Low-frequency seismic signals recorded by OBS at Stromboli volcano (Southern Tyrrhenian Sea).pdf

Low-frequency seismic signals recorded by OBS at Stromboli volcano (Southern Tyrrhenian Sea) Tiziana Sgroi,1 Caterina Montuori,1 Roberto Agrusta,2 and Paolo Favali1,2 Received 27 October 2008; revised 23 January 2009; accepted 27 January 2009; published 24 February 2009. [1] Five three-component broadband ocean bottom seismometers (OBSs) were deployed on the seafloor around the Aeolian Islands (Southern Tyrrhenian Sea). By comparing OBSs digital seismograms, we found a low- frequency seismicity recorded only at OBS05, the nearest seafloor station to Stromboli volcano. This seismicity appears in the form of a continuous seismic signal (tremor-like-signal) as well as a considerable number of shock-like events. We focused on recordings from OBS05 to verify their correlation with Stromboli volcanic activity. From the spectral analysis, we observed low-frequency events (LP events), superposed upon the continuous background noise (tremor). LP events and tremor, showing similar energy fluctuations and frequency content, appear to be produced by the same dynamic processes. We interpret this low-frequency seismicity as probably originating from a continuous uprising of gas bubbles from the deeper part of the Stromboli magmatic column. This could highlight the existence of a deeper source for low-frequency seismicity. Citation: Sgroi, T., C. Montuori, R. Agrusta, and P. Favali (2009), Low-frequency seismic signals recorded by OBS at Stromboli volcano (Southern Tyrrhenian Sea), Geophys. Res. Lett., 36, L04305, doi:10.1029/ 2008GL036477. 1. Introduction [2] Stromboli is one of seven volcanic islands in the Aeolian Archipelago (Southern Tyrrhenian Sea, Italy). The island rises about 3,000 m from the seafloor and stands 924 m a.s.l. The volcano has been steadily erupting for over 2,000 years and perhaps even as long as 5,000 years [Allard et al., 1994]. The present eruptive behaviour is characterised by intermittent explosive activity during which well- collimated gas jets, laden