Coseismic deformations of the 2015 MW 7.8 Gorkha earthquake and interseismic strain accumulation in the Himalayan tectonic belt and Tibetan plateau

Abstract

The principal strain rate, derived from GPS velocities from the Tibetan Plateau and the India Plate, shows that the Himalayan tectonic belt exhibits compression deformation in a NE–NS–NE direction from the west to the east. The GPS velocity profiles reflect that the distribution of strain accumulation is uneven: there is a 17.1mm/yr. compressive deformation distributed over 400km along 85° E longitude, a 20.9–22.2mm/yr. compressive deformation dispersed across 400–500km along 79° E longitude, and a 15.3–16.9mm/yr. compressive deformation spread across 500–600km along 91° E longitude. The MW 7.8 Gorkha earthquake occurred at the edge of an intense compression deformation zone of about 6.0×10−8/yr. in a north–south direction, and an about 90% compressive strain is absorbed in the 300km region near the Main Frontal Thrust (MFT). Coseismic displacements, larger than three standard deviations (3SD), are mainly concentrated within 360km from the epicenter. The nodal plane of the main shock divides the areas where tensile strain release in an exponential attenuation pattern is dominant to the north, and where compressive strain with upward movement is dominant to the south. The results inversed by the SDM program reveal that the maximal slip of the Gorkha earthquake is 5.33m, and its moment magnitude is MW 7.85, and the largest stress drop is 4.21Mpa. Slips larger than 0.5m are mainly distributed in a region approximately 135km×105km, which show that the rupture of the Gorkha earthquake does not reach the surface. Finally, we estimate that the recurrence period of this earthquake is about 166±20years according to the strain accumulation before the earthquake and the coseismic release feature.