HR: 11:20h
AN: S42B-05    [Abstracts]
TI: Array observations and analyses of Cascadia deep tremor
AU: * McCausland, W A
EM: wam5@u.washington.edu
AF: Univeristy of Washington, Earth and Space Sciences Box 351310, Seattle, WA 98103 United States
AU: Malone, S
EM: steve@ess.washington.edu
AF: Univeristy of Washington, Earth and Space Sciences Box 351310, Seattle, WA 98103 United States
AU: Creager, K
EM: kcc@ess.washington.edu
AF: Univeristy of Washington, Earth and Space Sciences Box 351310, Seattle, WA 98103 United States
AU: Crosson, R
EM: crosson@u.washington.edu
AF: OV-INGV, Via Diocleziano 328, Napoli, 80124 Italy
AU: La Rocca, M
EM: mlarocca@ov.ingv.it
AF: Univeristy of Washington, Earth and Space Sciences Box 351310, Seattle, WA 98103 United States
AU: Saccoretti, G
EM: gilberto@ov.ingv.it
AF: OV-INGV, Via Diocleziano 328, Napoli, 80124 Italy
AB: The July 8-24, 2004 Cascadia Episodic Tremor and Slip (ETS) event was observed using three small aperture seismic arrays located near Sooke, BC, Sequim, WA, and on Lopez Island, WA. Initial tremor burst epicenters located in the Strait of Juan de Fuca and were calculated using the relative arrivals of band-passed, rectified regional network signals. Most subsequent epicenters migrated to the northwest along Vancouver Island and a few occurred in the central to southern Puget Sound. Tremor bursts lasting on the order of a few seconds can be identified across the stations of any of the three arrays. Individual bursts from distinct back-azimuths often occur within five seconds of each other, indicating the presence of spatially distributed but near simultaneous tremor. None of this was visible at such a fine scale using Pacific Northwest Seismograph Network (PNSN). Several array processing techniques, including beam-forming, zero-lag cross correlation and multiple signal classification (MUSIC), are being investigated to determine the optimal technique for exploring the temporal and spatial evolution of the tremor signals during the whole ETS. The back-azimuth and slowness of consecutive time windows for a one half-hour period of strong tremor were calculated using beam-forming with a linear stack, with an nth-root stack, and using zero-lag cross-correlation. Results for each array and each method yield consistent estimates of back azimuth and slowness. Beam-forming with a nonlinear stack produces results similar to the linear case but with larger uncertainty. Among the arrays, the back-azimuths give a reasonable estimate of the tremor epicenter that is consistent with the network determined epicentral locations.
DE: 7230 Seismicity and seismotectonics
DE: 8110 Continental tectonics--general (0905)
DE: 7200 SEISMOLOGY
DE: 1208 Crustal movements--intraplate (8110)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting