Insights into Mt. Etna’s Shallow Plumbing System from the Analysis of Infrasound Signals, August 2007–December 2009
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Previous studies performed on Mt. Etna on short and discontinuous time intervals indicate the North East Crater (NEC) as the most active source of infrasound. The source mechanism of NEC infrasound events was modeled as a double resonance. This lead to infer the connection between the NEC and both the southeast crater (SEC) and the eruptive fissure (EF), that opened at the beginning of the 2008–2009 eruption. Nevertheless, there are still several open questions that need to be addressed. For instance, the steadiness of NEC event features should be studied, as well as the orderliness of spectral changes of NEC events time-related to eruptive activity of other vents. The investigation of such topics is strongly enhanced by the possibility of analysing infrasound signals during year-long time periods. With this aim about 40,000 infrasound events, recorded at Mt. Etna from August 2007 to December 2009 were analysed by using spectral and location techniques. It was noted in particular that the NEC events featured periods with very steady waveforms and spectral characteristics lasting from days to months with slow or sudden variations. The most important eruptive episodes occurring at the SEC or the EF were accompanied by significant spectral changes in NEC events. In light of such systematic behaviour the connection between the NEC and the SEC/EF plumbing systems was not considered temporary but rather stable even during a relatively long time interval (2006–2009). Moreover, study of NEC event spectral features and their changes over multiple years supports the double resonance source model. Such a model, together with the inferred connections between NEC and SEC/EF feeding systems, implies that level fluctuations of a magma column inside the NEC conduit correspond to magmastatic pressure decrease/increase inside the main plumbing system. These findings open up new and interesting possibilities for monitoring magma pressure changes inside the Mt. Etna plumbing system.
KeywordsInfrasound Shallow plumbing system explosive activity source modelling Mt. Etna
We wish to thank Luciano Scuderi for carefully managing the permanent infrasound network and for the lab tests on the G.R.A.S. microphones. We acknowledge Sonia Calvari for the lucrative discussions. We also wish to thank the FP7-MC-ITN project NEMOH (GA Number: 289976) for its support. This work was partially funded by Grant INGV-DPC 2007–2009 (project V3_Lava). SV wishes to thank IPGP, BQR, PPF for its support (IPGP contribution number). We are grateful for the editor and anonymous reviewers for their useful suggestions that greatly improved the paper.
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