Variability in Diatom-Based Coseismic Subsidence Estimates Over Multiple Earthquake Cycles in a Southern Oregon Tidal Wetland, Cascadia Subduction Zone
Description:
Along the Cascadia subduction zone (CSZ), foraminifera-based estimates of coseismic subsidence have enhanced our understanding of 1700 CE earthquake rupture dynamics by serving as the data base for models that constrain areas of relatively high and low slip along the megathrust. These coseismic subsidence estimates are produced through transfer functions (TF), which are statistical models that employ the empirical relationships between modern microfossil assemblages and their corresponding elevations relative to a tidal datum to reconstruct past sea levels using microfossils recovered in cores. However, dissolution of foraminifera in low pH environments limits the applicability of foraminifera-based TFs across some pre-1700 CE contacts, especially in southern Oregon where coastal marshes archive a ~7000-year record of CSZ earthquakes. Here we use diatoms, a microscopic algae composed of dissolution-resistant silica, to produce quantitative TF-based coseismic subsidence estimates across 6 earthquake contacts in cores collected along Fahys Creek, a tributary of the Coquille River. Inferred timing of these events ranges from the most recent earthquake of 1700 CE to ~4500 cal yr BP. Our diatom-based TF reconstructions of the pre- and post-earthquake environments are consistent with a sudden change from upland/high-marsh soils to low-marsh/tidal flat environments. Coseismic subsidence estimates across the 6 contacts show variable amounts of coseismic subsidence, ranging from ~0.5m to >2m. Future work will incorporate subsidence estimates from an additional site ~40 km to the south at Sixes River. A transect of correlative coseismic estimates in southern Oregon at the two sites will enhance understanding of temporal and spatial variability of deformation from CSZ ruptures and will inform how upper plate structures (e.g., Cape Blanco anticline) affect coseismic subsidence.
Session: Constraining Seismic Hazard in the Cascadia Subduction Zone [Poster]
Type: Poster
Date: 4/20/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: David Bruce
Student Presenter: Yes
Invited Presentation:
Authors
David Bruce Presenting Author Corresponding Author bruced@vt.edu Virginia Tech |
Tina Dura tinadura@vt.edu Virginia Tech |
Robert Witter rwitter@usgs.gov U.S. Geological Survey |
Harvey Kelsey hmk1@humboldt.edu Humboldt State University |
Eileen Hemphill-Haley eileen.hemphill-haley@humboldt.edu Humboldt State University |
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Variability in Diatom-Based Coseismic Subsidence Estimates Over Multiple Earthquake Cycles in a Southern Oregon Tidal Wetland, Cascadia Subduction Zone
Category
Constraining Seismic Hazard in the Cascadia Subduction Zone