Abstract

Sediment flows generate ground vibrations by exerting basal force fluctuations on the riverbed, which motivates the use of seismology to indirectly measure flow properties. Linking the force fluctuations and properties of highly concentrated sediment flows, however, remains particularly challenging due to complexities that arise from grain-to-grain interactions. Here we conduct downscaled flume experiments designed to investigate the influence of grain scale processes on the generation of force fluctuations for stratified sediment flows associated with significant grain sorting. We demonstrate that, under such flow conditions, the amplitude of force fluctuations decreases as the volumetric solid concentration increases. We suggest that this dependency reflects the negative relationship between volumetric solid concentration and particle agitation, which in turn controls the amplitude of force fluctuations. We therefore advance that volumetric solid should be incorporated in seismic models as a key parameter describing the particle agitation of highly concentrated sediment flows.