3.2.11 Pn anisotropy of the Indian shield

High-resolution P-wave velocity and anisotropy structure of the hitherto elusive uppermost mantle beneath the Indian shield and its surrounding regions are obtained using 19,500 regional Pn phases from 172 broadband seismic stations (Illa et al., 2021a). The effect of continental rifting, collision and orogeny is reflected in the Pn velocity image. The cratons in the Indian shield have uppermost mantle velocities ranging from 8.02 to 8.42±0.05 km/s. Prominent highs and lows are observed in the shield region related to mantle deformation episodes, as the Indian plate has experienced major tectonic activity during and after the breakup from the Gondwanaland. The Pn and SKS anisotropic fast axis directions are consistent, except for the Indian shield, revealing that the Indian cratons are distinct with an altered uppermost mantle preserving the remnant anisotropy. The FPAs are consistent in the collision environments in the west, Himalaya, and Burmese arc region.

3.2.12 Anisotropy of NW DVP using Surface waves

The anisotropic and isotropic variations within the crust and upper mantle beneath the NW DVP are investigated using surface waves (Sharma J., et al., 2021). Results reveal different intra-crustal layers, lid, and a low-velocity zone (LVZ). The LVZ comprises a uniform asthenospheric low-velocity layer (LVL) of average VSV  4.44 km/s and VSH  4.47 km/s, and another LVL with an average VSV  4.45 km/s and VSH  4.41 km/s. A negative radial anisotropy is observed in the LVZ, indicating the dominance of vertical flow. This could be related to partial melts, volatile materials and/or a thermal anomaly.