HR: 0800h
AN: S51C-1018    [Abstracts]
TI: Characteristics of Tremor During the Entire July 2004 Cascadia Episodic Tremor and Slip event
AU: * McCausland, W A
EM: wam5@u.washington.edu
AF: University of Washington, Dept. of Earth & Space Sciences Box 351310, Seattle, WA 98195
AU: Malone, S
EM: steve@ess.washington.edu
AF: University of Washington, Dept. of Earth & Space Sciences Box 351310, Seattle, WA 98195
AU: La Rocca, M
EM: mlarocca@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, Via Diocleziano 328, Napoli, 80124 Italy
AU: Creager, K
EM: kcc@ess.washington.edu
AF: University of Washington, Dept. of Earth & Space Sciences Box 351310, Seattle, WA 98195
AB: The July 2004 Cascadia episodic tremor and slip (ETS) event was recorded and analyzed using three geographically distributed small aperture seismic arrays (600m) located near Sooke, BC, Sequim, WA, and on Lopez Island, WA. We analyzed the tremor sequence in the 1 to 6 Hz frequency band in overlapping windows (12s length)using zero-lag cross correlation and polarization analysis in order to obtain a continuous record of the back-azimuth, slowness, and particle motion of tremor sources throughout the ETS episode. During periods without tremor, the average interstation correlations for each array range between 0.2 and 0.4, and observed azimuths are randomly distributed. During periods of strong tremor, the average correlation for each array is typically between 0.5 and 0.8, and azimuths are stable over periods of minutes. Observed apparent velocities are greater than 4 km/s and polarization analysis indicates that the wave-field is composed primarily of SH-waves, both of which are consistent with a deep source of shear wave energy. Azimuths and slownesses are consistent with previously obtained hypocentral locations and apparent velocities calculated using the relative arrival times of energy bursts on Pacific Northwest Seismograph Network.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8150 Plate boundary: general (3040)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: Fall Meeting 2005