Earthquake Shocks Around Delhi-NCR and the Adjoining Himalayan Front: A Seismotectonic Perspective

An increase in the number of earthquakes and subsequent clustering in northwest India, particularly around the Delhi-National Capital Region (NCR) and adjacent NW Himalayan front, provides a good opportunity to understand the underpinning tectonic controls and the likelihood of any large earthquake in the future. The 2001 M w 7.7 Bhuj, 2011 M w 6.9 Sikkim and 2015 M w 7.8 and 7.3 Nepal earthquakes (and 2004 M w 9.2 Sumatra event) are important in this context. We analyzed the seismicity around the Delhi-NCR and the adjoining Himalayan front, including event clustering and the spatio-temporal distribution of b-values, in the context of kinematics and the regional geodynamics. The overall moderate-to-low b-values, both in time and space, since 2016, provide information regarding an increase and subsequent stabilization of the stress field in the study area. The analysis led to the identification of (1) a structurally guided stress field in the region between the Kachchh and the NW Himalaya that coincides with the direction of Indian plate convergence and (2) frequent occurrences of earthquakes particularly in the Delhi, Kangra and Uttarkashi areas. We propose that faults in western Peninsular India, which pass through the margins of the Aravalli Range, the Marwar basin, and the isostatically over-compensated Indo-Gangetic Plains beneath the under-plated Indian lithosphere, act as stress guides; concentrating and increasing stress in regions of lithospheric flexure. This enhanced stress may trigger a large earthquake.