Co-existing fast and slow afterslip processes following the 2015 Gorkha (M_W7.8) earthquake resolved by full time-series inversion

The 2015 Gorkha (M_W=7.8) earthquake ruptured the downdip portion of the Main Himalayan Thrust. Afterslip following this event provides valuable insights into the frictional properties on the thrust interface, yet its amplitude and distribution remain controversial. In this study, we incorporate long-term GNSS and InSAR data and correct for the viscoelastic relaxation simulated using a regional 3-D viscoelastic model. We adopt the corrected data in a novel inversion algorithm and resolve two spatially separated afterslip processes with different decay times: fast afterslip near the bottom of the coseismic rupture, possibly stopped the mainshock and triggered the M_W7.3 aftershock 17 days later, and slow afterslip extending further downdip. By comparing the afterslip and aftershock patterns, we identify distinct partitioning of seismic and aseismic slip behaviors at the bottom of the seismogenic zone, which reflects local heterogeneities in frictional properties at the transition depths.