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Sample records for california earthquake sequence

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

    PubMed

    Bakun, W H; McEvilly, T V

    1979-09-28

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

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

    USGS Publications Warehouse

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

    1997-01-01

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

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

    SciTech Connect

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

    1982-06-10

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

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

    SciTech Connect

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

    1989-02-01

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

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

    USGS Publications Warehouse

    Stein, R.S.; Lisowski, M.

    1983-01-01

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

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

    USGS Publications Warehouse

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

    1996-01-01

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

  7. Earthquake education in California

    USGS Publications Warehouse

    MacCabe, M. P.

    1980-01-01

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

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

    SciTech Connect

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

    2007-07-09

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

  9. Forecasting southern california earthquakes.

    PubMed

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

    1982-09-17

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

  10. California earthquake history

    USGS Publications Warehouse

    Toppozada, T.; Branum, D.

    2004-01-01

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

  12. Active Crustal Deformation in the Area of San Carlos, Baja California Sur, Mexico as Shown by Data of Local Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Munguía, Luis; González-Escobar, Mario; Navarro, Miguel; Valdez, Tito; Mayer, Sergio; Aguirre, Alfredo; Wong, Victor; Luna, Manuel

    2015-12-01

    We analyzed earthquakes of sequences that occurred at different times near San Carlos, a town of approximately 5000 inhabitants. The seismic sequences happened during March-April 1989, October 2000-June 2001, and 5-15 February 2004 at about 200 km west of the Pacific-North America plate boundary. The strong shaking from initial earthquakes of the first two sequences prompted the installation of temporary seismic stations in the area. With data recorded by these stations, we found an earthquake distribution that is consistent with the northwest segment of the Santa Margarita fault. Both the focal depth, that seemed to increase in E-NE direction, and a composite fault-plane solution, obtained from polarity data of the small earthquakes, were also consistent with the main characteristics of that fault. We also found that our normal-faulting mechanism (east side down) was quite similar to centroid moment tensor solutions for earthquakes with M w 5.4 and 5.3 that occurred in the area in February 2004. It is likely, then, that these larger earthquakes also occurred along the Santa Margarita Fault. To get some insight into the regional stress pattern, we compared the above mechanisms with mechanisms reported for other earthquakes of the Pacific margin of Baja California Sur and the Gulf of California regions. We observed that focal mechanisms of the two regions have T axes of stress that plunge sub horizontally in E-NE average direction. The corresponding P axes have N-NW average trend, but for the Pacific earthquakes these axes plunge at angles that are ~35° larger than those for the Gulf earthquakes. These more vertically inclined P axes of compressive stress mean substantial oblique fault motions. The mixture of oblique and strike-slip components of fault motions, as the focal mechanisms show, confirms a transtensional stress regime for the region. Before this research, we knew little about the seismicity and styles of faulting in the area. Now we know that

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

    PubMed

    Jaumé, S C; Sykes, L R

    1992-11-20

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

  14. Virtual California: studying earthquakes through simulation

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  15. SCEC Earthquake Simulator Comparison Results for California

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  16. Stress Drops for Potentially Induced Earthquake Sequences

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Stress drop, the difference between shear stress acting across a fault before and after an earthquake, is a fundamental parameter of the earthquake source process and the generation of strong ground motions. Higher stress drops usually lead to more high-frequency ground motions. Hough [2014 and 2015] observed low intensities in "Did You Feel It?" data for injection-induced earthquakes, and interpreted them to be a result of low stress drops. It is also possible that the low recorded intensities could be a result of propagation effects. Atkinson et al. [2015] show that the shallow depth of injection-induced earthquakes can lead to a lack of high-frequency ground motion as well. We apply the spectral ratio method of Imanishi and Ellsworth [2006] to analyze stress drops of injection-induced earthquakes, using smaller earthquakes with similar waveforms as empirical Green's functions (eGfs). Both the effects of path and linear site response should be cancelled out through the spectral ratio analysis. We apply this technique to the Guy-Greenbrier earthquake sequence in central Arkansas. The earthquakes migrated along the Guy-Greenbrier Fault while nearby injection wells were operating in 2010-2011. Huang and Beroza [GRL, 2015] improved the magnitude of completeness to about -1 using template matching and found that the earthquakes deviated from Gutenberg-Richter statistics during the operation of nearby injection wells. We identify 49 clusters of highly similar events in the Huang and Beroza [2015] catalog and calculate stress drops using the source model described in Imanishi and Ellsworth [2006]. Our results suggest that stress drops of the Guy-Greenbrier sequence are similar to tectonic earthquakes at Parkfield, California (the attached figure). We will also present stress drop analysis of other suspected induced earthquake sequences using the same method.

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

    SciTech Connect

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

    1996-12-31

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

  18. Description of earthquake sequences using complex network theory: the cases of Italy (L'Aquila, 2009) and Southern California (Baja, 2010)

    NASA Astrophysics Data System (ADS)

    Daskalaki, E.; Papadopoulos, G. A.; Minadakis, G.; Spiliotis, K.; Siettos, C.

    2013-12-01

    Complex networks pertain to the structure of many real-world systems influencing their dynamics. Earthquakes are a highly complex natural process that develops in the space-time-size domains given that the state of the seismogenic layer of the Earth is characterized by self-organized criticality. Over the last years, complex network theory was tested as a tool to quantify the topological characteristics of seismic activity aiming to investigate possible correlation patterns between earthquakes. With the aid of complex network theory, we have analyzed foreshock and aftershock sequences associated with the mainshocks of L'Aquila (Italy), 6th April 2009, Mw=6.3, and of Baja (Southern California) 4th April 2010, Mw=7.2. After testing the catalogues for data completeness on the basis of the magnitude-frequency relationship, we selected magnitude cut-off of 1.3 and 1.0, respectively. We constructed the underlying network that describes the evolution of the two sequences in space and extracted the statistical properties of the underlying topology resulting in characteristic scale-free and small-world structures. We found that the corresponding earthquake networks form a scale-free degree distribution and we computed their basic statistical measures, such as the Average Clustering Coefficient, Mean Path Length and Entropy. Taking into account a spatio-temporal sensitivity analysis, we found that the statistical measures of the two networks change considerably before and after the two main shocks, thus underlying the space-time clustering of the sequences. Our findings are in agreement with the ones obtained by using well established classical methods of statistical seismology. Thus, we believe that the proposed approach has the potential to serve as a supplementary or stand-alone methodology towards the better assessment of seismicity clusters

  19. The October 17, 1989, Loma Prieta, California, earthquake and its aftershocks: Geometry of the sequence from high-resolution locations

    SciTech Connect

    Dietz, L.D.; Ellsworth, W.L. )

    1990-08-01

    Hypocenters of the Loma Prieta sequence form a dipping zone that rises from the mainshock hypocenter and is parallel to the mainshock nodal plane. Most aftershocks cluster around the perimeter of the zone, surrounding a relatively aseismic center which approximates the region of mainshock rupture. At its southeastern end, the dipping aftershock zone warps into a vertical surface that corresponds to the San Andreas fault. In the central and northwestern parts of the zone at depths above {approximately}10 km, the aftershocks define numerous disjoint fault structures. The large component of reverse-slip observed in this event agrees with a simple model for slip on a dipping plane within a compressional fault bend. The authors do not believe that the Loma Prieta earthquake occurred on the Sargent fault. However, they are unable to conclude whether it ruptured the principal plate boundary fault or a less frequently active fault.

  20. 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)

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

    1995-01-01

    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.

  1. The parkfield, california, earthquake prediction experiment.

    PubMed

    Bakun, W H; Lindh, A G

    1985-08-16

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

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

    USGS Publications Warehouse

    2007 Working Group on California Earthquake Probabilities

    2008-01-01

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

  4. The mass balance of earthquakes and earthquake sequences

    NASA Astrophysics Data System (ADS)

    Marc, O.; Hovius, N.; Meunier, P.

    2016-04-01

    Large, compressional earthquakes cause surface uplift as well as widespread mass wasting. Knowledge of their trade-off is fragmentary. Combining a seismologically consistent model of earthquake-triggered landsliding and an analytical solution of coseismic surface displacement, we assess how the mass balance of single earthquakes and earthquake sequences depends on fault size and other geophysical parameters. We find that intermediate size earthquakes (Mw 6-7.3) may cause more erosion than uplift, controlled primarily by seismic source depth and landscape steepness, and less so by fault dip and rake. Such earthquakes can limit topographic growth, but our model indicates that both smaller and larger earthquakes (Mw < 6, Mw > 7.3) systematically cause mountain building. Earthquake sequences with a Gutenberg-Richter distribution have a greater tendency to lead to predominant erosion, than repeating earthquakes of the same magnitude, unless a fault can produce earthquakes with Mw > 8 or more.

  5. California earthquakes: why only shallow focus?

    PubMed

    Brace, W F; Byerlee, J D

    1970-06-26

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

  6. Migration of historical earthquakes in California

    USGS Publications Warehouse

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

    1988-01-01

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

  7. Building the Southern California Earthquake Center

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    USGS Publications Warehouse

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

    1973-01-01

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

  9. Infrasonic observations of the Northridge, California, earthquake

    SciTech Connect

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

    1994-09-01

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

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

    USGS Publications Warehouse

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

    1973-01-01

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

  11. Prospective Tests of Southern California Earthquake Forecasts

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  13. Hotspots, Lifelines, and the Safrr Haywired Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Ratliff, J. L.; Porter, K.

