Probabilistic Hazard Assessment of Coseismic Elastic Surface Deformation for the Leech River Valley–Devil's Mountain Fault System Using Stochastic Source Modeling

This study investigates the effect of incorporating the Devil's Mountain Fault (DMF) and its interaction with the Leech River Valley Fault (LRVF) on the elastic surface deformation hazard in and near the city of Victoria, British Columbia, Canada. Previously, the surface deformation hazard of the region has been characterized by considering the LRVF rupture alone. Recent geological surveys show that the LRVF continues eastward and connects with the DMF. Considering only the LRVF as the main seismic source may underestimate the surface deformation hazard of the region. Hence, a probabilistic fault‐slip‐induced deformation hazard model is developed for the LRVF–DMF system. The new model incorporates a range of plausible fault lengths and uncertainties in earthquake occurrence frequencies and evaluates potential interactions between the two faults. Ground deformations are calculated using stochastic source modeling and analytical ground deformation equations. Hazard estimates are computed for the region with and without accounting for the multisegment rupture of the LRVF–DMF system to determine its influence on expected elastic surface deformation. The deformation metric considered represents the continuous elastic deformation field at the ground surface resulting from slip on the modeled fault plane. It is therefore distinct from the principal and distributed surface rupture displacements commonly considered in conventional probabilistic fault displacement hazard assessment (PFDHA) studies. The results indicate that the LRVF–DMF rupture scenario has the largest contribution to total hazard among all rupture scenarios at selected sites around Victoria. Its contribution is higher than 90% at large deformation values and increases the expected deformation by a maximum of 28 cm (from 1 cm) compared to the LRVF rupture at 0.5% probability of exceedance in 50 years.