Forecasting volcanic eruptions by geophysical methods: the case of Vesuvius and Campi Flegrei, Italy

The assessment of a monitoring system aimed at eruption forecasting is a relevant scientific and civil protection objective for Mt.Vesuvius and Campi Flegrei, due to the million inhabitants living close to these explosive volcanoes. The search for precursors of volcanic eruptions is currently mainly based on the phenomenological analysis of seismicity patterns and the detection of anomalous strain episodes. The latter lead to significant observations of phenomena preceding volcanic eruptions. The strain measured at borehole dilatometers during the basaltic Izu-Oshima eruption in 1986-1987 and on Hekla in 1991 are however the first clear geophysical signals observed prior to an eruption. Other recent explosive eruptions were preceded by characteristic swarms of long period earthquakes and volcanic tremor several hours to days before the eruptions (Redoubt, Rabaul, Pinatubo, Galeras). Only recently has some significant progress been made on a quantitative approach for interpreting seismic and strain data on volcanoes in terms of eruption modeling and forecasting. The scarcity of broadband seismic observations and the lack of adequate borehole geophysical monitoring systems is however still a major drawback: for volcano geophysics. This limits the effectiveness of forecasting methods.