Source characteristics of Yutian earthquake in 2008 inversed from co-seismic deformation field mapped by InSAR

On 21 March 2008, an Ms7.3 earthquake occurred at Quickbird, Yutian County, Xinjiang. The earthquake is located in the depopulated Kunlun Mountains of an elevation over 5000m, featured by thin air, cold weather and extremely bad conditions, where field investigations would be formidable. Besides, there is no station for deformation measurements in an area of several hundreds km2 surrounding the epicenter. Consequently, there is little knowledge on the causative fault and coseismic deformation of this event. We attempt to fill this gap by means of satellite remote sensing and DInSAR (Differential Interferometric Synthetic Aperture Rader).We attempt to reveal the features of the causative fault of this shock and its coseismic deformation field by a sensitivity- based iterative fitting (SBIF) method. Our work is based on analysis and interpretation to high-resolution satellite images as well as DInSAR data from the satellite Envisat SAR, coupled with seismicity, focal mechanism solutions and active tectonics in this region. The result shows that the 22km-long, nearly NS trending surface rupture zone by this event lies on a range-front alluvial platform in the Qira County. It is characterized by distinct linear traces and simple structure with 1~3m-wide individual seams and maximum 6.5m width of a collapse fracture. Along the rupture zone are seen many secondary fractures and fault-bounded blocks by collapse, exhibiting remarkable extension. The coseismic deformation affected a big range 100km and 40km. D-InSAR analysis indicates that the interferometric deformation field is dominated by extensional faulting with a small strike-slip component. Along the causative fault, the western wall fell down and the eastern wall, that is the active unit, rose up, both with westerly vergence.The minimum subsidence displacement is -2.6m in the LOS, and the maximum uplift is 1.2m. The maximum relative vertical dislocation reaches 4.1m,which is located at the distance of 10km along the fault from the starting rupture point to south. The fault plane is 42km long, extending from north to south in arc shape with variable dip angles from 70° at the surface to 52° at the depth of 20km.The larger slip areas are concentrated on three areas, forming a belt with the depth less than 8km along dip, length of 30km along strike on fault plane. The largest slip area with the maximum slip 10.5m is located at the area with distance of 10km from the starting edge along the strike.