Application of double-difference relocation technique to aftershocks of 2008 Wenchuan earthquake using waveform cross-correlation

We collected seismic records of 4240　3.0le;MSle;5.0 aftershocks of the 2008 Wenchuan earthquake for the period of 12 May 2008 to 31 August 2009. By using waveform cross correlation and double-difference method, 2441 events of them were relocated. The errors are 0.4 km in horizontal and 0.7 km in vertical direction, respectively. It is found that the depth of aftershocks concentrate in 10mdash;20 km range, and the epicenters distribute close to the strike of the central Longmenshan fault. The aftershock epicenters spread in horizontal belt for southwestern section of the aftershock zone, and in vertical belt for northeastern section. The aftershock depth abruptly change from 20 km to 10 km near Beichuan. This implies that the spatial distribution of aftershocks show different characteristics along Longmenshan fault, confirming the previous viewpoint that the fault is thrust in SW, while strike-slip in NE. Comparison of the aftershock relocation result with the existing shallow seismic exploration profiles reveals that the aftershock belts well match the known shallow geological active faults.