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TitleCoulomb Stress Changes Resulting from the Mw 7.7 2012 Haida Gwaii Earthquake
AuthorHobbs, T EORCID logo; Brillon, C; Cassidy, J FORCID logo; Dragert, H; Dosso, S E
SourceSeismological Research Letters 85, 2, 2014 p. 465
LinksOnline - En ligne (HTML)
LinksOnline - En ligne (PDF, 3.37 MB, page 465)
Alt SeriesEarth Sciences Sector, Contribution Series 20140004
PublisherSeismological Society of America
MeetingSeismological Society of America Annual Meeting; Anchorage, AK; US; April 30 - May 2, 2014
Mediaon-line; digital
File formathtml; pdf
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 Western Canada Geohazards Project
AbstractThis study examines spatial changes to the local stress field resulting from the October 28, 2012, Mw 7.7 Haida Gwaii earthquake, which occurred west of Moresby Island off the coast of British Columbia. This event is thought to have occurred on a NE-dipping, blind thrust fault rather than on the sub-vertical Queen Charlotte Fault that represents the Pacific-North American plate boundary. This was the largest earthquake along the Canadian portion of this plate boundary since the 1949 Ms 8.1 Queen Charlotte earthquake.
The USGS software `Coulomb' is used to quantitatively estimate the effect of the mainshock on the background stress field, the known aftershock nodal planes, and the nearby Queen Charlotte Fault. We use two different mainshock finite fault models, both of which are seismologically-derived (by Lay and Hayes, separately) and subsequently adapted by K. Wang to account for the motion detected at four nearby GPS stations. We also use the best-located set of aftershocks with information provided by a temporary array of ocean bottom seismometers. Preliminary results indicate an apparent clustering of aftershocks slightly seaward of the main thrust, which is consistent with the modeled zone of promoted normal failure likely related to extension in the footwall. Using existing models, we have found a high number of aftershocks to be consistent with triggering by the mainshock, suggesting that static stress is a dominant control in the months following a large earthquake in this area. Additionally, we find loading, greater than the threshold for triggering, on the Queen Charlotte Fault in an area believed to be within a seismic gap. This work provides an improved understanding of the evolving seismic hazard along the Queen Charlotte margin, while simultaneously testing the usefulness of Coulomb modeling in this environment.
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.

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