Modelling of crustal composition and Moho depths and their Implications toward seismogenesis in the Kumaon\u2013Garhwal Himalaya

Prantik Mandal,D Srinivas,G Suresh,D Srinagesh

doi:10.1038/s41598-021-93469-1

Prantik Mandal, D Srinivas + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-93469-1

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Journal: Scientific Reports	Publication Date: Jul 7, 2021
Citations: 14	License type: open-access

Affiliation: National Geophysical Research Institute

Abstract

We image the lateral variations in the Moho depths and average crustal composition across the Kumaon–Garhwal (KG) Himalaya, through the H–K stacking of 1400 radial PRFs from 42 three-component broadband stations. The modelled Moho depth, average crustal Vp/Vs, and Poisson’s ratio estimates vary from 28.3 to 52.9 km, 1.59 to 2.13 and 0.17 to 0.36, respectively, in the KG Himalaya. We map three NS to NNE trending transverse zones of significant thinning of mafic crust, which are interspaced by zones of thickening of felsic crust. These mapped transverse zones bend toward the north to form a NE dipping zone of maximum changes in Moho depths, below the region between Munsiari and Vaikrita thrusts. The 1991 Mw6.6 Uttarakashi and 1999 Mw6.4 Chamoli earthquakes have occurred on the main Himalayan thrust (MHT), lying just above the mapped zone of maximum changes in Moho depths. Modelled large values of average crustal Vp/Vs (> 1.85) could be attributed to the high fluid (metamorphic fluids) pressure associated with the mid-crustal MHT. Additionally, the serpentinization of the lowermost crust resulted from the continent–continent Himalayan collision process could also contribute to the increase of the average crustal Vp/Vs ratio in the region.

Highlights

The continent–continent collision between the Indian and Eurasian plates at ~ 55 Ma led to the formation of the Himalayan mountain chain and the Tibetan plateau, the largest continental plateau on the earth
The thinnest crust of 28.3 km thickness is obtained at BTL (Table 1), which is less than the estimates of Moho depths (~ 35–45 km) in the northwest H imalaya[18] and Garhwal Lesser Himalaya[5]
The thickest crust of 52.9 km is noticed at PAUR (Table 1), which falls in a zone of thickening of crust, with an average crustal thickness of 45.18 km

Summary

Introduction

The continent–continent collision between the Indian and Eurasian plates at ~ 55 Ma led to the formation of the Himalayan mountain chain and the Tibetan plateau, the largest continental plateau on the earth. The lower flat portion of the MHT has been shown as the nucleation zones for the 1991 Uttarkashi, Mw6.8 and 1999 Chamoli, M w 6.4 e arthquakes[12] This GAP area has not experienced any large earthquake during the last 500 years, it is imperative to study the seismicity vis-â-vis the crustal structure for understanding the seismo-tectonics and the seismic hazard associated with the Uttarakhand region in the central Himalaya. The main link fault for all major thrusts including many local faults in the region defines a low angle north dipping plane, separating the under-thrusting Indian plate from the overriding Eurasian plate This detachment plane is named as the main Himalayan thrust (MHT), on which most of the major Himalayan earthquakes have occurred. It is observed that these phases are quite clear on the estimated radial RFs for almost all the stations (Figs. 2a–l, S2a-0, and S3a-j)

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Conclusion