# Computational Mathematics and Scientific Computing Seminar

## Efficient Probabilistic Tsunami Hazard Assessment using Clustering and Multi-resolution Modeling

**Speaker:**
Randall J LeVeque, Applied Mathematics, University of Washington

**Location:**
Warren Weaver Hall (online)

**Date:**
Sept. 25, 2020, 10 a.m.

**Synopsis:**

For coastal regions on the margin of a subduction zone, near-field megathrust earthquakes are the source of the most extreme tsunami hazards, and are important to handle properly as one aspect of any Probabilistic Tsunami Hazard Assessment (PTHA). Typically, great variability in inundation depth at a coastal location is possible due to the extreme variation in extent and pattern of slip over the fault surface. We use a Karhunen-Lo\`eve expansion to express the probability density function for all possible events, with parameters that are geophysically reasonable for the Cascadia Subduction Zone. We use importance sampling techniques to adequately sample the tails of the distribution and properly re-weight the probability assigned to the resulting realizations. We then use coarse-grid simulation results to group the realizations into a small number of clusters that we believe will give similar inundation patterns in the region of interest, so that only one fine-grid tsunami simulation needs to be computed from a representative member of each cluster. These can be combined with the coarse-grid simulations for other members of the cluster to more cheaply obtain results very similar to those found using all fine-grid simulations. This talk is based on joint work that is more fully described in https://eartharxiv.org/yreqw/.