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  1. Landslides triggered by the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

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

    1996-01-01

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

  2. 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.

  3. 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.

  4. 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.

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

    USGS Publications Warehouse

    Jones, L.; Aki, K.; Boore, D.; Celebi, M.; Donnellan, A.; Hall, J.; Harris, R.; Hauksson, E.; Heaton, T.; Hough, S.; Hudnut, K.; Hutton, K.; Johnston, M.; Joyner, W.; Kanamori, H.; Marshall, G.; Michael, A.; Mori, J.; Murray, M.; Ponti, D.; Reasenberg, P.; Schwartz, D.; Seeber, L.; Shakal, A.; Simpson, R.; Thio, H.; Tinsley, J.; Todorovska, M.; Trifunac, M.; Wald, D.; Zoback, M.L.

    1994-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Donnellan, A.

    1994-01-01

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

  7. 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

  8. The Northridge Earthquake--A Giant Physics Laboratory.

    ERIC Educational Resources Information Center

    Carrington, Fred

    1994-01-01

    Describes and attempts to explain the sporadic devastating effects of the Northridge (California) Earthquake of January 17, 1994, as being the result of constructive interference from P and S earthquake waves. (MVL)

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

    USGS Publications Warehouse

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

    1996-01-01

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

  10. Dynamic deformations and the M6.7, Northridge, California earthquake

    USGS Publications Warehouse

    Gomberg, J.

    1997-01-01

    A method of estimating the complete time-varying dynamic formation field from commonly available three-component single station seismic data has been developed and applied to study the relationship between dynamic deformation and ground failures and structural damage using observations from the 1994 Northridge, California earthquake. Estimates from throughout the epicentral region indicate that the horizontal strains exceed the vertical ones by more than a factor of two. The largest strains (exceeding ???100 ??strain) correlate with regions of greatest ground failure. There is a poor correlation between structural damage and peak strain amplitudes. The smallest strains, ???35 ??strain, are estimated in regions of no damage or ground failure. Estimates in the two regions with most severe and well mapped permanent deformation, Potrero Canyon and the Granada-Mission Hills regions, exhibit the largest strains; peak horizontal strains estimates in these regions equal ???139 and ???229 ??strain respectively. Of note, the dynamic principal strain axes have strikes consistent with the permanent failure features suggesting that, while gravity, sub-surface materials, and hydrologic conditions undoubtedly played fundamental roles in determining where and what types of failures occurred, the dynamic deformation field may have been favorably sized and oriented to initiate failure processes. These results support other studies that conclude that the permanent deformation resulted from ground shaking, rather than from static strains associated with primary or secondary faulting. They also suggest that such an analysis, either using data or theoretical calculations, may enable observations of paleo-ground failure to be used as quantitative constraints on the size and geometry of previous earthquakes. ?? 1997 Elsevier Science Limited.

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

    USGS Publications Warehouse

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

    2010-01-01

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

  12. Masonry infill performance during the Northridge earthquake

    SciTech Connect

    Flanagan, R.D.; Bennett, R.M.; Fischer, W.L.; Adham, S.A.

    1996-03-08

    The response of masonry infills during the 1994 Northridge, California earthquake is described in terms of three categories: (1) lowrise and midrise structures experiencing large near field seismic excitations, (2) lowrise and midrise structures experiencing moderate far field excitation, and (3) highrise structures experiencing moderate far field excitation. In general, the infills provided a positive beneficial effect on the performance of the buildings, even those experiencing large peak accelerations near the epicenter. Varying types of masonry infills, structural frames, design conditions, and construction deficiencies were observed and their performance during the earthquake indicated. A summary of observations of the performance of infills in other recent earthquakes is given. Comparison with the Northridge earthquake is made and expected response of infill structures in lower seismic regions of the central and eastern United States is discussed.

  13. Signatures of the seismic source in EMD-based characterization of the 1994 Northridge, California, earthquake recordings

    USGS Publications Warehouse

    Zhang, R.R.; Ma, S.; Hartzell, S.

    2003-01-01

    In this article we use empirical mode decomposition (EMD) to characterize the 1994 Northridge, California, earthquake records and investigate the signatures carried over from the source rupture process. Comparison of the current study results with existing source inverse solutions that use traditional data processing suggests that the EMD-based characterization contains information that sheds light on aspects of the earthquake rupture process. We first summarize the fundamentals of the EMD and illustrate its features through the analysis of a hypothetical and a real record. Typically, the Northridge strong-motion records are decomposed into eight or nine intrinsic mode functions (IMF's), each of which emphasizes a different oscillation mode with different amplitude and frequency content. The first IMF has the highest-frequency content; frequency content decreases with an increase in IMF component. With the aid of a finite-fault inversion method, we then examine aspects of the source of the 1994 Northridge earthquake that are reflected in the second to fifth IMF components. This study shows that the second IMF is predominantly wave motion generated near the hypocenter, with high-frequency content that might be related to a large stress drop associated with the initiation of the earthquake. As one progresses from the second to the fifth IMF component, there is a general migration of the source region away from the hypocenter with associated longer-period signals as the rupture propagates. This study suggests that the different IMF components carry information on the earthquake rupture process that is expressed in their different frequency bands.

  14. Lessons learned from the 1994 Northridge Earthquake

    SciTech Connect

    Eli, M.W.; Sommer, S.C.

    1995-04-01

    Southern California has a history of major earthquakes and also has one of the largest metropolitan areas in the United States. The 1994 Northridge Earthquake challenged the industrial facilities and lifetime infrastructure in the northern Los Angeles (LA) area. Lawrence Livermore National Laboratory (LLNL) sent a team of engineers to conduct an earthquake damage investigation in the Northridge area, on a project funded jointly by the United States Nuclear Regulatory Commission (USNRC) and the United States Department of Energy (USDOE). Many of the structures, systems, and components (SSCs) and lifelines that suffered damage are similar to those found in nuclear power plants and in USDOE facilities. Lessons learned from these experiences can have some applicability at commercial nuclear power plants.

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

    USGS Publications Warehouse

    Jibson, R.W.

    2002-01-01

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

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

    ERIC Educational Resources Information Center

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

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    USGS Publications Warehouse

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

    1998-01-01

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

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

    USGS Publications Warehouse

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

    2001-01-01

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

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

    USGS Publications Warehouse

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

    1996-01-01

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

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

    USGS Publications Warehouse

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

    1997-01-01

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Fuis, Gary S.; Clayton, Robert W.; Davis, Paul M.; Ryberg, Trond; Lutter, William J.; Okaya, David A.; Hauksson, Egill; Prodehl, Claus; Murphy, Janice M.; Benthien, Mark L.; Baher, Shirley A.; Kohler, Monica D.; Thygesen, Kristina; Simila, Gerry; Keller, G. Randy

    2003-02-01

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

  4. Directional topographic site response at Tarzana observed in aftershocks of the 1994 Northridge, California, earthquake: Implications for mainshock motions

    USGS Publications Warehouse

    Spudich, P.; Hellweg, M.; Lee, W.H.K.

    1996-01-01

    The Northridge earthquake caused 1.78 g acceleration in the east-west direction at a site in Tarzana, California, located about 6 km south of the mainshock epicenter. The accelerograph was located atop a hill about 15-m high, 500-m long, and 130-m wide, striking about N78??E. During the aftershock sequence, a temporary array of 21 three-component geophones was deployed in six radial lines centered on the accelerograph, with an average sensor spacing of 35 m. Station COO was located about 2 m from the accelerograph. We inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion. We identified a 3.2-Hz resonance that is a transverse oscillation of the hill (a directional topographic effect). The top/base amplification ratio at 3.2 Hz is about 4.5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill. This resonance is seen most strongly within 50 m of COO. Other resonant frequencies were also observed. A strong lateral variation in attenuation, probably associated with a fault, caused substantially lower motion at frequencies above 6 Hz at the east end of the hill. There may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill, causing particle motions (not spectral ratios) at the top of the hill to be rotated about 20?? away from the direction transverse to the hill. The resonant frequency, but not the amplitude, of our observed topographic resonance agrees well with theory, even for such a low hill. Comparisons of our observations with theoretical results indicate that the 3D shape of the hill and its internal structure are important factors affecting its response. The strong transverse resonance of the hill does not account for the large east-west mainshock motions. Assuming linear soil response, mainshock east-west motions at the Tarzana accelerograph

  5. Stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Deng, J.; Hudnut, K.; Gurnis, M.; Hauksson, E.

    1999-01-01

    Following the M(w) 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.Following the Mw 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.

  6. Nonlinear soil response in the vicinity of the Van Norman Complex following the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Cultrera, G.; Boore, D.M.; Joyner, W.B.; Dietel, C.M.

    1999-01-01

    Ground-motion recordings obtained at the Van Norman Complex from the 1994 Northridge, California, mainshock and its aftershocks constitute an excellent data set for the analysis of soil response as a function of ground-motion amplitude. We searched for nonlinear response by comparing the Fourier spectral ratios of two pairs of sites for ground motions of different levels, using data from permanent strong-motion recorders and from specially deployed portable instruments. We also compared the amplitude dependence of the observed ratios with the amplitude dependence of the theoretical ratios obtained from 1-D linear and 1-D equivalent-linear transfer functions, using recently published borehole velocity profiles at the sites to provide the low-strain material properties. One pair of sites was at the Jensen Filtration Plant (JFP); the other pair was the Rinaldi Receiving Station (RIN) and the Los Angeles Dam (LAD). Most of the analysis was concentrated on the motions at the Jensen sites. Portable seismometers were installed at the JFP to see if the motions inside the structures housing the strong-motion recorders differed from nearby free-field motions. We recorded seven small earthquakes and found that the high-frequency, low-amplitude motions in the administration building were about 0.3 of those outside the building. This means that the lack of high frequencies on the strong-motion recordings in the administration building relative to the generator building is not due solely to nonlinear soil effects. After taking into account the effects of the buildings, however, analysis of the suite of strong- and weak-motion recordings indicates that nonlinearity occurred at the JFP. As predicted by equivalent-linear analysis, the largest events (the mainshock and the 20 March 1994 aftershock) show a significant deamplification of the high-frequency motion relative to the weak motions from aftershocks occurring many months after the mainshock. The weak-motion aftershocks

  7. California State University, Northridge: Hybrid Lab Courses

    ERIC Educational Resources Information Center

    EDUCAUSE, 2014

    2014-01-01

    California State University, Northridge's Hybrid Lab course model targets high failure rate, multisection, gateway courses in which prerequisite knowledge is a key to success. The Hybrid Lab course model components incorporate interventions and practices that have proven successful at CSUN and other campuses in supporting students, particularly…

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

    USGS Publications Warehouse

    Parise, M.; Jibson, R.W.

    2000-01-01

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

  10. Character and origins of ground rupturing and ground deformation during the 28 June 1992 Landers, California earthquake (as well as the 1989 Loma Prieta and 1994 Northridge earthquakes). Final report

    SciTech Connect

    Johnson, A.M.

    1996-09-17

    The overall objective of the research has been to understand the form and significance of surface rupture produced by earthquakes. Specific objectives are to describe fracturing and other manifestations of broad belts of ground rupture during the Landers earthquake and to mechanically analyze the structures that form along the belts. The author has learned much about ground rupture during earthquakes, even though he has studied only three earthquakes to date: Loma Prieta, Landers and Northridge.

  11. Implications of the Northridge earthquake for strong ground motions from thrust faults

    USGS Publications Warehouse

    Somerville, P.; Saikia, C.; Wald, D.; Graves, R.

    1996-01-01

    The peak accelerations recorded on alluvial sites during the Northridge earthquake were about 50% larger than the median value predicted by current empirical attenuation relations at distances less than about 30 km. This raises the question of whether the ground motions from the Northridge earthquake are anomalous for thrust events or are representative of ground motions expected in future thrust earthquakes. Since the empirical data base contains few strong-motion records close to large-thrust earthquakes, it is difficult to assess whether the Northridge ground motions are anomalous based on recorded data alone. For this reason, we have used a broadband strong-motion simulation procedure to help assess whether the ground motions were anomalous. The simulation procedure has been validated against a large body of strong-motion data from California earthquakes, and so we expect it to produce accurate estimates of ground motions for any given rupture scenario, including blind-thrust events for which no good precedent existed in the strong-motion data base until the occurrence of the Northridge earthquake. The ground motions from the Northridge earthquake and our simulations of these ground motions have a similar pattern of departure from empirical attenuation relations for thrust earthquakes: the peak accelerations are at about the 84th percentile level for distances within 20 to 30 km and follow the median level for larger distances. This same pattern of departure from empirical attenuation relations was obtained in our simulations of the peak accelerations of an Elysian Park blind-thrust event prior to the occurrence of the Northridge earthquake. Since we are able to model this pattern with broadband simulations, and had done so before the Northridge earthquake occurred, this suggests that the Northridge strong-motion records are not anomalous and are representative of ground motions close to thrust faults. Accordingly, it seems appropriate to include these

  12. Response of Olive View Hospital to Northridge and Whittier earthquakes

    USGS Publications Warehouse

    Celebi, M.

    1997-01-01

    The purpose of this paper is to study the response of the conventionally designed new Olive View Medical Center (OVMC) building at 16 km from the epicenter of the January 17, 1994 Northridge, California earthquake (Ms = 6.8). OVMC is on an alluvial deposit. The building was subjected to design level peak accelerations during the earthquake and suffered only limited structural and nonstructural damage. The recorded motions at different levels of the OVMC building as well as its associated free-field sites are analyzed using spectral analyses and system identification techniques. The new OVMC building was conservatively designed in 1976 with very high lateral load resisting capability - particularly as a reaction to the detrimental fate of the original Olive View Hospital that was heavily damaged during the 1971 San Fernando earthquake. The original hospital building was later razed. The replacement structure, the new cross-shaped OVMC building, experienced peak acceleration of 2.31g at the roof while its peak ground floor acceleration was 0.82g. The free-field peak acceleration was 0.91g. The lateral load resisting system of the OVMC building consists of concrete shear walls in the lower two stories and steel shear walls at the perimeter of the upper four stories. Spectral analysis shows that this stiff structure was not affected by the long duration pulses of the motions recorded at this site.

  13. A coccidioidomycosis outbreak following the Northridge, Calif, earthquake

    USGS Publications Warehouse

    Schneider, E.; Hajjeh, R.A.; Spiegel, R.A.; Jibson, R.W.; Harp, E.L.; Marshall, G.A.; Gunn, R.A.; McNeil, M.M.; Pinner, R.W.; Baron, R.C.; Burger, R.C.; Hutwagner, L.C.; Crump, C.; Kaufman, L.; Reef, S.E.; Feldman, G.M.; Pappagianis, D.; Werner, S.B.

    1997-01-01

    Objective. - To describe a coccidioidomycosis outbreak in Ventura County following the January 1994 earthquake, centered in Northridge, Calif, and to identify factors that increased the risk for acquiring acute coccidioidomycosis infection. Design. - Epidemic investigation, population- based skin test survey, and case-control study. Setting. - Ventura County, California. Results. - In Ventura County, between January 24 and March 15, 1994, 203 outbreak-associated coccidioidomycosis cases, including 3 fatalities, were identified (attack rate [AR], 30 cases per 100 000 population). The majority of cases (56%) and the highest AR (114 per 100 000 population) occurred in the town of Simi Valley, a community located at the base of a mountain range that experienced numerous landslides associated with the earthquake. Disease onset for cases peaked 2 weeks after the earthquake. The AR was 2.8 times greater for persons 40 years of age and older than for younger persons (relative risk, 2.8; 95% confidence interval [CI], 2.1-3.7; P<.001). Environmental data indicated that large dust clouds, generated by landslides following the earthquake and strong aftershocks in the Santa Susana Mountains north of Simi Valley, were dispersed into nearby valleys by northeast winds. Simi Valley case-control study data indicated that physically being in a dust cloud (odds ratio, 3.0; 95% CI, 1.6-5.4; P<.001) and time spent in a dust cloud (P<.001) significantly increased the risk for being diagnosed with acute coccidioidomycosis. Conclusions. - Both the location and timing of cases strongly suggest that the coccidioidomycosis outbreak in Ventura County was caused when arthrospores were spread in dust clouds generated by the earthquake. This is the first report of a coccidioidomycosis outbreak following an earthquake. Public and physician awareness, especially in endemic areas following similar dust cloud- generating events, may result in prevention and early recognition of acute

  14. GPS detection of ionospheric perturbations following the January 17, 1994, northridge earthquake

    NASA Technical Reports Server (NTRS)

    Calais, Eric; Minster, J. Bernard

    1995-01-01

    Sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements produce pressure waves that propagate at infrasonic speeds in the atmosphere. At ionospheric altitudes low frequency acoustic waves are coupled to ionispheric gravity waves and induce variations in the ionoispheric electron density. Global Positioning System (GPS) data recorded in Southern California were used to compute ionospheric electron content time series for several days preceding and following the January 17, 1994, M(sub w) = 6.7 Northridge earthquake. An anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter was observed. The signal frequency and phase velocity are consistent with results from numerical models of atmospheric-ionospheric acoustic-gravity waves excited by seismic sources as well as previous electromagnetic sounding results. It is believed that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the Northridge earthquake.

  15. USGS response to an urban earthquake, Northridge '94

    USGS Publications Warehouse

    Updike, Randall G.; Brown, William M.; Johnson, Margo L.; Omdahl, Eleanor M.; Powers, Philip S.; Rhea, Susan; Tarr, Arthur C.

    1996-01-01

    For the past 2 years, the USGS has rigorously pursued over 40 tasks focused on the USGS Northridge Earthquake Mission. This document is a summary report of the USGS findings; additional technical reports on specific USGS tasks are appearing in various scientific journals and USGS publications.

  16. Surface Fractures Formed in the Potrero Canyon, Tapo Canyon, and McBean Parkway Areas in Association with the 1994 Northridge, California Earthquake

    USGS Publications Warehouse

    Rymer, Michael J.; Treiman, Jerome A.; Powers, Thomas J.; Fumal, Thomas E.; Schwartz, David P.; Hamilton, John C.; Cinti, Francesca R.

    2001-01-01

    INTRODUCTION The magnitude 6.7 (M6.7) Northridge earthquake of 17 January 1994 strongly shook the Los Angeles urban region, resulting in 33 direct deaths, more than 20,000 people forced out of their homes, and an estimated $20 billion in damage (Hall, 1994). The earthquake was caused by slip on a previously unrecognized south-dipping fault buried beneath the San Fernando Valley. Slip on the fault propagated from a depth of about 19 km to about 8 km below the ground surface (USGS and SCEC, 1994). Although there was no surface faulting associated with the causative fault, surface fractures did develop along at least one fault (Mission Wells fault) and also in areas without recognized faults (Hart and others, 1995; Hecker and others, 1995a, 1995b; Rymer and others, 1995; Treiman, 1995). The term 'surface fractures' is used herein to describe ground breakage that is not associated with primary faulting or with triggered, secondary, surface faulting on a deep seismogenic fault. This report describes fault- and nonfault-related surface fractures that occurred at three sites, Potrero Canyon, Tapo Canyon, and the McBean Parkway area, 22 to 28 km north-northwest of the main shock (Fig. 1). Investigation of these sites documents far reaching effects of even moderately large earthquakes. Study of such effects has become increasingly important with further urbanization and development. Hecker and others (1995a, 1995b) documented the distribution of surface deformation associated with the Northridge earthquake in the Granada Hills area. The search for surface faulting and surface fracturing was initiated within hours of the earthquake. Both ground and airborne searches were made of the region. After fresh surface fractures were found in Potrero Canyon, aerial photographs were taken of the area (including the McBean Parkway site) by I.K. Curtis, on 21 January 1994, at scales of about 1:2,000 and 1:6,000. These aerial photographs were studied under high magnification to

  17. California State University, Northridge: Innovative Curriculum Design for Midcareer Professionals

    ERIC Educational Resources Information Center

    Minassians, Henrik P.

    2012-01-01

    Universities that focus on urban research should exploit the advantage of their location by matching their curricular strengths to the needs of their respective communities. This article describes how Public Sector Programs (PSP) at California State University, Northridge (CSUN) developed extensive graduate degree and certificate programs in…

  18. Seismic constraints and coulomb stress changes of a blind thrust fault system, 2: Northridge, California

    USGS Publications Warehouse

    Stein, Ross S.; Lin, Jian

    2006-01-01

    We review seismicity, surface faulting, and Coulomb stress changes associated with the 1994 Northridge, California, earthquake. All of the observed surface faulting is shallow, extending meters to tens of meters below the surface. Relocated aftershocks reveal no seismicity shallower than 2 km depth. Although many of the aftershocks lie along the thrust fault and its up-dip extension, there are also a significant number of aftershocks in the core of the gentle anticline above the thrust, and elsewhere on the up-thrown block. These aftershocks may be associated with secondary ramp thrusts or flexural slip faults at a depth of 2-4 km. The geological structures typically associated with a blind thrust fault, such as anticlinal uplift and an associated syncline, are obscured and complicated by surface thrust faults associated with the San Fernando fault that overly the Northridge structures. Thus the relationship of the geological structure and topography to the underlying thrust fault is much more complex for Northridge than it is for the 1983 Coalinga, California, earthquake. We show from a Coulomb stress analysis that secondary surface faulting, diffuse aftershocks, and triggered sequences of moderate-sized mainshocks, are expected features of moderate-sized blind thrust earthquakes.

  19. Height changes in the epicentral region preceding the January 17, 1994 Northridge earthquake

    USGS Publications Warehouse

    Castle, Robert O.; Packard, Robert F.; Dinitz, Laura B.

    2000-01-01

    Analysis of the results of repeated levelings through the epicentral region of the Mw 6.7, 1994 Northridge earthquake has disclosed the occurrence of differential uplift in this area that preceded the earthquake. Although the distribution of the relevant vertical-control data is somewhat sparse, in both space and time, those data that we have recovered indicate that this uplift exceeded 0.10 m and peaked 20-25 km west of the 1994 epicenter. While our data also indicate that this deformational event must have occurred during the period 1978-1989, evidence based on the character and magnitude of misclosures developed from 1987 and 1989 surveys argue that the deformation occurred largely during the period 1987-1989. The preseismic vertical-displacement field that preceded the Northridge earthquake is similar in form and, less certainly, magnitude to that which preceded the Mw 6.7, 1971 San Fernando earthquake; other possible, but less significant southern California analogues include the deformational events that preceded the Mw 5.3, 1973 Point Mugu and Mw 5.9, 1987 Whittier Narrows earthquakes. The small but growing number of recognized aseismic deformational episodes that preceded small to moderate magnitude earthquakes in southern California suggests that the deployment of the dense array of continuously recording GPS receivers planned for southern California can be expected to detect and more accurately describe such events than was heretofore possible. Moreover, if the relation between the duration of these deformational anomalies and the magnitudes of any ensuing earthquakes can be much more clearly established, the near perfect temporal control on position afforded by GPS suggests that we may be on the threshold of a realistic earthquake warning system.

  20. Northridge earthquake damage caused by geologic focusing of seismic waves

    PubMed

    Davis; Rubinstein; Liu; Gao; Knopoff

    2000-09-01

    Despite being located 21 kilometers from the epicenter of the 1994 Northridge earthquake (magnitude 6.7), the city of Santa Monica experienced anomalously concentrated damage with Mercalli intensity IX, an intensity as large as that experienced in the vicinity of the epicenter. Seismic records from aftershocks suggest that the damage resulted from the focusing of seismic waves by several underground acoustic lenses at depths of about 3 kilometers, formed by the faults that bound the northwestern edge of the Los Angeles basin. The amplification was greatest for high-frequency waves and was less powerful at lower frequencies, which is consistent with focusing theory and finite-difference simulations.

  1. Analysis of tank damage during the 1994 Northridge earthquake

    SciTech Connect

    Haroun, M.A.; Bhatia, H.

    1995-12-31

    The damage sustained by cylindrical liquid storage tanks during the 1994 Northridge earthquake is summarized. It included elephant foot buckling, anchor failure and roof-shell connection separation. A few of the important lessons learned, in particular, as related to the accuracy of code computations in predicting the actual behavior of these structures are outlined. A detailed case study is presented to illustrate the application of current seismic design standards to a damaged unanchored tank and to demonstrate the use of a state-of-the-art finite element analysis in assessing the seismic safety of the same tank.

  2. Combined GPS and InSAR models of postseismic deformation from the Northridge Earthquake

    NASA Technical Reports Server (NTRS)

    Donnellan, A.; Parker, J. W.; Peltzer, G.

    2002-01-01

    Models of combined Global Positioning System and Interferometric Synthetic Aperture Radar data collected in the region of the Northridge earthquake indicate that significant afterslip on the main fault occurred following the earthquake.

  3. Liquefaction and soil failure during 1994 northridge earthquake

    USGS Publications Warehouse

    Holzer, T.L.

    1999-01-01

    The 1994 Northridge, Calif., earthquake caused widespread permanent ground deformation on the gently sloping alluvial fan surface of the San Fernando Valley. The ground cracks and distributed deformation damaged both pipelines and surface structures. To evaluate the mechanism of soil failure, detailed subsurface investigations were conducted at four sites. Three sites are underlain by saturated sandy silts with low standard penetration test and cone penetration test values. These soils are similar to those that liquefied during the 1971 San Fernando earthquake, and are shown by widely used empirical relationships to be susceptible to liquefaction. The remaining site is underlain by saturated clay whose undrained shear strength is approximately half the value of the earthquake-induced shear stress at this location. This study demonstrates that the heterogeneous nature of alluvial fan sediments in combination with variations in the ground-water table can be responsible for complex patterns of permanent ground deformation. It may also help to explain some of the spatial variability of strong ground motion observed during the 1994 earthquake. ?? ASCE,.

  4. GPS Observations of Postseismic Deformation Associated With the 1994 Northridge Earthquake

    NASA Technical Reports Server (NTRS)

    Donnellan, A.

    1995-01-01

    Measurement of postseismic deformation following the 1994 M 6.7 Northridge earthquake indicates continued shortening of the region since the earthquake with motion slowing over a an exponential time scale of 3 years. Afterslip best explains the data, but that is still being tested.

  5. Mechanism of gas pipeline failures on Balboa Boulevard during the 1994 Northridge earthquake

    SciTech Connect

    Nishio, Nobuaki

    1995-12-31

    A possible mechanism of gas pipeline failures on Balboa Boulevard during the 1994 Northridge earthquake is proposed. This mechanism is the one that has been adopted by the Japan Gas Association in the Recommended Practice for the Earthquake-Resistant Design of Gas Pipelines. The possible mode of ground displacement that might have caused the above pipeline failures is also discussed.

  6. 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)

  7. Surface Deformation and Slip Distribution of the 1994 Northridge Earthquake Determined from InSAR

    NASA Astrophysics Data System (ADS)

    Severson, C. M.; Funning, G. J.; Marshall, S. T.

    2011-12-01

    The January 17, 1994 M6.7 Northridge earthquake occurred in the densely populated suburbs to the northwest of Los Angeles, California. Occurring on a previously unknown blind thrust fault, it was the most costly earthquake in United States history causing 60 deaths and ~20 billion dollars in damage. In the interval since the earthquake, several other blind thrusts have been identified in the area. In order to quantify the influence, in terms of stress changes, of the Northridge event on surrounding faults detailed knowledge of the location, orientation and amount of fault slip is important. Existing Interferometric Synthetic Aperture Radar (InSAR) models of this earthquake typically were developed by fitting the pattern of displacements by trial and error, and were therefore somewhat subjective. In the 15 years since the original studies were published a number of new modeling tools and community data products have been developed that should enable us to produce more detailed, objective and robust results. We measure the coseismic deformation of this earthquake using InSAR. A pair of descending images from the European Space Agency's ERS-1 satellite, spanning from 11/08/1993 to 12/06/1995, containing the earthquake are processed using the ROI_PAC software, and show uplift of up to ~45 cm centered on 118.508° W, 34.321° N. These data have been subsampled using a quadtree decomposition. Using this data, we first employ a nonlinear inversion to determine the parameters of the single rectangular dislocation that best fits the data. The best-fitting fault has strike: 110°, dip: 40.6° to the southwest, length: 14.2 km, width: 8.5 km, top fault depth: 6.7 km, slip: 2m, and moment: 1.1*1019 Nm. These results are relatively consistent with other published geodetic work (eg. Hudnut, 1996, Massonnet and Feigl, 1996), and the global CMT moment estimate. In detail, however, slip on a single rectangular dislocation does not completely model the observed deformation. Residual

  8. Evaluation and analysis of the performance of masonary infills during the Northridge earthquake

    SciTech Connect

    Bennett, R.M.; Fischer, W.L.; Flanagan, R.D.; Tenbus, M.A.

    1996-02-01

    Observations were made of the behavior of masonry infills in structural frames during the Northridge earthquake, and an analytical technique was developed for analyzing infilled frame structures. Infills near the epicenter suffered significant damage, but in several cases contributed to the seismic resistance and life safety performance. Older infill buildings in downtown Los Angeles experienced intensity of shaking similar to that expected in central/eastern United States earthquakes. The infills experienced some cracking, but otherwise complemented the lateral resistance of the weak building frames. This suggests infill frame buildings in moderate seismic zones may provide at least life safety functions without the need for expensive retrofit. A developed analytical technique was used to analyze two buildings for which the observed behavior and records from the Northridge earthquake were available. The analytical technique was based on using a piecewise linear equivalent strut for the infill. Parameters for the strut were obtained by examining the results of a wide variety of experimental infill tests. The strut method is easy to incorporate in standard linear analyses, and converges quite rapidly. The strut method was applied to two structures that had records from the Northridge earthquake. Very favorable comparisons between the analytical method and observed response were obtained. Recommendations were made concerning evaluation of the vulnerability of infills to earthquakes, and the construction of infills.

  9. Climate Science Program at California State University, Northridge

    NASA Astrophysics Data System (ADS)

    Steele Cox, H.; Klein, D.; Cadavid, A. C.; Foley, B.

