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<p>Seismic anisotropy is a robust mechanism to infer the strength and direction of deformation in the crust, lithosphere, and sub-lithospheric mantle. This study presents new shear wave splitting (SWS) measurements from the Sikkim Himalaya region utilizing the core refracted (SKS/SKKS/PKS) and crustal (direct-S) seismic phases to understand the mantle and crustal-scale deformation patterns, respectively. Significant time delays (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\delta t\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>δ</mi> <mi>t</mi> </mrow> </math></EquationSource> </InlineEquation>) and consistent NW-SE oriented fast polarization directions (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\phi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ϕ</mi> </math></EquationSource> </InlineEquation>) at all seismic station locations emphasize the dominance of Indo-Eurasian collisional tectonics in governing the deformation patterns beneath Sikkim. The boundary conditions implied by collisional tectonics require deformation with a large amount of shortening of the lithosphere beneath this Sikkim region. A similar crustal deformation pattern (NE-SW) led by the alignment of maximum shear stress is observed throughout this Himalayan region, suggesting that the huge collisional tectonic force influences the coupled crust-mantle dynamics. The deformation in the proximity of regional crustal-scale structures is controlled by the shape-preferred orientation of cracks/voids. Throughout the Sikkim Himalaya, the majority of crustal anisotropy parameters seem to be dominated by the maximum shear (arc-parallel) of convergence tectonics.</p>

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Lithospheric deformation beneath the Sikkim Himalaya and tectonic implications: anisotropic contributions from crust and mantle

  • 期刊论文

  • 发表日期：

    2025年9月20日

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  • Debasis D. Mohanty

摘要

Seismic anisotropy is a robust mechanism to infer the strength and direction of deformation in the crust, lithosphere, and sub-lithospheric mantle. This study presents new shear wave splitting (SWS) measurements from the Sikkim Himalaya region utilizing the core refracted (SKS/SKKS/PKS) and crustal (direct-S) seismic phases to understand the mantle and crustal-scale deformation patterns, respectively. Significant time delays ( \(\delta t\) δ t ) and consistent NW-SE oriented fast polarization directions ( \(\phi \) ϕ ) at all seismic station locations emphasize the dominance of Indo-Eurasian collisional tectonics in governing the deformation patterns beneath Sikkim. The boundary conditions implied by collisional tectonics require deformation with a large amount of shortening of the lithosphere beneath this Sikkim region. A similar crustal deformation pattern (NE-SW) led by the alignment of maximum shear stress is observed throughout this Himalayan region, suggesting that the huge collisional tectonic force influences the coupled crust-mantle dynamics. The deformation in the proximity of regional crustal-scale structures is controlled by the shape-preferred orientation of cracks/voids. Throughout the Sikkim Himalaya, the majority of crustal anisotropy parameters seem to be dominated by the maximum shear (arc-parallel) of convergence tectonics.