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Read Full Article (file size: 198409 bytes) Cited by
GEOPHYSICAL RESEARCH LETTERS,
VOL. 34,
L04306,
doi:10.1029/2006GL028634,
2007
Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA
Lizet B. Christiansen
U.S. Geological Survey, Menlo Park, California, USA
Shaul Hurwitz
U.S. Geological Survey, Menlo Park, California, USA
Steven E. Ingebritsen
U.S. Geological Survey, Menlo Park, California, USA
Abstract
We analyze seismic data from the San Andreas Fault (SAF) near Parkfield, California, to test for annual modulation in seismicity
rates. We use statistical analyses to show that seismicity is modulated with an annual period in the creeping section of the
fault and a semiannual period in the locked section of the fault. Although the exact mechanism for seasonal triggering is
undetermined, it appears that stresses associated with the hydrologic cycle are sufficient to fracture critically stressed
rocks either through pore-pressure diffusion or crustal loading/unloading. These results shed additional light on the state
of stress along the SAF, indicating that hydrologically induced stress perturbations of ∼2 kPa may be sufficient to trigger
earthquakes.
Received 2
November
2006;
accepted 22
January
2007;
published 23
February
2007.
Keywords: triggered seismicity;
Parkfield;
annual modulation.
Index Terms: 3270 Mathematical Geophysics: Time series analysis (1872, 4277, 4475); 5112 Physical Properties of Rocks: Microstructure; 8045 Structural Geology: Role of fluids; 8111 Tectonophysics: Continental tectonics: strike-slip and transform; 8164 Tectonophysics: Stresses: crust and lithosphere.
Read Full Article (file size: 198409 bytes) Cited by
Citation: Christiansen, L. B., S. Hurwitz, and S. E. Ingebritsen
(2007),
Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA,
Geophys. Res. Lett.,
34,
L04306,
doi:10.1029/2006GL028634.
This paper is not subject to U.S. copyright. Published in 2007 by the
American Geophysical Union.
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