HR: 10:50h
AN: T12C-03    [Abstracts]
TI: Teleseismically-induced tremor near Parkfield, CA - a cacophony or a symphony?
AU: * Vidale, J E
EM: vidale@ess.washington.edu
AF: ESS Dept, U of Washington, Seattle, WA 98195-1310,
AU: Peng, Z
EM: zhigang.peng@eas.gatech.edu
AF: Earth & Atmos Sciences, Georgia Tech, Atlanta, GA 930332-034,
AU: Creager, K C
EM: kcc@ess.washington.edu
AF: ESS Dept, U of Washington, Seattle, WA 98195-1310,
AU: Bodin, P
EM: pbodin@ess.washington.edu
AF: ESS Dept, U of Washington, Seattle, WA 98195-1310,
AB: The tremor triggered near Parkfield, CA by the 2002 Denali and 2004 Sumatra earthquakes was strong and well recorded by the dense regional CISN and the borehole HRSN networks. Peng et al. (this meeting) survey tremors triggered by a larger set of 12 regional and teleseismic events, providing a broader context. In the case of both the 2002 M7.9 Denali and 2004 M9.1 Sumatra earthquakes, the tremor emanates from at least two source regions deep within the SAF. The first source region is 40 km NW of the SAFOD in the creeping section of the SAF, and the second region is 40 km SE of the SAFOD near Cholame, close to the location where most of the non-triggered tremor has been found previously (Nadeau and Dolenc, Science, 2005). The Denali earthquake triggered tremor is in phase with the surface waves for about 400s. The northern region started tremoring first by about 100s, and both regions quieted before the end of the surface waves. The wavetrain for the 2004 M9.1 Sumatra earthquake was long enough that tremors were also excited by the weak diffracted P waves, and tremor turned up the volume for an hour upon the arrival of the surface waves, underwent a sudden and curious hiatus for 500s before the end of the surface waves, then re-started and continued for at least an hour after the passage of the surface waves. It is easy to suggest that the tremor was accompanied by deep slip on the SAF, but creep and strain data indicate any slip was too small to generate a detectable surface deformation. These observations suggest a component of driven, instantaneous, perhaps Coulomb-friction response with an added dose of self-sustaining, dribbling activity more suggestive of the oozing of fluids.
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting