Constraints on Cascadia Subduction Zone Paleoearthquakes from Terrestrial Shaking Proxies and Coseismic Land-level Change
Description:
The impacts and nature of past great Cascadia Subduction Zone (CSZ) earthquakes, and the risk posed to the Pacific Northwest from future events, are poorly constrained. Past work using evidence from written histories, paleoliquefaction, coastal subsidence, and near- and far-field tsunami deposits allow for a wide-range of earthquake rupture styles, magnitudes, and shaking intensities for a given ‘event’ in the geologic record. However, most studies focus on a single geologic proxy to investigate these events. Here, we present an integrated method for assessing the likelihood of simulated CSZ earthquakes using a combination of terrestrial shaking proxies and estimates of coastal land-level change throughout Cascadia. Complementary constraints on minimum and maximum paleoshaking intensities from coastal landslides, liquefaction, and fragile geologic features are combined with coseismic coastal subsidence estimates to leverage a diverse and geospatially continuous set of constraints on past CSZ earthquake rupture scenarios. This integrated paleoseismic record is compared to a suite of CSZ earthquake simulations for megathrust earthquakes of magnitude 8.65 – 9.15 with varying down-dip extents of slip and source characteristics to compute misfit between the geologic record and simulated ground motions. We assess misfit between the geologic record and simulations at a full-margin scale to assess global performance and identify local discrepancies along-strike to identify possible variations in source behavior. To assess the sensitivity of these results to different modeling approaches, we test different statistical methods for integrating the geologic proxy data, calculating the misfit, and incorporating geochronological uncertainty. Preliminary results show the sensitivity to how different geologic proxies are integrated on preferred earthquake simulations, as well as how incorporating subaqueous data (i.e., offshore and lacustrine) could further improve these models.
Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - IV
Type: Oral
Date: 5/1/2024
Presentation Time: 04:45 PM (local time)
Presenting Author: Alex
Student Presenter: No
Invited Presentation:
Authors
Alex Grant Presenting Author Corresponding Author agrant@usgs.gov U.S. Geological Survey |
Erin Wirth emoriarty@usgs.gov U.S. Geological Survey |
Audrey Dunham adunham@usgs.gov U.S. Geological Survey |
Sean LaHusen slahusen@usgs.gov U.S. Geological Survey |
Brett Maurer adunham@usgs.gov University of Washington |
Devin McPhillips dmcphillips@usgs.gov U.S. Geological Survey |
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Constraints on Cascadia Subduction Zone Paleoearthquakes from Terrestrial Shaking Proxies and Coseismic Land-level Change
Session
From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments