Indian plate passed over four plumes during its way towards Eurasian plate. These interactions with plumes certainly affected the upper mantle and crust of Indian plate as manifested by its thinned lithosphere and relatively low shear velocities both in crust and upper mantle, but the depth extent of these effects of plume-lithosphere interaction remains ambiguous. In this study, we investigate the mantle transition zone beneath Indian shield using P-to-S receiver functions computed at 24 stations covering the entirety of the Indian shield to investigate the depth extent of the imprints of the plume-lithosphere interaction as well as to study the lateral variations of transition zone beneath a stable intraplate setting like the Indian shield. Our results show good agreement with the results of previous studies as well as with the tomographic models in terms of the average apparent depths of the 410 and 660 discontinuities and the transition zone thickness. However, unlike previous studies, we find a compelling evidence of a persistent mid transition zone discontinuity beneath all the stations and a low velocity layer beneath some regions. We also investigated the frequency dependence of amplitudes of receiver functions and found most of the stations showed strong dependence of amplitudes on frequency. Based on the evidence from our investigation, we demarcate the regions potentially containing relatively more weight percentage of water inside the otherwise considered ‘dry’ mantle transition zone. These regions should be further investigated in detail by a dense seismic network and a realistic 3-D velocity model.

For estimation of surface wave group velocity at a given period (T), the epicentral distance is divided by the difference in the arrival time of the corresponding group and the origin time of the earthquake. Hence, it is assumed that such waves are generated at the source/epicenter of the earthquake. However, this assumption is not correct. This work describes an effort to understand and quantify the amount of error that can creep into the estimated surface-wave group velocity values due to wrong assumptions used during their estimation. The error may affect the group velocity values especially when regional earthquake data is used for velocity estimation. The analysis was carried out using a horizontal layer over the halfspace model. Errors were estimated at different epicentral distances and periods for different layer thicknesses (H). Also, focal depth (h) was varied from 5 km to just 5 km above the layer boundary for each model. It is observed that for any combination of h, H, and T, error in estimated group velocity decrease rapidly with epicentral distance. The present work gives us some idea about what is the minimum epicentral distance from which data can be included for estimation of group velocity without adding significant error with such a wrong assumption. It is observed that the minimum epicentral distance at which error becomes less than or equal to a given percentage error decreases with increasing focal depth, i.e. lower is the difference between crustal thickness and focal depth, the lower is the error at a given epicentral distance and period. This means that when the difference between crustal thickness and the focal depth is low, even local earthquake data may be used without adding much error in the estimated group velocity values. For a given value of crustal thickness, focal depth, and epicentral distance, error increase with increasing period.