Analysis of Structural Information from Aftershock Clouds—A Case Study of the 2008 Ms 8.0 Wenchuan Earthquake

Abstract

Abstract We present a method to quantitatively analyze the characteristics of clusters and extract cluster centers in aftershock clouds to study the corresponding structural information. Based on a cluster center approach, a 3D rupture surface is constructed based on the aftershocks of the Wenchuan earthquake. The geometric characteristics of the rupture surfaces show that the Longmenshan fault zone should be divided into seven segments from south to north, and for most of the rupture surfaces, there are two discontinuities at depths of 10 and 20 km. According to the cluster characteristic distance of each rupture branch, the number of aftershocks within the cluster distance is counted. The statistical results show that 22% of the aftershocks of the Wenchuan earthquake occurred on the rupture surface parallel to the main fault and that the rest occurred along other nonparallel rupture surfaces or were scattered. The complex branches of rupture surfaces and the existence of rupture surfaces penetrating the 10 km deep discontinuity layer are two common characteristics of the XI intensity area. The change in tendency of the fracture surface between depths of 10 and 20 km may restrain the continued northward extension of the XI intensity area.