Amplified coseismic loess failure and postseismic landslide acceleration triggered by the 2023 Jishishan, China earthquake

Moderate-sized earthquakes of magnitude 6 are typically considered not as destructive as larger earthquakes (>M7), but this may be different when triggering geohazards in semi-arid environments. Agricultural production in such environments relies on irrigation, which increases liquefaction susceptibility, particularly in loess deposits that are highly porous, prone to structure collapse, and amplifying seismic hazards. Despite this, the combined impact of agricultural activities and loess amplification on secondary earthquake hazards has been largely overlooked. In this study, we investigated the hazards triggered by a Mw 6.1 earthquake in Jishishan County, Gansu Province, China, a region connecting the Tibetan and Loess Plateaus. Our results, derived from satellite and drone observations, field surveys, and P-wave and S-wave velocity structure inversion, reveal significantly exacerbated seismic hazards, including 9340 densely distributed coseismic landslides, a deadly 3-km-long liquefaction-induced mudflow enabled by irrigation and land reclamation, and loess-amplified seismic subsidence exceeding 0.5 m. These severe hazards are rare for earthquakes of this magnitude and underscore how agricultural activities and the unconsolidated nature of loess deposits exacerbate landsliding and damage during moderate-sized earthquakes. Additionally, we identified 372 earthquake-accelerated landslides (EALs) using time-series InSAR. Compared to coseismic loess landslides, EAL is prone to occur in the far field with weaker seismic shaking. This study provides critical insights for improving the prevention and mitigation of earthquake-induced hazards in semi-arid loess environments, particularly those impacted by frequent anthropogenic modifications.