Assessment of geodetic strain and stress variations in Nepal due to 25 April 2015 Gorkha earthquake: Insights from the GNSS data analysis and b-value

Abstract

A magnitude MW7.8 earthquake occurred on 25 April 2015 (referred as Gorkha earthquake). We have analyzed the spatial variation of b-value and two-dimensional strain within Nepal Himalaya before and after the Gorkha earthquake. We have used continuous Global Navigation Satellite System (GNSS) data from 30 stations in the Nepal region for geodetic strain estimation and earthquake data for b-value estimation. The GNSS data were processed using double differencing technique for the accurate position of each station. The precise velocity vectors show a general azimuth of north east for all the stations and have been used to derive two-dimensional strain. Between epicenters of Gorkha (25 April 2015) and Dolakha earthquakes (12 May 2015), we observed high co-seismic horizontal displacements (0.2 m to 2 m). In the Pre-seismic deformation study, maximum strain accumulation (56.40 × 10−9) and low b-value (0.79–0.89) was observed in and around the Western Nepal region, which may be responsible for the 2015 Gorkha earthquake. The potential seismic zones were identified by GIS based integration of geodetic strain and b-value map and superimposition using weighted overlay method. The Maximum strain and low b-value are now observed in the eastern part of Nepal. Hence, the spatial disposition of elastic energy has changed after the two major earthquakes and continuous seismic hazard assessment is required in the eastern Nepal.