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Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary

Padgett, JS; Engelhart, SE; Kelsey, HM; Witter, RC; Cahill, N

Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary Thumbnail


Authors

JS Padgett

HM Kelsey

RC Witter

N Cahill



Abstract

We examine fossil foraminiferal assemblages from 20 sediment cores to assess sudden relative sea-level (RSL) changes across three mud-over-peat contacts at three salt marshes in northern Humboldt Bay, California (~44.8°N, −124.2°W). We use a validated foraminiferal-based Bayesian transfer function to evaluate the variability of subsidence stratigraphy at a range of 30-6000 m across an estuary. We use the consistency in RSL reconstructions to support estimates of coseismic subsidence from megathrust earthquakes. To assess the variability of subsidence estimates, we analyzed: nine examples of the 1700 CE earthquake (average of 0.64 ±0.14 m subsidence; range of 0.24 ± 0.27 to 1.00 ± 0.44 m), five examples of the ca. 875 cal a BP earthquake (average of 0.43 ±0.16 m; range of 0.41 ± 0.36 to 0.48 ± 0.39 m), and six examples of the ca. 1120 cal a BP earthquake (average of 0.70±0.18 m; range of 0.47 ± 0.36 to 0.80 ± 0.49 m). Our subsidence estimates suggest ~±0.3 m of within-site (intrasite) variability, which is consistent with previous research. We also identify inconsistencies between sites (intersite) at northern Humboldt Bay greater than one-sigma uncertainties, driven by variable foraminiferal assemblages in the mud overlying the 1700 CE subsidence contact. Therefore, we recommend at least two quantitative microfossil reconstructions across the same stratigraphic sequence from different marsh sites within an estuary to account for estimate variability and provide increased confidence in vertical coseismic deformation estimates. Our results have broad implications for quantitative, microfossil-based reconstructions of coseismic subsidence at temperate coastlines globally.

Citation

Padgett, J., Engelhart, S., Kelsey, H., Witter, R., & Cahill, N. (2022). Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary. Journal of Quaternary Science, 37(7), 1294-1312. https://doi.org/10.1002/jqs.3446

Journal Article Type Article
Acceptance Date May 24, 2022
Online Publication Date Jul 1, 2022
Publication Date 2022-10
Deposit Date May 25, 2022
Publicly Available Date Jul 14, 2022
Journal Journal of Quaternary Science
Print ISSN 0267-8179
Electronic ISSN 1099-1417
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 37
Issue 7
Pages 1294-1312
DOI https://doi.org/10.1002/jqs.3446

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Publisher Licence URL
http://creativecommons.org/licenses/by-nc-nd/4.0/

Copyright Statement
Advance Online Version © 2022 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.





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