Diatom Evidence of Tsunami Inundation Extent Following the Great Ca. 1700 Ce Earthquake(s) at the Salmon River Estuary, Oregon, USA
Description:
Although the Cascadia Subduction Zone (CSZ) has not experienced a great (>Mw 8) megathrust earthquake in more than 300 years, coastal marshes along the CSZ preserve widespread stratigraphic evidence from the most recent great earthquake, or series of earthquakes, circa (ca.) 1700 CE. At the Salmon River estuary, stratigraphic evidence of earthquake subsidence and tsunami inundation ca. 1700 is preserved as intertidal wetland soils sharply capped by sand overlain by intertidal silt. The inland extent of sandy deposits above buried wetland soils has been used as a minimum inundation constraint in tsunami modeling. However, observations of modern tsunamis have demonstrated that the true inundation extent can exceed the inland limit of sandy sediment deposition by 50% or more in extensive, relatively flat, coastal plains, while mud-sized tsunami sediments can be deposited up to the full extent of inundation. Because sediment availability, site morphology, and deposit preservation contribute to the variability in tsunami deposit thickness, high-resolution tsunami deposit mapping is necessary to accurately estimate the inundation extents of prehistoric tsunamis. Through careful analyses of fossil diatoms, grain size, and computed tomography (CT) scans, we search for evidence of tsunami inundation in the fine-grained sediment above earthquake subsidence contacts in cores beyond the previously mapped inland extent of tsunami-deposited sand from the ca. 1700 CE rupture at the Salmon River estuary. Preliminary results show the diatom assemblage observed within the sandy portion of the mapped tsunami deposit are also found in silty sediments above the ca. 1700 CE earthquake subsidence contact at sites beyond the mapped inland extent of sandy tsunami deposits. Fragmentation of diatoms is consistent with transport in a tsunami both in sandy and silty tsunami sediments. Delineating the full extent of tsunami inundation along the CSZ provides more accurate constraints for tsunami and earthquake source models of past events and will improve our understanding of potential impacts and hazards of future events.
Session: Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Michael
Student Presenter: Yes
Invited Presentation:
Authors
Michael Priddy Presenting Author Corresponding Author mspriddy@vt.edu Virginia Tech |
Tina Dura tinadura@vt.edu Virginia Tech |
Andrea Hawkes hawkesa@uncw.edu University of North Carolina Wilmington |
Harvey Kelsey hmk1@humboldt.edu California State Polytechnic University, Humboldt |
SeanPaul La Selle slaselle@usgs.gov U.S. Geological Survey |
Robert Witter rwitter@usgs.gov U.S. Geological Survey |
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Diatom Evidence of Tsunami Inundation Extent Following the Great Ca. 1700 Ce Earthquake(s) at the Salmon River Estuary, Oregon, USA
Category
Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior