, whereas the probable eruptive volumes for the mafic vents are generally smaller. Data have been compiled for large explosive eruptions (>? 5 km3 in deposit volume) in the Cascade Range during the past 1.2 m.y. in order to estimate probabilities of eruption. For erupted volumes >?5 km3, the rate of occurrence since 13.6 ka is much higher than for the entire period, and we use these data to calculate the annual probability of a large eruption at 4.6x10-4. For erupted volumes ?10 km3, the rate of occurrence has been reasonably constant from 630 ka to the present, giving more confidence in the estimate, and we use those data to calculate the annual probability of a large eruption in the next year at 1.4x10-5.

Nathenson, Manuel; Clynne, Michael A.; Muffler, L.J. Patrick

2012-01-01

315

A reevaluation of the Pallett Creek earthquake chronology based on new AMS radiocarbon dates, San Andreas fault, California  

NASA Astrophysics Data System (ADS)

The Pallett Creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern San Andreas fault. Previous estimates of earthquake ages at Pallett Creek were determined by decay counting radiocarbon methods. That method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers. In contrast, accelerator mass spectrometry (AMS) radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section. We present 65 new AMS radiocarbon dates that span nine ground-rupturing earthquakes at Pallett Creek. Overall, the AMS dates are similar to and reveal no dramatic bias in the conventional dates. For many layers, however, individual charcoal samples were younger than the conventional dates, leading to earthquake ages that are overall slightly younger than previously reported. New earthquake ages are determined by Bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints. The new chronology is more regular than previously published records in large part due to new samples constraining the age of event R. The closed interval from event C to 1857 has a mean recurrence of 135 years (? = 83.2 years) and a quasiperiodic coefficient of variation (COV) of 0.61. We show that the new dates and resultant earthquake chronology have a stronger effect on COV than the specific membership of this long series and dating precision improvements from sedimentation rates.

Scharer, Katherine M.; Biasi, Glenn P.; Weldon, Ray J., II

2011-12-01

316

Evidence for large-magnitude paleo-earthquakes on the Ventura fault: Implications for earthquake recurrence, fault slip rate, and seismic hazard assessment in southern California  

NASA Astrophysics Data System (ADS)

New borehole, high-resolution seismic reflection, and geochronologic data reveal the ages and displacements of the two most recent large-magnitude earthquakes on the Ventura fault, the central segment of a large, multi-fault reverse fault system that extends for >200 km along the southern edge of the central and western Transverse Ranges fault system. Based on geomorphology and analysis of high-resolution seismic data acquired in 2010, we drilled 17 hollow stem auger boreholes and cone penetrometer tests along two transects across the locus of most recent folding above the Ventura fault. At Day Road in downtown Ventura, our 23-m-deep boreholes revealed a well-bedded alluvial section with many units that are traceable continuously along the entire 375 m length of the transect. Stratigraphic relationships indicate that the prominent topographic scarp at this site records ~6 m of uplift during fold growth in the most-recent earthquake on the underlying Ventura blind thrust ramp. Similarly, sedimentary growth observed in the borehole cross section indicates ~4.5 m of growth during the penultimate event, with an event horizon located at the base of a growth interval between 4 and 8.5 m depth south of the scarp. Six 14C and 14 OSL ages collected from the four hollow-stem auger boreholes at this site constrain the timing of the two most recent events on the Ventura blind thrust fault to post-2900 B.P. and 4700 × 350 to 5460 × 330 years before present; dating of additional shallow luminescence samples should help narrow the age range of the MRE. The large amounts of uplift in the two folding events indicate that they formed in response to large-displacement, and therefore large-magnitude earthquakes, likely involving rupture of the Ventura fault together with thrust ramps to both the west (e.g., Pitas Point fault) and east (Southern San Cayetano and eastern San Cayetano faults). These thrust faults form the middle section of a >200-km-long, east-west belt of large, interconnected reverse faults that extends along the southern edge of the Transverse Ranges. Although each of these faults represents a major seismic source in its own right, we are exploring the possibility of even larger-magnitude, multi-segment ruptures that may link these faults to other major faults to the east and west. The proximity of this large reverse-fault system to several major population centers, including the metropolitan Los Angeles region, and the potential for tsunami generation during offshore ruptures of the western parts of the system, emphasize the importance of understanding the behavior of these faults for seismic hazard assessment.

Mcauliffe, L. J.; Dolan, J. F.; Hubbard, J.; Shaw, J. H.; Pratt, T. L.; Rhodes, E. J.

2013-12-01

317

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

E-print Network

fault in the Salton sea to the north (Fig. 1). Because sediments cover many of the faults, mapping between the prin- cipal plate boundary fault zone in the northern Gulf of California/Salton trough region

318

Coseismic fault slip associated with the 1992 M(sub w) 6.1 Joshua Tree, California, earthquake: Implications for the Joshua Tree-Landers earthquake sequence  

NASA Technical Reports Server (NTRS)

Coseismic surface deformation associated with the M(sub w) 6.1, April 23, 1992, Joshua Tree earthquake is well represented by estimates of geodetic monument displacements at 20 locations independently derived from Global Positioning System and trilateration measurements. The rms signal to noise ratio for these inferred displacements is 1.8 with near-fault displacement estimates exceeding 40 mm. In order to determine the long-wavelength distribution of slip over the plane of rupture, a Tikhonov regularization operator is applied to these estimates which minimizes stress variability subject to purely right-lateral slip and zero surface slip constraints. The resulting slip distribution yields a geodetic moment estimate of 1.7 x 10(exp 18) N m with corresponding maximum slip around 0.8 m and compares well with independent and complementary information including seismic moment and source time function estimates and main shock and aftershock locations. From empirical Green's functions analyses, a rupture duration of 5 s is obtained which implies a rupture radius of 6-8 km. Most of the inferred slip lies to the north of the hypocenter, consistent with northward rupture propagation. Stress drop estimates are in the range of 2-4 MPa. In addition, predicted Coulomb stress increases correlate remarkably well with the distribution of aftershock hypocenters; most of the aftershocks occur in areas for which the mainshock rupture produced stress increases larger than about 0.1 MPa. In contrast, predicted stress changes are near zero at the hypocenter of the M(sub w) 7.3, June 28, 1992, Landers earthquake which nucleated about 20 km beyond the northernmost edge of the Joshua Tree rupture. Based on aftershock migrations and the predicted static stress field, we speculate that redistribution of Joshua Tree-induced stress perturbations played a role in the spatio-temporal development of the earth sequence culminating in the Landers event.

Bennett, Richard A.; Reilinger, Robert E.; Rodi, William; Li, Yingping; Toksoz, M. Nafi; Hudnut, Ken

1995-01-01

319

Fault systems of the 1971 San Fernando and 1994 Northridge earthquakes, southern California: Relocated aftershocks and seismic images from LARSE II  

USGS Publications Warehouse

We have constructed a composite image of the fault systems of the M 6.7 San Fernando (1971) and Northridge (1994), California, earthquakes, using industry reflection and oil test well data in the upper few kilometers of the crust, relocated aftershocks in the seismogenic crust, and LARSE II (Los Angeles Region Seismic Experiment, Phase II) reflection data in the middle and lower crust. In this image, the San Fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of ???25?? from near the surface at the Northridge Hills fault, in the northern San Fernando Valley, to the San Andreas fault in the middle to lower crust. It follows a prominent aseismic reflective zone below and northward of the main-shock hypocenter. Interpreted upward splays off this decollement include the Mission Hills and San Gabriel faults and the two main rupture planes of the San Fernando earthquake, which appear to divide the hanging wall into shingle- or wedge-like blocks. In contrast, the fault system for the Northridge earthquake appears simple, at least east of the LARSE II transect, consisting of a fault that extends 20 km southward at a dip of ???33?? from ???7 km depth beneath the Santa Susana Mountains, where it abuts the interpreted San Fernando decollement, to ???20 km depth beneath the Santa Monica Mountains. It follows a weak aseismic reflective zone below and southward of the mainshock hypocenter. The middle crustal reflective zone along the interpreted San Fernando decollement appears similar to a reflective zone imaged beneath the San Gabriel Mountains along the LARSE I transect, to the east, in that it appears to connect major reverse or thrust faults in the Los Angeles region to the San Andreas fault. However, it differs in having a moderate versus a gentle dip and in containing no mid-crustal bright reflections.

Fuis, G.S.; Clayton, R.W.; Davis, P.M.; Ryberg, T.; Lutter, W.J.; Okaya, D.A.; Hauksson, E.; Prodehl, C.; Murphy, J.M.; Benthien, M.L.; Baher, S.A.; Kohler, M.D.; Thygesen, K.; Simila, G.; Keller, G.R.

2003-01-01

320

Inversion of travel time data for earthquake locations and three- dimensional velocity structure in the Eureka Valley area, eastern California  

Microsoft Academic Search

We develop an earthquake travel time inversion methodology suitable for determining three-dimensional velocity structure and fault plane orientation for an area with little a priori information. Using a cascaded combination of a nonlinear simulated annealing optimization and linearized inversion, we investigate local three-dimensional compressional velocity structure and estimate the orientation of a fault plane in the Eureka Valley area of

A. M. Asad; S. K. Pullammanappallil; R. Anooshehpoor; J. N. Louie

2007-01-01

321

Liquefaction Hazard Maps for Three Earthquake Scenarios for the Communities of San Jose, Campbell, Cupertino, Los Altos, Los Gatos, Milpitas, Mountain View, Palo Alto, Santa Clara, Saratoga, and Sunnyvale, Northern Santa Clara County, California  

USGS Publications Warehouse

Maps showing the probability of surface manifestations of liquefaction in the northern Santa Clara Valley were prepared with liquefaction probability curves. The area includes the communities of San Jose, Campbell, Cupertino, Los Altos, Los Gatos Milpitas, Mountain View, Palo Alto, Santa Clara, Saratoga, and Sunnyvale. The probability curves were based on complementary cumulative frequency distributions of the liquefaction potential index (LPI) for surficial geologic units in the study area. LPI values were computed with extensive cone penetration test soundings. Maps were developed for three earthquake scenarios, an M7.8 on the San Andreas Fault comparable to the 1906 event, an M6.7 on the Hayward Fault comparable to the 1868 event, and an M6.9 on the Calaveras Fault. Ground motions were estimated with the Boore and Atkinson (2008) attenuation relation. Liquefaction is predicted for all three events in young Holocene levee deposits along the major creeks. Liquefaction probabilities are highest for the M7.8 earthquake, ranging from 0.33 to 0.37 if a 1.5-m deep water table is assumed, and 0.10 to 0.14 if a 5-m deep water table is assumed. Liquefaction probabilities of the other surficial geologic units are less than 0.05. Probabilities for the scenario earthquakes are generally consistent with observations during historical earthquakes.

Holzer, Thomas L.; Noce, Thomas E.; Bennett, Michael J.

