Lithospheric structure beneath the Upper Indus Basin and its adjacent regions from inversion of surface wave dispersion

Abstract

We propose an enhanced model of the crust and upper mantle structure beneath the Upper Indus Basin, derived from the combined inversion of Rayleigh and Love wave group velocity dispersion data from 164 seismic events recorded by 58 stations, covering periods from 4 to 100 s. By using the Genetic Algorithm approach within this joint inversion process, we developed a detailed shear wave velocity model for the region. The earthquakes were categorized into three clusters based on their epicentral locations, allowing for a detailed analysis beneath the western, central, and eastern segments of the Upper Indus Basin. The analysis shows a gradual increase in crustal thickness from the west to the east, with an average thickness of ∼61.8 km and a shear wave velocity ∼ 4.6 km/s. The Lithosphere-Asthenosphere Boundary (LAB) is identified at a depth of 160 km, indicated by a velocity decrease of about 1.6 %. Our results also reveal a sedimentary cover of ∼4 km and we postulate a felsic crust similar to southern Pamir, which could have resulted from the loss of mafic lower crust by lithospheric delamination or foundering due to gravitational instability. We state the absence of mid-crustal low velocity layer within the Basin and also discard the possibility of any requirement for radial anisotropy, based on the adequate fit of Rayleigh and Love the dispersion data with minimal uncertainty. The study provides a significant refinement of the crustal and upper mantle structure of the Upper Indus Basin, contributing valuable insights into regional tectonics.