Analysis of Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data reveals coseismic and early postseismic (4–88 days) surface displacements associated with the 25 April 2015, Mw 7.8 Gorkha, Nepal, earthquake. The pattern of early postseismic surface uplift and subsidence is found to be opposite to that of the coseismic motion. InSAR and GPS data were jointly inverted for coseismic and postseismic slip on the Main Himalayan Thrust (MHT). We consider a complex ramp‐flat‐ramp‐flat subsurface structure of the MHT with four connected fault planes dipping toward north from the Main Frontal Thrust (MFT). The inverted coseismic slip distribution follows an elliptical pattern, extending east‐southeastward from the hypocenter with maximum amplitude of 5.7 m above the upper edge of the midcrustal ramp. We infer early postseismic afterslip (4–16 days) of 0.2–0.47 m toward downdip of the coseismic slip asperity and another patch with 0.1–0.2 m slip toward east. The shallow portion of the MHT toward south is found to have remained unruptured during the earthquake, nor did it slip aseismically after the earthquake, suggesting possibility of large events in the future.

The deadly 25 April 2015 Gorkha earthquake (Mw = 7.8) and aftershocks have partially released the accumulated interseismic strain along the Main Himalayan Thrust (MHT). Postseismic deformation associated with this earthquake is mainly confined to the north of the rupture. This suggests possible occurrence of future large events towards west or south, where MHT is locked. Asperities arising due to heterogeneity in the stress-strain patterns are believed to play a major role in controlling the coseismic rupture propagation. We determine interseismic coupling along the MHT and spatial variations in total strain rate using two decades of GPS, InSAR and sprit leveling data. Further, b-values derived from the seismicity data are used to identify zones of stress accumulation. We demonstrate that the 2015 earthquake ruptured an asperity which hosted high strain and stress accumulation prior to the event. A similar asperity towards west of the epicenter with unreleased strain energy is identified. This could spawn a future large earthquake akin in magnitude to the 2015 Gorkha event. These findings compel a revisit of the seismic hazard assessment of the central Himalaya.

The India-Eurasia collision, driven by tectonic forcing, is modulated by nontectonic forcing allied to seasonal variations in the neighboring regions. To decipher the ground deformation in response to hydrological mass variations of the Himalaya and North India, we analyzed continuous Global Positioning System (cGPS) observations from 50 sites together with Gravity Recovery and Climate Experiment (GRACE) data for the period 2004-2015. Vertical components of surface deformation derived from GPS and GRACE show moderate to high-level amplitude correlation with a slope value of 0.76 and a level of phase delay from ±25°to ±30°. The average weighted root-mean-square reduction (WRMS) of 17.72% suggests the prominence of hydrological mass variations particularly over the sub-Himalaya and Indo-Gangetic Plain (IGP). GPS-derived vertical deformation after correcting the hydrological effects utilizing GRACE observations suggests that the sub-Himalaya and IGP are undergoing subsidence and the surrounding areas show uplift. In addition to the tectonic and nontectonic forcings, an unsustainable consumption of groundwater associated to irrigation and other anthropogenic uses influence the subsidence rate in the IGP and sub-Himalaya. Further, 2-D elastic dislocation modeling suggests that GRACE correction to the GPS vertical velocity causes a reduction in the subsurface slip rate estimation over the Main Himalayan Thrust (MHT) system by 12.06% and improves the chi-square misfit by 20.32%.

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