Cybershake NZ v18.6: New Zealand simulation-based probabilistic seismic hazard analysis

Brendon A. Bradley, Karim Tarbali, Robin L. Lee, Jonney Huang, D Lagrava, V Polak, J Motha, & Sung Bae

Submitted August 14, 2018, SCEC Contribution #8536, 2018 SCEC Annual Meeting Poster #008

This poster presents the computational workflow and results of the June 2018 version (v18.6) of probabilistic seismic hazard analysis (PSHA) in New Zealand based on physics-based ground motion simulations (`Cybershake NZ'). A total of ~12,000 finite fault simulations are undertaken and seismic hazard results computed on a spatially-variable grid of ~19,000 stations, with distributed seismicity sources considered via conventional empirical ground motion models.

In the current work completed to date, the Graves and Pitarka (2010, 2015) hybrid broadband ground motion simulation approach is utilized considering a transition frequency of 0.25 Hz, a detailed crustal model with a grid spacing of 0.4 km, and an empirically-calibrated local site response model. Additional simulations at finer computational scales are in preparation for faults with significant contribution to the hazard. A Monte Carlo scheme is used to sample variability in the seismic source parametrization (e.g. hypocenter location and slip distribution), with the total number of ruptures for each fault being a function of the rupture magnitude. We adopt a ‘forward’ simulation approach (as opposed to using reciprocity) because: (i) of the large number of stations relative to rupture realizations considered (i.e., 12,000 ruptures vs. 19,000 stations); (ii) a computational grid that is determined on a rupture-specific basis to optimize the domain size for a targeted minimum ground motion amplitude; and (iii) our near-term intention to include plasticity. As a result of (i) and (ii), there is not appreciable benefits to using reciprocity. Furthermore, the use of a dense grid of ~19,000 points at which seismic hazard is computed enables truly site-specific seismic hazard analysis and subsequent use of simulated ground motions in response history analysis of structural and geotechnical systems. Intensity measures for sample scenario ruptures and subsequently generated hazard curves and uniform hazard map across the country are presented. Treatment of uncertainty in the context of simulation-based PSHA, and improvements for future versions of the ongoing effort are discussed.

Key Words
Cybershake NZ, ground motion simulation

Citation
Bradley, B. A., Tarbali, K., Lee, R. L., Huang, J., Lagrava, D., Polak, V., Motha, J., & Bae, S. (2018, 08). Cybershake NZ v18.6: New Zealand simulation-based probabilistic seismic hazard analysis. Poster Presentation at 2018 SCEC Annual Meeting.


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