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TitleCoulomb stress changes following the Mw 7.7 2012 Haida Gwaii Earthquake
AuthorHobbs, T; Brillon, C; Cassidy, J; Dosso, S; Dragert, H
SourceCanadian Geophysical Union Annual Meeting, abstracts ; 2013 p. 1
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130064
PublisherCanadian Geophysical Union
MeetingCanadian Geophysical Union Annual Meeting: Joint Meeting with CMOS and CWRA; Saskatoon; CA; May 26-30, 2013
Mediaon-line; digital
File formathtml
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
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractThis study examines spatial changes to the Coloumb stress field resulting from the Oct. 27, 2012 Mw 7.7 Haida Gwaii earthquake off coastal British Columbia, the relationship with well-located aftershocks, and the potential changes to shear and/or normal stresses along the Queen Charlotte Fault. The Queen Charlotte-Fairweather Fault extends from northern Vancouver Island to the Gulf of Alaska and is Canada's most seismically active plate boundary. Focal mechanisms in this region are predominantly right-lateral strike-slip but with an element of oblique convergence between the Pacific and North American Plates off Moresby Island. The October 27, 2012 Mw 7.7 earthquake to the west of Moresby Island was the largest earthquake along the Canadian portion of this plate boundary since the Ms 8.1 earthquake of 1949. The 2012 event was a thrust earthquake with an along-margin rupture of ~120 km along the west coast of Haida Gwaii. This earthquake likely occurred on a previously unknown blind fault dipping gently to the NE rather than on the main, sub-vertical Queen Charlotte Fault. Nonetheless, the 2012 event potentially altered stresses on the primary Queen Charlotte Fault and it is possible that unclamping from this earthquake could promote future strike-slip events on the Queen Charlotte Fault. We use two mainshock finite fault models, of Shao and Ji and of Hayes, along with the Coulomb v3.3 stress model to compute stress-field changes and compare with accurate aftershocks locations (determined using a consistent set of stations and phases). Preliminary results indicate an apparent clustering of deep aftershocks just seaward of the main thrust, which are likely related to extension in the footwall. This work is part of a larger effort to characterize stress along the Queen Charlotte-Fairweather Fault system and its relation to a sequence of possibly inter-related earthquakes dating back to the late 19th century.
Summary(Plain Language Summary, not published)
The October 2012 magnitude 7.7 earthquake resulted in up to 4 m of movement along a fault just off the west coast of Haida Gwaii. Movement along the fault extended more than 100-km's along the coast and extended about 50 km offshore. This very substantial movement of rocks has changed the stress field in the Haida Gwaii region (including along the Queen Charlotte Fault) and will likely influence the locations of aftershocks and, perhaps, future earthquakes. In this study we compute the changes in the stress field associated with the 2012 Haida Gwaii earthquake and find that many of the offshore aftershocks fall with in the region of predicted maximum stress change. This will contribute to improved assessments of earthquake hazards in the region.