Cybershake NZ v20.8: New Zealand simulation-based probabilistic seismic hazard analysis

Abstract

This poster presents the computational components and results of the August 2020 version (v20.8) of probabilistic seismic hazard analysis (PSHA) in New Zealand based on physics-based ground motion simulations (‘Cybershake NZ’). A total of 11,875 finite fault simulations were undertaken and seismic hazard results are computed on a spatially-variable grid of 25,948 stations with distributed seismicity sources considered via conventional empirical ground motion models. In this latest version, a NZ-specific modification of the Graves and Pitarka (2010,2015) hybrid broadband ground motion simulation approach was utilized based on improvements identified from extensive validation efforts (including the inclusion of moderate magnitude in our validation dataset). Specific simulation features include a transition frequency of 0.5 Hz (previously 0.25Hz), a detailed crustal model (NZVM v2.03) that represents eight distinct sedimentary basins in NZ using a grid spacing of 0.2 km, and an empirically-calibrated local site response model. A Monte Carlo scheme is used to sample variability in the seismic source parametrization (i.e. varying the hypocentre location and slip distribution for each realization) with the total number of ruptures for each source being a function of the source magnitude. The generated non-uniform hazard maps across the country are presented. Comparisons with previous versions also highlight the advancements that have been made. Immediate near-term plans associated with new features associated with crustal velocity modelling, simulation methodology, and treatment of modelling uncertainty are also discussed.