The application of foraminifera to characterize tsunami sediment and quantify coseismic subsidence along the Sumatra and Cascadia subduction zones

Written and instrumental records rarely span enough time to recognize the range of a regions earthquake and tsunami hazards but these may be preserved in prehistoric records by the sediments they leave behind. To address this scientific and societal need my thesis has two research interests: (1) characterize sediments deposited by the 2004 Indian Ocean tsunami; and (2) use foraminifers to reconstruct coastal subsidence during the AD 1700 giant Cascadia earthquake.;I analyzed the stratigraphy, grain size distribution and foraminiferal assemblages of pre-tsunami and tsunami sediment from the December 26 th 2004 Indian Ocean tsunami at five sites along the Malaysia-Thailand Peninsula. At each site, three to five stratigraphic units were identified and contained between one and three fining upward sequences reflecting waning flow separated by coarser sand layers reflecting high energy run-up. Foraminifera were able to differentiate pre-tsunami sediment from tsunami sediment and provided estimates of sediment provenance and deposition style.;Previous reconstructions of coastal subsidence for the AD 1700 giant Cascadia earthquake in Oregon have been hampered by large unquantified error estimates (0.5 -- 1.5 m). I have produced a contemporary foraminiferal dataset consisting of 83 samples and 18 species from five Oregon intertidal zones. I have shown that Oregon intertidal zones can be divided into ecological-elevation dependent zones making them applicable for paleomarsh reconstructions: Zones I and Ia (upland and high marsh) dominated by Trochamminita irregularis, Balticammina pseudomacrescens, Haplophragmoides wilberti and Trochammina inflata; Zone Ib (middle marsh) composed of Trochammina inflata, Haplophragmoides wilberti, and Jadammina macrescens: and Zone II (low marsh and tidal flat) dominated by Miliammina fusca.;I developed a foraminiferal-based transfer function, which produced high-precision (+/-0.27-0.30 m) reconstructions of paleomarsh elevation from fossil sediment sequences incorporating the AD 1700 giant earthquake. Reconstructions were supported by lithostratigraphy, faunal zonation, and diatom and carbon isotope analyses. Estimates of coseismic subsidence varied between 0.36 m and 0.90 m with error estimates ranging from 0.27 m to 0.32 m. Compared to previous research these results further refine envelops of coseismic estimated subsidence and suggest differences in the magnitude of slip and strain accumulation for the AD 1700 giant Cascadia earthquake.