Gravity Changes and Characteristics of Its Positive Change Area Before the 2013 Lushan Ms 7.0 Earthquake in Sichuan Province, China

Abstract Various observation data, including underground fluid, seismicity, and gravity, have been used in earthquake prediction, but the limited understanding of these data has raised doubts about the predictability of earthquakes. On 20 April 2013, the Ms 7.0 Lushan earthquake occurred on the eastern margin of the Qinghai–Tibet Plateau, with a significant gravity increase in the southern region of the epicenter before the earthquake. The underground medium in this gravity-increased area shows locally high conductivity and high Poisson’s ratio characteristics, indicating that the underground structure of this area is closely related to fluids. The surface deformation and seismic activity characteristics of this area are also significantly different from those of the surrounding areas. These factors indicate that the regional gravity increase before the earthquake has a tectonic basis, and its characteristics have various manifestations and can be identified using inversion results of surface observation data. These characteristics provide location clues for the identification of gravity precursors of earthquakes. Deformation data from the same period suggest that the gravity increase may be the result of the diffusion of deep-fluid material following local crustal expansion.