Insights into Mt. Etna’s Shallow Plumbing System from the Analysis of Infrasound Signals, August 2007–December 2009

Previous studies performed on Mt. Etna on short anddiscontinuous time intervals indicate the North East Crater (NEC)as the most active source of infrasound. The source mechanism ofNEC infrasound events was modeled as a double resonance. Thislead to infer the connection between the NEC and both thesoutheast crater (SEC) and the eruptive fissure (EF), that opened atthe beginning of the 2008–2009 eruption. Nevertheless, there arestill several open questions that need to be addressed. For instance,the steadiness of NEC event features should be studied, as well asthe orderliness of spectral changes of NEC events time-related toeruptive activity of other vents. The investigation of such topics isstrongly enhanced by the possibility of analysing infrasound signalsduring year-long time periods. With this aim about 40,000 infrasoundevents, recorded at Mt. Etna from August 2007 to December2009 were analysed by using spectral and location techniques. Itwas noted in particular that the NEC events featured periods withvery steady waveforms and spectral characteristics lasting fromdays to months with slow or sudden variations. The most importanteruptive episodes occurring at the SEC or the EF were accompaniedby significant spectral changes in NEC events. In light of suchsystematic behaviour the connection between the NEC and theSEC/EF plumbing systems was not considered temporary but ratherstable even during a relatively long time interval (2006–2009).Moreover, study of NEC event spectral features and their changesover multiple years supports the double resonance source model.Such a model, together with the inferred connections between NECand SEC/EF feeding systems, implies that level fluctuations of amagma column inside the NEC conduit correspond to magmastaticpressure decrease/increase inside the main plumbing system. Thesefindings open up new and interesting possibilities for monitoringmagma pressure changes inside the Mt. Etna plumbing system.