Present-day deformation rates along the northern edge of Tibet, using SAR interferometry
Cécile Lasserre(1) , Anne Socquet(2)
, Gilles Peltzer(2)
, Olivier Cavalié(1)
, and Jianbao Sun(3)
24 rue Lhomond,
(2) UCLA, 595 Charles E. Young Drive E., Los Angeles, CA 90095, United States
(3) CEA, Beijing 9803, Beijing 9803#, China
The tectonics of the northern Tibetan plateau is characterized by large strike-slip and thrust fault systems, accommodating the deformation induced by the collision between India and Asia. Since 1992, the ERS1 and ERS2 satellites have been acquiring SAR data over this vast region, providing scientists with a rich archive of imagery and interferometry data to support geological investigations. In ten years, the ERS instruments have captured the co-seismic and post-seismic surface displacements associated with the largest earthquakes ever recorded by seismic instruments in central Asia (1997 and 2001), as well as the slow, gradual strain accumulation along faults that have remained silent during this period.
We concentrate our efforts on estimating interseismic deformation along three sections of the main faults of northeastern Tibet. We use image pairs covering time intervals of 2 to 7 years to construct line of sight surface velocity maps. Difficulties to estimate ground motion along the northern edge of Tibet include (1) the 3 km topographic step between Tibet and Tarim across the Altyn Tagh fault, enhancing the tropospheric effects in the phase delays, and (2) the combination of strike-slip and thrust faults, producing partial trade-off in the observed line of sight displacement. We attempt to mitigate tropospheric delays using an empirical method based on the local correlation between phase and topography. We use simple elastic models that include both strike-slip and thrust faults to estimate slip rates on both types of fault. Near longitude E90, the data are consistent with a 10-17 mm/yr strike-slip motion on the Altyn Tagh fault, combined with a 1-2 mm/yr of thrust motion on a large thrust developped ~100 km north of the strike-slip fault. Near the city of Aksai (N39,E95), the line of sight surface displacement field observed in the vicinity of the Altyn Tagh fault is consistent with a 10-15 mm/yr of left-lateral movement on the fault. Similar studies are currently in progress along the Kunlun and Haiyuan faults, south and east of the Qaidam basin. The ten years series of data acquired by the ERS satellites should be continued by the ENVISAT satellite and other future missions to provide scientists with essential data to understand the physics of the deformation of continents and the generation of earthquakes.