HR: 10:20h
AN: S11H-01    [PDF]
TI: The Common Phenomenon of Transient-Triggered Seismicity
AU: * Bodin, P
EM: bodin@ceri.memphis.edu
AF: Center for Earthquake Research and Information, The University of Memphis, 3876 Central Ave., Suite 1, Memphis, TN 38152
AU: Gomberg, J
EM: gomberg@usgs.gov
AF: U.S. Geological Survey, 3876 Central Ave., Suite 2, Memphis, TN 38152
AU: Larson, K
EM: Kristine.Larson@colorado.edu
AF: Department of Aerospace Engineering Sciences, University of Colorado at Boulder, Boulder, CO 80309
AU: Dragert, H
EM: dragert@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd, Sidney, BC V8L 4B2 Canada
AB: The 2002 M7.9 Denali, Alaska earthquake triggered seismicity rate increases at many sites throughout British Columbia and into the US through northern Utah and Nevada. Denali triggered rate increases occurred in areas not clearly tectonically active, implying that even in areas where ambient stressing rates may be low, the crust may still be critically stressed. These observations demonstrate that remote earthquake triggering caused by the 1992 M7.4 Landers, California, earthquake did not reflect some peculiarity of the region or earthquake. Rather, earthquakes may be triggered by transient deformations nearly anywhere. Rate increases are not clearly apparent in seismicity catalogs, and we observe them in high-pass filtered, broadband seismic data recorded continuously at seismographs operated by the Geological Survey of Canada and various U.S. networks. Seismicity rates increase nearly concurrently with the arrival of the Denali earthquake seismic waves and at sites in the direction of theoretically expected maximum seismic wave radiation from the Denali mainshock. We verify the latter using on-scale seismic data supplemented with 1 Hz GPS data recorded in British Columbia and the US at distances where seismographs went off-scale. Based on the temporal coincidence we infer a causal relation between the transient deformations associated with Denali earthquake surface waves and the seismicity rate increases. Therefore, measurements of the time between the passage of seismic waves and rate increase onsets can provide constraint on underlying physical triggering mechanisms. Noting that rate increases are not observed at sites where recorded peak wave velocities exceed those at more distant triggered sites, we hypothesize that wave frequency matters and attempt to identify the spectral band of seismic waves for which the wave amplitudes best correlate with the rate changes.
DE: 7209 Earthquake dynamics and mechanics
DE: 7230 Seismicity and seismotectonics
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting