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

The Garhwal-Kumaun region (29 degrees-31.5 degrees N; 77 degrees-81 degrees 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 approximate to 12 km for Garhwal region and approximate to 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.