Mantle Deformation Beneath India Inferred from Shear Wave Splitting

Roy, S. K.; Kumar, M. Ravi; Srinagesh, D.

doi:10.1007/s12594-021-1849-1

Cited by 3 publications

(1 citation statement)

References 71 publications

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“…Around ∼ 2500 published individual shear wave splitting measurements from more than 350 broadband seismic stations are synthesized to present the mantle deformation scenario beneath India (Roy et al, 2021a). On a continental scale, the delay times are found to cluster around 0.8 s, with the FPAs predominantly along the APM direction.…”

Section: Synthesis Of Upper Mantle Anisotropy Beneath Indiamentioning

confidence: 99%

INSA National Report on Seismological Research in India: 2019 – 2022

Manglik

2023

Preprint

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The Indian National Science Academy (INSA), the National Adhering body representing India in the International Union of Geodesy and Geophysics (IUGG), submits a National Report to the IUGG during its General Assembly, held every four years. The present chapter is a compilation for the International Association of Seismology and Physics of the Earth's Interior (IASPEI), one of the eight Associations of the IUGG, encompassing the scientific activities carried out in the country during 2019-2022, in the field of seismology. The chapter is arranged to categorize the contributions under internal structure of the Indian lithosphere and sub-lithospheric mantle, crust and upper mantle deformation, seismic attenuation, seismic hazards, triggered seismicity, environmental seismology, paleoseismology and seismological networks. In addition, the chapter includes activities related to societal projects and outreach programs. It is not an exhaustive review of the entire Indian contribution to seismology and allied fields during this period but a window to the topics covered within the framework of IASPEI.During the reporting period, researchers from several Indian R&D and Academic Institutions continued adding new results on the crustal and upper mantle structure of the Indian shield, both at regional and geological province scale. The Himalaya has been a major focus of seismological research for many Institutes who operated broadband seismological networks from Kashmir to Arunachal along the Himalayan arc. The data from these networks have facilitated in enhancing our understanding of the structure of the Main Himalayan Thrust, crustal and upper mantle structure as well as the dip of the underthrusting Indian plate, seismicity monitoring, and estimation of attenuation. Some of these networks also include accelerographs for strong ground motion studies. A few studies also focused on mapping of the mantle transition zone beneath the Indian Ocean Geoid Low. The studies on anthropogenic seismicity added near-field investigations in the Koyna -Warna region through borehole seismology. Organization of the Joint Scientific Assembly of IAGA and IASPEI during 21-27 August 2021 (JSA-2021) was a major event during this period related to the IUGG activities. Originally, the event was planned to be hosted at Hyderabad, India, but due to the COVID-19 pandemic it was organized in virtual mode. Initiatives have been taken to nucleate the field of environmental seismology in the country.

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Section: Synthesis Of Upper Mantle Anisotropy Beneath Indiamentioning

confidence: 99%

INSA National Report on Seismological Research in India: 2019 – 2022

Manglik

2023

Preprint

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Insights into the mechanisms forging seismic anisotropy in the upper mantle beneath India

Roy,

Kumar,

Kanaujia

et al. 2024

Tectonophysics

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Evidence for weak azimuthal anisotropy beneath the Kumaon-Garhwal Himalaya

Devi,

Roy,

Kanaujia

et al. 2024

Geophysical Journal International

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Summary This study attempts to interrogate the upper mantle deformation pattern beneath the Kumaon-Garhwal region, located in the western Himalaya, using shear wave splitting (SWS) analysis of core-refracted (XK(K)S) phases recorded at 53 broadband stations. The fast polarisation azimuths (FPAs) revealed by 338 well constrained measurements are dominantly clustered around ENE-WSW, with a few along the NE and E-W directions. The delay times vary from 0.2 to 1.4 s, with an average of 0.6 s that is smaller than that for the Indian shield (∼0.8 s), central and eastern Himalayas. The northern part of the lesser Himalaya shows a slightly smaller delay time compared to the southern part, which is attributed to the weakening of azimuthal anisotropy caused by the dipping of the Indian lithosphere. In order to understand the crustal contribution, its anisotropy is measured by analysing the splitting of Ps conversions from the Moho (Pms), akin to that of the XK(K)S phases. However, reliable results for crustal anisotropy could be obtained only at 10 stations. The average delay time due to crustal anisotropy is 0.47 s, with a variation from 0.2 to 0.9 s. Although the dominant period of Pms is smaller than that of SK(K)S, crustal anisotropy contributing to splitting of the latter phases cannot be ruled out. The orientation of FPAs obtained from Pms phases is found to be parallel or sub-parallel to those from XK(K)S phases, suggesting a similar deformation mechanism in the mid- to lower-crust and upper mantle. On the basis of FPAs derived from XK(K)S measurements, the Kumaon-Garhwal Himalaya (KGH) region can be divided into four sub-regions. In the western and eastern parts, the FPAs are mostly aligned along NE and ENE-WSW, and NE, respectively. In the central and south-eastern parts, their orientation is along ENE-WSW and NW, respectively. The strong ENE-WSW orientation in the central part could result from a slightly variable anisotropy in the crust to the upper part of the lithosphere or basal topography causing deflection of mantle flow. Also, the NW orientation in the south-eastern part of KGH is associated with a shallow source within the lithosphere. Application of the spatial coherency technique to single-layered anisotropic parameters results in a depth of 220-240 km, implying that the dominant source of anisotropy could lie in the upper mantle.

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Mantle Deformation Beneath India Inferred from Shear Wave Splitting

Cited by 3 publications

References 71 publications

INSA National Report on Seismological Research in India: 2019 – 2022

INSA National Report on Seismological Research in India: 2019 – 2022

Insights into the mechanisms forging seismic anisotropy in the upper mantle beneath India

Evidence for weak azimuthal anisotropy beneath the Kumaon-Garhwal Himalaya

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