A Study on Segmentation Characteristics of Aftershock Source Parameters of the Wenchuan M8.0 Earthquake in 2008

We use the seismic data recorded at the network stations of Sichuan Province to determine source parameters of 1070 aftershocks with ML ≥ 3.0 of the Wenchuan M8.0 event on 12 May 2008. Before the calculation, the attenuation effects and site responses are removed accurately. The result shows that there is a linear relation between seismic moment and magnitude, and the stress drop and apparent stress increase with increasing magnitude. The temporal and spatial process of stress drop derived from seismic data with ML3.0 shows that the stress drop of Wenchuan aftershocks decays with time as a whole after the mainshock occurred. Bounded by the line along Huya–Beichuan–Anxian, the activity level and stress drop in the Longmen Shan fault appear to be segmental. Aftershocks with ML ≥5.0 mainly occurred at the west of Beichuan in the Longmen Shan fault and the values of stress drop in this area are lower before May 17. Meanwhile, the activity level between Beichuan and Qingchuan is weak comparatively and the stress drop there maintains a high level. However, the primary area of aftershocks with ML ≥5.0 shifted to between Beichuan and Qingchuan after May 17 and the biggest aftershock of M6.4 took place in Qingchuan on May 25 and the change of stress drop with time of the aftershocks appeared to become smooth since then.