    2014-12-01

    Though California has experienced many large earthquakes (San Francisco, 1906; Loma Prieta, 1989; Northridge, 1994), the San Francisco Bay Area has not had a damaging earthquake for 25 years. Earthquake risk and surging reliance on smartphones and the Internet to handle everyday tasks raise the question: is an increasingly technology-reliant Bay Area prepared for potential infrastructure impacts caused by a major earthquake? How will a major earthquake on the Hayward Fault affect lifelines (roads, power, water, communication, etc.)? The U.S. Geological Survey Science Application for Risk Reduction (SAFRR) program's Haywired disaster scenario, a hypothetical two-year earthquake sequence triggered by a M7.05 mainshock on the Hayward Fault, addresses these and other questions. We explore four geographic aspects of lifeline damage from earthquakes: (1) geographic lifeline concentrations, (2) areas where lifelines pass through high shaking or potential ground-failure zones, (3) areas with diminished lifeline service demand due to severe building damage, and (4) areas with increased lifeline service demand due to displaced residents and businesses. Potential mainshock lifeline vulnerability and spatial demand changes will be discerned by superimposing earthquake shaking, liquefaction probability, and landslide probability damage thresholds with lifeline concentrations and with large-capacity shelters. Intersecting high hazard levels and lifeline clusters represent potential lifeline susceptibility hotspots. We will also analyze possible temporal vulnerability and demand changes using an aftershock shaking threshold. The results of this analysis will inform regional lifeline resilience initiatives and response and recovery planning, as well as reveal potential redundancies and weaknesses for Bay Area lifelines. Identified spatial and temporal hotspots can provide stakeholders with a reference for possible systemic vulnerability resulting from an earthquake sequence.

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

    PubMed

    Silver, P G; Valette-Silver, N J

    1992-09-01

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

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

    USGS Publications Warehouse

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

    2012-01-01

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

  17. Rupture directivity of moderate earthquakes in northern California

    USGS Publications Warehouse

    Seekins, Linda C.; Boatwright, John

    2010-01-01

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

  18. A slow earthquake sequence on the San Andreas fault

    USGS Publications Warehouse

    Linde, A.T.; Gladwin, M.T.; Johnston, M.J.S.; Gwyther, R.L.; Bilham, R.G.

    1996-01-01

    EARTHQUAKES typically release stored strain energy on timescales of the order of seconds, limited by the velocity of sound in rock. Over the past 20 years, observations and laboratory experiments have indicated that capture can also occur more slowly, with durations up to hours. Such events may be important in earthquake nucleation and in accounting for the excess of plate convergence over seismic slip in subduction zones. The detection of events with larger timescales requires near-field deformation measurements. In December 1992, two borehole strainmeters close to the San Andreas fault in California recorded a slow strain event of about a week in duration, and we show here that the strain changes were produced by a slow earthquake sequence (equivalent magnitude 4.8) with complexity similar to that of regular earthquakes. The largest earthquakes associated with these slow events were small (local magnitude 3.7) and contributed negligible strain release. The importance of slow earthquakes in the seismogenic process remains an open question, but these observations extend the observed timescale for slow events by two orders of magnitude.

  19. A slow earthquake sequence on the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Linde, Alan T.; Gladwin, Michael T.; Johnston, Malcolm J. S.; Gwyther, Ross L.; Bilham, Roger G.

    1996-09-01

    EARTHQUAKES typically release stored strain energy on timescales of the order of seconds, limited by the velocity of sound in rock. Over the past 20 years, observations1-13 and laboratory experiments14 have indicated that rupture can also occur more slowly, with durations up to hours. Such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones. The detection of events with larger timescales requires near-field deformation measurements. In December 1992, two borehole strainmeters close to the San Andreas fault in California recorded a slow strain event of about a week in duration, and we show here that the strain changes were produced by a slow earthquake sequence (equivalent magnitude 4.8) with complexity similar to that of regular earthquakes. The largest earthquakes associated with these slow events were small (local magnitude 3.7) and contributed negligible strain release. The importance of slow earthquakes in the seismogenic process remains an open question, but these observations extend the observed timescale for slow events by two orders of magnitude.

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

    SciTech Connect

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

    1997-12-31

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

  1. The magnitude distribution of declustered earthquakes in Southern California

    PubMed Central

    Knopoff, Leon

    2000-01-01

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

  2. Identification and Characterization of Earthquake Swarms in Southern California

    NASA Astrophysics Data System (ADS)

    Shearer, P. M.; Zhang, Q.

    2015-12-01

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

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

    USGS Publications Warehouse

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

    2009-01-01

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

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

    PubMed Central

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  6. Earthquake Apparent Stress Scaling for the 1999 Hector Mine Sequence

    NASA Astrophysics Data System (ADS)

    Walter, W. R.; Mayeda, K.

    2003-12-01

    There is currently a disagreement within the geophysical community on the way earthquake energy scales with magnitude. One set of studies finds evidence that energy release per seismic moment (apparent stress) is constant (e.g. Choy and Boatwright, 1995; McGarr, 1999; Ide and Beroza, 2001). Other studies find the apparent stress increases with magnitude (e.g. Kanamori et al., 1993; Abercrombie, 1995; Mayeda and Walter, 1996; Izutani and Kanamori, 2001). The resolution of this issue is complicated by the difficulty of accurately accounting for attenuation, radiation inhomogeneities, bandwidth and determining the seismic energy radiated by earthquakes over a wide range of event sizes in a consistent manner. We try to improve upon earlier results by using consistent techniques over common paths for a wide range of sizes and seismic phases. We have examined about 130 earthquakes from the Hector Mine earthquake sequence in Southern California. These earthquakes range in size from the October 16,1999 Mw=7.1 mainshock down to ML=3.0 aftershocks into 2000. The mainshock has unclipped Pg and Lg phases at a number of high quality regional stations (e.g. CMB, ELK, TUC) where we can use the common path to examine apparent stress scaling relations directly. We are careful to avoid any event selection bias that would be related to apparent stress values. We fix each stations path correction using the independent moment and energy estimates for the mainshock. We then use those corrections to determine the seismic energy for each event based on regional Lg spectra. We use a modeling technique (MDAC) based on a modified Brune (1970) spectral shape but without any assumptions of corner-frequency scaling (Walter and Taylor, 2002). We perform similar analysis using the Pg spectra. We find the energy estimates for the same events are consistent for Lg estimates, Pg estimates and the estimates using the independent regional coda envelope technique (Mayeda and Walter, 1996; Mayeda et al

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Shedlock, Kaye M.

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  11. Historic Ground Failures in Northern California Triggered by Earthquakes

    USGS Publications Warehouse

    Youd, T. Leslie; Hoose, Seena N.

    1978-01-01

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

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

    USGS Publications Warehouse

    Kilb, Debi; Gomberg, J.

    1999-01-01

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

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

    PubMed

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

    1978-09-01

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

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

    USGS Publications Warehouse

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

    1978-01-01

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

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

    USGS Publications Warehouse

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

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1989-04-01

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

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

    USGS Publications Warehouse

    Mori, J.; Abercrombie, R.E.

    1997-01-01

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

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

    USGS Publications Warehouse

    Stuart, W.D.

    1985-01-01

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

  19. Search for seismic forerunners to earthquakes in central California

    USGS Publications Warehouse

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

    1977-01-01

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

  20. Crustal deformation in great California earthquake cycles

    NASA Technical Reports Server (NTRS)

    Li, Victor C.; Rice, James R.

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    USGS Publications Warehouse

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

    1996-01-01

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

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

    USGS Publications Warehouse

    Hough, S.E.; Kanamori, H.

    2002-01-01

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

  4. Crustal deformation in Great California Earthquake cycles

    NASA Technical Reports Server (NTRS)

    Li, Victor C.; Rice, James R.

    1987-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    USGS Publications Warehouse

    Oppenheimer, David H.; Eaton, Jerry P.

    1984-01-01

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

  7. Tidal stress triggering of earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Bucholc, Magda; Steacy, Sandy

    2016-05-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    PubMed

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

    1989-04-01

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

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

    USGS Publications Warehouse

    Rubinstein, Justin L.

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Dengler, L.

    2006-12-01

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

  12. Accessing Data From the Southern California Earthquake Data Center

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

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

    SciTech Connect

    Johnson, A.M.; Johnson, N.A.; Johnson, K.M.; Wei, W.; Fleming, R.W.; Cruikshank, K.M.; Martosudarmo, S.Y.

    1997-12-31

    The June 28, 1992, M{sub s} 7.5 earthquake at Landers, California, which occurred about 10 km north of the community of Yucca Valley, California, produced spectacular ground rupturing more than 80 km in length (Hough and others, 1993). The ground rupturing, which was dominated by right-lateral shearing, extended along at least four distinct faults arranged broadly en echelon. The faults were connected through wide transfer zones by stepovers, consisting of right-lateral fault zones and tension cracks. The Landers earthquakes occurred in the desert of southeastern California, where details of ruptures were well preserved, and patterns of rupturing were generally unaffected by urbanization. The structures were varied and well-displayed and, because the differential displacements were so large, spectacular. The scarcity of vegetation, the aridity of the area, the compactness of the alluvium and bedrock, and the relative isotropy and brittleness of surficial materials collaborated to provide a marvelous visual record of the character of the deformation zones. The authors present a series of analecta -- that is, verbal clips or snippets -- dealing with a variety of structures, including belts of shear zones, segmentation of ruptures, rotating fault block, en echelon fault zones, releasing duplex structures, spines, and ramps. All of these structures are documented with detailed maps in text figures or in plates (in pocket). The purpose is to describe the structures and to present an understanding of the mechanics of their formation. Hence, most descriptions focus on structures where the authors have information on differential displacements as well as spatial data on the position and orientation of fractures.

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

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

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

    SciTech Connect

    Rundle, J.B.

    1988-06-10

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

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

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Abdel-Gawad, M.; Silverstein, J.

    1973-01-01

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

  19. Earthquake!

    ERIC Educational Resources Information Center

    Hernandez, Hildo

    2000-01-01

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

  20. Fluid injection triggering of 2011 earthquake sequence in Oklahoma

    NASA Astrophysics Data System (ADS)

    Keranen, K. M.; Savage, H. M.; Abers, G. A.; Cochran, E. S.

