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GPS observations of crustal deformation associated with the 2012 Mw 7.8 Haida Gwaii earthquake

Lisa Nykolaishen, Herb Dragert, Kelin Wang, Thomas S. James and Michael Schmidt
GPS observations of crustal deformation associated with the 2012 Mw 7.8 Haida Gwaii earthquake (in 2012 Haida Gwaii and 2013 Craig earthquakes at the Pacific North America plate boundary (British Columbia and Alaska), Thomas S. James (editor), John F. Cassidy (editor), Garry C. Rogers (editor) and Peter J. Haeussler (editor))
Bulletin of the Seismological Society of America (May 2015) 105 (2B): 1241-1252

Abstract

On 28 October 2012, an M (sub w) 7.8 earthquake occurred off the west coast of Haida Gwaii, British Columbia. Although past large events at this margin reflect strike-slip motion between the Pacific and North American plates (e.g., 1949 M (sub s) 8.1), this earthquake involved low-angle thrust faulting with a slip direction almost perpendicular to the margin, a consequence of slip partitioning at this obliquely convergent margin. To refine regional source models, we investigated the coseismic and postseismic displacements using a network of Global Positioning System (GPS) sites. Coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south-southwest, with 30 cm of subsidence. The only continuously recording GPS station on Haida Gwaii at the time of the earthquake, about 80 km from the epicenter, provides a robust coseismic displacement estimate of 22 cm to the south-southwest. The coseismic results are consistent with a shallow-dipping thrust rupture underlying the Queen Charlotte terrace, immediately seaward of the Queen Charlotte fault. These results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data. Estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm, with a systematic along-strike variation in azimuth from south-southwest to southeast from north to south in the study area. Besides viscoelastic stress relaxation, these postseismic trends may indicate afterslip on the deeper plate interface beneath northern Moresby Island and possibly aseismic slip along the Queen Charlotte or subparallel faults offshore of southern Moresby Island.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 105
Serial Issue: 2B
Title: GPS observations of crustal deformation associated with the 2012 Mw 7.8 Haida Gwaii earthquake
Title: 2012 Haida Gwaii and 2013 Craig earthquakes at the Pacific North America plate boundary (British Columbia and Alaska)
Author(s): Nykolaishen, LisaDragert, HerbWang, KelinJames, Thomas S.Schmidt, Michael
Author(s): James, Thomas S.editor
Author(s): Cassidy, John F.editor
Author(s): Rogers, Garry C.editor
Author(s): Haeussler, Peter J.editor
Affiliation: Geological Survey of Canada, Pacific Geoscience Centre, Sidney, BC, Canada
Affiliation: Geological Survey of Canada, Pacific Geoscience Centre, Natural Resources Canada,, Sidney, BC, Canada
Pages: 1241-1252
Published: 201505
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 42
Accession Number: 2015-085133
Categories: SeismologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N52°00'00" - N53°00'00", W133°00'00" - W132°00'00"
Secondary Affiliation: U. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201536
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