We use space geodetic data to investigate coseismic and postseismic deformation due to the 2015 Mw 7.8 Gorkha earthquake that occurred along the central Himalayan arc. Because the earthquake area is characterized by strong variations in surface relief and material properties, we developed finite element models that explicitly account for topography and 3‐D elastic structure. We computed the line‐of‐sight displacement histories from three tracks of the Sentinel‐1A/B Interferometric Synthetic Aperture Radar (InSAR) satellites, using persistent scatter method. InSAR observations reveal an uplift of up to ∼70 mm over ∼20 months after the main shock, concentrated primarily at the downdip edge of the ruptured asperity. GPS observations also show uplift, as well as southward movement in the epicentral area, qualitatively similar to the coseismic deformation pattern. Kinematic inversions of GPS and InSAR data and forward models of stress‐driven creep suggest that the observed postseismic transient is dominated by afterslip on a downdip extension of the seismic rupture. A poroelastic rebound may have contributed to the observed uplift and southward motion, but the predicted surface displacements are small. We also tested a wide range of viscoelastic relaxation models, including 1‐D and 3‐D variations in the viscosity structure. Models of a low‐viscosity channel previously invoked to explain the long‐term uplift and variations in topography at the plateau margins predict opposite signs of horizontal and vertical displacements compared to those observed. Our results do not preclude a possibility of deep‐seated viscoelastic response beneath southern Tibet with a characteristic relaxation time greater than the observation period (2 years).
We use surface deformation measurements including Interferometric Synthetic Aperture Radar data acquired by the ALOS-2 mission of the Japanese Aerospace Exploration Agency and Global Positioning System (GPS) data to invert for the fault geometry and coseismic slip distribution of the 2015 M w 7.8 Gorkha earthquake in Nepal. Assuming that the ruptured fault connects to the surface trace of the Main Frontal Thrust (MFT) fault between 84.34 ∘ E and 86.19 ∘ E, the best fitting model suggests a dip angle of 7 ∘. The moment calculated from the slip model is 6.08 × 10 20 Nm, corresponding to the moment magnitude of 7.79. The rupture of the 2015 Gorkha earthquake was dominated by thrust motion that was primarily concentrated in a 150 km long zone 50 to 100 km northward from the surface trace of the Main Frontal Thrust (MFT), with maximum slip of ∼ 5.8 m at a depth of ∼8 km. Data thus indicate that the 2015 Gorkha earthquake ruptured a deep part of the seismogenic zone, in contrast to the 1934 Bihar-Nepal earthquake, which had ruptured a shallow part of the adjacent fault segment to the east.
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