On 21 March 2008,a Ms7.3 earthquake occurred at Quickbird,Yutian County,Xinjiang.We attempt to reveal the features of the causative fault of this shock and its coseismic deformation field.Our work is based on analysis and interpretation to high-resolution satellite images as well as differential interferometric synthetic aperture radar(D-InSAR) data from the satellite Envisat SAR,coupled with seismicity,focal mechanism solutions and active tectonics in this region.The result shows that the 40km-long,nearly NS trending surface rupture zone by this event lies on a range-front alluvial platform in Qira County.It is characterized by distinct linear traces and simple structure with 1-3-m-wide individual seams and maximum 6.5m width of a collapse fracture.Along the rupture zone many secondary fractures and fault-bounded blocks are seen,exhibiting remarkable extension.The coseismic deformation affected a large area 100×100km2.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.Because of the big deformation gradients near the seismogenic fault,no interference fringes are seen on images,and what can be determined is a vertical displacement 70cm or more between the two fault walls.According to the epicenter and differential occurrence times from the National Earthquake Information Center,China Earthquake Network Center,Harvard and USGS,it is suggested that the seismic fault ruptured from north to south.
