3D crustal structure of the Jammu and Kashmir Himalaya: signatures of
mid-crustal ramp and Lesser Himalayan duplex
Abstract
We use teleseismic data from the Jammu and Kashmir Seismological
NETwork, to perform P-wave receiver function spatial and
common-conversion-point (CCP) stacks, and joint inversion with
Rayleigh-wave group-velocity dispersion, to construct 3D Vs model of the
Jammu and Kashmir (J&K) Himalaya. 2D-CCP and Vs profiles reveal
increasing crustal thickness from the foreland-to-hinterland, and an
under-thrust Indian crust beneath J&K. The Moho positive
impedance-contrast boundary is at ∼45 km depth beneath Sub-Himalaya and
deepens to ∼70 km beneath Higher-to-Tethyan Himalaya, with an overall
gentle NE dip. The Main Himalayan Thurst (MHT) forms a low velocity
layer (LVL) with negative impedance contrast, and has a flat–ramp
geometry. The flat segment is beneath Sub-to-Lesser Himalaya at 6–10 km
depth, and dips ∼4◦. The mid-crustal (frontal) ramp is beneath Kishtwar
Higher-Himalaya and Zanskar Ranges at 10–16 km depth, and dips
∼13–17◦. Significant along-arc variation in crustal structure is
observed between east (Kishtwar) and west (Kashmir Valley) segments.
Beneath the Kishtwar Window we image a Lesser Himalayan duplex (LHD)
bound between MHT sole-thrust and MCT roof-thrust. LHD horses dip at
high angle to the bounding structures and are illuminated by moderate
seismicity. Beneath the Pir-Panjal Ranges and Kashmir Valley, the
underthrust crust is ∼10 km thicker, has higher crustal Vs , and a
shallower flat MHT at ∼10 km depth. The westward shallowing of the MHT
occurs through a lateral ramp beneath Kishtwar Himalaya. Aftershocks of
the 2013 Kishtwar earthquake concentrate on the MHT frontal and lateral
ramp intersection, and possibly marks the down-dip locked-to-creep
transition.