By accommodating ∼50% of the India-Eurasia plate convergence, the Main Himalayan Thrust (MHT) is considered to be a seismogenic zone with potential for generating large earthquakes (Avouac, 2003; Bilham, 2004). The recent 2015 Gorkha earthquake partly ruptured a known seismic gap on the central MHT between the 1505 M 8.5 earthquake to the west and the 1934 M 8.2 earthquake to the east (Figure 1). Seismological studies reveal that the rupture of the Gorkha earthquake initiated 15-18 km beneath the Gorkha region, then propagated eastward for ∼140 km (e.g., Avouac et al., 2015; Fan & Shearer, 2015; Lay et al., 2017). Geodetic slip models indicate that coseismic slip of the earthquake was concentrated on the subhorizontal décollement at a depth of 10-15 km, whereas the shallow portion of the fault remains unbroken (e.g., Diao et al., 2015; Elliott et al., 2016). After the event, significant postseismic surface deformation has been observed by Global Positioning System (GPS) and InSAR (Interferometric Synthetic Aperture Radar) techniques (e.g., Mencin et al., 2016; K. Wang & Fialko, 2018). Based on these postseismic observations, several previous studies have investigated two main mechanisms: afterslip and viscoelastic relaxation. Postseismic deformation in early periods is mostly attributed to afterslip at the downdip extension of the coseismic slip (