Average crustal thickness and Poisson’s ratio beneath the Kali River Valley, Kumaon Himalaya

Abstract

Crustal thickness and Poisson's ratios were estimated at 13 broadband seismological stations established in a profile along the Kali river valley, Kumaon (Central) Himalaya. The seismological profile extends from the Indo-Gangetic plain (IGP) in the south to the Higher Himalaya in the north, passing through the Sub and Lesser Himalaya. The Receiver Function (RF) method has been adopted to investigate the crustal structure beneath the profile. Time domain iterative deconvolution method has been adopted for RF computation. The H-k stacking method has been adopted to analyze the RFs for obtaining average crustal thickness and Poisson’s ratio (σ) of the crust beneath each station. The study reveals that the crustal thickness beneath the IGP is ∼38 km which gradually increases up to ∼41 km at the northernmost station located in the Higher Himalaya. The values of σ vary from 0.23 to 0.28. The value of σ is low in the Sub-Himalaya and outer Lesser Himalaya suggesting more of a felsic composition of crust. A Significantly high value of σ (∼0.28) is observed in the Dharchula region of the Chiplakot Crystalline belt which is coincident with a large number of micro-to-moderate magnitude earthquakes forming a cluster at shallow to mid-crustal depths. The high Poisson’s ratio is possibly due to the presence of fluids/partial melts at mid-crustal depth. The presence of fluids influences the rheological property and controls the mechanical and shear strength of crustal rocks producing a cluster of seismicity observed beneath the Dharchula region.