Variation in the Main Himalayan Thrust (MHT) within the Central Himalayan Seismic Gap using teleseismic P -wave coda autocorrelation: implications for seismic hazard

SUMMARY The seismic hazard due to higher magnitude Himalayan earthquakes largely depends on the geometry of the underthrusting Indian Plate beneath the Himalayas, that is, the Main Himalayan Thrust (MHT). For an objective assessment of seismic hazard in the central Himalayan seismic gap, we determine the geometry of the MHT along 4 ∼SW-NE oriented arc-normal seismic profiles covering the central Himalayan seismic gap. We use teleseismic P-wave coda autocorrelation on waveforms recorded at 117 broad-band seismic stations spread along these profiles, with an interstation spacing of 3–5 km. The results show that along these seismic profiles, the MHT is mostly of flat-ramp-flat geometry. However, the mid-crustal ramp within the MHT shows variations in its location, dip angle and width. We also observe variations in the MHT near the main frontal thrust and main boundary thrust. The observed variations in the MHT geometry within the central Himalayan seismic gap thus suggest the possibility of along-strike segmentation of the Himalayan arc, and different seismic hazard scenarios may be present during any possible higher magnitude earthquake in the central Himalayan seismic gap.