Abstract The southeastern margin of the Tibetan Plateau is crucial to understanding the dynamics of the Indian–Eurasian continental collision and potential causes of the plateau uplift. In the current study, we use fundamental mode surface wave group velocity (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$U_g$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>U</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation>) tomography and the fast-marching method to examine the shear velocity structure of the crust and upper mantle beneath northeastern India and the Tibetan Plateau with <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$1^\circ \times 1^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mn>1</mn> <mo>∘</mo> </msup> <mo>×</mo> <msup> <mn>1</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> resolution. The waveforms of 568 regional earthquakes that were detected at 326 seismic stations throughout the study region were combined to create the <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$U_g$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>U</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation> dataset for periods of 4–70 s. A well-constrained quasi 3-D isotropic shear wave velocity tomographic image down to <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\sim$</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>100 km depth is produced utilising the non-linear damped least square method by inverting the dispersion curves extracted from each node point of the Rayleigh and Love wave <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$U_g$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>U</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation> maps. Radial anisotropic maps across the study area observed from the disparity between vertically (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">$V_{SV}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>V</mi> <mrow> <mi mathvariant="italic">SV</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) and horizontally (<InlineEquation ID="IEq7"> <EquationSource Format="TEX">$V_{SH}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>V</mi> <mrow> <mi mathvariant="italic">SH</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) polarized shear wave velocity measurements signify lateral differences within the crust. Consequently, the observed variations in the velocity structure and radial anisotropy along with the crustal thickness in the Tibetan Plateau support the concept that the region serves as a pathway for material migration moving east and southeastwards. Lower velocity in the Tethyan Himalayan upper crust (<InlineEquation ID="IEq8"> <EquationSource Format="TEX">$\sim$</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>2.8 km/s), Lhasa middle crust (<InlineEquation ID="IEq9"> <EquationSource Format="TEX">$\sim$</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>3.2 km/s) and lower crust in the Qiangtang and Songpan–Ganzi terranes (<InlineEquation ID="IEq10"> <EquationSource Format="TEX">$\sim$</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>3.5 km/s) reflects the channel flow directed outwards from the Tibetan Plateau, southwards and southeast-wards across the Lhasa Terrane and rotate around the Eastern Himalayan Syntaxis, respectively. Observations of the velocity structure also suggest the possibility of a flow accumulation near the southern Yunnan province at 26<InlineEquation ID="IEq11"> <EquationSource Format="TEX">$^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </math></EquationSource> </InlineEquation>N. Research highlights <UnorderedList Mark="Bullet"> <ItemContent> Quasi-3D shear velocity model of the crust and upper mantle beneath NE India and eastern Tibet. </ItemContent> <ItemContent> Mid- to lower-crustal low-velocity zones reveal partial melt and ductile channel flow. </ItemContent> <ItemContent> Radial anisotropy patterns confirm lateral variations and flow pathways around the Eastern Himalayan Syntaxis. </ItemContent> <ItemContent> Crustal flow is confined by the Indian plate at depth and accumulates near southern Yunnan. </ItemContent> </UnorderedList>

Crustal architecture delineated from shear velocity and radial anisotropic pattern across the northeast India and eastern Tibetan Plateau: An implication of crustal material flow

期刊论文
发表日期：

2026年3月19日

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Arun Kumar Dubey,
Niptika Jana,
Chandrani Singh,
M Ravi Kumar,
Arun Singh,
Dipankar Saikia,
Sukanta Sarkar

摘要

Abstract

The southeastern margin of the Tibetan Plateau is crucial to understanding the dynamics of the Indian–Eurasian continental collision and potential causes of the plateau uplift. In the current study, we use fundamental mode surface wave group velocity ( $U_g$ $U_{g}$ ) tomography and the fast-marching method to examine the shear velocity structure of the crust and upper mantle beneath northeastern India and the Tibetan Plateau with $1^\circ \times 1^\circ$ $1^{\circ} \times 1^{\circ}$ resolution. The waveforms of 568 regional earthquakes that were detected at 326 seismic stations throughout the study region were combined to create the $U_g$ $U_{g}$ dataset for periods of 4–70 s. A well-constrained quasi 3-D isotropic shear wave velocity tomographic image down to $\sim$ $\sim$ 100 km depth is produced utilising the non-linear damped least square method by inverting the dispersion curves extracted from each node point of the Rayleigh and Love wave $U_g$ $U_{g}$ maps. Radial anisotropic maps across the study area observed from the disparity between vertically ( $V_{SV}$ $V_{SV}$ ) and horizontally ( $V_{SH}$ $V_{SH}$ ) polarized shear wave velocity measurements signify lateral differences within the crust. Consequently, the observed variations in the velocity structure and radial anisotropy along with the crustal thickness in the Tibetan Plateau support the concept that the region serves as a pathway for material migration moving east and southeastwards. Lower velocity in the Tethyan Himalayan upper crust ( $\sim$ $\sim$ 2.8 km/s), Lhasa middle crust ( $\sim$ $\sim$ 3.2 km/s) and lower crust in the Qiangtang and Songpan–Ganzi terranes ( $\sim$ $\sim$ 3.5 km/s) reflects the channel flow directed outwards from the Tibetan Plateau, southwards and southeast-wards across the Lhasa Terrane and rotate around the Eastern Himalayan Syntaxis, respectively. Observations of the velocity structure also suggest the possibility of a flow accumulation near the southern Yunnan province at 26 $^\circ$ $^{\circ}$ N.

Research highlights

Quasi-3D shear velocity model of the crust and upper mantle beneath NE India and eastern Tibet.

Mid- to lower-crustal low-velocity zones reveal partial melt and ductile channel flow.

Radial anisotropy patterns confirm lateral variations and flow pathways around the Eastern Himalayan Syntaxis.

Crustal flow is confined by the Indian plate at depth and accumulates near southern Yunnan.