Using tectonic block modeling to quantify the impact of potentially–active faults on seismic hazard and risk in western Canada

Richard Henry Styron , Tiegan Hobbs, Murray Journeay

In order to understand the impact of large, potentially active faults on seismic hazard and risk in western Canada, faults in the region are characterized using a geodetic-geologic block model. The results are then integrated into Canada's existing national seismic hazard and risk models. To do this, potentially active faults are mapped to build a block model around them; then, several thousand geodetic velocities and several hundred Quaternary geologic slip rates are inverted to estimate slip rates on the mapped faults. The block model yields low to moderate slip rates (<2 mm/yr) on most faults, except along the Queen Charlotte and Denali fault systems. These faults are then incorporated into Canada's 6th Generation Seismic Hazard Model and changes in hazard and risk at key population centers are evaluated. While absolute changes in hazard are modest in most locations, relative increases of several times the original hazard levels are found at sites near newly-added faults, especially in the eastern portion of the study region. Risk modeling indicates potential increases in expected losses, with some communities showing >10 times higher losses at the 475--year return period. However, the sparsity of geodetic and geologic data across much of western Canada significantly limits confidence in these results. Our findings suggest that these or similar faults may pose meaningful hazard, and that additional geodetic monitoring and geologic investigation are urgently needed to better constrain their activity and impact on seismic hazard and risk across the region.