    2012-12-01

    Significant earthquakes are increasingly occurring within the United States midcontinent, with nine having moment-magnitude (Mw) ≥4.0 and five with Mw≥5.0 in 2011 alone. In parallel, wastewater injection into deep sedimentary formations has increased as unconventional oil and gas resources are developed. Injected fluids may lower normal stress on existing fault planes, and the correlation between injection wells and earthquake locations led to speculation that many 2011 earthquakes were triggered by injection. The largest earthquake potentially related to injection (Mw5.7) struck in November 2011 in central Oklahoma. Here we use aftershocks to document the fault patterns responsible for the M5.7 earthquake and a prolific sequence of related events, and use the timing and spatial correlation of the earthquakes with injection wells and subsurface structures to show that the earthquakes were likely triggered by fluid injection. The aftershock sequence details rupture along three distinct fault planes, the first of which reaches within 250 meters of active injection wells and within 1 km of the surface. This earthquake sequence began where fluids are injected at low pressure into a depleted oil reservoir bound by faults that effectively seal fluid flow. Injection into sealed compartments allows reservoir pressure to increase gradually over time, suggesting that reservoir volume, in this case, controls the triggering timescale. This process allows multi-year lags between the commencement of fluid injection and triggered earthquakes.

  1. Remote triggering of deep earthquakes in the 2002 Tonga sequences.

    PubMed

    Tibi, Rigobert; Wiens, Douglas A; Inoue, Hiroshi

    2003-08-21

    It is well established that an earthquake in the Earth's crust can trigger subsequent earthquakes, but such triggering has not been documented for deeper earthquakes. Models for shallow fault interactions suggest that static (permanent) stress changes can trigger nearby earthquakes, within a few fault lengths from the causative earthquake, whereas dynamic (transient) stresses carried by seismic waves may trigger earthquakes both nearby and at remote distances. Here we present a detailed analysis of the 19 August 2002 Tonga deep earthquake sequences and show evidence for both static and dynamic triggering. Seven minutes after a magnitude 7.6 earthquake occurred at a depth of 598 km, a magnitude 7.7 earthquake (664 km depth) occurred 300 km away, in a previously aseismic region. We found that nearby aftershocks of the first mainshock are preferentially located in regions where static stresses are predicted to have been enhanced by the mainshock. But the second mainshock and other triggered events are located at larger distances where static stress increases should be negligible, thus suggesting dynamic triggering. The origin times of the triggered events do not correspond to arrival times of the main seismic waves from the mainshocks and the dynamically triggered earthquakes frequently occur in aseismic regions below or adjacent to the seismic zone. We propose that these events are triggered by transient effects in regions near criticality, but where earthquakes have difficulty nucleating without external influences. PMID:12931183

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

    USGS Publications Warehouse

    Hough, Susan E.; Martin, Stacey

    2015-01-01

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

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

    USGS Publications Warehouse

    Reimer, G.M.

    1981-01-01

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

  4. The Virtual Quake earthquake simulator: a simulation-based forecast of the El Mayor-Cucapah region and evidence of predictability in simulated earthquake sequences

    NASA Astrophysics Data System (ADS)

    Yoder, Mark R.; Schultz, Kasey W.; Heien, Eric M.; Rundle, John B.; Turcotte, Donald L.; Parker, Jay W.; Donnellan, Andrea

    2015-12-01

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

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

    USGS Publications Warehouse

    Hudnut, Ken; King, Nancy

    2001-01-01

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

  6. 1957 Gobi-Altay, Mongolia, earthquake as a prototype for southern California's most devastating earthquake

    USGS Publications Warehouse

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

    1996-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Verdecchia, A.; Carena, S.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    USGS Publications Warehouse

    Harp, Edwin L.; Jibson, Randall W.

    1995-01-01

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

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

    USGS Publications Warehouse

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

    1973-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  15. Retrospective Evaluation of Earthquake Forecasts during the 2010-12 Canterbury, New Zealand, Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Werner, M. J.; Marzocchi, W.; Taroni, M.; Zechar, J. D.; Gerstenberger, M.; Liukis, M.; Rhoades, D. A.; Cattania, C.; Christophersen, A.; Hainzl, S.; Helmstetter, A.; Jimenez, A.; Steacy, S.; Jordan, T. H.

    2014-12-01

    The M7.1 Darfield, New Zealand (NZ), earthquake triggered a complex earthquake cascade that provides a wealth of new scientific data to study earthquake triggering and the predictive skill of statistical and physics-based forecasting models. To this end, the Collaboratory for the Study of Earthquake Predictability (CSEP) is conducting a retrospective evaluation of over a dozen short-term forecasting models that were developed by groups in New Zealand, Europe and the US. The statistical model group includes variants of the Epidemic-Type Aftershock Sequence (ETAS) model, non-parametric kernel smoothing models, and the Short-Term Earthquake Probabilities (STEP) model. The physics-based model group includes variants of the Coulomb stress triggering hypothesis, which are embedded either in Dieterich's (1994) rate-state formulation or in statistical Omori-Utsu clustering formulations (hybrid models). The goals of the CSEP evaluation are to improve our understanding of the physical mechanisms governing earthquake triggering, to improve short-term earthquake forecasting models and time-dependent hazard assessment for the Canterbury area, and to understand the influence of poor-quality, real-time data on the skill of operational (real-time) forecasts. To assess the latter, we use the earthquake catalog data that the NZ CSEP Testing Center archived in near real-time during the earthquake sequence and compare the predictive skill of models using the archived data as input with the skill attained using the best available data today. We present results of the retrospective model comparison and discuss implications for operational earthquake forecasting.

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

    USGS Publications Warehouse

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

    2015-01-01

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

  17. Thermal infrared anomaly indicating unformed strong earthquake sequences

    NASA Astrophysics Data System (ADS)

    Yao, Qinglin; Qiang, Zuji

    2015-01-01

    By processing and analyzing many satellite remote sensing images in infrared channels, we found visual evidence indicating earthquake sequences. In a sequence, large earthquakes could migrate thousands of kilometers along a linear route from one land mass to another, and infrared anomalies also cover these land masses. The sequence has at least two types: (1) quakes alternately occurring at two ends of a belt, or (2) quakes progressively migrating along a far-flung route. The former can be foreshowed in a single infrared belt with a legible directed structure and higher brightness temperature; the latter can be identified in advance from the shift, veer, and deformation of more areas with a higher brightness temperature. The thermal infrared anomalies with a shorter duration are used to predict the quake-sequence evolving in a longer period. Two sorts of sequences can meet and form a more complex structure that can also be shown in advance by an anomalous infrared area. These studies on the seismic sequences will provide a potent means for analyzing earthquake-pregnant fields and estimating the location of unformed earthquake sequences.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  20. The 2011 Tohoku earthquake sequences detected by IMS hydroacoustic array

    NASA Astrophysics Data System (ADS)

    Yun, S.; Lee, W.

    2011-12-01

    A Mw 9.1 thrust-fault earthquake has been occurred in the Pacific coast of Tohoku, Japan, on March 11, 2011. It is the fourth largest earthquake ever recorded since modern seismographs installed, and hundreds of strong aftershocks (M > 5) have been accompanied. We applied a cross-correlation method to the continuous data recorded in the Hawaii hydroacoustic array operated by International Monitoring System (IMS), and calculated back-azimuths of T-waves generated by the earthquake sequences. The back-azimuth values of the major events show somewhat scattered pattern, which is a different feature from that of the Great Sumatra-Andaman Earthquake. This may imply that the rupture is not likely to propagate linearly through the thrust fault line. Several aftershocks, however, clearly show gradual back-azimuthal change toward North. These differences might be caused by complex and diverse source mechanisms of the earthquakes. Combining hydroacoustic data obtained by other IMS hydroacoustic stations, if available, we could resolve a better azimuthal change regarding the earthquake sequence.

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

    SciTech Connect

    Not Available

    1980-07-15

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

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

    USGS Publications Warehouse

    Stump, B.

    1980-01-01

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

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

    USGS Publications Warehouse

    Spall, H.

    1979-01-01

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

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

    ERIC Educational Resources Information Center

    California State Office of Emergency Services, Sacramento.

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

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

    PubMed

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

    1974-06-21

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

  6. The 2013 Crete (Hellenic Arc) Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Karakostas, V. G.; Papadimitriou, E. E.; Vallianatos, F.

    2014-12-01

    The western Hellenic Arc is a well known place of active interplate deformation, where the convergence motion vector is perpendicular to the subduction front. On 12 October 2013 this area was hit by a strong (Mw=6.7) earthquake, occurred on a thrust fault onto the coupled part of the overriding and descending plates, with the compression axis being oriented in the direction of plate convergence. This was the first strong (M>6.0) event to have occurred onto this segment of the descending slab, which has accommodated the largest (M8.3) known earthquake in the Mediterranean area, and to be recorded by the Hellenic Unified Seismological Network (HUSN) that has been considerably improved in the last five years. The first 2-days relocated seismicity shows activation of the upper part of the descending slab, downdip of the plate interface and forming a relatively narrow aftershock area on map view. The less densely visited by aftershocks area, where the main shock is also encompassed, is considered as the high-slip area along the downdip portion of the subducting plane. Dense concentration of the intraslab aftershocks are probably due to the increase of static stress generated by the main shock. A spectacular feature of the aftershock activity concerns the lateral extension of the slipped area, which appears very sharply defined. This provides evidence on localized coupling and aseismically creeping areas, explaining the low coupling ratio in the Hellenic Arc, as it derives from comparison between relative plate motion and seismic energy release. Elucidating the issue of how far the associated large-slip zone might be extended along the plate interface during the main rupture is crucial in assessing future earthquake hazards from subduction events in the study area. This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the "THALES Program: SEISMO FEAR HELLARC" project.

