Review on Bougue gravity anomaly and crustal density structure in Sichuan-Yunnan and its adjacent areas

Abstract

Sichuan-Yunnan and its adjacent area are the main places where the eastward material flow from the Tibet Plateau escapes and spins to SE-SSE with active geological formations and frequent seismic activity. The study of the crustal structure and material transport characteristics of this region is important to reveal the mechanism of earthquake occurrence here. It can also deepen the understanding of the tectonic activity mechanism of the southeastern margin of the Tibet Plateau. This paper summarizes recent achievements and important advances in the study of regional Bouguer gravity anomaly and crustal density structure in Sichuan-Yunnan and its adjacent areas. (1) Bouguer gravity anomaly information of eight gravity profiles was obtained by using gravity and GNSS positioning techniques, and the basic framework of crustal density structure of the southeastern margin of the Qinghai-Tibet Plateau and its adjacent areas was constructed by using gravity inversion techniques constrained by various geophysical observations. (2) New gravitational evidence of clockwise rotation of the Sichuan-Yunnan rhomboid massif was found through the separation and extraction of gravity signals by wavelet decomposition and normalized gradient. (3) Through the scientific research of the Yushu MS7.1, Lushan MS7.0 and Ludian MS6.5 earthquakes, we have deepened our understanding of the seismogenic tectonic environment in the southeastern margin of the Tibet Plateau. There are significant differences in density distribution on sides of the left-slip shear fault zone (Ganzi-Yushu, Xianshuihe and Xiaojiang) and the large thrust nappe structure (Longmen Shan), both of which are regional seismicity-controlled faults. The seismicity of the Ludian earthquake zone may be related to the eastward migration of the Xiaojiang fault zone. The nappe characteristics and detachment structure of the Longmenshan fault zone may be an important factor in the occurrence of the Lushan earthquake at the Houshan fault.

Keywords

• sichuan-yunnan region
• gravity detection
• bouguer gravity anomaly
• crustal density structure
• seismogenic tectonic environment