Tsunami Risk for Insurance Portfolios From Megathrust Earthquakes in Cascadia Subduction Zone

Abstract eng:
The 2011 Tohoku megathrust earthquake of magnitude 9.0 (M W ) showed the potential of significant loss to insurance industry due to tsunami. Large magnitude earthquakes at the Cascadia Subduction Zone (CSZ) can cause the most devastating tsunami hazard in the pacific basin to the west coast of USA including Washington, Oregon, and north California coastlines. The perception of tsunami risk in the industry has been small compared to the risk from the shake damage. To improve managing the tsunami risk for USA coastal cities, Risk management Solution (RMS) first modeled the historical 1700 Cascadia tsunami event and evaluated the maximum tsunami waves at different stations offshore of west coast of USA as well as coastal inundation. Then we developed a set of stochastic slip distributions along the CSZ corresponding to the large earthquakes with moment magnitude (M W ) higher than 8.0 and modeled the tsunami wave propagation and coastal inundation. Each tsunami event is built based on seismic characteristics of the CSZ ruptures and a slip model that provides a non-uniform slip distribution. Non-uniform slip distributions are used to provide a realistic set of possible tsunami generating earthquakes and are constrained by the paleo-seismic records of offshore uplifts along west of USA. The vertical seafloor/coastline deformations including uplift and subsidence are computed using a triangular dislocation model that captures the complexities of the subduction zone geometry. These deformations are then used as initial conditions to a high-resolution numerical model that simulates the tsunami wave propagation and coastal inundations. Parallel computations are applied on Graphic Processing Units (GPUs) to overcome the large numerical computational efforts needed to model the entire west coast of USA. Variable land surface roughness based on land cover data is used to simulate the accurate hydraulics of coastal inundation. The tsunami hazard maps are developed for the entire west coast of USA starting from Washington state coast at north to California state coasts in south. In addition the histograms of maximum tsunami waves for key coastal cities are provided. This paper mainly covers the hazard aspect of tsunami evaluation and simulation for west coast of USA. In parallel RMS has developed an extensive study on the vulnerability of infrastructures and buildings along west of USA as well as the detailed information of exposure. The hazard model will later be combined with the vulnerability model and exposure model to provide a comprehensive understanding of tsunami risk and economic loss along the west coast of USA due to megathrust earthquakes in CSZ.

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