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Examining Possible Links Between Tectonic Tremor and Crustal Earthquakes on the Leech River Fault System in Northern Cascadia

Description: 

Along the Cascadia margin, tremor occurrence related to episodic tremor and slip (ETS) events are modulated by the structure of the continental plate. In particular, tremor is generally spatially anticorrelated with major crustal faults and forearc earthquakes; however, the Leech River fault (LRF)—a major fault zone on Southern Vancouver Island—coincides with two high-density tremor clusters. In this study we examine the relationship between tremor and crustal earthquakes in the LRF system. The tremor catalogue is computed using our recently-developed differential-traveltime Bayesian inversion method and includes events during the 2003-2006 deployment of the Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity (POLARIS) array, and the relocated catalogue in the LRF system is provided by Li et al. (2018). With enhanced resolution of tremor depths, we show that most tremor is coincident with the surface of the low-velocity zone between 20 and 35 km depths where the LRF zone terminates.

Preliminary results show that the shallowest tremor events are preferentially colocated with deeper seismicity in the vicinity of the LRF, which may be evidence that fluid-driven tremor-genic processes exist on this forearc fault system away the subduction fault. Alternatively, what appears to be shallow tremor may in fact be microseismicity induced by changes to the stress field resulting from slow slip on the megathrust. Evidence of a widely-eroded subduction fault zone and/or underplated forearc in northern Cascadia suggests that ETS is a multifaceted phenomenon resulting from complex structures at depth. Considering the proximity of the LRF to metropolitan areas and recent evidence that it has hosted large events in the last ~10,000 years, the relationship between this fault and periodic slow slip events directly beneath it may help unify our understanding of the tectonic setting and its associated seismic hazards.

Session: Crustal Deformation and Seismic Hazard in Western Canada, Cascadia and Alaska

Type: Oral

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Madison Bombardier

Student Presenter: Yes

Invited Presentation: 

Authors