HR: 1330h
AN: T52A-0241    [PDF]
TI: INTERSEISMIC STRAIN ALONG THE SUMATRA SUBDUCTION ZONE: A CASE FOR A LOCKED FAULT PORTION EXTENDING WELL BELOW THE FOREARC MOHO
AU: * Simoes, M
EM: simoes@gps.caltech.edu
AF: Laboratoire de Geologie - Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: * Simoes, M
EM: simoes@gps.caltech.edu
AF: GPS department - California Institute of Technology, 1200 E. California Bvd, Pasadena, CA 91125 United States
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Laboratoire de Geologie - Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: GPS department - California Institute of Technology, 1200 E. California Bvd, Pasadena, CA 91125 United States
AU: Cattin, R
EM: cattin@geologie.ens.fr
AF: Laboratoire de Geologie - Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Henry, P
EM: henry@geologie.ens.fr
AF: Laboratoire de Geologie - Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Natawidjaja, D H
EM: danny@gps.caltech.edu
AF: GPS department - California Institute of Technology, 1200 E. California Bvd, Pasadena, CA 91125 United States
AB: A current and most accepted view about the seismogenic zone along subduction zones is that the downdip extent of the locked fault portion would correspond either to the 350$\deg$C isotherm if this temperature is reached above the Moho, or to the intersection with the forearc Moho for colder subduction zones [Oleskevich et al., 1999]. This limit would reflect the transition from slip-weakening friction to aseismic stable-sliding, or else ductile flow. In the first case, when the downdip end of the locked zone is temperature-controlled, stable-sliding of quartzo-feldspathic rocks would be the controlling factor, while the systematic presence of serpentinite or other hydrated minerals is advocated to explain aseismic interplate slip in the mantle at temperatures much less that the 750$\deg$C needed for ductile flow of mantle rocks [Peacock and Hyndman, 1999]. Here, we consider the case of the Sumatra subduction zone where the ~53 Myr Indian oceanic crust subducts below an island-arc characterized by a relatively thin crust, with a Moho depth estimated to ~23 km. We model interseismic deformation from a creeping dislocation embedded in an elastic half-space, using the back-slip approach. In addition to recently published GPS velocities, we take advantage of recent data on the pattern and rate of interseismic uplift that have been obtained from the study of coral growth [Natawidjaja, 2003; Sieh et al., 1999]. These data are found to put tight constraints on the horizontal position of the downdip limit of the locked fault zone, at 127 +/- 4/2 km from the trench. This position corresponds to a depth between 40 and 58 km and to a temperature of 269$\deg$C +/- 155$\deg$C, when compared with thermal modeling. So, in this particular setting, the locked fault portion extends well into the mantle. However, temperature is not high enough to advocate stable sliding or ductile flow of unaltered or altered mantle rocks. This case appeals to some reappraisal of the physical control on the depth of the locked fault zone along subduction zones. References. Natawidjaja, D.H., Neotectonics of the Sumatran fault and paleogeodesy of the Sumatran subduction zone., PhD thesis, California Institute of Technology, Pasadena, 2003. Oleskevich, D.A., R.D. Hyndman, and K. Wang, The updip and downdip limit to great subduction earthquakes : thermal and structural models of Cascadia, South Alaska, SW Japan and Chile., Journal of Geophysical Research, 104 (B7), 14965-14991, 1999. Peacock, S.M., and R.D. Hyndman, Hydrous minerals in the mantle wedge and the maximum depth of subdcution thrust earthquakes., Geophysical Research Letters, 26 (16), 2517-2520, 1999. Sieh, K., S.N. Ward, D. Natawidjaja, and B.W. Suwargadi, Crustal deformation at the Sumatra subduction zone revealed by coral data., Geophysical Research Letters, 26 (20), 3141-3144, 1999.
DE: 1206 Crustal movements--interplate (8155)
DE: 3902 Creep and deformation
DE: 7230 Seismicity and seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting