Earthquake Ground Motion and 3D Georgia Basin Amplification in Southwest British Columbia: Deep Juan de Fuca Plate Scenario Earthquakes

摘要

Finite-difference modeling of 3D long-period (>2 s) ground motions for large (M_w 6.8) scenario earthquakes is conducted to investigate effects of the Georgia basin structure on ground shaking in Greater Vancouver, British Columbia, Canada. Scenario earthquakes include deep (>40 km) subducting Juan de Fuca (JdF) plate earthquakes, simulated in locations congruent with known seismicity. Two sets of simulations are performed for a given scenario earthquake using models with and without Georgia basin sediments. The chosen peak motion metric is the geometric mean of the two orthogonal horizontal components of motion. The ratio between predicted peak ground velocity (PGV) for the two simulations is applied here as a quantitative measure of amplification due to 3D basin structure. A total of 10 deep subducting JdF plate earthquakes are simulated within 100 km of Greater Vancouver. Simulations are calibrated using records from the 2001 Mw 6.8 Nisqually earthquake. On average, the predicted level of average PGVat stiff soil sites across Greater Vancouver for an M_w 6.8 JdF plate earthquake is 3.2 cm=s (modified Mercalli intensity IV-V). The average increase in PGV due to basin structure across Greater Vancouver is 3.1. Focusing of northnortheast- propagating surface waves by shallow (<1 km) basin structure increases ground motion in a localized region of south Greater Vancouver; hence, scenario JdF plate earthquakes located ≥80 km south-southwest of Vancouver are potentially the most hazardous.