Gravity survey for buried geological structure of the Chengdu Plain, SW China

Abstract

The 2008 Wenchuan Ms 8.0 earthquake resulted in huge casualty and heavy strike to the local economy. Consequently, Chengdu Plain, with dense population and short distance to the highly active Longmen Shan fault zone needs an evaluation of the risk of earthquake as soon as possible. As part of a big project, we conducted mapping of gravity anomaly of Chengdu Plain in order to locate the possible buried fault zones beneath the Chengdu Plain. In this project a total of 640 km2 area was surveyed, and 230 relative gravity data have been collected along six profiles with each extending to about 70 km across the plain area. 140 more spots were measured around the city area in order to have a more precise delineation of geological structures beneath the city region. The Bouguer gravity anomaly has been calculated to delineate the large-scale anomaly trend on the surface. Data analyses presented that a coincidence between the sedimentation thickness and the residual gravity anomaly. The minimum residual anomalies suggested locations where depo-centers used to located (Pengzhou-Chongzhou, across Xinsheng County). The long-wave trend of Bouguer anomaly which reflects the deeply buried Moho discontinuity presented a northwest dipping trend of this density boundary underneath the plain region.