2008-01-01

322

A reevaluation of the Pallett Creek earthquake chronology based on new AMS radiocarbon dates, San Andreas fault, California  

USGS Publications Warehouse

The Pallett Creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern San Andreas fault. Previous estimates of earthquake ages at Pallett Creek were determined by decay counting radiocarbon methods. That method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers. In contrast, accelerator mass spectrometry (AMS) radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section. We present 65 new AMS radiocarbon dates that span nine ground-rupturing earthquakes at Pallett Creek. Overall, the AMS dates are similar to and reveal no dramatic bias in the conventional dates. For many layers, however, individual charcoal samples were younger than the conventional dates, leading to earthquake ages that are overall slightly younger than previously reported. New earthquake ages are determined by Bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints. The new chronology is more regular than previously published records in large part due to new samples constraining the age of event R. The closed interval from event C to 1857 has a mean recurrence of 135years (?? = 83.2 years) and a quasiperiodic coefficient of variation (COV) of 0.61. We show that the new dates and resultant earthquake chronology have a stronger effect on COV than the specific membership of this long series and dating precision improvements from sedimentation rates. Copyright 2011 by the American Geophysical Union.

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

2011-01-01

323

Earthquakes and Schools  

ERIC Educational Resources Information Center

Earthquakes are low-probability, high-consequence events. Though they may occur only once in the life of a school, they can have devastating, irreversible consequences. Moderate earthquakes can cause serious damage to building contents and non-structural building systems, serious injury to students and staff, and disruption of building operations.…

National Clearinghouse for Educational Facilities, 2008

2008-01-01

324

The search for repeating earthquakes in the northern San Francisco Bay area Nader Shakibay Senobari and Gareth J. Funning University of California, Riverside  

NASA Astrophysics Data System (ADS)

Repeating earthquakes (REs) are sequences of identical repeating events, which are recurring either irregularly (aperiodic) or nearly regularly (quasi-periodic). There are two important characteristics of the events in a RE sequence: they have the same source characteristics (i.e. magnitude and mechanism) and they have the same location and therefore their waveforms at the same stations are extremely similar. Several authors have proposed that the quasi-periodic REs result from recurrent rupture of a small locked patch on a fault surface surrounded by a larger area of creep. The implication is that any detection of characteristic REs along a fault can be interpreted as a signature of the creep at depth on that fault. In addition, REs can be used for locating faults and determining their geometries at depth. In this study, we are looking for REs on the northern Rodgers Creek and southern Maacama faults near Santa Rosa, CA. There is some observational evidence for creep along portions of these faults (e.g. from InSAR, alignment arrays and offset cultural features) but the depth of creep on both faults is still unknown. Finding the locations of REs in this area, and combining them with geodetic data, will help us to place stronger constraints on the distributions of aseismic slip on both the Rodgers Creek and Maacama faults. In order to identify such events, we use data from the Northern California Seismic Network (NCSN) for the period from 1984 to July 2013. We used earthquake waveforms from 2080 events located inside a 25 by 30 km area around Santa Rosa. We choose 7 stations located both inside and outside the selection area at distances of up to 50 km. We calculate the coherence for all pairs of events for each station during the time that the sensor has not been changed (mostly from 1987 to 2013). We align the waveforms using P arrival times from the NCSN catalog. The time windows for the seismogram analysis are set at 0.2 sec before and 10.2 sec after the P-wave arrivals. This time window always contains the S phase, which guarantees that the waves have the same S-P time (i.e. the same location) if they have high cross-correlation coefficients. We calculate the cross-correlation function by allowing a maximum time shift of 0.5 sec (50 samples) in the time domain. An earthquake pair is chosen to be a candidate for REs when the maximum cross-correlation coefficients at 1-15 Hz are larger than 0.95 at four or more stations. We then link a pair of REs with another pair if the two share the same earthquake. We find 49 such clusters of highly correlated events that are candidates for RE sequences. Using the northern California double-difference earthquake catalog (Waldhauser and Schaff, 2008), we find that they are mostly located close to the Rodgers Creek fault trace. In order to confirm whether these clusters are indeed REs, additional tests (e.g. phase and amplitude coherence, time recurrence, visually inspect) must be performed.

Shakibay Senobari, N.; Funning, G.

2013-12-01

325

A change in fault-plane orientation between foreshocks and aftershocks of the Galway Lake earthquake, ML = 5.2, 1975, Mojave desert, California  

USGS Publications Warehouse

A marked change is observed in P/SV amplitude ratios, measured at station TPC, from foreshocks to aftershocks of the Galway Lake earthquake. This change is interpreted to be the result of a change in fault-plane orientation occurring between foreshocks and aftershocks. The Galway Lake earthquake, ML= 5.2, occurred on June 1, 1975. The first-motion fault-plane solutions for the main shock and most foreshocks and aftershocks indicate chiefly right-lateral strike-slip on NNW-striking planes that dip steeply, 70-90??, to the WSW. The main event was preceded by nine located foreshocks, ranging in magnitude from 1.9 to 3.4, over a period of 12 weeks, starting on March 9, 1975. All of the foreshocks form a tight cluster approximately 1 km in diameter. This cluster includes the main shock. Aftershocks are distributed over a 6-km-long fault zone, but only those that occurred inside the foreshock cluster are used in this study. Seismograms recorded at TPC (?? = 61 km), PEC (?? = 93 km), and CSP (?? = 83 km) are the data used here. The seismograms recorded at TPC show very consistent P/SV amplitude ratios for foreshocks. For aftershocks the P/SV ratios are scattered, but generally quite different from foreshock ratios. Most of the scatter for the aftershocks is confined to the two days following the main shock. Thereafter, however, the P/SV ratios are consistently half as large as for foreshocks. More subtle (and questionable) changes in the P/SV ratios are observed at PEC and CSP. Using theoretical P/SV amplitude ratios, one can reproduce the observations at TPC, PEC and CSP by invoking a 5-12?? counterclockwise change in fault strike between foreshocks and aftershocks. This interpretation is not unique, but it fits the data better than invoking, for example, changes in dip or slip angle. First-motion data cannot resolve this small change, but they permit it. Attenuation changes would appear to be ruled out by the fact that changes in the amplitude ratios, PTPC/PPEC and ptpc/pcsp, are observed, and these changes accompany the changes in P/SV. Observations for the Galway Lake earthquake are similar to observations for the Oroville, California, earthquake (ML = 5.7) of August 1, 1975, and the Brianes Hills, California, earthquake (ML = 4.3) of January 8, 1977 (Lindh et al., Science Vol. 201, pp. 56-59). A change in fault-plane orientation between foreshocks and aftershocks may be understandable in terms of early en-echelon cracking (foreshocks) giving way to shear on the main fault plane (main shock plus aftershocks). Recent laboratory data (Byerlee et al., Tectonophysics, Vol. 44, pp. 161-171) tend to support this view. ?? 1979.

Fuis, G.S.; Lindh, A.G.

1979-01-01

326

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

USGS Publications Warehouse

One of the most significant effects of the 17 January, 1994 Northridge, California earthquake (M=6.7) was the triggering of thousands of landslides over a broad area. Some of these landslides damaged and destroyed homes and other tructures, blocked roads, disrupted pipelines, and caused other serious damage. Analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes. We analyzed the frequency, distribution, and geometries of triggered landslides in the Santa Susana 7.5??? quadrangle, an area of intense seismic landslide activity near the earthquake epicenter. Landslides occured primarily in young (Late Miocene through Pleistocene) uncemented or very weakly cemented sediment that has been repeatedly folded, faulted, and uplifted in the past 1.5 million years. The most common types of landslide triggered by the earthquake were highly disrupted, shallow falls and slides of rock and debris. Far less numerous were deeper, more coherent slumps and block slides, primarily occuring in more cohesive or competent materials. The landslides in the Santa Susana quadrangle were divided into two samples: single landslides (1502) and landslide complexes (60), which involved multiple coalescing failures of surficial material. We described landslide, morphologies by computing simple morphometric parameters (area, length, width, aspect ratio, slope angle). To quantify and rank the relative susceptibility of each geologic unit to seismic landsliding, we calculated two indices: (1) the susceptibility index, which is the ratio (given as a percentage) of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit: and (2) the frequency index [given in landslides per square kilometer (ls/km2)], which is the total number of landslides within each geologic unit divided by the outcrop area of that unit. Susceptibility categories include very high (>2.5% landslide area or >30 1s/km2). high (1.0-2.5% landslide area or 10-30 1s/km2), moderate (0.5-1.0% landslide area or 3-10 1s/km2), and low (<0.5% landslide area and <3 1s/km2). ?? 2000 Elsevier Science B.V. All rights reserved.

Parise, M.; Jibson, R.W.

2000-01-01

327

On the resolution of shallow mantle viscosity structure using post-earthquake relaxation data: Application to the 1999 Hector Mine, California, earthquake  

USGS Publications Warehouse

Most models of lower crust/mantle viscosity inferred from postearthquake relaxation assume one or two uniform-viscosity layers. A few existing models possess apparently significant radially variable viscosity structure in the shallow mantle (e.g., the upper 200 km), but the resolution of such variations is not clear. We use a geophysical inverse procedure to address the resolving power of inferred shallow mantle viscosity structure using postearthquake relaxation data. We apply this methodology to 9 years of GPS-constrained crustal motions after the 16 October 1999 M = 7.1 Hector Mine earthquake. After application of a differencing method to isolate the postearthquake signal from the “background” crustal velocity field, we find that surface velocities diminish from ?20 mm/yr in the first few months to ?2 mm/yr after 2 years. Viscoelastic relaxation of the mantle, with a time-dependent effective viscosity prescribed by a Burgers body, provides a good explanation for the postseismic crustal deformation, capturing both the spatial and temporal pattern. In the context of the Burgers body model (which involves a transient viscosity and steady state viscosity), a resolution analysis based on the singular value decomposition reveals that at most, two constraints on depth-dependent steady state mantle viscosity are provided by the present data set. Uppermost mantle viscosity (depth ? 60 km) is moderately resolved, but deeper viscosity structure is poorly resolved. The simplest model that explains the data better than that of uniform steady state mantle viscosity involves a linear gradient in logarithmic viscosity with depth, with a small increase from the Moho to 220 km depth. However, the viscosity increase is not statistically significant. This suggests that the depth-dependent steady state viscosity is not resolvably different from uniformity in the uppermost mantle.

Pollitz, Fred F.; Thatcher, Wayne R.

