12:15 PM - 1:15 PM
[P-39] Using tsunami deposits and modeling to study tsunami history and sources in Washington State, USA
Keywords:tsunami source, tsunami deposit, Cascadia, tsunami modeling, paleotsunami
Washington State, on the Pacific coast of the United States, has many tsunami sources, including the Cascadia subduction zone, shallow faults that cross waterways, submarine and subaerial landslides, and distant source trans-Pacific tsunamis. However, Washington has had very few tsunamis in the last 150 years, and of those, only landslide and distant source tsunamis have been observed. Because of this, accurate assessments of future tsunami size and frequency must rely on the study of paleotsunami deposits and the modeling of tsunami flow and sediment transport. A tidal marsh at Discovery Bay, along the Strait of Juan de Fuca, is an ideal setting to study the history of tsunamis from various sources. There are at least nine distinct tsunami deposits spanning the last 2,500 years in the marsh deposits at Discovery Bay; and several thinner, less distinct deposits that may represent distant source tsunamis, such as the 1964 Great Alaska Earthquake tsunami, which flooded the site. The marsh contains a deposit inferred to be from the 1700 A.D. Cascadia earthquake, and some of the older deposits are likely from earlier Cascadia tsunamis. Tsunami deposits can be used to provide estimates of tsunami inundation extent, flow depths, and current velocities, which can be compared to output from tsunami inundation models. Tsunami deposits can also be used to study tsunami sources. A collaboration with Tohoku University modeling tsunami sediment transport using the characteristics of tsunami deposits will test various sources. There are a greater number of tsunami deposits at Discovery Bay than known tsunamis or earthquakes in the same timespan, so further study must be done to accurately assess the tsunami hazard in Discovery Bay and the Strait of Juan de Fuca.