Enzo Rizzo

Inner structure of La Fossa di Vulcano (Vulcano Island, southern Tyrrhenian Sea, Italy) revealed by high-resolution electric resistivity tomography coupled with self-potential, temperature, and CO2 diffuse degassing measurements

La Fossa cone is an active stratovolcano located on Vulcano Island in the Aeolian Archipelago (southern Italy). Its activity is characterized by explosive phreatic and phreatomagmatic eruptions producing wet and dry pyroclastic surges, pumice fall deposits, and highly viscous lava flows. Nine 2-D electrical resistivity tomograms (ERTs; electrode spacing 20 m, with a depth of investigation >200 m) were obtained to image the edifice. In addition, we also measured the self-potential, the CO2 flux from the soil, and the temperature along these profiles at the same locations. These data provide complementary information to interpret the ERT profiles. The ERT profiles allow us to identify the main structural boundaries (and their associated fluid circulations) defining the shallow architecture of the Fossa cone. The hydrothermal system is identified by very low values of the electrical resistivity ( 400 Ω m). Inside the crater it is possible to follow the plumbing system of the main fumarolic areas. On the flank of the edifice a thick layer of tuff is also marked by very low resistivity values (in the range 1–20 Ω m) because of its composition in clays and zeolites. The ashes and pyroclastic materials ejected during the nineteenth-century eruptions and partially covering the flank of the volcano correspond to relatively resistive materials (several hundreds to several thousands Ω m). We carried out laboratory measurements of the electrical resistivity and the streaming potential coupling coefficient of the main materials forming the volcanic edifice. A 2-D simulation of the groundwater flow is performed over the edifice using a commercial finite element code. Input parameters are the topography, the ERT cross section, and the value of the measured streaming current coupling coefficient. From this simulation we computed the self-potential field, and we found good agreement with the measured self-potential data by adjusting the boundary conditions for the flux of water. Inverse modeling shows that self-potential data can be used to determine the pattern of groundwater flow and potentially to assess water budget at the scale of the volcanic edifice.

2D electrical resistivity imaging of some complex landslides in the Lucanian Apennine chain, southern Italy

We use high-resolution electrical resistivity imaging to delineate the geometry of complex landslides in the Lucanian Apennine chain of southern Italy, to identify the discontinuity between the landslide material and bedrock, and to locate possible surfaces of reactivation. The Lucanian Apennine chain is characterized by high hydrogeological hazard and shows a complete panorama of mass movements. In this area, all typologies of landslides markedly predisposed and tightly controlled by the geostructural characteristics, are found: rotational and translational slides, rototranslational slides, earth and mudflows, as well as deep-seated gravitational slope phenomena with a predominance of rototranslational slides evolving as earthflow slides. Three test sites, characterized by complex geology and a high hydrogeologic hazard, are studied. The Giarrossa and Varco Izzo earthflow slides are located to the west and east of the town of Potenza, whereas the Latronico slide is located close to the town of Latronico....

The use of electrical resistivity tomographies in active tectonics: examples from the Tyrnavos Basin, Greece

Abstract A 2D Electrical Resistivity Tomography (ERT) survey was carried out in the tectonically active Tyrnavos Basin, Eastern Thessaly, Greece. The principal aims of this research are to test the efficiency of this relatively new geoelectrical technique when applied to the recognition and the geometrical characterisation of active faults and to improve our tectonic knowledge of the investigated area. We therefore carried out several tests performing the geophysical prospecting across morphotectonic scarps or fault traces along which the Late Quaternary tectonic activity is well documented by previous structural, stratigraphic, morphotectonic and palaeoseismological researches. The tests concerned the electrode spacing, the maximum depth of investigation, the quality-to-costs ratio, etc. In a second phase of the survey, we applied this geophysical methodology to specific sites along the major tectonic structures bordering the Tyrnavos Basin, in order to obtain, firstly, a better tectonic knowledge of the area, secondly, to solve particular and local geological problems and, thirdly, to help deciding between ambiguities left unsolved by superficial surveys. Accordingly, numerous ERT with different electrode spacing (from 2 up to 50 m) and depth of investigation (from 0.5 to 120 m) were performed with a dipole-dipole array using a multielectrode system, with 32 electrodes equally spaced along a straight line, for data acquisition. Combining advanced technologies for data acquisition and new tomographic techniques for resistivity data inversion, we obtain a large data-set of high-resolution electrical images of the subsurface across active faults. General and particular results concerning the application of ERT techniques for mapping subsurface active faults are discussed, while advantages and limits in applying this geophysical methodology are emphasised.

