Gravity field and lithospheric mechanical properties of Longmenshan fault zone and its surrounding areas

After the 2008 Wenchuan M_S8.0 earthquake, a M_S7.0 earthquake occurred in Lushan County, Sichuan Province, on April 20, 2013. The seismogenic structure of the two earthquakes both belong to Longmenshan fault zone. By using the latest gravity and topography dataset, this paper calculates 2D lithospheric effective elastic thickness of the Longmenshan fault zone and its surrounding areas with lithospheric elastic plate model. Based on the lithosphere mechanical properties, the characteristics of two gravity profiles which across the two epicenters are analyzed. And combining with previous researches in the area, the lithospheric mechanical deformation is also analyzed. The results show that, with the boundary of Longmenshan, the effective elastic thickness of Sichuan basin located on the Yangtze Plate is about 33(±4) km, whereas that of the Songpan-Garze block is about 13(±4) km at the northwest of Longmenshan, which indicates that the lithospheric mechanical strengths are obviously different for the two blocks. The effective elastic thickness of the southern Longmenshan region (including the scope of the two earthquake epicenters) is less than the northern, suggesting that the southern region is more prone to lithospheric deformation, which can be used to explain the lithospheric dynamic conditions for great earthquake occurrence in tectonics.