Prospecting and Research on Fine Crustal Structure by Using Multi‐Geophysics Survey Methods in Shanghai Region

Abstract

AbstractThe fine seismic velocity structure, electrical conductivity structure and geometrical construction of the crust in Shanghai region and the coupled relationship between the deep and shallow structures are investigated by using multi‐geophysics exploration methods, such as shallow seismic reflection, deep seismic reflection, highresolution seismic refraction, deep seismic wide angle reflection/refraction and magnetotelluric sounding. This experiment is the first high‐resolution comprehensive deep survey profile in Shanghai and its conjoined regions. The research results indicate that the crust in the region can be divided into three layers, namely upper crust, middle crust and lower crust. The upper crust is 12~14 km thick with a seismic velocity of 5.7~5.9 km/s, the middle crust is about 10 km thick with a velocity of 5.9~6.2 km/s and the lower crust is 10~11 km thick with a velocity of 6.2~6.3 km/s. The depth of Moho in the region is 31~33 km. There is a thin velocity gradient layer (about 6 km thick) in the upper part of the lower crust, but the velocity gradient becomes greater near the Moho interface. There are 12 main faults interpreted in the experimental profile. Except for three faults, which have dislocated G interface (crystal basement) and extended below the bottom interface (whose depth is about 10 km) of the upper crust, the other faults have ended above G interface at 3 to 5 km depth, or have converged at G interface. Moreover, there is only a high conductivity layer (about 2 km thick) within crust at 13~15 km depth. Therefore, there is no deep structure condition for potential big earthquakes in the local region. However, the active rupture zones near the Earth's surface are potential seismic source zone.