HR: 0800h
AN: T21A-0346    [Abstracts]
TI: How Repeatable are Episodic Tremor and Slip Events in Cascadia?
AU: * Sweet, J R
EM: jrsweet@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195, United States
AU: Wech, A G
EM: wech@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195, United States
AU: Creager, K C
EM: kcc@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195, United States
AU: Rubinstein, J L
EM: justin@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195, United States
AB: We employ a cross correlation method to locate deep non-volcanic tremor in western Washington during the July 2004, September 2005, and January 2007 Episodic Tremor and Slip (ETS) events. We use these locations to explore the spatio-temporal evolution of tremor and how consistently it behaves from event to event. We find that the 2004 and 2005 events were remarkably similar from start to end, while the 2007 episode had some similarities and some differences relative to the previous two events. A striking feature that is common to all three ETS episodes is that tremor amplitude was at its maximum when emanating from near Port Angeles, Washington. The 2004 and 2005 sequences were remarkably similar; they initiated in the eastern Straits of Juan de Fuca and migrated southwest towards Port Angeles. Both sequences then bifurcated, with tremor migrating both to the northwest and to the southeast. The 2007 sequence, in contrast, began in southern Puget Sound and migrated northwest to southern Vancouver Island. All three sequences were located within the same geographic area, roughly between the surface projection of the 30 and 45 km depth contours of the plate interface. We analyze tremor amplitude using data from six temporary, small-aperture seismic arrays. Tremor amplitude, corrected for attenuation and geometric spreading, exhibited a nearly linear increase over the first five days of each ETS sequence. The greatest amplitude for the 2004 and 2005 sequences occurred near Port Angeles during bifurcation. Interestingly, the amplitude was highest in the same area during the 2007 sequence, even though it simply migrated through the region. This maximum amplitude could be related to physical properties of the fault surface at that location or to increased stress caused by tidal forcing from the Straits of Juan de Fuca. Indeed, ETS tremor from these three episodes appears to be strongly modulated by tidal forcing.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8123 Dynamics: seismotectonics
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting