6. Conclusions
The results from this study reveal significant difference in the S-wave velocity structure of the crust between the Songpan-Ganzi Block and the Sichuan Basin. The eastward extrusion of the Songpan-Ganzi Block is obstructed by the rigid crust beneath the Sichuan Basin, which might be the cause for stress accumulation and release leading to seismic activities. Our results also indicate that the eastward material flow induced by the extrusion of the Tibet Plateau occurred at this region.