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TitleIdentifying active structures using double-difference earthquake relocations in southwest British Columbia and the San Juan Islands, Washington
AuthorBalfour, N J; Cassidy, J F; Dosso, S E
SourceBulletin of the Seismological Society of America vol. 102, no. 2, 2012 p. 639-649,
Alt SeriesEarth Sciences Sector, Contribution Series 20110032
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92G/01; 92G/02; 92G/07; 92G/08; 92G/09; 92G/10; 92H/04; 92H/05; 92H/12
AreaGeorgia Strait; San Juan Islands; Washington; Canada; United States
Lat/Long WENS-123.0000 -121.7500 49.6667 48.7500
Lat/Long WENS-123.3333 -122.6667 48.8333 48.2500
Subjectsgeophysics; earthquakes; earthquake mechanisms; earthquake risk; earthquake studies; seismology; seismicity
Illustrationslocation maps; plots
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
Released2012 03 29
AbstractThis paper applies double-difference earthquake relocation techniques to investigate sources of seismicity in southwest British Columbia, Canada, and the San Juan Islands, Washington. The study area is a complex region of deformation and has the potential for large earthquakes in the North Americancrust. Double-difference earthquake relocation techniques are applied to identify otherwise-hidden active structures that may pose a hazard to nearby population and infrastructure. We present evidence for previously unrecognized active structures using precise relative earthquake relocations obtained using both catalog and waveform cross-correlation data. Results have significantly reduced errors over routine catalog locations and show lineations in areas of clustered seismicity. In southwest British Columbia, these lineations or streaks appear to be hidden structures that do not disrupt near-surface sediments; however, in the San Juan Islands the identified lineation could be related to recently mapped surface expressions of faults identified from seismic reflection and multibeam bathymetric surveys. We use a variety of velocity models for the relocations and find that inappropriate models lead to artifacts at layer boundaries and increased vertical errors.