Tsunami deposits and tsunami modeling of the 900 AD Seattle Fault event in northern Puget Sound

Andrew Raulerson
April 2015

Problem To Be Addressed and Hypothesis

Puget Sound is vulnerable to tsunamis that could cause catastrophic infrastructure and potential fatalities. About 1,100 years ago, an earthquake on the Seattle Fault generated a tsunami that flooded low-lying areas in at least six known sites in eastern Puget Sound, as far north as the Snohomish delta in Everett and as far south as Gorst near Bremerton (Adams, 1992; Atwater & Moore, 1992; Bucknam et al., 1992; Bourgeois & Johnson, 2001; Arcos, 2012) (Figure 1). These few paleotsunami field sites begin to illustrate the hazard posed by a rupture of the Seattle Fault, yet they do not define the extent of coastline inundated by that tsunami. Understanding the behavior of the 900 AD tsunami will provide significant knowledge that can be used in hazard planning throughout Puget Sound.

The goal of this project is to model the 900 AD tsunami for Puget Sound and validate the model based on observed tsunami deposit field sites. I will look for tsunami deposits at a new location, the Elger Bay marsh on Camano Island, because it lies between areas where evidence of inundation have and have not been found. A tsunami deposit, or lack thereof, will allow me to validate model simulations that predict where the tsunami still had the energy and size to inundate low-lying areas and leave a deposit. This project is a collaboration with the Island County Department of Emergency Management (ICDEM), who plans to use my results to evaluate and/or revise their current hazard mitigation plan and to add to their community outreach programs.

Full Thesis Proposal (PDF format)