2010-01-01

328

Swarms, Mogi Doughnuts, and Earthquake Triggering Models  

NASA Astrophysics Data System (ADS)

Earthquakes cluster strongly in time and space, but it is not yet clear how much of this clustering can be explained as triggering from previous events (such as occurs for aftershock sequences following large earthquakes) and how much the clustering may reflect underlying physical processes (such as slow slip or fluid flow). Here we examine recent high-resolution catalogs and discuss two aspects of southern California seismicity that deviate from standard earthquake triggering models, indicating that these models do not account for all of the processes involved in earthquake occurrence. (1) We study 71 isolated sequences of 40 or more earthquakes occurring within a 2-km-radius volume and a four-week interval. 57 of the 71 bursts are difficult to interpret as primarily a mainshock and its Omori-law- abiding foreshocks and aftershocks because they exhibit a more complicated evolution in space, time, and magnitude; we identify 18 of these sequences as particularly swarm-like. Similar results are seen for greater numbers of sequences identified using larger spatial and temporal windows. Evidence against a simple cascade of elastic stress triggering includes the presence of an interval of steady seismicity rate, the tendency of the largest event to strike later in the sequence, the large spatial extent of some of the swarms compared to their cumulative moment, and the weak correlation between the number of events in each burst and the magnitude of the largest event in each burst. Both aftershock-like and swarm-like seismicity bursts are distributed across the entire study region, indicating that they are a general feature of tectonic faulting, rather than limited to a few geological conditions such as volcanic or geothermal areas. However, there is some evidence that swarms occur more frequently in regions of high heat flow, such as Coso and the Salton Trough. (2) We examine the average space-time behavior of seismicity preceding M 2--5 earthquakes in southern California and identify regions of enhanced activity in a 1-day period preceding larger earthquakes at distances comparable to their predicted source radii. The difference in precursory behavior between large and small earthquakes is subtle but statistically significant when averaged over many earthquakes, and has similarities to the "Mogi doughnut" seismicity pattern observed to occur prior to some M 6 and larger earthquakes. This observation conflicts with many earthquake triggering models, in which prior seismicity increases the probability of a future earthquake in the same region but does not change the size distribution of the triggered events, which is governed by the Gutenberg-Richter magnitude-frequency relation. These models thus predict no difference in the average seismicity prior to earthquakes of any specified size, contrary to our observations for southern California.

Shearer, P. M.; Vidale, J. E.; Lin, G.; Peng, Z.

2008-12-01

329

Probable epizootic chlamydiosis in wild California (Larus californicus) and ring-billed (Larus delawarensis) gulls in North Dakota  

USGS Publications Warehouse

During the summer of 1986, more than 400 California gulls (Larus californicus) and ring-billed gulls (Larvus delawarensis), primarily fledglings, died on an island in Lake Sakakawea near New Town, North Dakota (USA). Mortality was attributed largely to chlamydiosis. Necropsy findings in nine carcasses included splenomegaly (n = 9), hepatomegaly (n = 4), and pericarditis (n = 1). Livers from three California gulls and two ring-billed gulls, and spleens from the same five birds plus a third ring-billed gull were positive for Chlamydia psittaci by the direct immunofluorescence test. Chlamydia psittaci was isolated from separate pools of liver and spleen from one California gull and one ring-billed gull. This is believed to be the first record of epizootic chlamydiosis in gulls and the second report of epizootic chlamydial mortality in wild birds in North America.

Franson, J.C.; Pearson, J.E.

1995-01-01

330

Probable epizootic chlamydiosis in wild California (Larus californicus) and ring-billed (Larus delawarensis) gulls in North Dakota.  

PubMed

During the summer of 1986, more than 400 California gulls (Larus californicus) and ring-billed gulls (Larvus delawarensis), primarily fledglings, died on an island in Lake Sakakawea near New Town, North Dakota (USA). Mortality was attributed largely to chlamydiosis. Necropsy findings in nine carcasses included splenomegaly (n = 9), hepatomegaly (n = 4), and pericarditis (n = 1). Livers from three California gulls and two ring-billed gulls, and spleens from the same five birds plus a third ring-billed gull were positive for Chlamydia psittaci by the direct immunofluorescence test. Chlamydia psittaci was isolated from separate pools of liver and spleen from one California gull and one ring-billed gull. This is believed to be the first record of epizootic chlamydiosis in gulls and the second report of epizootic chlamydial mortality in wild birds in North America. PMID:8592370

Franson, J C; Pearson, J E

1995-07-01

331

Chapter C. The Loma Prieta, California, Earthquake of October 17, 1989 - Fire, Police, Transportation and Hazardous Materials  

USGS Publications Warehouse

The papers in this chapter discuss some of the failures and successes that resulted from the societal response by a multitude of agencies to the Loma Prieta earthquake. Some of the lessons learned were old ones relearned. Other lessons were obvious ones which had gone unnoticed. Still, knowledge gained from past earthquakes spawned planning and mitigation efforts which proved to be successful in limiting the aftermath effects of the Loma Prieta event. At least four major areas of response are presented in this chapter: the Oakland Police Department response to the challenge of controlled access to the Cypress freeway collapse area without inhibiting relief and recovery efforts; search and rescue of the freeway collapse and the monumental crisis management problem that accompanied it; the short- and long-term impact on transbay transportation systems to move a large work force from home to business; and the handling of hazardous material releases throughout the Bay Area.

Van Anne, Craig, (Edited By); Scawthorn, Charles R.

1994-01-01

332

Tectonics, Earthquakes, Volcanoes  

NSDL National Science Digital Library

Students do background reading on plate tectonics and associated geologic hazards. In the first part of this exercise, students use on-line courseware from California State University, Los Angeles (Virtual Earthquake) to investigate seismograph records and use these records to determine earthquake epicenters and magnitudes. In the second part, they complete a crossword puzzle designed to help them master new vocabulary related to plate tectonics.

Holmgren, Camille

333

Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Earth Structures and Engineering Characterization of Ground Motion  

USGS Publications Warehouse

This chapter contains two papers that summarize the performance of engineered earth structures, dams and stabilized excavations in soil, and two papers that characterize for engineering purposes the attenuation of ground motion with distance during the Loma Prieta earthquake. Documenting the field performance of engineered structures and confirming empirically based predictions of ground motion are critical for safe and cost effective seismic design of future structures as well as the retrofitting of existing ones.

Holzer, Thomas L.

1998-01-01

334

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

NASA Technical Reports Server (NTRS)

Interferometric synthetic aperture radar (InSAR) data over the area of the Hector Mine earthquake (Mw 7.1, 16 October 1999) reveal postseismic deformation of several centimeters over a spatial scale of 0.5 to 50 km. We analyzed seven SAR acquisitions to form interferograms over four time periods after the event. The main deformations seen in the line-of-sight (LOS) displacement maps are a region of subsidence (60 mm LOS increase) on the northern end of the fault, a region of uplift (45 mm LOS decrease) located to the northeast of the primary fault bend, and a linear trough running along the main rupture having a depth of up to 15 mm and a width of about 2 km. We correlate these features with a double left-bending, rightlateral, strike-slip fault that exhibits contraction on the restraining side and extension along the releasing side of the fault bends. The temporal variations in the near-fault postseismic deformation are consistent with a characteristic time scale of 135 + 42 or - 25 days, which is similar to the relaxation times following the 1992 Landers earthquake. High gradients in the LOS displacements occur on the fault trace, consistent with afterslip on the earthquake rupture. We derive an afterslip model by inverting the LOS data from both the ascending and descending orbits. Our model indicates that much of the afterslip occurs at depths of less than 3 to 4 km.

Jacobs, Allison; Sandwell, David; Fialko, Yuri; Sichoix, Lydie

2002-01-01

335

Predicted Surface Displacements for Scenario Earthquakes in the San Francisco Bay Region  

USGS Publications Warehouse

In the immediate aftermath of a major earthquake, the U.S. Geological Survey (USGS) will be called upon to provide information on the characteristics of the event to emergency responders and the media. One such piece of information is the expected surface displacement due to the earthquake. In conducting probabilistic hazard analyses for the San Francisco Bay Region, the Working Group on California Earthquake Probabilities (WGCEP) identified a series of scenario earthquakes involving the major faults of the region, and these were used in their 2003 report (hereafter referred to as WG03) and the recently released 2008 Uniform California Earthquake Rupture Forecast (UCERF). Here I present a collection of maps depicting the expected surface displacement resulting from those scenario earthquakes. The USGS has conducted frequent Global Positioning System (GPS) surveys throughout northern California for nearly two decades, generating a solid baseline of interseismic measurements. Following an earthquake, temporary GPS deployments at these sites will be important to augment the spatial coverage provided by continuous GPS sites for recording postseismic deformation, as will the acquisition of Interferometric Synthetic Aperture Radar (InSAR) scenes. The information provided in this report allows one to anticipate, for a given event, where the largest displacements are likely to occur. This information is valuable both for assessing the need for further spatial densification of GPS coverage before an event and prioritizing sites to resurvey and InSAR data to acquire in the immediate aftermath of the earthquake. In addition, these maps are envisioned to be a resource for scientists in communicating with emergency responders and members of the press, particularly during the time immediately after a major earthquake before displacements recorded by continuous GPS stations are available.

Murray-Moraleda, Jessica R.

2008-01-01

336

The Distribution of Earthquakes: An Earthquake Deficit?  

NSDL National Science Digital Library

In this activity, students use online resources to investigate the occurrence of earthquakes in Southern California to decide if there has been a 'deficit', that is, not enough earthquakes in the area in historical time to release the amount of strain energy that plate tectonics is constantly supplying to the crust. In the first two parts, they must determine the appropriate year to begin their study of historic earthquake records (from 1860-1900), and then they must decide if the energy released by past earthquakes has been equivalent to the amount of energy accumulating through the action of plate tectonics over the same number of years. In part three, they perform an analysis of their findings by answering a set of questions. References are included.

Marquis, John

337

Measuring Earthquakes: Intensity Maps  

NSDL National Science Digital Library

This set of exercises will introduce students to the construction of earthquake intensity maps, familiarize them with the Modified Mercalli Intensity Scale, and give them the opportunity to build their own maps online in order to locate the epicenter of an earthquake. In the first exercise, they will use intensity data from the 1986 North Palm Springs, California earthquake to create an isoseismal map. In the second, they will use a special interactive page of dynamic HTML to plot intensities that they assign based on reports, and attempt to determine the epicenter based on the area of highest intensity.

338

Earthquakes Canada  

NSDL National Science Digital Library

This is the earthquake information page of the Natural Resources Canada Geologic Survey. It contains links to reports, maps, and lists of recent earthquakes, information and hazards as well as earthquake research and network and data archives. Links also connect to information on earthquake hazards, products and publications, a site to report earthquakes, and a link to other earthquake resources.

