Aseismic slip on the San Andreas Fault south of Loma Prieta

Geophysical Research Letters
By: , and 

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Abstract

Two digital creepmeters installed within the San Andreas fault zone after the 18 Oct 1989 Loma Prieta main shock show less than 1 cm of post seismic right-lateral slip in the four months following the earthquake. At Mt. Madonna road a 23 mm coseismic fracture slipped a further 3 mm after heavy rain, and at Nyland Ranch near San Juan Bautista the fault slipped approximately 9 mm starting 42 days after the main shock. If the current trend at Nyland Ranch persists, more than 2 cm of post seismic slip will develop by 1991. At both sites minor left-lateral displacements occurred which are attributed to near-surface soil effects. The abutments of the railroad bridge across the Pajaro River at Chittenden, which were extended by the 1906 earthquake, were not extended during the Loma Prieta event although they have evidently moved apart by more than 7 cm since bridge reconstruction in 1940. This corresponds to 10 cm of right-lateral slip which could be related to M>5 events in mid-century or could be due to aseismic slip at a mean rate of 2.1 mm/a. The absence of significant surface slip within the fault zone in the decades before and the months following the Loma Prieta event suggests either that near-surface deformation is distributed over a wide zone or that a slip deficit remains. Several authors have proposed this region as a future location for M≈5 events.

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Publication type Article
Publication Subtype Journal Article
Title Aseismic slip on the San Andreas Fault south of Loma Prieta
Series title Geophysical Research Letters
DOI 10.1029/GL017i009p01445
Volume 17
Issue 9
Year Published 1990
Language English
Publisher American Geophysical Union
Description 4 p.
First page 1445
Last page 1448
Country United States
State California
Other Geospatial Loma Prieta, San Andreas Fault
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