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[1] Understanding the mechanisms of magma ascent preceding eruptions, and in particular the subvolcanic system that stores and transports magma to the surface, is of crucial relevance for hazard and risk assessment. We propose here a statistical model describing the rise of magma from the reservoir through the transport region via stress induced fracturing mechanisms of the medium. The model reproduces the general statistical properties of erupted volume, P( V), and inter-eruption time, P(t), found in catalogue data for closed conduit volcanoes. We also investigate conditional distribution ( e. g., the probability, P( V vertical bar t), to have a volume, V, erupted after a waiting time, t), which can have important practical implications.

Abstract An integrated approach that combines geophysical surveys and numerical simulations is proposed to study the processes that govern the fluid flow along active fault zones. It is based on the reconstruction of the architecture of the investigated fault system, as well as the identification of possible paths for fluid migration, according to the distribution of geophysical parameters retrieved by multi-methodological geophysical prospecting. The aim is to establish, thanks to constraints deriving from different types of data (e.g., geological, geochemical and/or hydrogeological data), an accurate 3D petrophysical model of the survey area to be used for simulating, by numerical modelling, the physical processes likely taking place in the imaged system and its temporal evolution. The effectiveness of the proposed approach is tested in an active fault zone in the Matese Mts (southern Italy), where recent, accurate geochemical measurements have registered very high anomalous values of non-volcanic natural emissions of CO2. In particular, a multi-methodological geophysical survey, consisting of electrical resistivity tomography, self-potential and passive seismic measurements, integrated with geological data, was chosen to define the 3D petrophysical model of the investigated system and to identify possible source geometries. Three different scenarios were assumed corresponding to three different CO2 source models. The one that hypothesizes a source located along the fault plane at the depth of the carbonate basement was found to be the best candidate to represent the test site. Indeed, the performed numerical simulations provide CO2 flow estimates comparable with the values observed in the investigated area. These findings are promising for gas hazards, as they suggest that numerical simulations of different CO2 degassing scenarios could forecast possible critical variations in the amount of CO2 emitted near the fault.

The magnetotelluric (MT) method is useful for monitoring geophysical processes because of a large dynamic depth range. In this paper, a feasibility study of employing continuous MT observations to monitor hydrothermal systems for both volcanic hazard assessment and geothermal energy exploitation is presented. Sensitivity of the MT method has been studied by simulating spatial and temporal evolution of temperature and gas saturation distributions in a hydrothermal system, and by calculating the MT response at different time steps. Two possible scenarios have been considered: the first is related to an increase in the fluid flow rate at the system source, the second is associated to an increase in the permeability of the rocks hosting the hydrothermal system. Numerical simulations have been performed for each scenario, and the sensitivity of the MT monitoring has been analyzed by evaluating the time interval needed to observe significant variations in the MT response. This study has been applied to the hydrothermal system of the Campi Flegrei (southern Italy) and it has shown that continuous MT measurements are not sensitive enough to detect a significant increase in the source fluid flow rate over time intervals less than ten years. On the contrary, if the permeability of the upwelling zone increases, a measurable change in the MT response occurs over a time interval ranging from six months to three years, depending on the extent of the permeability increase. Such findings are promising and suggest that continuous MT observations in active volcanic areas can be useful for imaging volcano-hydrothermal system activity.

A new approach to the interpretation of magnetic anomalies generated by geological structures resembling simple geometrical bodies is presented. The method is based on the Genetic-Price hybrid Algorithm (GPA) recently proposed by the authors for the inversion of potential-field data, specifically of self-potential signals. In this paper, the effectiveness of the proposed algorithm is tested on magnetic data for retrieving the parameters of the anomaly causative sources. First, the testing is performed on synthetic noise-free and noisy signals due to magnetized sphere-, dike- and fault-like models, then the analysis is extended to field magnetic anomalies. Concerning the synthetic data analyses, a very good agreement is obtained between assumed and retrieved source parameters. Specifically, the error between true and inverted parameter sets was found to be no higher than 9% even by adding 15% of Gaussian white random noise to the initial dataset. As for the study of field data, the values of depth, horizontal position, effective magnetization intensity and angle provided by the proposed GPA method compare well with those obtained by other interpretative approaches. Finally, the results of the GPA application to the inversion of magnetic data measured in the Mt. Somma-Vesuvius volcanic area are reported. In particular, the interpretation of the magnetic anomalies along a SW-NE profile in terms of multiple dikes provides information about depth and location of buried volcanic structures that match well those from other geophysical and geological analyses.

