Fault Source Modeling of the 2008 Wenchuan Earthquake Based on ALOS/PALSAR Data

We use crustal deformation data sets derived from satellite-based synthetic aperture radar (SAR) to develop a fault source model of the 2008 M w  7.9 Wenchuan earthquake, China, that occurred at the Longmen Shan fault zone. The data sets include interferometric SAR (InSAR), range offset, and azimuth offset data acquired at seven ascending paths. The range and azimuth offset data are particularly important, exhibiting a single major rupture to the northeast (NE) and multiple ruptures to the southwest (SW). Our preferred model consists of six segments; four follow the previously mapped traces of the Beichuan fault (BF) and its NE extension, one corresponds to the Pengguan fault (PF) to the SW, and the other is included to represent a conjugate fault to the SW. Fixing the location and geometry of those segments, we solve the variable slip distribution whose patch size increases toward the greater depth; we use a nonnegative least-squares method with a smoothing constraint on the distributed slip. The geodetically estimated moment is 1.05×10 21 N m ( M w =7.9), which is close to the seismological estimate and suggests that there are insignificant postseismic signals in the data. Maximum slip of ∼10 m, consisting of both thrust and right-lateral slip components, is identified at the shallowest patches to the NE along the BF. The multiple fault segments to the SW show that the thrust slip component initially dominates, and the strike slip becomes significant toward the NE. Examining the sensitivity of the predicted azimuth offset data to the assumed dip angle, we found that the dip angle changed significantly from 35°–45° at the SW fault segment for the PF to 80°–90° at the NE extension of the BF.