Infrasound unmasks flow turbulence as a significant seismic source within debris flows

Debris flows represent a major hazard in mountain environments. Recently, the use of seismo-acoustic signals to study and monitor debris flows has gained attention. Debris flows, indeed, generate both seismic and infrasonic waves, whose source mechanisms are not yet completely clear. We present the seismo-acoustic analysis of a debris-flow event at Illgraben (Switzerland). The array processing of infrasonic data reveals that coherent infrasound is preferentially radiated at channel irregularities, acting as predominant acoustic sources because of the intense flow turbulence. The high cross-correlation observed between the infrasonic and seismic signals during the event suggests that a significant component of the seismic signal is produced by the turbulent flow and correlates with infrasound. Our work defines additional constraints on the seismo-acoustic radiation by debris flows and highlights how infrasonic and seismic signals can be used to detect and track events in near real time.