On the spatio-temporal variation in b-value after 25 April 2015 Gorkha, Nepal earthquake

Abstract

In the present study, the spatial-temporal distribution of b-value along the five faults area (the Judi fault, Thaple fault, Kathmandu fault, Motihari-GauriShanker fault, and Motihari-Everest fault) was investigated after the Gorkha earthquake (MW7.8). The earthquake catalog of 10,500 events was prepared by compiling the published catalogs. The study area is bounded in the central Himalaya from 26.5° to 29° in latitude direction and 84° to 87° in longitude direction. The frequency magnitude distribution shows the variation of the b-value along with fault areas from 0.45 to 0.69, indicating a common characteristic of aftershock sequences. In particular, the Judi fault area, Thaple fault area, and Motihari-Everest fault area are characterized by the low b-values of 0.45 ± 0.02, 0.48 ± 0.02, and 0.55 ± 0.04, respectively. These regions could be the source region for future earthquakes. The low b-value observed for fault areas are also consistent with the thrust faulting pattern in the region as indicated by the focal mechanism of mainshock and major aftershocks. The temporal variation of b-value shows inevitable fluctuations during 25 April to 12 May 2015. Among the area selected, the Motihari-Everest fault area is in critical strain (mechanically locked) conditions, as indicated by the stepwise energy release pattern.