  7. Impact of the January-February 1980 earthquake sequence on various structures at the Lawrence Livermore National Laboratory

    SciTech Connect

    Murray, R.C.; Nelson, T.A.; Coats, D.W.; Ng, D.S.; Weaver, H.J.

    1981-02-04

    On January 24, 1980, California's Livermore Valley was rocked by a moderate earthquake that caused some damage to the Lawrence Livermore National Laboratory (LLNL). The earthquake, which measured 5.5 on the Richter scale and was centered about 20 km (12 mi) northwest of the Laboratory, produced estimated peak horizontal ground acceleration at LLNL of between 0.15 and 0.3 g. The earthquake was part of a sequence that included two sharp aftershocks (magnitudes 5.2 and 4.2) within 1.5 minutes of the initial event. A second earthquake (magnitude 5.8) struck on January 26, and several lesser earthquakes occurred during the next few weeks. This paper describes the damage impact of the January 24 earthquake, including: background information on LLNL, discussion of pre-earthquake seismic safety philosophy, and description of the impact of the January 24 earthquake, including a description of the seismic setting of the Laboratory, a discussion of the ground motion, and a summary of damage. This paper also describes a data gathering and reduction effort at LLNL in the aftermath of the January earthquakes.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Qiong; Shearer, Peter M.

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Qiong; Shearer, Peter M.

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1995-05-01

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Li, Q.; Liu, M.

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    USGS Publications Warehouse

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

    1974-01-01

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

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

    PubMed

    Johnston, M J; Mortensen, C E

    1974-12-13

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

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

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1990-01-01

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

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

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Meng, L.; Shi, B.

    2010-12-01

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

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    USGS Publications Warehouse

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

    1981-01-01

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

  4. The 2011 Hawthorne, Nevada, Earthquake Sequence; Shallow Normal Faulting

    NASA Astrophysics Data System (ADS)

    Smith, K. D.; Johnson, C.; Davies, J. A.; Agbaje, T.; Knezevic Antonijevic, S.; Kent, G.

    2011-12-01

    An energetic sequence of shallow earthquakes that began in early March 2011 in western Nevada, near the community of Hawthorne, has slowly decreased in intensity through mid-2011. To date about 1300 reviewed earthquake locations have been compiled; we have computed moment tensors for the larger earthquakes and have developed a set of high-precision locations for all reviewed events. The sequence to date has included over 50 earthquakes ML 3 and larger with the largest at Mw 4.6. Three 6-channel portable stations configured with broadband sensors and accelerometers were installed by April 20. Data from the portable instruments is telemetered through NSL's microwave backbone to Reno where it is integrated with regional network data for real-time notifications, ShakeMaps, and routine event analysis. The data is provided in real-time to NEIC, CISN and the IRIS DMC. The sequence is located in a remote area about 15-20 km southwest of Hawthorne in the footwall block of the Wassuk Range fault system. An initial concern was that the sequence might be associated with volcanic processes due to the proximity of late Quaternary volcanic flows; there have been no volcanic signatures observed in near source seismograms. An additional concern, as the sequence has proceeded, was a clear progression eastward toward the Wassuk Range front fault. The east dipping range bounding fault is capable of M 7+ events, and poses a significant hazard to the community of Hawthorne and local military facilities. The Hawthorne Army Depot is an ordinance storage facility and the nation's storage site for surplus mercury. The sequence is within what has been termed the 'Mina Deflection' of the Central Walker Lane Belt. Faulting along the Whiskey Flat section of the Wassuk front fault would be primarily down-to-the-east, with an E-W extension direction; moment tensors for the 2011 earthquake show a range of extension directions from E-W to NW-SE, suggesting a possible dextral component to the Wassuk

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

    NASA Astrophysics Data System (ADS)

    Parsons, Tom

    2008-03-01

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

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

    USGS Publications Warehouse

    Parsons, T.

    2008-01-01

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

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

    USGS Publications Warehouse

    Parsons, Tom

    2008-01-01

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

  8. Physically-based modelling of the competition between surface uplift and erosion caused by earthquakes and earthquake sequences.

    NASA Astrophysics Data System (ADS)

    Hovius, Niels; Marc, Odin; Meunier, Patrick

    2016-04-01

    Large earthquakes deform Earth's surface and drive topographic growth in the frontal zones of mountain belts. They also induce widespread mass wasting, reducing relief. Preliminary studies have proposed that above a critical magnitude earthquake would induce more erosion than uplift. Other parameters such as fault geometry or earthquake depth were not considered yet. A new seismologically consistent model of earthquake induced landsliding allow us to explore the importance of parameters such as earthquake depth and landscape steepness. We have compared these eroded volume prediction with co-seismic surface uplift computed with Okada's deformation theory. We found that the earthquake depth and landscape steepness to be the most important parameters compared to the fault geometry (dip and rake). In contrast with previous studies we found that largest earthquakes will always be constructive and that only intermediate size earthquake (Mw ~7) may be destructive. Moreover, with landscapes insufficiently steep or earthquake sources sufficiently deep earthquakes are predicted to be always constructive, whatever their magnitude. We have explored the long term topographic contribution of earthquake sequences, with a Gutenberg Richter distribution or with a repeating, characteristic earthquake magnitude. In these models, the seismogenic layer thickness, that sets the depth range over which the series of earthquakes will distribute, replaces the individual earthquake source depth.We found that in the case of Gutenberg-Richter behavior, relevant for the Himalayan collision for example, the mass balance could remain negative up to Mw~8 for earthquakes with a sub-optimal uplift contribution (e.g., transpressive or gently-dipping earthquakes). Our results indicate that earthquakes have probably a more ambivalent role in topographic building than previously anticipated, and suggest that some fault systems may not induce average topographic growth over their locked zone during a

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

    PubMed

    1990-01-19

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

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

    USGS Publications Warehouse

    Working Group on Northern California Earthquake Potential

    1996-01-01

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

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

    USGS Publications Warehouse

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

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

    USGS Publications Warehouse

    Gerstenberger, Matt; Wiemer, Stefan; Jones, Lucy

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. The 2007 Nazko, British Columbia, earthquake sequence: Injection of magma deep in the crust beneath the Anahim volcanic belt

    USGS Publications Warehouse

    Cassidy, J.F.; Balfour, N.; Hickson, C.; Kao, H.; White, R.; Caplan-Auerbach, J.; Mazzotti, S.; Rogers, Gary C.; Al-Khoubbi, I.; Bird, A.L.; Esteban, L.; Kelman, M.; Hutchinson, J.; McCormack, D.

    2011-01-01

    On 9 October 2007, an unusual sequence of earthquakes began in central British Columbia about 20 km west of the Nazko cone, the most recent (circa 7200 yr) volcanic center in the Anahim volcanic belt. Within 25 hr, eight earthquakes of magnitude 2.3-2.9 occurred in a region where no earthquakes had previously been recorded. During the next three weeks, more than 800 microearthquakes were located (and many more detected), most at a depth of 25-31 km and within a radius of about 5 km. After about two months, almost all activity ceased. The clear P- and S-wave arrivals indicated that these were high-frequency (volcanic-tectonic) earthquakes and the b value of 1.9 that we calculated is anomalous for crustal earthquakes but consistent with volcanic-related events. Analysis of receiver functions at a station immediately above the seismicity indicated a Moho near 30 km depth. Precise relocation of the seismicity using a double-difference method suggested a horizontal migration at the rate of about 0:5 km=d, with almost all events within the lowermost crust. Neither harmonic tremor nor long-period events were observed; however, some spasmodic bursts were recorded and determined to be colocated with the earthquake hypocenters. These observations are all very similar to a deep earthquake sequence recorded beneath Lake Tahoe, California, in 2003-2004. Based on these remarkable similarities, we interpret the Nazko sequence as an indication of an injection of magma into the lower crust beneath the Anahim volcanic belt. This magma injection fractures rock, producing high-frequency, volcanic-tectonic earthquakes and spasmodic bursts.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    USGS Publications Warehouse

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

    1992-01-01

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

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

    USGS Publications Warehouse

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

    1985-01-01

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

  19. Landslide distribution resulting from the 2015 Gorkha, Nepal earthquake sequence

    NASA Astrophysics Data System (ADS)

    Collins, B. D.; Jibson, R.

    2015-12-01

    Thousands of landslides (predominantly rock slides and rock falls) were triggered as a result of the 2015 Gorkha, Nepal earthquake sequence. Given the steep, high relief of the epicentral zones and the widely distributed population of Nepal in these regions, hundreds of fatalities occurred as a direct result of landsliding. Further, roads, hydroelectric plants, and other critical infrastructure were subjected to considerable secondary hazards including highly weakened slopes and inundation from lake impoundments that formed upslope of valley-blocking landslide dams. As part of a humanitarian and scientific mission to Nepal supported by the U.S. Agency for International Development, Office of Foreign Disaster Assistance, we conducted landslide assessments throughout earthquake-affected areas (report available at http://dx.doi.org/10.3133/ofr20151142) and, in the process, developed a sense for the overall landslide distribution resulting from the earthquakes. Whereas landslides were abundant near the major earthquake epicenters, few landslides were observed in many steep areas of the country where effects would normally have been expected. For example, although avalanches and ice and rock falls occurred near Mt. Everest, located approximately 220 km from the April 25 epicenter, we noted few landslides in a similar area of steep terrain located 40 km closer to the epicenter. Similarly, although we noted entire mountainsides covered by landslides within 20 km of the mainshock epicenter, we observed many other mountainsides within this same region lacking any indication of ground disturbance. Observations of shattered ridgetops with ridge parallel fractures at several locations indicate that topographically-amplified ground shaking occurred in some areas. This, along with the complex geology and the asymmetric directionality of rupture, could help explain the landslide distribution and thus where hazards are most likely from similar future earthquakes in central Nepal.

