P-wave velocity models and their reliability for MTr6 (a–d) and MTr8 (e–h). (a) P-wave velocity model for MTr6, where V
= 8.0km/s immediately below the uppermost mantle is an assumed value. (b) Ray diagrams for MTr6. (c) Initial pattern for the checkerboard test applied to MTr6 model. (d) Results of the checkerboard test for MTr6, and (e–h) results for MTr8. Black dashed lines indicate the Moho, and yellow lines in (a, b) represent the lower boundary limits of the heterogeneity. All checkerboard patterns down to a depth of 15 km are recovered, indicating that each constructed velocity model down to a depth of 15 km is reliable.