Magnetic features of the magmatic intrusion that occurred in the 2007 eruption at Stromboli Island (Italy) |
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| Authors: | Rosalba Napoli Gilda Currenti Ciro Del Negro Agnese Di Stefano Filippo Greco Enzo Boschi |
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| Institution: | 1.Istituto Nazionale di Geofisica e Vulcanologia,Sezione di Catania,Catania,Italy;2.Dipartimento di Ingegneria Elettrica, Elettronica e dei Sistemi,Università di Catania,Catania,Italy |
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| Abstract: | Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February
27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal
thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures
in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation
of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those
calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion.
No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced
magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal
state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related
to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field
was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging
between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days. |
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