339

Earthquake Early Warning: Real-time Testing of an On-site Method Using Waveform Data from the Southern California Seismic Network  

NASA Astrophysics Data System (ADS)

We have implemented an on-site early warning algorithm using the infrastructure of the Caltech/USGS Southern California Seismic Network (SCSN). We are evaluating the real-time performance of the software system and the algorithm for rapid assessment of earthquakes. In addition, we are interested in understanding what parts of the SCSN need to be improved to make early warning practical. Our EEW processing system is composed of many independent programs that process waveforms in real-time. The codes were generated by using a software framework. The Pd (maximum displacement amplitude of P wave during the first 3sec) and Tau-c (a period parameter during the first 3 sec) values determined during the EEW processing are being forwarded to the California Integrated Seismic Network (CISN) web page for independent evaluation of the results. The on-site algorithm measures the amplitude of the P-wave (Pd) and the frequency content of the P-wave during the first three seconds (Tau-c). The Pd and the Tau-c values make it possible to discriminate between a variety of events such as large distant events, nearby small events, and potentially damaging nearby events. The Pd can be used to infer the expected maximum ground shaking. The method relies on data from a single station although it will become more reliable if readings from several stations are associated. To eliminate false triggers from stations with high background noise level, we have created per station Pd threshold configuration for the Pd/Tau-c algorithm. To determine appropriate values for the Pd threshold we calculate Pd thresholds for stations based on the information from the EEW logs. We have operated our EEW test system for about a year and recorded numerous earthquakes in the magnitude range from M3 to M5. Two recent examples are a M4.5 earthquake near Chatsworth and a M4.7 earthquake near Elsinore. In both cases, the Pd and Tau-c parameters were determined successfully within 10 to 20 sec of the arrival of the P-wave at the station. The Tau-c values predicted the magnitude within 0.1 and the predicted average peak-ground-motion was 0.7 cm/s and 0.6 cm/s. The delays in the system are caused mostly by the packetizing delay because our software system is based on processing miniseed packets. Most recently we have begun reducing the data latency using new qmaserv2 software for the Q330 Quanterra datalogger. We implemented qmaserv2 based multicast receiver software to receive the native 1 sec packets from the dataloggers. The receiver reads multicast packets from the network and writes them into shared memory area. This new software will fully take advantage of the capabilities of the Q330 datalogger and significantly reduce data latency for EEW system. We have also implemented a new EEW sub-system that compliments the currently running EEW system by associating Pd and Tau-c values from multiple stations. So far, we have implemented a new trigger generation algorithm for real-time processing for the sub-system, and are able to routinely locate events and determine magnitudes using the Pd and Tau-c values.

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

2007-12-01

340

Occurrence of a predicted earthquake on the San Andreas fault  

USGS Publications Warehouse

In May 1985 we predicted1 that an earthquake would occur on the San Andreas fault near Stone Canyon, California within a year. The prediction was based on the observation of seismic quiescence-defined as a significant decrease in the average occurrence rate of earthquakes within the source volume of the future mainshock. A mainshock of magnitude ML = 4.6 occurred on 31 May 1986, rupturing exactly the specified segment of the fault. This is the first successful prediction of an earthquake along the San Andreas fault, and the probability to have come true by chance is <5%. Although the prediction addressed only a small main-shock, its success was significant because the location, size and occurrence time were correctly specified for an earthquake in a populated area. Larger earthquakes will undoubtedly be successfully predicted by the same method in the future, but the major segments of the San Andreas fault near San Francisco and Los Angeles have such a low-background seismicity rate that the method will probably not be applicable there. ?? 1987 Nature Publishing Group.

Wyss, M.; Burford, R.O.

1987-01-01

341

Response of streamflow to multiple earthquakes Michael Manga  

E-print Network

Response of streamflow to multiple earthquakes Michael Manga Department of Earth and Planetary, University of California, Los Angeles, California, USA Michael Boone Department of Earth and Planetary, to several large earthquakes. We find that flow increased after three earthquakes, and that the observed

Manga, Michael

342

Putting Down Roots in Earthquake Country  

NSDL National Science Digital Library

Putting Down Roots in Earthquake Country is an informational Web site provided by the Southern California Earthquake Center. Citizens can learn about the San Andreas fault, other California faults, how to build and maintain an earthquake safe house, how to survive an earthquake, how they are measured and what the magnitude means, common earthquake myths, and much more. As a safety and an educational site, this unique resource does a good job of presenting a lot of information, illustrations, and graphics in an easy-to-follow format that helps explain this powerful and potentially deadly natural occurrence.

343

High-resolution seismic reflection surveys and modeling across an area of high damage from the 1994 Northridge earthquake, Sherman Oaks, California  

USGS Publications Warehouse

Approximately 3.6 km of P-wave seismic-reflection data were acquired along two orthogonal profiles in Sherman Oaks, California to determine whether shallow (less than 1-km depth) geologic structures contributed to the dramatic localized damage resulting from the 1994 Northridge earthquake. Both lines, one along Matilija Avenue and one along Milbank Street, crossed areas of both high and low damage. We believe these data reveal a geologic structure in the upper 600 m that contributed to the increased earthquake ground shaking in the high-damage areas south of and along the Los Angeles River. Of interest in these data is a reflection interpreted to be from bedrock that can be traced to the north along the Matilija Avenue profile. This reflecting interface, dipping northward at 15°–22°, may be an important impedance boundary because it is the lower boundary of a wedge of overlying low-velocity sediments. The wedge thins and terminates in the area where we interpret down-warped reflections as evidence of a shallow subbasin. The low-velocity subbasin sediments (Vs of 200 m/sec Vp of 500 m/sec) may be up to 150 m thick beneath the channelized Los Angeles River. The area across the subbasin experienced greater earthquake damage from possible geometric focusing effects. Three-dimensional basin effects may be responsible for the variable damage pattern, but from these seismic profiles it is not possible to determine the regional structural trends. Two-dimensional elastic and SH-mode finite-difference modeling of the imaged structural geometry along Matilija Avenue suggests that a peak horizontal-velocity amplification factor of two-and-over can be explained in the high-damage area above the shallow subbasin and sediment wedge. Amplification factors up to 5 were previously observed in aftershock data, at frequencies of 2 to 6 Hz. Amplification in the elastic simulation at the Santa Monica Mountains range-front on the southern end of the Matilija profile, with the geologic layering and geometry interpreted from the seismic data, is also consistent with aftershock observations.

Stephenson, William J.; Williams, Robert A.; Odum, Jack K.; Worley, David M.

2000-01-01

344

Aftershocks of the 2010 Mw 7.2 El Mayor-Cucapah earthquake revealcomplex faulting in the Yuha Desert, California  

USGS Publications Warehouse

We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ~40 m horizontally and ~120 m vertically.Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American-Pacific plate boundary and en echelon, conjugate features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three-dimensional analysis reveals individual and intersecting fault planes that are limited in their along-strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner.

Kroll, K.; Cochran, Elizabeth S.; Richards-Dinger, K.; Sumy, Danielle

2013-01-01

345

A preliminary study of the Santa Barbara, California, earthquake of August 13, 1978, and its major aftershocks  

USGS Publications Warehouse

The ML5.1 Santa Barbara earthquake of August 13, 1978 occurred at lat 34 ? 22.2'N., long 119 ? 43.0' 4 km south of Santa Barbara, Calif. at a depth of 12.5 km in the northeast Santa Barbara Channel, part of the western Transverse Ranges geomorphic-structural province. This part of the province is characterized by seismically active, east-trending reverse faults and rates of coastal uplift that have averaged up to about 10 m/1000 years over the last 45,000 years. No surface rupture was detected onshore. Subsurface rupture propagated northwest from the main shock toward Goleta, 15 km west of Santa Barbara, where a maximum acceleration of 0.44 g was measured at ground level and extensive minor damage occurred; only minor injuries were reported. A fairly well-constrained fault-plane solution of the main shock and distribution of the aftershocks indicate that left-reverse-oblique slip occurred on west-northwest-trending, north-dipping reverse faults; inadequate dip control precludes good correlation with any one of several mapped faults. Had the earthquake been larger and rupture propagated to the southeast or a greater distance to the northwest, it could have posed a hazard to oilfield operations. The fault-plane solution and aftershock pattern closely fit the model of regional deformation and the solution closely resembles those of five previously mapped events located within a 15-km radius.

Lee, William Hung Kan; Johnson, C.E.; Henyey, T.L.; Yerkes, R.L.

1978-01-01

346

Slip Rates, Recurrence Intervals and Earthquake Event Magnitudes for the southern Black Mountains Fault Zone, southern Death Valley, California  

NASA Astrophysics Data System (ADS)

The normal-oblique Black Mountain Fault zone (BMFZ) is part of the Death Valley fault system. Strong ground-motion generated by earthquakes on the BMFZ poses a serious threat to the Las Vegas, NV area (pop. ~1,428,690), the Death Valley National Park (max. pop. ~20,000) and Pahrump, NV (pop. 30,000). Fault scarps offset Holocene alluvial-fan deposits along most of the 80-km length of the BMFZ. However, slip rates, recurrence intervals, and event magnitudes for the BMFZ are poorly constrained due to a lack of age control. Also, Holocene scarp heights along the BMFZ range from <1 m to >6 m suggesting that geomorphic sections have different earthquake histories. Along the southernmost section, the BMFZ steps basinward preserving three post-late Pleistocene fault scarps. Surveys completed with a total station theodolite show scarp heights of 5.5, 5.0 and 2 meters offsetting the late Pleistocene, early to middle Holocene, to middle-late Holocene surfaces, respectively. Regression plots of vertical offset versus maximum scarp angle suggest event ages of <10 - 2 ka with a post-late Pleistocene slip rate of 0.1mm/yr to 0.3 mm/yr and recurrence of <3300 years/event. Regression equations for the estimated geomorphically constrained rupture length of the southernmost section and surveyed event displacements provides estimated moment magnitudes (Mw) between 6.6 and 7.3 for the BMFZ.

Fronterhouse Sohn, M.; Knott, J. R.; Bowman, D. D.

2005-12-01

347

Permanent GPS Geodetic Array in Southern California  

NASA Technical Reports Server (NTRS)

The southern California Permanent GPS Geodetic Array (PGGA) was established in the spring of 1990 to evaluate continuous Global Positioning System (GPS) measurements as a new too] for monitoring crustal deformation. Southern California is an ideal location because of the relatively high rate of tectonic deformation, the high probability of intense seismicity, the long history of conventional and space geodetic measurements, and the availability of a well developed infrastructure to support continuous operations. Within several months of the start of regular operations, the PGGA recorded far-field coseismic displacements induced by the June 28, 1992 (M(sub w)=7.3), Landers earthquake, the largest magnitude earthquake in California in the past 40 years and the first one to be recorded by a continuous GPS array. Only nineteen months later, on 17 January 1994, the PGGA recorded coseismic displacements for the strongest earthquake to strike the Los Angeles basin in two decades, the (M(sub e)=6.7) Northridge earthquake. At the time of the Landers earthquake, only seven continuous GPS sites were operating in southern California; by the beginning of 1994, three more sites had been added to the array. However, only a pair of sites were situated in the Los Angeles basin. The destruction caused by the Northridge earthquake spurred a fourfold increase in the number of continuous GPS sites in southern California within 2 years of this event. The PGGA is now the regional component of the Southern California Integrated GPS Network (SCIGN), a major ongoing densification of continuous GPS sites, with a concentration in the Los Angeles metropolitan region. Continuous GPS provides temporally dense measurements of surface displacements induced by crustal deformation processes including interseismic, coseismic, postseismic, and aseismic deformation and the potential for detecting anomalous events such as preseismic deformation and interseismic strain variations. Although strain meters yield much higher short-term resolution to a period of about 1 year, a single continuous GPS site is significantly less expensive than a single strain meter and probably has better long-term stability beyond a 1-year period. Compared to less frequent field measurements, continuous GPS provides the means to better characterize the errors in GPS position measurements and thereby obtain more realistic estimates of derived parameters such as site velocities.

