Seismic Precursory Velocity Changes Associated with Debris Flows in Tianmogou Inferred from Ambient Noise Interferometry

Global warming has accelerated glacier retreat and permafrost degradation in high-elevation regions, significantly increasing the frequency and magnitude of glacier-related debris flows. This study focuses on Tianmogou, a debris-flow-prone catchment on the Tibetan Plateau, where three broadband seismometers were deployed for continuous monitoring during the active period. Using ambient noise interferometry, relative seismic velocity changes (dv/v) and the effective decorrelation coefficient (dCe) were calculated to achieve high-resolution characterization of the temporal evolution of subsurface mechanical properties.The results show that dv/v exhibits pronounced seasonal variations and is significantly negatively correlated with soil temperature, while short-term hydrological processes, such as intense rainfall and snowmelt, lead to rapid dv/v decreases accompanied by marked dCe increases. Notably, several hours prior to multiple debris-flow events, persistent dv/v reductions and rapid dCe increases were consistently observed as precursory signals, with rainfall-triggered events (e.g., 10 July 2020) displaying particularly prominent precursory characteristics. By jointly analyzing seismic velocity changes, precipitation, and soil moisture, this study reveals the progressive degradation of subsurface media during debris-flow initiation and demonstrates the potential of seismic methods for long-term hazard monitoring in glacial and periglacial environments.