3D Crustal Structure of the Jammu and Kashmir Himalaya: Signatures of Mid-Crustal Ramp and Lesser Himalayan Duplex

The NW Himalayan "seismic gap" lies between the 1905 and 2005 earthquake rupture zones and straddles the meisoseismal zone of the 1555-Kashmir earthquake. Sufficient elastic strain has now accumulated across this region to drive a mega-thrust earthquake. We model the crustal structure and geometry of the Main Himalayan Thrust (MHT) using Jammu and Kashmir Seismological NETwork data. P-wave receiver-function spatial and common-conversion-point (CCP) stacks, and joint inversion with Rayleigh-wave group-velocities are used to construct 3D V-s model of the region. This model reveals increasing crustal thickness from foreland-to-hinterland, and an under-thrust Indian crust beneath NW Himalaya. The Moho is at similar to 45 km depth beneath Sub-Himalaya deepening to similar to 70 km beneath Higher-to-Tethyan Himalaya with a gentle NE dip. The MHT forms a low-velocity layer and has a flat-ramp geometry. The flat segment is beneath Sub-to-Lesser Himalaya at 6-10 km depth, and dips similar to 4 degrees. The mid-crustal (frontal) ramp is beneath Kishtwar Higher-Himalaya and Zanskar Range at 10-16 km depth, and dips similar to 13-17 degrees. Crustal structure varies along-arc between east (Kishtwar) and west (Kashmir Valley) segments. A Lesser Himalayan duplex (LHD) lies beneath the Kishtwar Window and is bound by MHT and Main Central Thrust. The LHD high-angle imbricate structures are illuminated by moderate seismicity. Beneath Kashmir Valley, the underthrust crust is similar to 10 km thicker, has higher crustal V-s, and a shallower MHT at similar to 10 km depth. The westward shallowing of MHT occurs through a lateral ramp. Aftershocks of the 2013-Kishtwar earthquake concentrate on the frontal-lateral ramp intersection and mark the MHT down-dip locked-to-creep transition.