HR: 0830h
AN: G31B-0713    [PDF]
TI: Cascadia Episodic Tremor and Slip: An Ideal Target for PBO Studies
AU: * Dragert, H
EM: dragert@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Rogers, G
EM: rogers@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Wang, K
EM: wang@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Kao, H
EM: kao@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Cassidy, J
EM: cassidy@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Schmidt, M
EM: schmidt@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd., Sidney, BC V8L 4B2 Canada
AB: One of the most intriguing recent findings made possible by high-precision geodesy is the discovery of "Episodic Tremor and Slip" (ETS) along the northern Cascadia Margin. Analyses of continuous GPS data from both the Western Canada Deformation Array (WCDA) and the Pacific Northwest Geodetic Array (PANGA) have resolved transient horizontal surface displacements of 2 to 5 mm occurring over a period of 6 to 15 days in a direction opposite to long-term deformation motions. These brief reversals of motion are accompanied by unique low-frequency (1 to 5 Hz) tremors that have a source region which coincides with, or directly overlies, the region of the subducting slab interface where transient slip occurs. Furthermore, for the plate interface underlying southern Vancouver Island and northwestern Washington State, ETS events appear to occur with surprising regularity, having a recurrence interval of 14.5 $\pm$2 months. For ETS events which involved larger areas, both tremor activity and slip displacements have been observed to migrate in northwest and southeast directions, parallel to the strike of the subduction zone, at rates of 5 to 15 km per day. The physical processes which give rise to this dynamic behavior on the deeper subduction interface are not yet understood. More detailed seismic, GPS, and strainmeter observations are required along the full length of the Cascadia Margin to map the exact aerial extent and depth range of ETS events and to monitor the temporal evolution of individual events. Such detailed observations will allow correlations with structure, rheology, and thermal regimes, and provide critical data for modeling and understanding this phenomena and evaluating its role in seismic hazard estimates in the Pacific Northwest.
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
DE: 1294 Instruments and techniques
DE: 8123 Dynamics, seismotectonics
SC: Geodesy [G]
MN: 2003 Fall Meeting