HR: 10:20h
AN: S42B-01 INVITED     [Abstracts]
TI: Spatial Distribution of Seismic Tremors During Episodic Tremor and Slip Events in Southern Vancouver Island
AU: * Kao, H
EM: hkao@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre 9860 West Saanich Road P.O.Box 6000, Sidney, BC V8L4B2 Canada
AU: Shan, S
EM: sshan@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre 9860 West Saanich Road P.O.Box 6000, Sidney, BC V8L4B2 Canada
AU: Rogers, G
EM: grogers@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre 9860 West Saanich Road P.O.Box 6000, Sidney, BC V8L4B2 Canada
AU: Dragert, H
EM: hdragert@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre 9860 West Saanich Road P.O.Box 6000, Sidney, BC V8L4B2 Canada
AU: Cassidy, J F
EM: jcassidy@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre 9860 West Saanich Road P.O.Box 6000, Sidney, BC V8L4B2 Canada
AB: We study the seismic tremors that occurred during the last two Episodic Tremor and Slip (ETS) events in southern Vancouver Island. A combined dataset, including three-component broadband seismic waveforms recorded by both permanent and temporary stations, is used to delineate the spatial distribution of ETS tremors and their origin times. The majority of ETS tremors are located by the Source-Scanning Algorithm that systematically scans the entire model space for seismic sources consistent with the observed waveforms. For a few relatively large and isolated tremors, the solutions are further verified by conventional earthquake location methods and/or 3-D relocation technique. The epicenters of most tremors are confined to a limited band bounded approximately by the horizontal locations of 30- and 45-km depth contours of the subducting plate interface. The depth range, on the other hand, is wide and spans from the upper crust to within the subducted Juan de Fuca slab, with a peak at the depth of 25-35 km. Detailed uncertainty study rejects the possibility of the wide depth range being an artifact of analysis. There seems to be an anti-correlation between the locations of tremors and background seismicity. Moreover, many ETS tremors appear to coincide with the strong seismic reflectors within the overriding crust where no local earthquakes have been observed. A comparison of frequency spectra for tremors and for local earthquakes shows that tremor spectra are comparable to those of magnitude ~1.5 earthquakes in the frequency range of 1-5 Hz, but their corresponding high-frequency (>5 Hz) content is an order of magnitude smaller. These observed characteristics suggest that the ETS tremors and background seismicity involve different physical processes.
DE: 9350 North America
DE: 7230 Seismicity and seismotectonics
DE: 8150 Plate boundary--general (3040)
DE: 1242 Seismic deformations (7205)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting