Modelling the Crust beneath the Kashmir valley in Northwestern Himalaya

Abstract:

We investigate the crustal structure beneath five broadband seismic stations in the NW-SE trending
oval shaped Kashmir valley sandwiched between the Zanskar and the Pir Panjal ranges of the
northwestern Himalaya. Three of these sites were located along the southwestern edge of the valley and
the other two adjoined the southeastern. Receiver Functions (RFs) at these sites were calculated using
the iterative time domain deconvolution method and jointly inverted with surface wave dispersion
data to estimate the shear wave velocity structure beneath each station. To further test the results of
inversion, we applied forward modelling by dividing the crust beneath each station into 4-6
homogeneous, isotropic layers. Moho depths were separately calculated at different piercing points
from the inversion of only a few stacked receiver functions of high quality around each piercing point.
These uncertainties were further reduced to ±2 km by trial forward modelling as Moho depths were
varied over a range of ±6 km in steps of 2 km and the synthetic receiver functions matched with the
inverted ones. The final values were also found to be close to those independently estimated using the
H-K stacks. The Moho depths on the eastern edge of the valley and at piercing points in its
southwestern half are close to 55 km, but increase to about 58 km on the eastern edge, suggesting that
here, as in the central and Nepal Himalaya, the Indian plate dips northeastwards beneath the Himalaya.
We also calculated the Vp/Vs ratio beneath these 5 stations which were found to lie between 1.7 and
1.76, yielding a Poisson’s ratio of ~0.25 which is characteristic of a felsic composition.