Some examples of GPR prospecting for monitoring of the monumental heritage

In this paper three case histories of ground penetrating radar (GPR) for the monitoring of historical buildings are presented. They aim to present the specific valence of the GPR in the field of the diagnostic of historical buildings, which is a promising field of research, due to the increasing awareness of the relevance (even economic) of the cultural heritage. The presented GPR prospecting cases have been performed on three different constructive elements typical of historical buildings (a wall, a masonry pillar and a marble column) in order to be the answer to different problems such as the characterization of the masonry, the detection of cracks and the imaging of metallic reinforcement bars.

Transport infrastructure surveillance and monitoring by electromagnetic sensing: the ISTIMES project

The ISTIMES project, funded by the European Commission in the frame of a joint Call “ICT and Security” of the Seventh Framework Programme, is presented and preliminary research results are discussed. The main objective of the ISTIMES project is to design, assess and promote an Information and Communication Technologies (ICT)-based system, exploiting distributed and local sensors, for non-destructive electromagnetic monitoring of critical transport infrastructures. The integration of electromagnetic technologies with new ICT information and telecommunications systems enables remotely controlled monitoring and surveillance and real time data imaging of the critical transport infrastructures. The project exploits different non-invasive imaging technologies based on electromagnetic sensing (optic fiber sensors, Synthetic Aperture Radar satellite platform based, hyperspectral spectroscopy, Infrared thermography, Ground Penetrating Radar-, low-frequency geophysical techniques, Ground based systems for displacement monitoring). In this paper, we show the preliminary results arising from the GPR and infrared thermographic measurements carried out on the Musmeci bridge in Potenza, located in a highly seismic area of the Apennine chain (Southern Italy) and representing one of the test beds of the project.

GPR and microwave tomography for detecting shallow cavities in the historical area of ‘‘Sassi of Matera’’ (southern Italy)

The results of a geophysical survey carried out in the historical area of “Sassi of Matera” (Basilicata region, southern Italy) are presented and discussed. Matera is one of the most fascinating and ancient towns of the Mediterranean area and is listed in the UNESCO World Heritage List. It represents an example of a town where the communities developed a cave-life culture in the cavities excavated through the substratum of the hill of Matera. The urban area of Matera, therefore, is characterized by a complex system of interconnected and overlapping ancient shallow cavities: residences, galleries, cisterns, crypts, graves, etc. Consequently, local surface deformation phenomena are often observed. We describe the results from a ground-penetrating radar (GPR) survey carried out in St. Rocco Square, one of the most interesting areas of the historical centre of Matera, that was affected by both spread out and local subsidence phenomena. Great attention was paid to GPR data processing and inversion. In particular, a novel microwave tomography approach was applied to obtain high-resolution images of shallow ancient cavities that caused the local surface deformations. Moreover, the GPR survey was integrated with an electrical resistivity tomography survey in order to prospect those subsurface zones with a high electrical conductivity, where GPR investigation was not possible. The geophysical investigation enabled us to identify the cause of the subsidence phenomena and to reconstruct the geometry of the complex system of shallow cavities partially filled with unconsolidated material.

Magnetic, GPR and geoelectrical measurements for studying the archaeological site of ‘Masseria Nigro’ (Viggiano, southern Italy)

The results of a geophysical survey carried out at the archaeological site of Masseria Nigro, located on a fluvial terrace on the north-eastern flank of the Agri valley (Viggiano, Basilicata Region), are presented and discussed. The site includes an important ancient structure, developed in successive phases between the 4th and 3rd centuries BC and destroyed after the Roman conquest. Magnetic mapping, GPR profiling and electrical resistivity tomography were applied in the course of geophysical exploration in the archaeological area. The application of these methods revealed information about buried ancient walls, helping to define the boundaries of the whole building. During the first phase of the excavation, archaeologists targeted only the western part of the ancient structure (about 1000 m 2 ), but the geophysical survey performed in a second phase was able to cover the entire ancient structure (1400 m 2 ), enabling the archaeologists to define the extent of the buried structures. Our findings confirmed the hypothesis of the larger extent of the archaeological area in the eastern part and revealed the complete plan of the ancient building.

