Evidence of heterogeneous and unstable anisotropic settings beneath the Northeast Indian lithosphere from characterization of null splitting measurements

Characterization of null splitting measurements obtained from nine broadband stations from the northeast Indian region using core-refracted seismic phases suggests a better understanding of the geometry and strength of anisotropy of the medium and solves the critical aspects of these null splitting effects in this highly anisotropic area. The null splitting results establish a certain connection with their azimuthal origins and emphasize upon the large and complex tectonic forces as major sources to control the deformation patterns and null effects of this region. Though in majority of the studies, the null measurements are not emphasized or neglected for discussion, their proper distribution and interpretation suggests a better understanding of the geometry, strength and distribution of the heterogeneity. The present study emphasizes only on the null characteristics of the northeast Indian region and solves their dependency on the backazimuthal distribution of events, source polarization and fast/slow axis of rotation, to decipher a particular function with each other. This study allows recognizing and characterizing the nulls according to their origin and focuses on their relations with the reliable splitting measurements from the same region of study. This helps in obtaining a better understanding of the occurrence of null splittings and clear geometry of heterogeneity for this region. Apart from the azimuthal distribution, the presence of complex geological features, collision tectonics, lithospheric strains, absolute plate motion related asthenosphere drag and fossil vertical lineation of olivine, play major roles in creation of unstable layers of settings beneath the northeast Indian region leading to null measurements.