Interseismic Strain Along the Northern Edge of Tibet Using SAR Interferometry

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The current rate of strain concentrated along the Altyn Tagh and Kunlun fault systems in northern Tibet is being determined using the technique of radar interferometry. These fault systems play a key role in the dynamics of the continental deformation in Asia, yet their slip rate and associated deformation are still poorly known. Currently debated issues include the respective amounts of the convergence between India and Asia that are absorbed by crustal thickening and by lateral extrusion of continental blocks, or the characterization of the distribution of deformation throughout the continent. These issues are unresolved because of the poor knowledge of the present-day kinematics in the collision zone. In addition, northern Tibet has been the locus of two large earthquakes in 1997 and 2001 producing a disruption in the current inter-seismic strain pattern in the northern part of the collision zone. Spatially continuous maps of the line of sight displacement of the ground along active fault zones are being constructed by interferometric processing of synthetic aperture radar (SAR) data. This research exploits the extensive archive of ERS SAR data covering the northern Tibet area that have been acquired by the European Space Agency since 1992. Errors in the data due to poor orbit determination and troposphere phase propagation delay are reduced using a baseline re-estimation procedure and data averaging, following the approach developed with radar data of California. Line of sight displacement maps are then combined to constrain deformation process models of long-term fault creep and of co-seismic slip and post-seismic relaxation for the 1997 and 2001 events. The data are used to determine distribution of inter-seismic strain in the vicinity of the Kunlun and Altyn Tagh faults, far-field slip-rate associated with the faults and variation of rates along the length of the faults, surface displacement associated with the 1997 and 2001 earthquakes, possible linkage between these two events, influence of post-seismic processes on the strain accumulation in other sections of the fault. Slip rates are being compared with long-term rates inferred from geological observations.