HR: 1340h
AN: S13B-0197    [Abstracts]
TI: Aftershock Densities, Peak Ground Motions, and Earthquake Triggering
AU: * Gomberg, J
EM: gomberg@usgs.gov
AF: U.S. Geological Survey, 3876 Central Ave. Suite 2, Memphis, TN 38152 United States
AU: Felzer, K
EM: kfelzer@gps.caltech.edu
AF: U.S. Geological Survey, 525 Wilson Ave., Pasadena, CA 91106 United States
AU: Brodsky, E
EM: brodsky@ess.ucla.edu
AF: University of California, Los Angeles, 1708 Geology Building, Los Angeles, CA 90095 United States
AU: Vernon, F
EM: flvernon@ucsd.edu
AF: University of California, San Diego, IGPP 0225, La Jolla, CA 92093 United States
AU: Ishii, M
EM: mishii@smtp.ucsd.edu
AF: University of California, San Diego, IGPP 0225, La Jolla, CA 92093 United States
AB: Recent analyses show that the number of aftershocks decays with distance from the triggering mainshock as an inverse power-law with exponent ~1.4, for distances ranging from tens of meters to tens of kilometers from the mainshock fault, for mainshock magnitudes M 2 to M 6 (Felzer and Brodsky, 2005). This is in general agreement with the theoretical decay rate of the maximum amplitude of seismic body waves and with empirical and theoretical magnitude scaling relations. We test and refine these general hypothetical attenuation and scaling predictions using ground motion observations recorded by several strong motion networks around the world, including the HiNet network in Japan and the Anza, CISN, and USGS and CSMIP strong motion networks in southern California. We find the aftershock densities and peak ground motions decay similarly in the far field (roughly distances from one mainshock fault length to 100 km). Peak displacements and aftershocks decay at a power law rate of ~1.4, while peak velocities and accelerations decay slightly faster. In the near field the peak ground motions show a change in scaling at distances that correlate with the dimensions of the fault; this change is not seen in the aftershock density decay rate. This can be explained by correcting for the fact that ground motions are measured at a point whereas aftershock densities measure the total number of aftershocks per unit distance from the mainshock fault. The peak ground motions scale with rupture dimension in a manner consistent with empirical scaling relations of aftershock numbers with magnitude. All these aftershock and peak ground motion characteristics appear remarkably similar regardless of the magnitude, location, or type of earthquake, suggesting the inferences drawn apply generally. Our results imply that dynamic deformation amplitude primarily determines the likelihood of triggering, if we assume that the crust has a higher density of potential aftershock faults near the mainshock, as expected in a fault zone, such that the effective dimension, D, of the fault system is close to 1.0. We also use our results to derive a quantitative relationship between dynamic deformation amplitude and the number of aftershocks triggered.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005