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The Modern San Andreas Fault

Allen, Clarence R. (1981) The Modern San Andreas Fault. In: The Geotectonic Development of California. Rubey volume. No.1. Prentice-Hall , Englewood Cliffs, NJ, pp. 511-534. ISBN 9780133539387.

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Although the San Andreas fault was once viewed by most geologists as a grossly aberrant tectonic feature, it is now recognized as representing normal plate-tectonic processes and is, in fact, one of the simpler of the transform faults that cut the continents. The fault zone is continuous for at least 1100 km, but individual surface traces are en echelon segments of much more limited extent, and they represent fracture processes that currently are not fully understood. Studies of both the fault's physiographic expression and its recent earthquake history emphasize the remarkable temporal repeatability of seismic events along it; during Holocene time, earthquakes and their associated effects have repeated one another at given localities with almost uncanny reproducibility. Two great earthquakes occurred along the fault in 1857 and 1906, and although two remaining segments have not broken in large events during the historic record, the most likely next great earthquake is a repeat of the 1857 event. Seismographic stations in California now number perhaps 500, and the recent dramatic increases have shown that epicenters tend to markedly "pull in" toward the active fault trace in some segments but not others. In general, the parts of the fault showing concentrated alignments of small shocks are the same parts that display continuous or episodic surface creep. Currently locked segments of the fault, presumably those of highest seismic hazard, are characterized by very low, scattered seismicity. Short-term epicenter maps are thus not necessarily a good representation of long-term seismic hazard, which is much better portrayed by geologic studies of the fault's Holocene history, using radiometric dating of offset and disturbed strata. The 1857 and 1906 earthquakes represent the types of events we must be prepared for in the future, although their engineering effects were not as great as often imagined. The hazards of both surface fault displacements and heavy ground shaking are not yet fully understood, but appear to be problems capable of solution in the foreseeable future.

Item Type:Book Section
Additional Information:© 1981 Prentice-Hall. Most of our knowledge of current seismicity in southern California comes from the Southern California Seismographic Network, which is mainly supported by the U.S. Geological Survey (Contract No. 14-08-0001-16719), with contributing support from the State of California (Division of Mines and Geology Agreement No. 5-9015) and the Caltech Earthquake Research Affiliates. The author appreciates the critical comments of John C. Crowell, Kerry E. Sieh, and Robert E. Wallace. Contribution Number 3286, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
Funding AgencyGrant Number
State of California Division of Mines and Geology5-9015
Caltech Earthquake Research AffiliatesUNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences3286
Series Name:Rubey volume
Issue or Number:1
Record Number:CaltechAUTHORS:20140811-123920147
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48300
Deposited By: Tony Diaz
Deposited On:11 Aug 2014 19:49
Last Modified:03 Oct 2019 07:02

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