A Comparison of Foraminiferal and Diatom-Based Transfer Function Estimates of Coseismic Subsidence During the 1700 Ce Earthquake Along the Oregon and California Coast
Description:
At the Cascadia subduction zone, quantitative foraminiferal-based coseismic subsidence estimates are most often used to constrain earthquake and tsunami source models. However, ecological factors affecting foraminifera such as dissolution in low pH environments, mixing across subsidence contacts, and limited supratidal and subtidal range can limit their application and accuracy. Diatoms have the potential to produce more accurate quantitative estimates of coseismic subsidence because they are composed of dissolution-resistant siliceous valves, do not burrow through sediment, have high species turnover in the intertidal zone, and are found in freshwater environments. Here, we develop a diatom-based Bayesian transfer function (BTF), which uses the empirical relationship between modern diatom assemblages and elevation within the tidal frame to estimate relative sea level (i.e., land level) changes from fossil diatom assemblages in cores and outcrops. We use a new modern dataset of >150 diatom samples from tidal wetlands along the Oregon and northern California coasts. We apply our diatom-based BTF to the 1700 CE earthquake contact at 13 Oregon and California coastal sites that also have existing foraminiferal-based BTF coseismic subsidence estimates. We find that at most sites diatom subsidence estimates are at the upper range (e.g., Salmon River) or exceed (e.g., Nestucca) foraminifera-based estimates. At Netarts Bay, the new larger diatom-based subsidence estimates are more similar to subsidence estimates at adjacent sites and help resolve ambiguities in rupture models for the 1700 CE earthquake. Future work will focus on understanding why foraminifera might underestimate subsidence and how diatom ecological factors can improve subsidence estimates, as well as determining the sensitivity of earthquake and tsunami source models to decimeter-scale increases in coseismic subsidence.
Session: Constraining Seismic Hazard in the Cascadia Subduction Zone
Type: Oral
Date: 4/20/2023
Presentation Time: 02:00 PM (local time)
Presenting Author: Tina Dura
Student Presenter: No
Invited Presentation:
Authors
Tina Dura Presenting Author Corresponding Author tinadura@vt.edu Virginia Tech |
Eileen Hemphill-Haley ehhaley@gmail.com California State Polytechnic University, Humboldt |
Niamh Cahill niamh.Cahill@mu.ie Maynooth University |
Harvey Kelsey harvey.Kelsey@humboldt.edu California State Polytechnic University, Humboldt |
Andrea Hawkes hawkesa@uncw.edu UNC Wilmington |
Diego Melgar dmelgarm@uoregon.edu University of Oregon |
David Bruce bruced@vt.edu Virginia Tech |
Isabel Hong isabel.hong@villanova.edu Villanova University |
Simon Engelhart simon.e.engelhart@durham.ac.uk Durham University |
Robert C Witter rwitter@usgs.gov U.S. Geological Survey, Anchorage, Alaska, United States |
Jason Padgett jpadgett@usgs.gov U.S. Geological Survey, Santa Cruz, California, United States |
Nelson Alan alannels@gmail.com U.S. Geological Survey, Golden, Colorado, United States |
Yvonne Milker yvonne.milker@uni-hamburg.de University of Hamburg, Hamburg, , Germany |
Ben Horton bphorton@ntu.edu.sg Nanyang Technological University, Singapore, , Singapore |
A Comparison of Foraminiferal and Diatom-Based Transfer Function Estimates of Coseismic Subsidence During the 1700 Ce Earthquake Along the Oregon and California Coast
Category
Constraining Seismic Hazard in the Cascadia Subduction Zone