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TitleThe 17 November, 2009 Haida Gwaii (Queen Charlotte Islands), British Columbia, Earthquake Sequence
AuthorCassidy, J F; Rogers, G C; Brillon, C; Kao, H; Mulder, T; Dragert, H; Bird, A L; Bentkowski, W
SourceSeismological Society of America Annual Meeting, Abstracts; Seismological Research Letters vol. 81, no. 2, 2010, 1 pages
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20100025
MeetingSeismological Society of America Annual Meeting; Portland, OR; US; April 21-23, 2010
Mediapaper; on-line; digital
ProvinceBritish Columbia
NTS103B; 103C/16; 103F; 103G/13; 103J/04; 103K/01; 103K/02; 103K/03; 103K/04
AreaHaida Gwaii; Queen Charlotte Islands
Lat/Long WENS-133.5000 -131.0000 54.2500 52.0000
Subjectsgeophysics; earthquakes; earthquake studies; earthquake risk; earthquake mechanisms; earthquake magnitudes
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractOn November 17, 2009, a magnitude 6.5 earthquake struck off the southern tip of Haida Gwaii (Queen Charlotte Islands). This earthquake was felt across much of north-central British Columbia to distances of nearly 500 km. Due to its remote and offshore location, no damage was reported. This region is an active transform boundary just north of the Cascadia subduction zone where the Queen Charlotte Fault (QCF) separates the Pacific and North American plates off the outer coast of Haida Gwaii. This fault has experienced earthquakes as large as magnitude 8.1 in the past. However, the 2009 event did not occur on the QCF, but rather was located about 20-30 km to the west. The predominantly strike-slip focal mechanism that we determined does not align with the QCF or relative plate motion vectors in the area, but it is rotated about 30 degrees clockwise. The earthquake was followed by an unusually rich aftershock sequence. The largest aftershock, Mw 5.5, occurred seven minutes after the mainshock. Smaller aftershocks continued for nearly two months. Early aftershocks appeared to extend in an NE-SW direction, but after several weeks a NW-SE alignment of aftershocks also became apparent. Preliminary locations of the aftershocks indicate that the majority (assuming ruptures identical to the mainshock) fit the regions of enhanced Coulomb stress from the mainshock rupture. We apply refined location techniques to improve the relative locations of these events and to better understand their relationship to the tectonic structure of this complex region.