Interseismic plate coupling along the Uttarakhand Himalaya from GNSS and ALOS-2 InSAR

Differing interpretations of the strength of interseismic plate coupling along the Main Himalayan Thrust (MHT), particularly the possible existence of weak coupling zones, have led to widely varying assessments of the associated seismic hazards along the megathrust with potential impacts for more than half a billion people. Here, we focus on the kinematic status of the MHT in the Uttarakhand Himalaya, the location of one of the proposed low-coupling regions. We use an updated compilation of Global Navigation Satellite System (GNSS) data, along with Interferometric Synthetic Aperture Radar (InSAR) satellite imagery, to estimate the slip deficit and characterize the width of the MHT that is accumulating elastic strain. GNSS-derived horizontal displacements indicate a slip deficit of ∼18 mm/year, with an MHT that is locked up to a width of ∼115 km. We use ALOS-2 InSAR imagery to quantify the interseismic vertical deformation in the same region and identify a peak uplift of 4–6 mm/year. We apply the Elastic Subducting Plate Model (ESPM) to characterize the fault slip responsible for this vertical deformation while avoiding the vertical motion artifacts introduced by backslip or deep dislocation models. Both the GNSS and InSAR measurements are consistent with a shallow MHT that is fully locked from the surface to a depth of ∼20 km. Our results also indicate that the megathrust in the Uttarakhand Himalaya is highly coupled (>0.8) and the accumulated strain energy is equivalent to one Mw 8.1 megathrust earthquake every 100 years along this ∼300 km section of the megathrust.