Surface Wave Tomography of India

We present group velocity dispersion results from a study of regional distance range fundamental mode Rayleigh waves propagating across the Indian region. One-dimensional path average dispersion measurements have been made for 1001 source-receiver paths and these have been combined to produce tomographic images between 15s and 60s period. These results have significantly higher lateral resolution for the Indian region than is currently available from global and Asian group velocity studies. Testing of the model shows that the average resolution across the region ranges from 5 to 7.5 degrees for the periods used in this study. The Indian Shield is characterized by high group velocities for waves sampling the crust and uppermost mantle. Comparatively lower velocities are observed for the Himalaya due to the thickened crust and the Gangetic plains due to the mollasse sediments and recent alluvium cover in the Himalayan foredeep. The northern Bay of Bengal shows extremely low group velocities due to the thick sediment blanket of the Bengal fan. The Shillong Plateau has high group velocities similar to those observed for the south Indian Shield. The Katawaz Basin in southern Pakistan shows low velocities similar to those seen in the Bay of Bengal. The geometry of the velocity contours south of the Katawaz Basin matches well with the prograding Indus fan into the Arabian Sea. Finally, the Tibetan Plateau has the thickest crust in the region and shows lower group velocities compared to the Indian Shield and the Himalaya at all frequencies.