Analysis of the b, p values, and the fractal dimension of aftershocks sequences following two major earthquakes in central Himalaya.

On April 25 of 2015, earthquake of 7.6 M struck the central Himalayan region having epicenter at Barpak village in the Gorkha district of Nepal. The event was followed by 7.0 M earthquake known as Dolakha earthquake, epicenter on the border of Dolakha and Sindhupalchowk. In this study, the b-value, aftershock decay rate p-value, and correlation fractal dimension were estimated for the aftershock sequences. The data used were obtained from the National Earthquake Monitoring and Research Centre (NEMRC), Nepal. The b-values 0.89 ± 0.05 and 0.90 ± 0.07 were computed for aftershocks after Gorkha and Dolakha event, respectively. A significant increase in b-values were reported following the Gorkha earthquake and Dolakha earthquake. The slip procured in the primary fault is respectively 60 % and 56 % after the events. The aftershocks sequences after both events were modelled by the Omori-Utsu law with p = 1.2 ± 0.11 and p = 0.76 ± 0.04. The observed b and p values after the earthquake sequences may correlate well with the large slip experienced by the seismogenic fault. This study sheds light on the mechanism behind the preparation of the significant earthquakes in the tectonic regions of the Himalaya.