HR: 08:15h
AN: T31C-02    [Abstracts]
TI: Coseismic and Postseismic Slip on the Sumatran Megathrust Following the 2005 Nias-Simeulue, Indonesia Earthquake
AU: * Hsu, Y
EM: yaru@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Simons, M
EM: simons@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Briggs, R
EM: briggs@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Meltzner, A
EM: meltzner@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125 United States
AU: Bock, Y
EM: ybock@popmail.ucsd.edu
AF: Institute of Geophysics and Planetary Physics, SIO, UCSD, La Jolla, CA 92093 United States
AU: Subarya, C
EM: csubarya@bakosurtanal.go.id
AF: National Coordination Agency for Surveying and Mapping, Cibinong, Cibinong, 16911 Indonesia
AU: Prawirodirdjo, L
EM: linette@gpsmail.ucsd.edu
AF: Institute of Geophysics and Planetary Physics, SIO, UCSD, La Jolla, CA 92093 United States
AB: Continuous GPS data collected before and after the 2005 Nias-Simeulue earthquake (Mw 8.6) show a maximum co-seismic horizontal displacement of 4.5 m and uplift of 2.9 m above the megathrust rupture. Postseismic displacements in the subsequent 4 months increased the horizontal displacement by 0.56 m and diminished the vertical by 0.15 m. Using these GPS data as well as vertical deformations measured from coral microatolls, we invert for the co-seismic and post-seismic slip distribution using an elastic-half space model that assumes a 450 km long, 250 km wide planar fault. The optimum fault dip angle is 15°. Coseismic slip occurred on two major patches, below the forearc islands of Nias and Simeuleu. Slip was as high as 11 m on the Nias patch and 7 m on the Simeulue patch. Modeling of postseismic displacements from the cGPS data indicates that afterslip within the first 4 months occurred both updip and downdip of the coseismic patches, with up to about 1 m of cumulative slip on the updip portion. We solve for the spatial and temporal evolution of afterslip using the Extended Network Inversion Filter. Shallow afterslip rates reached a maximum of about 3 m/yr and decayed to about 0.3 m/yr in four months. The cumulative afterslip on the updip portion of the plate interface is only 10% of the maximum coseismic slip. Deep afterslip decayed more slowly than updip afterslip, from a maximum of no more than about 0.6 m/yr. Both shallow and deep afterslip seem to have resulted from rate-strengthening frictional slip in response to the coseismic stress changes. These data provide unprecedented insight on the variation of interplate frictional properties and on how long-term tectonic deformation of the forearc relates to large subduction events.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: Fall Meeting 2005