Comparing Intensity Variation of the 2001 Nisqually Earthquake with Geology in Victoria, British Columbia

This article compares the variation in observed intensity of the 2001 MW 6.8 Nisqually, Washington, earthquake in Victoria, British Columbia (150 km from the epicenter), with amplification hazard predictions based on the average shear-wave velocity of geologic units. Modified Mercalli intensities were assigned from 750 felt reports collected by online Web submission augmented by door-to-door canvassing in regions of particular interest. An intensity map was created based on high-resolution (sub-city block) georeferencing with the Canadian postal code system. Site-specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear-wave velocity substrates (bedrock and glacial till versus soft clay and peat). Overall, the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear-wave velocities across greater Victoria.