  20. Deformation of slopes damaged during the 2015 Nepal earthquake sequence

    NASA Astrophysics Data System (ADS)

    Rosser, N. J.; Brain, M.; Densmore, A.; Jordan, C.; Williams, J.; Kincey, M.; Oven, K.

    2015-12-01

    The 2015 Nepal Earthquake Sequence (EQS; the Gorkha EQ (eqG), Mw 7.8 [25/04/15]; the Kodari EQ (eqK), Mw 6.7 [26/05/15]; and Dolakha EQ (eqD), Mw 7.3 [12/05/15], plus associated aftershocks) triggered widespread landsliding, strongly evident in satellite imagery. In addition to the observed failures, pervasive ground cracking has been widely reported in Nepal. This is indicative of hillslope 'damage' (weakening) and, hence, the onset of shear surface development in as-yet unfailed slopes - a phenomenon previously observed in areas subjected to high-magnitude earthquake ground shaking and subsequent ongoing landsliding. Recent work on the efficacy of earthquakes in triggering landslides has proposed that the occurrence of failures is a function of damage accumulated in the slope. We present a unique field monitoring dataset on continuing slope deformation from hillslopes damaged during the 2015 Nepal EQS, in response to precipitation and continuing seismicity. Our study site is the Upper Bhote Koshi (UBK), with sites chosen from a chronology of landslide inventories captured from remotely sensed imagery since the Gorkha earthquake. Instruments were deployed during the monsoon on new and pre-existing landslides, and across cracked ground to monitoring precipitation inputs, slope-scale (micro-)seismicity, and slope displacements. Using our dataset, we draw preliminary conclusions on how the spatially-variable legacy of damage accumulated during high-magnitude earthquake-induced ground shaking events is manifest in patterns, rates and styles of post-seismic slope deformation.

  1. Dual megathrust slip behaviors of the 2014 Iquique earthquake sequence

    NASA Astrophysics Data System (ADS)

    Meng, Lingsen; Huang, Hui; Bürgmann, Roland; Ampuero, Jean Paul; Strader, Anne

    2015-02-01

    The transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes. A Mw 8.2 earthquake occurred on April 1st, 2014 in the Iquique seismic gap of northern Chile. This event was preceded by a long foreshock sequence including a 2-week-long migration of seismicity initiated by a Mw 6.7 earthquake. Repeating earthquakes were found among the foreshock sequence that migrated towards the mainshock hypocenter, suggesting a large-scale slow-slip event on the megathrust preceding the mainshock. The variations of the recurrence times of the repeating earthquakes highlight the diverse seismic and aseismic slip behaviors on different megathrust segments. The repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip, while repeaters that occurred both before and after the mainshock were in the area complementary to the mainshock rupture. The spatiotemporal distribution of the repeating earthquakes illustrates the essential role of propagating aseismic slip leading up to the mainshock and illuminates the distribution of postseismic afterslip. Various finite fault models indicate that the largest coseismic slip generally occurred down-dip from the foreshock activity and the mainshock hypocenter. Source imaging by teleseismic back-projection indicates an initial down-dip propagation stage followed by a rupture-expansion stage. In the first stage, the finite fault models show an emergent onset of moment rate at low frequency (< 0.1 Hz), while back-projection shows a steady increase of high frequency power (> 0.5 Hz). This indicates frequency-dependent manifestations of seismic radiation in the low-stress foreshock region. In the second stage, the rupture expands in rich bursts along the rim of a semi-elliptical region with episodes of re-ruptures, suggesting delayed failure of asperities. The high-frequency rupture remains within an

  2. Dual Megathrust Slip Behaviors of the 2014 Iquique Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Meng, L.; Huang, H.; Burgmann, R.; Ampuero, J. P.; Strader, A. E.

    2014-12-01

    The transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes. A M 8.2 earthquake occurred on April 1st, 2014 in the Iquique seismic gap of Northern Chile. This event was preceded by a 2-week-long foreshock sequence including a M 6.7 earthquake. Repeating earthquakes are found among the foreshock sequence that migrated towards the mainshock area, suggesting a large scale slow-slip event on the megathrust preceding the mainshock. The variations of the recurrence time of repeating earthquakes highlights the diverse seismic and aseismic slip behaviors on different megathrust segments. The repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip, while other repeaters occurred both before and after the mainshock in the area complementary to the mainshock rupture. The spatial and temporal distribution of the repeating earthquakes illustrate the essential role of propagating aseismic slip in leading up to the mainshock and aftershock activities. Various finite fault models indicate that the coseismic slip generally occurred down-dip from the foreshock activity and the mainshock hypocenter. Source imaging by teleseismic back-projection indicates an initial down-dip propagation stage followed by a rupture-expansion stage. In the first stage, the finite fault models show slow initiation with low amplitude moment rate at low frequency (< 0.1 Hz), while back-projection shows a steady initiation at high frequency (> 0.5 Hz). This indicates frequency-dependent manifestations of seismic radiation in the low-stress foreshock region. In the second stage, the high-frequency rupture remains within an area of low gravity anomaly, suggesting possible upper-crustal structures that promote high-frequency generation. Back-projection also shows an episode of reverse rupture propagation which suggests a delayed failure of asperities in

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    SciTech Connect

    Hough, Susan E.

    2008-07-08

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

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

    USGS Publications Warehouse

    Stein, Ross S.

    2008-01-01

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

  6. Seismic sequences, swarms, and large earthquakes in Italy

    NASA Astrophysics Data System (ADS)

    Amato, Alessandro; Piana Agostinetti, Nicola; Selvaggi, Giulio; Mele, Franco

    2016-04-01

    In recent years, particularly after the L'Aquila 2009 earthquake and the 2012 Emilia sequence, the issue of earthquake predictability has been at the center of the discussion in Italy, not only within the scientific community but also in the courtrooms and in the media. Among the noxious effects of the L'Aquila trial there was an increase of scaremongering and false alerts during earthquake sequences and swarms, culminated in a groundless one-night evacuation in northern Tuscany in 2013. We have analyzed the Italian seismicity of the last decades in order to determine the rate of seismic sequences and investigate some of their characters, including frequencies, min/max durations, maximum magnitudes, main shock timing, etc. Selecting only sequences with an equivalent magnitude of 3.5 or above, we find an average of 30 sequences/year. Although there is an extreme variability in the examined parameters, we could set some boundaries, useful to obtain some quantitative estimates of the ongoing activity. In addition, the historical catalogue is rich of complex sequences in which one main shock is followed, seconds, days or months later, by another event with similar or higher magnitude We also analysed the Italian CPT11 catalogue (Rovida et al., 2011) between 1950 and 2006 to highlight the foreshock-mainshock event couples that were suggested in previous studies to exist (e.g. six couples, Marzocchi and Zhuang, 2011). Moreover, to investigate the probability of having random foreshock-mainshock couples over the investigated period, we produced 1000 synthetic catalogues, randomly distributing in time the events occured in such period. Preliminary results indicate that: (1) all but one of the the so-called foreshock-mainshock pairs found in Marzocchi and Zhuang (2011) fall inside previously well-known and studied seismic sequences (Belice, Friuli and Umbria-Marche), meaning that suggested foreshocks are also aftershocks; and (2) due to the high-rate of the italian

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

    USGS Publications Warehouse

    Harris, Ruth A.

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Jones, L.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. The 2008 Mw 6.0 Wells, Nevada Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Smith, K.; Depolo, D.; Torrisi, J.; Edwards, N.; Biasi, G.; Slater, D.

    2008-12-01

    The Mw 6.0 February 21, 2008 (06:16 AM PDT) Wells, Nevada normal faulting earthquake occurred in Town Creek Flat about 8 km northeast of the small community of Wells. A preliminary set of about 1000 aftershock relocations clearly defines a 55-60 degree southeast dipping fault plane. The structure projects to the surface along the southern end of the Snake Range, although no surface offsets have been identified. The earthquake occurred east of the Ruby Mountains and Snake Range west dipping range front faults, possibly on a northern extension of an east dipping normal fault system on the eastern side of the East Humbolt Range. The depth of the mainshock is estimated to be 10.5 km with the aftershock sequence extending to about 15 km. Typical of moderate sized Basin and Range earthquakes, the early aftershock period included several earthquakes of M > 4 and these were felt strongly by the residents of Wells. From the preliminary relocations, the source radius of the mainshock is estimated to be about 4 km, resulting in an estimated displacement of 55 to 83 cm and static stress drop of 72 to 86 bars, depending on the seismic moment estimate used. Aftershock relocations suggest a radial rupture mechanism. Fortunately, the EarthScope USArray network was operating in Nevada at the time of the event and provided unique controls on the mainshock and early aftershock locations. The earthquake occurred in an area of relatively low seismic hazard and the only permanent seismograph in the region was the U.S. National Network broadband station east of the Ruby Mountains south of Wells. The University of Utah and University of Nevada deployed locally recorded strong motion instruments in the Wells area. Also, an 8 station IP telemetered strong motion network, jointly deployed by the U.S. Geological Survey and University of Nevada Reno, provided real-time data for quick high-quality aftershock relocations and ground motion estimates. In addition, the University of Utah

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

    USGS Publications Warehouse

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

    2004-01-01

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

  12. The chi-Chi earthquake sequence: active, out-of-sequence thrust faulting in taiwan

    PubMed

    Kao; Chen

    2000-06-30

    We combined precise focal depths and fault plane solutions of more than 40 events from the 20 September 1999 Chi-Chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central Taiwan is a moderately dipping (20 degrees to 30 degrees ) thrust fault away from the deformation front. A second, subparallel seismic zone lies about 15 kilometers below the main thrust. These seismic zones differ from previous models, indicating that both the basal decollement and relic normal faults are aseismic. PMID:10875915

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

    PubMed

    Gao; Silver; Linde; Sacks

    2000-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    USGS Publications Warehouse

    Reimer, G.M.

