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sumatra turbidites

HR: 0800h
AN: T11D-2129 Poster
TI: Testing the validity of using turbidites as an earthquake proxy on the Sumatran margin
AU: Sumner, E
EM: esther.sumner@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: Siti, M
EM: Marina.Siti@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: *McNeill, L C
EM: lcmn@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: Talling, P J
EM: Peter.Talling@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: Wynn, R
EM: rbw1@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: Henstock, T
EM: then@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, Southampton, United Kingdom
AU: Djajadihardja, Y
EM: iyung@ceo.bppt.go.id
AF: Agency for the Assessment and Application of Technology (BPPT), Jakarta, Indonesia
AU: Permana, H
EM: permhp@yahoo.com
AF: Research Center for Geotechnology, Indonesia Institute for Sciences, Bandung, Indonesia
AB: The second largest earthquake ever recorded (Mw 9.2) occurred on the Sumatran margin on 26th December 2004; the earthquake and consequent tsunami resulted in the deaths of over 200,000 people around the Indian Ocean; in 2005 a second large earthquake (Mw 8.7) occurred, killing over 2000 people. It has been proposed that the deposits from submarine turbidity currents (turbidites) can be used to reconstruct earthquake records for some convergent margins. This is based on the assumption that large earthquakes cause shaking that triggers submarine landslides; these slope failures become diluted as they move downslope, generating turbidity currents that spread out over large geographical areas; and that the turbidites deposited by these earthquake-generated flows can then be sampled, dated and correlated. In 2009 sediment cores were collected on three seismic segments along the Sumatran margin (between Simeulue and the Batu Islands) with the aim of comparing the frequencies of earthquakes across different seismic segments. The focus of our initial research has been to analyse the distribution of deposits related to the two most recent large earthquakes in 2004 and 2005 in order to validate the method of using turbidites as earthquake indicators across the Sumatran margin. Surprisingly, we found no evidence of deposits from the 2004 and 2005 earthquakes in slope basins on the accretionary prism within our study area. We did find potential evidence of recent deposits in the trench. However, accurate dating of trench deposits has proved difficult as they do not correlate with the turbidite record in slope basin cores and do not contain carbonate material for AMS dating. We are also currently using geochemical techniques and AMS dating to test whether an ash layer found at a similar depth in cores on one of the seismic segments can be correlated. If this ash layer is correlatable, then it contains different numbers of turbidites between it and the present-day seafloor in adjacent slope basins and in the trench. The lack of deposits related to recent earthquakes in slope basins; the lack of correlation between slope and trench cores; and potentially the variable number of turbidites in adjacent basins over the same time period suggests that turbidites do not provide a simple and reliable record of large earthquakes on the Sumatran margin.
DE: [7221] SEISMOLOGY / Paleoseismology
DE: [7240] SEISMOLOGY / Subduction zones
DE: [9340] GEOGRAPHIC LOCATION / Indian Ocean
SC: Tectonophysics (T)
MN: 2010 Fall Meeting