Insights into the great Mw 7.9 Nepal earthquake of 25 April 2015

The 2015 Mw 7.9 earthquake occurred in the Nepal Himalaya between the Indian and Asian plates. The gravity modelling has been carried out along a 2D trench-orthogonal profile passing through the epicentre of this earthquake. The projections of mainshocks and aftershocks show their major confinement around the bending segment of the Indian upper crust (IUC). The operative shallowly plunging maximum compressive stress led to the accumulation of strain energy around the bending zone of the IUC, and triggered thrust-dominated southward movement of the Indian crustal block along a shallowly, dipping shear plane in the anisotropic layer. This can be broadly explained by three-stage rupture processes: the first one was associated with slow nucleation and rupture growth for early similar to 15 sec, the second one migrated upward, rupturing the uppermost part of the IUC for the next similar to 10 sec, and the third one propagated very fast during deformation for the remaining similar to 25 sec till the fracture-tip reached the overlying brittle Asian crust.