Development of Offshore Probabilistic Tsunami Exceedance Amplitudes for Asce 7-16

Abstract eng:
We have developed probabilistic tsunami offshore amplitude exceedance maps, with an average return period of 2500 yr, for the five Pacific states of the USA to be used as basis for the tsunami design guidelines of ASCE 7-16. These maps are based on a comprehensive integration over tsunamigenic earthquakes on all the circum-Pacific subduction zones. Thanks to the linear behavior of tsunami waves in the deep ocean, we are able to use an efficient Green’s function summation approach to model, which enabled us to integrate over thousands of events. An integral part of the analysis is the formal inclusion of epistemic uncertainties, resulting from a limited understanding of the physical processes as well their aleatory variability due to the randomness in natural processes. We can divide the offshore tsunami hazard problem into two stages: the source characterization and deep ocean propagation. In the source characterization, many of the epistemic uncertainties and aleatory variabilities are identical to those specified in probabilistic seismic hazard analysis (PSHA). The biggest difference is in the details of slip distributions, which are very significant in tsunami excitation, especially for near-field tsunamis, but are not used in PSHA. We have used a simplified asperity model to include this variability. These offshore hazard maps are used to anchor the tsunami inundation zones included in ASCE 7-16, developed by NOAA, and are also used as a constraint for site-specific inundation studies as prescribed in the standards.

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