Rosalba Napoli

Ground and marine magnetic surveys of the lower eastern flank of Etna volcano (Italy)

Abstract In 1996 and 1997, two high-resolution magnetic surveys, one on land and the other at sea, were carried out on the lower eastern flank of Mount Etna. The magnetic surveys, covering an area of about 400 km2, aimed to elucidate the relationships between the main tectonic and morphologic features of this flank of Mount Etna. Major features include widespread NNW- and NNE-trending active faults and the Valle del Bove, a depression considered to be the source area of the Chiancone deposit, the largest Etnean volcaniclastic sequence. Magnetic surveys show anomalies that roughly follow the trend of active main structures. Although few magnetization measurements are available for the most representative outcrops of the lower eastern side of Mount Etna, interpretation of the anomalies defines the underground geometry of the Chiancone deposit and its relationship with volcano stratigraphic units and the underlying sedimentary rocks. In particular, a volume of about 14 km3 was ascribed to the Chiancone deposit. Such a large amount of material was likely produced by a catastrophic event, and deposited at different periods at the exit of the Valle del Bove in an area produced by the interaction, on a regional scale, of the main tectonic structures affecting this flank of the volcano.

Capturing the fingerprint of Etna volcano activity in gravity and satellite radar data

Long-term and high temporal resolution gravity and deformation data move us toward a better understanding of the behavior of Mt Etna during the June 1995 – December 2011 period in which the volcano exhibited magma charging phases, flank eruptions and summit crater activity. Monthly repeated gravity measurements were coupled with deformation time series using the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique on two sequences of interferograms from ERS/ENVISAT and COSMO-SkyMed satellites. Combining spatiotemporal gravity and DInSAR observations provides the signature of three underlying processes at Etna: (i) magma accumulation in intermediate storage zones, (ii) magmatic intrusions at shallow depth in the South Rift area, and (iii) the seaward sliding of the volcanos eastern flank. Here we demonstrate the strength of the complementary gravity and DInSAR analysis in discerning among different processes and, thus, in detecting deep magma uprising in months to years before the onset of a new Etna eruption.

Magnetic Field Monitoring at Mt. Etna During the Last 20 Years

Over the past few decades we have been intensively monitoring the magnetic field on Mt. Etna. The largest anomaly, about 10 nT, was observed in the geomagnetic time series recorded in 1981 and associated with the March 17-23 eruption. It was interpreted as the joint effect of piezomagnetism and thermal demagnetization engendered by an intrusive dike. A convincing case of thermomagnetic effects was observed during the 1989 fissure eruption, when repeated measurements at intervals of 3 months for two years revealed the slow buildup of a 130 nT anomaly. The anomaly vanished laterally within 0.2 km from the surface expression of the fissure system. The nature and structure of the anomaly is consistent with the location and time of cooling of a shallow dike. Between September and December 1995 geomagnetic changes, greater than 8 nT, associated with the renewal of the NE craters activity were detected. The center of the magnetic anomaly source, which was thought to be the region heated by high-temperature fluids and gases originating from fresh magma, was estimated, by the spatial distribution of the variation rate, to be at a depth of 500 m near the 1991-93 eruptive vents. Finally, significant changes, ranging from 2 to 7 nT, in the local magnetic field closely related to the main phases of the 2001 eruption were observed. Piezomagnetic models were used to calculate the expected geomagnetic changes for each volcanic process. Model parameters were based on estimated fault geometry using seismic and ground deformation data from each event.

GEOFIM: A WebGIS application for integrated geophysical modeling in active volcanic regions

We present GEOFIM (GEOphysical Forward/Inverse Modeling), a WebGIS application for integrated interpretation of multiparametric geophysical observations. It has been developed to jointly interpret scalar and vector magnetic data, gravity data, as well as geodetic data, from GPS, tiltmeter, strainmeter and InSAR observations, recorded in active volcanic areas. GEOFIM gathers a library of analytical solutions, which provides an estimate of the geophysical signals due to perturbations in the thermal and stress state of the volcano. The integrated geophysical modeling can be performed by a simple trial and errors forward modeling or by an inversion procedure based on NSGA-II algorithm. The software capability was tested on the multiparametric data set recorded during the 2008-2009 Etna flank eruption onset. The results encourage to exploit this approach to develop a near-real-time warning system for a quantitative model-based assessment of geophysical observations in areas where different parameters are routinely monitored.

