Empirical ground motion relations for earthquakes in the Cascadia region

Empirical relations are developed to describe response spectral amplitudes as a function of earthquake magnitude, focal depth, and distance, for earthquakes in the Cascadia region of southwestern British Columbia and northwestern Washington State. The relations are based on regression of response spectra data from crustal, subcrustal, and subduction earthquakes recorded on rock and soil sites. The relations apply to earthquakes of moment magnitude, M, in the range of M equal to or greater than 4 but less than or equal to 8.2 with focal depths from 1 to 60 km, at distances up to several hundred kilometers. Most of the data for moderate-to-large events (M equal to or greater than 4 but less than 7) are from the Cascadia region, while those for very large events (M equal to or greater than 7.5) are from other subduction zones.