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TitleTemporal evolution of an episodic tremor and slip event along the northern Cascadia margin
AuthorDragert, H; Wang, K
SourceJournal of Geophysical Research vol. 116, B12406, 2011 p. 1-12, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20110268
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92B; 92C; 92F; 92G
AreaCascadia Margin; Washington; Canada; United States
Lat/Long WENS-126.0000 -121.5000 49.5000 46.0000
Subjectstectonics; plate tectonics; tectonic environments; tectonic interpretations; plate boundaries; continental margins; global positioning system
Illustrationslocation maps; plots; tables
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
Released2011 12 29
AbstractEpisodic tremor and slip (ETS) have now been observed along the northern Cascadia margin for over 15 years. Recent densification of GPS coverage and the introduction of Gladwin borehole strainmeters (BSMs) under the Plate Boundary Observatory have enabled the derivation of improved slip models and have allowed more detailed monitoring of the migration of the slip surface during prolonged ETS events. For this study we examine the along-strike migration of the May 2008 ETS as determined from the GPS and BSM observations. GPS sites overlying the 30 km depth contour of the subducting plate interface show that the slip initiates west of northern Puget Sound and propagates bidirectionally. Shear strain time series at regional BSM sites confirm this bidirectional expansion of the slip zone. In a simple model of along-strike propagation constrained by the GPS and BSM time series, the speed of the northwest propagation varies from 8, then to 2, and then to 15 km/d, but the speed of the south propagation stays at 6 km/d. The tremors observed for this ETS episode show a similar bidirectional migration pattern and similar changes in northwest migration velocity, but the migration front is slightly ahead of the slip propagation front. These results provide important information for understanding the mechanics of ETS.