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Seismicity rate changes along the central California coast due to stress changes from the 2003 M 6.5 San Simeon and 2004 M 6.0 Parkfield earthquakes

Bulletin of the Seismological Society of America

By:
and
DOI: 10.1785/0120080239

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Abstract

We investigated the relationship between seismicity rate changes and modeled Coulomb static stress changes from the 2003 M 6.5 San Simeon and the 2004 M 6.0 Parkfield earthquakes in central California. Coulomb stress modeling indicates that the San Simeon mainshock loaded parts of the Rinconada, Hosgri, and San Andreas strike-slip faults, along with the reverse faults of the southern Los Osos domain. All of these loaded faults, except for the San Andreas, experienced a seismicity rate increase at the time of the San Simeon mainshock. The Parkfield earthquake occurred 9 months later on the loaded portion of the San Andreas fault. The Parkfield earthquake unloaded the Hosgri fault and the reverse faults of the southern Los Osos domain, which both experienced seismicity rate decreases at the time of the Parkfield event, although the decreases may be related to the decay of San Simeon-triggered seismicity. Coulomb stress unloading from the Parkfield earthquake appears to have altered the aftershock decay rate of the southern cluster of San Simeon after-shocks, which is deficient compared to the expected number of aftershocks from the Omori decay parameters based on the pre-Parkfield aftershocks. Dynamic stress changes cannot explain the deficiency of aftershocks, providing evidence that static stress changes affect earthquake occurrence. However, a burst of seismicity following the Parkfield earthquake at Ragged Point, where the static stress was decreased, provides evidence for dynamic stress triggering. It therefore appears that both Coulomb static stress changes and dynamic stress changes affect the seismicity rate.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Seismicity rate changes along the central California coast due to stress changes from the 2003 M 6.5 San Simeon and 2004 M 6.0 Parkfield earthquakes
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120080239
Volume
99
Issue:
4
Year Published:
2009
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
2280
Last page:
2292