P wave velocity structure below India and Tibet incorporating anisotropic delay time effects

Abstract

We incorporate the effects of anisotropy to refine the continental‐scale 3‐D isotropic velocity model previously produced for India and Tibet by inverting 52,050 teleseismic P wave residuals. We have exploited a total of 1648 individual SKS splitting parameters to calculate the P wave travel time corrections due to azimuthal anisotropy. Our results suggest that anisotropy affects the P wave delays significantly (−0.3 to +0.5 s). Integration of these corrections into the 3‐D modeling is achieved in two ways: (a) a priori adjustment to the delay time vector and (b) inverting only for anisotropic delays by introducing strong damping above 80 km and below 360 km depths and then subtracting the obtained anisotropic artifact image from the isotropic image, to get the corrected image. Under the assumption of azimuthal anisotropy resulting from lattice preferred orientation (LPO) alignment due to horizontal flow, the bias in isotropic P wave tomographic images is clear. The anisotropy corrected velocity perturbations are in the range of ±1.2% at depths of around 150 km and reduced further at deeper levels. Although the bias due to anisotropy does not affect the gross features, it does introduce certain artifacts at deeper levels.

Seismic hazard evaluation of Nepal region: a particular emphasis on 2015 Gorkha earthquake scenario

“…To analyse the b-value pattern in the Gorkha region in detail, the spatial variations are studied for before, after, and the aftershocks consequences for the Gorkha earthquake. A time window of 21 years (2000-2021) of seismicity in the Nepal Himalayan region is taken into consideration for studying the signi cant stress variation pattern in this region, which signi es the advent of this major earthquake as a consequence of enormous accumulated stress due to most complex tectonics in this region (Mohanty et al, 2016).…”

“…In the past, signi cant studies have been carried out in Nepal in geophysics, geodynamics and seismology (Singh et al, 2017;Mohanty et al, 2016;Singh et al, 2015;Molnar, 1984). Schelling and Arita (1991) studied the thrust tectonics and crustal shortening along with the structure of the far-eastern Nepal Himalayas.…”

A review of seismological research in India during the past five years (2015-2019)

“…Further, the crustal thickness in Himalayas appears to follow the elevation. The regional continental scale 3D isotropic velocity model (Singh, et al, 2014) was refined by incorporating the effects of azimuthal anisotropy using the shear wave (SK(K)S) splitting Singh,et al, 2015) results (Mohanty et al, 2016). Although the P wave delays significantly (-0.3 to +0.5 s) due to anisotropy, the bias due to it does not affect the gross features and only introduces certain artefacts at deeper levels (> 150 km).…”

Possible depth and source localization of seismic anisotropy beneath Shillong Plateau and Himalayan foredeep region: An implication towards deformation mechanisms

“…There are a few seismological studies based upon the SWS analysis which contribute towards the deformation pattern and their causative mechanisms beneath this region (Hazarika, Yadav, Sriram, & Rai, 2013; Mandal & Mohanty, 2021; Mohanty & Mandal, 2021; Mohanty & Mondal, 2020; Mohanty & Singh, 2021; Mondal et al, 2021; Roy, Kumar, & Srinagesh, 2014; Saikia et al, 2018; A. Singh, Kumar, Raju, & Ramesh, 2006). Similarly, very limited research studies have been published to understand the dynamic geological settings and processes of this region and nearby through seismic tomographic studies (Mohanty et al, 2016; Raoof, Mukhopadhyay, Koulakov, & Kayal, 2017; C. Singh et al, 2015; A. Singh et al, 2016, 2017). But unfortunately, there is no research so far available to identify the source localization and depth estimation of anisotropy, which is of more importance to understand the concerned geodynamics in a more comprehensive way to solve the critical geological process and mantle deformation pattern that govern the tectonics of a particular region.…”

“…Singh, Kumar, Raju, & Ramesh, 2006). Similarly, very limited research studies have been published to understand the dynamic geological settings and processes of this region and nearby through seismic tomographic studies (Mohanty et al, 2016;Raoof, Mukhopadhyay, Koulakov, & Kayal, 2017;C. Singh et al, 2015;A.…”