    1985-01-01

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

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

    PubMed

    Nadeau, Robert M; Guilhem, Aurélie

    2009-07-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  20. Searching for Unknown Earthquakes in the Guy-Greenbrier, Arkansas, Earthquake Sequence using Efficient Waveform Similarity Search

    NASA Astrophysics Data System (ADS)

    Yoon, C. E.; OReilly, O. J.; Bergen, K.; Huang, Y.; Beroza, G. C.

    2015-12-01

    Recent seismicity rate increases in the central United States have been attributed to injection of wastewater from oil and gas production. One example is the Guy-Greenbrier, Arkansas, earthquake sequence, which occurred from July 2010 through October 2011, and was potentially induced by fluid injection into nearby disposal wells (Horton, 2012). Although the Arkansas seismic network is sparse, a single 3-component station WHAR recorded continuous data before, during, and after this earthquake sequence at distances ranging from 2-9 km. Huang and Beroza (2015) used template matching to detect over 100 times the number of cataloged earthquakes by cross-correlating the continuous data with waveform templates based on known earthquakes to search for additional low-magnitude events. Because known waveform templates do not necessarily fully represent all seismic signals in the continuous data, small earthquakes from unknown sources could have escaped detection. We use a method called Fingerprint And Similarity Thresholding (FAST) to detect additional low-magnitude earthquakes that were missed by template matching. FAST enables fast, scalable search for earthquakes with similar waveforms without making prior assumptions about the seismic signal of interest. FAST, based on a data mining technique, first creates compact "fingerprints" of waveforms by extracting discriminative features, then uses locality-sensitive hashing to organize and efficiently search for similar fingerprints (and therefore similar earthquake waveforms) in a probabilistic manner. With FAST, each search query is processed in near-constant time, independent of the dataset size; this computational efficiency is gained at the expense of an approximate, rather than exact, search. During one week of continuous data at station WHAR, from 2010-07-01 to 2010-07-08, FAST detected over 200 uncataloged earthquakes that were not found through template matching. These newly detected earthquakes have the potential to

  1. Approximate Entropy as a Measure of Irregularity in Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Kozuch, M.; Wang, L.

    2001-12-01

    Approximate Entropy (ApEn) is a mathematical technique that creates a suite of statistical information that grades changes in the irregularity of a time series. In seismology, identifying regions or time periods that are undergoing changes in seismic activity would enable seismologists to know when or where to search for physical triggering mechanisms. ApEn measures the (logarithmic) likelihood that runs of patterns that are close (within tolerance r) for (window length) m observations remain close on next incremental comparisons (Pincus et al., 1996). The greater likelihood of remaining close (e.g. regularity) produces smaller ApEn values. Thus, ApEn is a relative measure of regularity. Chaos algorithms per se are generally inappropriate for some data since there may be mixed random models involved, and often the findings are nonreplicable with large error bars. ApEn, on the other hand, is a measure that may be used to determine the properties of the entire time-series or temporal changes in the system without having to model the system in itself. We tested the ApEn algorithm on earthquake sequences in New Zealand to investigate how effective the technique would be in discriminating changes in seismicity prior to large earthquakes. Synthetic catalogs that contained regular sequences of earthquakes (e.g. all magnitude 3s every 1 day), showed distinct sensitivity to ApEn when suddenly faced with a step in magnitudes. ApEn showed a spike of irregularity across the step. This exercise was performed for a number of synthetic cases to understand the sensitivity of ApEn to changes in seismicity (in both magnitude and time). When analyzing real data, we found ApEn to be most sensitive to interevent times rather than magnitude changes. Thus, it is possible that quiescent periods may actually contain a signature that reveals the buildup of "signal" to a main shock.

  2. Interaction of the san jacinto and san andreas fault zones, southern california: triggered earthquake migration and coupled recurrence intervals.

    PubMed

    Sanders, C O

    1993-05-14

    Two lines of evidence suggest that large earthquakes that occur on either the San Jacinto fault zone (SJFZ) or the San Andreas fault zone (SAFZ) may be triggered by large earthquakes that occur on the other. First, the great 1857 Fort Tejon earthquake in the SAFZ seems to have triggered a progressive sequence of earthquakes in the SJFZ. These earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1.7 kilometers per year along the SJFZ after the 1857 earthquake. Second, the similarity in average recurrence intervals in the SJFZ (about 150 years) and in the Mojave segment of the SAFZ (132 years) suggests that large earthquakes in the northern SJFZ may stimulate the relatively frequent major earthquakes on the Mojave segment. Analysis of historic earthquake occurrence in the SJFZ suggests little likelihood of extended quiescence between earthquake sequences. PMID:17818388

  3. Potentially induced earthquakes in Oklahoma, USA: links between wastewater injection and the 2011 Mw 5.7 earthquake sequence

    USGS Publications Warehouse

    Keranen, Katie M.; Savage, Heather M.; Abers, Geoffrey A.; Cochran, Elizabeth S.

    2013-01-01

    Significant earthquakes are increasingly occurring within the continental interior of the United States, including five of moment magnitude (Mw) ≥ 5.0 in 2011 alone. Concurrently, the volume of fluid injected into the subsurface related to the production of unconventional resources continues to rise. Here we identify the largest earthquake potentially related to injection, an Mw 5.7 earthquake in November 2011 in Oklahoma. The earthquake was felt in at least 17 states and caused damage in the epicentral region. It occurred in a sequence, with 2 earthquakes of Mw 5.0 and a prolific sequence of aftershocks. We use the aftershocks to illuminate the faults that ruptured in the sequence, and show that the tip of the initial rupture plane is within ~200 m of active injection wells and within ~1 km of the surface; 30% of early aftershocks occur within the sedimentary section. Subsurface data indicate that fluid was injected into effectively sealed compartments, and we interpret that a net fluid volume increase after 18 yr of injection lowered effective stress on reservoir-bounding faults. Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible, and modifies our common criteria for fluid-induced events. The progressive rupture of three fault planes in this sequence suggests that stress changes from the initial rupture triggered the successive earthquakes, including one larger than the first.

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

    PubMed

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

    2015-01-01

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

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

    ERIC Educational Resources Information Center

    2003

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  7. The 2006-2007 Kuril Islands great earthquake sequence

    USGS Publications Warehouse

    Lay, T.; Kanamori, H.; Ammon, C.J.; Hutko, Alexander R.; Furlong, K.; Rivera, L.

    2009-01-01

    The southwestern half of a ???500 km long seismic gap in the central Kuril Island arc subduction zone experienced two great earthquakes with extensive preshock and aftershock sequences in late 2006 to early 2007. The nature of seismic coupling in the gap had been uncertain due to the limited historical record of prior large events and the presence of distinctive upper plate, trench and outer rise structures relative to adjacent regions along the arc that have experienced repeated great interplate earthquakes in the last few centuries. The intraplate region seaward of the seismic gap had several shallow compressional events during the preceding decades (notably an MS 7.2 event on 16 March 1963), leading to speculation that the interplate fault was seismically coupled. This issue was partly resolved by failure of the shallow portion of the interplate megathrust in an MW = 8.3 thrust event on 15 November 2006. This event ruptured ???250 km along the seismic gap, just northeast of the great 1963 Kuril Island (Mw = 8.5) earthquake rupture zone. Within minutes of the thrust event, intense earthquake activity commenced beneath the outer wall of the trench seaward of the interplate rupture, with the larger events having normal-faulting mechanisms. An unusual double band of interplate and intraplate aftershocks developed. On 13 January 2007, an MW = 8.1 extensional earthquake ruptured within the Pacific plate beneath the seaward edge of the Kuril trench. This event is the third largest normal-faulting earthquake seaward of a subduction zone on record, and its rupture zone extended to at least 33 km depth and paralleled most of the length of the 2006 rupture. The 13 January 2007 event produced stronger shaking in Japan than the larger thrust event, as a consequence of higher short-period energy radiation from the source. The great event aftershock sequences were dominated by the expected faulting geometries; thrust faulting for the 2006 rupture zone, and normal faulting for

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    USGS Publications Warehouse

    Simpson, Robert W.

    1994-01-01

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

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

    USGS Publications Warehouse

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Mualchin, Lalliana

    2011-03-01

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

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

    USGS Publications Warehouse

    Jones, Lucile M.

    1985-01-01

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

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    USGS Publications Warehouse

    Bolt, B. A.

    1987-01-01

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

  15. Faulting and earthquake triggering during the 1783 Calabria seismic sequence

    NASA Astrophysics Data System (ADS)

    Jacques, E.; Monaco, C.; Tapponnier, P.; Tortorici, L.; Winter, T.

    2001-12-01

    earthquake 124yr before (1659 November 5, M ~6), which had already released stress locally. The occurrence of the last 1783 event (28 March) is not as simply accounted for by Coulomb modelling, in part because it remains unclear which fault slipped and how deep this event was. Overall, the 1783 sequence increased the Coulomb failure stress by several bars south of the Messina Strait and north of the epicentral region of the 1693 SE Sicily (Catania-Noto) earthquakes. 125yr later, this same region was the site of the 1908 Messina earthquake, also a normal faulting event. Our study thus provides one convincing example in which Coulomb stress modelling brings insight into the spatial dynamics of seismic sequences.

