The Broadband Seismic Network of Stromboli Volcano, Italy

Abstract

Stromboli is a volcanic island that is part of the Aeolian arch in the Mediterranean Sea (Italy). It is one of the most active volcanoes in Europe. Its moderate, but persistent, explosive activity makes it an ideal site for studies into the seismogenic processes in volcanic areas (Auger et al. 2006; Chouet et al. 2003; Chouet et al. 2008; D’Auria and Martini 2008; Del Pezzo et al. 1992; Esposito et al. 2008; Jaupart and Vergniolle 1989; Martini et al. 2007); it also attracts a lot of tourists. In the past, this combination of tourism and volcanic activity was not considered to be dangerous, but over the past few decades, Stromboli has produced stronger explosions that have in some cases injured people visiting the summit area. Moreover, in the recent history of Stromboli, two effusive eruptions have occurred that were accompanied by dangerous phenomena such as tsunami and vulcanian explosions. The first of these effusive eruptions (on 28 December 2002) produced a lava flow on the Sciara del Fuoco side, which is the northwest flank of the island. Two days later, a landslide occurred on this flank, which resulted in the propagation of a 10-m tsunami wave around the coasts of the island. These events demonstrate that Stromboli can be dangerous, even if its activity is not very energetic. Indeed, the Sciara del Fuoco structure is a weakness zone of the volcanic edifice that fractures when the explosive activity increases, giving rise to this effusive activity (Martini et al. 2007). Moreover, during the past two effusive eruptions, vulcanian explosions were associated with the end stages of the effusive phases. These damaged the village of Ginostra and caused fires in the vegetation. For these reasons, in January 2003, the Istituto Nazionale di Geofisica e Vulcanologia (INGV; the Italian National Institute of Geophysics and Volcanology) started to install a broadband seismic network that is designed to monitor Stromboli’s volcanic activity. This nature of the activity requires broadband instruments because the eruptive processes generate signals that span a wide range of frequencies (Chouet et al. 2003; Neuberg et al. 1994). At present, the typical seismic signals that are being recorded on Stromboli are: volcanic tremors with frequencies of 1–6 Hz; explosion quakes that include components with different frequency contents, ranging from some tens of seconds up to 10 Hz; long-period (LP) earthquakes with frequencies of 1–6 Hz; volcano-tectonic (VT) earthquakes with a frequency band of 1–20 Hz; and landslide signals with frequencies of 1–10 Hz. In particular, very long period (VLP) events with frequencies of 0.02–1 Hz are associated with the Strombolian explosions and represent the lower frequency content of the explosion quakes. Furthermore, the network records regional and teleseismic events.