    2012-12-01

    Due to its interdisciplinary nature, climate science poses wide-ranging challenges for science and mathematics students seeking careers in this field. There is a compelling need for universities to provide coherent programs in climate science in order to train future climate scientists. With funding from NASA Innovations in Climate Education (NICE), California State University, Northridge (CSUN), is creating the CSUN Climate Science Program. An interdisciplinary team of faculty members is working in collaboration with UCLA, Santa Monica College and NASA/JPL partners to create a new curriculum in climate science. The resulting sequence of climate science courses, or Pathway for studying the Mathematics of Climate Change (PMCC), is integrated into a Bachelor of Science degree program in the Applied Mathematical Sciences offered by the Mathematics Department at CSUN. The PMCC consists of courses offered by the departments of Mathematics, Physics, and Geography and is designed to prepare students for Ph.D. programs in technical fields relevant to global climate change and related careers. The students who choose to follow this program will be guided to enroll in the following sequence of courses for their 12 units of upper division electives: 1) A newly created course junior level course, Math 396CL, in applied mathematics which will introduce students to applications of vector calculus and differential equations to the study of thermodynamics and atmospheric dynamics. 2) An already existing course, Math 483, with new content on mathematical modeling specialized for this program; 3) An improved version of Phys 595CL on the mathematics and physics of climate change with emphasis on Radiative Transfer; 4) A choice of Geog 407 on Remote Sensing or Geog 416 on Climate Change with updated content to train the students in the analysis of satellite data obtained with the NASA Earth Observing System and instruction in the analysis of data obtained within a Geographical

  10. The January 17, 1994 Northridge Earthquake: Effects on selected industrial facilities and lifelines

    SciTech Connect

    Eli, M.W.; Sommer, S.C.; Roche, T.R.; Merz, K.L.

    1995-02-01

    Revision 0 of this report is being published in February 1995 to closely mark the one-year anniversary of the Northridge Earthquake. A September 1994 Draft version of the report was reviewed by DOE and NRC, and many of the review comments are incorporated into Revision 0. While this revision of the report is not entirely complete, it is being made available for comment, review, and evaluation. Since the report was written by several authors, sections of the report have slightly different styles. Several sections of Revision 0 are not complete, but are planned to be completed in Revision 1. The primary unfinished section is Section 3.3 on Electric Power Transmission. Other sections of Revision 0, such as Section 4.5.2 on the Energy Technology Engineering Center and 3.2 on Electric Power Generation, will be enhanced with further detailed information as it becomes available. In addition, further data, including processed response spectra for investigated facilities and cataloging of relay performance, will be added to Revision 1 depending upon investigation support. While Revision 0 of this report is being published by LLNL, Revision 1 is planned to be published by EPRI. The anticipated release date for Revision 1 is December 1995. Unfortunately, the one-year anniversary of the Northridge Earthquake was also marked by the devastating Hyogo-Ken Nanbu (or Hanshin-Awaji) Earthquake in Kobe, Japan. As compared to the Northridge Earthquake, there were many more deaths, collapsed structures, destroyed lifelines, and fires following the Kobe Earthquake. Lessons from the Kobe Earthquake will both reemphasize topics discussed in this report and provide further issues to be addressed when designing and retrofitting structures, systems, and components for seismic strong motion.

  11. A hospital as victim and responder: the Sepulveda VA Medical Center and the Northridge earthquake.

    PubMed

    Chavez, C W; Binder, B

    1996-01-01

    Many hospital emergency plans focus on the hospital as a disaster responder, with a fully operational medical facility, able to receive and treat mass casualties from a clearly defined accident scene. However, hospitals need to prepare a response for extreme casualty events such as earthquakes, tornadoes, or hurricanes. This article describes the planning, mitigation, response, and recovery of a major medical--surgical center thrust into a victim responder role following the devastating Northridge earthquake. The subsequent evacuation and care of patients, treatment of casualties, incident command, prior education and training, and recovery issues are addressed.

  12. Crustal Structure Across the Northridge Earthquake Region Using Wide-Angle Seismic Profiling along the LARSE II Transect

    NASA Astrophysics Data System (ADS)

    Okaya, D.; Fuis, G.; Godfrey, N.; Murphy, J.; Clayton, R.; ten Brink, U.

    2001-12-01

    A crustal transect across the 1994 Northridge earthquake region was completed in 1999 with the acquisition of land reflection/refraction data in LARSE II (Los Angeles Region Seismic Experiment, Phase II). These data are combined with onshore-offshore refraction profiling plus multichannel seismic (MCS) data and ocean bottom seismometer (OBS) data collected in 1994 as part of LARSE I. The total data set forms a complete 280-km onshore-offshore transect from the southern California Borderlands, across the Northridge earthquake region, the Transverse Ranges, the San Andreas fault, the Mojave Desert, and Tehachapi Mts. The onshore-offshore experiment in 1994 used data from 47 land stations (vertical-component Refteks) and eight OBS's in the Borderlands. These instruments collected approx. 150 km of MCS airgun sources produced by the R/V Ewing. The land experiment in 1999 used 93 variable-sized explosions (5-4000 lbs) recorded into an array of portable seismographs 150 km long extending from the Malibu coastline to the Tehachapi Mts. For the southern 90 km, instrument spacing was 100 m including through the urban San Fernando and Santa Clarita Valleys (km 12-47), where LARSE data is augmented by industry reflection and well data. The Mojave Desert segment (km 77-101) also has industry reflection and well data. We present the crustal structure along this transect derived from first arrival traveltime tomography and reflection ray trace modeling. We compare these results to a separate LARSE transect 50-80 km to the east through the Los Angeles Basin and San Gabriel Mts.

  13. Site response for urban Los Angeles using aftershocks of the Northridge earthquake

    USGS Publications Warehouse

    Hartzell, S.; Leeds, A.; Frankel, A.; Michael, J.

    1996-01-01

    Ground-motion records from aftershocks of the 1994 Northridge earthquake are used to estimate site response in the urban Los Angeles area. Over 1300 shear-wave records from 61 sources and 90 sites are used in a linear inversion for source and site-response spectra. The methodology makes no assumptions about the shape of the source spectrum. To obtain a stable unique inverse, a Q model and geometrical spreading factor are assumed. In addition, the site response at a hardrock site is constrained to be approximately 1.0 with a kappa of 0.02. The site-response spectra compare favorably with the results of previous and on-going investigations in Los Angeles. A couple of first-order effects are lower site response in the surrounding mountains, dominated by Mesozoic and Tertiary rocks, and higher values in the San Fernando and Los Angeles Basins, containing surficial Pleistocene and Holocene alluvial deposits. Results show good correlation of high site-response spectral values with localized areas of severe damage (Interstate 10 collapse, Sherman Oaks, Northridge, Interstate 5/14 collapse). However, widespread trends in site response across the sedimentary basins are not obvious. The data suggest that site responses are lower near the southern margin of the San Fernando Valley for sources to the north, due to north-dipping sedimentary structures. But the general pattern of site response is characterized by high variability on length scales less than a kilometer. Variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit. For some of the alluvial basin sites, surface-wave generation is a significant contributor to elevated site response at lower frequencies, below 2 Hz. The total damage pattern for the Northridge earthquake is influenced by strong source directivity to the north and strong local site effects. The correlation of weak-motion site-response estimates with areas of significant damage

  14. Estimation of Future Earthquake Losses in California

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    Recent developments in earthquake hazards and damage modeling, computing, and data management and processing, have made it possible to develop estimates of the levels of damage from earthquakes that may be expected in the future in California. These developments have been mostly published in the open literature, and provide an opportunity to estimate the levels of earthquake damage Californians can expect to suffer during the next several decades. Within the past 30 years, earthquake losses have increased dramatically, mostly because our exposure to earthquake hazards has increased. All but four of the recent damaging earthquakes have occurred distant from California's major population centers. Two, the Loma Prieta earthquake and the San Fernando earthquake, occurred on the edges of major populated areas. Loma Prieta caused significant damage in the nearby Santa Cruz and in the more distant, heavily populated, San Francisco Bay area. The 1971 San Fernando earthquake had an epicenter in the lightly populated San Gabriel Mountains, but caused slightly over 2 billion dollars in damage in the Los Angeles area. As urban areas continue to expand, the population and infrastructure at risk increases. When earthquakes occur closer to populated areas, damage is more significant. The relatively minor Whittier Narrows earthquake of 1987 caused over 500 million dollars in damage because it occurred in the Los Angeles metropolitan area, not at its fringes. The Northridge earthquake had fault rupture directly beneath the San Fernando Valley, and caused about 46 billion dollars in damage. This vast increase in damage from the San Fernando earthquake reflected both the location of the earthquake directly beneath the populated area and the 23 years of continued development and resulting greater exposure to potential damage. We have calculated losses from potential future earthquake, both as scenarios of potential earthquakes and as annualized losses considering all the potential

  15. 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. 

  16. Nonlinear sediment response during the 1994 Northridge earthquake: Observations and finite source simulations

    SciTech Connect

    Field, E.H.; Zeng, Y.; Johnson, P.A.; Beresnev, I.A.

    1998-11-01

    We have addressed the long-standing question regarding nonlinear sediment response in the Los Angeles region by testing whether sediment amplification was similar between the Northridge earthquake and its aftershocks. Comparing the weak- and strong-motion site response at 15 sediment sites, we find that amplification factors were significantly less for the main shock implying systematic nonlinearity. The difference is largest between 2 and 4 Hz (a factor of 2), and is significant at the 99{percent} confidence level between 0.8 and 5.5 Hz. The inference of nonlinearity is robust with respect to the removal of possibly anomalous sediment sites and how the reference-site motion is defined. Furthermore, theoretical ground-motion simulations show no evidence of any bias from finite source effects during the main shock. Nonlinearity is also suggested by the fact that the four sediment sites that contain a clear fundamental resonance for the weak motion exhibit a conspicuous absence of the peak in the strong motion. Although we have taken the first step of establishing the presence of nonlinearity, it remains to define the physics of nonlinear response and to test the methodologies presently applied routinely in engineering practice. The inference of nonlinearity implies that care must be exercised in using sediment site data to study large earthquakes or predict strong ground motion. {copyright} 1998 American Geophysical Union

  17. Using safety inspection data to estimate shaking intensity for the 1994 Northridge earthquake

    USGS Publications Warehouse

    Thywissen, K.; Boatwright, J.

    1998-01-01

    We map the shaking intensity suffered in Los Angeles County during the 17 January 1994, Northridge earthquake using municipal safety inspection data. The intensity is estimated from the number of buildings given red, yellow, or green tags, aggregated by census tract. Census tracts contain from 200 to 4000 residential buildings and have an average area of 6 km2 but are as small as 2 and 1 km2 in the most densely populated areas of the San Fernando Valley and downtown Los Angeles, respectively. In comparison, the zip code areas on which standard MMI intensity estimates are based are six times larger, on average, than the census tracts. We group the buildings by age (before and after 1940 and 1976), by number of housing units (one, two to four, and five or more), and by construction type, and we normalize the tags by the total number of similar buildings in each census tract. We analyze the seven most abundant building categories. The fragilities (the fraction of buildings in each category tagged within each intensity level) for these seven building categories are adjusted so that the intensity estimates agree. We calibrate the shaking intensity to correspond with the modified Mercalli intensities (MMI) estimated and compiled by Dewey et al. (1995); the shapes of the resulting isoseismals are similar, although we underestimate the extent of the MMI = 6 and 7 areas. The fragility varies significantly between different building categories (by factors of 10 to 20) and building ages (by factors of 2 to 6). The post-1940 wood-frame multi-family (???5 units) dwellings make up the most fragile building category, and the post-1940 wood-frame single-family dwellings make up the most resistant building category.

  18. A method for mapping apparent stress and energy radiation applied to the 1994 Northridge earthquake fault zone-revisited

    USGS Publications Warehouse

    McGarr, A.; Fletcher, Joe B.

    2001-01-01

    McGarr and Fletcher (2000) introduced a technique for estimating apparent stress and seismic energy radiation associated with small patches of a larger fault plane and then applied this method to the slip model of the Northridge earthquake (Wald et al., 1996). These results must be revised because we did not take account of the difference between the seismic energy near the fault and that in the farfield. The fraction f(VR) of the near-field energy that propagates into the far-field is a monotonic function that ranges from 0.11 to 0.40 as rupture velocity VR increases from 0.6?? to 0.95??, where ?? is the shear wave speed. The revised equation for apparent stress for subfault ij is taij = f(VR) ????/ 2 Dij??? D(t)ij2dt, where ?? is density, D(t)ij is the time-dependent slip, and Dij is the final slip. The corresponding seismic energy is Eaij = ADijtaij, where A is the subfault area. Our corrected distributions of apparent stress and radiated energy over the Northridge earthquake fault zone are about 35% of those published before.

  19. Power systems after the Northridge earthquake: Emergency operations and changes in seismic equipment specifications, practice, and system configuration

    SciTech Connect

    Schiff, A.J.; Tognazzini, R.; Ostrom, D.

    1995-12-31

    The Northridge earthquake caused extensive damage to high voltage substation equipment, and for the first time the failure of transmission towers. Power was lost to much of the earthquake impacted area, and 93% of the customers were restored within 24 hours. To restore service, damage monitoring, communication and protective equipment, such as current-voltage transformers, wave traps, and lightning arresters, were removed or bypassed and operation restored. To improve performance some porcelain members are being replaced with composite materials for bushings, current-voltage transformers and lightning arresters. Interim equipment seismic specifications for equipment have been instituted. Some substations are being re-configured and rigid bus and conductors are being replaced with flexible conductors. Non-load carrying conductors, such as those used on lightning arrester, are being reduced in size to reduce potential interaction problems. Better methods of documenting damage and repair costs are being considered.

  20. A method for mapping apparent stress and energy radiation applied to the 1994 Northridge earthquake fault zone

    USGS Publications Warehouse

    McGarr, A.; Fletcher, Joe B.

    2000-01-01

    Using the Northridge earthquake as an example, we demonstrate a new technique able to resolve apparent stress within subfaults of a larger fault plane. From the model of Wald et al. (1996), we estimated apparent stress for each subfault using τa = (G/β)/2 where G is the modulus of rigidity, β is the shear wave speed, and is the average slip rate. The image of apparent stress mapped over the Northridge fault plane supports the idea that the stresses causing fault slip are inhomogeneous, but limited by the strength of the crust. Indeed, over the depth range 5 to 17 km, maximum values of apparent stress for a given depth interval agree with τa(max)=0.06S(z), where S is the laboratory estimate of crustal strength as a function of depth z. The seismic energy from each subfault was estimated from the product τaDA, where A is subfault area and D its slip. Over the fault zone, we found that the radiated energy is quite variable spatially, with more than 50% of the total coming from just 15% of the subfaults.

  1. WGCEP Historical California Earthquake Catalog

    USGS Publications Warehouse

    Felzer, Karen R.; Cao, Tianqing

    2008-01-01

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

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

    USGS Publications Warehouse

    Field, Edward H.; Milner, Kevin R.; ,

    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.

  3. Calculation of broadband time histories of ground motion, Part II: Kinematic and dynamic modeling using theoretical Green's functions and comparison with the 1994 northridge earthquake

    USGS Publications Warehouse

    Hartzell, S.; Guatteri, Mariagiovanna; Mai, P.M.; Liu, P.-C.; Fisk, M. R.

    2005-01-01

    In the evolution of methods for calculating synthetic time histories of ground motion for postulated earthquakes, kinematic source models have dominated to date because of their ease of application. Dynamic models, however, which incorporate a physical relationship between important faulting parameters of stress drop, slip, rupture velocity, and rise time, are becoming more accessible. This article compares a class of kinematic models based on the summation of a fractal distribution of subevent sizes with a dynamic model based on the slip-weakening friction law. Kinematic modeling is done for the frequency band 0.2 to 10.0. Hz, dynamic models are calculated from 0.2 to 2.0. Hz. The strong motion data set for the 1994 Northridge earthquake is used to evaluate and compare the synthetic time histories. Source models are propagated to the far field by convolution with 1D and 3D theoretical Green’s functions. In addition, the kinematic model is used to evaluate the importance of propagation path effects: velocity structure, scattering, and nonlinearity. At present, the kinematic model gives a better broadband fit to the Northridge ground motion than the simple slip-weakening dynamic model. In general, the dynamic model overpredicts rise times and produces insufficient shorter-period energy. Within the context of the slip-weakening model, the Northridge ground motion requires a short slip-weakening distance, on the order of 0.15 m or less. A more complex dynamic model including rate weakening or one that allows shorter rise times near the hypocenter may fit the data better.

  4. Terrestrial LIDAR investigation of the December 2003 and January 2007 activations of the Northridge Bluff landslide, Daly City, California

    USGS Publications Warehouse

    Collins, Brian D.; Kayen, Robert; Reiss, Thomas; Sitar, Nicholas

    2007-01-01

    On December 20, 2003 and again on January 1, 2007, landslides occurred along the coastal bluff that forms the west boundary of Daly City, California sending debris as far as 290 meters downhill and 90 meters into the ocean. This area is known for large landslide events where 150-meter tall coastal bluffs extend southward along the west boundary of San Francisco and San Mateo Counties (Fig. 1). The 2003 and 2007 landslide events occurred west of Northridge Drive in Daly City and just south of Avalon Canyon, which bisects the bluffs in this area (Fig. 2). Residential development, utility lines and roads occupy the land immediately east of this location. As part of a comprehensive project to investigate the failure mechanisms of coastal bluff landslides in weakly lithified sediments along the west coast of the United States, members of the U.S. Geologic Survey (USGS) Coastal and Marine Geology (CMG) Program performed reconnaissance mapping of these landslide events including collection of high-resolution topographic data using CMG's terrestrial LIDAR laser scanning system. This report provides a brief background on each landslide event and presents topographic datasets collected following each event. Downloadable contour data, images, and FGDC-compliant metadata of the surfaces generated from the LIDAR data are also provided. LIDAR data collection and processing techniques used to generate the datasets are outlined. Geometric and volumetric measurements are also presented along with high-resolution cross-sections through various areas of the slide masses and discussion concerning the slides present (2007) configuration is provided.

  5. Calculation of broadband time histories of ground motion: Comparison of methods and validation using strong-ground motion from the 1994 Northridge earthquake

    USGS Publications Warehouse

    Hartzell, S.; Harmsen, S.; Frankel, A.; Larsen, S.

    1999-01-01

    This article compares techniques for calculating broadband time histories of ground motion in the near field of a finite fault by comparing synthetics with the strong-motion data set for the 1994 Northridge earthquake. Based on this comparison, a preferred methodology is presented. Ground-motion-simulation techniques are divided into two general methods: kinematic- and composite-fault models. Green's functions of three types are evaluated: stochastic, empirical, and theoretical. A hybrid scheme is found to give the best fit to the Northridge data. Low frequencies ( 1 Hz) are calculated using a composite-fault model with a fractal subevent size distribution and stochastic, bandlimited, white-noise Green's functions. At frequencies below 1 Hz, theoretical elastic-wave-propagation synthetics introduce proper seismic-phase arrivals of body waves and surface waves. The 3D velocity structure more accurately reproduces record durations for the deep sedimentary basin structures found in the Los Angeles region. At frequencies above 1 Hz, scattering effects become important and wave propagation is more accurately represented by stochastic Green's functions. A fractal subevent size distribution for the composite fault model ensures an ??-2 spectral shape over the entire frequency band considered (0.1-20 Hz).

  6. A Final Case Study of SCALE Activities at California State University, Northridge: How Institutional Context Influenced a K-20 STEM Education Change Initiative. WCER Working Paper No. 2009-5

    ERIC Educational Resources Information Center

    Hora, Matthew T.; Millar, Susan B.

    2009-01-01

    This qualitative case study reports on processes and outcomes of the National Science Foundation (NSF)-funded System-Wide Change for All Learners and Educators (SCALE) project at the California State University, Northridge (CSUN). It addresses a critical challenge in studying systemic reform in complex organizations: the lack of methodologies that…

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

    USGS Publications Warehouse

    ,

    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).

  8. Earthquake Preparedness 101: Guidelines for Colleges and Universities.

    ERIC Educational Resources Information Center

    California Governor's Office, Los Angeles. Office of Emergency Services.

    This document presents guidelines on emergency response and business recovery for colleges and universities in the event of an earthquake. The guidelines, developed by California institutions and revised based on experience with the Northridge earthquake, are provided under the following headings: (1) "To the President or Chancellor"; (2) "To the…

  9. 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.

  10. 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

  11. 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.

  12. Migration of historical earthquakes in California

    NASA Astrophysics Data System (ADS)

    King, Chi-Yu; Ma, Zongjin

    1988-12-01

    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).

  13. Ground-motion variability resulting from the January 17, 1994, M = 6.6 Northridge earthquake at the interchange between highways 14 and I-5 in the northern San Fernando Valley

    SciTech Connect

    Hutchings, L.; Jarpe, S.; Kasameyer, P.; McCallen, D.; Heuze, F.; Lewis, P.; Cullen, J.

    1994-02-04

    Lawrence Livermore National Laboratory responded to the 17 January 1994, Northridge earthquake by sending an information gathering team to observe and study the collapse of the interchange between highways 14 and I-5 in the northern San Fernando Valley. This field team examined the structural failure at the interchange and the surface soil conditions, and they installed high-grain RefTek seismic recorders to record aftershocks. We recorded aftershocks for two weeks. Analyses of aftershock recordings in this report illustrate the degree of differential support motion for this site, and the higher than expected ground motion from an earthquake of this size and distance. We used the aftershock recordings of small earthquakes as empirical Green`s functions and synthesized strong ground motion at three sites in the interchange area. Results presented here are based on an assumption that the geology of the interchange area remained linear in its response to the main event.

  14. Mentoring Through Research as a Catalyst for the Success of Under-represented Minority Students in the Geosciences at California State University Northridge

    NASA Astrophysics Data System (ADS)

    Marsaglia, K. M.; Pedone, V.; Simila, G. W.; Yule, J. D.

    2002-12-01

    The Catalyst Program of the Department of Geological Sciences at California State University Northridge has been developed by four faculty members who were the recipients of a three-year award (2002-2005) from the National Science Foundation. The goal of the program is to increase minority participation and success in the geosciences. The program seeks to enrich the educational experience by introducing students at all levels to research in the geosciences and to decrease obstacles that affect academic success. Both these goals are largely achieved by the formation of integrated high school, undergraduate, and graduate research groups, which also provide fulfilling and successful peer mentorship. The Catalyst Program provides significant financial support to participants to allow them to focus their time on their education. New participants first complete a specially designed course that introduces them to peer-mentoring, collaborative learning, and geological research. Students of all experience levels then become members of research teams, which deepens academic and research skills as well as peer-mentor relationships. The program was highly successful in its inaugural year. To date, undergraduates and graduate students in the program coauthored six abstracts at professional meetings and one conference paper. High-school students gained first hand experience of a college course and geologic research. Perhaps the most important impacts of the program are the close camaraderie that has developed and the increased ability of the Catalyst students to plan and execute research with greater confidence and self-esteem.

  15. Earthquake hazard after a mainshock in california.

    PubMed

    Reasenberg, P A; Jones, L M

    1989-03-01

    After a strong earthquake, the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures. A stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock. The probabilities depend strongly on the model parameters, which are estimated with Bayesian statistics from both the ongoing aftershock sequence and from a suite of historic California aftershock sequences. Probabilities for damaging aftershocks and greater mainshocks are typically well-constrained after the first day of the sequence, with accuracy increasing with time.

  16. 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.

  17. 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

  18. 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.

  19. Some facts about aftershocks to large earthquakes in California

    USGS Publications Warehouse

    Jones, Lucile M.; Reasenberg, Paul A.

    1996-01-01

    aftershocks if they are located within a characteristic distance from the mainshock. This distance is usually taken to be one or two times the length of the fault rupture associated with the mainshock. For example, if the mainshock ruptured a 100 km length of a fault, subsequent earthquakes up to 100-200 km away from the mainshock rupture would be considered aftershocks. The fault rupture length was approximately 15 km in the 1994 Northridge earthquake, and 430 km in the great 1906 earthquake.

  20. School Safety Down to Earth: California's Earthquake-Resistant Schools.

    ERIC Educational Resources Information Center

    Progressive Architecture, 1979

    1979-01-01

    Schools in California being built to resist damage by earthquakes are part of a program to meet building standards established in 1933. The three new schools presented reflect the strengths and weaknesses of the program. (Author/MLF)

  1. Earthquake preparedness levels amongst youth and adults in Oakland, California

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  2. Celebrating the "Intellectual Heart": Emergent Meanings from a Post-Earthquake Organizational Communication Culture Perspective.

    ERIC Educational Resources Information Center

    McNamara, Catherine V.; And Others

    The Organizational Communication Culture (OCC) method, designed by Charles A. Bantz (1993) was utilized as the primary method for analyzing messages coming from the administration of California State University, Northridge, after the earthquake. Bantz feels that communication interactions in an organization bring meanings and expectations to that…

  3. The magnitude distribution of earthquakes near Southern California faults

    USGS Publications Warehouse

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

    2011-01-01

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

  4. 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.

  5. 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

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

    PubMed

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

    2011-10-01

    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.

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

    SciTech Connect

    McNutt, S.

    1990-01-01

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

  8. The Southern California Earthquake Survival Program

    USGS Publications Warehouse

    Harris, J.M.

    1989-01-01

    In July 1988, the Los Angeles County Board of Supervisors directed the Chief Administrative Office to develop an educational program aimed at improving earthquake preparedness among Los Angeles County residents. the board recognized that current earthquake education efforts were not only insufficient, but also often confusing and costly. The board unanimously approved the development of a program that would make earthquake preparedness a year-long effort by encouraging residents to take a different precaution each month. 

  9. Triggering of repeating earthquakes in central California

    USGS Publications Warehouse

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

    2014-01-01

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

  10. Earthquake site response in Santa Cruz, California

    USGS Publications Warehouse

    Carver, D.; Hartzell, S.H.

    1996-01-01

    Aftershocks of the 1989 Loma Prieta, California, earthquake are used to estimate site response in a 12-km2 area centered on downtown Santa Cruz. A total of 258 S-wave records from 36 aftershocks recorded at 33 sites are used in a linear inversion for site-response spectra. The inversion scheme takes advantage of the redundancy of the large data set for which several aftershocks are recorded at each site. The scheme decomposes the observed spectra into source, path, and site terms. The path term is specified before the inversion. The undetermined degree of freedom in the decomposition into source and site spectra is removed by specifying the site-response factor to be approximately 1.0 at two sites on crystalline bedrock. The S-wave site responses correlate well with the surficial geology and observed damage pattern of the mainshock. The site-response spectra of the floodplain sites, which include the heavily damaged downtown area, exhibit significant peaks. The largest peaks are between 1 and 4 Hz. Five floodplain sites have amplification factors of 10 or greater. Most of the floodplain site-response spectra also have a smaller secondary peak between 6 and 8 Hz. Residential areas built on marine terraces above the flood-plain experienced much less severe damage. Site-response spectra for these areas also have their largest peaks between 1 and 4 Hz, but the amplification is generally below 6. Several of these sites also have a secondary peak between 6 and 8 Hz. The response peaks seen at nearly all sites between 1 and 4 Hz are probably caused by the natural resonance of the sedimentary rock column. The higher amplifications at floodplain sites may be caused by surface waves generated at the basin margins. The secondary peak between 6 and 8 Hz at many sites may be a harmonic of the 1- to 4-Hz peaks. We used waveforms from a seven-station approximately linear array located on the floodplain to calculate the apparent velocity and azimuth of propagation of coherent

  11. 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.

  12. Earthquake locations and seismic velocity models for Southern California

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    Earthquake locations are fundamental to studies of earthquake physics, fault orientations and Earth's deformation. Improving earthquake location accuracy has been an important goal branch in seismology for the past few decades. In this dissertation, I consider several methods to improve both relative and absolute earthquake locations. Chapter 2 is devoted to the comparison of different relative earthquake location techniques based on synthetic data, including the double-difference and source-specific station term (SSST) method. The shrinking box SSST algorithm not only provides similar improvements in relative earthquake locations compared to other techniques, but also improves absolute location accuracy compared to the simple SSST method. Chapter 4 describes and documents the COMPLOC software package for implementing the shrinking box SSST algorithm. Chapter 3 shows how absolute locations for quarry seismicity can be obtained by using remote sensing data, which is useful in providing absolute reference locations for three-dimensional velocity inversions and to constrain the shallow crustal structure in simultaneous earthquake location and velocity inversions. Chapter 5 presents and tests a method to estimate local Vp/Vs ratios for compact similar earthquake clusters using the precise P- and S-differential times obtained using waveform cross-correlation. Chapter 6 describes a new three-dimensional seismic velocity model for southern California obtained using the "composite event method" applied to the SIMULPS tomographic inversion algorithm. Based on this velocity model and waveform cross-correlation, Chapter 7 describes how a new earthquake location catalog is obtained for about 450,000 southern California earthquakes between 1981 and 2005.

  13. 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.

  14. 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.

  15. The San Ardo, California, earthquake of 24 November 1985

    USGS Publications Warehouse

    Poley, C.M.

    1988-01-01

    Presented here are the main shock focal-plane solution and accompnaying aftershock hypocentral distribution of an M = 4.5 earthquake that occurred at 1921 UTC on the 24 November 1985 (at latitude 36??2.3'N and at longitude 120??52.1'W) at 11.3km depth, near the town of San Ardo, California. -Author

  16. 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.

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

    USGS Publications Warehouse

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

    2002-01-01

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

  18. 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

  19. 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.

  20. 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.

  1. Deterministic Earthquake Hazard Assessment by Public Agencies in California

    NASA Astrophysics Data System (ADS)

    Mualchin, L.

    2005-12-01

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

  2. Predictability of repeating earthquakes near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Zechar, J. Douglas; Nadeau, Robert M.

    2012-07-01

    We analyse sequences of repeating microearthquakes that were identified by applying waveform coherency methods to data from the Parkfield High-Resolution Seismic Network. Because by definition all events in a sequence have similar magnitudes and locations, the temporal behaviour of these sequences is naturally isolated, which, coupled with the high occurrence rates of small events, makes these data ideal for studying interevent time distributions. To characterize the temporal predictability of these sequences, we perform retrospective forecast experiments using hundreds of earthquakes. We apply three variants of a simple algorithm that produces sequence-specific, time-varying hazard functions, and we find that the sequences are predictable. We discuss limitations of these data and, more generally, challenges in identifying repeating events, and we outline the potential implications of our results for understanding the occurrence of large earthquakes.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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).

  8. Urban seismology - Northridge aftershocks recorded by multi-scale arrays of portable digital seismographs

    USGS Publications Warehouse

    Meremonte, M.; Frankel, A.; Cranswick, E.; Carver, D.; Worley, D.

