Tectonic seismicity at Stromboli volcano (Italy) from historical data and seismic records

We describe the main features of crustal tectonic seismicity in the area of Stromboli, Aeolian Islands, a volcano known worldwide for its typical Strombolian activity. We consider data from the Italian catalogues of earthquakes along with records of the local seismic network, covering the time span from 1885 to 1998. In the historical catalogues we find a low occurrence rate of earthquakes, with a small number of seismic events having intensity ≥ VIII in the Mercalli–Cancani–Sieberg scale. Recent instrumental data confirm this finding, achieving a maximum magnitude Md 3.7. We explain this low tectonic seismicity as the effect of conditions which allow only a limited storage of stress. From a seismic viewpoint, the Aeolian Archipelago shows two different seismogenic domains spatially separated by the Aeolian–Tindari–Giardini fault system. One domain, which includes the western and southern parts of the Aeolian Islands, is characterized by crustal seismic activity. The second domain, which includes the eastern part of the archipelago where Stromboli lies, has a large number of intermediate and deep earthquakes, but little crustal seismicity. We surmise that each domain has vertical heterogeneity separating ductile deformation from brittle failure of rock induced by temperature conditions and/or hydration/dehydration reactions, which affect the mechanical strength of the medium.