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TitleSeismic evidence for megathrust fault-valve behavior during episodic tremor and slip
AuthorGosselin, J M; Audet, PORCID logo; Estève, C; McLellan, M; Mosher, S G; Schaeffer, A JORCID logo
SourceScience Advances vol. 6, no. 4, eaay5174, 2020 p. 1-6, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190342
PublisherAmerican Association for the Advancement of Science
Mediaon-line; digital
File formatpdf; html
ProvinceBritish Columbia
NTS92B; 92C; 92F/01; 92F/02; 92F/03; 92F/04; 92F/05; 92F/06; 92F/07; 92F/08; 92G/02; 92G/03; 92G/04; 92G/05; 92G/06; 92G/07
AreaVancouver Island; Victoria; Vancouver; Washington State; Olympic Peninsula; Canada; United States of America
Lat/Long WENS-126.0000 -122.0000 49.5000 47.5000
Subjectstectonics; structural geology; geophysics; Science and Technology; Nature and Environment; bedrock geology; seismology; earthquakes; structural features; faults; crustal movements; tectonic setting; subduction zones; shear zones; fluid flow; pore fluids; pore pressures; seismic data; seismic waves; seismic velocities; anomalies; seismological network; Cascadia Subduction Zone; Juan de Fuca Plate; North American Plate; Global positioning systems
Illustrationsgeoscientific sketch maps; time series; plots; models
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2020 01 22
AbstractFault slip behavior during episodic tremor and slow slip (ETS) events, which occur at the deep extension of subduction zone megathrust faults, is believed to be related to cyclic fluid processes that necessitate fluctuations in pore-fluid pressures. In most subduction zones, a layer of anomalously low seismic wave velocities [low-velocity layer (LVL)] is observed in the vicinity of ETS and suggests high pore-fluid pressures that weaken the megathrust. Using repeated seismic scattering observations in the Cascadia subduction zone, we observe a change in the seismic velocity associated with the LVL after ETS events, which we interpret as a response to fluctuations in pore-fluid pressure. These results provide direct evidence of megathrust fault-valve processes during ETS.
Summary(Plain Language Summary, not published)
The Cascadia Subduction Zone in western Canada continues to present arguable the single most significant earthquake hazard to the entire country. Ongoing research into Cascadia and in fact subduction zones in general, believe that the presence and role play by fluids in the processes governing slip on the fault are of critical importance. In this study, we study in detail a handful of stations across southern Vancouver Island to examine the potential role fluid migration plays in the role of episodic tremor and slip (ETS) which occur regularly across Cascadia. The results of this work demonstrate that statistically significant changes in across fault properties occur in the days following an ETS event, which are interpreted to result from changes in the location pore fluid pressure along and near the fault interface.

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