    1996-01-01

    We deployed portable digital seismographs in the San Fernando Valley (SFV), the Los Angeles basin (LAB), and surrounding hills to record aftershocks of the 17 January 1994 Northridge California earthquake. The purpose of the deployment was to investigate factors relevant to seismic zonation in urban areas, such as site amplification, sedimentary basin effects, and the variability of ground motion over short baselines. We placed seismographs at 47 sites (not all concurrently) and recorded about 290 earthquakes with magnitudes up to 5.1 at five stations or more. We deployed widely spaced stations for profiles across the San Fernando Valley, as well as five dense arrays (apertures of 200 to 500 m) in areas of high damage, such as the collapsed Interstate 10 overpass, Sherman Oaks, and the collapsed parking garage at CalState Northridge. Aftershock data analysis indicates a correlation of site amplification with mainshock damage. We found several cases where the site amplification depended on the azimuth of the aftershock, possibly indicating focusing from basin structures. For the parking garage array, we found large ground-motion variabilities (a factor of 2) over 200-m distances for sites on the same mapped soil unit. Array analysis of the aftershock seismograms demonstrates that sizable arrivals after the direct 5 waves consist of surface waves traveling from the same azimuth as that of the epicenter. These surface waves increase the duration of motions and can have frequencies as high as about 4 Hz. For the events studied here, we do not observe large arrivals reflected from the southern edge of the San Fernando Valley.

  9. Separation of site effects and structural focusing in Santa Monica, California: A study of high-frequency weak motions from earthquakes and blasts recorded during the Los Angeles Region Seismic Experiment

    USGS Publications Warehouse

    Baher, S.; Davis, P.M.; Fuis, G.

    2002-01-01

    Near-surface site factors and the effects of deep structural focusing were estimated in the Santa Monica Mountains and Santa Monica, California, from a portable array of 75 seismic stations deployed during the Los Angeles Region Seismic Experiment, Phase II (LARSE II). The objective was to examine further the origin of seismic wave amplification in the region of intense damage south of the Santa Monica Fault from the Northridge earthquake. The analysis used normalized spectral amplitudes in the 4- to 8- and 8- to 12-Hz range in direct and coda waves from local earthquakes in Santa Paula, Northridge, Redlands, and Hector Mine. Coda waves indicated that site factor amplifications are larger south of the Santa Monica fault relative to the north. Spectral ratios of direct S waves, corrected for site effects, show additional amplificaton south of, and adjacent to, the Santa Monica fault, attributable to focusing by a deeper structure. Gao et al. (1996) concluded that localized focusing effects contributed to anomalous P- and S-wave amplification in the Santa Monica damage zone for Northridge aftershocks within a specified range of azimuths. In an attempt to reproduce the hypothesized focusing from the Northridge earthquake, two shots (4000 and 3750 lb.) were detonated, one at Pyramid Lake, a distance of about 69 km to the north-northwest of central Santa Monica, and the other near Fort Tejon, a distance of 91 km. The azimuth of the shots was chosen to be that expected to give anomalous amplification. At these distance steeply incident seismic energy from Pg/PmP waves are expected to pass through the underground focusing structure and be selectively amplified. After the local site factors are removed, the waveforms from the Fort Tejon shot exhibited localized amplification adjacent to and south of the fault, 2-3 times larger than that of the surrounding area. The effect is less for waves from the Pyramid Lake shot, which could be due to their higher angle of incidence

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Foreshocks and aftershocks of the Great 1857 California earthquake

    USGS Publications Warehouse

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

    1999-01-01

    The San Andreas fault is the longest fault in California and one of the longest strike-slip faults anywhere in the world, yet we know little about many aspects of its behavior before, during, and after large earthquakes. We conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 M 7.9 Fort Tejon earthquake on the central and southern segments of the fault. We began by searching archived first-hand accounts from 1857 through 1862, by grouping felt reports temporally, and by assigning modified Mercalli intensities to each site. We then used a modified form of the grid-search algorithm of Bakum and Wentworth, derived from empirical analysis of modern earthquakes, to find the location and magnitude most consistent with the assigned intensities for each of the largest events. The result confirms a conclusion of Sieh that at least two foreshocks ('dawn' and 'sunrise') located on or near the Parkfield segment of the San Andreas fault preceded the mainshock. We estimate their magnitudes to be M ~ 6.1 and M ~ 5.6, respectively. The aftershock rate was below average but within one standard deviation of the number of aftershocks expected based on statistics of modern southern California mainshock-aftershock sequences. The aftershocks included two significant events during the first eight days of the sequence, with magnitudes M ~ 6.25 and M ~ 6.7, near the southern half of the rupture; later aftershocks included a M ~ 6 event near San Bernardino in December 1858 and a M ~ 6.3 event near the Parkfield segment in April 1860. From earthquake logs at Fort Tejon, we conclude that the aftershock sequence lasted a minimum of 3.75 years.

  15. Geometry and earthquake potential of the shoreline fault, central California

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2013-01-01

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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. Deep structure in the region of the San Fernando and Santa Clarita Valleys, southern California, from LARSE II seismic imaging, earthquake relocation, and magnetic modeling -- a progress report

    NASA Astrophysics Data System (ADS)

    Fuis, G. S.; Ryberg, T.; Lutter, W. J.; Hauksson, E.; Richards-Dinger, K. B.; Hildenbrand, T. G.; Langenheim, V. E.; Murphy, J. M.; Okaya, D. A.

    2001-12-01

    The Los Angeles Region Seismic Experiment has as its chief goal seismic imaging of sedimentary basins and faults in the Los Angeles region in order to address earthquake hazards posed by these geologic features. Two 150-km-long transects were investigated, one (LARSE I) crossing the Los Angeles basin and San Gabriel Mts in a northeasterly direction through the vicinity of the 1987 M 5.9 Whittier Narrows earthquake, and a second (LARSE II) crossing the San Fernando Valley (SFV) and Santa Clarita Valley (SCV) in a northerly direction through the vicinities of the 1994 M 6.7 Northridge and 1971 M 6.7 San Fernando earthquakes. Along the LARSE II profile, seismic reflection data and relocated earthquakes suggest that the Northridge fault is a relatively simple plane dipping ~30o southward from ~8 km depth beneath the Santa Susana Mts (between the SFV and SCV) to the 1994 hypocenter at ~19 km depth. Relocated hypocenters suggest a deep part of the Santa Susana fault was activated during the Northridge aftershock sequence. In contrast, the 1971 San Fernando earthquake appears to have activated several faults in addition to the two rupture planes inferred by Heaton (1982), including the Northridge Hills blind thrust fault and a deep part of the San Gabriel fault. These two faults truncate reflections from the bottoms of the sedimentary basins in the SFV and SCV. We interpret the Northridge Hills blind thrust fault to truncate basin-bottom reflections beneath the SFV at ~5-6 km depth in the northern part of the SFV, and the San Gabriel fault to truncate similar reflections at ~3.5-4.5 km depth beneath the central part of the SCV. The San Gabriel fault projects to the 1971 hypocenter. In between the Northridge Hills blind thrust and San Gabriel faults, reflections are largely incoherent, and the velocity structure is complex. Below the 1971 hypocenter (at ~13 km depth), the San Fernando fault appears to be contained in a broad north-dipping zone of reflectivity in which

  5. 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.

  6. 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.

  7. 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.

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

    USGS Publications Warehouse

    Field, Edward H.; ,

    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.

  9. 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

  10. 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.

  11. Probability of one or more M ≥7 earthquakes in southern California in 30 years

    USGS Publications Warehouse

    Savage, J.C.

    1994-01-01

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

  12. 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

  13. Site-response maps for the Los Angeles region based on earthquake ground motions

    USGS Publications Warehouse

    Hartzell, Stephen H.; Harmsen, Stephen C.; Frankel, Arthur D.; Carver, David L.; Cranswick, Edward; Meremonte, Mark E.; Michael, John A.

    1996-01-01

    Ground-motion records from aftershocks of the 1994 Northridge earthquake and main-shock records from the 1971 San Fernando, 1987 Whittier Narrows, 1991 Sierra Madre, and 1994 Northridge earthquakes are used to estimate site response in the urban Los Angeles, California, area. Two frequency bands are considered, 0.5-1.5 Hz and 2.0-6.0 Hz. Instrument characteristics prevented going to lower frequencies, and frequencies above 6.0 Hz are less important to the building inventory. Site response determined at the instrumented locations is associated with the surficial geology and contoured to produce a continuous spatial estimation of site response. The maps in this report are preliminary and will evolve as more data become available and more analysis is done.

  14. 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.

  15. 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. 

  16. 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. 

  17. 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…

  18. 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

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

    USGS Publications Warehouse

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

    1995-01-01

    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. ?? 1995 Nature Publishing Group.

  20. 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.; 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.

  1. 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

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

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

    SELECT command, to perform queries on the GDVs, and developed a program which converts the MSQL to an SQL request. MSQL2SQL converts the MSQL command into a parse tree, and defines an API allowing each datacenter to traverse the parse tree and revise it to produce a data center-specific SQL request. The NCEDC converted the IRIS SeismiQuery program to use the GDVs and MSQL, installed it at the NCEDC, and distributed the software to IRIS, SCEC-DC, and other interested parties. The resulting program should be much easier to install and support at other data centers. The NCEDC is also working on several data center integration projects in order to provide users with seamless access to data. The NCEDC is collaborating with IRIS on the NETDC project and with UNAVCO on the GPS Seamless Archive Centers initiative. Through the newly formed California Integrated Seismic Network, we are working with the SCEC-DC to provide unified access to California earthquake data.

  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. 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.

  5. 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

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

    USGS Publications Warehouse

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

    1993-01-01

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

  7. 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.

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

    USGS Publications Warehouse

    ,

    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.

  9. 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

  10. 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.

  11. 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.

  12. A method for producing digital probabilistic seismic landslide hazard maps; an example from the Los Angeles, California, area

    USGS Publications Warehouse

    Jibson, Randall W.; Harp, Edwin L.; Michael, John A.

    1998-01-01

    The 1994 Northridge, California, earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability. These data sets include (1) a comprehensive inventory of triggered landslides, (2) about 200 strong-motion records of the mainshock, (3) 1:24,000-scale geologic mapping of the region, (4) extensive data on engineering properties of geologic units, and (5) high-resolution digital elevation models of the topography. All of these data sets have been digitized and rasterized at 10-m grid spacing in the ARC/INFO GIS platform. Combining these data sets in a dynamic model based on Newmark's permanent-deformation (sliding-block) analysis yields estimates of coseismic landslide displacement in each grid cell from the Northridge earthquake. The modeled displacements are then compared with the digital inventory of landslides triggered by the Northridge earthquake to construct a probability curve relating predicted displacement to probability of failure. This probability function can be applied to predict and map the spatial variability in failure probability in any ground-shaking conditions of interest. We anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure.

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

    USGS Publications Warehouse

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

    2009-01-01

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

  14. 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.

  15. 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.

  16. 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).

  17. Likelihood- and residual-based evaluation of medium-term earthquake forecast models for California

    NASA Astrophysics Data System (ADS)

    Schneider, Max; Clements, Robert; Rhoades, David; Schorlemmer, Danijel

    2014-09-01

    Seven competing models for forecasting medium-term earthquake rates in California are quantitatively evaluated using the framework of the Collaboratory for the Study of Earthquake Predictability (CSEP). The model class consists of contrasting versions of the Every Earthquake a Precursor According to Size (EEPAS) and Proximity to Past Earthquakes (PPE) modelling approaches. Models are ranked by their performance on likelihood-based tests, which measure the consistency between a model forecast and observed earthquakes. To directly compare one model against another, we run a classical paired t-test and its non-parametric alternative on an information gain score based on the forecasts. These test scores are complemented by several residual-based methods, which offer detailed spatial information. The experiment period covers 2009 June-2012 September, when California experienced 23 earthquakes above the magnitude threshold. Though all models fail to capture seismicity during an earthquake sequence, spatio-temporal differences between models also emerge. The overall best-performing model has strong time- and magnitude-dependence, weights all earthquakes equally as medium-term precursors of larger events and has a full set of fitted parameters. Models with this time- and magnitude-dependence offer a statistically significant advantage over simpler baseline models. In addition, models that down-weight aftershocks when forecasting larger events have a desirable feature in that they do not overpredict following an observed earthquake sequence. This tendency towards overprediction differs between the simpler model, which is based on fewer parameters, and more complex models that include more parameters.

  18. 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

  19. 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.

  20. 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.

  1. 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.; 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

  2. 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.

  3. 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

  4. 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.

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

    USGS Publications Warehouse

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

    1982-01-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Reimer, G. M.

    1984-03-01

    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.

  8. 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.

  9. 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

  10. 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

    2015-09-11

    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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

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

    USGS Publications Warehouse

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

    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 identified as being anomalous is not actually anomalous. Instead, it is just part of normal global-scale TEC variation. We conclude that the TEC anomaly reported by Pulinets et al. is unrelated to the Hector Mine earthquake.

  19. Identification and Reduction of Nonstructural Earthquake Hazards in California Schools.

    ERIC Educational Resources Information Center

    Greene, Marjorie; And Others

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

  20. 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…

  1. System Identification of Burbank Six-Story Building Using Earthquake Data

    SciTech Connect

    D'Amore, Enzo; Amaddeo, Carmen; Astaneh-Asl, Abolhassan

    2008-07-08

    This paper examines the problem of identifying the dynamic characteristics of an instrumented building using an input-output system identification method. The building studied was a six-story steel moment-resisting frame (SMRF) instrumented by the California Strong Motion Instrumentation Program (CSMIP). The building was shaken by several earthquakes and strong motion data of the building response was recorded during these earthquakes and were made available through SMIP. In particular the Whittier Narrows (October, 1987), the Sierra Madre (June, 1991) and the Northridge (January, 1994) earthquakes were considered in the studies reported here. The seismic performance of steel moment-framed buildings has been of particular interest after the 1994 Northridge earthquake because brittle fractures were discovered at the beam-column connection. The Eigensystem Realization Algorithm with Data Correlation (ERA/DC) and Observer/Kalman filter Identification (OKID) were used in these studies for system identification purposes. The identified modal properties of the structure were compared and verified with the spectral analysis of the response of the structure excited by three different earthquakes.

  2. 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.

  3. 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.

  4. 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

  5. Felt reports and intensity assignments for aftershocks and triggered events of the great 1906 California earthquake

    USGS Publications Warehouse

    Meltzner, Aron J.; Wald, David J.

    2002-01-01

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

  6. Multiscaling comparative analysis of time series and a discussion on "earthquake conversations" in California.

    PubMed

    Scafetta, Nicola; West, Bruce J

    2004-04-01

    Time series are characterized by complex memory and/or distribution patterns. In this Letter we show that stochastic models characterized by different statistics may equally well reproduce some pattern of a time series. In particular, we discuss the difference between Lévy-walk and fractal Gaussian intermittent signals and show that the adoption of complementary scaling analysis techniques may be useful to distinguish the two cases. Finally, we apply this methodology to the earthquake occurrences in California and suggest the possibility that earthquake occurrences are described by a colored ("long-range correlated") generalized Poisson model. PMID:15089646

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

    USGS Publications Warehouse

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

    1991-01-01

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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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

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

    NASA Astrophysics Data System (ADS)

    Pearce, F.; Lu, R.; Toksoz, N.

    2007-12-01

    Current approaches for focal depth estimation are typically based on travel times and result in large uncertainties primarily due to poor data coverage and inaccurate travel time picks. We propose an alternative method based on an adaptation of time-reversed acoustics (TRA). In the context of TRA theory, the autocorrelation of an earthquake recording can be thought of as the convolution of the source autocorrelation function with the autocorrelation of the Green's function describing propagation between source and receiver. Furthermore, the signal to noise ratio (S/N) of stationary phases in the Green's function may be improved by stacking the autocorrelations from many receivers. In this study, we employ such an approach to estimate the focal depth of shallow earthquakes based on the time lag between the direct P phase and pP converted phase, which is assumed to be stationary across the receiver array. Focal depth estimates are easily obtained by multiplying half the pP time lag by the average velocity above the earthquake. We apply this methodology to estimate focal depths for several local earthquakes in Southern California. Earthquake recordings were obtained from the Southern California Earthquake Center (SCEC) for events with accurate, independent estimates of focal depth below about 15 km, and local magnitudes between 4.0 and 6.0. We observe pP in the stacked autocorrelations that correspond to the focal depths listed in the SCEC catalog for earthquakes located throughout Southern California. The predictive capability of the method is limited by S/N, defined as the pP amplitude divided by the background noise level of the stacked correlation. By considering subsets of the Southern California array, we explore the sensitivity of the S/N on station density and location (i.e. epicentral distance & azimuth). We find S/N is generally better for subsets of receivers within regions with relatively simple geologic structure. We are currently developing an extension

  16. 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.

  17. 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.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  19. Living With Earthquakes in California: A Survivor's Guide

    NASA Astrophysics Data System (ADS)

    Grant, Lisa B.

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

  20. Permanent GPS Geodetic Array in Southern California

    NASA Technical Reports Server (NTRS)

    Green, Cecil H.; Green, Ida M.

    1998-01-01

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

  1. 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.

  2. Statiscal analysis of an earthquake-induced landslide distribution - The 1989 Loma Prieta, California event

    USGS Publications Warehouse

    Keefer, D.K.

    2000-01-01

    The 1989 Loma Prieta, California earthquake (moment magnitude, M=6.9) generated landslides throughout an area of about 15,000 km2 in central California. Most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter, where they were mapped during field investigations immediately following the earthquake. The distribution of these landslides is investigated statistically, using regression and one-way analysisof variance (ANOVA) techniques to determine how the occurrence of landslides correlates with distance from the earthquake source, slope steepness, and rock type. The landslide concentration (defined as the number of landslide sources per unit area) has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness. The landslide concentration differs substantially among the various geologic units in the area. The differences correlate to some degree with differences in lithology and degree of induration, but this correlation is less clear, suggesting a more complex relationship between landslide occurrence and rock properties. ?? 2000 Elsevier Science B.V. All rights reserved.

  3. 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.

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

    USGS Publications Warehouse

    Coordinated by Holzer, Thomas L.

    1992-01-01

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

  5. 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.

  6. Seismic response analysis of a 13-story steel moment-framed building in Alhambra, California

    USGS Publications Warehouse

    Rodgers, Janise E.; Sanli, Ahmet K.; Celebi, Mehmet

    2004-01-01

    The seismic performance of steel moment-framed buildings has been of particular interest since brittle fractures were discovered at the beam-column connections of some frames following the M6.7 1994 Northridge earthquake. This report presents an investigation of the seismic behavior of an instrumented 13-story steel moment frame building located in the greater Los Angeles area of California. An extensive strong motion dataset, ambient vibration data, engineering drawings and earthquake damage reports are available for this building. The data are described and subsequently analyzed. The results of the analyses show that the building response is more complex than would be expected from its highly symmetrical geometry. The building's response is characterized by low damping in the fundamental mode, larger peak accelerations in the intermediate stories than at the roof, extended periods of vibration after the cessation of strong input shaking, beating in the response, and significant torsion during strong shaking at the top of the concrete piers which extend from the basement to the second floor. The analyses of the data and all damage detection methods employed except one method based on system identification indicate that the response of the structure was elastic in all recorded earthquakes. These findings are in general agreement with the results of intrusive inspections (meaning fireproofing and architectural finishes were removed) conducted on approximately 5 percent of the moment connections following the Northridge earthquake, which found no earthquake damage.

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

    Distant as well as local earthquakes have induced groundwater-level changes persisting for days to weeks at Long Valley caldera, California. Four wells open to formations as deep as 300 m have responded to 16 earthquakes, and responses to two earthquakes in the 3-km-deep Long Valley Exploratory Well (LVEW) show that these changes are not limited to weathered or unconsolidated near-surface rocks. All five wells exhibit water-level variations in response to earth tides, indicating they can be used as low-resolution strainmeters. Earthquakes induce gradual water-level changes that increase in amplitude for as long as 30 days, then return more slowly to pre-earthquake levels. The gradual water-level changes are always drops at wells LKT, LVEW, and CH-10B, and always rises at well CW-3. At a dilatometer just outside the caldera, earthquake-induced strain responses consist of either a step followed by a contractional strain-rate increase, or a transient contractional signal that reaches a maximum in about seven days and then returns toward the pre-earthquake value. The sizes of the gradual water-level changes generally increase with earthquake magnitude and decrease with hypocentral distance. Local earthquakes in Long Valley produce coseismic water-level steps; otherwise the responses to local earthquakes and distant earthquakes are indistinguishable. In particular, water-level and strain changes in Long Valley following the 1992 M7.3 Landers earthquake, 450 km distant, closely resemble those initiated by a M4.9 local earthquake on November 22, 1997, during a seismic swarm with features indicative of fluid involvement. At the LKT well, many of the response time histories are identical for 20 days after each earthquake, and can be matched by a theoretical solution giving the pore pressure as a function of time due to diffusion of a nearby, instantaneous, pressure drop. Such pressure drops could be produced by accelerated inflation of the resurgent dome by amounts too

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

    USGS Publications Warehouse

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

    2003-01-01

    Distant as well as local earthquakes have induced groundwater-level changes persisting for days to weeks at Long Valley caldera, California. Four wells open to formations as deep as 300 m have responded to 16 earthquakes, and responses to two earthquakes in the 3-km-deep Long Valley Exploratory Well (LVEW) show that these changes are not limited to weathered or unconsolidated near-surface rocks. All five wells exhibit water-level variations in response to earth tides, indicating they can be used as low-resolution strainmeters. Earthquakes induce gradual water-level changes that increase in amplitude for as long as 30 days, then return more slowly to pre-earthquake levels. The gradual water-level changes are always drops at wells LKT, LVEW, and CH-10B, and always rises at well CW-3. At a dilatometer just outside the caldera, earthquake-induced strain responses consist of either a step followed by a contractional strain-rate increase, or a transient contractional signal that reaches a maximum in about seven days and then returns toward the pre-earthquake value. The sizes of the gradual water-level changes generally increase with earthquake magnitude and decrease with hypocentral distance. Local earthquakes in Long Valley produce coseismic water-level steps; otherwise the responses to local earthquakes and distant earthquakes are indistinguishable. In particular, water-level and strain changes in Long Valley following the 1992 M7.3 Landers earthquake, 450 km distant, closely resemble those initiated by a M4.9 local earthquake on November 22, 1997, during a seismic swarm with features indicative of fluid involvement. At the LKT well, many of the response time histories are identical for 20 days after each earthquake, and can be matched by a theoretical solution giving the pore pressure as a function of time due to diffusion of a nearby, instantaneous, pressure drop. Such pressure drops could be produced by accelerated inflation of the resurgent dome by amounts too

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  10. 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

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

    USGS Publications Warehouse

    Keefer, David K.

    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.

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

    USGS Publications Warehouse

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

    1988-01-01

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

  13. 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.

  14. 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).

  15. 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).

  16. 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.

  17. 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.; 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.

  18. 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

  19. 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

  20. 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

  1. 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

  2. Analysis of Foreshock Sequences in California and Implications for Earthquake Triggering

    NASA Astrophysics Data System (ADS)

    Chen, Xiaowei; Shearer, Peter M.

    2016-01-01

    We analyze foreshock activity in California and compare observations with simulated catalogs based on a branching aftershock-triggering model. We first examine foreshock occurrence patterns for isolated M ≥ 5 earthquakes in southern California from 1981 to 2011 and in northern California from 1984 to 2009. Among the 64 M ≥ 5 mainshocks, excluding 3 swarms and 3 doubles, 53 % of the rest are preceded by at least one foreshock within 30 days and 5 km. Foreshock occurrence appears correlated with mainshock faulting type and depth. Foreshock area is correlated with the magnitude of the largest foreshock and the number of foreshocks, however, it is not correlated with mainshock magnitude. We then examine the occurrence pattern of all seismicity clusters without a minimum magnitude requirement, and the possibility that they are "foreshocks" of larger mainshocks. Only about 30 % of the small clusters lead to a larger cluster. About 66 % of the larger clusters have foreshock activities, and the spatial distribution pattern is similar to M ≥ 5 mainshocks, with lower occurrence rates in the Transverse Range and central California and higher occurrence rates in the Eastern California Shear Zone and the Bay Area. These results suggest that foreshock occurrence is largely controlled by the regional tectonic stress field and fault zone properties. In special cases, foreshock occurrence may be useful for short-term forecasting; however, foreshock properties are not reliably predictive of the magnitude of the eventual "mainshock". Comparison with simulated catalogs suggest that the "swarmy" features and foreshock occurrence rate in the observed catalogs are not well reproduced from common statistical models of earthquake triggering.

  3. 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

  4. Characterizing potentially induced earthquake rate changes in the Brawley Seismic Zone, southern California

    USGS Publications Warehouse

    Llenos, Andrea L.; Michael, Andrew J.

    2016-01-01

    The Brawley seismic zone (BSZ), in the Salton trough of southern California, has a history of earthquake swarms and geothermal energy exploitation. Some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields, particularly at the North Brawley Geothermal Field (NBGF) and at the Salton Sea Geothermal Field (SSGF). We explore this issue by examining earthquake rate changes and interevent distance distributions in these fields. In Oklahoma and Arkansas, where considerable wastewater injection occurs, increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid‐injection‐induced seismicity. Here, we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas. We use stochastic epidemic‐type aftershock sequence models to detect changes in the underlying seismogenic processes, shown by statistically significant changes in the model parameters. The most robust model changes in the SSGF roughly occur when large changes in net fluid production occur, but a similar correlation is not seen in the NBGF. Also, although both background seismicity rate and aftershock productivity increased for fluid‐injection‐induced earthquake rate changes in Oklahoma and Arkansas, the background rate increases significantly in the BSZ only, roughly corresponding with net fluid production rate increases. Moreover, in both fields the interevent spacing does not change significantly during active energy projects. This suggests that, although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions, earthquake rates may still be driven by fluid injection or extraction rates, particularly in the SSGF.

  5. 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.

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

    USGS Publications Warehouse

    Wesson, R.L.

    1987-01-01

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

  7. 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.

  8. Ductility Enhancement of Post-Northridge Connections by Multilongitudinal Voids in the Beam Web

    PubMed Central

    Celikag, Murude; Hedayat, Amir A.

    2013-01-01

    Since the earthquakes in Northridge and Kobe in 1994 and 1995, respectively, many investigations have been carried out towards improving the strength and ductility of steel beam to column pre- and post-Northridge connections. In order to achieve these objectives, recent researches are mainly focused on three principles: reducing the beam section to improve the beam ductility, adding different kinds of slit damper to beam and column flanges to absorb and dissipate the input earthquake energy in the connection and strengthening the connection area using additional elements such as rib plates, cover plates, and flange plates to keep the plastic hinges away from the column face. This paper presents a reduced beam section approach via the introduction of multilongitudinal voids (MLV) in the beam web for various beam depths varying from 450 mm to 912 mm. ANSYS finite element program was used to simulate the three different sizes of SAC sections: SAC3, SAC5, and SAC7. Results showed an improvement in the connection ductility since the input energy was dissipated uniformly along the beam length and the total rotation of the connection was over four percent radian. PMID:24311977

  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 populated area, it may cause ...

  10. 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

  11. 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).

  12. 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.

  13. CSMIP (California Strong Motion Instrumentation Program) strong-motion records from the Santa Cruz Mountains (Loma Prieta), California earthquake of 17 October 1989

    SciTech Connect

    Shakal, A.; Reichle, M.; Ventura, C.; Cao, T.; Sherburne, R.; Savage, M.; Darragh, R.; Petersen, C.

    1990-01-01

    Strong-motion records were recovered from 93 stations of the California Strong Motion Instrumentation Program (CSMIP) after the earthquake. CSMIP provides information on the force of ground motion and the deformation induced in structures and in rock and soil by earthquake-generated ground motion. This information is recorded by strong-motion sensors placed in engineered structures and at free field (ground) sites, and is used by earthquake engineers and earth scientists to improve the design of earthquake-resistant structures. The strong-motion instrumentation program was established after the San Fernando earthquake in 1971. A total of 125 records were recovered from the 93 CSMIP stations which recorded the Loma Prieta event. These 125 records contain data from a total of 690 strong-motion sensors. These data are important because of the unique structures and sites at which records were obtained during this event. Some highlights of particular interest are included in this paper.

  14. 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

  15. Combining Dynamic Earthquake and Tsunami Models With Case Studies Offshore Alaska and Southern California

    NASA Astrophysics Data System (ADS)

    Ryan, Kenny

    Earthquakes and their corresponding tsunamis pose significant hazard to popu- lated regions around the world. Therefore, it is critically important that we seek to more fully understand the physics of the combined earthquake-tsunami system. One way to address this goal is through numerical modeling. The work discussed herein focuses on combining dynamic earthquake and tsunami models through the use of the Finite Element Method (FEM) and the Finite Difference Method (FDM). Dynamic earthquake models ac- count for the force that the entire fault system exerts on each individual element of the model for each time step, so that earthquake rupture takes a path based on the physics of the model; dynamic tsunami models can incorporate water height variations to produce water wave formation, propagation, and inundation. Chapter 1 provides an introduction to some important concepts and equations of elastodynamics and fluid dynamics as well as a brief example of the FEM. In Chapter 2, we investigate the 3-D effects of realistic fault dynamics on slip, free surface deformation, and resulting tsunami formation from an Mw 9 megathrust earthquake offshore Southern Alaska. Corresponding tsunami models, which use a FDM to solve linear long-wave equations, match sea floor deformation, in time, to the free surface deformation from the rupture simulations. Tsunamis generated in this region could have large adverse effects on Pacific coasts. In Chapter 3, we construct a 3-D dynamic rupture model of an earthquake on a reverse fault structure offshore Southern California to model the resulting tsunami, with a goal of elucidating the seismic and tsunami hazard in this area. The corresponding tsunami model uses final seafloor displacements 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. In Chapter 4, we begin to evaluate 2-D earthquake source parameters

  16. 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

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

    USGS Publications Warehouse

    Gomberg, J.

    1996-01-01

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

  18. 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.

  19. 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

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

    USGS Publications Warehouse

    Roeloffs, E.; Quilty, E.

    1997-01-01

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

  1. 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)

  2. 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…

  3. Structure of the San Fernando Valley region, California: implications for seismic hazard and tectonic history

    USGS Publications Warehouse

    Langenheim, V.E.; Wright, T.L.; Okaya, D.A.; Yeats, R.S.; Fuis, G.S.; Thygesen, K.; Thybo, H.

