Earthquakes and Vancouver Island

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Why do we have earthquakes? … Pacific Plate British Columbia Vancouver Juan de Seattle Fuca Plate Washington Locked subduction earthquake Portland source zone Oregon 200 km California NRCan Natural Resources Canada How likely are we to have a damaging earthquake?… M 8-9 M 7 M 6 Subduction earthquakes Pacific Plate British Columbia Vancouver Juan de Seattle Fuca Plate Washington Locked subduction earthquake Portland source zone Oregon 200 km California Natural Resources Canada Clague et al., 2006 Crustal earthquakes 7 8 9 6 5 4 3 1 2 potential active fault Clague et al., 2006 1 Straight Creek fault 2 Seattle fault 3 southern Whidbey Island fault 4 Devil Mountain fault 5 Leech River fault 6 Cowichan Lake fault 7 Beaufort Range fault 8 Strait of Georgia fault 9 Vedder and Sumas Mountain fault Prince 1946 Prince 2001 Rupert Vancouver Island Rupert Nisqually, Washington earthquake Shake maps earthquake magnitude 7.3 (Mercali intensity) magnitude 6.9 Campbell River: 75% of chimneys General alarm. collapse VII Difficult to stand. Damage to buildings. >$2 billion Lions Gate dollars in Bridge sways Courtenay: Felt by everyone. damage Post Office VI Difficult to walk. wall collapses Objects fall. Vancouver Vancouver Felt outdoors, Port Alberni: Victoria V Victoria Hundreds of Buildings sway. houses lose Seattle Seattle chimneys. Water Felt by most mains break. buildings IV people indoors. Power out for sway 10 days. Portland Portland Clague and Turner, 2003 0 km 300 0 km 300 fig27.cdr Pacific Plate British Columbia Nootka fault Vancouver Juan de Seattle Fuca Plate Washington Locked subduction earthquake Portland source zone Oregon 200 km California As in real estate, it’s location, location, location! … Magnitude 7 Significant damage Disaster Magnitude 6 Minor losses Major damage Magnitude 4 Ho-hum! Conversation piece Effects of strong earthquakes • Ground shaking • Tsunami • Liquefaction • Landslides • Fire • Aftershocks Effects of strong earthquakes • Ground shaking • Tsunami • Liquefaction • Landslides • Fire • Aftershocks Ground motion depends on many things… … including geology and topography NRCan Ground motion amplification Clague and Turner, 2003 Effects of strong earthquakes • Ground shaking • Tsunami • Liquefaction • Landslides • Fire • Aftershocks Tsunami tsunami wave cm 300 crest 200 100 0 -100 -200 -300 trough fig102.cdr Effects of strong earthquakes • Ground shaking • Tsunami • Liquefaction • Landslides • Fire • Aftershocks Liquefaction Christchurch 2011 sand volcano crack landslide clay stream liquefied sand clay Effects of strong earthquakes • Ground shaking • Liquefaction • Landslides • Fire • Aftershocks CBC Duncan Wyllie Effects of strong earthquakes • Ground shaking • Liquefaction • Landslides • Fire • Aftershocks Kobe 1995 San Francisco 1906 Effects of strong earthquakes • Ground shaking • Ground rupture • Liquefaction • Landslides • Fire • Aftershocks .

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Seismicity in Cascadia
Lithos 332–333 (2019) 55–66 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Seismicity in Cascadia Michael G. Bostock ⁎, Nikolas I. Christensen, Simon M. Peacock Department of Earth, Ocean and Atmospheric Sciences, The University of British Columbia, Canada article info abstract Article history: We examine spatio-geometric patterns in the density of seismicity within the Cascadia forearc to gain insight into Received 11 July 2018 controls on seismogenesis. Tremor epicenters exhibit the most regular distribution defining a 40–80 km wide 27 December 2018 band extending along almost the entire convergent margin from the southern terminus of Gorda plate subduc- Accepted 23 February 2019 tion in northern California to the central Explorer plate below northern Vancouver Island. Based on prior charac- Available online 26 February 2019 terization of constituent low-frequency earthquakes, the up- and down-dip limits of tremor are assumed to fl Keywords: represent slab isodepth contours at nominal values of 28 and 45 km, between which uids at near-lithostatic Seismicity overpressures are trapped within the subducting slab. Epicenters of earthquakes within the North American Tremor crust are anticorrelated with those of tremor, and concentrated in Washington and northern California where Cascadia they are sandwiched between tremor and the Cascade volcanic arc. Seismicity within the subducting plate Fluids possesses the most limited epicentral distribution. Seismicity is confined to shallow depths off Vancouver Island Subduction and in northern California, and projects to greater depths beneath Washington and southern British Columbia. Forearc Comparison of seismicity patterns with long-wavelength slab geometry and thermo-petrologic constraints sug- Serpentinization gests that seismicity occurrence in Cascadia is governed by an interplay between slab strain, metamorphic dehy- Eclogitization dration within the subducting oceanic plate, and a plate boundary seal that controls where fluids enter the Volcanism overriding plate.
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Geologic History of Siletzia, a Large Igneous Province in the Oregon And
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United States Department of the Interior Geological Survey
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IJURCA: International Journal of Undergraduate Research & Creative Activities
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