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Microfossil measures of rapid sea-level rise: Timing of response of two microfossil groups to a sudden tidal-flooding experiment in Cascadia

July 13, 2017

Comparisons of pre-earthquake and post-earthquake microfossils in tidal sequences are accurate means to measure coastal subsidence during past subduction earthquakes, but the amount of subsidence is uncertain, because the response times of fossil taxa to coseismic relative sea-level (RSL) rise are unknown. We measured the response of diatoms and foraminifera to restoration of a salt marsh in southern Oregon, USA. Tidal flooding following dike removal caused an RSL rise of ∼1 m, as might occur by coseismic subsidence during momentum magnitude (Mw) 8.1–8.8 earthquakes on this section of the Cascadia subduction zone. Less than two weeks after dike removal, diatoms colonized low marsh and tidal flats in large numbers, showing that they can record seismically induced subsidence soon after earthquakes. In contrast, low-marsh foraminifera took at least 11 months to appear in sizeable numbers. Where subsidence measured with diatoms and foraminifera differs, their different response times may provide an estimate of postseismic vertical deformation in the months following past megathrust earthquakes.

Citation Information

Publication Year 2017
Title Microfossil measures of rapid sea-level rise: Timing of response of two microfossil groups to a sudden tidal-flooding experiment in Cascadia
DOI 10.1130/G38832.1
Authors B. P. Horton, Yvonne Milker, T. Dura, Kelin Wang, W.T. Bridgeland, Laura S. Brophy, M. Ewald, Nicole Khan, S.E. Engelhart, Alan R. Nelson, Robert C. Witter
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Index ID 70190059
Record Source USGS Publications Warehouse
USGS Organization Geologic Hazards Science Center