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 amplitude asymmetry and initial polarity of seismic induced ionospheric perturbations around the epicenter are considered to be important in providing information about the rupture propagation and related vertical surface deformation. To comprehend this, we study ionospheric perturbations related to the 12 May 2015, Mw 7.3 Nepal earthquake. We model the coseismic slip associated with the event using the interferometric synthetic aperture radar derived surface deformation data. The ionospheric perturbations associated with the obtained surface deformation are explained in terms of rupture propagation, favorable geomagnetic field‐wave coupling, and satellite geometry effects. We discuss the effects of phase cancelation on the perturbation evolution for various receiver satellite line‐of‐sight configurations invoking an elementary version of satellite geometry factor. The present study thus elucidates further the role of nontectonic forcing mechanisms while identifying ground source pattern using the associated ionospheric perturbations.

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.

We report unique observations of crustal deformation caused by the seasonal water level changes of Tehri reservoir in the Garhwal region of NW Himalaya from GPS measurements and Interferometric Synthetic Aperture Radar (InSAR) analysis. All GPS sites along the Himalaya are strongly influenced by seasonal hydrological and atmospheric loading. However, the GPS site KUNR located near the reservoir additionally exhibits anomalous variations due to seasonal water loading and unloading by the reservoir. Our InSAR analysis confirms that the seasonal filling of the reservoir causes measurable subsidence in its neighbourhood. In addition to the elastic deformation caused by the seasonal reservoir loading and the negligible poroelastic deformation caused by associated fluid pressure changes, there is an unaccounted biannual deformation in the east component of the GPS time-series which we suspect to be caused by altered hydrological conditions due to the reservoir operations. Understanding crustal deformation processes due to such anthropogenic sources helps in separating deformation caused by tectonic, hydrological and atmospheric effects from that caused by these activities.

The Ninetyeast Ridge, a linear trace of the Kerguelen hot spot in the Indian Ocean, was emplaced on a rapidly drifting Indian plate. Magma production rates along the ridge track are computed using gravity-derived excess crustal thickness data. The production rates change between 2 and 15 m 3 /s over timescales of 3-16 Myr. Major variations in magma production rates are primarily associated with significant changes in the Indian plate velocity with low-production phases linked to high plate velocity periods. The lowest magma production rate (2 m 3 /s) at 62 Ma is associated with the rapid northward drift of Indian plate under the influence of the Reunion mantle plume. The contemporaneous slowing of the African plate coincides with increase in magma production rate along the Walvis Ridge in the Atlantic Ocean. The present study suggests that variations in the Indian plate motion and frequent ridge jumps have a major role in controlling the magma production, particularly on long-period cycles (~16 Myr). Short-period variations (~5 Myr) in magma productions may be associated with intrinsic changes in the plume, possibly due to the presence of solitary waves in the plume conduit.