Unravelling volcanic tremor source at mount etna from quantitative multiparametric analysis and moment tenso inversion.

Abstract

UNRAVELLING VOLCANIC TREMOR SOURCE AT MOUNT ETNA FROM QUANTITATIVE MULTIPARAMETRIC ANALYSIS AND MOMENT TENSOR INVERSION

Developments of multiparametric monitoring networks, real time analysis techniques and the acquisition of high-resolution data, have allowed to improve the knowledge of the structures and dynamics that characterize the active volcanoes. To understand the dynamics of an active volcano, it is possible to proceed with two different types of studies: i) multiparametric studies based on the joint analysis of different data (such as geophysical, geochemical, petrological data); ii) detailed studies concerning specific data. In order to understand source volcanic tremor at Mt. Etna volcano, volcanic tremor recorded during the vigorous summit of 2011-2012 was analyzed. In particular, this thesis shows the results obtained from the investigation of the volcanic tremor source through a duplex study: i) a multiparametric study based on the quantitative comparison between different time series such as volcanic tremor amplitudes and geochemical data such as soil CO2 flux and the SO2 flux at summit craters; ii) a moment tensor inversion analysis of volcanic tremor recorded during a lava fountain episode of the considered period. For these studies, data acquired from the multiparametric monitoring network managed by Istituto Nazionale di Geofisica e Vulcanologia were used.The quantitative comparison between seismic and geochemical data was performed in order to identify and quantitatively estimate similar trends variations between the compared time series, both synchronous and characterized by time lags. To this end, four different analysis techniques have been implemented, such as Cross-Correlation, Randomized Cross-Correlation, wavelet analysis and linear regression. The obtained results allowed to infer pressurization and depressurization dynamics of the plumbing system during the different eruptive phases observed during the considered period. The moment tensor inversion analysis of the volcanic tremor recorded at Mt. Etna represents a novelty. Specifically, this analysis was applied to volcanic tremor recorded during the lava fountain episode that occurred on 5 August 2011, one of the most vigorous of the 25 episodes that characterized the 2011-2012 period. The results allowed to highlight a source mechanism generated by a sub-horizontal crack near the summit crater area, which can be interpreted as a valve through which gas-rich magma is ejected during the lava fountain activities.