Insights into initiation of typhoon-induced deep-seated landslides in Southeast coastal China

Typhoon-induced deep-seated landslides are prone to cause mass casualties to coastal regions once they occur. On 10th August 2019, typhoon “Lekima” triggered the deadliest landslide in recent decades in Southeast coastal China (32 deaths). To investigate the possible failure mechanism of this catastrophic event, we conducted in situ investigations and image analysis to determine the geological characteristics and performed numerical modelling of transient variation in slope stability throughout the typhoon. Generalized modelling analysis was further designed to research the impacts of some landslide settings and forcing factors on this type of geohazard. Our findings show that cracks within the weathered rock played vital roles in the landslide initiation. Cracks-induced strength reduction made the saturated rock provide insufficient resistance to stabilize the slope. Preferential infiltration promotes the saturation of sliding mass within a short-duration typhoon, responsible for the rapid failure. Furthermore, the impact of trees on slope stability depends heavily on landslide settings. Constrained by the limited growth depth of roots, though both beneficial and detrimental mechanisms of trees show minor impacts on the development of a deep-seated sliding surface, trees and geological settings converged to produce the failure mode of the Yongjia landslide. Roots significantly enhanced the shallow soil layer and the soil–rock interface is simulated to be the potential sliding surface in the absence of trees. Results suggest future landslide risk assessments in Southeast coastal China to specify the meteorological and geological conditions, which would greatly improve the aim to predict the spatiotemporal distribution of landslides throughout a typhoon.