    2011-01-01

    Industry seismic reflection data, oil test well data, interpretation of gravity and magnetic data, and seismic refraction deep-crustal profiles provide new perspectives on the subsurface geology of San Fernando Valley, home of two of the most recent damaging earthquakes in southern California. Seismic reflection data provide depths to Miocene–Quaternary horizons; beneath the base of the Late Miocene Modelo Formation are largely nonreflective rocks of the Middle Miocene Topanga and older formations. Gravity and seismic reflection data reveal the North Leadwell fault zone, a set of down-to-the-north faults that does not offset the top of the Modelo Formation; the zone strikes northwest across the valley, and may be part of the Oak Ridge fault system to the west. In the southeast part of the valley, the fault zone bounds a concealed basement high that influenced deposition of the Late Miocene Tarzana fan and may have localized damage from the 1994 Northridge earthquake. Gravity and seismic refraction data indicate that the basin underlying San Fernando Valley is asymmetric, the north part of the basin (Sylmar subbasin) reaching depths of 5–8 km. Magnetic data suggest a major boundary at or near the Verdugo fault, which likely started as a Miocene transtensional fault, and show a change in the dip sense of the fault along strike. The northwest projection of the Verdugo fault separates the Sylmar subbasin from the main San Fernando Valley and coincides with the abrupt change in structural style from the Santa Susana fault to the Sierra Madre fault. The Simi Hills bound the basin on the west and, as defined by gravity data, the boundary is linear and strikes ~N45°E. That northeast-trending gravity gradient follows both the part of the 1971 San Fernando aftershock distribution called the Chatsworth trend and the aftershock trends of the 1994 Northridge earthquake. These data suggest that the 1971 San Fernando and 1994 Northridge earthquakes reactivated portions of

  4. 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.

  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. 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

  7. An Update on the Activities of the Collaboratory for the Study of Earthquake Predictability

    NASA Astrophysics Data System (ADS)

    Liukis, M.; Schorlemmer, D.; Yu, J.; Maechling, P. J.; Zechar, J. D.; Werner, M. J.; Jordan, T. H.

    2013-12-01

    The Collaboratory for the Study of Earthquake Predictability (CSEP) supports a global program to conduct prospective earthquake forecast experiments. There are now CSEP testing centers in California, New Zealand, Japan, and Europe, and 364 models are under evaluation. In this presentation, we describe how the testing center hosted by the Southern California Earthquake Center (SCEC) has evolved to meet CSEP objectives and share our experiences in operating the center. The SCEC testing center has been operational since September 1, 2007, and currently hosts 1-day, 3-month, 1-year and 5-year forecasts, both alarm-based and probabilistic, for California, the western Pacific, and a global testing region. We are currently working to reduce testing latency and to develop procedures to evaluate externally-hosted forecasts and predictions. These efforts are related to CSEP support of the USGS program in operational earthquake forecasting and a Department of Homeland Security project to register and test external forecast procedures from experts outside seismology. We describe the open-source CSEP software that is available to researchers as they develop their forecast models (http://northridge.usc.edu/trac/csep/wiki/MiniCSEP). We also discuss how we apply CSEP infrastructure to geodetic transient detection and the evaluation of ShakeAlert system for earthquake early warning (EEW), and how CSEP procedures are being adopted for intensity prediction and ground motion prediction experiments. cseptesting.org

  8. Relative Contributions of Geothermal Pumping and Long-Term Earthquake Rate to Seismicity at California Geothermal Fields

    NASA Astrophysics Data System (ADS)

    Weiser, D. A.; Jackson, D. D.

    2015-12-01

    In a tectonically active area, a definitive discrimination between geothermally-induced and tectonic earthquakes is difficult to achieve. We focus our study on California's 11 major geothermal fields: Amedee, Brawley, Casa Diablo, Coso, East Mesa, The Geysers, Heber, Litchfield, Salton Sea, Susanville, and Wendel. The Geysers geothermal field is the world's largest geothermal energy producer. California's Department of Oil Gas and Geothermal Resources provides field-wide monthly injection and production volumes for each of these sites, which allows us to study the relationship between geothermal pumping activities and seismicity. Since many of the geothermal fields began injecting and producing before nearby seismic stations were installed, we use smoothed seismicity since 1932 from the ANSS catalog as a proxy for tectonic earthquake rate. We examine both geothermal pumping and long-term earthquake rate as factors that may control earthquake rate. Rather than focusing only on the largest earthquake, which is essentially a random occurrence in time, we examine how M≥4 earthquake rate density (probability per unit area, time, and magnitude) varies for each field. We estimate relative contributions to the observed earthquake rate of M≥4 from both a long-term earthquake rate (Kagan and Jackson, 2010) and pumping activity. For each geothermal field, respective earthquake catalogs (NCEDC and SCSN) are complete above at least M3 during the test period (which we tailor to each site). We test the hypothesis that the observed earthquake rate at a geothermal site during the test period is a linear combination of the long-term seismicity and pumping rates. We use a grid search to determine the confidence interval of the weighting parameters.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  10. 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

  11. Spatial-temporal variation of low-frequency earthquake bursts near Parkfield, California

    USGS Publications Warehouse

    Wu, Chunquan; Guyer, Robert; Shelly, David R.; Trugman, D.; Frank, William; Gomberg, Joan S.; Johnson, P.

    2015-01-01

    Tectonic tremor (TT) and low-frequency earthquakes (LFEs) have been found in the deeper crust of various tectonic environments globally in the last decade. The spatial-temporal behaviour of LFEs provides insight into deep fault zone processes. In this study, we examine recurrence times from a 12-yr catalogue of 88 LFE families with ∼730 000 LFEs in the vicinity of the Parkfield section of the San Andreas Fault (SAF) in central California. We apply an automatic burst detection algorithm to the LFE recurrence times to identify the clustering behaviour of LFEs (LFE bursts) in each family. We find that the burst behaviours in the northern and southern LFE groups differ. Generally, the northern group has longer burst duration but fewer LFEs per burst, while the southern group has shorter burst duration but more LFEs per burst. The southern group LFE bursts are generally more correlated than the northern group, suggesting more coherent deep fault slip and relatively simpler deep fault structure beneath the locked section of SAF. We also found that the 2004 Parkfield earthquake clearly increased the number of LFEs per burst and average burst duration for both the northern and the southern groups, with a relatively larger effect on the northern group. This could be due to the weakness of northern part of the fault, or the northwesterly rupture direction of the Parkfield earthquake.

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

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    We model tsunami inundation and runup heights in Crescent City, California triggered by possible earthquakes on the Cascadia Subduction Zone (CSZ). The CSZ is believed capable of producing great earthquakes with magnitudes of M w ~ 9.0 or greater. We simulate plausible CSZ rupture scenarios and calculate inundation using MOST. We benchmark our CSZ inundation projections against mapped flooded areas and tide gauge data from the 1964 tsunami, which destroyed 29 city blocks, and also from the damaging 15 November 2006 Kuril Islands tsunami. Results suggest that inundation from CSZ tsunamis could extend over 3 km inland, twice as far as the limits of the 1964 inundation. Crescent City is most vulnerable to slip on the Gorda segment of the CSZ. Rupture of the northern or Juan De Fuca segment produces lower water heights than the 1964 event. At Crescent City, CSZ ruptures produce a leading elevation wave that arrives only minutes after the earthquake. Educational and self-evacuation are essential to save lives.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  15. 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.

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

    SciTech Connect

    Prentice, C.S.

    1989-01-01

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

  17. Transient stress-coupling between the 1992 Landers and 1999 Hector Mine, California, earthquakes

    USGS Publications Warehouse

    Masterlark, Timothy; Wang, H.F.

    2002-01-01

    A three-dimensiona l finite-element model (FEM) of the Mojave block region in southern California is constructed to investigate transient stress-coupling between the 1992 Landers and 1999 Hector Mine earthquakes. The FEM simulates a poroelastic upper-crust layer coupled to a viscoelastic lower-crust layer, which is decoupled from the upper mantle. FEM predictions of the transient mechanical behavior of the crust are constrained by global positioning system (GPS) data, interferometric synthetic aperture radar (InSAR) images, fluid-pressure data from water wells, and the dislocation source of the 1999 Hector Mine earthquake. Two time-dependent parameters, hydraulic diffusivity of the upper crust and viscosity of the lower crust, are calibrated to 10-2 m2.sec-1 and 5 ?? 1018 Pa.sec respectively. The hydraulic diffusivity is relatively insensitive to heterogeneous fault-zone permeability specifications and fluid-flow boundary conditions along the elastic free-surface at the top of the problem domain. The calibrated FEM is used to predict the evolution of Coulomb stress during the interval separating the 1992 Landers and 1999 Hector Mine earthquakes. The predicted change in Coulomb stress near the hypocenter of the Hector Mine earthquake increases from 0.02 to 0.05 MPa during the 7-yr interval separating the two events. This increase is primarily attributed to the recovery of decreased excess fluid pressure from the 1992 Landers coseismic (undrained) strain field. Coulomb stress predictions are insensitive to small variations of fault-plane dip and hypocentral depth estimations of the Hector Mine rupture.

  18. Source processes of industrially-induced earthquakes at the Geysers geothermal area, California

    USGS Publications Warehouse

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

    1999-01-01

    Microearthquake activity at The Geysers geothermal area, California, mirrors the steam production rate, suggesting that the earthquakes are industrially induced. A 15-station network of digital, three-component seismic stations was operated for one month in 1991, and 3,900 earthquakes were recorded. Highly-accurate moment tensors were derived for 30 of the best recorded earthquakes by tracing rays through tomographically derived 3-D VP and VP / VS structures, and inverting P-and S-wave polarities and amplitude ratios. The orientations of the P-and T-axes are very scattered, suggesting that there is no strong, systematic deviatoric stress field in the reservoir, which could explain why the earthquakes are not large. Most of the events had significant non-double-couple (non-DC) components in their source mechanisms with volumetric components up to ???30% of the total moment. Explosive and implosive sources were observed in approximately equal numbers, and must be caused by cavity creation (or expansion) and collapse. It is likely that there is a causal relationship between these processes and fluid reinjection and steam withdrawal. Compensated linear vector dipole (CLVD) components were up to 100% of the deviatoric component. Combinations of opening cracks and shear faults cannot explain all the observations, and rapid fluid flow may also be involved. The pattern of non-DC failure at The Geysers contrasts with that of the Hengill-Grensdalur area in Iceland, a largely unexploited water-dominated field in an extensional stress regime. These differences are poorly understood but may be linked to the contrasting regional stress regimes and the industrial exploitation at The Geysers.

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

    USGS Publications Warehouse

    Macgregor-Scott, N.; Walter, A.

    1988-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Roeloffs, Evelyn A.

    1998-01-01

    Coseismic water level rises in the 30-m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes. Coseismic changes in static strain cannot explain these water level rises because (1) the well is insensitive to strain at tidal periods; (2) for the distant earthquakes, the expected coseismic static strain is extremely small; and (3) the water level response is of the incorrect sign for the local earthquakes. These water level changes must therefore be caused by seismic waves, but unlike seismic water level oscillations, they are monotonic, persist for days or weeks, and seem to be caused by waves with periods of several seconds rather than long-period surface waves. Other investigators have reported a similar phenomenon in Japan. Certain wells consistently exhibit this type of coseismic water level change, which is always in the same direction, regardless of the earthquake's azimuth or focal mechanism, and approximately proportional to the inverse square of hypocentral distance. To date, the coseismic water level rises in the B V well have never exceeded the seasonal water level maximum, although their sizes are relatively well correlated with earthquake magnitude and distance. The frequency independence of the well's response to barometric pressure in the frequency band 0.1 to 0.7 cpd implies that the aquifer is fairly well confined. High aquifer compressibility, probably due to a gas phase in the pore space, is the most likely reason why the well does not respond to Earth tides. The phase and amplitude relationships between the seasonal water level and precipitation cycles constrain the horizontal hydraulic diffusivity to within a factor of 4.5, bounding hypothetical earthquake-induced changes in aquifer hydraulic properties. Moreover, changes of hydraulic conductivity and/or diffusivity throughout the aquifer would not be expected to change the water level in the same direction at every time

  1. Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California

    USGS Publications Warehouse

    DeLong, Stephen B.; Lienkaemper, James J.; Pickering, Alexandra J; Avdievitch, Nikita N.

    2015-01-01

    The A.D. 2014 M6.0 South Napa earthquake, despite its moderate magnitude, caused significant damage to the Napa Valley in northern California (USA). Surface rupture occurred along several mapped and unmapped faults. Field observations following the earthquake indicated that the magnitude of postseismic surface slip was likely to approach or exceed the maximum coseismic surface slip and as such presented ongoing hazard to infrastructure. Using a laser scanner, we monitored postseismic deformation in three dimensions through time along 0.5 km of the main surface rupture. A key component of this study is the demonstration of proper alignment of repeat surveys using point cloud–based methods that minimize error imposed by both local survey errors and global navigation satellite system georeferencing errors. Using solid modeling of natural and cultural features, we quantify dextral postseismic displacement at several hundred points near the main fault trace. We also quantify total dextral displacement of initially straight cultural features. Total dextral displacement from both coseismic displacement and the first 2.5 d of postseismic displacement ranges from 0.22 to 0.29 m. This range increased to 0.33–0.42 m at 59 d post-earthquake. Furthermore, we estimate up to 0.15 m of vertical deformation during the first 2.5 d post-earthquake, which then increased by ∼0.02 m at 59 d post-earthquake. This vertical deformation is not expressed as a distinct step or scarp at the fault trace but rather as a broad up-to-the-west zone of increasing elevation change spanning the fault trace over several tens of meters, challenging common notions about fault scarp development in strike-slip systems. Integrating these analyses provides three-dimensional mapping of surface deformation and identifies spatial variability in slip along the main fault trace that we attribute to distributed slip via subtle block rotation. These results indicate the benefits of laser scanner surveys along

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

    USGS Publications Warehouse

    Roeloffs, E.A.

    1998-01-01

    Coseismic water level rises in the 30-m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes. Coseismic changes in static strain cannot explain these water level rises because (1) the well is insensitive to strain at tidal periods; (2) for the distant earthquakes, the expected coseismic static strain is extremely small; and (3) the water level response is of the incorrect sign for the local earthquakes. These water level changes must therefore be caused by seismic waves, but unlike seismic water level oscillations, they are monotonic, persist for days or weeks, and seem to be caused by waves with periods of several seconds rather than long-period surface waves. Other investigators have reported a similar phenomenon in Japan. Certain wells consistently exhibit this type of coseismic water level change, which is always in the same direction, regardless of the earthquake's azimuth or focal mechanism, and approximately proportional to the inverse square of hypocentral distance. To date, the coseismic water level rises in the BV well have never exceeded the seasonal water level maximum, although their sizes are relatively well correlated with earthquake magnitude and distance. The frequency independence of the well's response to barometric pressure in the frequency band 0.1 to 0.7 cpd implies that the aquifer is fairly well confined. High aquifer compressibility, probably due to a gas phase in the pore space, is the most likely reason why the well does not respond to Earth tides. The phase and amplitude relationships between the seasonal water level and precipitation cycles constrain the horizontal hydraulic diffusivity to within a factor of 4.5, bounding hypothetical earthquake-induced changes in aquifer hydraulic properties. Moreover, changes of hydraulic conductivity and/or diffusivity throughout the aquifer would not be expected to change the water level in the same direction at every time

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  4. Earthquakes

    ERIC Educational Resources Information Center

    Roper, Paul J.; Roper, Jere Gerard

    1974-01-01

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

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

    USGS Publications Warehouse

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

    2013-01-01

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

  6. G-larmS: An Infrastructure for Geodetic Earthquake Early Warning, applied to Northern California

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Integrating geodetic data into seismic earthquake early warning (EEW) is critical for accurately resolving magnitude and finite fault dimensions in the very largest earthquakes (M>7). We have developed G-larmS, the Geodetic alarm System, as part of our efforts to incorporate geodetic data into EEW for Northern California. G-larmS is an extensible geodetic EEW infrastructure that analyzes positioning time series from real-time GPS processors, such as TrackRT or RTNET. It is currently running in an operational mode at the Berkeley Seismological Laboratory (BSL) where we use TrackRT to produce high sample rate displacement time series for 62 GPS stations in the greater San Francisco Bay Area with 3-4 second latency. We employ a fully triangulated network scheme, which provides resiliency against an outage or telemetry loss at any individual station, for a total of 165 basestation-rover pairs. G-larmS is tightly integrated into seismic alarm systems (CISN ShakeAlert, ElarmS) as it uses their P-wave detection alarms to trigger its own processing and sends warning messages back to the ShakeAlert decision module. Once triggered, G-larmS estimates the static offset at each station pair and inputs these into an inversion for fault slip, which is updated once per second. The software architecture and clear interface definitions of this Python implementation enable straightforward extensibility and exchange of specific algorithms that operate in the individual modules. For example, multiple modeling instances can be called in parallel, each of which applying a different strategy to infer fault and magnitude information (e.g., pre-defined fault planes, full grid search, least squares inversion, etc.). This design enables, for example, quick tests, expansion and algorithm comparisons. Here, we present the setup and report results of the first months of operation in Northern California. This includes analysis of system latencies, noise, and G-larmS' response to actual events. We

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

    NASA Astrophysics Data System (ADS)

    Perry, S.

    2003-12-01

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

  8. Evidence of shallow fault zone strengthening after the 1992 M7.5 landers, california, earthquake

    PubMed

    Li; Vidale; Aki; Xu; Burdette

    1998-01-01

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

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

    USGS Publications Warehouse

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

    1983-01-01

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

  10. 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.

  11. 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.

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

    USGS Publications Warehouse

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

    2006-01-01

    Using a short-baseline seismic array (U.S. Geological Survey Parkfield Dense Seismograph Array [UPSAR]) about 12 km west of the rupture initiation of the 28 September 2004 M 6.0 Parkfield, California, earthquake, we have observed the movement of the rupture front of this earthquake on the San Andreas fault. The sources of high-frequency arrivals at UPSAR, which we use to identify the rupture front, are mapped onto the San Andreas fault using their apparent velocity and back azimuth. Measurements of apparent velocity and back azimuth are calibrated using aftershocks, which have a compact source and known location. Aftershock back azimuths show considerable lateral refraction, consistent with a high-velocity ridge on the southwest side of the fault. We infer that the initial mainshock rupture velocity was approximately the Rayleigh speed (with respect to slower side of the fault), and the rupture then slowed to about 0.66?? near the town of Parkfield after 2 sec. The last well-correlated pulse, 4 sec after S, is the largest at UPSAR, and its source is near the region of large accelerations recorded by strong-motion accelerographs and close to northern extent of continuous surface fractures on the southwest fracture zone. Coincidence of sources with preshock and aftershock distributions suggests fault material properties control rupture behavior. High-frequency sources approximately correlate with the edges of asperities identified as regions of high slip derived from inversion of strong-motion waveforms.

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

    USGS Publications Warehouse

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

    1998-01-01

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

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

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2000-01-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

  16. 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.

  17. 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.

  18. Monitoring of the stress state variations of the Southern California for the purpose of earthquake prediction

    NASA Astrophysics Data System (ADS)

    Gokhberg, M.; Garagash, I.; Bondur, V.; Steblov, G. M.

    2014-12-01

    The three-dimensional geomechanical model of Southern California was developed, including a mountain relief, fault tectonics and characteristic internal features such as the roof of the consolidated crust and Moho surface. The initial stress state of the model is governed by the gravitational forces and horizontal tectonic motions estimated from GPS observations. The analysis shows that the three-dimensional geomechanical models allows monitoring of the changes in the stress state during the seismic process in order to constrain the distribution of the future places with increasing seismic activity. This investigation demonstrates one of possible approach to monitor upcoming seismicity for the periods of days - weeks - months. Continuous analysis of the stress state was carried out during 2009-2014. Each new earthquake with М~1 and above from USGS catalog was considered as the new defect of the Earth crust which has some definite size and causes redistribution of the stress state. Overall calculation technique was based on the single function of the Earth crust damage, recalculated each half month. As a result each half month in the upper crust layers and partially in the middle layers we revealed locations of the maximal values of the stress state parameters: elastic energy density, shear stress, proximity of the earth crust layers to their strength limit. All these parameters exhibit similar spatial and temporal distribution. How follows from observations all four strongest events with М ~ 5.5-7.2 occurred in South California during the analyzed period were prefaced by the parameters anomalies in peculiar advance time of weeks-months in the vicinity of 10-50 km from the upcoming earthquake. After the event the stress state source disappeared. The figure shows migration of the maximums of the stress state variations gradients (parameter D) in the vicinity of the epicenter of the earthquake 04.04.2010 with М=7.2 in the period of 01.01.2010-01.05.2010. Grey lines

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    USGS Publications Warehouse

    Luetgert, James H.; Mooney, Walter D.

    1985-01-01

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

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

    SciTech Connect

    Stevenson, J.D.

    1995-11-01

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

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

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2002-01-01

    The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggest that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital

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

    USGS Publications Warehouse

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

    1999-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Reilinger, R.

    1984-01-01

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

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

    USGS Publications Warehouse

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

    2007-01-01

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

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

    USGS Publications Warehouse

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

    2008-01-01

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

  7. 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.

  8. Earthquakes

    USGS Publications Warehouse

    Shedlock, Kaye M.; Pakiser, Louis Charles

    1998-01-01

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

  9. Simulating Large-Scale Earthquake Dynamic Rupture Scenarios On Natural Fault Zones Using the ADER-DG Method

    NASA Astrophysics Data System (ADS)

    Gabriel, Alice; Pelties, Christian

    2014-05-01

    In this presentation we will demonstrate the benefits of using modern numerical methods to support physic-based ground motion modeling and research. For this purpose, we utilize SeisSol an arbitrary high-order derivative Discontinuous Galerkin (ADER-DG) scheme to solve the spontaneous rupture problem with high-order accuracy in space and time using three-dimensional unstructured tetrahedral meshes. We recently verified the method in various advanced test cases of the 'SCEC/USGS Dynamic Earthquake Rupture Code Verification Exercise' benchmark suite, including branching and dipping fault systems, heterogeneous background stresses, bi-material faults and rate-and-state friction constitutive formulations. Now, we study the dynamic rupture process using 3D meshes of fault systems constructed from geological and geophysical constraints, such as high-resolution topography, 3D velocity models and fault geometries. Our starting point is a large scale earthquake dynamic rupture scenario based on the 1994 Northridge blind thrust event in Southern California. Starting from this well documented and extensively studied event, we intend to understand the ground-motion, including the relevant high frequency content, generated from complex fault systems and its variation arising from various physical constraints. For example, our results imply that the Northridge fault geometry favors a pulse-like rupture behavior.

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

    NASA Astrophysics Data System (ADS)

    Thurber, C.; Sessions, R.

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

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Merifield, P. M.; Lamar, D. L. (Principal Investigator)

    1974-01-01

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    USGS Publications Warehouse

    Prejean, Stephanie G.; Ellsworth, William L.

    2001-01-01

    To investigate seismic source parameter scaling and seismic efficiency in the Long Valley caldera, California, we measured source parameters for 41 earthquakes (M 0.5 to M 5) recorded at 2 km depth in the Long Valley Exploratory Well. Borehole recordings provide a wide frequency bandwidth, typically 1 to 200–300 Hz, and greatly reduce seismic noise and path effects compared to surface recordings. We calculated source parameters in both the time and frequency domains for P and S waves. At frequencies above the corner frequency, spectra decay faster than ω3, indicating that attenuation plays an important role in shaping the spectra (path averaged Qp = 100–400, Qs = 200–800). Source parameters are corrected for attenuation and radiation pattern. Both static stress drops and apparent stresses range from approximately 0.01 to 30 MPa. Although static stress drops do not vary with seismic moment for these data, our analyses are consistent with apparent stress increasing with increasing moment. To estimate tectonic driving stress and seismic efficiencies in the region, we combined source parameter measurements with knowledge of the stress field and a Coulomb failure criterion to infer a driving stress of 40–70 MPa. Subsequent seismic efficiencies are consistent with McGarr's (1999) hypothesis of a maximum seismic efficiency of 6%.

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

    USGS Publications Warehouse

    Julian, B.R.

    1983-01-01

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

  16. Geophysical setting of the 2000 ML 5.2 Yountville, California, earthquake: Implications for seismic Hazard in Napa Valley, California

    USGS Publications Warehouse

    Langenheim, V.E.; Graymer, R.W.; Jachens, R.C.

    2006-01-01

    The epicenter of the 2000 ML 5.2 Yountville earthquake was located 5 km west of the surface trace of the West Napa fault, as defined by Helley and Herd (1977). On the basis of the re-examination of geologic data and the analysis of potential field data, the earthquake occurred on a strand of the West Napa fault, the main basin-bounding fault along the west side of Napa Valley. Linear aeromagnetic anomalies and a prominent gravity gradient extend the length of the fault to the latitude of Calistoga, suggesting that this fault may be capable of larger-magnitude earthquakes. Gravity data indicate an ???2-km-deep basin centered on the town of Napa, where damage was concentrated during the Yountville earthquake. It most likely played a minor role in enhancing shaking during this event but may lead to enhanced shaking caused by wave trapping during a larger-magnitude earthquake.

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

    USGS Publications Warehouse

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

    1981-01-01

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

  18. Multifrequential periodogram analysis of earthquake occurrence: An alternative approach to the Schuster spectrum, with two examples in central California

    NASA Astrophysics Data System (ADS)

    Dutilleul, Pierre; Johnson, Christopher W.; Bürgmann, Roland; Wan, Yongge; Shen, Zheng-Kang

    2015-12-01

    Periodic earthquake occurrences may reflect links with semidiurnal to multiyear tides, seasonal hydrological loads, and ~14 month pole tide forcing. The Schuster spectrum is a recent extension of Schuster's traditional test for periodicity analysis in seismology. We present an alternative approach: the multifrequential periodogram analysis (MFPA), performed on time series of monthly earthquake numbers. We explore if seismicity in two central California regions, the Central San Andreas Fault near Parkfield (CSAF-PKD) and the Sierra Nevada-Eastern California Shear Zone (SN-ECSZ), exhibits periodic behavior at periods of 2 months to several years. Original and declustered catalogs spanning up to 26 years were analyzed with both methods. For CSAF-PKD, the MFPA resolves ~1 year periodicities, with additional statistically significant periods of ~6 and ~4 months; for SN-ECSZ, it finds a strong ~14 month periodic component. Unlike the Schuster spectrum, the MFPA has an exact modified statistic at non-Fourier frequencies. Informed by the MFPA period estimates, trigonometric models with periods of 12, 6, and 4 months (Model 1) and 14.24 and 12 months (Model 2) were fitted to time series of earthquake numbers. For CSAF-PKD, Model 1 shows a peak annual earthquake occurrence during August-November and a secondary peak in April. Similar peaks, or troughs, are found in annual and semiannual components of pole tide and tide-induced stress model time series and fault normal-stress reduction from seasonal hydrological unloading. For SN-ECSZ, the dominant ~14 month periodicity prevents regular annual peaking, and Model 2 provides a better fit (ΔR>¯adjusted2: 2.4%). This new MFPA application resolves several periodicities in earthquake catalogs that reveal external periodic forcing.

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

    SciTech Connect

    Not Available

    1990-01-01

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

  20. Earthquake warning system for Japan Railways’ bullet train; implications for disaster prevention in California

    USGS Publications Warehouse

    Nakamura, Y.; Tucker, B. E.

    1988-01-01

    Today, Japanese society is well aware of the prediction of the Tokai earthquake. It is estimated by the Tokyo earthquake. It is estimated by the Tokyo muncipal government that this predicted earthquake could kill 30,000 people. (this estimate is viewed by many as conservative; other Japanese government agencies have made estimates but they have not been published.) Reduction in the number deaths from 120,000 to 30,000 between the Kanto earthquake and the predicted Tokai earthquake is due in large part to the reduction in the proportion of wooden construction (houses). 

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

    NASA Astrophysics Data System (ADS)

    Kanu, Chinaemerem; Johnson, Kaj

    2011-04-01

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

  2. Coseismic offsets recorded by borehole strainmeters from the 2014, Mw 6.0 South Napa, California earthquake: Reconciling tidal calibrations with earthquake source models.

    NASA Astrophysics Data System (ADS)

    Langbein, J. O.

    2015-12-01

    The 24 August 2014 Mw 6.0 South Napa, California earthquake produced significant offsets on 12 borehole strainmeters in the San Francisco Bay area. These strainmeters are located between 24 and 80 km from the source and the observed offsets ranged up to 400 parts-per-billion (ppb), which exceeds their nominal precision by a factor of 100. However, the observed offsets in tidally-calibrated strains have RMS deviation of 130 ppb from strains predicted by previously published moment tensor derived from seismic data. Here, I show that the large misfit can be reduced by a combination of better tidal calibration and better modeling of the strain field from the earthquake. Borehole strainmeters require in-situ calibration, which historically has been accomplished by comparing their measurements of Earth tides with the strain-tides predicted by a model. Although borehole strainmeters accurately measure the deformation within the borehole, the long-wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument. Previous analyses of surface-mounted, strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30%. The poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30% and making small adjustments to the point-source model of the earthquake, which reduces the RMS misfit from 130 to 18 ppb. This suggests that calibrations derived solely from tidal models limits the accuracy of borehole strainmeters. On the other hand, the revised calibration derived here becomes testable on strain measurements from future, large Bay area events.

  3. Recent Developments within the Collaboratory for the Study of Earthquake Predictability

    NASA Astrophysics Data System (ADS)

    Liukis, M.; Werner, M. J.; Schorlemmer, D.; Yu, J.; Maechling, P. J.; Zechar, J. D.; Jordan, T. H.

    2014-12-01

    The Collaboratory for the Study of Earthquake Predictability (CSEP) supports a global program to conduct prospective earthquake forecast experiments. There are now CSEP testing centers in California, New Zealand, Japan, and Europe, with 430 models under evaluation. In this presentation, we describe how the Southern California Earthquake Center (SCEC) testing center has evolved to meet CSEP objectives and we share our experiences in operating the center. The SCEC testing center has been operational since September 1, 2007, and currently hosts 30-minute, 1-day, 3-month, 1-year and 5-year forecasts, both alarm-based and probabilistic, for California, the Western Pacific, and a global testing region. We have reduced testing latency, implemented prototype evaluation of M8 forecasts and currently develop procedures to evaluate externally-hosted forecasts and predictions. These efforts are related to CSEP support of the USGS program in operational earthquake forecasting and a Department of Homeland Security project to register and test external forecast procedures from experts outside seismology. Retrospective experiment for the 2010 Darfield earthquake sequence formed an important addition to the CSEP activities where the predictive skills of physics-based and statistical forecasting models are compared. We describe the open-source CSEP software that is available to researchers as they develop their forecast models (http://northridge.usc.edu/trac/csep/wiki/MiniCSEP). We also discuss applications of CSEP infrastructure to geodetic transient detection and the evaluation of ShakeAlert system for earthquake early warning (EEW), and how CSEP procedures are being adopted for intensity prediction and ground motion prediction experiments.

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

    USGS Publications Warehouse

    Sherrouse, Benson C.; Hester, David J.

