Study of coseimic displacement field of the YUSHU MS 7.1 earthquake derived from Envisat/Asar data

We used the radar data from the satellite ENVISAT/ASAR of ESA and the differential interferometric synthetic aperture radar (D-InSAR) technology to derive the coseismic displacement field produced by the Yushu, Qinghai Province, China Ms 7.1 earthquake on 14 April 2010. Based on processing SAR data acquired before and after the event by the two-pass method, we obtained the interferometric fringe map which covered the causative fault (Ganzi-Yushu fault) and determined the deformation scope caused by the shock. Three arc second SRTM DEM was used for removing the topographic phase. Atmospheric delayed phase related to terrain was eliminated. MCF phase unwrapping method was performed to the interferometric fringe map for yielding digital image of the interferometric displacement field, which was analyzed by displacement contours and the profile across the fault. The result shows that the Yushu Ms 7.1 earthquake has produced a surface deformation area of about 89km×59km, along the Ganzi-Yushu fault. But in the vicinity of the fault, about 70km×27km, the deformation fringes are dense and thin, meaning the deformation gradient is big, where should be main devastated region. The whole deformation field is captured by a set of ellipse-like fringes, which converge towards the fault indicative of increasing gradient and amplitude of displacements, exhibiting sunk north wall and uplifted south wall in sight line. This movement direction in sight line just agrees with the left motion faulting of Ganzi-Yushu fault. We can count at least 6 fringes, equivalent to a displacement of 17cm in southern side and 10 fringes equivalent to a displacement of 28cm in northern side. The maximum relative displacement between the north and south walls at least reach 45cm that appears nearby the Jiegu Town of Yushu county in Qinghai Province, where is the most destroyed area in the event. Along the fault strike, there are three locally distorted areas, respectively present at the - - epicenter and around the Jiegu Town. The profile across the fault indicates that deformation is highly variable gradients with profound heterogeneity near the fault. All these results are coincide with the field investigation. Interferometric synthetic aperture radar (InSAR) has become an important geodetic imaging technique to map deformation of Earth´s surface. Particularly, this method has been successfully employed to measure coseismic surface displacements produced by several great earthquakes.