HR: 08:30h
AN: S11C-03    [Abstracts]
TI: Remotely Triggered Earthquakes Following Moderate Mainshocks: Where, When, Why?
AU: * Hough, S E
EM: hough@gps.caltech.edu
AF: U.S. Geological Survey, 525 S. Wilson Ave., Pasadena, CA 91106 United States
AB: Considering regional seismicity fluctuations following 31 recent 4.8<Mw<M7.1 earthquakes in southern and central California, earthquake rates are found to increase on average to distances of at least 200 km. Although these more distant events might fairly be considered aftershocks, a redefinition of the conventional term seems impractical; the term ``remotely triggered earthquakes'' (RTEs) is thus preferred for events that occur more than a few mainshock lengths away from a mainshock. While pervasive long-distance triggering has been documented following some large (M>7) mainshocks, triggering following moderate mainshocks is generally at a lower level and is often not obviously distinguishable from normal background seismicity. However, the larger number of moderate mainshocks allows results to be stacked to address several key questions, for example, why and where do RTEs occur? Weak but persistent preferential triggering is observed at the distance range where SmS waves are of high amplitude, suggesting an amplitude-dependent, relatively high-frequency triggering mechanism. Regarding their geographical distributions, preliminary results reveal that RTEs cluster preferentially in several regions that are expected to be sensitive to triggering: geothermal and volcanic areas such as Coso, Cerro Prieto, and the Brawley Seismic Zone. However, RTEs are also observed to occur preferentially in other regions, including a swath along the central Garlock fault, the central/eastern San Gabriel Mountains, and the Mecca Hills. One cannot appeal to intermittently high background seismicity rates to explain these observations. Several of these areas are, however, inferred from InSAR and other results to be characterized by especially high strain rates. Remotely triggered earthquakes may thus serve as beacons that illuminate zones in the crust where strain--and presumably stress--is high.
UR: http://pasadena.wr.usgs.gov/office/hough/agu05.html
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005