HR: 14:10h
AN: S13D-03    [Abstracts]
TI: The Effect of Vibration on Stick-slip Behavior in Sheared Granular Media: Implications for Earthquake Recurrence and Triggering
AU: * Johnson, P
EM: paj@lanl.gov
AF: Geophysics Group EES-11 Los Alamos National Laboratory of the University of California, MS D443, Los Alamos, NM 87545, United States
AU: Savage, H
EM: hms178@psu.edu
AF: Department of Geosciences Pennsylvania State University, 503 Deike Building, University Park, PA 16802-2714, United States
AU: Knuth, M
EM: mwknuth@geology.wisc.edu
AF: Department of Geosciences Pennsylvania State University, 503 Deike Building, University Park, PA 16802-2714, United States
AU: Knuth, M
EM: mwknuth@geology.wisc.edu
AF: Department of Geology and Geophysics University of Wisconsin-Madison, 1215 W Dayton St., Madison, WI 53706, United States
AU: Gomberg, J
EM: gomberg@usgs.gov
AF: US Geological Survey University of Washington Dept of Earth and Space Sciences, Box 351310, Seattle, WA 98195-1310, United States
AU: Marone, C
EM: cjm@geosc.psu.edu
AF: Department of Geosciences Pennsylvania State University, 503 Deike Building, University Park, PA 16802-2714, United States
AB: Dynamic earthquake triggering remains a compelling mystery: how do transient seismic waves with strains of order 10-6 trigger earthquakes, often with failure occurring long after the waves have passed? To better understand the physics of dynamic triggering, we conducted laboratory studies of stick-slip in granular media and its response to applied acoustic vibration. Glass beads were used to simulate granular fault zone wear material, sheared in a double-direct configuration under constant normal stress, while subject to transient or continuous perturbation by acoustic waves. Here we show that small magnitude failure events, corresponding to triggered aftershocks in the glass bead layers, occur when applied sound-wave amplitudes exceed several microstrain, in accord with a nonlinear mechanism proposed previously (Nature, 473 871-874 (2005). The acoustic waves also cause large slip events to be delayed significantly relative to those observed without wave perturbation. Remarkably, the effects are observed for several major-event cycles after the termination of the acoustic signal, indicating a strain memory in the granular material despite the severe material reset that takes place during a large stick-slip event. The material memory looks suspiciously like the nonlinear slow dynamics observed in rock, granular media, some sintered metals and nearly all damaged solids.
DE: 7209 Earthquake dynamics (1242)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting