Tsunamigenic Fault Sources in the Salish Sea, Washington State

Session: Understanding Non-Traditional Seismic Tsunami Hazards
Type: Oral
Date: 4/28/2020
Time: 05:00 PM
Room: 120 + 130
Description: 

We are in the process of mapping the probabilistic tsunami hazard at the terminal locations of the Washington State Ferry system using procedures consistent with those laid out in ASCE 7-16. We considered earthquake sources in three categories: distant megathrust sources (e.g. Alaska), the Cascadia megathrust and local crustal faults (Salish Sea crustal faults). For the distant and regional sources, we are using the two-phase method where the inundation is based on the probabilistic offshore exceedance amplitudes. We add the local sources by computing tsunami inundation of alternative source instances directly and combine these with the results of the offshore inundation analysis.

In this presentation we will discuss the characterization and significance of the crustal sources for tsunami hazard. Although the crustal faults in the Salish Sea are much smaller than the Cascadia subduction zone and have much lower slip rates, the fact that this region and in particular Puget Sound are not directly exposed to the Cascadia subduction zone means that these structures may locally be the dominant source for tsunami hazard. The faults in the area generally divided into several zones, some of which are much wider and diffuse than others. From South to North these are theTacoma fault zone, Seattle fault zone, Southern Whidbey Island fault zone, Utsalady Point fault zone, Devils Mountain fault zone and the Skipjack fault zone. The Tacoma, Seattle, Southern Whidbey and Devils Mountain Fault zones are primarily dip-slip (thrust) faults, and therefore have the highest tsunamigenic potential. Currently, we have limited ourselves to these structures, most of which have been represented in the USGS fault model though alternative epistemic branches. We are using the USGS logic tree as much as a starting point and use systematic variations in slip distribution to represent the aleatory variability. Due to the vicinity to the ferry terminals of several of these faults, it is important to take into account the epistemic uncertainties in the different branch locations and their mode of rupture.

Presenting Author: Hong Kie Thio

Authors