Investigating earthquake legacy effect on hillslope deformation using InSAR‐derived time series

Abstract

AbstractMountainous landscapes affected by strong earthquakes typically exhibit higher landslide susceptibility in post‐seismic periods compared to pre‐seismic conditions. This concept is referred to as the earthquake legacy effect, which needs to be better understood to develop an accurate post‐seismic landslide hazard assessment. The earthquake legacy effect is mainly assessed by monitoring either rapid landslide occurrences or slow‐moving landslides over time. However, landslide inventories provide discrete information both in spatial and temporal domains, whereas monitoring only selected slow‐moving landslides discards the response of hillslopes exposed to a given earthquake. Therefore, to provide a more comprehensive understanding of the concept, this research focuses on post‐seismic hillslope evolution by examining the deformation time series generated from the Interferometric Synthetic Aperture Radar technique over the area affected by the 2017 Mw 6.4 Nyingchi earthquake, China. We also analyse factors controlling these InSAR‐derived hillslope deformations. Our results show a high coherence between hydrologic conditions (i.e., precipitation and terrestrial water storage) and surface deformation in pre‐ and post‐seismic periods. The earthquake disturbs this strong correlation for a while (~2 years) right after the seismic tremor, and then, a seasonal deformation pattern depending on hydrologic conditions appears again. Our findings show that the average post‐seismic hillslope deformation is still higher than its pre‐seismic counterpart approximately four and a half years after the earthquake. These findings trigger further research questions regarding whether hillslopes could fully recover after a major earthquake or gain a new level of hillslope susceptibility caused by intense ground shaking.