Green, Cecil H.; Green, Ida M.

1998-01-01

348

Complex earthquakes and Teichmuller Curtis T. McMullen  

E-print Network

Complex earthquakes and Teichm¨uller theory Curtis T. McMullen University of California, Berkeley by an earthquake path. In this paper we show any earthquake path R T (S) extends to a proper holomorphic mapping of a simply- connected domain D into Teichm¨uller space, where R D C. These complex earthquakes relate Weil

349

Source parameters for small events associated with the 1986 North Palm Springs, California, earthquake determined using empirical Green functions  

USGS Publications Warehouse

Using small events as empirical Green functions, source parameters were estimated for 25 ML 3.4 to 4.4 events associated with the 1986 North Palm Springs earthquake. The static stress drops ranged from 3 to 80 bars, for moments of 0.7 to 11 ?? 1021 dyne-cm. There was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock. The highest values were outside the main area of slip, and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock. -from Authors

Mori, J.; Frankel, A.

1990-01-01

350

Late Holocene slip rate of the San Andreas fault and its accommodation by creep and moderate-magnitude earthquakes at Parkfield, California  

USGS Publications Warehouse

Investigation of a right-laterally offset channel at the Miller's Field paleoseismic site yields a late Holocene slip rate of 26.2 +6.4/-4.3 mm/yr (1??) for the main trace of the San Andreas fault at Park-field, California. This is the first well-documented geologic slip rate between the Carrizo and creeping sections of the San Andreas fault. This rate is lower than Holocene measurements along the Carrizo Plain and rates implied by far-field geodetic measurements (~35 mm/yr). However, the rate is consistent with historical slip rates, measured to the northwest, along the creeping section of the San Andreas fault (<30 mm/yr). The paleoseismic exposures at the Miller's Field site reveal a pervasive fabric of clay shear bands, oriented clockwise oblique to the San Andreas fault strike and extending into the upper-most stratigraphy. This fabric is consistent with dextral aseismic creep and observations of surface slip from the 28 September 2004 M6 Parkfield earthquake. Together, this slip rate and deformation fabric suggest that the historically observed San Andreas fault slip behavior along the Parkfield section has persisted for at least a millennium, and that significant slip is accommodated by structures in a zone beyond the main San Andreas fault trace. ?? 2011 Geological Society of America.

Toke, N.A.; Arrowsmith, J.R.; Rymer, M.J.; Landgraf, A.; Haddad, D.E.; Busch, M.; Coyan, J.; Hannah, A.

2011-01-01

351

A stochastic estimate of ground motion at Oceano, California, for the M 6.5 22 December 2003 San Simeon earthquake, derived from aftershock recordings  

USGS Publications Warehouse

The U.S. Geological Survey deployed a digital seismic station in Oceano, California, in February 2004, to investigate the cause of damage and liquefaction from the 22 December 2003 M 6.5 San Simeon earthquake. This station recorded 11 M > 2.8 aftershocks in almost 8 weeks. We analyze these recordings, together with recordings of the mainshock and the same aftershocks obtained from nearby stations in Park Hill and San Luis Obispo, to estimate the mainshock ground motion in Oceano. We estimate the Fourier amplitude spectrum using generalized spectral ratio analysis. We test a set of aftershocks as Green's functions by comparing simulated and recorded acceleration amplitude spectra for the mainshock at San Luis Obispo and Park Hill. We convolve the aftershock accelerograms with a stochastic operator to simulate the duration and phase of the mainshock accelerograms. This approximation allows us to extend the range of aftershocks that can be used as Green's functions to events nearly three magnitude units smaller than the mainshock. Our realizations for the mainshock accelerogram at Oceano yield peak ground accelerations distributed as 28% ?? 4%g. We interpret these realizations as upper bounds for the actual ground motion, because our analysis assumes a linear response, whereas the presence of liquefaction indicates that the ground behaved nonlinearly in Oceano.

Di, Alessandro C.; Boatwright, J.

2006-01-01

352

Coseismic and initial postseismic deformation from the 2004 Parkfield, California, earthquake, observed by global positioning system, electronic distance meter, creepmeters, and borehole strainmeters  

USGS Publications Warehouse

Global Positioning System (GPS), electronic distance meter, creepmeter, and strainmeter measurements spanning the M 6.0 Parkfield, California, earthquake are examined. Using these data from 100 sec through 9 months following the main-shock, the Omori's law, with rate inversely related to time, l/t p and p ranging between 0.7 and 1.3, characterizes the time-dependent deformation during the post-seismic period; these results are consistent with creep models for elastic solids. With an accurate function of postseismic response, the coseismic displacements can be estimated from the high-rate, 1-min sampling GPS; and the coseismic displacements are approximately 75% of those estimated from the daily solutions. Consequently, fault-slip models using daily solutions overestimate coseismic slip. In addition, at 2 months and at 8 months following the mainshock, postseismic displacements are modeled as slip on the San Andreas fault with a lower bound on the moment exceeding that of the coseismic moment.

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

2006-01-01

353

Deformation of Compliant Fault Zones Induced by Nearby Earthquakes: Theoretical Investigations in Three Dimensions and Applications to The East California Shear Zone  

E-print Network

Using dynamic modeling of earthquake rupture on a strike-slip fault and seismic wave propagation in a three dimensional inhomogeneous elastoplastic medium, I investigate the inelastic response of compliant fault zones to nearby earthquakes. I...

Kang, Jingqian

2014-02-21

354

Homogeneous catalogs of earthquakes.  

PubMed

The usual bias in earthquake catalogs against shocks of small magnitudes can be removed by testing the randomness of the magnitudes of successive shocks. The southern California catalog, 1933-1967, is found to be unbiased in the sense of the test at magnitude 4 or above; the cutoff is improved to M = 3 for the subcatalog 1953-1967. PMID:16578700

Knopoff, L; Gardner, J K

1969-08-01

355

Earthquake Prediction is Coming  

ERIC Educational Resources Information Center

Describes (1) several methods used in earthquake research, including P:S ratio velocity studies, dilatancy models; and (2) techniques for gathering base-line data for prediction using seismographs, tiltmeters, laser beams, magnetic field changes, folklore, animal behavior. The mysterious Palmdale (California) bulge is discussed. (CS)

MOSAIC, 1977

1977-01-01

356

World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China  

E-print Network

. Southern California, Los Angeles, California 9089-2531, U.S.A. Email: mtodorov@usc.edu, URL: http://www.usc.edu/dept/civil_eng/EarthquakeThe 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China are shown for the NS response of Millikan Library in Pasadena, California, during several earthquakes

Southern California, University of

357

An approximate estimate of the earthquake risk in the United Arab Emirates  

NASA Astrophysics Data System (ADS)

The UAE is not as safe from earthquake disasters as often assumed. The magnitude 5.1 earthquake of 11 March 2002 in Fujairah Masafi demonstrated that earthquakes can occur in the UAE. The threat of large earthquakes in southern Iran is well known to seismologist, but people generally do not realize that the international expert team that assessed the earthquake hazard for the entire world placed the UAE into the same class as many parts of Iran and Turkey, as well as California. There is no question that large earthquakes will occur again in southern Iran and that moderate earthquakes will happen again in the UAE. The only question is: when will they happen? From the history of earthquakes, we have an understanding, although limited to the last few decades, of what size earthquakes may be expected. For this reason, it is timely to estimate the probable consequences in the UAE of a large to great earthquake in southern Iran and a moderate earthquake in the UAE themselves. We propose to estimate the number of possible injuries, fatalities, and the financial loss in building value that might occur in the UAE in several future likely earthquakes. This estimate will be based on scenario earthquakes with positions and magnitudes determined by us, based on seismic hazard maps. Scenario earthquakes are events that are very likely to occur in the future, because similar ones have happened in the past. The time when they may happen will not be estimated in this work. The input for calculating the earthquake risk in the UAE, as we propose, will be the census figures for the population and the estimated properties of the building stock. WAPPMERR is the only research group capable to make these estimates for the UAE. The deliverables will be a scientific manuscript to be submitted to a reviewed journal, which will contain tables and figures showing the estimated numbers of (a) people killed and (b) people injured (slightly and seriously counted separately), (c) buildings damaged, and (d) an estimate of the financial loss, broken down by settlements, in several possible scenario earthquakes. The number of buildings damaged in each settlement will be broken down into five classes measuring the degree of damage. The estimated loss in value of buildings due to earthquake damage will be expressed in terms of percentage of the current value that would be required to restore the buildings.

Al-Homoud, A.; Wyss, M.

2003-04-01

358

High-resolution seismic reflection/refraction imaging from Interstate 10 to Cherry Valley Boulevard, Cherry Valley, Riverside County, California: implications for water resources and earthquake hazards  

USGS Publications Warehouse

This report is the second of two reports on seismic imaging investigations conducted by the U.S. Geological Survey (USGS) during the summers of 1997 and 1998 in the Cherry Valley area in California (Figure 1a). In the first report (Catchings et al., 1999), data and interpretations were presented for four seismic imaging profiles (CV-1, CV-2, CV-3, and CV-4) acquired during the summer of 1997 . In this report, we present data and interpretations for three additional profiles (CV-5, CV-6, and CV-7) acquired during the summer of 1998 and the combined seismic images for all seven profiles. This report addresses both groundwater resources and earthquake hazards in the San Gorgonio Pass area because the shallow (upper few hundred meters) subsurface stratigraphy and structure affect both issues. The cities of Cherry Valley and Beaumont are located approximately 130 km (~80 miles) east of Los Angeles, California along the southern alluvial fan of the San Bernardino Mountains (see Figure 1b). These cities are two of several small cities that are located within San Gorgonio Pass, a lower-lying area between the San Bernardino and the San Jacinto Mountains. Cherry Valley and Beaumont are desert cities with summer daytime temperatures often well above 100 o F. High water usage in the arid climate taxes the available groundwater supply in the region, increasing the need for efficient management of the groundwater resources. The USGS and the San Gorgonio Water District (SGWD) work cooperatively to evaluate the quantity and quality of groundwater supply in the San Gorgonio Pass region. To better manage the water supplies within the District during wet and dry periods, the SGWD sought to develop a groundwater recharge program, whereby, excess water would be stored in underground aquifers during wet periods (principally winter months) and retrieved during dry periods (principally summer months). The SGWD preferred a surface recharge approach because it could be less expensive than a recharging program based on injection wells. However, at an existing surface recharge site, surface recharge of the aquifer was limited by the presence of clayrich layers that impede the downward percolation of the surface water. In boreholes, these clay-rich layers were found to extend from the near surface to about 50 m depth. If practical, the SGWD desired to relocate the recharge ponds to another location within the Cherry Valley–Beaumont area. This required that sites be found where the clay-rich layers were absent. The SGWD elected to explore for such sites by employing a combination of drilling and seismic techniques. A number of near-surface faults have been suggested in the Cherry Valley-Beaumont area (Figure 1b). However, there may be additional unmapped faults that underlie the alluvial valley of San Gorgonio Pass. Because faults are known to act as barriers to lateral groundwater flow in alluvial groundwater systems, mapped and unmapped subsurface faults in the Cherry Valley-Beaumont area would likely influence groundwater flow and the lateral distribution of recharged water. These same faults may pose a significant hazard to the local desert communities and to greater areas of southern California due to the presence of lifelines (water, electrical, gas, transportation, etc.) that extend through San Gorgonio Pass to larger urban areas. The three principal goals of the seismic investigation presented in this report were to laterally map the subsurface stratigraphic horizons, locate faults that may act as barriers to groundwater flow, and measure velocities of shallow sediments that may give rise to amplified shaking during major earthquakes.

