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Earthquakes displacement and fault slip-rates in Tibet from ERS interferometry

Gilles Peltzer(1) and Mike Taylor(1)

(1) University of California Los Angeles, 595 Charles Young Dr. East, Los Angeles, CA 90095, United States

Abstract

The tectonics of the Tibetan plateau is characterized by large fault systems accommodating a significant fraction of the deformation induced by the collision between India and Asia. Because of difficult access to this remote region, many of these faults have remained unexplored and little is known about their current slip-rate and their contribution to the deformation within or around the plateau. 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 two 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. Earthquakes: ERS data from three adjacent ERS tracks revealed the details of the 170 km-long surface break of the M7.6, 1997 event and the associated displacement field. The data from 6 adjacent tracks barely covered the 400 km-long surface break produced by the M7.8, 2001 event. In both cases, these observations allowed us to derive fault slip models for the earthquake with a resolution exceeding that achieved in regions highly populated with ground-based geodetic instruments such as California. Interseismic deformation: In other parts of Tibet, we have measured interseismic strain accumulation along strike-slip faults using image pairs covering time intervals of 4 to 7 years. 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 ~2 cm/yr of left-lateral creep on the deep part of the fault. Such a rate confirms the major role played by this fault in accommodating the north-eastward movement of the plateau with respect to stable Eurasia. The same approach has revealed surprisingly fast rates on smaller faults along the Karakorum-Jiali fault zone in central Tibet. These faults contribute to the lateral extrusion of small crustal wedges and north-south contraction in the interior of Tibet. These findings demonstrate the enormous potential of long time series of SAR observations to detect and measure the effects of localized strain in fault zones in response to the far field motion of tectonic plates. 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 of the generation of earthquakes.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry