Rockfalls at the Soufière Hills volcano, Montserrat: scaling law between potential energy loss, energy dissipated as seismic waves and duration

Seismic signals associated with rockfalls can provide important information on the characteristics of the source (volume, duration, location). As such, seismic data from the Piton de la Fournaise volcano were used to evidence a scaling law between the energy dissipated as seismic waves and the duration of granular flows (Hilbert et al., 2011, doi:10.1029/2011JF002038). This study was completed by analytical analysis and numerical simulations showing that a similar scaling law exists between the loss of potential energy of an event and the duration of its propagation phase. Thus, this previous study shows that the coefficient of this scaling law is a strong indicator of the effect of topography on the flow dynamics. Morever, this study was used to estimate the volumes of granular flows using seismic records and to constitute databases of rockfall characteristics (volume, location, and occurrence time) in order to study the relationship between rockfall activity and processes related to volcanic activity. Our study aims to test whether a similar scaling law can be observed at the Soufiere Hills Volcano (Montserrat Island, Lesser Antilles) despite differences of settings: -at Piton de la Fournaise, most rockfalls propagate from one side of the Dolomieu crater to its center, whereas at the Soufière Hills volcano, they spread from the dome to the sea shore. -the properties of constituting rocks is quite different. The Piton de la Fournaise is a shield volcano, whereas the Soufrière is an andesitic volcano. The signal processing developed for the data of Piton de la Fournaise was applied to the seismic data of a 3 days crisis with 200 rockfalls and pyroclastic flows at the Soufière Hills volcano. A similar scaling law between seismic energy and potential energy was found. This result suggests that such study could be relevant at a more general level. Later on, the computation of the seismic energy was enhanced using frequency dependent parameters (anelastic attenuation, etc.).