Seismic crustal shear velocity structure across NW Himalaya and Ladakh-Karakoram using receiver function modelling: Evidence of the Main Himalayan Thrust

Abstract

To understand the nature of the underthrusting Indian Moho and Main Himalayan Thrust across the NW Himalaya and Ladakh-Karakoram (southern Tibet), we calculate the shear velocity models by inverting teleseismic receiver functions at 15 seismic stations. The crustal shear wave velocity models show that the Indian crust underthrusts gently. The depth of Indian Moho increases from ~46 km below the Gangetic Plain to ~78 km at the southern flank of the Karakoram Fault. The crustal velocity models also show a continuous intra-crustal low-velocity layer across the NW Himalaya and Ladakh-Karakoram. We combine our results with earlier results of magnetotelluric and seismological studies in this area. We infer that the observed intra-crustal low-velocity layer from the NW Himalaya to the southern flank of the Karakoram Fault is a possible expression of the Main Himalayan Thrust (MHT) in this region. Moreover, we observe higher shear velocities in the lowermost crust beneath the Higher Himalaya and Ladakh; and interpret them as the possible presence of the (partially) eclogitesed rocks in the lowermost crust.