Eugenio Privitera

Continuous soil radon monitoring during the July 2006 Etna eruption

[1] Continuous soil radon monitoring was carried out near the Southeast Crater (SEC) of Mt. Etna during the 10-day July 2006 Strombolian-effusive eruption. This signal was compared with simultaneously acquired volcanic tremor and thermal radiance data. The onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4–5 orders of magnitude, which we interpret as precursors. Minor changes in eruptive behavior did not produce significant variations in the monitored parameters. The remarkably high radon concentrations we observed are unprecedented in the literature. We interpret peaks in radon activity as due primarily to microfracturing of uranium-bearing rock. These observations suggest that radon measurements in the summit area of Etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions. Citation: Neri, M., B. Behncke, M. Burton, G. Galli, S. Giammanco, E. Pecora, E. Privitera, and D. Reitano (2006), Continuous soil radon monitoring during the July 2006 Etna eruption, Geophys. Res. Lett., 33, L24316, doi:10.1029/ 2006GL028394.

Mt. Etna Volcano: A Seismological Framework

Mount Etna is one of the most active and powerful basaltic volcanoes in the world, with an historical record of documented eruptions going back over 2000 years. It is located in eastern Sicily in a complex geodynamic framework, where major regional structural lineaments play a key role in the dynamic processes of the volcano [e.g., Bonaccorso et al., 1996]. Several years of structural and geophysical observations have revealed how the majority of the eruptive fracture systems activated in the last 30 years correspond to those of historical eruptions [e.g., Azzaro and Neri, 1992]. The orientation of the fractures coincides mostly with two structural trends, NNW-SSE and NE-SW, observed both in the volcanic area and in the regional context. These alignments are hypothesized to be the main volcano-genetic structures [e.g., Bonaccorso et al., 1996; Gresta et al., 1998] controlling the evolution of Mt. Etna, as their interference establishes a weak zone along which magma can rise from depth [Rasa et al., 1995]. In the second half of the last century, after nearly 20 years without any major flank eruption, a series of effusive eruptions started in 1971. In the following 15 years, fourteen main sub-terminal and/or flank eruptions affected different eruptive systems [e.g., Azzaro and Neri, 1992]. Afterwards, about two years withouth eruptive activity separated the October 1986-March 1987 eruption from that of 1989, which was one of the most important in terms of effusion rate. This eruption was probably preceded by a major intrusive episode [Ferrucci et al., 1993; Rymer et al., 1993] which also fed the 1991-1993 flank eruption. The latter was the most important lateral eruption at Mt. Etna in the last three centuries, both in terms of duration (476 days) and volume of lava erupted (ca. 250 x 106 m3). After the end of this eruption, volcanic activity was confined to the summit area until the July-August 2001 flank eruption. Seismological observations have provided information on both the dynamics and structure of the volcano, in addition to their interaction with the regional tectonic structures. Today it appears clear that volcanism and tectonics in the Etnean area interact closely [e.g., Bonaccorso et al., 1996; Cocina et al., 1998; Bonaccorso, 2001; Bonaccorso and Patane, 2001; Patane and Privitera, 2001], although the problem of the driving mechanisms of magma upwelling remains an open question. Unfortunately, the local, permanent seismic network had a low density of stations prior to 1990 which severely affected hypocentral location constraints and our knowledge on magma dynamics in the shallower crust. Only from the early 1990\s has seismic data been available in digital format for a significant number of stations as well as for three-component sensors [e.g., Patane et al., 1999; Barberi et al., 2000; Patane and Privitera, 2001; Patane et al., 2003]. These improvements have allowed to put high-quality constraints on seismic activity occurring at almost all depths in recent years, and to perform studies which tackle the link between seismicity and eruptive activity. In this paper we present an overview of seismic activity affecting the volcano in the period 1978-2001. In particular, we focus our attention on the years between 1988 and 2001. We discuss the interaction between the regional and local stress field in this time span, and define seismic constraints on the magma source which yielded eruptive activity.

Seismic and infrasonic evidences for an impulsive source of the shallow volcanic tremor at Mt. Etna, Italy

During a seismo-acoustic experiment we recorded volcanic tremor around the summit craters of Mt. Etna volcano. Tremor shows amplitude modulation, which disappear ≈ 900 m from the crater area. The infrasonic wavefield is coherent even at distances of ≈ 750 m. Time delay between infrasonic transient is stable around 1.3 s and is consistent with the position of the source in the Voragine crater. Amplitude modulation of tremor is well correlated (0.72) with infrasound amplitude with a time lag of 0.37 s. coherent with a shallow position of the source. Amplitude of volcanic tremor decays over increasing distances according to geometrical spreading of body waves. Tremor wavefield shows a linear polarization following the same time occourrence as the infrasonic pulses. Polarization azimuth indicates that wavefield rectilinearity is mostly due to P-waves. We infer that most of the volcanic tremor we recorded at Mt. Etna is generated by superimposition of small impulsive sources acting at 1–2 s rate caused by pressure instability during magma degassing.