Summary Debris-flows are among the most dangerous types of landslide often induced by intense rainfall events and favored by the presence of unconsolidated soils on steep slopes. In this framework, the knowledge of the electrical resistivity distribution of the cover materials is useful to define their lithological and physical characteristics, as they provide information about the saturation level of the cover and the areas more prone to slide. Nevertheless, the use of conventional electrode layouts for 3D-resistivity imaging is limited by the difficulty to operate in contexts with complex topography. In this work, a non-conventional 3D electrode configuration is proposed for a high-resolution characterization of Mt. Faito pyroclastic covers (Campania Region, southern Italy). The adopted scheme has been able to provide a very detailed image of the investigated slope allowing to discriminate the different horizons within the pyroclastic cover as well as the different degree of fracturing of the carbonate bedrock. The obtained resolution has been found higher than that provided by a conventional 2.5D ERT survey performed in the same survey area.

The thermal evolution of the Phlegraean magmatic system (southern Italy) is studied by analyzing the influence of the thermal property variations on the solution of the heat conduction equation. The aim of this paper is to verify if appropriate choices of thermal parameters can reproduce, at least to greater depths, the high temperatures measured in the geothermal wells, drilled inside the caldera, under the assumption of heat loss from a magma chamber by conduction. Since the main purpose is to verify the plausibility of such an assumption, rather simple models of the magmatic system are adopted and only major volcanic events (i.e., the Campanian Ignimbrite and the Neapolitan Yellow Tuff eruptions) are considered. The results of the simulated two-dimensional model scenarios show that by assuming an extended source region, whose emplacement time is longer than 40 ka, heat conduction mechanisms can provide temperatures as high as those measured at depths deeper than about 2000 m. On the other hand, the 1D simulations show that appropriate choices for the thermal conductivity depth profiles can reproduce the observed temperatures at depths deeper than about 1000 m. These findings question the apparent consensus that convection is the only dominant form of heat transfer at Phlegraean Fields and might motivate new research for reconstructing the thermal evolution of the Phlegraean magmatic system.

Integration of archaeoseismic observations, geological and geophysical surveys and a critical review of historical written sources contributed to shed light on the effects of the 847 CE earthquake that struck a large area of southern-central Italy. New archaeoseismic evidence of a strong earthquake which occurred around the middle of the ninth century CE comes from two Medieval archaeological sites along the Volturno Valley, between Campania and Molise regions. Historical documentation and its evidence include the tilting of pillars in the Basilica of Santa Maria near Alvignano (northern Campania region) and a collapsed masonry wall in the Abbey of San Vincenzo al Volturno near Isernia (northern Molise region). At Alvignano, a site so far unrecorded in seismic catalogues for the 847 earthquake, geoelectrical and georadar investigations were used to explore the subsoil and study local site conditions, which could have influenced co-seismic ground motion. Interpretation of geophysical surveys calibrated by stratigraphy of available boreholes document the presence of altered pyroclastic deposits, which likely enhanced site effects at Alvignano. Analysis of damage historical descriptions and of archaeological reports indicates that the 847 seismic event damaged a wide area between Latium, Campania and Molise, with destruction of the town of Isernia and damages in Rome. Because the damaged area for this medieval earthquake is loosely defined in literature, the present study represents a contribution to better define the shaking area and provide new hints on the extent and location of the possible seismogenic source.

We simulated the pattern of activity of a strato-volcano by using a cellular automaton model where magma is allowed to ascend to the surface through self-organized crack networks. Magma rises toward the surface by filling connected paths of fractures until the magma's density is less than that of surrounding rocks. If magma enters a region with negative or neutral buoyancy, it cools and solidifies; as a result, the local density profile is modified, and magmatic dikes are formed. We simulated the temporal evolution of high-density pathways of dikes that magma may eventually utilize to reach the surface. We showed that if a shallow neutral–negative buoyancy zone is restored after eruptions, due to, for example, piecemeal or chaotic collapses, a characteristic timescale appears in the inter-event repose time distribution. Such characteristic repose time represents the average time that magma takes to form a high-density pathway through the less dense rock layer, and it may give a hint to predict possible eruptive scenarios. Even if the model includes many simplifying assumptions in the definition of magma–rock interaction, the results obtained from simulations are consistent with the eruptive behavior of the Mt. Somma-Vesuvius volcano for the 1631–1944 period.

