CGRG Bibliography of Canadian Geomorphology
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Author : Cassidy, J.F.; Rogers, G.C.; and Molnar, S.
Date : 2002.
Title : Seismic site response across Greater Vancouver, British Columbia obtained from recordings of the Nisqually Earthquake.
Publication : Seismological Society of America 2002, Annual Meeting 17-19 April 2002. Victoria Conference Centre, Victoria, British Columbia
Issue :
Page(s) :
Abstract
The 28 February, 2001 M=6.8 Nisqually earthquake was felt strongly in southwestern British Columbia, causing highrises to sway, and some minor damage. We use recordings from the strong motion network in Greater Vancouver that is operated by the Geological Survey of Canada and BC Hydro, to examine the variation in ground shaking across this urban region. Of particular interest is the seismic response of the thick, unconsolidated Holocene sediments of the Fraser River delta. There was a significant variation in ground shaking across greater Vancouver (at an epicentral distance range of 210-250 km). On bedrock, peak acceleration values of about 0.2% g were recorded, whereas soil sites showed peak ground accelerations up to 2.7% g. The Nisqually earthquake recordings provide the first opportunity to examine the longer period response (2-10 s) of the delta. Compared to recent crustal earthquakes (1997 M=4.3 Georgia Strait and 1996 M=5.1 Duvall, Washington); the Nisqually recordings show a similar pattern at higher frequencies (>3-4 Hz) - that is slight attenuation on the thick soils relative to bedrock. However, at low frequencies (long periods up to 10 s), the Nisqually recordings show greater amplification on the delta, relative to bedrock, compared to the previous datasets. We use the program SHAKE to examine the predicted response of sites on the centre of the delta (300 m of Holocene soil), and the edge of the delta (a few m of Holocene soil), compared to the observed waveforms to better assess possible 2D and 3D basin effects and their frequency variation.
Bibliography of Canadian Geomorphology