HR: 13:55h
AN: S42G-02    [PDF]
TI: Temporal and Spatial Distribution of the Tremors in the Episodic Tremor and Slip (ETS) Event Observed Beneath the Northern Cascadia Subduction Zone in Early 2003
AU: * Kao, H
EM: hkao@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, BC V8L4B2 Canada
AU: Shan, S
EM: sjshan@shaw.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, BC V8L4B2 Canada
AU: Rogers, G
EM: grogers@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, 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, Sidney, BC V8L4B2 Canada
AU: Dragert, H
EM: hdragert@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, BC V8L4B2 Canada
AB: The tremors associated with the most recent ETS event observed along the northern Cascadia margin were recorded in the greatest detail to date, by a combination of stations from CNSN, POLARIS, and the deployment of a temporal broadband seismic network in the region. Because no clear arrivals of P or S phases can be identified, we develop a method, called "source-scanning", to locate the tremors and to image their source distribution in both time and space. The algorithm systematically examined three-component continuous digital waveforms (from late February to late March, 2003) recorded at 25 broadband seismic stations (spacing at an interval of about 10 km) and identified more than 1600 tremor events with sufficient waveform quality to give coherent patterns of source configuration. The identified events span a width of about 50 km beneath the southern portion of the Vancouver Island and north Washington State. Events to the west generally have source depths shallower than those to the east. When projected onto a cross section perpendicular to the trench axis, the majority of tremors occurred in the vicinity of the inferred plate interface between the subducted Juan de Fuca plate and the overriding North America plate. However, they tend to distribute within a zone of over 10-15 km thick rather than along a plane. The images of many tremor sources show elongated shapes shallowly dipping toward the east, consistent with the geometric configuration of the interplate thrust zone. We hypothesize that the ETS events are the manifestation of the rheological/mechanical behavior along or immediately above the deep portion of the plate interface.
DE: 7215 Earthquake parameters
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
DE: 8105 Continental margins and sedimentary basins
DE: 9350 North America
SC: Seismology [S]
MN: 2003 Fall Meeting