Volcanoes are complex dynamical systems that manifest their activity in a wide range of eruptions with different explosivity. In this paper, we propose a cellular automaton model aimed at capturing the key features of the magma ascent dynamics that reproduces the great variability of volcanic explosivity. The novelty of our approach consists in considering an eruption not as an event caused by overpressure in the magma chamber but as the result of transport of discrete magma batches from the reservoir to the surface along preformed crack networks. Since gas is lost during the ascent, the time for the rise of magma is crucial. In our model, such a time is related to the opening of connected paths of fractures in the surrounding rocks, which are described by means of a time dependent Self-Organized-Criticality field. We analyze statistical distributions of eruptions in terms of gas losses and find that eruptions with the lowest degree of explosiveness are characterized by small erupted volumes, even if they are much more likely to occur than explosive eruptions. On the contrary, explosive eruptions, which in our model essentially correspond to percolative events that directly connect the magma reservoir to the surface, are rare events that can be very huge.

Landslides are natural hazards occurring in response to triggers of different origins, which can act with different intensities and durations. Despite the variety of conditions that cause a landslide, the analysis of landslide inventories has shown that landslide events associated with different triggers can be characterized by the same probability distribution. We studied a cellular automaton, able to reproduce the landslide frequency-size distributions from catalogues. From the comparison between our synthetic probability distribution and the landslide area probability distribution of three landslide inventories, we estimated the typical size of a single cell of our cellular automaton model to be from 35–100 m2, which is important information if we are interested in monitoring a test area. To determine the probability of occurrence of a landslide of size s, we show that it is crucial to get information about the rate at which the system is approaching instability rather than the nature of the trigger. By varying such a driving rate, we find how the probability distribution changes and, in correspondence, how the size and the lifetime of the most probable events evolve. We also introduce a landslide-event magnitude scale based on the driving rate. Large values of the proposed intensity scale are related to landslide events with a fast approach to instability in a long distance of time, while small values are related to landslide events close together in time and approaching instability slowly.

In this paper, we propose a new approach for modelling the development of instabilities in pyroclastic covers induced by rainfall events. The approach is based on high-resolution 2D electrical resistivity tomography (ERT) and on a cellular automaton model aimed to simulate landslide events. A local and time-dependent Factor of Safety of a slope, that depends on electrical resistivity and the slope angle, is introduced. We show the results of a model run on data acquired in a test area of the Campania Region (Italy), where shallow landslides involving pyroclastic soils are very frequent and often triggered by critical rainfall events. The shown example would just emphasize the potentiality of the proposed conceptual model, which integrates geophysical and statistical analyses, in the framework of the landslide hazard, since its validation and calibration is the next step that has to be taken.

In order to gain insight into the study of natural avalanches dynamics, we illustrate a statistical model based on a dissipative dynamical variable associated to a position dependent factor of safety field. This model, as experimentally demonstrated, is able to reproduce the complex structure of landslide events, such as power-law distributions. In this paper, we introduce an explicit dependence of the safety factor on the electrical resistivity to simulate landslide events in pyroclastic soils. An application of the model to data acquired in a test area characterized by flowslide events (Monte Albino, Campania Region - South Italy) bear witness the relevant role played by the resistivity measurements in the landslide hazard assessment.

Due to very fast industrial growth and urbanization, problems of environmental contaminations are growing rapidly. The soil and groundwater pollution is one of the most important concerns that have received attention at local, regional and global levels because of their impact on public health. The use of geophysical techniques is of great help for environmental studies because they not only give the localization of polluted areas, but also provide an estimate of the extent of contamination, through the determination of the most likely contaminated volumes. To identify possible soil and groundwater contamination, integrated analysis of resistivity, chargeability and self-potential data has been performed in a survey area located in the town of Castel San Giorgio (Salerno, Italy) in the western basin of Solofrana river valley. This area is periodically affected by flooding induced by severe or significant rainfall, which cause the river to overflow and contribute to potential soil and groundwater contamination by heavy metals discharged from the tanning plants operating in the upper part of the valley.

The landslides occurred in Campania Region (southern Italy) during last fifteen years have stressed the extreme susceptibility of the ash-fall deposits that cover the mountains surrounding the Mt. Somma-Vesuvius volcano. The resistivity tomography technique is able to give a very detailed image of the subsoil structural pattern on the basis of the high resistivity contrasts characterising the Campanian geological settings susceptible to landslides, i.e. pyroclastic soils overlapping a carbonate and/or lava basement. We describe a new conceptual approach that combines electrical resistivity tomographies and laboratory analyses to study the hazard assessment of pyroclastic covers. We report the results of a high-resolution 2D resistivity survey carried out in a test area (Sarno Mountains, southern Italy), and the results of laboratory analyses performed on undisturbed samples collected from the same area, devoted to the determination of characteristic curves electrical resistivity vs. water content. We use such characteristic curves to evaluate the water content of the investigated slope. Finally, we estimate the local empirical safety factor, recently introduced by the authors, in terms of local resistivities and slope angles and compare the values of this parameter with those of the 1D safety factor commonly used in the slope stability assessment.