Learning about Hydrothermal Volcanic Activity by Modeling Induced Geophysical Changes

Motivated by ongoing efforts to understand the nature and the energy potential of geothermal resources, we devise a coupled numerical model (hydrological, thermal, mechanical), which may help in the characterization and monitoring of hydrothermal systems through computational experiments. Hydrothermal areas in volcanic regions arise from a unique combination of geological and hydrological features which regulate the movement of fluids in the vicinity of magmatic sources capable of generating large quantities of steam and hot water. Numerical simulations help in understanding and characterizing rock-fluid interaction processes and the geophysical observations associated with them. Our aim is the quantification of the response of different geophysical observables (i.e. deformation, gravity and magnetic field) to hydrothermal activity on the basis of a sound geological framework (e.g. distribution and pathways of the flows, the presence of fractured zones, caprock). A detailed comprehension and quantification of the evolution and dynamics of the geothermal systems and the definition of their internal state through a geophysical modeling approach are essential to identify the key parameters for which the geothermal system may fulfill the requirements to be exploited as a source of energy. For the sake of illustration only, the numerical computations are focused on a conceptual model of the hydrothermal system of Vulcano Island by simulating a generic 1-year unrest and estimating different geophysical changes. We solved (i) the mass and energy balance equations of flow in porous media for temperature, pressure and density changes, (ii) the elastostatic equation for the deformation field and (iii) the Poisson’s equations for gravity and magnetic potential fields. Under the model assumptions, a generic unrest of 1-year engenders on the ground surface low amplitude changes in the investigated geophysical observables, that are, however, above the accuracies of the modern state-of-the-art instruments. Devising multidisciplinary and easy-to-use computational experiments enable us to learn how the hydrothermal system responds to un unrest and which fingerprints it may leave in the geophysical signals.

A review of the volcano-magnetic effects observed between 1981 and 1995 on Mount Etna (Italy)

Abstract Detection of local magnetic field perturbations has often been proposed for monitoring the modifications within the volcanic edifice of the stress field or of the thermodynamic state and providing a tool for prediction of eruptions. In order to evaluate the suitability of magnetic monitoring on Mt. Etna, we analysed two historic series of magnetic data recorded there: i) during the 1981 eruption and ii) immediately after 1989 eruption. Moreover, we examined time series associated with the intense explosive activity of Etna in 1995 summer provided by the present permanent magnetic network which was set up between 1994 and 1995.

A multidisciplinary strategy for in-situ and remote sensing monitoring of areas affected by pressurized fluids: Application to mud volcanoes: A multidisciplinary environmental monitoring strategy

A multidisciplinary strategy integrating a data set obtained using different mthods and techniques, ranging from remote sensing (UAV system, FTIR, thermal imaging) to direct field measurements (soil heat flux, soil CO2 flux, gravimetry and geomagnetism) proved highly capable of modeling regions affected by pressurized fluids circulation and extreme natural environments. As a test site, the Salinelle mud volcanoes area, located close to the city of Paternò (Sicily), was selected. This area is characterized by gas exhalations through water/mud vents. Detailed morpho-structural information, GIS thematic maps and geochemail signature of the released gas were quickly retrieved. This study showed that by integrating and harmonizing many disciplines of geosciences it is possible to get a comprehensive geological model of the studied area. Results, showed the accurate detection of structural setting of such an area and the opportunuty to monitor the spatial/temporal evolution of water/mud vents. The proposed approach allowed to expand the use of each single technique beyond its traditional applications and to make it a potential tool for many fields of geoscience.

Design and application of an adaptive nonstationary filter for noise reduction in volcanomagnetic monitoring at Mt Etna

Volcanomagnetic monitoring is critically dependent on the ability to detect and isolate local magnetic variations related to volcanic activity. Accurate detection of volcanomagnetic anomalies attributable to the dynamics of volcanoes requires removal from measurements of the Earths magnetic field, fluctuations of external origin which may be up to hundreds of nanotesla during geomagnetic storms. The commonly used method of taking simple differences of the total intensity with respect to the simultaneous value at a remote reference is only partially successful. Variations in the difference fields are thought to arise principally from contrasting electromagnetics of rock properties at magnetometer sites. With the aim of improving the noise reduction of geomagnetic time series from the magnetic network of Mt Etna, we developed an adaptive filtering. Magnetic vector data are included as input to the filter, to account for the orientation of the magnetic field. The filter is able to estimate and adapt the model parameters continuously by means of the new observations, so that the estimated signal closely matches the observed data. Therefore, the filtering accuracy is improved in order to reduce the residual components. Experimental data collected on Mt Etna during 2010 are analysed to relate the field variation at a given station to the field at other sites, filtering out undesired noise and enhancing signal-to-noise ratio.

INVERSE MODELING IN GEOPHYSICAL APPLICATIONS

The interpretation of the potential fleld data is an useful tool that allows for both investigating the subsurface structures and providing a quantitative evaluation of the geophysical process preceding and accompanying period of volcanic unrest. Potential fleld inversion problem are required to combine forward models with appropriate optimization algorithms and automatically flnd the best set of parameters that well matches the available observations. Indeed, investigations on the mathematical equations to be inverted, have revealed that these models are ill-posed and highly non-linear. Numerical methods for modeling potential fleld observations are proposed and applied on real dataset.