Exploring Seismic Hazard Scenarios of Potentially Active Faults in the Southern Coast Mountains of British Columbia, Canada

ABSTRACT The southern Coast Mountains of British Columbia, Canada, lie landward of the northern Cascadia subduction zone margin. These mountains host an abundance of mapped faults, many of which are inherited from a complex deformational history. Geologic and geodetic evidence point to the possibility of some of these faults being active, posing a threat of future damaging earthquakes. However, the glacial history and slow deformation of the mountain belt impose challenges on identifying which faults are active. Although an in-depth investigation of all the faults is ideal, it is difficult to conduct due to the abundance of faults and the scale of the region. In this study, we quantified the potential impact of a selection of these faults to nearby population centers to gain insights on prioritization for further studies. We analyzed the seismic hazard curves of eight major potentially active faults and compared them with the seismic sources from the sixth-Generation Canadian Seismic Hazard model. We used hypothetical occurrence rates to reflect a range of possible values for Holocene-active faults. We then calculated the changes in the uniform-hazard spectra at a 2% probability of exceedance in 50 yr, relative to the reference model. The results indicate that source-to-site distance is the most influential factor for determining which faults contribute the most shaking intensity for a particular site. Furthermore, the increase in hazard relative to the reference model is greatest at long spectral periods, which affect taller buildings and structures. Our findings suggest that the Fraser fault, Britannia shear zone, Alouette Lake fault, and other candidate faults near Vancouver should be prioritized for future investigation. This analysis may be useful in other regions where shallow fault activity is in question, and prioritization is required to direct limited resources for study.