Quaternary activity of the Luodian-Zhoupu buried fault in the Shanghai region: Integrated exploration and research

Abstract

The Luodian-Zhoupu fault is an important NW-trending buried active fault that runs through the downtown area of Shanghai City. Its Quaternary activity significantly affects the urban geological safety. We applied a set of integrated geophysical methods to carry out high-precision gravity, shallow seismic and controlled source audio magneto telluric (CSAMT) explorations in the study area, and studied the distribution pattern and activity level of the Luodian-Zhoupu fault, combining with joint borehole profile and optically stimulated luminescence chronology. The exploration results reveal good ductility of the fault in southern Shanghai, and the fault trace is well reflected in the profiles of gravity, CSAMT and shallow artificial seismicity. Gravity area measurements show that the fault appears as a group of nearly parallel fault tracks in southern Shanghai. The buried depths of the shallowest breakpoints researched by the shallow seismic exploration and joint borehole profile method are in good agreement (~200 m). TCSAMT profile displays obvious deep fault features. The research outcomes from the profiles with geophysical exploration and joint borehole indicate no obvious trace of the fault breaking into the overlying Middle Pleistocene, and it is believed that the latest active age of the fault is the Early Pleistocene referring to the result of optically stimulated luminescence dating. Since the Luodian-Zhoupu fault is closely related to regional historical seismic events, and the regional stress state is currently NW-compressive, with the fault prone to tensile and torsional activities, its activity and seismic risk characteristics require continuous attention.

Keywords

• luodian-zhoupu buried fault
• quaternary activity
• integrated geophysical exploration
• joint borehole profile