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

Abstract

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.

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adopted from Singh et al. (2006) and Mohanty and Mondal (2020). g, h Similar scatter plot for delay time (δt) with BAZ for RC and SC analyses, respectively, where the horizontal solid line in each figure indicates the average splitting delay time

Fig. 5

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Acknowledgements

DDM is thankful for the permission provided by the Director, CSIR-NEIST for this publication (NMN-202025). The National Geophysical Research Institute (NGRI) and the Ministry of Earth Sciences (MoES) are acknowledged for providing seismological data for this study. DDM is thankful to the Co-Editor-in-Chief, Prof. Ramon Zuñiga and the anonymous reviewers for their valuable suggestions which helped in improving the manuscript. A thank is also due to Dr Saurabh Baruah, Chief Scientist, CSIR-NEIST, for making the data available for processing. This study is supported by an Early Career Research grant from Science and Engineering Research Board (SERB), India, vide project grant no. ECR/2018/001293.The figures are made using the Generic Mapping Tools software (Wessel and Smith 1998).

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Correspondence to Debasis D. Mohanty.

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Communicated by Prof. Ramón Zúñiga (CO-EDITOR-IN-CHIEF).

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Mohanty, D.D., Mandal, P. Evidence of heterogeneous and unstable anisotropic settings beneath the Northeast Indian lithosphere from characterization of null splitting measurements. Acta Geophys. (2021). https://doi.org/10.1007/s11600-021-00676-5

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Keywords

  • Shear-wave splitting
  • Null anisotropy
  • Northeast Indian lithosphere
  • Absolute Plate Motion (APM)
  • Mantle anisotropy