Seismogenic stress field beneath Mt. Etna (South Italy) and possible relationships with volcano-tectonic features

Abstract Shallow shear-type seismic activity occurring beneath the Etna volcano during 1990–1995 has been analysed for hypocenter locations, focal mechanisms and stress tensor inversion. The results have been examined jointly with Electronic Distance Measurements and tiltmeter data collected in the same period and reported in the literature. Significant seismicity located in the upper 10 km was found to be confined to the time intervals in which ground deformation data indicated inflation of the volcano edifice (e.g., the periods preceding the December 1991–March 1993 and August 1995–March 1996 eruptive phases). The shocks mostly occurred in a sector approximately centered on the crater area and elongated in the East–West direction. The causative seismogenic stress shows a low-dip East–West orientation of σ 1 . In agreement with existing knowledge on relationships between local fault systems and magma uprise processes, the shallow seismicity in question is tentatively explained as being due to lateral compression by magma inside a nearly North–South system. The volcano deflation phase revealed by Electronic Distance Measurements and tilt data during the 1991–1993 major eruption was not accompanied by any significant shear-type shallow event. Below the depth of 10 km, the North–South prevailing orientation of σ 1 reflects the dominant role of the regional stress.

Multiparametric study of the February-April 2013 paroxysmal phase of Mt. Etna New South-East crater

European FP7 MED-SUV (MEditerranean SUpersite Volcanoes). Grant Number: 308665 European Research Council European FP7 (FP/2007-2013)/ERC. Grant Number: 279802 SIGMA (Sistema Integrato di sensori in ambiente cloud per la Gestione Multirischio Avanzata)

Insights into Mt. Etna’s Shallow Plumbing System from the Analysis of Infrasound Signals, August 2007–December 2009

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.

Probabilistic Reasoning Over Seismic Time Series: Volcano Monitoring by Hidden Markov Models at Mt. Etna

From January 2011 to December 2015, Mt. Etna was mainly characterized by a cyclic eruptive behavior with more than 40 lava fountains from New South-East Crater. Using the RMS (Root Mean Square) of the seismic signal recorded by stations close to the summit area, an automatic recognition of the different states of volcanic activity (QUIET, PRE-FOUNTAIN, FOUNTAIN, POST-FOUNTAIN) has been applied for monitoring purposes. Since values of the RMS time series calculated on the seismic signal are generated from a stochastic process, we can try to model the system generating its sampled values, assumed to be a Markov process, using Hidden Markov Models (HMMs). HMMs analysis seeks to recover the sequence of hidden states from the observations. In our framework, observations are characters generated by the Symbolic Aggregate approXimation (SAX) technique, which maps RMS time series values with symbols of a pre-defined alphabet. The main advantages of the proposed framework, based on HMMs and SAX, with respect to other automatic systems applied on seismic signals at Mt. Etna, are the use of multiple stations and static thresholds to well characterize the volcano states. Its application on a wide seismic dataset of Etna volcano shows the possibility to guess the volcano states. The experimental results show that, in most of the cases, we detected lava fountains in advance.

Design of a seismo-acoustic station for Antarctica

In recent years, seismological studies in Antarctica have contributed plenty of new knowledge in many fields of earth science. Moreover, acoustic investigations are now also considered a powerful tool that provides insights for many different objectives, such as analyses of regional climate-related changes and studies of volcanic degassing and explosive activities. However, installation and maintenance of scientific instrumentation in Antarctica can be really challenging. Indeed, the instruments have to face the most extreme climate on the planet. They must be tolerant of very low temperatures and robust enough to survive strong winds. Moreover, one of the most critical tasks is powering a remote system year-round at polar latitudes. In this work, we present a novel seismo-acoustic station designed to work reliably in polar regions. To enable year-round seismo-acoustic data collection in such a remote, extreme environment, a hybrid powering system is used, integrating solar panels, a wind generator, and batteries. A power management system was specifically developed to either charge the battery bank or divert energy surplus to warm the enclosure or release the excess energy to the outside environment. Finally, due to the prohibitive environmental conditions at most Antarctic installation sites, the station was designed to be deployed quickly.