Seismicity and stress inversion study in the Kangra–Chamba region of north-west Himalaya

The seismotectonic of the Kangra–Chamba region, the source zone of the 1905 great Kangra earthquake (M 8.0), has been studied analysing about 350 local earthquakes recorded by broadband seismological network under operation in NW Himalaya. The study reveals that the seismic activity is concentrated to the north of surface trace of the Main Boundary Thrust, Panjal Thrust and Chamba Thrust. The hypocenters are confined within 40 km depth with higher concentration in the uppermost crust. Fault plane solutions of 41 selected local earthquakes are examined. The fault plane solutions for shallow earthquakes (<10 km) predominantly shows thrust mechanisms, whereas earthquakes below ~10 km depth shows normal faulting mechanism. The stress tensor study reveals maximum compressional stress (σ1) with trends 29°N and plunges at 6°, and the minimum stress (σ3) trends at 134°N and plunges at 67° in the upper 10-km crust favouring thrust mechanism of the earthquakes with a NE-directed regional compressive stress. In the deeper part, σ1 trends at 244°N and plunges at 59° while σ3 shows extension trending at 9°N with a plunge of 20° giving evidence of extensional tectonics in the central part of the study area. The NE-dipping thrust sheets existing in the region as well as SW-dipping Chenab Normal Fault merges with the detachment that creates a complex tectonic interaction which is responsible for generating normal faulting earthquakes below the detachment plane.