Analysis of Geological Background of Seismic Activity in the Chengdu Plain from Data of Seismic Prospecting for Oil

Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum organizations in Sichuan and of the results of seismic prospecting and detailed exploration in Chengdu depression during the last 20 years permitted us to study the types and distribution of hidden structures in Chengdu depression and its adjacent areas, in particular, to identify in detail the “hidden faults" in the Chenngdu-Deyang area on the one hand; The obtained data indicate that the NE-trending Xinjin fault runs northward and dies out in the south of Penzhen town of Shuangliu County. Meanwhile, we studied genetic relations of seismic activity to active faults and their corresponding movement characteristics on the other hand. Moreover, the surface faults and deep-seated faults are clearly defined and outlined, and 5 types of seismogenic faults suggested. The knowledge thus obtained enables us to delimit the focal zones for potential strong earthquakes in Chengdu depression. The study suggests that a zone of 40 km wide and more than 100 km long on sides along the Chengdu-Deyang line has a stable seismogeological background and good engineering-seismological conditions.