    2008-01-01

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

  5. Echo-sounding method aids earthquake hazard studies

    USGS Publications Warehouse

    ,

    1995-01-01

    Dramatic examples of catastrophic damage from an earthquake occurred in 1989, when the M 7.1 Lorna Prieta rocked the San Francisco Bay area, and in 1994, when the M 6.6 Northridge earthquake jolted southern California. The surprising amount and distribution of damage to private property and infrastructure emphasizes the importance of seismic-hazard research in urbanized areas, where the potential for damage and loss of life is greatest. During April 1995, a group of scientists from the U.S. Geological Survey and the University of Tennessee, using an echo-sounding method described below, is collecting data in San Antonio Park, California, to examine the Monte Vista fault which runs through this park. The Monte Vista fault in this vicinity shows evidence of movement within the last 10,000 years or so. The data will give them a "picture" of the subsurface rock deformation near this fault. The data will also be used to help locate a trench that will be dug across the fault by scientists from William Lettis & Associates.

  6. Seismic velocity variations along the rupture zone of the 1989 Loma Prieta earthquake, California

    NASA Astrophysics Data System (ADS)

    Lin, G.; Thurber, C. H.

    2012-09-01

    We revisit the rupture zone of the 1989 Mw6.9 Loma Prieta earthquake, central California, by developing high-resolution three-dimensional (3-D)Vp and Vp/Vs models. We apply the simul2000 inversion method and algorithm to a set of "composite" events, which have greater number of picks per event and reduced random picking errors compared with traditional master events. Our final P-wave velocity model generally agrees with previous studies, showing a high velocity body of above 6.7 km/s in the southeast rupture zone of the main shock. The 3-DVp/Vs model, however, has different features, with low Vp/Vs in the upper crust and high Vp/Vs anomalies in deeper layers of the rupture zone. We interpret the low Vp/Vs at shallow depths to be granitic rocks, whereas at greater depths the areas of higher Vp/Vs(around 1.725-1.75) presumably are mafic rocks. The resulting 3-D velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area. We then applied a similar event cluster analysis, waveform cross-correlation, and differential time relocation methods to improve relative event location accuracy. Over 88% of the seismicity falls into similar event clusters. A dramatic sharpening of seismicity patterns is obtained after using these methods. The medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical. Differential times from cross-correlation are used to estimatein situnear-sourceVp/Vsratio within each event cluster. The high-resolutionVp/Vs method confirms the trend of the velocity variations from the tomographic results, although absolute values are slightly different.

  7. 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.

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

    SciTech Connect

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

    2012-01-23

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

  9. Virtual California, ETAS, and OpenHazards web services: Responding to earthquakes in the age of Big Data

    NASA Astrophysics Data System (ADS)

    Yoder, M. R.; Schultz, K.; Rundle, J. B.; Glasscoe, M. T.; Donnellan, A.

    2014-12-01

    The response to the 2014 m=6 Napa earthquake showcased data driven services and technologies that aided first responders and decision makers to quickly assess damage, estimate aftershock hazard, and efficiently allocate resources where where they were most needed. These tools have been developed from fundamental research as part of a broad collaboration -- facilitated in no small party by the California Earthquake Clearinghouse, between researchers, policy makers, and executive decision makers and practiced and honed during numerous disaster response exercises over the past several years. On 24 August 2014, and the weeks following the m=6 Napa event, it became evident that these technologies will play an important role in the response to natural (and other) disasters in the 21st century. Given the continued rapid growth of computational capabilities, remote sensing technologies, and data gathering capacities -- including by unpiloted aerial vehicles (UAVs), it is reasonable to expect that both the volume and variety of data available during a response scenario will grow significantly in the decades to come. Inevitably, modern Data Science will be critical to effective disaster response in the 21st century. In this work, we discuss the roles that earthquake simulators, statistical seismicity models, and remote sensing technologies played in the the 2014 Napa earthquake response. We further discuss "Big Data" technologies and data models that facilitate the transformation of raw data into disseminable information and actionable products, and we outline a framework for the next generation of disaster response data infrastructure.

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

    USGS Publications Warehouse

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

    1985-01-01

    Short-term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes. Instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur, and it is now recognized that even to have the possibility of a reliable earthquake-prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals. We are conducting experiments to determine the maximum signal-to-noise improvement that can be obtained in drill holes. In a 592 m well in the Mojave Desert near Hi Vista, California, we measured water-level changes with amplitudes greater than 10 cm, induced by earth tides. By removing the effects of barometric pressure and the stress related to earth tides, we have achieved a sensitivity to volumetric strain rates of 10-9 to 10-10 per day. Further improvement may be possible, and it appears that a successful earthquake-prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km, assuming that the premonitory strain signals are, in fact, present. ?? 1985 Birkha??user Verlag.

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

    USGS Publications Warehouse

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

    2002-01-01

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

  12. Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake

    NASA Astrophysics Data System (ADS)

    Floyd, Michael A.; Walters, Richard J.; Elliott, John R.; Funning, Gareth J.; Svarc, Jerry L.; Murray, Jessica R.; Hooper, Andy J.; Larsen, Yngvar; Marinkovic, Petar; Bürgmann, Roland; Johanson, Ingrid A.; Wright, Tim J.

    2016-07-01

    Following earthquakes, faults are often observed to continue slipping aseismically. It has been proposed that this afterslip occurs on parts of the fault with rate-strengthening friction that are stressed by the main shock, but our understanding has been limited by a lack of immediate, high-resolution observations. Here we show that the behavior of afterslip following the 2014 South Napa earthquake in California varied over distances of only a few kilometers. This variability cannot be explained by coseismic stress changes alone. We present daily positions from continuous and survey GPS sites that we remeasured within 12 h of the main shock and surface displacements from the new Sentinel-1 radar mission. This unique geodetic data set constrains the distribution and evolution of coseismic and postseismic fault slip with exceptional resolution in space and time. We suggest that the observed heterogeneity in behavior is caused by lithological controls on the frictional properties of the fault plane.

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

    USGS Publications Warehouse

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

    2008-01-01

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

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

    USGS Publications Warehouse

    Sokolov, V.; Wald, D.J.

    2002-01-01

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

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

    SciTech Connect

    Foxall, B

    2003-02-26

    The objective my research has been to synthesize current understanding of the tectonics and faults of the Los Angeles Basin and surrounding region to quantify uncertainty in the characterization of earthquake sources used for geologically- and geodetically-based regional earthquake likelihood models. This work has focused on capturing epistemic uncertainty; i.e. uncertainty stemming from ignorance of the true characteristics of the active faults in the region and of the tectonic forces that drive them. In the present context, epistemic uncertainty has two components: First, the uncertainty in source geometrical and occurrence rate parameters deduced from the limited geological, geophysical and geodetic observations available; and second. uncertainties that result from fundamentally different interpretations of regional tectonic deformation and faulting. Characterization of the large number of active and potentially active faults that need to be included in estimating earthquake occurrence likelihoods for the Los Angeles region requires synthesis and evaluation of large amounts of data and numerous interpretations. This was accomplished primarily through a series of carefully facilitated workshops, smaller meetings involving key researchers, and email groups. The workshops and meetings were made possible by the unique logistical and financial resources available through SCEC, and proved to be extremely effective forums for the exchange and critical debate of data and interpretations that are essential in constructing fully representative source models. The main products from this work are a complete source model that characterizes all know or potentially active faults in the greater Los Angeles region. which includes the continental borderland as far south as San Diego, the Ventura Basin, and the Santa Barbara Channel. The model constitutes a series of maps and representative cross-sections that define alternative fault geometries, a table containing rault

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

    USGS Publications Warehouse

    Sims, J.D.

    1973-01-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    USGS Publications Warehouse

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

    2007-01-01

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

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

    USGS Publications Warehouse

    Johnston, Malcolm J. S.

    1993-01-01

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

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

    USGS Publications Warehouse

    Coordinated by Holzer, Thomas L.

    1998-01-01

    Professional Paper 1552 focuses on the response of buildings, lifelines, highway systems, and earth structures to the earthquake. Losses to these systems totaled approximated $5.9 billion. The earthquake displaced many residents from their homes and severely disrupted transportation systems. Some significant findings were: * Approximately 16,000 housing units were uninhabitable after the earthquake including 13,000 in the San Francisco Bay region. Another 30,000-35,000 units were moderately damaged in the earthquake. Renters and low-income residents were particularly hard hit. * Failure of highway systems was the single largest cause of loss of life during the earthquake. Forty-two of the 63 earthquake fatalities died when the Cypress Viaduct in Oakland collapsed. The cost to repair and replace highways damaged by the earthquake was $2 billion, about half of which was to replace the Cypress Viaduct. * Major bridge failures were the result of antiquated designs and inadequate anticipation of seismic loading. * Twenty one kilometers (13 mi) of gas-distribution lines had to be replaced in several communities and more than 1,200 leaks and breaks in water mains and service connections had to be excavated and repaired. At least 5 electrical substations were badly damaged, overwhelming the designed redundancy of the electrical system. * Instruments in 28 buildings recorded their response to earthquake shaking that provided opportunities to understand how different types of buildings responded, the importance of site amplification, and how buildings interact with their foundation when shaken (soil structure interaction).

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The SCSN is the modern digital ground motion seismic network in Southern California and performs the following tasks: 1) Operates remote seismic stations and the central data processing systems in Pasadena; 2) Generates and reports real-time products including location, magnitude, ShakeMap, aftershock probabilities and others; 3) Responds to FEMA, CalOES, media, and public inquiries about earthquakes; 4) Manages the production, archival, and distribution of waveforms, phase picks, and other data at the SCEDC; 5) Contributes to development and implementation of the demonstration EEW system called CISN ShakeAlert. Initially, the ShakeAlert project was funded through the US Geological Survey (USGS) and in early 2012, the Gordon and Betty Moore Foundation provided three years of new funding for EEW research and development for the US west coast. Recently, we have also received some Urban Areas Security Initiative (UASI) funding to enhance the EEW capabilities for the local UASI region by making our system overall faster, more reliable and redundant than the existing system. The additional and upgraded stations will be capable of decreasing latency and ensuring data delivery by using more reliable and redundant telemetry pathways. Overall, this will enhance the reliability of the earthquake early warnings by providing denser station coverage and more resilient data centers than before. * Seismic Datalogger upgrade: replaces existing dataloggers with modern equipment capable of sending one-second uncompressed packets and utilizing redundant Ethernet telemetry. * GPS upgrade: replaces the existing GPS receivers and antennas, especially at "zipper array" sites near the major faults, with receivers that perform on-board precise point positioning to calculate position and velocity in real time and stream continuous data for use in EEW calculations. * New co-located seismic/GPS stations: increases station density and reduces early warning delays that are incurred by travel

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

    USGS Publications Warehouse

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

    2004-01-01

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

  3. Recent Achievements of the Collaboratory for the Study of Earthquake Predictability

    NASA Astrophysics Data System (ADS)

    Jackson, D. D.; Liukis, M.; Werner, M. J.; Schorlemmer, D.; Yu, J.; Maechling, P. J.; Zechar, J. D.; Jordan, T. H.

    2015-12-01

    Maria Liukis, SCEC, USC; Maximilian Werner, University of Bristol; Danijel Schorlemmer, GFZ Potsdam; John Yu, SCEC, USC; Philip Maechling, SCEC, USC; Jeremy Zechar, Swiss Seismological Service, ETH; Thomas H. Jordan, SCEC, USC, and the CSEP Working Group The Collaboratory for the Study of Earthquake Predictability (CSEP) supports a global program to conduct prospective earthquake forecasting experiments. CSEP testing centers are now operational in California, New Zealand, Japan, China, and Europe with 435 models under evaluation. The California testing center, operated by SCEC, has been operational since Sept 1, 2007, and currently hosts 30-minute, 1-day, 3-month, 1-year and 5-year forecasts, both alarm-based and probabilistic, for California, the Western Pacific, and worldwide. We have reduced testing latency, implemented prototype evaluation of M8 forecasts, and are currently developing formats and procedures to evaluate externally-hosted forecasts and predictions. These efforts are related to CSEP support of the USGS program in operational earthquake forecasting and a DHS project to register and test external forecast procedures from experts outside seismology. A retrospective experiment for the 2010-2012 Canterbury earthquake sequence has been completed, and the results indicate that some physics-based and hybrid models outperform purely statistical (e.g., ETAS) models. The experiment also demonstrates the power of the CSEP cyberinfrastructure for retrospective testing. Our current development includes evaluation strategies that increase computational efficiency for high-resolution global experiments, such as the evaluation of the Global Earthquake Activity Rate (GEAR) model. We describe the open-source CSEP software that is available to researchers as they develop their forecast models (http://northridge.usc.edu/trac/csep/wiki/MiniCSEP). We also discuss applications of CSEP infrastructure to geodetic transient detection and how CSEP procedures are being

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

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    The San Pedro Shelf (SPS) region of the inner California Borderland offshore southern California poses a significant seismic hazard to the contiguous Los Angeles Area, as a consequence of late Cenozoic compressional reactivation of mid-Cenozoic extensional faults. The extent of the hazard, however, is poorly understood because of the complexity of fault geometries and uncertainties in earthquake locations. The major faults in the region include the Palos Verdes, THUMS Huntington Beach and the Newport-Inglewood fault zones. We report here the analysis and interpretation of wide-angle seismic-reflection and refraction data recorded as part of the Los Angeles Region Seismic Experiment line 1 (LARSE 1), multichannel seismic (MCS) reflection data obtained by the USGS (1998-2000) and industry borehole stratigraphy. The onshore-offshore velocity model, which is based on forward modeling of the refracted P-wave arrival times, is used to depth migrate the LARSE 1 section. Borehole stratigraphy allows correlation of the onshore and offshore velocity models because state regulations prevent collection of deep-penetration acoustic data nearshore (within 3 mi.). Our refraction study is an extension of ten Brink et al., 2000 tomographic inversion of LARSE I data. They found high velocities (> 6 km/sec) at about ~3.5 km depth from the Catalina Fault (CF) to the SPS. We find these velocities, shallower (around 2 km depth) beneath the Catalina Ridge (CR) and SPS, but at a depth 2.5-3.0 km elsewhere in the study region. This change in velocity structure can provide additional constraints for the tectonic processes of this region. The structural horizons observed in the LARSE 1 reflection data are tied to adjacent MCS lines. We find localized folding and faulting at depth (~2 km) southwest of the CR and on the SPS slope. Quasi-laminar beds, possible of pelagic origin follow the contours of earlier folded (wavelength ~1 km) and faulted Cenozoic sedimentary and volcanic rocks. Depth to

  5. Liquefaction and other ground failures in Imperial County, California, from the April 4, 2010, El Mayor-Cucapah earthquake

    USGS Publications Warehouse

    McCrink, Timothy P.; Pridmore, Cynthia L.; Tinsley, John C.; Sickler, Robert R.; Brandenberg, Scott J.; Stewart, Jonathan P.

    2011-01-01

    The Colorado River Delta region of southern Imperial Valley, California, and Mexicali Valley, Baja California, is a tectonically dynamic area characterized by numerous active faults and frequent large seismic events. Significant earthquakes that have been accompanied by surface fault rupture and/or soil liquefaction occurred in this region in 1892 (M7.1), 1915 (M6.3; M7.1), 1930 (M5.7), 1940 (M6.9), 1950 (M5.4), 1957 (M5.2), 1968 (6.5), 1979 (6.4), 1980 (M6.1), 1981 (M5.8), and 1987 (M6.2; M6.8). Following this trend, the M7.2 El Mayor-Cucapah earthquake of April 4, 2010, ruptured approximately 120 kilometers along several known faults in Baja California. Liquefaction caused by the M7.2 El Mayor-Cucapah earthquake was widespread throughout the southern Imperial Valley but concentrated in the southwest corner of the valley, southwest of the city centers of Calexico and El Centro where ground motions were highest. Although there are few strong motion recordings in the very western part of the area, the recordings that do exist indicate that ground motions were on the order of 0.3 to 0.6g where the majority of liquefaction occurrences were found. More distant liquefaction occurrences, at Fites Road southwest of Brawley and along Rosita Canal northwest of Holtville were triggered where ground motions were about 0.2 g. Damage to roads was associated mainly with liquefaction of sandy river deposits beneath bridge approach fills, and in some cases liquefaction within the fills. Liquefaction damage to canal and drain levees was not always accompanied by vented sand, but the nature of the damage leads the authors to infer that liquefaction was involved in the majority of observed cases. Liquefaction-related damage to several public facilities - Calexico Waste Water Treatment Plant, Fig Lagoon levee system, and Sunbeam Lake Dam in particular - appears to be extensive. The cost to repair these facilities to prevent future liquefaction damage will likely be prohibitive. As

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

    USGS Publications Warehouse

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

    2007-01-01

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

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

    USGS Publications Warehouse

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

    2002-01-01

    Residual displacements for large earthquakes can sometimes be determined from recordings on modern digital instruments, but baseline offsets of unknown origin make it difficult in many cases to do so. To recover the residual displacement, we suggest tailoring a correction scheme by studying the character of the velocity obtained by integration of zeroth-order-corrected acceleration and then seeing if the residual displacements are stable when the various parameters in the particular correction scheme are varied. For many seismological and engineering purposes, however, the residual displacement are of lesser importance than ground motions at periods less than about 20 sec. These ground motions are often recoverable with simple baseline correction and low-cut filtering. In this largely empirical study, we illustrate the consequences of various correction schemes, drawing primarily from digital recordings of the 1999 Hector Mine, California, earthquake. We show that with simple processing the displacement waveforms for this event are very similar for stations separated by as much as 20 km. We also show that a strong pulse on the transverse component was radiated from the Hector Mine earthquake and propagated with little distortion to distances exceeding 170 km; this pulse leads to large response spectral amplitudes around 10 sec.

  8. 3-D P- and S-wave velocity structure and low-frequency earthquake locations in the Parkfield, California region

    NASA Astrophysics Data System (ADS)

    Zeng, Xiangfang; Thurber, Clifford H.; Shelly, David R.; Harrington, Rebecca M.; Cochran, Elizabeth S.; Bennington, Ninfa L.; Peterson, Dana; Guo, Bin; McClement, Kara

    2016-09-01

    To refine the 3-D seismic velocity model in the greater Parkfield, California region, a new data set including regular earthquakes, shots, quarry blasts and low-frequency earthquakes (LFEs) was assembled. Hundreds of traces of each LFE family at two temporary arrays were stacked with time-frequency domain phase weighted stacking method to improve signal-to-noise ratio. We extend our model resolution to lower crustal depth with LFE data. Our result images not only previously identified features but also low velocity zones (LVZs) in the area around the LFEs and the lower crust beneath the southern Rinconada Fault. The former LVZ is consistent with high fluid pressure that can account for several aspects of LFE behaviour. The latter LVZ is consistent with a high conductivity zone in magnetotelluric studies. A new Vs model was developed with S picks that were obtained with a new autopicker. At shallow depth, the low Vs areas underlie the strongest shaking areas in the 2004 Parkfield earthquake. We relocate LFE families and analyse the location uncertainties with the NonLinLoc and tomoDD codes. The two methods yield similar results.

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

    USGS Publications Warehouse

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

    1994-01-01

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

  10. San Andreas fault geometry at Desert Hot Springs, California, and its effects on earthquake hazards and groundwater

    USGS Publications Warehouse

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Gandhok, G.

    2009-01-01

    The Mission Creek and Banning faults are two of the principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. Structural characteristics of the faults affect both regional earthquake hazards and local groundwater resources. We use seismic, gravity, and geological data to characterize the San Andreas fault zone in the vicinity of Desert Hot Springs. Seismic images of the upper 500 m of the Mission Creek fault at Desert Hot Springs show multiple fault strands distributed over a 500 m wide zone, with concentrated faulting within a central 200 m wide area of the fault zone. High-velocity (up to 5000 m=sec) rocks on the northeast side of the fault are juxtaposed against a low-velocity (6.0) earthquakes in the area (in 1948 and 1986) occurred at or near the depths (~10 to 12 km) of the merged (San Andreas) fault. Large-magnitude earthquakes that nucleate at or below the merged fault will likely generate strong shaking from guided waves along both fault zones and from amplified seismic waves in the low-velocity basin between the two fault zones. The Mission Creek fault zone is a groundwater barrier with the top of the water table varying by 60 m in depth and the aquifer varying by about 50 m in thickness across a 200 m wide zone of concentrated faulting.

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

    SciTech Connect

    Greene, H.G.; Chase, T.E.; Hicks, K.R. ); Gardner-Taggart, J.; Ledbetter, M.T.; Barminski, R. ); Baxter, C. )

    1991-09-01

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

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

    USGS Publications Warehouse

    Boore, D.M.

    1999-01-01

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

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

    USGS Publications Warehouse

    ,

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    October 21, 2008 marks the 140th anniversary of the M7 1868 Hayward earthquake. This large earthquake, which occurred slightly before 8 AM, caused extensive damage to San Francisco Bay Area and remains the nation's 12th most lethal earthquake. Property loss was extensive and about 30 people were killed. This earthquake culminated a decade-long series of earthquakes in the Bay Area which started with an M~6 earthquake in the southern Peninsula in 1856, followed by a series of four M5.8 to M6.1 sized earthquakes along the northern Calaveras fault, and ended with a M~6.5 earthquake in the Santa Cruz Mountains in 1865. Despite this flurry of quakes, the shaking from the 1868 earthquake was the strongest that the new towns and growing cities of the Bay Area had ever experienced. The effect on the brick buildings of the time was devastating: walls collapsed in San Francisco, Oakland, and San Jose, and buildings cracked as far away as Napa, Santa Rosa, and Hollister. The area that was strongly shaken (at Modified Mercalli Intensity VII or higher) encompassed about 2,300 km2. Aftershocks continued into November 1868. Surface cracking of the ground along the southern end of the Hayward Fault was traced from Warm Springs in Fremont northward 32 km to San Leandro. As Lawson (1908) reports, "the evidence to the northward of San Leandro is not very satisfactory. The country was then unsettled, and the information consisted of reports of cow- boys riding on the range". Analysis of historical triangulation data suggest that the fault moved as far north as Berkeley, and from these data the average slip along the fault is inferred to be about 1.9 ± 0.4 meters. The paleoseismic record from the southern end of the Hayward Fault provides evidence for 10 earthquakes before 1868. The average interval between these earthquakes is 170 ± 80 years, but the last five earthquakes have had an average interval of only 140 ± 50 years. The 1868 Hayward earthquake and more recent analogs such

  15. 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

  16. 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

    2016-10-01

    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

  17. 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

  18. Earthquakes, September-October 1984

    USGS Publications Warehouse

    Person, W.J.

    1985-01-01

    In the United States, Wyoming experienced a couple of moderate earthquakes, and off the coast of northern California, a strong earthquake shook much of the northern coast of California and parts of the Oregon coast. 

  19. Borehole strainmeter measurements spanning the 2014, Mw6.0 South Napa Earthquake, California: The effect from instrument calibration

    USGS Publications Warehouse

    Langbein, John O.

    2015-01-01

    The 24 August 2014 Mw6.0 South Napa, California earthquake produced significant offsets on 12 borehole strainmeters in the San Francisco Bay area. These strainmeters are located between 24 and 80 km from the source and the observed offsets ranged up to 400 parts-per-billion (ppb), which exceeds their nominal precision by a factor of 100. However, the observed offsets of tidally calibrated strains differ by up to 130 ppb from predictions based on a moment tensor derived from seismic data. The large misfit can be attributed to a combination of poor instrument calibration and better modeling of the strain fit from the earthquake. Borehole strainmeters require in-situ calibration, which historically has been accomplished by comparing their measurements of Earth tides with the strain-tides predicted by a model. Although the borehole strainmeter accurately measure the deformation within the borehole, the long-wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument. Previous analyses of surface-mounted, strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30%. The poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30% and making small adjustments to the point-source model of the earthquake, which reduces the RMS misfit from 130 ppb to 18 ppb. This suggests that relying on tidal models to calibrate borehole strainmeters significantly reduces their accuracy.

  20. Borehole strainmeter measurements spanning the 2014 Mw6.0 South Napa Earthquake, California: The effect from instrument calibration

    NASA Astrophysics Data System (ADS)

    Langbein, John

    2015-10-01

    The 24 August 2014 Mw6.0 South Napa, California earthquake produced significant offsets on 12 borehole strainmeters in the San Francisco Bay area. These strainmeters are located between 24 and 80 km from the source, and the observed offsets ranged up to 400 parts per billion (ppb), which exceeds their nominal precision by a factor of 100. However, the observed offsets of tidally calibrated strains differ by up to 130 ppb from predictions based on a moment tensor derived from seismic data. The large misfit can be attributed to a combination of poor instrument calibration and better modeling of the strain field from the earthquake. Borehole strainmeters require in situ calibration, which historically has been accomplished by comparing their measurements of Earth tides with the strain tides predicted by a model. Although the borehole strainmeter accurately measures the deformation within the borehole, the long-wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument. Previous analyses of surface-mounted, strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30%. The poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30% and making small adjustments to the point source model of the earthquake, which reduces the RMS misfit from 130 ppb to 18 ppb. This suggests that relying on tidal models to calibrate borehole strainmeters significantly reduces their accuracy.

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

    USGS Publications Warehouse

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

    1999-01-01

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

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

    PubMed

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

    1993-06-11

    The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma). PMID:17810202

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

    USGS Publications Warehouse

    Celebi, Mehmet

    1998-01-01

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

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

    USGS Publications Warehouse

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

    1993-01-01

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

  5. The variability of PSV response spectra across a dense array deployed during the Northridge aftershock sequence

    USGS Publications Warehouse

    Field, E.H.; Hough, S.E.

    1997-01-01

    This study addresses the variability of pseudo-velocity response spectra across an array deployed on stiff soil in the San Fernando Valley during the Northridge (Mw 6.7) aftershock sequence. The separation between stations ranged from 0.5 to 5 km, and the aftershock magnitudes ranged from 2.3 to 4.0. We find that 95-percent of observed response spectra are within a factor of 1.9 to 2.6 of the network average. Statistically significant relative amplification factors were found for some of the sites, but the variability of observed response spectra is not significantly reduced by correcting for these effects. This implies that microzonation efforts on less than 5-km distance scales are not warranted at these types of sites. We also found a distance dependence for the response-spectral variability between neighboring sites. 95-percent are within a factor of ???2.3 at 0.5 km, increasing to 95-percent within a factor of ???4.2 at 5 km. No frequency dependence in these values could be resolved. Additional work is needed to examine the influence of other factors such as earthquake magnitude.

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

    USGS Publications Warehouse

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

    2003-01-01

    After the Landers earthquake (Mw = 7.3, 1992.489) a linear array of 10 monuments extending about 30 km N50??E on either side of the earthquake rupture plus a nearby offtrend reference monument were surveyed frequently by GPS until 2003.2. The array also spans the rupture of the subsequent Hector Mine earthquake (Mw = 7.1, 1999.792 . The pre-Landers velocities of monuments in the array relative to interior North America were estimated from earlier trilateration and very long baseline interferometry measurements. Except at the reference monument, the post-Landers velocities of the individual monuments in the array relaxed to their preseismic values within 4 years. Following the Hector Mine earthquake the velocities of the monuments relaxed to steady rates within 1 year. Those steady rates for the east components are about equal to the pre-Landers rates as is the steady rate for the north component of the one monument east of the Hector Mine rupture. However, the steady rates for the north components of the 10 monuments west of the rupture are systematically ???10 mm yr1 larger than the pre-Landers rates. The relaxation to a steady rate is approximately exponential with decay times of 0.50 ?? 0.10 year following the Landers earthquake and 0.32 ?? 0.18 year following the Hector Mine earthquake. The postearthquake motions of the Landers array following the Landers earthquake are not well approximated by the viscoelastic-coupling model of Pollitz et al. [2000]. A similar viscoelastic-coupling model [Pollitz et al., 2001] is more successful in representing the deformation after the Hector Mine earthquake.

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

    USGS Publications Warehouse

    Schiff, Anshel J.

    1998-01-01

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

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

    SciTech Connect

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

    1987-01-01

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

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

    USGS Publications Warehouse

    Reasenberg, Paul A.

    1997-01-01

    While the damaging effects of the earthquake represent a significant social setback and economic loss, the geophysical effects have produced a wealth of data that have provided important insights into the structure and mechanics of the San Andreas Fault system. Generally, the period after a large earthquake is vitally important to monitor. During this part of the seismic cycle, the primary fault and the surrounding faults, rock bodies, and crustal fluids rapidly readjust in response to the earthquake's sudden movement. Geophysical measurements made at this time can provide unique information about fundamental properties of the fault zone, including its state of stress and the geometry and frictional/rheological properties of the faults within it. Because postseismic readjustments are rapid compared with corresponding changes occurring in the preseismic period, the amount and rate of information that is available during the postseismic period is relatively high. From a geophysical viewpoint, the occurrence of the Loma Prieta earthquake in a section of the San Andreas fault zone that is surrounded by multiple and extensive geophysical monitoring networks has produced nothing less than a scientific bonanza. The reports assembled in this chapter collectively examine available geophysical observations made before and after the earthquake and model the earthquake's principal postseismic effects. The chapter covers four broad categories of postseismic effect: (1) aftershocks; (2) postseismic fault movements; (3) postseismic surface deformation; and (4) changes in electrical conductivity and crustal fluids.

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

    SciTech Connect

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

    1990-06-10

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

  11. Evaluation of Seismic Hazards at California Department of Transportation (CALTRANS)Structures

    NASA Astrophysics Data System (ADS)

    Merriam, M. K.

    2005-12-01

    The California Department of Transportation (CALTRANS) has responsibility for design, construction, and maintenance of approximately 12,000 state bridges. CALTRANS also provides oversight for similar activities for 12,200 bridges owned by local agencies throughout the state. California is subjected to a M6 or greater seismic event every few years. Recent earthquakes include the 1971 Mw6.6 San Fernando earthquake which struck north of Los Angeles and prompted engineers to begin retrofitting existing bridges and re-examine the way bridges are detailed to improve their response to earthquakes, the 1989 Mw6.9 Loma Prieta earthquake which destroyed the Cypress Freeway and damaged the San Francisco-Oakland Bay Bridge, and the 1994 Mw6.7 Northridge earthquake in the Los Angeles area which heavily damaged four major freeways. Since CALTRANS' seismic performance goal is to ensure life-safety needs are met for the traveling public during an earthquake, estimating earthquake magnitude, peak bedrock acceleration, and determining if special seismic considerationsare needed at specific bridge sites are critical. CALTRANS is currently developing a fourth generation seismic hazard map to be used for estimating these parameters. A deterministic approach has been used to develop this map. Late-Quaternary-age faults are defined as the expected seismic sources. Caltrans requires site-specific studies to determine potential for liquefaction, seismically induced landslides, and surface fault rupture. If potential for one of these seismic hazards exists, the hazard is mitigated by avoidance, removal, or accommodated through design. The action taken, while complying with the Department's "no collapse" requirement, depends upon many factors, including cost.

