Precision evaluation and characteristics analysis of the coseismic deformation field of the 12th may 2008 Wenchuan Ms8.0 earthquake

Based on the improved DInSAR technology, this paper obtained the whole coseismic deformation field of the Wenchuan Ms 8.0 earthquake by 128 frames of Level1.0 data of ALOS PALSAR. By comparing with the continuous GPS survey results, the precision of coseismic deformation field was estimated as about 9.5 cm, better than half-wavelength of L-band. The whole coseismic deformation stripe has a total length of about 300 km, which encircles the NE-trend seismic ruptures, and is mostly distributed within 19-100 km from the fault rupture. The spatial distribution of coseismic deformation gradually narrows down from southwest to northeast, owing to the fact that the seismic energy gradually decayed along the NE-trend from Yingxiu where the seismic fracture begins to Qingchuan where it ends. There is a weak coherence zone near the seismic rupture relating to strong displacements, such as landslide, mud and rock flow, etc. And this weak coherence zone obviously extends wider in south Beichuan than in north Beichuan, which is corresponding to the fact that two parallel rupture faults exist in south Beichuan while only one exists in north Beichuan. The 471-track deformation is produced mainly by Qingchuan Ms 6.4 dextral-strike aftershock and other strong aftershocks, and therefore its deformation field is discontinuous with adjacent tracks. As a whole, northwest plate-Bayankala Block was uplifted, while southeast plate-rigid Sichuan Basin subsided, and both sides of the seismic rupture were uplifted. But there exist one subsided zone 10-30 km away from the rupture in the Bayankala Block. Synthetically analysis shows that, under the effect of the huge eastward pushing force from Tibet, the Bayankala Block was resisted by the rigid Sichuan Basin when it thrust along the high-angle seismic rupture, and then its east margin bent to form a subsided zone to absorb and release the strong eastward thrusting force.