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Title: Surface displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes

Abstract

The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes.

Authors:
 [1];  [2]
  1. (Stanford Univ., CA (United States) Geological Survey, Menlo Park, CA (United States))
  2. (Geological Survey, Menlo Park, CA (United States))
Publication Date:
OSTI Identifier:
5013969
Resource Type:
Journal Article
Resource Relation:
Journal Name: Science (Washington, D.C.); (United States); Journal Volume: 250:4985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; EARTHQUAKES; SEISMIC EFFECTS; GEOLOGIC FAULTS; SLIP; DATA ANALYSIS; GEODETIC SURVEYS; MAPS; ROCK MECHANICS; TECTONICS; DEVELOPED COUNTRIES; FEDERAL REGION IX; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; GEOPHYSICAL SURVEYS; MECHANICS; NORTH AMERICA; SEISMIC EVENTS; SURVEYS; USA; 580000* - Geosciences

Citation Formats

Segall, P., and Lisowski, M. Surface displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes. United States: N. p., 1990. Web. doi:10.1126/science.250.4985.1241.
Segall, P., & Lisowski, M. Surface displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes. United States. doi:10.1126/science.250.4985.1241.
Segall, P., and Lisowski, M. Fri . "Surface displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes". United States. doi:10.1126/science.250.4985.1241.
@article{osti_5013969,
title = {Surface displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes},
author = {Segall, P. and Lisowski, M.},
abstractNote = {The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes.},
doi = {10.1126/science.250.4985.1241},
journal = {Science (Washington, D.C.); (United States)},
number = ,
volume = 250:4985,
place = {United States},
year = {Fri Nov 30 00:00:00 EST 1990},
month = {Fri Nov 30 00:00:00 EST 1990}
}
  • The amplitudes of strong ground motions from the Loma Prieta earthquake recorded in the San Francisco and Oakland areas exceeded the levels predicted by standard empirical attenuation relations. Preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust. These reflections, which are identified on the basis of their arrival times and phase velocity, and by comparison with simulated accelerograms, were large and occurred at relatively close range because of the deep focalmore » depth of the earthquake and the strong velocity gradient at the base of the crust. These motions were further amplified, presumably by impedance contrast effects, at soft soil sites in San Francisco and Oakland. The effect of the critical reflections in amplifying peak accelerations of the Loma Prieta earthquake in the San Francisco and Oakland regions was as large as the effect of soft soil site conditions. Focal depth has an important influence on strong motion attenuation at distances beyond about 40 km, and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range. Further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in San Francisco and Oakland, and the conclusions drawn from that explanation.« less
  • This paper presents and analyzes the observations of the sand boils that emerged in the Marina District of San Francisco after the Loma Prieta Earthquake of October 17, 1989. The sand boils were located within the boundary of an old lagoon, the periphery of which was severely damaged in the 1906 San Francisco earthquake. During the 1989 Loma Prieta Earthquake, the soils underlying the Marina District amplified the ground motion as in 1906 and caused the liquefaction of the superficial sandy materials that were used to fill the old lagoon in 1915. Damage in the Marina District was concentrated alongmore » the edges of the old lagoon. The sand boils left behind by liquefaction were useful to delineate the liquefied area and to understand the ground displacement in the Marina District. The sand boils covered uniformly the liquefied area that experienced lateral spreading and settlement. The present work also indicates the high damage potential of transition zones between liquefiable and nonliquefiable soils.« less
  • Broadband source spectra of the 1989 Loma Prieta (M{sub W} = 6.9) and 1988 Armenian (M{sub W} = 6.7) earthquakes are computed at periods from 1 to 50 sec using digitally-recorded teleseismic P body waves. The effects of attenuation, geometrical spreading, and radiation pattern are removed from the spectra of individual stations, which are then averaged. The source spectra of the Loma Prieta and Armenian earthquakes are higher for their seismic moments than the spectra of 11 intraplate earthquakes studied by Zhuo and Kanamori (1987), which in turn are 2 to 4 times larger than average spectra of interplate subductionmore » zone earthquakes. The seismically radiated energy can be computed from the source spectrum using Haskell's (1964) formulation assuming a point source with no directivity. An Orowan stress drop can be obtained from the seismic energy and moment. The Orowan stress drops for the Loma Prieta and Armenian earthquakes are both about 20 bars, significantly higher than Orowan stress drops of recent large interplate earthquakes. There is a positive correlation between the Orowan stress drops and the estimated repeat times, consistent with the notion that mechanical fault strength increases with increasing interseismic period.« less
  • A small geodetic network spanning the San Andreas fault was measured 7, 77, 157, and 200 days following the October 17, 1989 Loma Prieta M7.1 earthquake. This network is located at the northwestern end of the rupture plane defined by the locations of numerous aftershocks. In the initial 70-day interval, the measured line-length changes revealed that 5.4 {plus minus} 0.4 mm of right-lateral slip occurred within the network. However, during the later 4 month interval only a marginally significant rate, 3.2 {plus minus} 1.4 mm/yr, of right-lateral slip could be detected. Thus, it appears that the measured slip is amore » typical response of the fault following a major shock in that the rate of slip decreases rapidly with time. However, the magnitude of the post-seismic slip is less than 0.5% of the inferred co-seismic slip at depth.« less
  • We estimate the ground motions produced by the 1906 San Francisco earthquake making use of the recently developed Song et al. (2008) source model that combines the available geodetic and seismic observations and recently constructed 3D geologic and seismic velocity models. Our estimates of the ground motions for the 1906 earthquake are consistent across five ground-motion modeling groups employing different wave propagation codes and simulation domains. The simulations successfully reproduce the main features of the Boatwright and Bundock (2005) ShakeMap, but tend to over predict the intensity of shaking by 0.1-0.5 modified Mercalli intensity (MMI) units. Velocity waveforms at sitesmore » throughout the San Francisco Bay Area exhibit characteristics consistent with rupture directivity, local geologic conditions (e.g., sedimentary basins), and the large size of the event (e.g., durations of strong shaking lasting tens of seconds). We also compute ground motions for seven hypothetical scenarios rupturing the same extent of the northern San Andreas fault, considering three additional hypocenters and an additional, random distribution of slip. Rupture directivity exerts the strongest influence on the variations in shaking, although sedimentary basins do consistently contribute to the response in some locations, such as Santa Rosa, Livermore, and San Jose. These scenarios suggest that future large earthquakes on the northern San Andreas fault may subject the current San Francisco Bay urban area to stronger shaking than a repeat of the 1906 earthquake. Ruptures propagating southward towards San Francisco appear to expose more of the urban area to a given intensity level than do ruptures propagating northward.« less