Upper Mantle Anisotropy beneath the Western Segment, NW Indian Himalaya, Using Shear Wave Splitting

Biswal, Shubhasmita; Kumar, S. V.; Roy, S. K.; Kumar, M. Ravi; Mohanty, William K.; Parija, Mahesh Prasad; Paul, Ajay; Roeske, Sarah M.

doi:10.2113/2020/8856812

“…They show compressional P-axis-oriented N-S and tensional t-axis E-W oriented for the entire Tethys Himalaya region. This observation accounts for a shear and E-W extension at the base of the Indian lithosphere as reported from upper mantle anisotropy [63]. These observations highlight the fact that the subduction process is related to the earthquakes at Moho depths for the Kinnaur Himalaya region.…”

Section: Discussionsupporting

confidence: 79%

Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis

Biswal

¹

,

Kumar

²

,

Mohanty

³

et al. 2022

Lithosphere

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The optimum 1D velocity model is calculated for the Kinnaur sector of the NW Himalaya utilizing the arrival time information of the local earthquakes (137 no.) recorded with 12 broadband seismic network within the azimuthal gap of ≤180°. This optimum 1D velocity model is a five-layer model and ranges from the surface to 90 km in the shallow mantle. P velocity varies from 5.5 km/s to 8.6 km/s in the crust and upper mantle, and S-wave velocity varies between 3.2 km/s and 4.9 km/s for the same range. When we relocated the earthquakes with the Joint Hypocenter Determination program incorporating the optimum 1D velocity model, it resulted in a lower RMS residual error of 0.23 s for the hypocenter locations compared to initial hypo71 locations. A total of 1274 P and 1272 S arrival times were utilized to compute station delays. We observed positive variations in P-station delays from -0.19 s below the PULG station to 0.11 s below the SRHN station. Similarly, for S-station delays, we observed negative delays at each individual site from -0.65 s at LOSR station to -0.16 s at the SRHN station. This large variation in P- and S-station delays corresponds to the 3D nature of the subsurface below the Kinnaur Himalaya. The relocated seismicity is clustered along the STD fault at sub-Moho and Moho depths ranging between 40 km and 80 km. The seismicity distribution aligned across the strike of the STD and along the strike of the Kaurik-Chango fault (KCF) can be attributed to the cross-fault interactions of the KCF and the STD fault in the area. We also observed bimodal depth distribution of seismicity in the Higher and Tethys Himalayas. The occurrence of earthquakes down to a depth of ~0-40 km and 50-80 km in the study area can be interpreted in terms of stress contribution from interseismic stress loading associated with the India-Eurasia collision tectonics. The presence of hypocentres in the shallow mantle at 120 km depth highlights the strength of the mantle, which seems to be deforming in a brittle manner below the region. The computed focal mechanisms exhibit generally the flexing of the Indian plate below the Lesser Himalaya with shear parallel to the strike of the MCT and extension orthogonal to it. This study shows deformation over the entire crust and shallow upper mantle levels, with differential stress conditions. Thus, we can consider the crust and the shallow upper mantle down to depths of 120 km to be seismogenic in nature and is capable of producing the microseismicity beneath the Kinnaur Himalaya.

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“…Upper mantle anisotropy beneath the western Himalaya is investigated using data from 62 broadband seismic stations (Biswal et al, 2020;Kumar V.P., et al, 2022). Of these 62 stations, around 18 stations are located along a linear profile in the Kumaun-Garhwal Himalaya traversing the Himalaya from south to north.…”

Section: Western Himalayamentioning

confidence: 99%

“…Of these 62 stations, around 18 stations are located along a linear profile in the Kumaun-Garhwal Himalaya traversing the Himalaya from south to north. The study region mostly comprises of Himachal (Biswal et al, 2020) and Kumaun-Garhwal (Kumar V.P., et al, 2022) Himalaya. The FPAs are mainly oriented along the ENE-WSW and ∼ E-W directions, respectively, and a few in the NE direction (Fig.…”

Section: Western Himalayamentioning

confidence: 99%

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

Manglik

¹

2023

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0

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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.

show abstract

“…Of these 62 stations, around 18 stations are located along a linear profile in the Kumaun-Garhwal Himalaya traversing the Himalaya from south to north. The study region mostly comprises of Himachal (Biswal et al, 2020) and Kumaun-Garhwal (Kumar V.P., et al, 2022) Himalaya. The FPAs are mainly oriented along the ENE-WSW and ∼ E-W directions, respectively, and a few in the NE direction (see Fig.…”

Section: Western Himalayamentioning

confidence: 99%

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

Manglik

¹

2023

Preprint

2

0

View full text Add to dashboard Cite

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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Upper Mantle Anisotropy beneath the Western Segment, NW Indian Himalaya, Using Shear Wave Splitting

Cited by 8 publications

References 52 publications

Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis

Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis

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

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

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