Surface wave tomography studies beneath the Indian subcontinent

The Rayleigh wave group velocities at periods of 5 to 60 s across more than eighty propagation paths of the Indian subcontinent are used to construct estimated Rayleigh wave group velocity distribution maps of the region. Bac kus and Gilberts' inversion theory is applied for the surface wave tomograp hy studies. High values of Rayleigh wave group velocity are concentrated at periods of 30 to 60 a near the region of the Precambrian shield of central India, the China-East India border, the Pakistan-Kashmir border, the Indo- Burmese are and the west Nepal-Tibet border regions. Low values of group ve locity are located at periods of 10 to 20 s in the northernmost part of Ind ia beneath the Bangladesh shelf and beneath the northernmost part of the Ba y of Bengal Fan and the Arabian Sea, which may be due to the presence of th ick sediments in the region. Higher group velocities at periods of 40 to 60 s around the region of the West India-Pakistan border suggest thinning of the Indian lithosphere beneath the region. The nature of the high Rayleigh wave group velocities at periods of 30 to 60 s in the Peninsular shield and the Himalaya indicates the continuation of shield type structure beneath t he Himalaya. The nature of the Rayleigh wave group velocities in the Bay of Bengal indicates the continuation of the Ninetyeast Ridge up to the Bangla desh shelf below a depth of 25 km. (C) 1999 Elsevier Science Ltd. All right s reserved.