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

    NASA Astrophysics Data System (ADS)

    Oglesby, David; Ryan, Kenny; Geist, Eric

    2016-04-01

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

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

    USGS Publications Warehouse

    Yashinsky, Mark

    1998-01-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

  19. Draft Genome Sequence of "Candidatus Liberibacter asiaticus" from California.

    PubMed

    Zheng, Z; Deng, X; Chen, J

    2014-01-01

    We report here the draft genome sequence of "Candidatus Liberibacter asiaticus" strain HHCA, collected from a lemon tree in California. The HHCA strain has a genome size of 1,150,620 bp, 36.5% G+C content, 1,119 predicted open reading frames, and 51 RNA genes. PMID:25278540

  20. Education for Democracy: California Civic Education Scope & Sequence.

    ERIC Educational Resources Information Center

    Center for Civic Education, Calabasas, CA.

    California, the most populous and diverse state in the United States, must maintain its commitment to civic education. The curricular goal of democratic understanding and civic values is centered on an essential understanding of the nation's identity and constitutional heritage. This scope and sequence for civic education describes ways in which…

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

    USGS Publications Warehouse

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

    1978-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Perry, S.; Jordan, T.

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Martindale, D.; Evans, J. P.

    2002-12-01

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

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

    USGS Publications Warehouse

    Ward, Peter L.; Page, Robert A.

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    USGS Publications Warehouse

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

    1982-01-01

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

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

    SciTech Connect

    Lum, P K; Honda, K K

    1993-10-01

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

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

    USGS Publications Warehouse

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

    1985-01-01

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

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

    USGS Publications Warehouse

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

    1999-01-01

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

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

    PubMed

    Rutenberg, A

    1995-03-15

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

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

    USGS Publications Warehouse

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

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Mammoth Mountain is a cluster of dacitic domes erupted ~ 68 ka. It stands on the SW topographic rim of Long Valley caldera in eastern CA. Structurally, it is outboard of the caldera ring-fracture system and its magmatic system is genetically distinct from that of the caldera. It resides within a field of mafic (basaltic) vents that erupted between 190 - 8 ka. A series of phreatic explosions from the north flank of the mountain some 700 ybp attest to the infusion of heat to shallow depths shortly prior to the 600 ybp eruptions of the Inyo Domes 6 to 12 km north of the Mountain. Unrest beneath Mammoth Mountain since 1980 has included 1) swarms of brittle-failure earthquakes in the upper 10 km of the crust that define concentric elliptical ring-like patterns centered beneath the summit, 2) mid-crustal (depths 10 to 20 km) long-period volcanic earthquakes, 3) the onset of diffuse CO2 degassing in 1990 following an 11-month-long swarm of shallow (<10 km), brittle-failure earthquakes in 1989, 4) occasional very-long-period earthquakes at depths of ~ 3 km, and 5) brief swarms of lower-crustal, brittle-failure earthquakes at depths of 20 to 30 km, including sizable episodes June 16-17, 2006 and September 29-30, 2009. Seismic waveform correlation analysis at multiple stations reveals that these lower-crustal, brittle-failure swarms consist of tens to hundreds of repeated similar events and also serves to identify many events not included in the Northern California Seismic Network (NCSN) catalog. In the case of the 2009 episode, an evolution in waveform is clearly discernible over the sequence, suggesting a corresponding evolution in source location or mechanism. Work is ongoing to take advantage of the waveform similarity to estimate precise hypocentral locations of these events in order to distinguish between these possibilities.We suggest that the brittle-failure earthquakes at depths of 20 to 30 km are occurring within the more mafic mid- to lower-crust, which can remain

  15. Multi-sensor Integration of Space and Ground Observations of Pre-earthquake Anomalies Associated with M6.0, August 24, 2014 Napa, California

    NASA Astrophysics Data System (ADS)

    Ouzounov, Dimitar; Tramutoli, Valerio; Pulinets, Sergey; Liu, Tiger; Filizzola, Carolina; Genzano, Nicola; Lisi, Mariano; Petrov, Leonid; Kafatos, Menas

    2015-04-01

    We integrate multiple space-born and ground sensors for monitoring pre-earthquake geophysical anomalies that can provide significant early notification for earthquakes higher than M5.5 worldwide. The latest M6.0 event of August 24, 2014 in South Napa, California generated pre-earthquake signatures during our outgoing tests for California, and an experimental warning was documented about 17 days in advance. We process in controlled environment different satellite and ground data for California (and several other test areas) by using: a) data from the NPOES sensors recording OLR (Outgoing Longwave Radiation) in the infrared; b) 2/GNSS, FORMOSAT (GPS/TEC); c) Earth Observing System assimilation models from NASA; d) ground-based gas observations and meteorological data; e) TIR (Thermal Infrared) data from geostationary satellite (GOES). On Aug 4th, we detected (prospectively) a large anomaly of OLR transient field at the TOA over Northern California. The location was shifted in the northeast direction about 150 km from the Aug 23rd epicentral area. Compared to the reference field of August 2004 to 2014 the hotspot anomaly was the largest energy flux anomaly over the entire continental United States at this time. Based on the temporal and spatial estimates of the anomaly, on August 4th we issued an internal warning for a M5.5+ earthquake in Northern California within the next 1-4 weeks. TIR retrospective analysis showed significant (spatially extended and temporally persistent) sequences of TIR anomalies starting August 1st just in the future epicenter area and approximately in the same area affected by OLR anomalies in the following days. GPS/TEC retrospective analysis based on GIM and TGIM products show anomalies TEC variations 1-3 days, over region north form the Napa earthquake epicenter. The calculated index of atmospheric chemical potential based on the NASA numerical Assimilation weather model GEOS5 indicates for abnormal variations near the epicentral area days

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

    NASA Astrophysics Data System (ADS)

    Weiser, Deborah Anne

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

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

    USGS Publications Warehouse

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

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Harris, Ruth A.; Archuleta, Ralph J.

    1988-10-01

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

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

    USGS Publications Warehouse

    Keefer, David K., (Edited By)

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Dzeboev, Boris; Gvishiani, Alexei

    2016-04-01

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

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

    SciTech Connect

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

    1989-01-10

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

  5. Record-Breaking Intervals: Detecting Trends in the Incidence of Self-Similar Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Yoder, Mark R.; Rundle, John B.

    2015-08-01

    We introduce a method of resolving temporal incidence trends in earthquake sequences. We have developed a catalog partitioning method based on canonical earthquake scaling relationships, and have further developed a metric based on record-breaking interval (RBI) statistics to resolve increasing and decreasing seismicity in time series of earthquakes. We calculated the RBI metric over fixed-length sequences of earthquake intervals and showed that the length of those sequences is related to the magnitude of the earthquake to which the method is sensitive—longer sequences resolve large earthquakes, shorter sequences resolve small-magnitude events. This sequence length effectively constitutes a local temporal catalog constraint, and we show that spatial constraints can be defined from rupture length scaling. We have applied the method to several high-profile earthquakes and have shown that it consistently resolves aftershock sequences after a period of accelerating seismicity before the targeted mainshock. The method also suggests a minimum detectable (forecastable) mainshock magnitude on the basis of the catalog's minimum completeness magnitude.

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

    USGS Publications Warehouse

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

    2006-01-01

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

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

    USGS Publications Warehouse

    Frankel, Arthur; Mueller, Charles

    2008-01-01

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

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

    USGS Publications Warehouse

    Stein, Ross S.

    2007-01-01

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

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

    USGS Publications Warehouse

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

    2008-01-01

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

  10. Detection of crustal deformation from the Landers earthquake sequence using continuous geodetic measurements

    NASA Technical Reports Server (NTRS)

    Bock, Yehuda; Agnew, Duncan C.; Fang, Peng; Genrich, Joachim F.; Hager, Bradford H.; Herring, Thomas A.; Hudnut, Kenneth W.; King, Robert W.; Larsen, Shawn; Minster, J.-B.

    1993-01-01

    The first measurements are reported for a major earthquake by a continuously operating GPS network, the permanent GPS Genetic ARRY (PGGA) in southern California. The Landers and Big Bear earthquakes of June 28, 1992 were monitored by daily observations. Ten weeks of measurements indicate significant coseismic motion at all PGGA sites, significant postseismic motion at one site for two weeks after the earthquakes, and no significant preseismic motion. These measurements demonstrate the potential of GPS monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    2015-04-01

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

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

    USGS Publications Warehouse

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  19. Earthquake.

    PubMed

    Cowen, A R; Denney, J P

    1994-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Gurrola, Larry D.; Rockwell, Thomas K.

    1996-03-01

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

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

    USGS Publications Warehouse

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

    2009-01-01

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

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

    PubMed Central

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

    2002-01-01

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

  3. A graph theoretic approach to global earthquake sequencing: A Markov chain model

    NASA Astrophysics Data System (ADS)

    Vasudevan, K.; Cavers, M. S.

    2012-12-01

    We construct a directed graph to represent a Markov chain of global earthquake sequences and analyze the statistics of transition probabilities linked to earthquake zones. For earthquake zonation, we consider the simplified plate boundary template of Kagan, Bird, and Jackson (KBJ template, 2010). We demonstrate the applicability of the directed graph approach to hazard-related forecasting using some of the properties of graphs that represent the finite Markov chain. We extend the present study to consider Bird's 52-plate zonation (2003) describing the global earthquakes at and within plate boundaries to gain further insight into the usefulness of digraphs corresponding to a Markov chain model.

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

    NASA Astrophysics Data System (ADS)

    Provost, Ann-Sophie; Houston, Heidi

    2003-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Takauchi, Y.; Evans, John R.

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

  8. Earthquake!

    ERIC Educational Resources Information Center

    Markle, Sandra

    1987-01-01

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

  9. 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 ...

  10. 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 ...

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

    USGS Publications Warehouse

    Burford, R.O.

