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TitleRupture properties of the Mw 7.7 2012 Haida Gwaii earthquake from an Empirical Green's Function Method
AuthorHobbs, T E; Cassidy, J F; Dosso, S E
SourceSeismological Research Letters 85, 2, 2014 p. 547
Alt SeriesEarth Sciences Sector, Contribution Series 20140003
PublisherSeismological Society of America
MeetingSeismological Society of America Annual Meeting; Anchorage, AK; US; April 30 - May 2, 2014
Mediaon-line; digital
File formathtm
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
LinksOnline - En ligne (HTML)
LinksOnline - En ligne (PDF, 3.37 MB, page 547)
AbstractThis study examines rupture properties of the October 28, 2012, Mw 7.7 Haida Gwaii earthquake off the coast of British Columbia using an empirical Green's function (EGF) technique. Surface waveforms from a 2001 Mw 6.0 event, which ruptured only 15 km from the 2012 epicenter with an almost identical mechanism, are used as an EGF to be deconvolved from those of the 2012 mainshock. The resulting source-time function is free of path effects and instrument response, so the waveform displays only properties of the rupture itself. By examining azimuthal variations in these source-time functions we can constrain parameters such as average rupture velocity, rupture extent, and directivity. Additionally, information can be gathered about the possible existence of major sub-events and their locations. Preliminary results indicate that the overall rupture extends to the northwest for approximately 135-170 km along a direction similar to the strike (of 320 degrees). These findings are important, given that earthquakes with strong directivity, such as the 2002 Mw 7.9 Denali earthquake, have been shown to be capable of triggering earthquakes thousands of kilometers away. One important question to be addressed is whether there is a link between the Haida Gwaii event and the Mw 7.5 earthquake at Craig, Alaska (350 km northwest), just two months later. The Haida Gwaii earthquake was the largest event along the Canadian portion of the Pacific \{ North America plate boundary since the Ms 8.1 Queen Charlotte earthquake of 1949. Focal mechanisms in this region are predominantly right-lateral strike-slip but with an element of oblique convergence off Moresby Island. This work aims to elucidate important information about the rupture process, which is thought to have involved a blind thrust fault dipping gently to the NE rather than the main, sub-vertical Queen Charlotte Fault.
Summary(Plain Language Summary, not published)
The October 27, 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 earthquake was followed by thousands of aftershocks. In addition, another very large earthquake occurred 2 months later along the Queen Charlotte Fault, off the coast of Alaska, 330 km to the northwest. In this study we use global seismic datasets to examine the rupture directivity of the Haida Gwaii earthquake to help understand the potential for triggered earthquakes. This will contribute to improved assessments of earthquake hazards in the region and other areas of the world.