HR: 08:00h
AN: T41B-01    [Abstracts]
TI: Using a microfossil-based approach to constrain megathrust-induced coseismic land displacement in coastal Oregon, USA
AU: * Hawkes, A D
EM: hawkesa@sas.upenn.edu
AF: University of Pennsylvania, Earth and Environmental Sciences 240 South 33rd Street, Philadelphia, PA 19104, United States
AU: Horton, B P
EM: bphorton@sas.upenn.edu
AF: University of Pennsylvania, Earth and Environmental Sciences 240 South 33rd Street, Philadelphia, PA 19104, United States
AB: Paleoseismologists infer the amount of coseismic subsidence during plate-boundary earthquakes from stratigraphic changes in microfossils across sharp peat-mud and peat-sand contacts. However, the use of lithostratigraphic-based reconstructions is associated with a number of limitations, and these become particularly significant when examining low amplitude, short period variations that occur during a plate-boundary earthquake. To address this, paleoecologists working in the coastal zone have recently adopted a transfer- function approach to environmental reconstruction. Continuing subduction of the Juan de Fuca plate beneath the North America plate constitutes a major seismic hazard in the Pacific Northwest. The subduction zone interface presently lacks seismicity. The timing of the last great earthquake along the Cascadia subduction zone (1700AD) is now well refined by Japanese records of an orphan tsunami (no causal earthquake was felt in Japan) that was generated from an earthquake off the Pacific Northwest on the evening of January 26th 1700AD. I will apply the transfer function to modern foraminiferal datasets along coastal Oregon to analyze the fossil record and quantitatively determine the amount of vertical land movement associated with the 1700AD earthquake event. To date, we have collected 7 modern transects totaling 132 samples from the intertidal zone to the upland. We have also collected 9 cores recording the 1700AD earthquake. Furthermore, a 4m vibracore was collected and contains between 3 and 5 potential earthquake horizons. The 1700AD earthquake in the vibracore shows a distinct litho- and biostratigraphical change representing an instantaneous episode of subsidence of approximately 1m. However, development and application of the transfer function to such events will provide quantitative constrained estimates of coseismic land movement. Measurements that are more accurate are necessary to help modelers develop simulations that are more realistic in order to better assess earthquake and tsunami hazards. This will enable efficient and effective mitigation planning and preparation to minimize the personal and economic costs associated with such hazards.
DE: 3030 Micropaleontology (0459, 4944)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly