HR: 10:20h
AN: T12C-01    [Abstracts]
TI: Non-volcanic Tremor and Earthquakes Driven by the Large Transient Shear Stresses of the 2002 Denali Earthquake
AU: * Rubinstein, J L
EM: justin@ess.washington.edu
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AU: Vidale, J E
EM: john_vidale@mac.com
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AU: Gomberg, J
EM: gomberg@usgs.gov
AF: US Geological Survey, Box 351310, Seattle, WA 98195, United States
AU: Creager, K C
EM: kcc@ess.washington.edu
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AU: Bodin, P
EM: bodin@u.washington.edu
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AU: Malone, S D
EM: malone@ess.washington.edu
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AU: Wech, A G
EM: wech@washington.edu
AF: University of Washington, Department of Earth and Space Science Box 351310, Seattle, WA 98195, United States
AB: We identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude Mw = 7.8, 2002 Denali, Alaska earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate) strongly suggesting that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the resistance to sliding on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases without changes in normal stress on the subduction interface, effectively a frictional failure response to the driving stress. In addition to the Denali earthquake, we found 3 other teleseisms that triggered tremor on Vancouver Island and 25 that did not. As one would expect, larger amplitude waves appear necessary to trigger non-volcanic tremor, but other conditions also appear important. In particular, the timing of the triggering waves may be important, as tremor is more likely to be triggered shortly after an ETS event than at other times. We also find evidence that distant earthquakes may trigger ETS. Specifically, the ETS episodes with the longest lapse times since the previous ETS all occur within a few days of large teleseismic events, which is not the case for ETS episodes with more typical lapse times. The Denali earthquake also triggered small earthquakes on Vancouver Island at locations far from the triggered tremor. None of the other large teleseisms we examined produced a clear, immediate increase in seismicity rate, but a few others show possible increases.
UR: http://earthweb.ess.washington.edu/~justin/trigtrem.html
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8123 Dynamics: seismotectonics
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting