Aftershock analysis of the 2015 Gorkha-Dolakha (Central Nepal) earthquake doublet

On 25 April 2015, a large earthquake with moment-magnitude (M_w) 7.8 occurred at Gorkha (latitude 28.23° N and longitude 84.73° E) in Central Nepal. Just 17 days later, another large earthquake of M_w 7.3 occurred at Dolakha (latitude 27.80° N and longitude 86.06° E), about 140 km away from the previous epicenter. In this study, we deal with the aftershocks of these two earthquakes that occurred in the region (27°-28.5°N, 84°-87°E) spanning the period from 25 April 2015 to 28 May 2016 to find the spatiotemporal distribution patterns, the size distribution (b-value), and the aftershock decay rate (p-value) of this sequence. Aftershock epicenters of the 2015 Gorkha-Dolakha earthquake doublet are distributed over an area approximately 170 km in length and 70 km in width and largely confined in a depth range from 5 to 25 km. The spatial distribution of epicenters and known geological structures in this study reveals that aftershocks are limited on the east by the surface trace of the Everest lineament and on the south side by the surface trace of the segment of the Main Boundary Thrust (MBT). The estimated b-and p-values of this seismic sequence are 0.93 ± 0.03 and 0.79 ± 0.24, respectively. This b-value is higher than the b-value estimated by the previous studies, while the p-value corresponds in general with the p-value obtained by recent study in the region.