Friction weakening in granular flows deduced from seismic records at the Soufrière Hills Volcano, Montserrat

Abstract

Abstract Accurate modeling of rockfalls and pyroclastic flows is still an open issue, partly due to a lack of measurements related to their dynamics. Using seismic data from the Soufrière Hills Volcano, Montserrat, and granular flow modeling, we show that the power laws relating the seismic energy E s to the seismic duration t s and relating the loss of potential energy Δ E p to the flow duration t f are very similar, like the power laws observed at Piton de la Fournaise, Reunion Island. Observations showing that t f ≃ t s suggest a constant ratio E s /Δ E p ≃10 −5 . This similarity in these two power laws can be obtained only when the granular flow model uses a friction coefficient that decreases with the volume transported. Furthermore, with this volume‐dependent friction coefficient, the simulated force applied by the flow to the ground correlates well with the seismic energy, highlighting the signature of this friction weakening effect in seismic data.