Interseismic deformation along the central segment of the Altyn Tagh Fault (Tibet, China) determined by SAR interferometry

HR: 1340h
AN: G53A-0872 [Abstracts]
TI: Interseismic deformation along the central segment of the Altyn Tagh Fault (Tibet, China) determined by SAR interferometry
AU: * Socquet, A
EM: socquet@ucla.edu
AF: Department of Earth and Space Sciences, UCLA, Geology Building 595 Charles E. Young Drive East, Los Angeles, CA 90095 United States
AU: Peltzer, G
EM: gilles@altyn.ess.ucla.edu
AF: Department of Earth and Space Sciences, UCLA, Geology Building 595 Charles E. Young Drive East, Los Angeles, CA 90095 United States
AU: Peltzer, G
EM: gilles@altyn.ess.ucla.edu
AF: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA CA91109 United States
AU: Lasserre, C
EM: lasserre@geologie.ens.fr
AF: Department of Earth and Space Sciences, UCLA, Geology Building 595 Charles E. Young Drive East, Los Angeles, CA 90095 United States
AU: Lasserre, C
EM: lasserre@geologie.ens.fr
AF: Laboratoire de GＰlogie, Ecole Normale SupＳieure, 24 rue Lhomond, Paris, 75005 France
AB: We map the interseismic strain across the Altyn Tagh fault system using ERS satellites InSAR data. The time interval of the interferometric pairs spans up to 5.5 years, from 1996 to 2001. The data are not affected by the co-seismic displacements associated with the Mw=7.8, November 2001, Kunlun earthquake. The 1997 Mw=7.6, Manyi earthquake was located 500 km away from the interferograms area and generated negligible deformation in the study area. The main error source here comes from the phase propagation delay in the troposphere, enhanced by the topographic step of ~3000 m at the northern edge of the Tibet Plateau. To avoid large atmosphere-related errors, we selected SAR images acquired during the winter months when the atmosphere contains less precipitable water vapor than in the summer. For interferograms showing some stable, residual tropospheric effects, we apply a first-order correction using an empirical approach based on the local correlation between the phase delay and the topography. We focus here on the central segment of the fault, from 88°E to 92°E, where the relative Tibet / Tarim motion is partitioned between two main parallel structures separated by ~150 km: the Altyn Tagh sinistral strike-slip fault oriented N70°E, to the south, and a south-dipping thrust following the footwall of the Altyn Shan range to the north. In all interferograms, the range change observed across the Altyn Tagh fault is compatible with a left-lateral slip at depth on the fault. However, the horizontal motion along the fault is combined in the radar line of sight with the vertical motion produced by the adjacent thrust. We use a two-faults elastic half-space dislocation model to compute the surface deformation produced by strike-slip on the Altyn Tagh fault and up-dip movement on the northern thrust. We explore the range of possible slip rates that fit the InSAR observations and compare them with independent geodetic and neotectonic estimates that vary from 9 to 26 mm/yr of strike-slip in the area.
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 6924 Interferometry (1207, 1209, 1242)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 9320 Asia
SC: Geodesy [G]
MN: Fall Meeting 2005