  12. Seismic, structural, and individual factors associated with earthquake related injury

    PubMed Central

    Peek-Asa, C; Ramirez, M; Seligson, H; Shoaf, K

    2003-01-01

    Background: Earthquakes cause thousands of deaths worldwide every year, and systematic study of the causes of these deaths can lead to their prevention. Few studies have examined how multiple types of risk factors are related to physical injury during an earthquake. Methods: A population based case-control study was conducted to examine how individual characteristics, building characteristics, and seismic features of the 1994 Northridge, California, earthquake contributed to physical injury. Cases included fatal and hospital-admitted injuries caused by the earthquake. Controls were drawn from a population based phone survey of county residents. Cases were individually matched to two sets of controls: one matched by age and gender and one matched by location at the time of the earthquake. Results: Individuals over age 65 had 2.9 times the risk of injury as younger people (95% confidence interval (CI) 1.2 to 7.4) and women had a 2.4 times greater risk than men (95% CI 1.2 to 5.1). Location in multiple unit residential and commercial structures each led to increased injury risk compared with single unit residential structures, but the exact estimate varied depending on the control group used. With every increase in ground motion of 10%g, injury risk increased 2.2 times (95% CI 1.6 to 3.3). Conclusions: Controlling for other factors, it was found that individual, building, and seismic characteristics were independently predictive of increased injury risk. Prevention and preparedness efforts should focus on each of these as potential points of intervention. PMID:12642562

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The Northern California counties of Del Norte, Humboldt, and Mendocino account for over 30% of California's coastline and is one of the most seismically active areas of the contiguous 48 states. The region is at risk from earthquakes located on- and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ) and from distant sources elsewhere in the Pacific. In 1995 the California Geological Survey (CGS) published a scenario for a CSZ earthquake that included both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of government agencies, tribes, service groups, academia and the private sector, was formed to coordinate and promote earthquake and tsunami hazard awareness and mitigation in the three-county region. The RCTWG and its member agencies projects include education/outreach products and programs, tsunami hazard mapping, signage and siren planning. Since 2008, RCTWG has worked with the California Emergency Management Agency (Cal EMA) in conducting tsunami warning communications tests on the North Coast. In 2007, RCTWG members helped develop and carry out the first tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD. The RCTWG has facilitated numerous multi-agency, multi-discipline coordinated exercises, and RCTWG county tsunami response plans have been a model for other regions of the state and country. Eight North Coast communities have been recognized as TsunamiReady by the National Weather Service, including the first National Park the first State Park and only tribe in California to be so recognized. Over 500 tsunami hazard zone signs have been posted in the RCTWG region since 2008. Eight assessment surveys from 1993 to 2010 have tracked preparedness actions and personal awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist

  14. 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

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

    USGS Publications Warehouse

    O'Rourke, Thomas D.

    1992-01-01

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

  16. The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response

    USGS Publications Warehouse

    Coordinated by Mileti, Dennis S.

    1993-01-01

    Professional Paper 1553 describes how people and organizations responded to the earthquake and how the earthquake impacted people and society. The investigations evaluate the tools available to the research community to measure the nature, extent, and causes of damage and losses. They describe human behavior during and immediately after the earthquake and how citizens participated in emergency response. They review the challenges confronted by police and fire departments and disruptions to transbay transportations systems. And they survey the challenges of post-earthquake recovery. Some significant findings were: * Loma Prieta provided the first test of ATC-20, the red, yellow, and green tagging of buildings. It successful application has led to widespread use in other disasters including the September 11, 2001, New York City terrorist incident. * Most people responded calmly and without panic to the earthquake and acted to get themselves to a safe location. * Actions by people to help alleviate emergency conditions were proportional to the level of need at the community level. * Some solutions caused problems of their own. The police perimeter around the Cypress Viaduct isolated businesses from their customers leading to a loss of business and the evacuation of employees from those businesses hindered the movement of supplies to the disaster scene. * Emergency transbay ferry service was established 6 days after the earthquake, but required constant revision of service contracts and schedules. * The Loma Prieta earthquake produced minimal disruption to the regional economy. The total economic disruption resulted in maximum losses to the Gross Regional Product of $725 million in 1 month and $2.9 billion in 2 months, but 80% of the loss was recovered during the first 6 months of 1990. Approximately 7,100 workers were laid off.

  17. Surface faulting near Livermore, California, associated with the January 1980 earthquakes

    USGS Publications Warehouse

    Bonilla, Manuel G.; Lienkaemper, James J.; Tinsley, John C.

    1980-01-01

    The earthquakes of 24 January (Ms 5.8) 1980 north of Livermore, California, and 26 January (Ms 5.2), were accompanied by surface faulting in the Greenville fault zone and apparently in the Las Positas fault zone also. The surface faulting was discontinuous and of small displacement. The main rupture within the Greenville fault zone trended about N.38°W. It was at least 4.2 km long and may have extended southward to Interstate Highway 580, giving a possible length of 6.2 km; both of these lengths included more gaps than observed surface rupture. Maximum displacements measured by us were about 25 mm of right slip (including afterslip through 28 January); vertical components of as much as 50 mm were seen locally, but these included gravity effects of unknown amount. The main break within the Greenville fault zones is very close to a fault strand mapped by Herd (1977, and unpublished data). A subsidiary break within the Greenville fault zone was about 0.5 km. long, had a general trend of N.46°W., and lay 0.12 to 0.25 km east of the main break. It was characterized by extension of as much as 40 mm and right slip of as much as 20 mm. This break was no more than 25 m from a fault mapped by Herd (unpublished data). Another break within the Greenville fault zone lay about 0.3 km southwest of the projection of the main break and trended about N33°W. It was at least 0.3 km long and showed mostly extension, but at several places a right-lateral component (up to 5 mm) was seen. This break was 80 to 100 m from a strand of the Greenville fault mapped by Herd (1977). Extensional fractures within the Greenville fault zone on the frontage roads north and south of Interstate Highway 580 may be related to regional extension or other processes, but do not seem to have resulted from faulting of the usual kind. One exception in this group is a fracture at the east side of Livermore valley which showed progressive increase in right-lateral displacement in February and March, 1980, and

  18. Rate-and-State Southern California Earthquake Forecasts: Resolving Stress Singularities

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    In previous studies, we pseudo-prospectively evaluated time-dependent Coulomb stress earthquake forecasts, based on rate-and-state friction (Toda and Enescu, 2011 and Dieterich, 1996), against an ETAS null hypothesis (Zhuang et al., 2002). At the 95% confidence interval, we found that the stress-based forecast failed to outperform the ETAS forecast during the first eight weeks following the 10/16/1999 Hector Mine earthquake, in both earthquake number and spatial distribution. The rate-and-state forecast was most effective in forecasting far-field events (earthquakes occurring at least 50km away from modeled active faults). Near active faults, where most aftershocks occurred, stress singularities arising from modeled fault section boundaries obscured the Coulomb stress field. In addition to yielding physically unrealistic stress quantities, the stress singularities arising from the slip model often failed to indicate potential fault asperity locations inferred from aftershock distributions. Here, we test the effects of these stress singularities on the rate-and-state forecast's effectiveness, as well as mitigate stress uncertainties near active faults. We decrease the area significantly impacted by stress singularities by increasing the number of fault patches and introducing tapered slip at fault section boundaries, representing displacement as a high-resolution step function. Using recent seismicity distributions to relocate fault asperities, we also invert seismicity for a fault displacement model with higher resolution than the original slip distribution, where areas of positive static Coulomb stress change coincide with earthquake locations.

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

    SciTech Connect

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

    1990-07-01

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

  20. Report for borehole explosion data acquired in the 1999 Los Angeles Region Seismic Experiment (LARSE II), Southern California: Part I, description of the survey

    USGS Publications Warehouse

    Fuis, Gary S.; Murphy, Janice M.; Okaya, David A.; Clayton, Robert W.; Davis, Paul M.; Thygesen, Kristina; Baher, Shirley A.; Ryberg, Trond; Benthien, Mark L.; Simila, Gerry; Perron, J. Taylor; Yong, Alan K.; Reusser, Luke; Lutter, William J.; Kaip, Galen; Fort, Michael D.; Asudeh, Isa; Sell, Russell; Van Schaack, John R.; Criley, Edward E.; Kaderabek, Ronald; Kohler, Will M.; Magnuski, Nickolas H.

    2001-01-01

    The Los Angeles Region Seismic Experiment (LARSE) is a joint project of the U.S. Geological Survey (USGS) and the Southern California Earthquake Center (SCEC). The purpose of this project is to produce seismic images of the subsurface of the Los Angeles region down to the depths at which earthquakes occur, and deeper, in order to remedy a deficit in our knowledge of the deep structure of this region. This deficit in knowledge has persisted despite over a century of oil exploration and nearly 70 years of recording earthquakes in southern California. Understanding the deep crustal structure and tectonics of southern California is important to earthquake hazard assessment. Specific imaging targets of LARSE include (a) faults, especially blind thrust faults, which cannot be reliably detected any other way; and (b) the depths and configurations of sedimentary basins. Imaging of faults is important in both earthquake hazard assessment but also in modeling earthquake occurrence. Earthquake occurrence cannot be understood unless the earthquake-producing "machinery" (tectonics) is known (Fuis and others, 2001). Imaging the depths and configurations of sedimentary basins is important because earthquake shaking at the surface is enhanced by basin depth and by the presence of sharp basin edges (Wald and Graves, 1998, Working Group on California Earthquake Probabilities, 1995; Field and others, 2001). (Sedimentary basins are large former valleys now filled with sediment eroded from nearby mountains.) Sedimentary basins in the Los Angeles region that have been investigated by LARSE include the Los Angeles, San Gabriel Valley, San Fernando Valley, and Santa Clarita Valley basins. The seismic imaging surveys of LARSE include recording of earthquakes (both local and distant earthquakes) along several corridors (or transects) through the Los Angeles region and also recording of man-made sources along these same corridors. Man-made sources have included airguns offshore and borehole

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

    USGS Publications Warehouse

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

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    USGS Publications Warehouse

    Hill, D.P.

    1990-01-01

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

  5. 3D Spontaneous Rupture Models of Large Earthquakes on the Hayward Fault, California

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    We are constructing 3D spontaneous rupture computer simulations of large earthquakes on the Hayward and central Calaveras faults. The Hayward fault has a geologic history of producing many large earthquakes (Lienkaemper and Williams, 2007), with its most recent large event a M6.8 earthquake in 1868. Future large earthquakes on the Hayward fault are not only possible, but probable (WGCEP, 2008). Our numerical simulation efforts use information about the complex 3D fault geometry of the Hayward and Calaveras faults and information about the geology and physical properties of the rocks that surround the Hayward and Calaveras faults (Graymer et al., 2005). Initial stresses on the fault surface are inferred from geodetic observations (Schmidt et al., 2005), seismological studies (Hardebeck and Aron, 2008), and from rate-and- state simulations of the interseismic interval (Stuart et al., 2008). In addition, friction properties on the fault surface are inferred from laboratory measurements of adjacent rock types (Morrow et al., 2008). We incorporate these details into forward 3D computer simulations of dynamic rupture propagation, using the FaultMod finite-element code (Barall, 2008). The 3D fault geometry is constructed using a mesh-morphing technique, which starts with a vertical planar fault and then distorts the entire mesh to produce the desired fault geometry. We also employ a grid-doubling technique to create a variable-resolution mesh, with the smallest elements located in a thin layer surrounding the fault surface, which provides the higher resolution needed to model the frictional behavior of the fault. Our goals are to constrain estimates of the lateral and depth extent of future large Hayward earthquakes, and to explore how the behavior of large earthquakes may be affected by interseismic stress accumulation and aseismic slip.

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

    NASA Astrophysics Data System (ADS)

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

    1980-07-01

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

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

    SciTech Connect

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

    1980-07-01

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

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

    USGS Publications Warehouse

    Borcherdt, Roger D.

    1994-01-01

    Strong ground motion generated by the Loma Prieta, Calif., earthquake (MS~7.1) of October 17, 1989, resulted in at least 63 deaths, more than 3,757 injuries, and damage estimated to exceed $5.9 billion. Strong ground motion severely damaged critical lifelines (freeway overpasses, bridges, and pipelines), caused severe damage to poorly constructed buildings, and induced a significant number of ground failures associated with liquefaction and landsliding. It also caused a significant proportion of the damage and loss of life at distances as far as 100 km from the epicenter. Consequently, understanding the characteristics of the strong ground motion associated with the earthquake is fundamental to understanding the earthquake's devastating impact on society. The papers assembled in this chapter address this problem. Damage to vulnerable structures from the earthquake varied substantially with the distance from the causative fault and the type of underlying geologic deposits. Most of the damage and loss of life occurred in areas underlain by 'soft soil'. Quantifying these effects is important for understanding the tragic concentrations of damage in such areas as Santa Cruz and the Marina and Embarcadero Districts of San Francisco, and the failures of the San Francisco-Oakland Bay Bridge and the Interstate Highway 880 overpass. Most importantly, understanding these effects is a necessary prerequisite for improving mitigation measures for larger earthquakes likely to occur much closer to densely urbanized areas in the San Francisco Bay region. The earthquake generated an especially important data set for understanding variations in the severity of strong ground motion. Instrumental strong-motion recordings were obtained at 131 sites located from about 6 to 175 km from the rupture zone. This set of recordings, the largest yet collected for an event of this size, was obtained from sites on various geologic deposits, including a unique set on 'soft soil' deposits

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

    PubMed

    Deng; Gurnis; Kanamori; Hauksson

    1998-11-27

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

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

    PubMed

    Deng; Gurnis; Kanamori; Hauksson

    1998-11-27

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

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

    USGS Publications Warehouse

    Wells, Ray E.

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ross, S.; Jones, L.; Wilson, R. I.; Bahng, B.; Barberopoulou, A.; Borrero, J. C.; Brosnan, D.; Bwarie, J.; Geist, E. L.; Johnson, L.; Kirby, S. H.; Knight, W.; Long, K.; Lynett, P. J.; Miller, K.; Mortensen, C. E.; Nicolsky, D.; Oglesby, D. D.; Perry, S. C.; Plumlee, G. S.; Porter, K. A.; Real, C. R.; Ryan, K. J.; Suleimani, E.; Thio, H. K.; Titov, V.; Wein, A. M.; Whitmore, P.; Wood, N. J.

    2013-12-01

    The SAFRR Tsunami Scenario models a hypothetical but plausible tsunami, created by an Mw9.1 earthquake occurring offshore from the Alaskan peninsula, and its impacts on the California coast. We present the likely inundation areas, current velocities in key ports and harbors, physical damage and repair costs, economic consequences, environmental impacts, social vulnerability, emergency management, and policy implications for California associated with the tsunami scenario. The intended users are those who must make mitigation decisions before and rapid decisions during future tsunamis. Around a half million people would be present in the scenario's inundation area in residences, businesses, public venues, parks and beaches. Evacuation would likely be ordered for the State of California's maximum mapped tsunami inundation zone, evacuating an additional quarter million people from residences and businesses. Some island and peninsula communities would face particular evacuation challenges because of limited access options and short warning time, caused by the distance between Alaska and California. Evacuations may also be a challenge for certain dependent-care populations. One third of the boats in California's marinas could be damaged or sunk, costing at least 700 million in repairs to boats and docks, and potentially much more to address serious issues due to sediment transport and environmental contamination. Fires would likely start at many sites where fuel and petrochemicals are stored in ports and marinas. Tsunami surges and bores may travel several miles inland up coastal rivers. Debris clean-up and recovery of inundated and damaged areas will take days, months, or years depending on the severity of impacts and the available resources for recovery. The Ports of Los Angeles and Long Beach (POLA/LB) would be shut down for a miniμm of two days due to strong currents. Inundation of dry land in the ports would result in 100 million damages to cargo and additional

  13. 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.

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

    SciTech Connect

    Johnson, A.M.; Fleming, R.W. |

    1993-12-01

    The 1989 Loma Prieta, California, earthquake is characterized by the lack of major, throughgoing, coseismic, right-lateral faulting along strands of the San Andreas fault zone in the epicentral area. Instead, throughout the Summit Ridge area there are zones of tension cracks and left-lateral fracture zones oriented about N45 deg W, that is, roughly parallel to the San Andreas fault in this area. The left-lateral fractures zones are enigmatic because their left-lateral slip is opposite to the right-lateral sense of the relative motion between the Pacific and North American plates. We suggest that the enigmatic fractures can be understood if we assume that coesiesmic deformation was by right-lateral shear across a broad zone, about 0.5 km wide and 4 km long, beneath Summit Ridge. Contrary to most previous reports on the Loma Prieta earthquake, which assert that coseismic, right-lateral ground rupture was restricted to considerable (greater than 4 km) depths in the epicentral area, we find that nearly all the right-lateral offset is represented at the ground surface by the Summit Ridge shear zone.

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

    USGS Publications Warehouse

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

    2001-01-01

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

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

    USGS Publications Warehouse

    Wesson, R.L.; Nicholson, C.

    1988-01-01

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

  17. 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%.

  18. Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake

    SciTech Connect

    Johnson, A.M.; Cruikshank, K.M. |; Fleming, R.W.

    1993-12-31

    Surface rupturing during the 28 June 1992, Landers, California earthquake, east of Los Angeles, accommodated right-lateral offsets up to about 6 m along segments of distinct, en echelon fault zones with a total length of about 80 km. The offsets were accommodated generally not by faults -- distinct slip surfaces -- but rather by shear zones, tabular bands of localized shearing. In long, straight stretches of fault zones at Landers the rupture is characterized by telescoping of shear zones and intensification of shearing: broad shear zones of mild shearing, containing narrow shear zones of more intense shearing, containing even-narrower shear zones of very intense shearing, which may contain a fault. Thus the ground ruptured across broad belts of shearing with subparallel walls, oriented NW. Each broad belt consists of a broad zone of mild shearing, extending across its entire width (50 to 200 m), and much narrower (a few m wide) shear zones that accommodate most of the offset of the belt and are portrayed by en echelon tension cracks. In response to right-lateral shearing, the slices of ground bounded by the tension cracks rotated in a clockwise sense, producing left lateral shearing, and the slices were forced against the walls of the shear zone, producing thrusting. Even narrower shear zones formed within the narrow shear zones, and some of these were faults. Although the narrower shear zones probably are indicators to right-lateral fault segments at depth, the surface rupturing during the earthquake is characterized not by faulting, but by zones of shearing at various scales. Furthermore, understanding of the formation of the shear zones may be critical to understanding of earthquake faulting because, where faulting is associated with the formation of a shear zone, the faulting occurs late in the development of the shear zone. The faulting occurs after a shear zone or a belt of shear zones forms.

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

    SciTech Connect

    Beanland, S. . Earth Deformation Section); Clark, M.M. )

    1993-04-01

    The right-lateral Owens Valley fault zone (OVFZ) in eastern California extends north about 100 km from near the northwest shore of Owens Lake to beyond Big Pine. It passes through Lone Pine near the eastern base of the Alabama Hills and follows the floor of Owens Valley northward to the Poverty Hills, where it steps 3 km to the left and continues northwest across Crater Mountain and through Big Pine. Data from one site suggest an average net slip rate for the OVFZ of 1.5 [+-] 1 mm/yr for the past 300 ky. Several other sites yield an average Holocene net slip rate of 2 [+-] 1 mm/yr. The OVFZ apparently has experienced three major Holocene earthquakes. The minimum average recurrence interval is 5,000 years at the subsidiary Lone Pine fault, whereas it is 3,300 to 5,000 years elsewhere along the OVFZ. The prehistoric earthquakes are not dated, so an average recurrence interval need not apply. However, roughly equal (characteristic) displacement apparently happened during each Holocene earthquake. The Owens Valley fault zone accommodates some of the relative motion (dextral shear) between the North American and Pacific plates along a discrete structure. This shear occurs in the Walker Lane belt of normal and strike-slip faults within the mainly extensional Basin and Range Province. In Owens Valley displacement is partitioned between the OVFZ and the nearby, subparallel, and purely normal range-front faults of the Sierra Nevada. Compared to the OVFZ, these range-front normal faults are very discontinuous and have smaller Holocene slip rates of 0.1 to 0.8 mm/yr, dip slip. Contemporary activity on adjacent faults of such contrasting styles suggests large temporal fluctuations in the relative magnitudes of the maximum and intermediate principal stresses while the extension direction remains consistently east-west.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Displaced and toppled monuments in a cemetery are an effective means of assessing local ground motion during an earthquake. The MW 6.5 Offshore Northern California earthquake of January 10, 2010, was felt throughout northwestern California and caused moderate damage in coastal communities between Petrolia and Eureka. The earthquake was generated by left-lateral strike slip on a NE-trending fault within the subducting Gorda plate. Peak horizontal ground accelerations of -0.440g (E) and 0.279g (N) and vertical ground acceleration of -0.122g (up) were recorded in Ferndale, CA, on the North American plate 37km east southeast of the epicenter. We measured displaced and toppled monuments in the Ferndale cemetery as a means of assessing ground motion during the January 10, 2010 Offshore Northern California earthquake. The cemetery occupies a hillside that slopes gently to the northwest, and a dormant landslide underlies the cemetery. Approximately 30% of the monuments were displaced during the earthquake. Affects included toppled columns and urns; headstones, columns and large tomb covers that slid and rotated and relative to monument bases; tilted retaining walls and headstones; and liquefaction-related settling (or, less commonly, uplift) of monuments. We measured translation and rotation of 79 monuments displaced from their bases during the earthquake. Toppled monuments do not display a preferred orientation. Seven of the 18 toppled monuments fell to the southeast, but toppling occurred in all directions. For monuments that were displaced but not toppled, 1-10 cm of northwestward translation and 3-8° of clockwise rotation were most common; however, virtually all directions of translation and both clockwise and counterclockwise rotations and were recorded. Damage was not evenly distributed geographically. In general, damage was concentrated in the northern, topographically lower, part of the cemetery. Counterclockwise rotation of monuments occurred mainly along the

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

    USGS Publications Warehouse

    Bolton, Patricia A.

    1993-01-01

    Major earthquakes provide seismologists and engineers an opportunity to examine the performance of the Earth and the man-made structures in response to the forces of the quake. So, too, do they provide social scientists an opportunity to delve into human responses evoked by the ground shaking and its physical consequences. The findings from such research can serve to guide the development and application of programs and practices designed to reduce death, injury, property losses, and social disruption in subsequent earthquakes. This chapter contains findings from studies focused mainly on public response to the Loma Prieta earthquake; that is, on the behavior and perceptions of the general population rather than on the activities of specific organizations or on the impact on procedures or policies. A major feature of several of these studies is that the information was collected from the population throughout the Bay area, not just from persons in the most badly damaged communities or who had suffered the greatest losses. This wide range serves to provide comparisons of behavior for those most directly affected by the earthquake with others who were less directly affected by it but still had to consider it very 'close to home.'

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    USGS Publications Warehouse

    Rojstaczer, Stuart A.

    1994-01-01

    Seismic events have long been known to cause changes in the level of oceans, streams, lakes, and the water table. The great San Francisco earthquake of 1906 induced significant hydrologic changes that were qualitatively similar to those changes observed for the Loma Prieta earthquake. What is different is that the hydrologic data sets collected from the Loma Prieta event have enough detail to enable hypotheses on the causes for these changes to be tested. The papers in this chapter document changes in ocean level, stream morphology and flow, water table height, and ground-water flow rates in response to the earthquake. Although hydrologic disturbances may have occurred about 1 hour before the main shock, the papers in this chapter deal strictly with postevent hydrologic changes. The hydrologic responses reported here reflect changes that are not the result of surface rupture. They appear to be the result of landslides, the static displacements induced by the earthquake, and changes in the permeability of the near surface.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    High-resolution seismic CHIRP data can image direct evidence of earthquakes (i.e., offset strata) beneath lakes and the ocean. Nevertheless, direct evidence often is not imaged due to conditions such as gas in the sediments, or steep basement topography. In these cases, indirect evidence for earthquakes (i.e., debris flows) may provide insight into the paleoseismic record. The four sub-basins of the tectonically active Lake Tahoe Basin provide an ideal opportunity to image direct evidence for earthquake deformation and compare it to indirect earthquake proxies. We present results from high-resolution seismic CHIRP surveys in Emerald Bay, Fallen Leaf Lake, and Cascade Lake to constrain the recurrence interval on the West Tahoe Dollar Point Fault (WTDPF), which was previously identified as potentially the most hazardous fault in the Lake Tahoe Basin. Recently collected CHIRP profiles beneath Fallen Leaf Lake image slide deposits that appear synchronous with slides in other sub-basins. The temporal correlation of slides between multiple basins suggests triggering by events on the WTDPF. If correct, we postulate a recurrence interval for the WTDPF of ~3-4 k.y., indicating that the WTDPF is near its seismic recurrence cycle. In addition, CHIRP data beneath Cascade Lake image strands of the WTDPF that offset the lakefloor as much as ~7 m. The Cascade Lake data combined with onshore LiDAR allowed us to map the geometry of the WTDPF continuously across the southern Lake Tahoe Basin and yielded an improved geohazard assessment.

  5. Three-dimensional compressional wavespeed model, earthquake relocations, and focal mechanisms for the Parkfield, California, region

    USGS Publications Warehouse

    Thurber, C.; Zhang, H.; Waldhauser, F.; Hardebeck, J.; Michael, A.; Eberhart-Phillips, D.

    2006-01-01

    We present a new three-dimensional (3D) compressional vvavespeed (V p) model for the Parkfield region, taking advantage of the recent seismicity associated with the 2003 San Simeon and 2004 Parkfield earthquake sequences to provide increased model resolution compared to the work of Eberhart-Phillips and Michael (1993) (EPM93). Taking the EPM93 3D model as our starting model, we invert the arrival-time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast-southwest by 120 km northwest-southeast. We include catalog picks and cross-correlation and catalog differential times in the inversion, using the double-difference tomography method of Zhang and Thurber (2003). The principal Vp features reported by EPM93 and Michelini and McEvilly (1991) are recovered, but with locally improved resolution along the San Andreas Fault (SAF) and near the active-source profiles. We image the previously identified strong wavespeed contrast (faster on the southwest side) across most of the length of the SAF, and we also improve the image of a high Vp body on the northeast side of the fault reported by EPM93. This narrow body is at about 5- to 12-km depth and extends approximately from the locked section of the SAP to the town of Parkfield. The footwall of the thrust fault responsible for the 1983 Coalinga earthquake is imaged as a northeast-dipping high wavespeed body. In between, relatively low wavespeeds (<5 km/sec) extend to as much as 10-km depth. We use this model to derive absolute locations for about 16,000 earthquakes from 1966 to 2005 and high-precision double-difference locations for 9,000 earthquakes from 1984 to 2005, and also to determine focal mechanisms for 446 earthquakes. These earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure. The aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre-2004 seismicity

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

    USGS Publications Warehouse

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

    2005-01-01

    The Parkfield 2004 earthquake yielded the most extensive set of strong-motion data in the near-source region of a magnitude 6 earthquake yet obtained. The recordings of acceleration and volumetric strain provide an unprecedented document of the near-source seismic radiation for a moderate earthquake. The spatial density of the measurements alon g the fault zone and in the linear arrays perpendicular to the fault is expected to provide an exceptional opportunity to develop improved models of the rupture process. The closely spaced measurements should help infer the temporal and spatial distribution of the rupture process at much higher resolution than previously possible. Preliminary analyses of the peak a cceleration data presented herein shows that the motions vary significantly along the rupture zone, from 0.13 g to more than 2.5 g, with a map of the values showing that the larger values are concentrated in three areas. Particle motions at the near-fault stations are consistent with bilateral rupture. Fault-normal pulses similar to those observed in recent strike-slip earthquakes are apparent at several of the stations. The attenuation of peak ground acceleration with distance is more rapid than that indicated by some standard relationships but adequately fits others. Evidence for directivity in the peak acceleration data is not strong. Several stations very near, or over, the rupturing fault recorded relatively low accelerations. These recordings may provide a quantitative basis to understand observations of low near-fault shaking damage that has been reported in other large strike-slip earthquak.

  7. Long‐term time‐dependent probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3)

    USGS Publications Warehouse

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

    2015-01-01

    The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model, published previously, renewal models are utilized to represent elastic-rebound-implied probabilities. A new methodology has been developed that solves applicability issues in the previous approach for un-segmented models. The new methodology also supports magnitude-dependent aperiodicity and accounts for the historic open interval on faults that lack a date-of-last-event constraint. Epistemic uncertainties are represented with a logic tree, producing 5,760 different forecasts. Results for a variety of evaluation metrics are presented, including logic-tree sensitivity analyses and comparisons to the previous model (UCERF2). For 30-year M≥6.7 probabilities, the most significant changes from UCERF2 are a threefold increase on the Calaveras fault and a threefold decrease on the San Jacinto fault. Such changes are due mostly to differences in the time-independent models (e.g., fault slip rates), with relaxation of segmentation and inclusion of multi-fault ruptures being particularly influential. In fact, some UCERF2 faults were simply too long to produce M 6.7 sized events given the segmentation assumptions in that study. Probability model differences are also influential, with the implied gains (relative to a Poisson model) being generally higher in UCERF3. Accounting for the historic open interval is one reason. Another is an effective 27% increase in the total elastic-rebound-model weight. The exact factors influencing differences between UCERF2 and UCERF3, as well as the relative importance of logic-tree branches, vary throughout the region, and depend on the evaluation metric of interest. For example, M≥6.7 probabilities may not be a good proxy for other hazard or loss measures. This sensitivity, coupled with the

  8. Slip rate on the San Diego trough fault zone, inner California Borderland, and the 1986 Oceanside earthquake swarm revisited

    USGS Publications Warehouse

    Ryan, Holly F.; Conrad, James E.; Paull, C.K.; McGann, Mary

    2012-01-01

    The San Diego trough fault zone (SDTFZ) is part of a 90-km-wide zone of faults within the inner California Borderland that accommodates motion between the Pacific and North American plates. Along with most faults offshore southern California, the slip rate and paleoseismic history of the SDTFZ are unknown. We present new seismic reflection data that show that the fault zone steps across a 5-km-wide stepover to continue for an additional 60 km north of its previously mapped extent. The 1986 Oceanside earthquake swarm is located within the 20-km-long restraining stepover. Farther north, at the latitude of Santa Catalina Island, the SDTFZ bends 20° to the west and may be linked via a complex zone of folds with the San Pedro basin fault zone (SPBFZ). In a cooperative program between the U.S. Geological Survey (USGS) and the Monterey Bay Aquarium Research Institute (MBARI), we measure and date the coseismic offset of a submarine channel that intersects the fault zone near the SDTFZ–SPBFZ junction. We estimate a horizontal slip rate of about 1:5 0:3 mm=yr over the past 12,270 yr.

  9. Basin structure of the San Fernando and Santa Clarita Valleys and geometry of the Northridge and San Fernando faults as determined from the Los Angeles Region Seismic Experiment, Phase II (LARSE II)

    NASA Astrophysics Data System (ADS)

    Lutter, W. J.; Ryberg, T.; Fuis, G. S.; Murphy, J. M.; Okaya, D. A.

    2001-12-01

    We acquired combined refraction and low-fold reflection data along a north-south-trending profile through the epicentral regions of the 1994 M 6.7 Northridge and 1971 M 6.7 San Fernando earthquakes as part of the Los Angeles Region Seismic Experiment, Phase II (LARSE II). The chief goal of LARSE is to image sedimentary basins and faults in the Los Angeles region to better understand and mitigate earthquake hazards associated with sedimentary basins and hidden faults. The LARSE II profile crossed the San Fernando and Santa Clarita Valleys, locations of the Northridge and San Fernando earthquakes, respectively. Refraction and reflection data show asymmetric basins beneath both valleys. Stacked wide-angle basin-bottom reflections and iso-velocity lines dip gently northward from the Santa Monica Mts, on the south margin of the San Fernando Valley, to 5-6 km below sea level in the northern part of the San Fernando Valley. Similar reflections and iso-velocity lines dip southward from the Sierra Pelona, on the north margin of the Santa Clarita Valley, to 3.5-4.5 km below sea level at the San Gabriel fault, in the central part of the Santa Clarita Valley. In both valleys, the basin-bottom reflections are generally slightly below the 5 km/s iso-velocity line, indicating that ``basement'' beneath these two valleys has velocities generally upwards of 5 km/s. In the San Fernando Valley, the basin-bottom reflections are truncated on the north by what we interpret to be the Northridge Hills blind thrust fault. In the Santa Clarita Valley, these reflections are truncated on the south at the steeply north-dipping San Gabriel fault. The region between these two faults, including the Santa Susana Mts and the southern part of the Santa Clarita Valley is characterized by complexity in both the velocity model and reflectivity. Below ~10-km depth, reflectivity is higher in the hanging walls of the Northridge and San Fernando faults than in the footwalls. The Northridge fault dips ~30o

  10. The 3-D aftershock distribution of three recent M5~5.5 earthquakes in the Anza region,California

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Wdowinski, S.; Lin, G.

    2011-12-01

    The San Jacinto fault zone (SJFZ) exhibits the highest level of seismicity compared to other regions in southern California. On average, it produces four earthquakes per day, most of them at depth of 10-17 km. Over the past decade, an increasing seismic activity occurred in the Anza region, which included three M5~5.5 events and their aftershock sequences. These events occurred in 2001, 2005, and 2010. In this research we map the 3-D distribution of these three events to evaluate their rupture geometry and better understand the unusual deep seismic pattern along the SJFZ, which was termed "deep creep" (Wdowinski, 2009). We relocated 97,562 events from 1981 to 2011 in Anza region by applying the Source-Specific Station Term (SSST) method (Lin et al., 2006) and used an accurate 1-D velocity model derived from 3-D model of Lin et al (2007) and used In order to separate the aftershock sequence from background seismicity, we characterized each of the three aftershock sequences using Omori's law. Preliminary results show that all three sequences had a similar geometry of deep elongated aftershock distribution. Most aftershocks occurred at depth of 10-17 km and extended over a 70 km long segments of the SJFZ, centered at the mainshock hypocenters. A comparative study of other M5~5.5 mainshocks and their aftershock sequences in southern California reveals very different geometrical pattern, suggesting that the three Anza M5~5.5 events are unique and can be indicative of "deep creep" deformation processes. Reference 1.Lin, G.and Shearer,P.M.,2006, The COMPLOC earthquake location package,Seism. Res. Lett.77, pp.440-444. 2.Lin, G. and Shearer, P.M., Hauksson, E., and Thurber C.H.,2007, A three-dimensional crustal seismic velocity model for southern California from a composite event method,J. Geophys.Res.112, B12306, doi: 10.1029/ 2007JB004977. 3.Wdowinski, S. ,2009, Deep creep as a cause for the excess seismicity along the San Jacinto fault, Nat. Geosci.,doi:10.1038/NGEO684.

  11. 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

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

    USGS Publications Warehouse

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

    1993-01-01

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

  13. Directional Site Amplification Effect on Tarzana Hill, California

    NASA Astrophysics Data System (ADS)

    Graizer, V.; Shakal, A.

    2003-12-01

    Significantly amplified ground accelerations at the Tarzana Hill station were recorded during the 1987 Mw 5.9 Whittier Narrows and the 1994 Mw 6.7 Northridge earthquakes. Peak horizontal ground acceleration at the Tarzana station during the 1999 Mw 7.1 Hector Mine earthquake was almost twice as large as the accelerations recorded at nearby stations. The Tarzana site was drilled to a depth of 100 m. A low shear-wave velocity near the surface of 100 m/sec increasing to near 750 m/sec at 100 m depth was measured. The 20 m high hill was found to be well drained with a water table near 17 m. Modelo formation (extremely weathered at the surface to fresh at depth) underlies the hill. The subsurface geology and velocities obtained allow classification of this location as a soft-rock site. After the Northridge earthquake the California Strong Motion Instrumentation Program significantly increased instrumentation at Tarzana to study the unusual site amplification effect. Current instrumentation at Tarzana consists of an accelerograph at the top of Tarzana hill (Tarzana - Cedar Hill B), a downhole instrument at 60 m depth, and an accelerograph at the foot of the hill (Tarzana - Clubhouse), 180 m from the Cedar Hill B station. The original station, Tarzana - Cedar Hill Nursery A, was lost in 1999 due to construction. More than twenty events, including the Hector Mine earthquake, were recorded by all these instruments at Tarzana. Comparison of recordings and response spectra demonstrates strong directional resonance on the top of the hill in a direction perpendicular to the strike of the hill in the period range from 0.04 to 0.8 sec (1.2 to 25 Hz). There is practically no amplification from the bottom to the top of the hill for the component parallel to the strike of the hill. In contrast to accelerations recorded during the Hector Mine earthquake (high frequency part of seismic signal), displacements (relatively low frequency part of seismic signal) demonstrate almost no site

  14. Earthquakes, September-October, 1979

    USGS Publications Warehouse

    Person, W.J.

    1980-01-01

    In the United States, California experienced the strongest earthquake in that State since 1971. The quake, a M=6.8, occurred on October 15, in Baja California, Mexico, near the California border and caused injuries and damage. 

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

    USGS Publications Warehouse

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

    1993-01-01

    The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demonstrated that the North America-Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the Cascadia region. The shock occurred just north of the Mendocino Triple Junction and caused strong ground motion and moderate damage in the immediate area. Rupture initiated onshore at a depth of 10.5 kilometers and propagated up-dip and seaward. Slip on steep faults in the Gorda plate generated two magnitude 6.6 aftershocks on 26 April. The main shock did not produce surface rupture on land but caused coastal uplift and a tsunami. The emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity.

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

    USGS Publications Warehouse

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

    1993-01-01

    Several thousand earthquakes were recorded in each area. We report an initial investigation of the focal mechanisms based on P-wave polarities. Distortion by complicated three-dimensional crustal structure was minimized using tomographically derived three-dimensional crustal models. Events with explosive and implosive source mechanisms, suggesting cavity opening and collapse, have been tentatively identified at The Geysers. The new data show that some of these events do not fit the model of tensile cracking accompanied by isotropic pore pressure decreases that was suggested in earlier studies, but that they may instead involve combination of explosive and shear processes. However, the confirmation of earthquakes dominated by explosive components supports the model that the event are caused by crack opening induced by thermal contraction of the heat source.

  17. Postseismic deformation following the 1989 (M = 7.1) Loma Prieta, California, earthquake

    USGS Publications Warehouse

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

    1994-01-01

    Postseismic deformation along a 90-km profile bisecting the projected surface trace of the coseismic rupture of the 1989 Loma Prieta earthquake has been monitored by frequent GPS surveys for 3.3 years following the earthquake. In addition to the expected deformation associated with secular strain accumulation on the San Andreas and Calaveras Faults, deformation associated with postseismic readjustment has been detected. Most of that deformation can be attributed to 1.5 m right-lateral and 0.9 m reverse postseismic slip on a 5-km-wide downdip extension of the Loma Prieta rupture. In addition, there seems to be a 0.1 m postseismic collapse of the Loma Prieta rupture zone in the direction perpendicular to the plane of the rupture. -from Authors

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

    PubMed

    Peltzer, G; Rosen, P

    1995-06-01

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

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

    USGS Publications Warehouse

    Nigg, Joanne M.

    1998-01-01

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

  20. Earthquake recurrence on the Calaveras fault east of San Jose, California

    USGS Publications Warehouse

    Bufe, C.G.; Harsh, P.W.; Burford, R.O.

    1979-01-01

    Occurrence of small (3 ??? ML < 4) earthquakes on two 10-km segments of the Calaveras fault between Calaveras and Anderson reservoirs follows a simple linear pattern of elastic strain accumulation and release. The centers of these independent patches of earthquake activity are 20 km apart. Each region is characterized by a constant rate of seismic slip as computed from earthquake magnitudes, and is assumed to be an isolated locked patch on a creeping fault surface. By calculating seismic slip rates and the amount of seismic slip since the time of the last significant (M ??? 3) earthquake, it is possible to estimate the most likely date of the next (M ???- 3) event on each patch. The larger the last significant event, the longer the time until the next one. The recurrence time also appears to be increased according to the moment of smaller (2 < ML < 3) events in the interim. The anticipated times of future larger events on each patch, on the basis of preliminary location data through May 1977 and estimates of interim activity, are tabulated below with standard errors. The occurrence time for the southern zone is based on eight recurrent events since 1969, the northern zone on only three. The 95% confidence limits can be estimated as twice the standard error of the projected least-squares line. Events of M ??? 3 should not occur in the specified zones at times outside these limits. The central region between the two zones was the locus of two events (M = 3.6, 3.3) on July 3, 1977. These events occurred prior to a window based on the three point, post-1969 slip-time line for the central region. {A table is presented}. ?? 1979.

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

    USGS Publications Warehouse

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

    1984-01-01

    Five examples illustrate how geologic and seismologic information can be used to reduce the effects of earthquakes Included are procedures for anticipating damage to critical facilities, preparing, adopting, or implementing seismic safety studies, plans, and programs, retrofitting highway bridges, regulating development in areas subject to fault-rupture, and strengthening or removing unreinforced masonry buildings. The collective effect of these procedures is to improve the public safety, health, and welfare of individuals and their communities. ?? 1984 Springer-Verlag New York Inc.

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

    USGS Publications Warehouse

    Rymer, Michael J.; Treiman, Jerome A.; Kendrick, Katherine J.; Lienkaemper, James J.; Weldon, Ray J.; Bilham, Roger; Wei, Meng; Fielding, Eric J.; Hernandez, Janis L.; Olson, Brian P.E.; Irvine, Pamela J.; Knepprath, Nichole; Sickler, Robert R.; Tong, Xiaopeng; Siem, Martin E.

    2011-01-01

    Triggered slip in the Yuha Desert area occurred along more than two dozen faults, only some of which were recognized before the April 4, 2010, El Mayor-Cucapah earthquake. From east to northwest, slip occurred in seven general areas: (1) in the Northern Centinela Fault Zone (newly named), (2) along unnamed faults south of Pinto Wash, (3) along the Yuha Fault (newly named), (4) along both east and west branches of the Laguna Salada Fault, (5) along the Yuha Well Fault Zone (newly revised name) and related faults between it and the Yuha Fault, (6) along the Ocotillo Fault (newly named) and related faults to the north and south, and (7) along the southeasternmost section of the Elsinore Fault. Faults that slipped in the Yuha Desert area include northwest-trending right-lateral faults, northeast-trending left-lateral faults, and north-south faults, some of which had dominantly vertical offset. Triggered slip along the Ocotillo and Elsinore Faults appears to have occurred only in association with the June 14, 2010 (Mw5.7), aftershock. This aftershock also resulted in slip along other faults near the town of Ocotillo. Triggered offset on faults in the Yuha Desert area was mostly less than 20 mm, with three significant exceptions, including slip of about 50–60 mm on the Yuha Fault, 40 mm on a fault south of Pinto Wash, and about 85 mm on the Ocotillo Fault. All triggered slips in the Yuha Desert area occurred along preexisting faults, whether previously recognized or not.

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

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

    USGS Publications Warehouse

    Rymer, M.J.

    1990-01-01

    Five small-aperture (0.5 to 7.7 m) quadrilaterals were installed across the San Andreas fault and newly formed extensional cracks shortly after the October 17, 1989 Loma Prieta M7.1 earthquake. Measurements of line-length changes from as early as 4 d up to 184 d after the earthquake in nail quadrilaterals indicate a small amount of right-lateral postseismic slip on the San Andreas fault. The site near the southeast end of the 1989 aftershock zone on the San Andreas fault showed about 5??2 mm of postseismic right-lateral component of slip in addition to 23 mm of right-lateral coseismic movement. The site near the northwest end of aftershocks likewise showed about 5??2 mm of postseismic slip, but after only 5 mm of coseismic slip. The smal slip values, in spite of uncertainties, clearly show that the lack of coseismic surface slip associated with the earthquake was not followed by large postseismic slip. -from Author

  6. Slip in the 2004 Parkfield, California, Earthquake Measured on Alinement Arrays

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    Nineteen alinement arrays were installed in the early 1980s across the San Andreas fault zone near Parkfield and these were resurveyed frequently until 1991. We have recovered eleven of these arrays beginning the day after the September 28, 2004 earthquake. Assuming that the creep rate from the 1980s continued during the period 1991-2004, we can make preliminary estimates of slip associated with the 2004 earthquake. These estimates can be improved later by use of creepmeter and other data. North of Gold Hill to Parkfield, estimates of slip in the first 48 hours range from 6 to 10 centimeters. In the first three weeks slip here grew to 10-14 cm. From Gold Hill southward to Highway 46 slip is much lower in the early period, 0-2 cm, and has increased to 2-5 cm in the three weeks following the event. Our first observation on Middle Mountain, 7 days post-earthquake was for only 6.5 cm, smaller than slip near Parkfield, but it is now growing faster than other sites. The data from the array on the middle of the Southwest Fracture Zone (Ranchito Canyon Rd) showed 6.6 +/- 0.1 cm of coseismic slip. Since this array was installed in 1986, it has shown neither creep nor afterslip. Our preliminary projections of afterslip on the main fault trace suggest that the total surface slip associated with the 2004 event may be only about half of what occurred in the 1966 event.

  7. A century of oilfield operations and earthquakes in the greater Los Angeles Basin, southern California

    USGS Publications Warehouse

    Hauksson, Egill; Goebel, Thomas; Ampuero, Jean-Paul; Cochran, Elizabeth S.

    2015-01-01

    Most of the seismicity in the Los Angeles Basin (LA Basin) occurs at depth below the sediments and is caused by transpressional tectonics related to the big bend in the San Andreas fault. However, some of the seismicity could be associated with fluid extraction or injection in oil fields that have been in production for almost a century and cover ∼ 17% of the basin. In a recent study, first the influence of industry operations was evaluated by analyzing seismicity characteristics, including normalized seismicity rates, focal depths, and b-values, but no significant difference was found in seismicity characteristics inside and outside the oil fields. In addition, to identify possible temporal correlations, the seismicity and available monthly fluid extraction and injection volumes since 1977 were analyzed. Second, the production and deformation history of the Wilmington oil field were used to evaluate whether other oil fields are likely to experience similar surface deformation in the future. Third, the maximum earthquake magnitudes of events within the perimeters of the oil fields were analyzed to see whether they correlate with total net injected volumes, as suggested by previous studies. Similarly, maximum magnitudes were examined to see whether they exhibit an increase with net extraction volume. Overall, no obvious previously unidentified induced earthquakes were found, and the management of balanced production and injection of fluids appears to reduce the risk of induced-earthquake activity in the oil fields.

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

    USGS Publications Warehouse

    Spudich, Paul

    1996-01-01

    The October 17, 1989, Loma Prieta, Calif., earthquake (0004:15.2 G.m.t. October 18; lat 37.036? N., long 121.883? W.; 19-km depth) had a local magnitude (ML) of about 6.7, a surface-wave magnitude (MS) of 7.1, a seismic moment of 2.2x1019 N-m to 3.5x1019 N-m, a source duration of 6 to 15 s, and an average stress drop of at least 50 bars. Slip occurred on a dipping fault surface about 35 km long and was largely confined to a depth of about 7 to 20 km. The slip vector had a large vertical component, and slip was distributed in two main regions situated northwest and southeast of the hypocenter. This slip distribution caused about half of the earthquake's energy to be focused toward the urbanized San Francisco Bay region, while the other half was focused toward the southeast. Had the rupture initiated at the southeast end of the aftershock zone, shaking in the bay region would have been both longer and stronger. These source parameters suggest that the earthquake was not a typical shallow San Andreas-type event but a deeper event on a different fault with a recurrence interval of many hundreds of years. Therefore, the potential for a damaging shallow event on the San Andreas fault in the Santa Cruz Mountains may still exist.

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

    USGS Publications Warehouse

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

    1999-01-01

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

  10. Does Geothermal Energy Production Cause Earthquakes in the Geysers Region of Northern California?

    NASA Astrophysics Data System (ADS)

    Grove, K.; Bailey, C.; Sotto, M.; Yu, M.; Cohen, M.

    2003-12-01

    The Geysers region is located in Sonoma County, several hours north of San Francisco. At this location, hot magma beneath the surface heats ground water and creates steam that is used to make electricity. Since 1997, 8 billion gallons of treated wastewater have been injected into the ground, where the water becomes hot and increases the amount of thermal energy that can be produced. Frequent micro-earthquakes (up to magnitude 4.5) occur in the region and seem to be related to the geothermal energy production. The region is mostly uninhabited, except for several small towns such as Anderson Springs, where people have been extremely concerned about potential damage to their property. The energy companies are planning to double the amount of wastewater injected into the ground and to increase their energy production. Geothermal energy is important because it is better for the environment than burning coal, oil, or gas. Air and water pollution, which have negative impacts on living things, are reduced compared to power plants that generate electricity by burning fossil fuels. We have studied the frequency and magnitude of earthquakes that have occurred in the region since the early 1970s and that are occurring today. We used software to analyze the earthquakes and to look for patterns related to water injection and energy production. We are interested in exploring ways that energy production can be continued without having negative impacts on the people in the region.

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

    ERIC Educational Resources Information Center

    Baker, Natalie Danielle

    2013-01-01

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

  12. Differentiating Tectonic and Anthropogenic Earthquakes in the Greater Los Angeles Basin, Southern California

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Goebel, T.; Cochran, E. S.; Ampuero, J. P.

    2014-12-01

    The 2014 flurry of moderate earthquakes in the Los Angeles region raised the concern if some of this or past seismicity was of anthropogenic origin as opposed to being caused by ongoing transpressional tectonics. The Mw5.1 La Habra sequence is located near several major oil fields but the Mw4.4 Encino sequence was located away from oil fields, within the Santa Monica Mountains. The last century of seismicity in the Los Angeles area consists of numerous small and large earthquakes. Most of these earthquakes occur beneath the basin sediments and are associated with transpressional tectonics, related to the big bend in the San Andreas fault, but some could be associated with large oil fields. In particular, both the 1933 Mw6.4 Long Beach and the 1987 Mw5.9 Whittier Narrows earthquakes were spatially associated with two major oil fields, the Huntington Beach and Montebello fields. Numerous large oil fields have been in production for more than 125 years. The geographical locations of the oil fields follow major tectonic trends such as the Newport-Inglewood fault, the Whittier fault, and the thrust belt located at the north edge of the Los Angeles basin. More than 60 fields have oil wells and some of these have both disposal and fracking wells. Before fluid injection became common, Kovach (1974) documented six damaging events induced by fluid extraction from 1947 to 1961 in the Wilmington oil field. Since 1981 the waveform-relocated earthquake catalog for the Los Angeles basin is complete on the average above M2.0. We compare the spatial distribution of these events and the proximity of nearby active oil fields. We will also analyze the seismicity in the context of available monthly fluid extraction and injection volumes and search for temporal correlations. The La Habra sequence apparently correlates with temporal changes in extraction and injection volumes in the Santa Fe Springs oil field but not with activities in other oil fields within closer spatial proximity.

  13. Three-dimensional fault framework of the 2014 South Napa Earthquake, San Francisco Bay region, California

    NASA Astrophysics Data System (ADS)

    Graymer, R. W.

    2014-12-01

    Assignment of the South Napa earthquake to a mapped fault is difficult, as it occurred where three large, northwest-trending faults converge and may interact in the subsurface. The surface rupture did not fall on the main trace of any of these faults, but instead between the Carneros and West Napa faults and northwest along strike from the northern mapped end of the Franklin Fault. The 2014 rupture plane appears to be nearly vertical, based on focal mechanisms of the mainshock and connection of the surface trace/rupture to the relocated hypocenter (J. Hardebeck, USGS). 3D surfaces constructed from published data show that the Carneros Fault is a steeply west-dipping fault that runs just west of the near-vertical 2014 rupture plane. The Carneros Fault does not appear to have been involved in the earthquake, although relocated aftershocks suggest possible minor triggered slip. The main West Napa Fault is also steeply west-dipping and that its projection intersects the 2014 rupture plane at around the depth of the mainshock hypocenter. UAVSAR data (A. Donnellan, JPL) and relocated aftershocks suggest that the main West Napa Fault experienced triggered slip/afterslip along a length of roughly 20 km. It is possible that the 2014 rupture took place along a largely unrecognized westerly strand of the West Napa Fault. The Franklin Fault is a steeply east-dipping fault (with a steeply west-dipping subordinate trace east of Mare Island) that has documented late Quaternary offset. Given the generally aligned orientation of the 3D fault surfaces, an alternative interpretation is that the South Napa earthquake occurred on the northernmost reach of the Franklin Fault within it's 3D junction with the West Napa Fault. This interpretation is supported, but not proven, by a short but prominent linear feature in the UAVSAR data at Slaughterhouse Point west of Vallejo, along trend south-southeast of the observed coseismic surface rupture.

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

    USGS Publications Warehouse

    Hardebeck, J.L.; Aron, A.

    2009-01-01

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

  15. Along-strike variations in fault frictional properties along the San Andreas Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations

    USGS Publications Warehouse

    Harrington, R.M; Cochran, Elizabeth S.; Griffiths, E.M.; Zeng, X.; Thurber, C.

    2016-01-01

    Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San Andreas fault suggest slow‐slip earthquakes occur in a transition zone between the shallow fault, which accommodates slip by a combination of aseismic creep and earthquakes (<15  km depth), and the deep fault, which accommodates slip by stable sliding (>35  km depth). However, the spatial relationship between shallow earthquakes and LFEs remains unclear. Here, we present precise relocations of 34 earthquakes and 34 LFEs recorded during a temporary deployment of 13 broadband seismic stations from May 2010 to July 2011. We use the temporary array waveform data, along with data from permanent seismic stations and a new high‐resolution 3D velocity model, to illuminate the fine‐scale details of the seismicity distribution near Cholame and the relation to the distribution of LFEs. The depth of the boundary between earthquakes and LFE hypocenters changes along strike and roughly follows the 350°C isotherm, suggesting frictional behavior may be, in part, thermally controlled. We observe no overlap in the depth of earthquakes and LFEs, with an ∼5  km separation between the deepest earthquakes and shallowest LFEs. In addition, clustering in the relocated seismicity near the 2004 Mw 6.0 Parkfield earthquake hypocenter and near the northern boundary of the 1857 Mw 7.8 Fort Tejon rupture may highlight areas of frictional heterogeneities on the fault where earthquakes tend to nucleate.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    SciTech Connect

    Stevenson, J.D.

    1995-11-01

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

  19. Average Stress Drops of Southern California Earthquakes in the Context of Crustal Geophysics: Implications for Fault Zone Healing

    NASA Astrophysics Data System (ADS)

    Hauksson, Egill

    2015-05-01

    To understand how fault healing processes affect earthquake stress drops, we search for a possible dependency of stress drops on crustal conditions and geophysical parameters. We reanalyze the stress drop values of ~60,000 earthquakes in southern California which were originally determined by Shearer et al. J Geophys Res 111:B06303, (2006) using a spectral method. We modify the dataset to include only stress drops that are derived from at least 10 spectra and with corner frequencies between 3 and 30 Hz, and correct the rupture velocity for increasing S-wave speed with depth. We see no dependence of stress drop on moment magnitude or depth, except for a small, poorly determined increase from 15 to 25 km. We use six crustal geophysics parameters to search for obvious correlations that may explain changes in the mean values of the stress drops: (1) crustal thickness, (2) isostatic gravity, (3) heat flow, (4) shear strain rate, (5) crustal stress regime, and (6) style of faulting. None of the variables reduce the scatter but most can explain up to 10-20 % variations in the mean stress drops. The geographical distribution of the grouped mean stress drops includes very high stress drops near Ridgecrest, eastern California, as well as near fault jogs within the San Andreas Fault system. Low stress drops dominate in trans-tensional regions. Heat flow and GPS-based shear strain rate estimates have the largest influence on stress drop variations. In the range of low to medium heat flow, the stress drops increase with increasing heat flow. In contrast, at high heat flow in thin crust, the stress drops decrease systematically with increasing heat flow. Increasing shear strain rate systematically correlates with decreasing stress drops. The crustal stress regime and style of faulting also influence the stress drops as demonstrated by lower stress drops for north-northeast trending principal horizontal stress and in areas of dip-slip faulting. The mean variations in stress drops

  20. Source complexity of the 1987 Whittier Narrows, California, earthquake from the inversion of strong motion records

    USGS Publications Warehouse

    Hartzell, S.; Iida, M.

    1990-01-01

    Strong motion records for the Whittier Narrows earthquake are inverted to obtain the history of slip. Both constant rupture velocity models and variable rupture velocity models are considered. The results show a complex rupture process within a relatively small source volume, with at least four separate concentrations of slip. Two sources are associated with the hypocenter, the larger having a slip of 55-90 cm, depending on the rupture model. These sources have a radius of approximately 2-3 km and are ringed by a region of reduced slip. The aftershocks fall within this low slip annulus. Other sources with slips from 40 to 70 cm each ring the central source region and the aftershock pattern. All the sources are predominantly thrust, although some minor right-lateral strike-slip motion is seen. The overall dimensions of the Whittier earthquake from the strong motion inversions is 10 km long (along the strike) and 6 km wide (down the dip). The preferred dip is 30?? and the preferred average rupture velocity is 2.5 km/s. Moment estimates range from 7.4 to 10.0 ?? 1024 dyn cm, depending on the rupture model. -Authors

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

    NASA Astrophysics Data System (ADS)

    Maloney, J. M.; Driscoll, N. W.; Kent, G.; Brothers, D. S.; Baskin, R. L.; Babcock, J. M.; Noble, P. J.; Karlin, R. E.

    2011-12-01

    Previous work in the Lake Tahoe Basin (LTB), California, identified the West Tahoe-Dollar Point Fault (WTDPF) as the most hazardous fault in the region. Onshore and offshore geophysical mapping delineated three segments of the WTDPF extending along the western margin of the LTB. The rupture patterns between the three WTDPF segments remain poorly understood. Fallen Leaf Lake (FLL), Cascade Lake, and Emerald Bay are three sub-basins of the LTB, located south of Lake Tahoe, that provide an opportunity to image primary earthquake deformation along the WTDPF and associated landslide deposits. We present results from recent (June 2011) high-resolution seismic CHIRP surveys in FLL and Cascade Lake, as well as complete multibeam swath bathymetry coverage of FLL. Radiocarbon dates obtained from the new piston cores acquired in FLL provide age constraints on the older FLL slide deposits and build on and complement previous work that dated the most recent event (MRE) in Fallen Leaf Lake at ~4.1-4.5 k.y. BP. The CHIRP data beneath FLL image slide deposits that appear to correlate with contemporaneous slide deposits in Emerald Bay and Lake Tahoe. A major slide imaged in FLL CHIRP data is slightly younger than the Tsoyowata ash (7950-7730 cal yrs BP) identified in sediment cores and appears synchronous with a major Lake Tahoe slide deposit (7890-7190 cal yrs BP). The equivalent age of these slides suggests the penultimate earthquake on the WTDPF may have triggered them. If correct, we postulate a recurrence interval of ~3-4 k.y. These results suggest the FLL segment of the WTDPF is near its seismic recurrence cycle. Additionally, CHIRP profiles acquired in Cascade Lake image the WTDPF for the first time in this sub-basin, which is located near the transition zone between the FLL and Rubicon Point Sections of the WTDPF. We observe two fault-strands trending N45°W across southern Cascade Lake for ~450 m. The strands produce scarps of ~5 m and ~2.7 m, respectively, on the lake

  2. Post-earthquake relaxation evidence for laterally variable viscoelastic structure and elevated water concentration in the southwestern California mantle

    NASA Astrophysics Data System (ADS)

    Pollitz, F. F.

