Role of Liquefied Deposition Layers in Modulating Seismic Wave Generation in Surge‐Type Debris Flows

Abstract Surge‐type debris flows propagate as a sequence of surges, forming gradually thickening in situ deposition layers between surges that dynamically alter channel‐bed conditions. Seismic recordings from Jiangjia Ravine reveal a progressive attenuation of ground motion amplitude with surge sequence, despite comparable flow magnitudes—indicating a decoupling between flow scale and seismic response. We attribute this to the accumulation and liquefaction of inter‐surge deposition layers, rather than pre‐existing deposits. To quantify this mechanism, we adopt an effective transmission parameter ( ξ ) within a fluvial seismology‐based framework, and propose a sigmoid function linking ξ to normalized deposition layer thickness ( H *). This formulation significantly improves the prediction of seismic power spectral density (PSD) across surges and provides a transferable approach to characterize subsurface flow–bed interactions. Our findings underscore the critical role of bed structure evolution during flow in modulating debris‐flow‐induced seismic signals, with implications for real‐time monitoring and early warning in sediment‐rich catchments.