Modelling of Yingxiu-Beichuan fault zone based on refined DInSAR data of 2008 Wenchuan earthquake

- Fault slip was predominantly thrust in the SW and changed to dextral slip in NE.
- The dip angles of the Longmenshan fault system are increasing from the SW to NE.
- In the parallel fault zone, displacement has been transferred to the PF from YBF.
- PF is the main fault that intercepts the YBF at a depth of 13 km.
- Qingchuan fault segement is set to a blind thrust to match the actual fringe pattern.

Differential interferometric synthetic aperture radar (DInSAR) provides an essential constraint for forward modelling of seismic faulting. However, the crucial evidence of deformation along the very near vicinity of a seismic fault is often missing because chaotic ruptures destroy the InSAR signal coherence; such is the case of the Yingxiu-Beichuan fault zone of the 2008 Wenchuan earthquake. We developed an Adaptive Local Kriging (ALK) interpolation method to produce a refined DInSAR dataset which continues without the interruption of decoherence gaps. Thus the 3D configuration of the seismic faulting can be better constrained for forward modelling using the Poly3D software. Through parameter fine tuning in a sequence of trial and error simulation, the best fitting between the simulated interferogram and the ALK refined DInSAR interferograms is achieved using a structural model of the Yingxiu-Beichuan fault zone which comprises a total of 14 segments with dip angles varying from 20° to 60°, in the south-west, to 40° to 70°, in the north-east; some major fault segments are composed of multiple planes with varying dip angles. The model reveals that in the much disputed Beichuan-Pengguan area, the Yingxiu-Beichuan fault links with the Pengguan fault (which dips to the NW at ~ 30°) at a depth of ~ 13 km. These two structures are interpreted as representing the foreland propagation of the Yingxiu-Beichuan fault by footwall collapse, a process that, in the vicinity of the Pengguan fault, involves the transfer of displacement from the older, Yingxiu-Beichuan fault to the younger Pengguan fault.