Megathrust paleogeodesy at the Cascadia subduction zone

• Antragstellerin: Dr. Yvonne Milker
• Fachliche Zuordnung: Paläontologie
• Förderung: Förderung von 2012 bis 2014
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 220655384

I propose a project with two objectives. The first is to reconstruct earthquake-induced land-level changes for the four most recent earthquake cycles (past 2000 years) at the central Cascadia subduction zone. The Pacific coasts of the states of Oregon and Washington are considered as a type-area of subduction-zone paleoseismology because estuarine marshes of the region overlie a 3000-to-7000-year sediment record of land-level changes and tsunami deposition during many past magnitude 8-9 earthquakes. Sites with long, high-quality records extend along much of the 1200-km-long subduction zone. Despite two decades of study, the hazard posed by great subduction-zone earthquakes and tsunamis is uncertain and a better assessment is needed to help prevent huge property and human losses, like those of the past decade in the Indian Ocean and Japan. Earlier foraminiferal studies, most of them semi-quantitative, have shown the great potential of quantitative microfossil reconstructions for providing quantitative estimates of the land-level changes inferred from stratigraphic evidence of relative sea-level changes during past great earthquakes. Quantitative estimates of earthquake-induced land-level changes at Cascadia are available only for a few of the most recent earthquakes at a few sites and the precision is quite low with errors of >±0.5 m. Multivariate statistical analysis of modern and fossil foraminiferal assemblages can improve the precision and accuracy of land-level reconstructions. I plan to collect and study modern and fossil benthic foraminiferal records in and beneath marshes at the Coos Bay and Coquille River estuaries in southern Oregon. A key question that I will address is the optimal sample size when using intertidal benthic foraminifera for precise sea-level estimates (from which land-level changes are inferred). To further improve the accuracy of sea-level reconstructions, I will quantify species-environment relations using several multivariate statistical analyses on recent intertidal faunas. I will also study the influence of other key factors such as taphonomic processes on the reliability, accuracy, and precision of relative sea-level estimates. To quantitatively reconstruct sea-level changes, I will develop new transfer functions using modern benthic foraminiferal assemblages and evaluate their performance before applying them to fossil assemblages from sediment cores. The reconstruction of interseismic as well as coseismic vertical movement will improve numerical models of Cascadia earthquake cycles, resulting in a better assessment of the magnitude of past earthquakes at the Cascadia subduction zone.The second objective is to validate foraminiferal-based estimates of submergence through continuous observations of the Bandon Marsh National Wildlife Refuge flooding experiment. The tidal restoration of the Bandon Marsh, which simulates sudden subsidence during a great subduction-zone earthquake, provides a unique opportunity to observe and measure the physical and biological changes that occur during a “coseismic” sea-level rise and of “interseismic” changes as simulated by the stabilization of the marsh. My study of both sea-level rise and marsh stabilization will provide an excellent opportunity to better understand sedimentation processes and the re-colonization of benthic foraminferal faunas analogous to changes during past earthquake cycles.

• DFG-Verfahren: Sachbeihilfen
• Internationaler Bezug: USA
• Beteiligte Personen: Professor Dr. Benjamin P. Horton, Ph.D.; Professor Dr. Gerhard Schmiedl