CGRG Bibliography of Canadian Geomorphology
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Author : Blais-Stevens, A.; Clague, J.J.; and Rogers, G.C.
Date : 2003.
Title : Earthquake signature in Late Holocene Sediments in Saanich Inlet, British Columbia.
Publication : 3rd Canadian Conference on Geotechnique and Natural Hazards. Sheraton Hotel. Edmonton, Alberta, Canada. June 9 and 10, 2003.
Issue :
Page(s) :
Abstract
Short hydraulic piston cores collected in Saanich Inlet in 1989 and 1991, combined with longer piston cores collected in the same area in 1996 during Ocean Drilling Program Leg 169S, record a sequence of large earthquakes in southwestern British Columbia during the late Holocene. The sediment cores consist of rhythmically laminated (varved) marine mud with intercalated massive beds, interpreted to be debris flow deposits. Some of the extensive (>1 km) debris flow deposits are linked to past earthquakes, including the 1946 Vancouver Island earthquake (M7.3), a great (M~9) plate-boundary earthquake at the Cascadia subduction zone in January 1700, and a large crustal or plate-boundary earthquake about 1000 years ago. Earthquakes may also be responsible for debris flows in about AD 1600, 1500, 1250, 1150, 1000, 850, 800, 450, 350, 100, and BC 200, 220, 500, 900, 2000, and 2020. We estimated the average recurrence interval for crustal and subcrustal earthquakes by excluding known plate boundary events (shown in italics). The calculated recurrence interval, 268 years, corresponds to a peak acceleration of 0.24 g, derived from a recurrence relationship generated from earthquake statistics. A peak acceleration of about 0.24 g translates into seismic shaking of MM (Modified Mercalli) Intensity VII, a level of shaking that can produce submarine landslides. We conclude that most or all of the extensive debris flow deposits in Saanich Inlet were triggered by moderate to large earthquakes rather than by non-seismic processes.
Bibliography of Canadian Geomorphology