The activity characteristics and comprehensive geophysical evidence of the Zhangyan–Jinshanwei concealed active fault in Shanghai, China

Abstract

The concealed faults in the urban area of Shanghai are well-developed, accumulating several hundred meters of loose sediment layers since the Quaternary. Hindered by the complex and highly disturbed urban environment, the detection and characterization of concealed faults face challenges, posing significant geological risks for urban safety. This study employs high-precision gravity area measurements, high-resolution shallow seismic exploration, and geophysical exploration methods. It integrates geological stratification from surrounding boreholes, stress, and chronostratigraphy analyses (C14 and optically stimulated luminescence) to investigate the Quaternary and current activity of the Zhangyan–Jinshanwei fault. Results show that the fault exhibits good spatial continuity, with evidence reflected in Bouguer gravity anomalies and seismic time profiles. The Zhangyan–Jinshanwei fault is identified as a thrust fault with inherited and newly developed activity characteristics. Its overall trend is northwestward at 315°, dipping southwest, with a fault distance of approximately 10 meters along the bedrock surface. The upper fault point has been displaced to the mid-Pleistocene in the Quaternary. The most recent active period occurred during the mid-Pleistocene, and the current northwestward stress state makes the fault susceptible to extensional and torsional activities. Continuous attention is required for the ongoing activity of this fault. This study's detection approach and findings can serve as a reference for similar urban concealed active fault detection and activity analysis.

Keywords

• concealed active fault
• zhangyan–jinshanwei fault
• high precision gravity area measurement
• high-resolution shallow seismic exploration
• chronology
• crustal stress