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Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA

January 1, 2007

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.

Publication Year 2007
Title Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA
DOI 10.1029/2006GL028634
Authors L.B. Christiansen, Shaul Hurwitz, Steven E. Ingebritsen
Publication Type Article
Publication Subtype Journal Article
Series Title Geophysical Research Letters
Index ID 70032933
Record Source USGS Publications Warehouse
USGS Organization Volcano Hazards Program