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A Lack of Dynamic Triggering of Slow Slip and Tremor Indicates That the Shallow Cascadia Megathrust Offshore Vancouver Island Is Likely Locked
Author(s) -
McGuire Jeffrey J.,
Collins John A.,
Davis Earl,
Becker Keir,
Heesemann Martin
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl079519
Subject(s) - geology , subduction , seismology , episodic tremor and slip , trench , submarine pipeline , seafloor spreading , slip (aerodynamics) , borehole , tectonics , geotechnical engineering , geophysics , chemistry , physics , organic chemistry , layer (electronics) , thermodynamics
Great subduction zone earthquakes vary considerably in the updip extent of megathrust rupture. It is unclear if this diversity reflects variations in interseismic strain accumulation owing to the limited number of subduction zones with seafloor monitoring. We use a borehole seismic‐geodetic observatory installed at the updip end of the Cascadia fault offshore Vancouver Island to show that the megathrust there does not appear to slip in triggered tremor or slow‐slip events when subjected to moderate dynamic stress transients. Borehole tilt and seismic data from recent teleseismic M 7.6–8.1 earthquakes demonstrate a lack of triggered slow slip above the M w 4.0 level and an absence of triggered tremor despite shear‐stress transients of 1–10 kPa that were sufficient to trigger tremor on the downdip end of the interface. Our observations are most consistent with a model in which the Cascadia fault offshore Vancouver Island is locked all the way to the trench.