Increased flood exposure in the Pacific Northwest following earthquake-driven subsidence and sea-level rise

Climate-driven sea-level rise is increasing the frequency of coastal flooding worldwide, exacerbated locally by factors like land subsidence from groundwater and resource extraction. However, a process rarely considered in future sea-level rise scenarios is sudden (over minutes) land subsidence associated with great (>M8) earthquakes, which can exceed 1 m. Along the Washington, Oregon, and northern California coasts, the next great Cascadia subduction zone earthquake could cause up to 2 m of sudden coastal subsidence, dramatically raising sea level, expanding floodplains, and increasing the flood risk to local communities. Here, we quantify the potential expansion of the 1% floodplain (i.e., the area with an annual flood risk of 1%) under low (~0.5 m), medium (~1 m), and high (~2 m) earthquake-driven subsidence scenarios at 24 Cascadia estuaries. If a great earthquake occurred today, floodplains could expand by 90 km<sup>2</sup> (low), 160 km<sup>2</sup> (medium), or 300 km<sup>2</sup> (high subsidence), more than doubling the flooding exposure of residents, structures, and roads under the high subsidence scenario. By 2100, when climate-driven sea-level rise will compound the hazard, a great earthquake could expand floodplains by 170 km<sup>2</sup> (low), 240 km<sup>2</sup> (medium), or 370 km<sup>2</sup> (high subsidence), more than tripling the flooding exposure of residents, structures, and roads under the high subsidence scenario compared to the 2023 floodplain. Our findings can support decision-makers and coastal communities along the Cascadia subduction zone as they prepare for compound hazards from the earthquake cycle and climate-driven sea-level rise and provide critical insights for tectonically active coastlines globally.

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Publication Details

Journal
Proceedings of the National Academy of Sciences
Published
2025-04-28
DOI
https://doi.org/10.1073/pnas.2424659122
Citations
5
Primary Topic
earthquake and tectonic studies
Type
article
Field-Weighted Citation Impact
9.33

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article

Increased flood exposure in the Pacific Northwest following earthquake-driven subsidence and sea-level rise

Andra J. Garner, Diego Melgar, Robert Weiss, David T. Small et al.
5 citations
Proceedings of the National Academy of Sciences
earthquake and tectonic studies
9.33
article

Increased flood exposure in the Pacific Northwest following earthquake-driven subsidence and sea-level rise

Andra J. Garner, Diego Melgar, Robert Weiss, David T. Small, M. J. Willis, Robert C. Witter, S. La Selle, Tina Dura, Alan R. Nelson, Lydia Staisch, Jessica DePaolis, Richard W. Briggs, Harvey M. Kelsey, Jonathan C. Allan, Michael Priddy, Andrea D. Hawkes, Simon E. Engelhart, Benjamin P. Horton, William Paul Chilton, David Bruce
article en
5 citations

Abstract

Climate-driven sea-level rise is increasing the frequency of coastal flooding worldwide, exacerbated locally by factors like land subsidence from groundwater and resource extraction. However, a process rarely considered in future sea-level rise scenarios is sudden (over minutes) land subsidence associated with great (>M8) earthquakes, which can exceed 1 m. Along the Washington, Oregon, and northern California coasts, the next great Cascadia subduction zone earthquake could cause up to 2 m of sudden coastal subsidence, dramatically raising sea level, expanding floodplains, and increasing the flood risk to local communities. Here, we quantify the potential expansion of the 1% floodplain (i.e., the area with an annual flood risk of 1%) under low (~0.5 m), medium (~1 m), and high (~2 m) earthquake-driven subsidence scenarios at 24 Cascadia estuaries. If a great earthquake occurred today, floodplains could expand by 90 km<sup>2</sup> (low), 160 km<sup>2</sup> (medium), or 300 km<sup>2</sup> (high subsidence), more than doubling the flooding exposure of residents, structures, and roads under the high subsidence scenario. By 2100, when climate-driven sea-level rise will compound the hazard, a great earthquake could expand floodplains by 170 km<sup>2</sup> (low), 240 km<sup>2</sup> (medium), or 370 km<sup>2</sup> (high subsidence), more than tripling the flooding exposure of residents, structures, and roads under the high subsidence scenario compared to the 2023 floodplain. Our findings can support decision-makers and coastal communities along the Cascadia subduction zone as they prepare for compound hazards from the earthquake cycle and climate-driven sea-level rise and provide critical insights for tectonically active coastlines globally.

Proceedings of the National Academy of SciencesVol. 122(18)
United States Geological Survey (US), California Polytechnic State University (US), City University of Hong Kong (HK), Nanyang Technological University (SG), University of Oregon (US), Durham University (GB), Pacific Science Center (US), Earth Observatory of Singapore (SG), Rowan University (US), Virginia Tech (US), California State Polytechnic University (US)
National Science Foundation, U.S. Department of Defense, U.S. Department of Energy, National Aeronautics and Space Administration, Oak Ridge Associated Universities, National Research Foundation, National Research Foundation Singapore, Ministry of Education, India, Earth Observatory of Singapore, U.S. Geological Survey, Oak Ridge Institute for Science and Education, Division of Ocean Sciences, Division of Earth Sciences
Life below water
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earthquake and tectonic studies
9.33
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