For eastern Canada the GSC applied the Cornell-McGuire method to two new seismic source models, one historical and one geological. For western Canada the GSC used two source zone models but combined them with a deterministic estimate for a repeat of the 1700 A.D. Cascadia subduction earthquake. This is very different from the USGS's incorporation of Cascadia subduction earthquakes into its probabilistic model. The USGS employs spatially smoothed representations of historical seismicity for different magnitude events in combination with data from individual faults. Hazard is computed with a new suite of software developed by Frankel et al.
Probabilistic hazard is calculated without the use of subjective source zones.
An adaptive weighting was used to ensure that the rate of earthquakes within any calculated cell did not fall below the historic value, the final values maintain the hazard in the areas of historic seismicity and provide some additional hazard to low seismicity regions. The different physical properties of the crust in eastern and western North America, and different types of earthquakes, require the use of different strong ground motion relations. The Canadian and US choices are detailed below, with the references being given in Adams et al. Hence, US sites east of this boundary are computed with eastern attenuation and can be expected to yield higher hazard estimates than for adjacent Canadian sites. Frankel et al.