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Spectral Acceleration Basin Amplification Factors for Interface Cascadia Subduction Zone Earthquakes in Canada’s 2020 National Seismic Hazard Model

Session: Earthquake Science, Hazards and Policy in Cascadia II

Type: Oral

Date: 4/20/2021

Presentation Time: 06:00 PM Pacific

Description: 

Canada’s 2020 national seismic hazard model provides hazard estimates from interface Cascadia Subduction Zone (CSZ) earthquakes in southwestern Canada using four ground motion models (GMMs) with equal weights: Abrahamson et al. (2016), Zhao et al. (2006), Ghofrani and Atkinson (2014), and Atkinson and Macias (2009). Because Zhao et al. (2006) and Ghofrani and Atkinson (2014) were derived from data primarily from subduction earthquakes in Japan, their use in Canada’s national seismic hazard model includes a “Cascadia” factor to account for local site conditions. Despite this regional factor, the GMMs do not explicitly consider basin amplification effects from the Georgia sedimentary basin below Metro Vancouver. This study benchmarks ground motion shaking from a suite of 30 physics-based simulations of M9 CSZ earthquake scenarios, which explicitly account for the basin effects by means of a three-dimensional velocity model, to corresponding GMMs in Canada’s 2020 national seismic hazard model. We extend the site-specific and period-dependent basin amplification factors proposed by Kakoty et al. (2021) to consider all relevant GMMs. The weighted basin amplification factors at the deepest basin location range from 1.8 to 3.2 for periods in the 1 to 5-second range. We validate the proposed basin factors by comparing amplifications from simulations against those from strong motion recordings from the 2001 Nisqually earthquake and the 2015 Victoria earthquake.

Presenting Author: Preetish Kakoty

Student Presenter: Yes

Authors