Gandhok, G.; Catchings, R.D.; Goldman, M.R.; Horta, E.; Rymer, M.J.; Martin, P.; Christensen, A.

1999-01-01

359

Investigating Earthquake Hazards in the Northern Salton Trough, Southern California, Using Data From the Salton Seismic Imaging Project (SSIP)  

NASA Astrophysics Data System (ADS)

The southernmost San Andreas fault (SAF) system, in the northern Salton Trough (Salton Sea and Coachella Valley), is considered likely to produce a large-magnitude, damaging earthquake in the near future. The geometry of the SAF and the velocity and geometry of adjacent sedimentary basins will strongly influence energy radiation and strong ground shaking during a future rupture. The Salton Seismic Imaging Project (SSIP) was undertaken, in part, to provide more accurate information on the SAF and basins in this region. We report preliminary results from modeling four seismic profiles (Lines 4-7) that cross the Salton Trough in this region. Our southernmost line, Line 7, crosses the SAF near its southern terminus in the Salton Sea (near Salt Creek). Line 4 crosses the SAF at the northern end of the Salton Sea (at Box Canyon). Line 5 crosses the SAF (2 strands) in the Indio Hills (at Thousand Palms Oasis). Line 6, our northernmost line, crosses the SAF (3 strands) in the northern Coachella Valley (along a line from Palm Springs to Yucca Valley). Lines 4 to 6 terminate on the SW in the Peninsular Ranges, underlain by Mesozoic batholithic rocks, and terminate on the NE in or near the Little San Bernardino or Orocopia Mountains, underlain by Precambrian and Mesozoic igneous and metamorphic rocks. These lines cross the Coachella Valley, which is underlain by Miocene to Holocene sedimentary deposits. Line 7 crosses the Salton Sea and sedimentary basin deposits to the northeast similar to those of the Coachella Valley. On three lines (7, 4, 6) there is evidence from our seismic imaging, potential-field studies, and (or) earthquakes that active strands of the SAF dip moderately NE. From south to north, on Lines 7, 4, 5, and 6, maximum sedimentary basin depths are approximately 5.5?, 5.5, 3.5, and 3.5 km, respectively, as measured from the surface to the 5.3 km/s velocity contour. (In prior studies of the Imperial Valley, unmetamorphosed sediment is interpreted to lie above this approximate velocity contour.) Basement rocks that can be traced from the Peninsular Ranges to depth beneath the Coachella Valley are characterized by relatively high velocities, averaging 4.9 km/s at the surface and 6.4 km/s at a depth of 4 km. They are also characterized by high velocity gradients, averaging > 0.4/s. In contrast, rocks of the Little San Bernardino and Orocopia Mountains are characterized by relatively low velocities, averaging 3.9 km/s at the surface and 6.1 km/s at a depth of 4 km; and they are characterized by low velocity gradients, averaging < 0.4/s. The rocks of the Peninsular Ranges can be seen on Lines 4 and 6 extending at depth northeastward beyond the active surface trace(s) of the SAF. Strong ground shaking from the ShakeOut Scenario Earthquake (Perry et al., 2008) will be recalculated using our new non-vertical geometry for the SAF and the velocity and geometry of sedimentary basins that we have determined from SSIP data.

Fuis, G.; Hole, J. A.; Stock, J. M.; Driscoll, N. W.; Kent, G.; Harding, A. J.; Kell, A. M.; Goldman, M.; Rose, E.; Catchings, R. D.; Rymer, M. J.; Langenheim, V. E.; Scheirer, D. S.; Athens, N. D.; Tarnowski, J. M.

2012-12-01

360

Tidal triggering of low frequency earthquakes near Parkfield, California: Implications for fault mechanics within the brittle-ductile transition  

NASA Astrophysics Data System (ADS)

Studies of nonvolcanic tremor (NVT) have established the significant impact of small stress perturbations on NVT generation. Here we analyze the influence of the solid earth and ocean tides on a catalog of ˜550,000 low frequency earthquakes (LFEs) distributed along a 150 km section of the San Andreas Fault centered at Parkfield. LFE families are identified in the NVT data on the basis of waveform similarity and are thought to represent small, effectively co-located earthquakes occurring on brittle asperities on an otherwise aseismic fault at depths of 16 to 30 km. We calculate the sensitivity of each of these 88 LFE families to the tidally induced right-lateral shear stress (RLSS), fault-normal stress (FNS), and their time derivatives and use the hypocentral locations of each family to map the spatial variability of this sensitivity. LFE occurrence is most strongly modulated by fluctuations in shear stress, with the majority of families demonstrating a correlation with RLSS at the 99% confidence level or above. Producing the observed LFE rate modulation in response to shear stress perturbations requires low effective stress in the LFE source region. There are substantial lateral and vertical variations in tidal shear stress sensitivity, which we interpret to reflect spatial variation in source region properties, such as friction and pore fluid pressure. Additionally, we find that highly episodic, shallow LFE families are generally less correlated with tidal stresses than their deeper, continuously active counterparts. The majority of families have weaker or insignificant correlation with positive (tensile) FNS. Two groups of families demonstrate a stronger correlation with fault-normal tension to the north and with compression to the south of Parkfield. The families that correlate with fault-normal clamping coincide with a releasing right bend in the surface fault trace and the LFE locations, suggesting that the San Andreas remains localized and contiguous down to near the base of the crust. The deep families that have high sensitivity to both shear and tensile normal stress perturbations may be indicative of an increase in effective fault contact area with depth. Synthesizing our observations with those of other LFE-hosting localities will help to develop a comprehensive understanding of transient fault slip below the "seismogenic zone" by providing constraints on parameters in physical models of slow slip and LFEs.

Thomas, A. M.; Bürgmann, R.; Shelly, D. R.; Beeler, N. M.; Rudolph, M. L.

2012-05-01

361

Alaska Earthquake Information Center  

NSDL National Science Digital Library

Housed at the Geophysical Institute at the University of Alaska Fairbanks, the Alaska Earthquake Information Center reports and provides information on seismic activity in Alaska. While its southern Pacific coast colleague, California, gets a lot more attention when it comes to earthquakes, Alaska experienced a magnitude 6.7 earthquake already this summer and was rocked by a 7.9 in 2002. The site offers links to general information about the center, general earthquake information, research activities at the center, education and outreach materials (including information on seismology education projects), and much more. The site is well populated with materials and should provide a great resources for those interested in North American seismic events.

362

Earthquake Magnitude and Intensity  

NSDL National Science Digital Library

In this exercise, students compare the amount of shaking caused by historic earthquakes, and use data from seismograms to determine Richter magnitude. They will also investigate moment magnitude, an alternative to Richter magnitude, and calculate a seismic moment. In the second portion of the exercise, students investigate earthquake intensity and prepare a map of intensity values from the 1994 Northridge, California earthquake, using actual reports of its effects. Introductory materials explain the difference between earthquake magnitude and intensity, point out the logarithmic nature of the Richter scale, and present criteria for assigning modified Mercalli intensity values to a particular location. The exercise includes instructions, maps, data, and study questions. A bibliography is also provided.

Pinter, Nicholas

2012-04-26

363

Earthquake Magnitude and Intensity  

NSDL National Science Digital Library

In this exercise, students compare the amount of shaking caused by historic earthquakes, and use data from seismograms to determine Richter magnitude. They will also investigate moment magnitude, an alternative to Richter magnitude, and calculate a seismic moment. In the second portion of the exercise, students investigate earthquake intensity and prepare a map of intensity values from the 1994 Northridge, California earthquake, using actual reports of its effects. Introductory materials explain the difference between earthquake magnitude and intensity, point out the logarithmic nature of the Richter scale, and present criteria for assigning modified Mercalli intensity values to a particular location. The exercise includes instructions, maps, data, and study questions. A bibliography is also provided.

Pinter, Nicholas

364

Exploring finite-slip inversion with near-field seismic data: Analysis of the 2004 Parkfield earthquake, California  

NASA Astrophysics Data System (ADS)

Most common finite-slip inversion schemes are model-searching techniques conducted in the time domain. In this study, a frequency-based inversion method is proposed. It makes fewer assumptions than most current methods. Due to spatial-temporal trade-offs in the time domain, rupture velocity can bias the estimation when it is considered constant. Our approach does not prescribe the rupture velocity and slip rate functions. The model is also over-parameterize to avoid bias from too few unknowns. By dividing the fault plane into subfault patches, slip rate spectra and recorded spectra are formulated into a linear relationship. To provide good spatial resolution (~2 km), slip rate spectra are fit up to 3 Hz. Our objective function and constraints are convex, thus the global minimum can be found by convex optimization, which assures our solution is always unique. Physically plausible regularization constraints are used to stabilize the inversion and suppress the errors introduced by a simplified seismic velocity structure. Based on a Green's function sensitivity analysis, the model is also weighted during inversion to overcome spatially uneven resolution due to limited data coverage. After obtaining the spectrum for each fault patch, results are inverse Fourier transformed into the time domain. To demonstrate our approach, we analyze the well-studied 2004 Parkfield earthquake and compare our results to previous slip models and dynamic simulation results. Ultimately, we hope to achieve an improved understanding of the resolution limits and uncertainties in kinematic source inversions.

Fan, W.; Shearer, P. M.; Gerstoft, P.

2013-12-01

365

The effects of site response on source parameters deduced for the 1980 Long Valley, California earthquake sequence  

NASA Astrophysics Data System (ADS)

Data taken from the University of Nevada (UNR) array of surface-located wideband, digital, displacement seismographs placed over the 1980 Long Valley earthquake sequence show very strong site effects, which control spectral parameters and hence inferred source parameters, up to ML 5.0. Observations from 4,000 seismograms show that differences in site effects can lead to inferred seismic moments at least a factor of two lower than previously reported. Observed S-wave spectral corner frequencies show upper-bound cutoffs which are widely disparate at different sites (e.g., 15 Hz at MG1 and 6 Hz at WT1), thus fmax is quite variable by site. This high- frequency cutoff, clearly a site effect at WT1, could be misinterpreted as an apparent departure from source similarity for seismic moments below 1021 dyn-cm. Estimates of seismic moment and source duration from the UNR ‘rock’ sites may be more accurate than those previously published, both because the UNR instrumentation has greater resolution at longer periods (0.1 to 1.0 Hz) and because of less near-site signal distortion at high frequencies.

