Paolo Mauriello

Electric and electromagnetic outline of the Mount Somma-Vesuvius structural setting

Abstract We present and discuss the results of an integrated electrical and electromagnetic survey in the active volcanic area of Mount Somma–Vesuvius (Naples, Italy). Dipolar geoelectrics (DG), self-potential (SP) and magnetotellurics (MT) were used to investigate the shallow and deep regions of the volcanic area. The DG apparent resistivity pseudosection along a N–S profile across the Vesuvius cone showed the existence of a largely extended conductive zone, closely in correspondence to the Somma caldera, including in the middle the top terminal part of the Vesuvius main plumbing system. The SP data, collected over the whole volcanic area, showed the existence of a W–E-directed wide band of weak positive anomalies, indicating again a conductive zone, not only including the whole Somma caldera but also extending towards the Tyrrhenian sea. A roughly N–S-trending narrow fracture system, cutting the lowest Mount Somma eastern slopes, was further evident from the SP data. A new SP tomographic inversion procedure allowed to detect a large positively charged nucleus in the depth range 600–2200 m b.g.l., located beneath the westernmost portion of a former caldera, related to the Avellino plinian eruption. The geophysical interpretation of this large positive anomaly was made using Onsagers theory of coupled electrokinetic and thermoelectric flows. The final interpretation was that the shallow, conductive central zone is very likely made up of an intensively altered and mineralised block of cemented volcanic breccia. Finally, the MT data, distributed along two perpendicular profiles, enabled us to obtain the first significant picture of the deep electrical structure of the volcano. The Bostick inversion revealed the existence of a conductive intracrustal layer, including a perched more conductive zone located roughly beneath the central-western sector of the Vesuvius apparatus.

Looking inside Mount Vesuvius by potential fields integrated probability tomographies

Abstract First, we outline the theory of the three-dimensional (3D) probability tomography for any generic vector or scalar geophysical field and define an approach to the integrated tomography of any pair of geophysical data sets collected in the same area. Then, we discuss the results of the application of the 3D probability tomography to the Mount Vesuvius volcanic complex, considering gravity, magnetic and self-potential survey data. The most important feature resulting from the integrated tomography regards the Mt. Vesuvius plumbing system. A unique central conduit is outlined at the intersection between a W–E- and a N—S-trending vertical boundary planes. The top terminal part of this conduit appears completely filled with magnetized and less dense volcanic material. This new information, combined with previous indications about the probable existence of a magma reservoir at 8–10 km of depth, strengthen the hypothesis that Mount Vesuvius is still to be considered a highly hazardous volcano.

Principles of probability tomography for natural-source electromagnetic induction fields

The 3-D interpretation problem of natural‐source electromagnetic (EM) induction field data collected over a flat air‐earth boundary is dealt with using the concept of probability tomography. This paper presents a method to recognize the most probable localization of the induced electric charge accumulations across resistivity discontinuities and current channeling inside conductive bodies. We begin by writing the solutions for the electric (magnetic) ground surface EM field components in the frequency domain as a sum of elementary contributions, each resulting from a single induced‐charge (dipole) element. Then we express the total electric (magnetic) power associated with each EM field component as a sum of crosscorrelation integrals between the measured component and the homologous synthetic expression resulting from each causative induced‐charge (dipole) element. The synthetic component takes the key role of scanner function in the new imaging procedure. Moreover, using the crosscorrelation bounding in...

Quantitative integration of geophysical methods for archaeological prospection

Multi-method surveys have been used with the aim of detecting either sharp discontinuities (boundary of the cavity, fractures in the medium, etc.) or volumetric variations (bodies with different physical properties), at three different archaeological test sites. For the survey a combination of passive and active methods (magnetic, GPR and dipole–dipole geoelectric method) has been used. With all methods a high-resolution data acquisition method has been adopted with the aim of reconstructing a global vision of the area investigated. The enhancement of the processing technique towards the integration of different geophysical methods, enabling one to better define the location, depth and geometry of any archaeological body, has been adopted. Copyright

Localization of maximum-depth gravity anomaly sources by a distribution of equivalent point masses

A method is proposed for localizing the maximum depth sources of a gravity anomaly data set collected on a generally uneven, free surface topography. First, the Newtonian‐type integral defining the Bouguer anomaly function is solved as a sum of elementary contributions from pointlike mass contrast (Δ‐mass) elements. Using this solution, the power associated with the Bouguer effect is derived as a sum of crosscorrelation integrals between the Bouguer anomaly data function and a scanner function expressing the gravity effect from a pointlike Δ‐mass element. Finally, applying Schwarz’s inequality to a single crosscorrelation power term, a Δ‐mass occurrence function is introduced as a suitable tool for localizing the maximum‐depth sources (MDS) of a given gravity anomaly field. The MDS localization procedure consists of scanning the half‐space below the survey area by a unit strength Δ‐mass element and calculating the Δ‐mass occurrence function at the nodes of a 3‐D regular grid. The grid values exceeding in ...

