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.