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 Stro mbolian activity. We consider data from the Italian catalogues of earthquak es 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 ra te of earthquakes, with a small number of seismic events having intensity g reater than or equal to VIII in the Mercalli-Cancani-Sieberg scale. Recent instrumental data confirm this finding, achieving a maximum magnitude M-d 3 .7. We explain this low tectonic seismicity as the effect of conditions whi ch allow only a limited storage of stress. From a seismic viewpoint, the Ae olian Archipelago shows two different seismogenic domains spatially separat ed 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 pa rt of the archipelago where Stromboli lies, has a large number of intermedi ate and deep earthquakes, but little crustal seismicity. We surmise that ea ch domain has vertical heterogeneity separating ductile deformation from br ittle failure of rock induced by temperature conditions and/or hydration/de hydration reactions, which affect the mechanical strength of the medium. (C ) 1999 Elsevier Science B.V. All rights reserved.