Abstract:Using the inversion of gravity anomaly to test three-dimensional seismic wave velocity structures has some drawbacks, e.g., the solution is not unique and the reliability is not high. The surface wave inversion is fully fused to the gravity anomaly inversion equation, which reduces the non-uniqueness of the traditional inversion method and improves its reliability. Taking the Sichuan-Yunnan area as an example, the 3-D seismic velocity structure was analyzed using the fused gravity anomaly inversion method. Through conversion of velocity and density, the corresponding gravity anomaly data was obtained. Because surface wave frequency data were sensitive mainly to seismic shear wave velocity, gravity anomaly data and initial shear wave velocity were connected. According to the relationship between seismic wave velocity and rock density, an inversion equation of the gravity anomaly was obtained to analyze the velocity structure. Active blocks of the Sichuan-Yunnan area, in the range of 21.6°-34.2° N, 97.1°-105.9° E, were selected for experimental data. Through experimental analysis, it was found that the residual values of gravity anomaly data and surface wave frequency data were 6.24 mGal and 0.027 km/s, respectively, and the fitting effect was good. Through analysis of shear wave velocities at different depths in this area, it was found that at the 24-km depth, there are relatively low-velocity layers in the upper crust, and low-velocity layers in the middle and lower crusts at depths of 44 km. Resolution of this method for analyzing the structural solution of three-dimensional seismic wave velocity in the Sichuan-Yunnan region was high.