Peppin, William A.

1991-10-01

366

Applying time-reverse-imaging techniques to locate individual low-frequency earthquakes on the San Andreas fault near Cholame, California  

NASA Astrophysics Data System (ADS)

Observations of non-volcanic tremor have become ubiquitous in recent years. In spite of the abundance of observations, locating tremor remains a difficult task because of the lack of distinctive phase arrivals. Here we use time-reverse-imaging techniques that do not require identifying phase arrivals to locate individual low-frequency-earthquakes (LFEs) within tremor episodes on the San Andreas fault near Cholame, California. Time windows of 1.5-second duration containing LFEs are selected from continuously recorded waveforms of the local seismic network filtered between 1-5 Hz. We propagate the time-reversed seismic signal back through the subsurface using a staggered-grid finite-difference code. Assuming all rebroadcasted waveforms result from similar wave fields at the source origin, we search for wave field coherence in time and space to obtain the source location and origin time where the constructive interference is a maximum. We use an interpolated velocity model with a grid spacing of 100 m and a 5 ms time step to calculate the relative curl field energy amplitudes for each rebroadcasted seismogram every 50 ms for each grid point in the model. Finally, we perform a grid search for coherency in the curl field using a sliding time window, and taking the absolute value of the correlation coefficient to account for differences in radiation pattern. The highest median cross-correlation coefficient value over at a given grid point indicates the source location for the rebroadcasted event. Horizontal location errors based on the spatial extent of the highest 10% cross-correlation coefficient are on the order of 4 km, and vertical errors on the order of 3 km. Furthermore, a test of the method using earthquake data shows that the method produces an identical hypocentral location (within errors) as that obtained by standard ray-tracing methods. We also compare the event locations to a LFE catalog that locates the LFEs from stacked waveforms of repeated LFEs identified by cross-correlation techniques [Shelly and Hardebeck, 2010]. The LFE catalog uses stacks of at least several hundred templates to identify phase arrivals used to estimate the location. We find epicentral locations for individual LFEs based on the time-reverse-imaging technique are within ~4 km relative to the LFE catalog [Shelly and Hardebeck, 2010]. LFEs locate between 15-25 km depth, and have similar focal depths found in previous studies of the region. Overall, the method can provide robust locations of individual LFEs without identifying and stacking hundreds of LFE templates; the locations are also more accurate than envelope location methods, which have errors on the order of tens of km [Horstmann et al., 2013].

Horstmann, T.; Harrington, R. M.; Cochran, E.; Shelly, D. R.

2013-12-01

367

The 1999 Hector Mine Earthquake, Southern California: Vector Near-Field Displacements from ERS InSAR  

NASA Technical Reports Server (NTRS)

Two components of fault slip are uniquely determined from two line-of-sight (LOS) radar interferograms by assuming that the fault-normal component of displacement is zero. We use this approach with ascending and descending interferograms from the ERS satellites to estimate surface slip along the Hector Mine earthquake rupture. The LOS displacement is determined by visually counting fringes to within 1 km of the outboard ruptures. These LOS estimates and uncertainties are then transformed into strike- and dip-slip estimates and uncertainties; the transformation is singular for a N-S oriented fault and optimal for an E-W oriented fault. In contrast to our previous strike-slip estimates, which were based only on a descending interferogram, we now find good agreement with the geological measurements, except at the ends of the rupture. The ascending interferogram reveals significant west-sidedown dip-slip (approximately 1.0 m) which reduces the strike-slip estimates by 1 to 2 m, especially along the northern half of the rupture. A spike in the strike-slip displacement of 6 m is observed in central part of the rupture. This large offset is confirmed by subpixel cross correlation of features in the before and after amplitude images. In addition to strike slip and dip slip, we identify uplift and subsidence along the fault, related to the restraining and releasing bends in the fault trace, respectively. Our main conclusion is that at least two look directions are required for accurate estimates of surface slip even along a pure strike-slip fault. Models and results based only on a single look direction could have major errors. Our new estimates of strike slip and dip slip along the rupture provide a boundary condition for dislocation modeling. A simple model, which has uniform slip to a depth of 12 km, shows good agreement with the observed ascending and descending interferograms.

Sandwell, David T.; Sichoix, Lydie; Smith, Bridget

2002-01-01

368

Probable Causes of the Abnormal Ridge Accompanying the 2013-2014 California Drought: ENSO Precursor and Anthropogenic Warming Footprint  

SciTech Connect

The 2013-14 California drought was accompanied by an anomalous high-amplitude ridge system. The anomalous ridge was investigated using reanalysis data and the Community Earth System Model (CESM). It was found that the ridge emerged from continual sources of Rossby wave energy in the western North Pacific starting in late summer, and subsequently intensified into winter. The ridge generated a surge of wave energy downwind and deepened further the trough over the northeast U.S., forming a dipole. The dipole and associated circulation pattern is not linked directly with either ENSO or Pacific Decadal Oscillation; instead it is correlated with a type of ENSO precursor. The connection between the dipole and ENSO precursor has become stronger since the 1970s, and this is attributed to increased GHG loading as simulated by the CESM. Therefore, there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013-14, the associated drought and its intensity.

Wang, S-Y (Simon); Hipps, Lawrence; Gillies, Robert R.; Yoon, Jin-Ho

2014-05-16

369

Written in Stone Earthquake Animations  

NSDL National Science Digital Library

This group of brief animations shows destructive phenomena related to earthquakes and provides some advice on mitigating their effects. The collection includes an animation of Rayleigh waves, showing the reverse elliptical motion that makes them especially damaging; a demonstration of the difference in wave propagation and amplitude between hard rock and unconsolidated sediment; and an animation showing the relationship between earthquake magnitude and fault movement on the San Andreas Fault. For homeowners, there are animations depicting an unsecured cripple wall and chimney failure, with suggestions for strengthening these components. There are also animations of fault movement that occurred during specific earthquakes, including the 1994 Northridge earthquake, the 1992 Landers earthquake, and the 1906 San Francisco earthquake. The animations were developed for the educational video "Written in Stone," a project funded by and developed for the California Seismic Safety Commission.

Jeff Sale, Edcenter S.

370

Space-time characteristics of earthquake sources in various tectonic environments  

Microsoft Academic Search

Earthquake hazards are difficult to accurately evaluate along slow plate boundaries and in plate interiors because the locations of recorded earthquakes appear to have a higher probability of earthquakes than locations where none have been recorded. In these regions, a non-uniform earthquake hazard is often assumed. Assuming that the hazard is uniform, earthquake simulations created synthetic earthquake records with an

Laura C. Swafford

2009-01-01

371

Portals for Real-Time Earthquake Data and Forecasting: Challenge and Promise (Invited)  

NASA Astrophysics Data System (ADS)

Earthquake forecasts have been computed by a variety of countries world-wide for over two decades. For the most part, forecasts have been computed for insurance, reinsurance and underwriters of catastrophe bonds. However, recent events clearly demonstrate that mitigating personal risk is becoming the responsibility of individual members of the public. Open access to a variety of web-based forecasts, tools, utilities and information is therefore required. Portals for data and forecasts present particular challenges, and require the development of both apps and the client/server architecture to deliver the basic information in real time. The basic forecast model we consider is the Natural Time Weibull (NTW) method (JBR et al., Phys. Rev. E, 86, 021106, 2012). This model uses small earthquakes (';seismicity-based models') to forecast the occurrence of large earthquakes, via data-mining algorithms combined with the ANSS earthquake catalog. This method computes large earthquake probabilities using the number of small earthquakes that have occurred in a region since the last large earthquake. Localizing these forecasts in space so that global forecasts can be computed in real time presents special algorithmic challenges, which we describe in this talk. Using 25 years of data from the ANSS California-Nevada catalog of earthquakes, we compute real-time global forecasts at a grid scale of 0.1o. We analyze and monitor the performance of these models using the standard tests, which include the Reliability/Attributes and Receiver Operating Characteristic (ROC) tests. It is clear from much of the analysis that data quality is a major limitation on the accurate computation of earthquake probabilities. We discuss the challenges of serving up these datasets over the web on web-based platforms such as those at www.quakesim.org , www.e-decider.org , and www.openhazards.com.

Rundle, J. B.; Holliday, J. R.; Graves, W. R.; Feltstykket, R.; Donnellan, A.; Glasscoe, M. T.

2013-12-01

372

Types of Faults in California  

NSDL National Science Digital Library

This educational movie made using SCEC-VDO shows the differences between strike-slip faults and thrust faults in southern California.The Southern California Earthquake Center's Virtual Display of Objects SCEC-VDO is 3D visualization software that allows users to display study and make movies of earthquakes as they occur globally. SCEC-VDO was developed by interns of SCEC Undergraduate Studies in Earthquake Information Technology UseIT under the supervision of Sue Perry and Tom Jordan.

Interns of SCEC Undergraduate Studies in Earthquake Information Technology UseIT under the supervision of Sue Perry and Tom Jordan.

373

A feasibility study of data assimilation in numerical simulations of earthquake fault systems  

NASA Astrophysics Data System (ADS)

Topologically realistic simulations of earthquake faults systems have been constructed to understand the physics of interacting earthquake fault systems. We focus on one of these models, a simulation called Virtual California, that represents a model for the strike-slip fault system in California. In weather forecasting, current and past observations are routinely extrapolated forward to forecast future weather. The question addressed in this paper is whether a similar application of numerical simulations can be used in earthquake forecasting. Present simulation models are discussed and their ability to successfully generate earthquake recurrence statistics is demonstrated. An important question relates to how paleoseismic data can be used to constrain simulations, and whether these constrained simulations provide improved forecasts of future earthquakes. Here, we show first results from a consideration of these issues using a method of "datascoring". The data are divided into "training intervals" and "testing intervals". In the training intervals, the time history of paleoseismic data are used to evaluate space-time windows of simulations. Earthquakes following high-scoring space-time windows in the simulations are then used as a basis for developing waiting time statistics and used to forecast data in the testing intervals. In our present method, we focus on the problem of determining the timing of future earthquakes having magnitude m > 7. Our preliminary conclusion is that the amount of paleoseismic data currently available does not as yet improve the waiting time statistics to a level significantly beyond a random (temporal) predictor. However, this conclusion is based on a set of studies that are not extensive, so further investigations may well reveal important new avenues. In particular, it may be that the true value of this approach lies in defining the probable spatial locations of future earthquakes, rather than their timing.

