Spatiotemporal postseismic deformation due to the 2018 Palu-Donggala earthquake revealed the relative importance of viscoelastic relaxation and the afterslip distribution estimated from geodetic observations

Abstract The Palu region has attracted attention due to significant seismic activity, including a destructive earthquake in 2018. This study aims to investigate postseismic deformation following the 2018 Palu-Donggala earthquake using the Interferometric Synthetic Aperture Radar (InSAR) technique. We utilized Global Navigation Satellite System (GNSS) data to obtain the viscoelastic mechanism decay time. Therefore, we subtracted the viscoelastic relaxation signal to obtain spatiotemporal afterslip distribution inferred from the 2.5D InSAR observation based on the Steepest Descent Method (SDM). Our results suggest the viscoelastic mechanism is indispensable, with an optimal decay time of about 2 years after the earthquake. Based on the chi-square statistical test, the spatiotemporal afterslip model can explain the observation with good qualification. We found anomalies indicating non-decreasing slip, which is likely due to several factors, such as the presence of Slow Slip Events (SSE). These findings provide valuable insights regarding the potential for future earthquakes and have significant implications for disaster risk assessment in the Palu region and its surroundings.