Coseismic Seismic Velocity Variations of a Deep-Seated Landslide Caused by Two M6.5+ Earthquakes in Eastern Taiwan

Relative seismic velocity changes (dv/v) derived from ambient noise interferometry serve as a proxy for the internal rigidity or structural health of landslide materials. Strong ground motion often induces coseismic velocity drops, indicating damage within the shallow crust or the landslide body. This study focuses on the deep-seated, slow-moving Wuhe landslide in eastern Taiwan, which exhibits stable creeping with daily displacement rates ranging from 4 mm to 25 mm(Weng et al., 2025), to investigate its response to the September 2022 earthquake sequence, specifically the ML 6.6 Guanshan and ML 6.8 Chihshang earthquakes.To monitor temporal variations in the landslide's internal state, we applied the single-station cross-component (SC) technique to the Wuhe landslide using continuous ambient noise records. The seismic monitoring network comprises one geophone installed directly on the sliding mass and three reference stations located on stable bedrock outside the landslide area. This configuration aims to differentiate between landslide-specific structural changes and regional reference variations. The preliminary results showed that a clear seismic velocity reduction was found spatially within the landslide area. Through dv/v measurements with in-situ real-time kinematic (RTK) GPS data and strong-motion records, the coseismic velocity drops are in response to the accelerating surface displacement and strong ground shaking, and the spatial relationships between dv/v, surface movement and peak-ground acceleration (PGA) are systematically compared . In fact, the earthquake did not trigger catastrophic landsliding at the Wuhe site, Thus, we further investigate the recovery of landslide material properties following strong ground shaking. The post-seismic recovery duration captured by dv/v observations can help us to better understanding recovery mechanism of landslide material after earthquakes.