Integrated techniques for analysis and monitoring of historical monuments: the case of San Giovanni al Sepolcro in Brindisi, southern Italy

In this paper, an integrated prospecting performed in the atypical Romanesque church of San Giovanni al Sepolcro in Brindisi, southern Italy is presented. Ground-penetrating radar (GPR) and ultrasonic data have been gathered on the circular load-bearing colonnade of the monument. Here the results achieved on two of the columns are shown. The GPR data have been processed and have allowed to identify and focus the medieval internal metallic hinges joining the stone trunks in one of the columns and some reinforcement rebars in the other (and probably also the residual track of a restored fracture). The ultrasonic data have allowed to monitor the state of compactness and to assess the effectiveness of reinforcement interventions on the columns.

GPR investigations for the study and the restoration of the rose window of Troia Cathedral (southern Italy)

The development of cracks and distortions caused by past seismic events compromised the integrity of the rose window of Troia Cathedral, one of the most precious Romanesque monuments in southern Italy. Ground-penetrating radar (GPR) using high-frequency antennae (mainly 1500 MHz) was selected from among various non-destructive testing methods for its high-resolution imaging to scan the internal structure of the various architectural elements of the wheel window: the decimetre-diameter columns constituting the rays, the ring decorated with intersecting arched ribwork and the surrounding circular ashlar curb. GPR was employed in the classical continuous reflection mode, moving the antennae manually along the architectural elements and paying exceptional care in the acquisition and processing stages to avoid positioning errors. Indeed, the challenging aspects of this case study were the geometrical complexity and small dimensions of the structural elements, causing many logistic/coupling problems. In spite of this, through proper interpretation techniques, based on signal analysis (presence of reflections and diffractions, velocity and attenuation variations) and correlation with features detected by visual inspection of the external surfaces, the GPR survey provided useful information on the internal structure of the rose window, detecting fractures and the boundaries of previously restored parts and locating hidden metallic components connecting the architectural elements. Information on the internal structure and spatial distribution of metallic junctions was essential for gaining insight into building techniques in order to discriminate between restoration strategies which may require either total or partial dismantling of the rose window. GPR results provided crucial evidence in favour of one of the (conflicting) hypotheses about the original building techniques, leading to the selection of partial dismantling as the most suitable restoration strategy. Analysis of measurements revealed the potential of GPR in the field of cultural heritage restoration, even in those cases characterized by complex geometry, structural brittleness and logistic difficulties, such as that discussed in this paper.

QUICK SURVEY OF THE POSSIBLE CAUSES OF DAMAGE ENHANCEMENT OBSERVED IN SAN GIULIANO AFTER THE 2002 MOLISE, ITALY SEISMIC SEQUENCE

On October 31 and November 1, 2002, two earthquakes of magnitude 5.4 and 5.3 hit the area at the border between the Molise and Puglia regions in Southern Italy. The damage pattern in the epicentral area qualified the quake as an intensity VII MCS event, although providing a notable exception relevant to the small village of San Giuliano di Puglia. Since the first macroseismic survey, it appeared clear that in S. Giuliano the intensity was two degrees higher with respect to three neighbouring villages located within a radius of 3 km. Soon after the quake, our team started a campaign of microtremor HVSR measurements (Horizontal to Vertical Spectral Ratio), then we installed accelerometers and carried out damage and geological surveys. Finally, we performed a geoelectrical tomography and two profiles of Vs velocity with depth using the NASW technique (Noise Analysis of Surface Waves). The preliminary observations indicate that ground motion amplification is present in S. Giuliano within the frequency band that may affect building. A strong velocity contrast 20 m deep causes the predominant peak. More amplification could be due to more complicated, 2D effects. As regards the damage pattern, it divides S. Giuliano in three zones showing different characteristics and seismic behaviour. A building-by-building survey is still under way to better evaluate vulnerability variations in different zones of the village. However, the acquired data so far is sufficient to propose site amplification as a possible cause of the damage enhancement observed in S. Giuliano.