Coseismic and postseismic deformation of the 2008 Wenchuan Earthquake from InSAR

Abstract

On 12 May 2008,an M_w7.9 earthquake occurred on the Longmenshan fault system at the eastern margin of the Qinghai-Tihet Plateau near Wenchuan City.Here we obtained the ionospheric perturbations in Japanese ALOS/PALSAR images covering the epicenter of Wenchuan earthquake from the corresponding azimuth offsets,and determined highly precise and continuous InSAR surface displacements using those that are not strongly affected by ionospheric perturbations.Combing with the GPS coseismic deformation,a joint model considering both coseismic and postseismic phases is constructed to study the coseismic slip distribution of the Wenchuan earthquake and the viscous structure of the Longmenshan region.The best-fitting slip model suggests that the earthquake is an event with very complex fault rupture.The slips of Hongkou,Yuejiashan,Beichuan,and Hanwang segments are dominated by the thrust movement and the Qingchuan segment experiences a dominant right-lateral strike slip.The major slip occurred mainly at the depth of less than 10 km,with a maximum slip of 10.7 m on the northeastern Hongkou segment.The determined geodetic moment is approximately 9.28 × 10~(20) N ? m(M_w7.91),which is consistent with the results of seismology.The mid to lower crustal viscosity derived from the joint model in a Maxwell half-space is 2×10~(18) Pa ? s,which places a strong low bound on viscosity in the Longmenshan region.Postseismic displacements time series covering a longer time span might have the potential to improve this constraint.