Probabilistic Tsunami Hazard Maps for Application Through the California Seismic Hazard Mapping Act

Date: 4/25/2019

Time: 10:45 AM

Room: Cascade II

The California Tsunami Program has reviewed and finalized Probabilistic Tsunami Hazard Analysis (PTHA) maps for all 20 coastal and Bay Area counties, including those directly impacted by the southern Cascadia Subduction Zone (CSZ). A logic-tree approach of tsunami source characterization of the southern CSZ mirrored that of the most recent USGS National Seismic Hazard Maps. The associated coseismic land deformation was incorporated into the underlying digital elevation model prior to running numerical inundation models so that realistic inundation results would be represented.

The PTHA maps will be used for various community-level tsunami planning activities, primarily those related to life safety, land use, and construction. Evacuation time modeling was performed by partners at the USGS on three PTHA maps (475-, 975-, and 2475-year average return periods) to identify areas where evacuation challenges exist and constructing vertical evacuation or other mitigation solutions might be needed. The program developed a Scientific Review Panel to evaluate the accuracy and applicability of the PTHA products for use. A separate Tsunami Technical Application Panel, comprised of a dozen engineers and planners, is providing guidance to the state regarding the application of PTHA and evacuation products through the Seismic Hazard Mapping Act (SHMA). The SHMA provides a regulatory framework of hazard mitigation for project planning and construction of multi-unit developments and moderate-to-high capacity structures. Tsunami zones under the SHMA will be completed for California during the 2019-20 time frame.

Presenting Author: Rick Wilson

Authors