Energy and structural evolution process of high-altitude and long-runout landslides induced by a strong earthquake

Abstract

Restoring the dynamic evolution and energy transfer mechanisms of ancient, earthquake-induced long-runout landslides remains challenging. This study investigates the fluidization and momentum transfer mechanisms of the Mogangling landslide. We reconstructed the high-precision pre-failure topography using a contour-continuity restoration method to accurately define the initial energy state. A three-dimensional discrete element code was then employed to simulate the landslide kinematics over a duration of 87 s. During this process, the sliding mass achieved a maximum velocity of 27.5 ms-1. To elucidate internal momentum transfer, we quantitatively identified effective block collisions by applying an optimal prominence threshold of 30 % to velocity-distance curves. Furthermore, the Alpha Shape algorithm was utilized to extract the continuous structural evolution of the landslide mass. The simulation demonstrates that while the global mechanical energy of the system conforms to the law of conservation, energy at the individual block scale is non-conserved. Intense internal collisions facilitate a pushing effect, transferring kinetic energy from the rear to the frontal mass, thereby sustaining hyper-mobility and prolonging the runout distance. Crucially, this study quantifies the critical thresholds marking the transition from solid-phase sliding to granular-phase flow. The results indicate that macroscopic fluidization and maximum kinetic energy variation occur when the Volume Swelling (VS) rate reaches 29.46 % and the Area Growth (AG) rate reaches 319.59 %. These findings provide a quantitative link between microscopic energy dissipation and macroscopic structural fragmentation, offering vital dynamic parameters for hazard-chain modeling.