Locked Frontal and Lateral Ramps on the Main Himalayan Thrust Beneath NW Himalaya Illuminated by Precisely Located Seismicity

Abstract

Abstract The Kashmir “seismic gap” in NW Himalaya is marked by hinterland‐to‐foreland reduction in GPS‐geodetic arc‐normal convergence‐velocity and increase in horizontal strain‐rate, associated with occurrence of moderate‐to‐small earthquakes. We analyze continuous waveforms from Jammu and Kashmir seismological network (2015–2017) to detect and preliminarily locate 1064 events, followed by probabilistic non‐linear relocation of 360 well‐located local earthquakes, with magnitudes 0.6–4.7 and hypocentral depths 0–60 km. Hypocenters shallower than 20 km lie on or above the Main Himalayan Thrust (MHT), clustered beneath the Kishtwar Higher‐Himalaya. Hinterlandward dipping seismicity‐clusters coincide with a MHT mid‐crustal frontal ramp, marking a ∼50 km wide locked‐to‐creep transition. The frictionally‐locked up‐dip MHT segment is ∼100 km wide, capable of hosting a Mw∼ 8.4 earthquake, if ruptured completely. Clustered seismicity SW of the Kishtwar Window and to its east illuminate MHT lateral‐ramps, which may limit the rupture width and/or modulate the rupture propagation. Entirely seismogenic underthrust Indian‐crust poses additional hazard from large earthquakes within it.

Keywords

• NW Himalaya
• seismicity
• mid‐crustal ramps