HR: 16:15h
AN: S24A-02 INVITED    [Abstracts]
TI: Coseismic, Postseismic, and Interseismic Deformation, and Long-Term Segmentation Near the Boundary of the 2004 and 2005 Sunda Megathrust Ruptures
AU: * Meltzner, A J
EM: meltzner@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MC 100-23, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MC 100-23, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Briggs, R W
EM: briggs@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MC 100-23, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Philibosian, B E
EM: bphilibo@uoregon.edu
AF: Tectonics Observatory, California Institute of Technology, MC 100-23, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Chiang, H
EM: d91224004@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AU: Chiang, H
EM: d91224004@ntu.edu.tw
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455, United States
AU: Shen, C
EM: river@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AU: Shen, C
EM: river@ntu.edu.tw
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455, United States
AU: Suwargadi, B W
EM: bambang.suwargadi@geotek.lipi.go.id
AF: Puslit Geoteknologi LIPI, Komplek LIPI, Gd. 70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AU: Natawidjaja, D H
EM: danny@gps.caltech.edu
AF: Puslit Geoteknologi LIPI, Komplek LIPI, Gd. 70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AB: Simeulue Island, off the west coast of northern Sumatra, straddles the boundary of the 2004 and 2005 Sunda megathrust ruptures. The 2004 and 2005 earthquakes nucleated northwest and southeast of Simeulue, respectively, and each ruptured bilaterally toward the 100-km-long island. Cumulative uplift was 1.5 m at both the northwest and southeast tips of the island but diminished toward the island's center, where uplift was 0.5 m or less. Hence, although the 2004 and 2005 uplifts overlapped, there was an uplift deficit, or saddle, on central Simeulue. In addition to enabling observations of coseismic uplift, Porites coral microatolls enable measurements of postseismic and interseismic elevation changes. Whereas uplift in the year after May 2005 was negligible (< 10 cm) at the northwest and southeast ends of Simeulue, 30 cm of postseismic uplift occurred during that period in central Simeulue. Moreover, analysis of microatoll morphology indicates that, averaged over decades and longer, interseismic strain accumulation rates are lower in central Simeulue than at the island's ends. In the region of the Simeulue Saddle, we find evidence for up to ~20 cm of uplift at about the time of and possibly related to the M 7.3 foreshock of Nov 2002. Additionally, at one site in central Simeulue, we see evidence for multiple moderate (30-70 cm) subsidence events and multiple moderate (70 cm or less) uplift events over the past millennium. Although, in the fossil coral record, it is difficult to distinguish between single coseismic events, earthquake couplets a few years apart, and slow slip events spanning days to years, such subsidence and moderate uplift events are rare outside the Simeulue Saddle. These moderate events appear to be loosely clustered in time. Historical intensity data imply that prior to 2005 the last great earthquake caused by rupture of the megathrust under Nias island, to the south, occurred in A.D. 1861; initial U-Th dates from uplifted fossil microatolls suggest that, like the 2005 rupture, the 1861 rupture extended north to southern Simeulue, but that uplift did not extend to northern Simeulue. Additional preliminary U-Th dates from uplifted fossil microatolls suggest that earlier earthquakes, some time around A.D. 1843 and A.D. 1799, also involved rupture of Nias and southern Simeulue. Thus it appears that the ~1799, ~1843, 1861 and 2005 ruptures were similar in that they extended into but not through the Simeulue Saddle. However, at sites in southeastern Simeulue, uplifts in ~1799 and in ~1843 were much smaller than in 2005, and the ~1799, ~1843, and 1861 events may be regarded as a triplet. Altogether, these observations suggest that the Simeulue Saddle is a poorly coupled segment of the megathrust that serves as a persistent barrier to rupture.
DE: 1209 Tectonic deformation (6924)
DE: 7221 Paleoseismology (8036)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting