Potential seismogenic asperities in the Garhwal–Kumaun region, NW Himalaya: seismotectonic implications

The Garhwal–Kumaun region (29°–31.5°N; 77°–81°E) in NW Himalaya lies in the Central Seismic Gap where the accumulated strain energy is sufficient for a future great earthquake. A broadband seismic network is continuously monitoring the seismic activity in this region and recorded a total of 3634 well located seismic events justified within the acceptable error bars (ERZ, ERH < 5.0) from 2007 to 2018 with hypocentral distances ranging from 0 to 350 km. In the present work, frequency-magnitude distribution (b-value) and fractal dimension (Dc-value) are investigated along (NW–SE) and across (SW–NE) the strike of Garhwal–Kumaun Himalaya. The study area has been divided into three different seismogenic asperities. Our results revealed that the proximity of Rudraprayag–Chamoli region exhibits significant low b-value (0.702 ± 0.03) and Dc-value (1.38 ± 0.03) and indicates high stress accumulation. The region has witnessed 1999 Chamoli earthquake Mb 6.3 and 2017 Rudraprayag earthquake M 5.7. A detailed study of b-value and Dc-value variation as a function of depth is also examined. The composite trend in abrupt escalation of b-value is observed at depth ≈ 12 km for Garhwal region and ≈ 7 km for Kumaun region. A well demarcation of crustal heterogeneity, high stress regime and associated seismogenic asperity is plotted. The low b-value and Dc-value depth ranges are coinciding with mid-crustal ramp and exhibiting a potential zone (12–15 km) for future great earthquake in the Garhwal region.