HR: 0800h
AN: S31C-0565    [Abstracts]
TI: Evidence for Late Holocene Paleo Earthquakes on the Aceh Portion of the Sumatran Subduction Zone, Northwest Sumatra
AU: * Kelsey, H M
EM: hmk1@humboldt.edu
AF: Dept. of Geology, Humboldt State Univ., 1 Harpst St., Arcata, CA 95521, United States
AU: Rubin, C M
EM: charlier@geology.cwu.edu
AF: Department of Geological Sciences, Central Washington University, 400 E. University Way, Ellensburg, WA 98926, United States
AU: Horton, B
EM: bphorton@sas.upenn.edu
AF: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, United States
AU: Yulianto, E
EM: ekoy001@yahoo.com
AF: Research Center for Geotechnology, Gd.70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AU: Hawkes, A
EM: hawkesa@sas.upenn.edu
AF: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, United States
AU: Natawidjaja, D H
EM: danny@gps.caltech.edu
AF: Research Center for Geotechnology, Gd.70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AU: Daryono, M
EM: van_mudrik@yahoo.com
AF: Research Center for Geotechnology, Gd.70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AU: Grand Pre, C
EM: grandpre@sas.upenn.edu
AF: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, United States
AB: We investigated coastal lowland environments of the northwestern coast of Sumatra to determine whether there is stratigraphic evidence for rapid subsidence accompanying prehistoric subduction zone earthquakes on the Aceh portion of the Sumatran subduction zone. Characterizing late Holocene vertical land-level changes will help identify paleo subduction zone earthquakes and will help constrain the width of the slip patch during these earthquakes. Our preliminary results suggest that, at least at two times in the past ca. 4000 years, regional coseismic subsidence events have occurred along the northwestern Aceh coast and are recorded in stratigraphy from coastal wetland environments. The stratigraphic signature of two paleo earthquakes each includes a regionally-extensive buried tidal wetland soil. Although there are tsunami deposits above each of these regionally extensive buried soils, these tsunami deposits are not as thick or as extensive as the 2004 tsunami deposit that presently blankets the coastal lowland of northwest Sumatra. We also document that the 2004 Andaman-Aceh earthquake caused more than a meter of subsidence along portions of the northwestern Sumatra coast. Although our work is preliminary, we note two significant conclusions to date. First, paleo earthquakes of the Aceh portion of the Sumatran subduction zone are well recorded in coastal wetland stratigraphy as regionally extensive buried soils preserved because of coseismic subsidence. Second, unlike coastal areas of the southwest Pacific and eastern Indian oceans that are removed from active subduction margins, the Aceh coastal lowland stratigraphy records a multiple-thousand year record of relative sea level change, probably because in the particular setting of northwestern coastal Sumatra, local vertical tectonic displacement is the dominant process affecting relative sea level history in the last ca. 5000 years. This history of vertical tectonic displacements records a time-series of long term seismic behavior of the Sunda megathrust along the northwest coast of Sumatra.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7221 Paleoseismology (8036)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting