Analysis of generation factors for tectonic deformation in the Xigeda formation in southwestern China

The Xigeda formation is a set of interbreds comprised of half consolidated silt, fine sand and clay with clear lamination and total thickness of 300 m. It is dated to be the early Pleistocene and widespread distributed on the Quaternary planes of denudation and leveling. This formation has particular tectonic deformation as expressed by deformed belts confined to certain locations, which extend linearly over long distances. It also manifests itself as graben and horst sequences where fault planes are very straight. Various deformation styles, such as horizontal, vertical and oblique dislocations, normal, reverse and thrust faulting resulted in tilts of small blocks in different directions. The clay beds are intruded by underlying sand layers. Parallel ridges and depressions characterize the landscape. These phenomena of deformation are probably the result of intensive vibration of soil bodies during major earthquakes which caused instantaneous shear, compression and extension. The analysis of generation factors for such tectonic deformation provides a new approach for determination of areas with seismic risks, assessment of earthquake intensity and research of earthquake mechanisms.