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Session: Constraining Seismic Hazard in the Cascadia Subduction Zone

Type: Oral

Room: 208A

Date: 4/20/2023

Presentation Time: 02:00 PM Pacific

Presenting Author: Tina Dura

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.

Additional Authors

Tina Dura

Presenting Author Corresponding Author

tinadura@vt.edu

Virginia Tech, Blacksburg, Virginia, United States

Eileen Hemphill-Haley

ehhaley@gmail.com

California State Polytechnic University, Humboldt, Arcata, California, United States

Niamh Cahill

niamh.Cahill@mu.ie

Maynooth University, Kildare, , Ireland

Harvey M Kelsey

harvey.Kelsey@humboldt.edu

California State Polytechnic University, Humboldt, Arcata, California, United States

Andrea Hawkes

hawkesa@uncw.edu

UNC Wilmington, Wilmington, North Carolina, United States

Diego Melgar

dmelgarm@uoregon.edu

University of Oregon, Eugene, Oregon, United States

David Bruce

bruced@vt.edu

Virginia Tech, Blacksburg, Virginia, United States

Isabel Hong

isabel.hong@villanova.edu

Villanova University, Villanova, Pennsylvania, United States

Simon Engelhart

simon.e.engelhart@durham.ac.uk

Durham University, Durham, , United Kingdom

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

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