Probabilistic Seismic Hazard Analysis of Victoria, British Columbia: Considering an Active Fault Zone in the Nearby Leech River Valley

Jacob Kukovica, Hadi Ghofrani, & Sheri Molnar

Published October 1, 2019, SCEC Contribution #10175

There is a newly proposed active fault zone associated with the Leech River Valley, near the city of Victoria on southern Vancouver Island. The current Canadian seismic hazard model for the 2015 National Building Code of Canada (NBCC) does not consider this active fault zone; however, the interpretation of paleoseismic evidence suggests there to be at least three surface‐rupturing earthquakes to have exceeded moment magnitude 6 within the last 9000 yr. Probabilistic seismic hazard analyses (PSHAs) are performed for the city of Victoria with consideration of the Leech River Valley fault zone (LRVFZ) as an active fault source. We first reproduce the 2015 NBCC ground motions for Victoria to quantify percent change in predicted ground motions from inclusion of an active LRVFZ source. A suite of eight PSHA calculations are performed to capture uncertainties in implementing an LRVFZ source zone including maximum magnitude, magnitude–recurrence statistics, and magnitude–distance relations. At a return period of 2475 yr (i.e., 2% probability of exceedance in 50 yr), the current 2015 NBCC peak horizontal ground acceleration is 0.58g for Victoria, which could increase 9% on average to 0.63g (⁠0.02g one standard deviation) due to an active LRVFZ. If the Leech River Valley is the location of an active fault zone, the 2015 NBCC uniform hazard spectra motions in Victoria are predicted in this study to increase by a maximum of 1%–23% depending on the seismicity rate of the introduced LRVFZ.

Citation
Kukovica, J., Ghofrani, H., & Molnar, S. (2019). Probabilistic Seismic Hazard Analysis of Victoria, British Columbia: Considering an Active Fault Zone in the Nearby Leech River Valley. Bulletin of the Seismological Society of America, 109(5), 2050-2062.