Disparate behaviour of deformation patterns beneath northeast Indian lithosphere inferred from shear wave splitting analysis

Abstract

New shear wave splitting measurements are obtained from the North East Indian region utilizing the core refracted PKS/SKS/SKKS phases, suggesting the region as more complex and anisotropic in nature. The splitting parameters namely time delays (δt) and fast polarization directions (ϕ) are computed at nine stations and the results are found to be more consistent with the geologic/tectonic structures and present mantle deformation patterns under this particular region. The result streamlines the deformation patterns strictly into three categories. Significant anisotropy in the western fringe of Shillong plateau and surrounding regions implies an asthenospheric flow related strain dominating the splitting direction inline the direction of absolute plate motion (APM) of the Indian plate in a no net reference frame and discards the effects from lithospheric strain. The stations in Himalayan collision zone redefines an actual deformation pattern in ENE-WSW direction in line with the maximum shear plane construing the Himalayan arc at the northeast corner as a consequence of N-S Indo-Eurasian collisional derived lithospheric strain. The anisotropic effect at the Himalayan foredeep section signifies the lithospheric strain induced E-W deformation from N-S continental collision. Mapping the anisotropic layer depth under these stations also strengthens our anisotropic observations and geodynamics understanding of this region with a similar thought of ideas where the deformation patterns are supposed to be dominated by huge forces like APM and lithospheric strains with negligible effects from the local geological structures.