A Refined Chronology of Tsunami Deposition at Discovery Bay, Washington State
Description:
A tidal marsh at the head of Discovery Bay preserves the largest number of tsunami deposits in Washington State (USA). The location is an excellent geologic recorder of tsunamis because of its wave-amplifying, funnel-shaped morphology, an abundant sediment supply, and a tidal marsh that has sufficient accommodation space and preservation potential to preserve deposits. At Discovery Bay there are as many as ten 2-10 cm thick tsunami deposits, and at least six thinner layers < 2 cm thick that span the last ~3,000 years. Some of the thicker deposits undoubtedly resulted from Cascadia subduction zone earthquakes, based on both tsunami modeling and deposit ages. However, the number of deposits at Discovery Bay exceeds the number of known Cascadia earthquakes in the same time span, so additional tsunami sources including crustal faults, tsunamigenic landslides, and distant Pacific subduction zones may also be represented. One of the thinner deposits is probably from the 1964 Alaska Prince William Sound tsunami, which was observed at the site.
Two decades ago, tsunami deposits were first described and dated at Discovery Bay. We build on previous efforts with new observations and chronologic data. In 2007, part of the marsh that had been previously diked was restored to marshland, thus allowing access to a wider distribution of deposits than originally described. We present new stratigraphic mapping of tsunami deposits from two 3 meter-long vibracores, 38 gouge cores, and three cleared channel bank outcrops. To confirm visual stratigraphy in the vibracores, we obtained high resolution CT density imagery and X-ray fluorescence data. New bracketing maximum and/or minimum radiocarbon ages and 137Cs concentration data were used to create multiple Bayesian age-depth models, each with different assumptions, to (1) determine which model is most appropriate for this dataset and (2) identify the differences in age estimates that may be imposed by model choice. Our new chronology increases confidence in regional source correlations and identifies deposits that likely have non-Cascadia sources.
Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Carrie
Student Presenter: No
Invited Presentation:
Authors
Carrie Garrison-Laney Presenting Author Corresponding Author cegl@uw.edu University of Washington |
Jason Padgett jpadgett@usgs.gov U.S. Geological Survey |
Jessica Pilarczyk jessica_pilarczyk@sfu.ca Simon Fraser University |
Anthony Giang anthony_giang@sfu.ca Simon Fraser University |
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A Refined Chronology of Tsunami Deposition at Discovery Bay, Washington State
Session
From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments