HR: 08:00h
AN: T31C-01    [Abstracts]
TI: Surface uplift and subsidence during the giant Sumatran megathrust ruptures of 2004 and 2005
AU: * Briggs, R
EM: briggs@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MS 100-23 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Meltzner, A
T31C-01 AF: Tectonics Observatory, California Institute of Technology, MS 100-23 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Sieh, K
T31C-01 AF: Tectonics Observatory, California Institute of Technology, MS 100-23 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Natawidjaja, D
T31C-01 AF: Tectonics Observatory, California Institute of Technology, MS 100-23 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Natawidjaja, D
T31C-01 AF: Research Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Komplek LIPI Gedung #70LIPI, Bullet Jl. Sangkuriang-Cisitu 21/154D, Bandung, 40135 Indonesia
AU: Galetzka, J
T31C-01 AF: Tectonics Observatory, California Institute of Technology, MS 100-23 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Suwargadi, B
T31C-01 AF: Research Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Komplek LIPI Gedung #70LIPI, Bullet Jl. Sangkuriang-Cisitu 21/154D, Bandung, 40135 Indonesia
AU: Hsu, Y
T31C-01 AF: Seismological Laboratory, California Institute of Technology, MS 252-21, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Suprihanto, I
T31C-01 AF: Research Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Komplek LIPI Gedung #70LIPI, Bullet Jl. Sangkuriang-Cisitu 21/154D, Bandung, 40135 Indonesia
AU: Hananto, N
T31C-01 AF: Research Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Komplek LIPI Gedung #70LIPI, Bullet Jl. Sangkuriang-Cisitu 21/154D, Bandung, 40135 Indonesia
AU: Prayudi, D
T31C-01 AF: Research Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Komplek LIPI Gedung #70LIPI, Bullet Jl. Sangkuriang-Cisitu 21/154D, Bandung, 40135 Indonesia
AU: Simons, M
T31C-01 AF: Seismological Laboratory, California Institute of Technology, MS 252-21, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: Substantial coseismic vertical deformation occurred above the Sumatran megathrust during the giant December 2004 and March 2005 earthquakes. We took advantage of a widely occurring natural tide gauge, coral microatolls of the genus Porites, to measure this coseismic deformation. Uplift associated with the 2004 event occurred on the northern half of Simeulue island, from about 2.5° to 2.9° N. This half of the island tilted down to the southeast, with maximum uplift of 1.5 m on the northwestern tip of the island. This provides a tight constraint on the southeastern limit of megathrust rupture during the 2004 Aceh-Andaman earthquake. Uplift during the 2005 Nias-Simeulue earthquake extends southeastward from the middle of Simeulue island (at 2.8° N) and continues across Nias island and the Equator. Augmented by continuous GPS data from our Sumatran GPS Array (SuGAr), the corals provide a dense array of measurements above and surrounding the 2005 rupture. The principal features of the vertical deformation pattern are two asymmetric, trench-parallel anticlinal uplifts on the forearc islands of Nias and Simeulue and a broad submergence trough between these islands and the mainland coast. Maximum uplift is 2.9 m and maximum submergence is 1.15 m. Uplift abruptly decreases westward from the anticlinal crest, indicating that slip on the megathrust decreased between the islands and the trench. The anticlinal crest and the pivot line marking the transition from emergence to submergence are predominantly trench-parallel, but have a pronounced misalignment near the Banyak Islands between Nias and Simeulue. This suggests that a major structural feature, perhaps a tear in the overriding plate, divides the March 28 2005 rupture area into a Nias and a Simeulue patch. This observation is in agreement with elastic models that invert coral and GPS geodetic data for slip on the fault. These reveal that two subevents on the megathrust best fit the observed pattern of surface deformation for the March 28 earthquake, with maximum slip of ~11 m below Nias and ~7 m below Simeulue. Although an elastic model of slip on the megathrust can explain the pattern of deformation, the presence of uplifted late Quaternary coral terraces on the islands suggests that some portion of the uplift in 2005 may be preserved as permanent deformation of the overriding block.
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 4220 Coral reef systems (4916)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005