Investigating seismic hazard and site response in Victoria, British Columbia: Analysis of felt reports and ground motion recordings from the 2001 Nisqually earthquake

On 28 February 2001 the M_w 6.8 Nisqually earthquake was the largest earthquake in over 50 years to strike the Pacific Northwest. Over 700 felt reports were gathered from Victoria residents by an online web form and by a detailed door-to-door survey. Geocoding of felt reports allowed direct comparison with a previously published ground motion amplification hazard map. A trend of increasing intensity with increasing amplification hazard was found for geologic units in greater Victoria.; Strong-motion instrument recordings were used to study site response at eight sites in greater Victoria. The site response determined from the standard spectral ratio method and the horizontal—vertical spectral ratio method at the each site is similar in frequency and remarkably, in amplitude. The comparison of SHAKE91 modelled spectra with the observed Fourier amplitude spectra showed that the peak amplification at each site was caused by the local geology amplifying the ground motion.