Fig. 4. The node (107°E, 22.5°N) as an example to illustrate the process of inverting the S-wave velocity from the dispersion curve. The black triangles in the right panel represent the group velocity observation dispersion. The red solid line represents the theoretical group velocity dispersion generated by the final S-wave velocity model obtained from the inversion. The blue dashed line in the left panel represents the initial velocity model, whereas the red solid line represents the final S-wave velocity model obtained by the inversion.
Resolution analysis and results
Resolution analysis
In general, seismic tomography uses the checkerboard resolution test (CRT) to analyze the resolution and estimate the error of the results. However, Leveque et al. (1993) pointed out that the CRT used to analysis resolution may result in error. Yanovskaya (1997, 1998) used the mean scale and stretch of the mean area to estimate the imaging resolution, and the resolution of tomographic results is calculated based on the ray density and the ray azimuth distribution.
Fig. 5 represents the resolution of each period. The resolution radius distribution shows that the minimum resolution radius can reach within 50 km, whereas for most research areas, the resolution core radius can still reach 200 km. In this region, the obtained spatial average resolution radius is between 0 and 200 km, and the resolution radius is completely within the smooth radius allowed by the model parameters. According to the results of the resolution detection, we consider that the inversion results of most areas in our study are relatively reliable.