Mapping crustal stress and strain in southwest British Columbia

Abstract

[1] This paper investigates the orientation and sources of stress in the forearc of the Cascadia subduction zone in southwest British Columbia, using Bayesian inversion results from focal mechanism data and comparing results with GPS derived short-term strain rates. The subduction margin in this region includes a change in orientation from N-S in Washington State to NW-SE in British Columbia. Over 1000 focal mechanisms from North American crustal earthquakes have been calculated to identify the dominant style of faulting, and ∼600 were inverted to estimate the principal stress orientations and the stress ratio. Our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench, from approximately margin-normal along the coast to approximately margin-parallel 100-150 km inland from the coast. Comparing stress orientations with GPS data, we relate the margin-normal stress direction to subductionrelated strain rates due to the locked interface between the North American and Juan de Fuca plates just west of Vancouver Island. Further from the margin the plates are coupled less strongly, and the margin-parallel maximum horizontal compressive stress in the North American Plate relates to the northward push of the Oregon Block, which is also observed in the horizontal shortening direction of the residual strain rates, after the subduction component is removed.

Quaternary Rupture of a Crustal Fault beneath Victoria, British Columbia, Canada

“…1 and 2A) (see Cassidy et al, 2000;Mosher et al, 2000;Balfour et al, 2011). Several previous authors suggest that this fault, which places Jurassic-Cretaceous schists of the Leech River Complex to the north against Eocene basalts of the Metchosin Formation to the south ( Fig.…”

“…; Rockwell et al, 2000), and they may not be Kristin D. Morell, School of Earth and Ocean Sciences,University of Victoria,Victoria,British Columbia V8P 5C2,Canada,kmorell@ uvic.ca Mosher et al, 2000;Balfour et al, 2011). This point was exemplified by the 2010 M W 7.1 Darfield, New Zealand (Christchurch), earthquake and aftershocks that ruptured the previously unidentified Greendale fault (Gledhill et al, 2011).…”

“…1), where strain accrues due to the combined effects of northeastdirected subduction and the northward migration of the Oregon forearc block (McCaffrey et al, 2013), microseismicity data are sparse and do not clearly elucidate planar crustal faults Balfour et al, 2011). But geomorphic, (McCaffrey et al, 2013;Wells and Simpson, 2001).…”

Seismicity, Metamorphism, and Fluid Evolution Across the Northern Cascadia Fore Arc

“…Quartz vein networks develop syntectonically in horizontal compressional or transpressive regimes. Our observations can be considered in this context since the maximum principal stress in northern Cascadia is horizontal and oriented along strike (e.g., Balfour et al, 2011;Wang, 2000). High-angle reverse faults are unfavorably disposed to failure in this stress environment.…”

A revised crustal stress orientation database for Canada

“…New data are also added since data published elsewhere and from a previously unavailable dataset that had been maintained by the Alberta Geological Survey (AGS). The published data are compiled from a literature investigation of the following articles by Adams (1987), Balfour et al (2011, Bell and Bachu (2003), Buchbinder (1990), Du et al (2003), Eisbacher and Bielenstein (1971), Hamid (2008), Hurd and Zoback (2012), Konstantinovskaya et al (2012), Kim (2003), Kim et al (2006), Ma et al (2008), Mazzotti and Townend (2010), Michael and Buschkuehle (2008), Ruppert (2008), Steffen et al (2012), StLouisEQcenter (2010), Yassir and Dusseault (1992), and Zakharova and Goldberg (2014). The update adds up to 514 new records in Canada (Fig.…”