High-resolution crustal thickness and VP/VS ratio in Shanghai and its neighboring areas with its tectonic implications

Abstract

We present a high-resolution crustal model for Shanghai and its neighboring areas, derived from H-κ stacking of receiver functions at 114 seismic stations. Our model corroborates the major tectonic subdivisions of the area by revealing significant lateral variations in crustal structure. The average Moho depth is 31.4 km. A distinct “thick-outside, thin-inside” structure is observed, with a deeper Moho beneath the Jiangsu-Zhejiang Uplift Zone (average 34.2 km) and a shallower one in the Yangtze River Delta Depression Zone (average 30.4 km). A notable fault-bounded crustal thickening anomaly within the Depression Zone further indicates complex deformation. The V_P/V_S ratio exhibits large variation (1.6–2.1), featuring a prominent Y-shaped high V_P/V_S corridor (average 1.98) interpreted as mantle-derived mafic modification of the lower crust, and low V_P/V_S zones attributed to granites and Cenozoic fluid--rock interactions. The consistency of high V_P/V_S and crustal thickening suggests a process of magmatic addition and subsequent cooling. Collectively, these complex structures are the product of multi-stage tectonic events, including the Paleozoic Yangtze--Cathaysia collision and subsequent Mesozoic to Cenozoic extension and magmatism linked to the Paleo--Pacific Plate subduction and rollback. These findings provide crucial insights into the regional tectonic evolution and have important implications for seismic hazard assessment.