Marco Aloisi

Tilt signals at Mount Melbourne, Antarctica: evidence of a shallow volcanic source

Mount Melbourne (74°21′ S, 164°43′ E) is a quiescent volcano located in northern Victoria Land, Antarctica. Tilt signals have been recorded on Mount Melbourne since early 1989 by a permanent shallow borehole tiltmeter network comprising five stations. An overall picture of tilt, air and permafrost temperatures over 15 years of continuous recording data is reported. We focused our observations on long-term tilt trends that at the end of 1997 showed coherent changes at the three highest altitude stations, suggesting the presence of a ground deformation source whose effects are restricted to the summit area of Mount Melbourne. We inverted these data using a finite spherical body source, thereby obtaining a shallow deflation volume source located under the summit area. The ground deformation observed corroborates the hypothesis that the volcanic edifice of Mount Melbourne is active and should be monitored multidisciplinarily.

Present-day kinematics and deformation processes in the southern Tyrrhenian region: new insights on the northern Sicily extensional belt

We performed a new analysis of updated and accurate sets of seismic and GNSS data relative to the southern Tyrrhenian region. Detailed velocity field and crustal strain distribution coming from integration of episodic and continuous measurements at more than 160 geodetic sites (spanning the 1994-2015 period) have been evaluated together with the spatial distribution of recent seismicity and an updated catalogue of waveform inversion fault-plane solutions relative to the period 1976-2014. In agreement with previous investigations, we have found that the kinematics of the study area is quite homogeneous except for the north-eastern corner of Sicily which moves almost coherently with southern Calabria in response to the SE-ward rollback of the Ionian slab. The rest of the study region shows a NNW-trending velocity field in agreement with the direction of the Nubia-Eurasia convergence and it is mainly interested by a major compressive domain. NNW-oriented compression is particularly highlighted by seismic data along the E-W trending seismic belt located in the southern Tyrrhenian Sea. In the framework of such compressive regime, the E-W trending extensional domain of northern Sicily is also clearly depicted both by seismic and geodetic data. The cause of this extensional domain framed inside a mainly compressive one represents an open question in the recent scientific debate. Comparisons between our results and literature information on regional geology and crustal structure led us to investigate whether the extension could occur as local response to the thrusting dynamics of the southern Tyrrhenian belt, favoured by the presence of pre-existing weakness zones. We then propose a first attempt to evaluate such a possible causal relationship by means of Finite Element Method (FEM) and Coulomb Stress Change (CSC) modelling. In particular, we adopted a FEM approach to investigate the deformation pattern produced by thrust faulting of southern Tyrrhenian belt, along a 2D profile crossing both the compressive belt and the extensional one in northern Sicily. We also estimated the CSC due to the thrust faulting on normal receiving faults fairly reproducing pre-existing structures of northern Sicily. Modelling results indicate that the thrust faulting activity along the Southern Tyrrhenian compressive margin could be effective in promoting extensional processes in northern Sicily. We have so shown that the local response to thrust faulting activity may concur, even in combination with other processes, to generate the crustal stretching of northern Sicily.

Coupled Short- and Medium-Term Geophysical Signals at Etna Volcano: Using Deformation and Strain to Infer Magmatic Processes From 2009 to 2017

Due to the frequent eruptive activity of Etna volcano, it is of primary importance to interpret the near-real time geophysical data as best as possible in order to understand the unrest vs. eruptive timescales. After the main flank eruption of 2008-2009 and until 2017, Etna volcano was characterized by a lively eruptive activity of different phases. These comprised 44 lava fountain episodes that formed a new crater named New South East Crater (NSEC) during 2011-2013, two sequences of close episodes of lava fountains from the Voragine crater (VOR) on 3-5 December 2015 (4 events) and May 18-21, 2016 (3 events), as well as some periods of summit effusive activity with a more prolonged supply of lava flows during 2014. Several studies have described and modelled single episodes of lava fountains of both the NSEC and VOR. In particular, during lava fountainings the high precision data from borehole strain-meters revealed short-term changes, which allowedinference into the source of decompression at a shallow level (shallow plumbing system) of at ~ sea level for the events of the NSEC and at deeper level (~2-5 km b.s.l.) for those of VOR, respectively. In this study, we also considered the middle-term volcano recharging/discharging periods preceding/accompanying the different eruptive phases during 2009-2017, and through the deformation recorded by the permanent GPS network, we constrained the position of the sources. Together with the modelling deduced from the strain-meter data we produce a more complete representation of the different sources that characterized the different periods both in the middle-term (i.e. the preparatory phases showing inflation and the eruptive phases showing deflation) and in the short-term (i.e. the fast discharge associated with each eruptive event). Our highly resolved modelling explains the pathway of magma from the intermediate-shallow plumbing system to the surface. Our results are consistent with petrological constraints on the spatio-temporal evolution of magma transfer and storage.