Himachal Pradesh Seismological NETwork (HiPSNET): Structure of the Crust and the geometry of the Main Himalayan Thrust

The Himachal Pradesh Seismological NETwork (HiPSNET) was installed in 2019 across the northwestern Himachal Himalaya, comprising seven broadband seismograph systems. Teleseismic data with magnitude greater than 5.5 and in the distance range of 30-90° have been used to compute P-wave receiver functions (P-RFs). These P-RFs have been depth migrated to form a 2D common conversion point (CCP) stack profile across the strike of the Himalaya. The main features on the CCP profile are the positive impedance boundaries of the Moho and the mid-crust, and the negative impedance contrast boundary of the Main Himalayan Thrust (MHT). The Indian crust underthrust the Himachal Himalaya with a gentle dip of ~5-7° in the NE direction. The Moho depth increases from the foreland (SW) to the hinterland (NE). Beneath the Sub-Himalaya, the Moho is at a depth of ~45 km, and gradually deepens to ~60 km beneath the Lesser-Himalaya, and further to ~70 km beneath the Higher-to-Tethyan Himalaya. The MHT, associated with a low-velocity layer, has a flat-ramp geometry, and ranges in depth from ~10 km beneath the Sub-Himalaya to ~20 km beneath the Higher-Tethyan Himalaya. Precisely located small-to-moderate earthquakes, from previous studies, concentrate on or above the MHT frontal ramp structure. This possibly marks the locked-to-creep transition on the MHT, lying below the Higher-Himalaya.