    1988-01-01

    Records of shallow aseismic slip (fault creep) obtained along parts of the San Andreas and Calaveras faults in central California demonstrate that significant changes in creep rates often have been associated with local moderate earthquakes. An immediate postearthquake increase followed by gradual, long-term decay back to a previous background rate is generally the most obvious earthquake effect on fault creep. This phenomenon, identified as aseismic afterslip, usually is characterized by above-average creep rates for several months to a few years. In several cases, minor step-like movements, called coseismic slip events, have occurred at or near the times of mainshocks. One extreme case of coseismic slip, recorded at Cienega Winery on the San Andreas fault 17.5 km southeast of San Juan Bautista, consisted of 11 mm of sudden displacement coincident with earthquakes of ML=5.3 and ML=5.2 that occurred 2.5 minutes apart on 9 April 1961. At least one of these shocks originated on the main fault beneath the winery. Creep activity subsequently stopped at the winery for 19 months, then gradually returned to a nearly steady rate slightly below the previous long-term average. The phenomena mentioned above can be explained in terms of simple models consisting of relatively weak material along shallow reaches of the fault responding to changes in load imposed by sudden slip within the underlying seismogenic zone. In addition to coseismic slip and afterslip phenomena, however, pre-earthquake retardations in creep rates also have been observed. Onsets of significant, persistent decreases in creep rates have occurred at several sites 12 months or more before the times of moderate earthquakes. A 44-month retardation before the 1979 ML=5.9 Coyote Lake earthquake on the Calaveras fault was recorded at the Shore Road creepmeter site 10 km northwest of Hollister. Creep retardation on the San Andreas fault near San Juan Bautista has been evident in records from one creepmeter site for

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

    NASA Astrophysics Data System (ADS)

    Hardy, S.; Konter, B.

    2013-12-01

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

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

    USGS Publications Warehouse

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

    2013-01-01

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

  14. 8 January 2013 Mw=5.7 North Aegean Sea Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Kürçer, Akın; Yalçın, Hilal; Gülen, Levent; Kalafat, Doǧan

    2014-05-01

    The deformation of the North Aegean Sea is mainly controlled by the westernmost segments of North Anatolian Fault Zone (NAFZ). On January 8, 2013, a moderate earthquake (Mw= 5.7) occurred in the North Aegean Sea, which may be considered to be a part of westernmost splay of the NAFZ. A series of aftershocks were occurred within four months following the mainschock, which have magnitudes varying from 1.9 to 5.0. In this study, a total of 23 earthquake moment tensor solutions that belong to the 2013 earthquake sequence have been obtained by using KOERI and AFAD seismic data. The most widely used Gephart & Forsyth (1984) and Michael (1987) methods have been used to carry out stress tensor inversions. Based on the earthquake moment tensor solutions, distribution of epicenters and seismotectonic setting, the source of this earthquake sequence is a N75°E trending pure dextral strike-slip fault. The temporal and spatial distribution of earthquakes indicate that the rupture unilaterally propagated from SW to NE. The length of the fault has been calculated as approximately 12 km. using the afterschock distribution and empirical equations, suggested by Wells and Coppersmith (1994). The stress tensor analysis indicate that the dominant faulting type in the region is strike-slip and the direction of the regional compressive stress is WNW-ESE. The 1968 Aghios earthquake (Ms=7.3; Ambraseys and Jackson, 1998) and 2013 North Aegean Sea earthquake sequences clearly show that the regional stress has been transferred from SW to NE in this region. The last historical earthquake, the Bozcaada earthquake (M=7.05) had been occurred in the northeast of the 2013 earthquake sequence in 1672. The elapsed time (342 year) and regional stress transfer point out that the 1672 earthquake segment is probably a seismic gap. According to the empirical equations, the surface rupture length of the 1672 Earthquake segment was about 47 km, with a maximum displacement of 170 cm and average displacement

  15. Response and recovery lessons from the 2010-2011 earthquake sequence in Canterbury, New Zealand

    USGS Publications Warehouse

    Pierepiekarz, Mark; Johnston, David; Berryman, Kelvin; Hare, John; Gomberg, Joan S.; Williams, Robert A.; Weaver, Craig S.

    2014-01-01

    The impacts and opportunities that result when low-probability moderate earthquakes strike an urban area similar to many throughout the US were vividly conveyed in a one-day workshop in which social and Earth scientists, public officials, engineers, and an emergency manager shared their experiences of the earthquake sequence that struck the city of Christchurch and surrounding Canterbury region of New Zealand in 2010-2011. Without question, the earthquake sequence has had unprecedented impacts in all spheres on New Zealand society, locally to nationally--10% of the country's population was directly impacted and losses total 8-10% of their GDP. The following paragraphs present a few lessons from Christchurch.

  16. The foreshock sequence of large earthquakes: slow slip or cascade triggering?

    NASA Astrophysics Data System (ADS)

    Huang, H.; Meng, L.

    2014-12-01

    Large earthquakes such as the 2011 Mw 9.0 Tohoku-Oki earthquake and the 2014 Mw 8.1 Iquique earthquake are often preceded by foreshock sequences migrating toward the hypocenters of mainshocks. Understanding the underlying physical processes is crucial for imminent seismic hazard assessment. Some of these foreshock sequences are accompanied by repeating earthquakes, which are thought to be a manifestation of a large-scale background slow slip transient. The alternative interpretation is that the migrating seismicity is simply produced by the cascade triggering of mainshock-aftershock sequences following Omori's Law. In this case the repeating earthquakes are driven by the afterslip of the moderate to large foreshocks instead of an independent slow slip event. As an initial effort to discriminate these two hypotheses, we made a detailed analysis of the repeating earthquakes among the foreshock sequences of the 2014 Mw 8.1 Iquique earthquake. We observed that some significant foreshocks (M >= 5.5) are followed by the rapid occurrences of local repeaters, suggesting the contribution of afterslip. However the repeaters are distributed in a wide area (~40*80 km), which are difficult to be driven by only a few moderate to large foreshocks. Furthermore, the estimated repeater-inferred aseismic moment during the foreshock period is at least 3.041e19 Nm (5*5 km grid), which is of the same order with the total amount of seismic moment of all foreshocks (2.251e19 Nm). This comparison again supports the slow-slip model since the ratio of post-seismic to coseismic moment is small in most earthquakes. To estimate the contributions of the transient slow slip and cascade triggering in the initiation of large earthquakes, we propose to systematically search and analyze repeating earthquakes in all foreshock sequences preceding large earthquakes. The next effort will be made to the long precursory phase of large interplate earthquakes such as the 1999 Mw 7.6 Izimit earthquake and the

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  18. Spatio-temporal Variations of Characteristic Repeating Earthquake Sequences along the Middle America Trench in Mexico

    NASA Astrophysics Data System (ADS)

    Dominguez, L. A.; Taira, T.; Hjorleifsdottir, V.; Santoyo, M. A.

    2015-12-01

    Repeating earthquake sequences are sets of events that are thought to rupture the same area on the plate interface and thus provide nearly identical waveforms. We systematically analyzed seismic records from 2001 through 2014 to identify repeating earthquakes with highly correlated waveforms occurring along the subduction zone of the Cocos plate. Using the correlation coefficient (cc) and spectral coherency (coh) of the vertical components as selection criteria, we found a set of 214 sequences whose waveforms exceed cc≥95% and coh≥95%. Spatial clustering along the trench shows large variations in repeating earthquakes activity. Particularly, the rupture zone of the M8.1, 1985 earthquake shows an almost absence of characteristic repeating earthquakes, whereas the Guerrero Gap zone and the segment of the trench close to the Guerrero-Oaxaca border shows a significantly larger number of repeating earthquakes sequences. Furthermore, temporal variations associated to stress changes due to major shows episodes of unlocking and healing of the interface. Understanding the different components that control the location and recurrence time of characteristic repeating sequences is a key factor to pinpoint areas where large megathrust earthquakes may nucleate and consequently to improve the seismic hazard assessment.

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

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Appel, V. L.

    2002-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Granat, Robert; Donnellan, Andrea

    2011-01-01

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

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

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2012-01-01

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

  3. Near-field investigations of the Landers earthquake sequence, April to July 1992

    USGS Publications Warehouse

    Sieh, K.; Jones, L.; Hauksson, E.; Hudnut, K.; Eberhart-Phillips, D.; Heaton, T.; Hough, S.; Hutton, K.; Kanamori, H.; Lilje, A.; Lindvall, Scott; McGill, S.F.; Mori, J.; Rubin, C.; Spotila, J.A.; Stock, J.; Thio, H.K.; Treiman, J.; Wernicke, B.; Zachariasen, J.

    1993-01-01

    The Landers earthquake, which had a moment magnitude (Mw) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its Mw 6.1 preshock and Mw 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.

  4. Near-field investigations of the landers earthquake sequence, april to july 1992.

    PubMed

    Sieh, K; Jones, L; Hauksson, E; Hudnut, K; Eberhart-Phillips, D; Heaton, T; Hough, S; Hutton, K; Kanamori, H; Lilje, A; Lindvall, S; McGill, S F; Mori, J; Rubin, C; Spotila, J A; Stock, J; Thio, H K; Treiman, J; Wernicke, B; Zachariasen, J

    1993-04-01

    The Landers earthquake, which had a moment magnitude (M(w)) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M(w) 6.1 preshock and M(w) 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults. PMID:17807175

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

    USGS Publications Warehouse

    Hartzell, S.; Liu, P.

    1996-01-01

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

  6. Earthquakes.

    ERIC Educational Resources Information Center

    Walter, Edward J.

    1977-01-01

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

  7. Earthquakes.

    ERIC Educational Resources Information Center

    Pakiser, Louis C.

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

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

    USGS Publications Warehouse

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

    2002-01-01

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

  9. Long aftershock sequences within continents and implications for earthquake hazard assessment.

    PubMed

    Stein, Seth; Liu, Mian

    2009-11-01

    One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere. PMID:19890328

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

    USGS Publications Warehouse

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

    1988-01-01

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