    2014-12-01

    I re-examine the lower crust and mantle relaxation following two large events in the Mojave Desert: the 1992 M7.3 Landers and 1999 M7.1 Hector Mine, California, earthquakes. More than a decade of GPS time series from regional sites out to 250 km from the ruptures are used to constrain models of postseismic relaxation. Crustal motions in the Mojave Desert region are elevated for several years following each event, with perturbations from a pre-Landers background of order mm to cm per year. I consider afterslip and relaxation of the ductile lower crust and mantle to explain these motions. To account for broad scale relaxation, the Burgers body model is employed, involving Kelvin (transient) viscosity and rigidity and Maxwell (steady state) viscosity and rigidity. I use the code VISCO2.5D to perform 2.5D modeling of the postseismic relaxation (3D quasi-static motions computed on 2D, laterally heterogeneous viscoelastic structures; Pollitz, 2014 GJI). Joint afterslip / postseismic relaxation modeling of continuous GPS time series up to 10.46 years following the Hector Mine earthquake (i.e. up to the time of the 2010 M7.2 El Mayor-Cucapah earthquake) reveals that a northwest-trending `southwest domain' that envelopes the San Andreas fault system and western Mojave Desert has ~4 times larger Maxwell mantle viscosity than the adjacent `northeast domain' that extends inland and envelopes the Landers and Hector Mine rupture areas in the central Mojave Desert. This pattern is counter to that expected from regional heat flow, which is higher in the northeast domain, but it is explicable by means of a non-linear rheology that includes dependence on both strain rate and water concentration. I infer that the southwest domain mantle has a relatively low steady-state viscosity because of its high strain rate and water content. The relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic

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

    USGS Publications Warehouse

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

    1996-01-01

    We invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the April 25, 1992, M=7 Cape Mendocino, California, earthquake. The orientation of the model slip vector, which nearly parallels North America-Juan de Fuca relative plate convergence, and the location and orientation of the model fault relative to the offshore Cascadia megathrust, suggest that the 1992 Cape Mendocino earthquake is the first well-recorded event to relieve strain associated with the Cascadia subduction zone. We use data from three geodetic techniques: (1) the horizontal and vertical displacements of 13 monuments surveyed with the Global Positioning System, corrected for observed horizontal interseismic strain accumulation, (2) 88 section-elevation differences between leveling monuments, and (3) the uplift of 12 coastal sites observed from the die-off of intertidal marine organisms. Maximum observed displacements are 0.4 m of horizontal movement and 1.5 m of uplift along the coast. We use Monte Carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties. The optimal model using all the data resolves 4.9 m of slip on a 14 by 15 km fault that dips 28?? SE. The fault extends from 1.5 to 8.7 km in depth and the main-shock hypocenter is close to the downdip projection of the fault. The shallowly dipping fault plane is consistent with the observed aftershock locations, and the estimated geodetic moment is 3.1??1019 N m, 70% of the seismic moment. Other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry. If the earthquake is characteristic for this segment, the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years, with a 95% confidence range of 100-670 years. The coseismic uplift occurred in a region that also has high Quaternary uplift rates determined from marine terrace

  4. Observed and simulated ground motions in the San Bernardino basin region for the Hector Mine, California, earthquake

    USGS Publications Warehouse

    Graves, R.W.; Wald, D.J.

    2004-01-01

    During the MW 7.1 Hector Mine earthquake, peak ground velocities recorded at sites in the central San Bernardino basin region were up to 2 times larger and had significantly longer durations of strong shaking than sites just outside the basin. To better understand the effects of 3D structure on the long-period ground-motion response in this region, we have performed finite-difference simulations for this earthquake. The simulations are numerically accurate for periods of 2 sec and longer and incorporate the detailed spatial and temporal heterogeneity of source rupture, as well as complex 3D basin structure. Here, we analyze three models of the San Bernardino basin: model A (with structural constraints from gravity and seismic reflection data), model F (water well and seismic refraction data), and the Southern California Earthquake Center version 3 model (hydrologic and seismic refraction data). Models A and F are characterized by a gradual increase in sediment thickness toward the south with an abrupt step-up in the basement surface across the San Jacinto fault. The basin structure in the SCEC version 3 model has a nearly uniform sediment thickness of 1 km with little basement topography along the San Jacinto fault. In models A and F, we impose a layered velocity structure within the sediments based on the seismic refraction data and an assumed depth-dependent Vp/Vs ratio. Sediment velocities within the SCEC version 3 model are given by a smoothly varying rule-based function that is calibrated to the seismic refraction measurements. Due to computational limitations, the minimum shear-wave velocity is fixed at 600 m/sec in all of the models. Ground-motion simulations for both models A and F provide a reasonably good match to the amplitude and waveform characteristics of the recorded motions. In these models, surface waves are generated as energy enters the basin through the gradually sloping northern margin. Due to the basement step along the San Jacinto fault, the

  5. Earthquake watch

    USGS Publications Warehouse

    Hill, M.

    1976-01-01

     When the time comes that earthquakes can be predicted accurately, what shall we do with the knowledge? This was the theme of a November 1975 conference on earthquake warning and response held in San Francisco called by Assistant Secretary of the Interior Jack W. Carlson. Invited were officials of State and local governments from Alaska, California, Hawaii, Idaho, Montana, Nevada, utah, Washington, and Wyoming and representatives of the news media. 

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

    USGS Publications Warehouse

    Ryan, Holly F.; von Huene, Roland; Wells, Ray E.; Scholl, David W.; Kirby, Stephen; Draut, Amy E.; Dumoulin, J.A.; Dusel-Bacon, C.

    2012-01-01

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

  7. Non-double-couple earthquake mechanisms at the Geysers geothermal area, California

    USGS Publications Warehouse

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

    1996-01-01

    Inverting P- and S-wave polarities and P:SH amplitude ratios using linear programming methods suggests that about 20% of earthquakes at The Geysers geothermal area have significantly non-double-couple focal mechanisms, with explosive volumetric components as large as 33% of the seismic moment. This conclusion contrasts with those of earlier studies, which interpreted data in terms of double couples. The non-double-couple mechanisms are consistent with combined shear and tensile faulting, possibly caused by industrial water injection. Implosive mechanisms, which might be expected because of rapid steam withdrawal, have not been found. Significant compensated-linear-vector-dipole (CLVD) components in some mechanisms may indicate rapid fluid flow accompanying crack opening. Copyright 1996 by the American Geophysical Union.

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

    USGS Publications Warehouse

    Pampeyan, Earl H.

    1986-01-01

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

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

    USGS Publications Warehouse

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

    2006-01-01

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

  11. Finite-fault analysis of the 2004 Parkfield, California, earthquake using Pnl waveforms

    USGS Publications Warehouse

    Mendoza, C.; Hartzell, S.

    2008-01-01

    We apply a kinematic finite-fault inversion scheme to Pnl displacement waveforms recorded at 14 regional stations (Δ<2°) to recover the distribution of coseismic slip for the 2004 Parkfield earthquake using both synthetic Green’s functions (SGFs) calculated for one-dimensional (1D) crustal-velocity models and empirical Green’s functions (EGFs) based on the recordings of a single Mw 5.0 aftershock. Slip is modeled on a rectangular fault subdivided into 2×2 km subfaults assuming a constant rupture velocity and a 0.5 sec rise time. A passband filter of 0.1–0.5 Hz is applied to both data and subfault responses prior to waveform inversion. The SGF inversions are performed such that the final seismic moment is consistent with the known magnitude (Mw 6.0) of the earthquake. For these runs, it is difficult to reproduce the entire Pnl waveform due to inaccuracies in the assumed crustal structure. Also, the misfit between observed and predicted vertical waveforms is similar in character for different rupture velocities, indicating that neither the rupture velocity nor the exact position of slip sources along the fault can be uniquely identified. The pattern of coseismic slip, however, compares well with independent source models derived using other data types, indicating that the SGF inversion procedure provides a general first-order estimate of the 2004 Parkfield rupture using the vertical Pnl records. The best-constrained slip model is obtained using the single-aftershock EGF approach. In this case, the waveforms are very well reproduced for both vertical and horizontal components, suggesting that the method provides a powerful tool for estimating the distribution of coseismic slip using the regional Pnl waveforms. The inferred slip model shows a localized patch of high slip (55 cm peak) near the hypocenter and a larger slip area (~50 cm peak) extending between 6 and 20 km to the northwest.

  12. Post seismic deformation associated with the 1992 Mω=7.3 Landers earthquake, southern California

    USGS Publications Warehouse

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

    1997-01-01

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

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

    SciTech Connect

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

    1987-01-01

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

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

    SciTech Connect

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

    2008-05-15

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

  15. Dynamic triggering of creep events in the Salton Trough, Southern California by regional M ≥ 5.4 earthquakes constrained by geodetic observations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Wei, Meng; Liu, Yajing; Kaneko, Yoshihiro; McGuire, Jeffrey J.; Bilham, Roger

    2015-10-01

    Since a regional earthquake in 1951, shallow creep events on strike-slip faults within the Salton Trough, Southern California have been triggered at least 10 times by M ≥ 5.4 earthquakes within 200 km. The high earthquake and creep activity and the long history of digital recording within the Salton Trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes. Here, we document the history of fault creep events on the Superstition Hills Fault based on data from creepmeters, InSAR, and field surveys since 1988. We focus on a subset of these creep events that were triggered by significant nearby earthquakes. We model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate- and state-dependent friction. We find that the static stress changes from the causal earthquakes are less than 0.1 MPa and too small to instantaneously trigger creep events. In contrast, we can reproduce the characteristics of triggered slip with dynamic perturbations alone. The instantaneous triggering of creep events depends on the peak and the time-integrated amplitudes of the dynamic Coulomb stress change. Based on observations and simulations, the stress change amplitude required to trigger a creep event of a 0.01-mm surface slip is about 0.6 MPa. This threshold is at least an order of magnitude larger than the reported triggering threshold of non-volcanic tremors (2-60 kPa) and earthquakes in geothermal fields (5 kPa) and near shale gas production sites (0.2-0.4 kPa), which may result from differences in effective normal stress, fault friction, the density of nucleation sites in these systems, or triggering mechanisms. We conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the Superstition Hills Fault.

  16. Moving Mountains and Deep Crustal Earthquakes: Evidence for Deep Magma Injection Beneath Lake Tahoe, Nevada-California

    NASA Astrophysics Data System (ADS)

    Blewitt, G.; Smith, K. D.; von Seggern, D.

    2004-12-01

    We recently reported [Smith et al., Science 305, 2004] an unusually deep swarm of 1611 earthquakes that occurred in late 2003 at Lake Tahoe, California (depth 29-33 kilometer; Richter Magnitude [ML] < 2.2; sum of the moment magnitude of all events is Mw 3.1). This swarm was coeval with a GPS transient displacement of 6 ± 0.3 mm horizontally outward from the swarm and 7.9 ± 1.0 mm upward measured at the GPS station on Slide Mountain, Nevada (SLID) 18 km to the northeast. Station SLID is a part of the 53-station Basin and Range Geodetic Network (BARGEN) network, continuously operating since 1996 and one of the PBO Nucleus stations. Here we focus on the results of the geodetic analysis for SLID, and other BARGEN stations within 200 km of SLID, starting on 1 January 2000. The SLID transient displacement is 9.8 mm in a direction normal to the planar structure defined by the deep earthquake swarm, spanning the same time period of the swarm. The geodetic displacement here is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters/second up-dip along a 40-km2 structure striking N30° W and dipping 50° to the northeast. Assuming a stress drop of 10 MPa (reasonable for upper crustal earthquakes), this event has an equivalent seismic moment to a magnitude (Mw) 6.0 earthquake with a displacement of ~1 meter at the source. Applying Okada's model for a tensile crack at 28 km depth in the source region, a potency equivalent to a volume of 3.7 × 107 m3, or volumetric moment equivalent of Mw 6.4, fits the SLID observations. As there is no established evidence of recent volcanism (<1 Ma) in the Tahoe region, this discovery suggests the hypothesis that such deep magmatic events in

  17. The accuracy of seismic estimates of dynamic strains: an evaluation using strainmeter and seismometer data from Piñon Flat Observatory, California

    USGS Publications Warehouse

    Gomberg, Joan S.; Agnew, Duncan Carr

    1996-01-01

    The dynamic strains associated with seismic waves may play a significant role in earthquake triggering, hydrological and magmatic changes, earthquake damage, and ground failure. We determine how accurately dynamic strains may be estimated from seismometer data and elastic-wave theory by comparing such estimated strains with strains measured on a three-component long-base strainmeter system at Pin??on Flat, California. We quantify the uncertainties and errors through cross-spectral analysis of data from three regional earthquakes (the M0 = 4 ?? 1017 N-m St. George, Utah; M0 = 4 ?? 1017 N-m Little Skull Mountain, Nevada; and M0 = 1 ?? 1019 N-m Northridge, California, events at distances of 470, 345, and 206 km, respectively). Our analysis indicates that in most cases the phase of the estimated strain matches that of the observed strain quite well (to within the uncertainties, which are about ?? 0.1 to ?? 0.2 cycles). However, the amplitudes are often systematically off, at levels exceeding the uncertainties (about 20%); in one case, the predicted strain amplitudes are nearly twice those observed. We also observe significant ?????? strains (?? = tangential direction), which should be zero theoretically; in the worst case, the rms ?????? strain exceeds the other nonzero components. These nonzero ?????? strains cannot be caused by deviations of the surface-wave propagation paths from the expected azimuth or by departures from the plane-wave approximation. We believe that distortion of the strain field by topography or material heterogeneities give rise to these complexities.

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

    USGS Publications Warehouse

    Sipkin, S.A.

    1989-01-01

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

  19. Validation of simulated earthquake ground motions based on evolution of intensity and frequency content

    USGS Publications Warehouse

    Rezaeian, Sanaz; Zhong, Peng; Hartzell, Stephen; Zareian, Farzin

    2015-01-01

    Simulated earthquake ground motions can be used in many recent engineering applications that require time series as input excitations. However, applicability and validation of simulations are subjects of debate in the seismological and engineering communities. We propose a validation methodology at the waveform level and directly based on characteristics that are expected to influence most structural and geotechnical response parameters. In particular, three time-dependent validation metrics are used to evaluate the evolving intensity, frequency, and bandwidth of a waveform. These validation metrics capture nonstationarities in intensity and frequency content of waveforms, making them ideal to address nonlinear response of structural systems. A two-component error vector is proposed to quantify the average and shape differences between these validation metrics for a simulated and recorded ground-motion pair. Because these metrics are directly related to the waveform characteristics, they provide easily interpretable feedback to seismologists for modifying their ground-motion simulation models. To further simplify the use and interpretation of these metrics for engineers, it is shown how six scalar key parameters, including duration, intensity, and predominant frequency, can be extracted from the validation metrics. The proposed validation methodology is a step forward in paving the road for utilization of simulated ground motions in engineering practice and is demonstrated using examples of recorded and simulated ground motions from the 1994 Northridge, California, earthquake.

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

    USGS Publications Warehouse

    Savage, J.C.; Langbein, J.

    2008-01-01

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

  1. Earthquakes; July-August, 1978

    USGS Publications Warehouse

    Person, W.J.

    1979-01-01

    Earthquake activity during this period was about normal. Deaths from earthquakes were reported from Greece and Guatemala. Three major earthquakes (magnitude 7.0-7.9) occurred in Taiwan, Chile, and Costa Rica. In the United States, the most significant earthquake was a magnitude 5.6 on August 13 in southern California

  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. Problem Areas in Student Teaching and the California Scene.

    ERIC Educational Resources Information Center

    Forer, Ruth K.

    The paper describes the practicum requirements of the Special Education Teacher Preparation program at California State University at Northridge, and it notes problem areas in the roles of the principal, cooperating teacher, and the university professor. Field work requirements involving observation, participation, and student teaching at both the…

  4. Surface deformation before, during and after the 2014 South Napa, California, earthquake from a spatially dense network of survey and continuous GPS site

    NASA Astrophysics Data System (ADS)

    Floyd, M.; Funning, G.; Murray, J. R.; Svarc, J. L.; Herring, T.; Johanson, I. A.; Swiatlowski, J.; Materna, K.; Johnson, C. W.; Boyd, O. S.; Sutton, J. M.; Phillips, E.

    2014-12-01

    The South Napa, California, earthquake occurred on the West Napa Fault within a dense network of established GPS sites. Continuous sites from the Plate Boundary Observatory (PBO), Bay Area Regional Deformation (BARD) and other publicly-available networks lie mostly in the far-field, greater than 15 km from the epicenter. The near-field is covered by two networks of survey GPS sites, one observed by the University of California, Riverside (UCR) and MIT, and the other by the US Geological Survey (USGS). First, we present the pre-earthquake GPS velocity solution from the combination of these networks, covering the entire Pacific-North America plate boundary zone north of San Francisco Bay. We take 1-D fault-perpendicular profile and block model approaches to fit the GPS velocities, both with and without an explicit West Napa Fault, to update previous estimates of slip rates on faults to the east of the Rodgers Creek Fault, which include the West Napa and Green Valley Faults. Second, we present results from the survey GPS field response to the South Napa earthquake. 13 survey sites within 20 km of the epicenter were re-observed within 15 hours of the earthquake by a UCR-MIT group with assistance from UC Berkeley. An additional two sites to the north of the rupture were re-observed within 36 hours. A USGS-led group re-observed 17 sites within 25 km of the epicenter, as well as sites further afield. In total, 35 survey-mode GPS instruments were deployed to observe post-earthquake motions for up to four weeks after the event. Maximum displacements of greater than 20 cm are observed at two survey GPS sites within 2 km and either side of the surface rupture, in agreement with visual inspection of surface rupture offsets. Other observed survey sites within 20 km show at least 2 cm of displacement and 22 continuous GPS sites show displacements that are statistically significant at the 2-sigma level. Further, we show post-earthquake displacements over time as a result of this

  5. The 2006 Bahía Asunción Earthquake Swarm: Seismic Evidence of Active Deformation Along the Western Margin of Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    Munguía, Luis; Mayer, Sergio; Aguirre, Alfredo; Méndez, Ignacio; González-Escobar, Mario; Luna, Manuel

    2015-10-01

    The study of the Bahía Asunción earthquake swarm is important for two reasons. First, the earthquakes are clear evidence of present activity along the zone of deformation on the Pacific margin of Baja California. The swarm, with earthquakes of magnitude M w of up to 5.0, occurred on the coastline of the peninsula, showing that the Tosco-Abreojos zone of deformation is wider than previously thought. Second, the larger earthquakes in the swarm caused some damage and much concern in Bahía Asunción, a small town located in the zone of epicenters. We relocated the larger earthquakes with regional and/or local seismic data. Our results put the earthquake sources below the urban area of Bahía Asunción, at 40-50 km to the north of the teleseismically determined epicenters. In addition, these new locations are in the area of epicenters of many smaller events that were located with data from local temporary stations. This area trends in an E-W direction and has dimensions of approximately 15 km by 10 km. Most earthquakes had sources at depths that are between 4 and 9 km. A composite focal mechanism for the smaller earthquakes indicated right-lateral strike-slip motion and pure-normal faulting occurred during this swarm. Interestingly, the ANSS earthquake catalog of the United States Geological Survey (USGS) reported each one of these faulting styles for two large events of the swarm, with one of these earthquakes occurring 2 days before the other one. We associate the earthquake with strike-slip mechanism with the San Roque Fault, and the earthquake with the normal faulting style with the Asunción Fault. However, there is need of further study to verify this possible relation between the faults and the earthquakes. In addition, we recorded peak accelerations of up to 0.63g with an accelerometer installed in Bahía Asunción. At this site, an earthquake of M w 4.9 produced those high values at a distance of 4.1 km. We also used the acceleration dataset from this site

  6. The 2006 Bahía Asunción Earthquake Swarm: Seismic Evidence of Active Deformation Along the Western Margin of Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    Munguía, Luis; Mayer, Sergio; Aguirre, Alfredo; Méndez, Ignacio; González-Escobar, Mario; Luna, Manuel

    2016-10-01

    The study of the Bahía Asunción earthquake swarm is important for two reasons. First, the earthquakes are clear evidence of present activity along the zone of deformation on the Pacific margin of Baja California. The swarm, with earthquakes of magnitude M w of up to 5.0, occurred on the coastline of the peninsula, showing that the Tosco-Abreojos zone of deformation is wider than previously thought. Second, the larger earthquakes in the swarm caused some damage and much concern in Bahía Asunción, a small town located in the zone of epicenters. We relocated the larger earthquakes with regional and/or local seismic data. Our results put the earthquake sources below the urban area of Bahía Asunción, at 40-50 km to the north of the teleseismically determined epicenters. In addition, these new locations are in the area of epicenters of many smaller events that were located with data from local temporary stations. This area trends in an E-W direction and has dimensions of approximately 15 km by 10 km. Most earthquakes had sources at depths that are between 4 and 9 km. A composite focal mechanism for the smaller earthquakes indicated right-lateral strike-slip motion and pure-normal faulting occurred during this swarm. Interestingly, the ANSS earthquake catalog of the United States Geological Survey (USGS) reported each one of these faulting styles for two large events of the swarm, with one of these earthquakes occurring 2 days before the other one. We associate the earthquake with strike-slip mechanism with the San Roque Fault, and the earthquake with the normal faulting style with the Asunción Fault. However, there is need of further study to verify this possible relation between the faults and the earthquakes. In addition, we recorded peak accelerations of up to 0.63 g with an accelerometer installed in Bahía Asunción. At this site, an earthquake of M w 4.9 produced those high values at a distance of 4.1 km. We also used the acceleration dataset from this site

  7. Earthquakes, July-August 1991

    USGS Publications Warehouse

    Person, W.J.

    1992-01-01

    There was one major earthquake during this reporting period-a magnitude 7.1 shock off the coast of Northern California on August 17. Earthquake-related deaths were reported from Indonesia, Romania, Peru, and Iraq. 

  8. 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.

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

    USGS Publications Warehouse

    Parsons, Tom; Dreger, Douglas S.

    2000-01-01

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

  10. Seismically induced rock slope failures resulting from topographic amplification of strong ground motions: The case of Pacoima Canyon, California

    USGS Publications Warehouse

    Sepulveda, S.A.; Murphy, W.; Jibson, R.W.; Petley, D.N.

    2005-01-01

    The 1994 Northridge earthquake (Mw = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (Mw = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses. ?? 2005 Elsevier B.V. All rights reserved.

  11. Systematic search of triggered and ambient tectonic tremor in Southern California

    NASA Astrophysics Data System (ADS)

    Yang, H.; Peng, Z.

    2013-12-01

    Tectonic tremor has been extensively observed along the Parkfield-Cholame section of the San Andreas Fault in central California. In contrast, observations of either triggered or ambient tremor in southern California are quite sparse to date. In this study we conduct a systematic search of tectonic tremor around the Simi Valley (SV), the San Gabriel Mountain (SGM), and the San Jacinto Fault (SJF). We focus on these regions, mainly because of previous observations of triggered tremor at the SV and SJF, and evidence of near-lithostatic fluid under the SGM and deep creep along the SJF. We first search for tremor triggered by distant large earthquakes around the SV and the SGM in southern California. Out of 59 large earthquakes between 2000 and 2013, only the 2002 Mw 7.9 Denali Fault earthquake triggered clear tremor in the region. The observed travel times of the triggered tremors are consistent with theoretical predictions from tremor sources that are spatially clustered in the SV, close to the rupture zone of the 1994 Mw 6.7 Northridge earthquake. We also estimate the triggering stress threshold as ˜12 KPa from measuring the peak ground velocities near the tremor source. The lack of clear tremor beneath the SGM provides a 'negative' example for a region where tremor is expected to occur because of clear evidence of fluid-rich zones at the middle crust. The results imply that the necessary conditions for tremor to occur are more than fluid-induced low effective normal stress. In addition to tremor in the SV, we also investigate tremor along the SJF, where tremor was triggered by the 2002 Mw7.9 Denali Fault and the 2011 Mw9.1 Tohoku-Oki earthquakes. These triggered tremors provide natural templates of the low frequency earthquakes that can be used to perform matched-filter detection to search for additional tremors along the SJF. In addition, there are strain transients following the March 11, 2013, Mw 4.7 earthquake that are captured by PBO strainmeters near the SJF

  12. Can observations of earthquake scaling constrain slip weakening?

    NASA Astrophysics Data System (ADS)

    Abercrombie, Rachel E.; Rice, James R.

    2005-08-01

    We use observations of earthquake source parameters over a wide magnitude range (MW~ 0-7) to place constraints on constitutive fault weakening. The data suggest a scale dependence of apparent stress and stress drop; both may increase slightly with earthquake size. We show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes. We select 30 earthquakes well-recorded at 2.5 km depth at Cajon Pass, California. We use individual and empirical Green's function spectral analysis to improve the resolution of source parameters, including static stress drop (Δσ) and total slip (S). We also measure radiated energy ES. We compare the Cajon Pass results with those from larger California earthquakes including aftershocks of the 1994 Northridge earthquake and confirm the results of Abercrombie (1995): μES/M0<<Δσ (where μ= rigidity) and both ES/M0 and Δσ increase as M0 (and S) increases. Uncertainties remain large due to model assumptions and variations between possible models, and earthquake scale independence is possible within the resolution. Assuming that the average trends are real, we define a quantity G'= (Δσ- 2μES/M0)S/2 which is the total energy dissipation in friction and fracture minus σ1S, where σ1 is the final static stress. If σ1=σd, the dynamic shear strength during the last increments of seismic slip, then G'=G, the fracture energy in a slip-weakening interpretation of dissipation. We find that G' increases with S, from ~103 J m-2 at S= 1 mm (M1 earthquakes) to 106-107 J m-2 at S= 1 m (M6). We tentatively interpret these results within slip-weakening theory, assuming G'~G. We consider the common assumption of a linear decrease of strength from the yield stress (σp) with slip (s), up to a slip Dc. In this case, if either Dc, or more generally (σp-σd) Dc, increases with the final slip S we can match the observations, but this implies the unlikely result that the early weakening behaviour of

  13. Seismic site effects and the spatial interpolation of earthquake seismograms: results using aftershocks of the 1986 North Palm Springs, California, earthquake

    USGS Publications Warehouse

    Spudich, P.; Miller, D.P.

    1990-01-01

    We address the following two questions. Can a microearthquake's ground motions be modeled by incident P and S waves that excite a site transfer-function that is a smooth function of incidence angle? Given recorded ground motions from a set of earthquakes having known locations and mechanisms, can we derive such a site transfer-function and use it to obtain the ground motions that would result from an earthquake source occurring somewhere in the same volume but having a location and mechanism that are different from the recorded events? We express the site transfer-function as a sum of several terms having simple dependences upon incidence angle and azimuth. Each term is an independent function of time. Given a set of seismograms observed at the site, we solve a linear system of equations for the time dependences of each term. These time series may be used to calculate the seismograms that would have resulted from an earthquake having arbitrary mechanism and location. This step is an interpolation. We have applied this technique to seismograms after aftershocks of the 1986 North Palm Springs earthquake. -from Authors

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Stein, Seth; Tomasello, Joseph; Newman, Andrew

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

  18. Gradual Fault Weakening with Seismic Slip: Inferences from the Seismic Sequences of L'Aquila, 2009, and Northridge, 1994

    NASA Astrophysics Data System (ADS)

    Malagnini, Luca; Munafo', Irene; Cocco, Massimo; Nielsen, Stefan; Mayeda, Kevin; Boschi, Enzo

    2014-10-01

    We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L'Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following Abercrombie and Rice (Geophys J Int 162: 406-424, 2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by Malagnini et al. (Pure Appl. Geophys., this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters (including fracture energies) are based on best-fit grid-searches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of W alter and Taylor (A revised Magnitude and Distance Amplitude Correction (MDAC2) procedure for regional seismic discriminants, 2001). The source parameters presented in this paper must be considered as point-source estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by Abercrombie and Rice (Geophys J Int 162: 406-424, 2005), and (ii) an exponential decay. Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two

  19. Three-dimensional P- and S-wave velocity structure and low-frequency earthquake locations in the Parkfield, California region

    NASA Astrophysics Data System (ADS)

    Zeng, Xiangfang; Thurber, Clifford H.; Shelly, David R.; Harrington, Rebecca M.; Cochran, Elizabeth S.; Bennington, Ninfa L.; Peterson, Dana; Guo, Bin; McClement, Kara

    2016-06-01

    To refine the 3D seismic velocity model in the greater Parkfield, California region, a new dataset including regular earthquakes, shots, quarry blasts, and low-frequency earthquakes (LFEs) was assembled. Hundreds of traces of each LFE family at two temporary arrays were stacked with time-frequency domain phase weighted stacking (tf-PWS) method to improve signal-to-noise ratio. We extend our model resolution to lower crustal depth with LFE data. Our result images not only previously identified features but also low velocity zones (LVZs) in the area around the LFEs and the lower crust beneath the southern Rinconada Fault. The former LVZ is consistent with high fluid pressure that can account for several aspects of LFE behavior. The latter LVZ is consistent with a high conductivity zone in magnetotelluric studies. A new Vs model was developed with S picks that were obtained with a new auto-picker. At shallow depth, the low Vs areas underlie the strongest shaking areas in the 2004 Parkfield earthquake. A high Vp/Vs zone in the middle crust on the northwest side of the San Andreas Fault was also revealed. We relocate LFE families and analyze the location uncertainties with the NonLinLoc and tomoDD codes. The two methods yield similar results.

  20. Potential Effects of a Scenario Earthquake on the Economy of Southern California: Baseline County-Level Migration Characteristics and Trends 1995-2000 and 2001-2010

    USGS Publications Warehouse

    Sherrouse, Benson C.; Hester, David J.

    2008-01-01

    The Multi-Hazards Demonstration Project (MHDP) is a collaboration between the U.S. Geological Survey (USGS) and various partners from the public and private sectors and academia, meant to improve Southern California's resiliency to natural hazards. In support of the MHDP objectives, the ShakeOut Scenario was developed. It describes a magnitude 7.8 earthquake along the southernmost 300 kilometers (200 miles) of the San Andreas Fault, identified by geoscientists as a plausible event that will cause moderate to strong shaking over much of the eight-county (Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura) Southern California region. This report uses historical, estimated, and projected population data from several Federal and State data sources to estimate baseline characteristics and trends of the region's population migration (that is, changes in a person's place of residence over time). The analysis characterizes migration by various demographic, economic, family, and household variables for the period 1995-2000. It also uses existing estimates (beginning in 2001) of the three components of population change - births, deaths, and migration - to extrapolate near-term projections of county-level migration trends through 2010. The 2010 date was chosen to provide baseline projections corresponding to a two-year recovery period following the November 2008 date that was selected for the occurrence of the ShakeOut Scenario earthquake. The baseline characteristics and projections shall assist with evaluating the effects of inflow and outflow migration trends for alternative futures in which the simulated M7.8 earthquake either does or does not occur and the impact of the event on housing and jobs, as well as community composition and regional economy changes based on dispersion of intellectual, physical, economic, and cultural capital.

  1. Inferred Rheology and Petrology of Southern California and Northwest Mexico Mantle from Postseismic Deformation following the 2010 El Mayor-Cucapah Earthquake

    NASA Astrophysics Data System (ADS)

    Freed, A. M.; Dickinson, H.; Huang, M. H.; Fielding, E. J.; Burgmann, R.; Andronicos, C.

    2015-12-01

    The Mw 7.2 El Mayor-Cucapah (EMC) earthquake ruptured a ~120 km long series of faults striking northwest from the Gulf of California to the Sierra Cucapah. Five years after the EMC event, a dense network of GPS stations in southern California and a sparse array of sites installed after the earthquake in northern Mexico measure ongoing surface deformation as coseismic stresses relax. We use 3D finite element models of seismically inferred crustal and mantle structure with earthquake slip constrained by GPS, InSAR range change and SAR and SPOT image sub-pixel offset measurements to infer the rheologic structure of the region. Model complexity, including 3D Moho structure and distinct geologic regions such as the Peninsular Ranges an