Detailed crustal structures and seismotectonic environment surrounding the Su-Lu segment of the Tan-Lu fault zone in the eastern China mainland

摘要

The Tan-Lu fault zone (TLFZ) is one of the most important active faults in the eastern Chinese mainland, and the seismic activity of the Su-Lu segment is most prominent. The fault structures of the Su-Lu section are very complex and intersect with many other NW-striking and NE-striking fault zones, resulting in the extreme complexity of the crustal structure in this area. In this study, Bouguer gravity and aeromagnetic data are used to invert the crustal structures surrounding the Su-Lu segment and to construct a three-dimensional model. Our results indicate that the TLFZ presents obvious high anomalies in gravity and aeromagnetic fields, cuts through the Moho interface and acts as an upwelling passage for high-density materials from the uppermost mantle and asthenosphere. The gravity and aeromagnetic anomalies are greatly influenced by the crustal structures. Both the Moho and Curie interfaces are characterized by substantial undulations. The NW-striking and NE-striking faults intersect the TLFZ with different relations-for example, the Wuxi-Suqian fault and Cangshan-Nishan fault cut off the TLFZ with distinct gravity and aeromagnetic anomalies, and the Xintai-Mengyin fault and Mengshan piedmont fault cut off the western part of the TLFZ. In addition, most faults cut to the middle crust, and the lower crust is ductilely deformed because of magmatic underplating, reforming, remelting and thinning of the eastern North China block. Most earthquakes occur in the northern part of the Su-Lu segment, where magmatic activity is intense.