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TitleShear-wave velocity structure in the vicinity of the 2012 Mw 7.8 Haida Gwaii Earthquake from receiver function inversion
AuthorGosselin, J M; Cassidy, J FORCID logo; Dosso, S E
SourceBulletin of the Seismological Society of America vol. 105, no. 2B, 2015 p. 1-8,
Alt SeriesEarth Sciences Sector, Contribution Series 20140151
PublisherSeismological Society of America (SSA)
Mediaon-line; digital
File formatpdf
ProvinceWestern offshore region; British Columbia
NTS102O; 103B; 103C; 103F; 103G; 103J; 103K
AreaHaida Gwaii; Queen Charlotte
Lat/Long WENS-134.5000 -130.0000 54.5000 51.0000
Subjectsgeophysics; tectonics; earthquake studies; earthquakes; earthquake magnitudes; earthquake risk; earthquake mechanisms; earthquake foci; tectonic setting; aftershocks; landslides
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2015 04 07
AbstractThe thrust mechanism of the 2012 Mw 7.8 Haida Gwaii earthquake suggests convergence across the transpressive Pacific-North America plate boundary in the region is accommodated by underthrusting, with important consequences for seismic- and tsunami-hazard analysis. This article investigates the crustal structure and extent of subduction beneath Haida Gwaii by nonlinear inversion of receiver function data processed from teleseismic recordings at five land-based seismograph stations. Three of these stations were deployed since the 2012 earthquake to extend coverage to the southeast and have not been analyzed previously. The inversions provide estimates of the shear-wave velocity structure beneath much of Moresby Island. Results indicate a positive velocity contrast at approximately 18-26 km depth, interpreted as a shallow continental Moho. A 12-17 km thick low shear-wave velocity zone is also identified, which increases in depth from ~25 to 42 km along the direction of plate convergence, which is interpreted as subducting oceanic material. These results provide the first evidence that the subducting oceanic plate extends beneath the entirety of Moresby Island.
Summary(Plain Language Summary, not published)
The October 27, 2012 magnitude 7.7 earthquake resulted in up to 4 m of movement along a previously unknown fault just off the west coast of Moresby Island, Haida Gwaii. Following that earthquake, 6 new seismic stations were deployed on Moresby Island to help monitor aftershocks activity. We utilise seismic data from those new stations to map, for the first time, the detailed earth structure beneath Haida Gwaii. Using these new data we image the base of the continental crust at 17-29 km below Moresby Island. More importantly, we image a significant low-velocity zone that is dipping to the east beneath Moresby Island (at depths of 38-45 km). We interpret this as the Pacific Plate pushing beneath Haida Gwaii. This is critical new information for assessing ground shaking from future earthquakes.

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