Van Aalsburg, Jordan; Grant, Lisa B.; Yakovlev, Gleb; Rundle, Paul. B.; Rundle, John B.; Turcotte, Donald L.; Donnellan, Andrea

2007-08-01

374

Simulations of seismic hazard for the Pacific Northwest of the United States from earthquakes associated with the Cascadia subduction zone  

USGS Publications Warehouse

We investigate the impact of different rupture and attenuation models for the Cascadia subduction zone by simulating seismic hazard models for the Pacific Northwest of the U.S. at 2% probability of exceedance in 50 years. We calculate the sensitivity of hazard (probabilistic ground motions) to the source parameters and the attenuation relations for both intraslab and interface earthquakes and present these in the framework of the standard USGS hazard model that includes crustal earthquakes. Our results indicate that allowing the deep intraslab earthquakes to occur anywhere along the subduction zone increases the peak ground acceleration hazard near Portland, Oregon by about 20%. Alternative attenuation relations for deep earthquakes can result in ground motions that differ by a factor of two. The hazard uncertainty for the plate interface and intraslab earthquakes is analyzed through a Monte-Carlo logic tree approach and indicates a seismic hazard exceeding 1 g (0.2 s spectral acceleration) consistent with the U.S. National Seismic Hazard Maps in western Washington, Oregon, and California and an overall coefficient of variation that ranges from 0.1 to 0.4. Sensitivity studies indicate that the paleoseismic chronology and the magnitude of great plate interface earthquakes contribute significantly to the hazard uncertainty estimates for this region. Paleoseismic data indicate that the mean earthquake recurrence interval for great earthquakes is about 500 years and that it has been 300 years since the last great earthquake. We calculate the probability of such a great earthquake along the Cascadia plate interface to be about 14% when considering a time-dependent model and about 10% when considering a time-independent Poisson model during the next 50-year interval.

Petersen, M.D.; Cramer, C.H.; Frankel, A.D.

2002-01-01

375

Rating the Size of Earthquakes  

NSDL National Science Digital Library

This report describes how the work of K. Wadati, Charles F. Richter, Harry O. Wood, and Beno Gutenberg resulted in a way of rating earthquakes in southern California according to an instrumental analysis of the amount of energy they released in the form of seismic waves. This work resulted in the first use of the term "magnitude" for describing the amount of energy released by an earthquake, and in the development of the now-famous Richter Scale for quantifying earthquake magnitudes. Topics include the original definition of Richter magnitude and a brief synopsis of how Richter used earthquake data from southern California to graphically represent trace amplitude and develop a table of values that could be used to calculate magnitudes.

376

Parkfield: Earthquake Prediction: A Brief History  

NSDL National Science Digital Library

This report describes recent efforts at earthquake prediction, focusing on the modern era beginning in the mid- to late 1970's. Topics include a history of prediction efforts, the measurement of physical parameters in areas where earthquakes occur, and the development of a model upon which predictions could be based. The efforts centered around Parkfield, California, whose well-known seismic history allowed the development of a 'characteristic Parkfield earthquake' model and led to a formal prediction that a moderate-size earthquake would occur at Parkfield between 1985 and 1993. However, the anticipated earthquake did not occur until September 2004.

377

Earthquake forecasting: Statistics and Information  

E-print Network

We present an axiomatic approach to earthquake forecasting in terms of multi-component random fields on a lattice. This approach provides a method for constructing point estimates and confidence intervals for conditional probabilities of strong earthquakes under conditions on the levels of precursors. Also, it provides an approach for setting multilevel alarm system and hypothesis testing for binary alarms. We use a method of comparison for different earthquake forecasts in terms of the increase of Shannon information. 'Forecasting' and 'prediction' of earthquakes are equivalent in this approach.

Gertsik, V; Krichevets, A

2013-01-01

378

Earthquake-dammed lakes in New Zealand  

SciTech Connect

Eleven small lakes were formed by landslides caused by the 1929 Buller earthquake; four others were formed by other historic earthquakes in New Zealand. At least nine other New Zealand lakes are also dammed by landslides and were probably formed by prehistoric earthquakes. When recognized by morphology, synchronous age, and areal distribution, earthquake-dammed lakes could provide an estimate of paleoseismicity for the past few hundred or thousand years.

Adams, J.

1981-05-01

379

Sand boils without earthquakes  

USGS Publications Warehouse

Sedimentary deformation caused by liquefaction has become a popular means for inferring prehistoric strong earthquakes. This report describes a new mechanism for generating such features in the absence of earthquakes. Sand boils and a 180-m-long sand dike formed in Fremont Valley, California, when sediment-laden surface runoff was intercepted along the upslope part of a 500-m-long preexisting ground crack, flowed subhorizonally in the crack, and then flowed upward in the downslope part of the crack where it discharged as sand boils on the land surface. If the sand boils and their feeder dike were stratigraphically preserved, they could be misinterpreted as evidence for earthquake-induced liquefaction. -Authors

Holzer, T.L.; Clark, M.M.

1993-01-01

380

Earthquake Engineering Online Archive: Cypress Street Viaduct  

NSDL National Science Digital Library

This photograph shows an aerial view of a collapsed portion of the Cypress Street Viaduct, an elevated portion of Interstate 880, in Oakland, California. The damage was caused by the Loma Prieta Earthquake of October 17, 1989.

381

75 FR 22872 - California Disaster # CA-00154  

Federal Register 2010, 2011, 2012, 2013

...Administrative declaration of a disaster for the State of California dated 04/21/2010. Incident: Northern Baja California Earthquake. Incident Period: 04/04/2010 and continuing. Effective Date: 04/21/2010. Physical Loan Application...

2010-04-30

382

Social vulnerability analysis of earthquake risk using HAZUS-MH losses from a M7.8 scenario earthquake on the San Andreas fault  

NASA Astrophysics Data System (ADS)

Natural hazards research indicates earthquake risk is not equitably distributed. Demographic differences are significant in determining the risks people encounter, whether and how they prepare for disasters, and how they fare when disasters occur. In this study, we analyze the distribution of economic and social losses in all 88 cities of Los Angeles County from the 2008 ShakeOut scenario earthquake. The ShakeOut scenario earthquake is a scientifically plausible M 7.8 scenario earthquake on the San Andreas fault that was developed and applied for regional earthquake preparedness planning and risk mitigation from a compilation of collaborative studies and findings by the 2007 Working Group on California Earthquake Probabilities (WGCEP). The scenario involved 1) developing a realistic scenario earthquake using the best available and most recent earthquake research findings, 2) estimation of physical damage, 3) estimation of social impact of the earthquake, and 4) identifying changes that will help to prevent a catastrophe due to an earthquake. Estimated losses from this scenario earthquake include 1,800 deaths and $213 billion dollars in economic losses. We use regression analysis to examine the relationship between potential city losses due to the ShakeOut scenario earthquake and the cities' demographic composition. The dependent variables are economic and social losses calculated in HAZUS-MH methodology for the scenario earthquake. The independent variables -median household income, tenure and race/ethnicity- have been identified as indicators of social vulnerability to natural disasters (Mileti, 1999; Cutter, 2006; Cutter & Finch, 2008). Preliminary Ordinary Least Squares (OLS) regression analysis of economic losses on race/ethnicity, income and tenure, indicates that cities with lower Hispanic population are associated with lower economic losses. Cities with higher Hispanic population are associated with higher economic losses, though this relationship is trending and not significant. Race/ethnicity as a whole is a significant predictor of economic losses. While income by itself is not a predictor of economic losses, when adjusting for tenure and race/ethnicity, income becomes a significant predictor of economic losses. Cities with higher low-income population are associated with higher economic losses. Cities with higher renter occupied units are associated with lower economic losses. Finally, we find that income is a greater predictor of economic losses than being Hispanic. Preliminary Negative Binomial Regression analysis of race/ethnicity, income, and tenure to casualties indicates that cities with proportionally greater Hispanics and renters are associated with higher casualties. Cities with higher income are associated with fewer casualties.

Noriega, G. R.; Grant Ludwig, L.

2010-12-01

383

Savage Earth: The Restless Planet - Earthquakes  

NSDL National Science Digital Library

This article, entitled Earth: All Stressed Out, dicusses the reasons for crustal movement, the different types of faults and seismic waves, and an explanation of how the damage is caused. The article includes several animations that support the explanations, plus a video taken during a destructive California earthquake. There are also three sidebars that support the article. They are Learning from Earthquakes, Quake Prediction, and Build Smart. A companion animation illustrates how earthquake waves travel around and through the Earth.

384

Implementation of Real-Time Testing of Earthquake Early Warning Algorithms: Using the California Integrated Seismic Network (CISN) Infrastructure as a Test Bed for the P Amplitude and Period Monitor for a Single Station  

NASA Astrophysics Data System (ADS)

A necessary first step toward the goal of implementing proof-of-concept projects for earthquake early warning (EEW) is the real-time testing of the seismological algorithms. To provide the most appropriate environment, the CISN has designed and implemented a platform for such testing. We are testing the amplitude (Pd) and period (Tau-c) monitor developed for providing on-site earthquake early warning (EEW) using data from a single seismic station. We have designed and implemented a framework generator that can automatically generate code for waveform- processing systems. The framework generator is based on Code Worker software www.codeworker.org, which provides APIs and a scripting language to build parsers and template processing engines. Higher-level description of the waveform processing system is required to generate the waveform-processing framework. We have implemented Domain Specific Language DSL to provide description of the waveform-processing framework. The framework generator allows the developer to focus more on the waveform processing algorithms and frees him/her from repetitive and tedious coding tasks. It also has an automatic gap detector, transparent buffer management, and built in thread management. We have implemented the waveform-processing framework to process real-time waveforms coming from the dataloggers deployed throughout southern California by the Southern California Seismic Network. The system also has the capability of processing data from archived events to facilitate off-line testing. An application feeds data from MiniSEED packets into the Wave Data Area (WDA). The system that grabs the data from the WDA processes each real-time data stream independently. To verify results, sac files are generated at each processing step. Currently, we are processing broadband data streams from 160 stations and determining Pd and Tau-c as local earthquakes occur in southern California. We present the results from this testing and compare the detection capability of the EEW algorithm with the routine real-time processing of the Southern California Seismic Network.

Solanki, K.; Hauksson, E.; Kanamori, H.; Friberg, P.; Wu, Y.

2006-12-01

385

THE LAW AND POLICY OF EARTHQUAKE HAZARD IN THE CENTRAL UNITED STATES  

E-print Network

1 THE LAW AND POLICY OF EARTHQUAKE HAZARD IN THE CENTRAL UNITED STATES Thomas B. Ginsburg Timothy D .................................................................................................................. 1 II. EARTHQUAKE RISK IN THE MIDWEST.............................................................. 6 C. Probability of Future Damaging Earthquakes

386

The Road to Total Earthquake Safety  

Microsoft Academic Search

Cinna Lomnitz is possibly the most distinguished earthquake seismologist in all of Central and South America. Among many other credentials, Lomnitz has personally experienced the shaking and devastation that accompanied no fewer than five major earthquakes---Chile, 1939; Kern County, California, 1952; Chile, 1960; Caracas,Venezuela, 1967; and Mexico City, 1985. Thus he clearly has much to teach someone like myself, who

Cliff Frohlich

1999-01-01