Localization of magnetic sources underground by a probability tomography approach

A tomography method is proposed to image magnetic anomaly sources buried below a non-flat ground surface, using the expression of the total power associated with a measured magnetic field. It is shown that the total power can be written as a sum of crosscorrelation products between the magnetic field data set and the theoretical expression of the magnetic field generated by a source element of unitary strength. Then, applying Schwarzs inequality, an occurrence probability function is derived for imaging any distribution of magnetic anomaly sources in the subsurface. The tomographic procedure consists in scanning the half-space below the survey area by the unitary source and in computing the occurrence probability function at the nodes of a regular grid within the half-space. The grid values are finally contoured in order to single out the zones with high probability of occurrence of buried magnetic anomaly sources. Synthetic and field examples are discussed to test the resolution power of the proposed tomography.

Application of geoelectrical 3D probability tomography in a test-site of the archaeological park of Pompei (Naples, Italy)

The 3D geoelectric probability tomography method has been previously developed as a powerful approach to localize in the subsoil the sources of the apparent resistivity anomalies detected on the ground surface. We show that this method can be successfully applied in the archaeological park of Pompei to recognize buried remains of the ancient Roman urbanization including roads, squares and buildings which were heavily damaged and totally buried under a thick cover of volcanic fall products resulting from the well-known disastrous 79 AD Vesuvius eruption. A further development is made in this work concerning the identification of source poles and dipoles underground, ascribable to the physical centre of the bodies with anomalous resistivity and to their boundaries, respectively. Different imaging systems are used to enhance the quality of information derived from the tomography analysis.

The geophysical contribution to the safeguard of historical sites in active volcanic areas.: The Vesuvius case-history

The Earths surface is characterized by the presence of many active volcanoes, most of which are surrounded by ancient villages. High-valued historical sites are often so exposed that it becomes imperative to perform volcanic risk assessment including cultural heritage. For the safeguard of the historical property in volcanic areas, two major problems are definition of (a) criteria for diagnosis and evaluation of hazard and vulnerability, and (b) methods for risk prevention and mitigation. In this paper, we first review the state-of-the-art and most outstanding geophysical prospecting and modeling methods currently on the use, which contribute to the solution of the problems mentioned above. We then show the results of an application on the most alarming volcano in Italy, Mount Vesuvius in the Neapolitan area. The imaged configuration of the feeding and plumbing systems induces to consider Vesuvius a high-risk volcano with a high probability of pyroclastic flow in case of reactivation. Finally, we show the results from a modeling approach of a pyroclastic flow simulating the eruptive scenario of Vesuvius compatible with its internal structure and dynamics. The simulation shows that the emplacement of artificial barriers close to the eruptive vent is a practical solution to reduce the local radial momentum of the pyroclastic flow and to transfer the related energy to the vertical buoyant cloud. The Vesuvius case history allows us to conclude that the integrated geophysical surveying and modeling approach can notably contribute to make decisions and also for the protection of the historical heritage in active volcanic areas.

High-resolution geophysical prospecting with integrated methods. The ancient Acropolis of Veio (Rome, Italy)

The fundamental geophysical goal in archaeological prospection, in near-surface investigations and generally in environmental applications is to construct as complete as possible maps of subsurface targets. The main effort in archaeology is also the integration of different, absolutely non-invasive techniques, especially if they are used in the high-resolution three-dimensional tomographic mode. In the present work a combination of fluxgate differential magnetic, ground penetrating radar and dipole–dipole geoelectric methods has been used with the aim of detecting superficial structures (wall remains and traces of an ancient road) contained in an archaeological test area (ancient Acropolis of Veio, Rome). With all geophysical techniques a high-resolution data acquisition method has been adopted with the aim of reconstruction of a global vision of the area investigated (20 m×20 m). Some signal processing and tomographic representation techniques have been used for data elaboration and interpretation. The results of the geophysical surveys have been confirmed by direct archaeological excavations carried out only at anomalous zones.

A Geophysical Study of the Mount Etna Volcanic Area

A geophysical model of the Mt. Etna volcanic area (Sicily, Italy) is outlined by an integrated analysis of gravity, geoelectrical, magnetotelluric and seismic data. New 3D tomography and visualization systems are applied in order to extract the maximum information and to define, connect and assemble structures and related physical properties. All geophysical methods concur to single out a dense, rigid and resistive structure in the central part of the study area, about 10 km long in E-W direction, about 4 km wide in N-S direction and extending from near surface down to about 30 km of depth. The resistivity pattern shows also two conductive zones on both sides of the E-W barrier, in the depth range 15-30 km. Resistivities of a few Qm and a few tens Qm are estimated in the southern and northern conductive zone, respectively. A non-uniform feeding system is thus assumed to exist, instead of the ellipsoid-like uniform magma reservoir previously deduced from regional seismological data in the depth range 15-25 km. Moreover, the comparison with seismic tomographies from local earthquakes allows a central high velocity nucleus to be distinguished inside the upper portion of the resistive barrier, which is thus ascribed to a system of compact dikes tending to become highly fractured along the western and eastern edges. Finally, the impedivity analysis gives no support to the existence of any permanent shallower magma chambers, contributing, instead, to argue the presence of a plumbing system hydrothermally altered at medium-to-low temperatures.