Regional stress field in the area of Stromboli (Italy): insights into structural data and crustal tectonic earthquakes

Abstract

Crustal tectonic seismicity on Stromboli is here discussed along with the regional tectonic and geodynamic context of the Aeolian archipelago, Italy. The aim of this paper is to contribute to the reduction of the crucial gap in information concerning the tectonic activity originating at the volcano Stromboli in the last decade. It is indeed well known that Strombolian eruptions, related to the persistent state of activity on this volcano, allow a fast collection of seismic data which are mainly represented by explosion quakes and tremor. However, only some sporadic information concerns tectonic earthquakes due to their low occurrence rate. A catalog of 150 crustal tectonic earthquakes recorded at Stromboli from 1985 to 1996 is presented here. The analyses of the seismograms were carried out on the basis of the records of the station STR, located in the southwestern part of the island. The magnitude considered ranged from 1.5 to 3.7. Hypocentral location indicates foci at less than 12 km, although for the majority of the earthquakes, which are not recorded at the seismic stations deployed on the other islands of the Aeolian archipelago, a shallower (within a few kilometers) depth can be hypothesized. The strain release associated with the 150 tectonic earthquakes of our catalog was also evaluated. The low levels of occurrence and seismic energy release reached throughout the ca. twelve years analyzed here confirm the minor role played by processes of brittle failure of rocks. This aspect of seismic activity is nevertheless important as it can provide a contribution to the knowledge of the dynamics of this volcano. The focal mechanisms available, integrated with data from the literature, show the T-axes oriented about NE–SW and NW–SE. These findings are consistent with the deformative and tectonic characteristics of this volcanic edifice and of the Aeolian archipelago, which shows the same two directions of extension. This is in agreement with subduction, which is very old or which passively evolves towards the final stages, and is controlled by the transform activity of the Aeolian–Tindari–Giardini fault system.