S. Piscitelli

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.

Fluid injection induced seismicity reveals a NE dipping fault in the southeastern sector of the High Agri Valley (southern Italy)

On 2 June 2006 the wastewater produced during the oil and gas field exploitation in High Agri Valley (southern Italy) started to be managed by disposal through pumping the fluids back into the subsurface at the Costa Molina 2 (CM2) injection well, located in the southeastern sector of the valley. The onset of microearthquakes (Ml ≤ 2) after 4 days at about 1.3 km SW of CM2 well suggests fluid injection induced seismicity by the diffusion of pore pressure. Moreover, the space-time evolution of 196 high-resolution relocated events reveals a previously unmapped NE dipping fault. We investigate the physical processes related to the fluid injection induced seismicity and delineate the previously unmapped fault by jointly analyzing seismicity data, geological observations, fluid injection data, the stratigraphic log of the CM2 well, and the electrical resistivity tomography survey carried out in the study area.

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.

Robust Statistical Methods to Discriminate Extreme Events in Geoelectrical Precursory Signals: Implications with Earthquake Prediction

In this study, we propose a robuststatistical method to discern anomalous patternsin geoelectrical time series measured in a seismicarea of the Southern Apennine chain. First, a filteringprocedure to remove seasonal effects related tometeo-climatic fluctuations was carried out.Then, we selected an autoregressive model able todescribe the time fluctuations of geoelectricalsignals and propose a method to obtain an objectiveestimate of probability of occurrence for each extremeevent detected in the time series. Our applications inSouthern Italy allow us to hypothesize that theambiguity of short-term prediction is within thecomplicated dynamics of the physical processresponsible for electrical anomalies observed on theearths surface.

Geophysical and geochemical parameters jointly monitored in a seismic area of Southern Apennines (Italy)

Abstract In this work we analyze the geoelectrical and geochemical time series jointly recorded by means of Tramutola station during the period January 1995–September 1996. Since 1991 a research activity devoted to the analysis of geophysical and geochemical time series measured in a test site located in Southern Italy has been carried out. After a preliminary screening of spatial and temporal patterns of geochemical and geophysical phenomena observed in the investigated area, some multiparametric automatic stations, able to detect possible precursory phenomena, have been set up close to anomalous fluid emissions in Basilicata (Italy). The stations are equipped with sensors suitable for CO 2 , 222 Rn, electrical conductivity in water, temperature and self-potential. The main aims of this work are: a) to obtain a complete time series of possible precursory parameters; b) to apply statistical methods to discriminate anomalous patterns from background noise; c) to link geophysical and geochemical signals; d) to evaluate the possible correlation between anomalous patterns in precursory parameters and the local seismic activity.

Integrated near surface geophysics across the active Mount Marzano Fault System (southern Italy): seismogenic hints

Here, we describe an original geophysical multi-method approach applied to the Mount Marzano Fault System. This is one of the most hazardous seismogenic faults of the Apennines (Irpinia, southern Italy), and it was responsible for the 1980, Mw 6.9, earthquake, along with many others before. We carried out electrical resistivity tomography (ERT), ground penetrating radar (GPR) measurements, and horizontal-to-vertical spectral ratio (HVSR) microtremor analysis along several common transects designed across the potential and/or certain fault traces. The data obtained from these non-invasive, inexpensive, expeditious methods mutually integrate with and complement each other, providing a valuable subsurface image of the near surface fault architecture. ERT depicts the general shallow image of the fault zone and of the fault-controlled sedimentary basin, with the depth of the buried bedrock cross-correlated through ambient-noise HVSR results. GPR delineates the very shallow geometry of the fault and of the associated deformation. Coupled with previous paleoseismological studies, these data allow the evaluation of some fault parameters and the precise locating of the fault trace, to aid future paleoseismological investigations aimed at seismic risk reduction programs.

Analysis of ground deformation using SBAS-DInSAR technique applied to COSMO-SkyMed images, the test case of Roma urban area

Differential Synthetic Aperture Radar Interferometry (DInSAR) represents a well-established remote sensing technique for the investigation of ground deformation phenomena.Among the DInSAR techniques, the Small BAseline Subset (SBAS) approach exploits ground surface at two mapping scales, low and high resolution, and allows the detection and monitoring of local deformation processes that may affect single buildings or man-made structures in urban areas. This work investigates the capability improvement of the SBAS-DInSAR technique to analyse deformation processes in urban areas by exploiting SAR data acquired by the Cosmo-SkyMed (CSM) constellation in comparison with the results obtained from data of first generation ERS/ENVISAT radar systems of he European Space Agency. In particular, we extracted mean deformation velocity maps as seen by the three different radar systems and, for each coherent pixel, we retrieved the corresponding displacement time series. Our analysis was focused on the Torrino area where independent studies had already revealed significant deformation signals testified by the serious damages on many buildings in the area. Moreover, in order to understand the causes of the CSM observed displacement rates, reaching few cm per year, we also performed a comparative analysis between DInSAR products and independent information derived from electrical resistivity tomography data and geological maps.

Modelling tectonic features of the Kissamos and Paleohora areas, Western Crete (Greece): combining geological and geophysical surveys

The purpose of this survey is the fault zone determination in Kissamos (NW Crete) and Paleohora (SW Crete) basins. The study area is located within the central forearc of the Hellenic subduction zone. 2D electrical resistivity tomography (ERT) has been applied to reveal fault zones. Ground-truthed fault evidence in the coast northwest of Kastelli–Kissamou and northeast of Paleohora is incorporated into the ERT data. Thirteen ERT profiles were obtained at several sites. Seven of the eight ERT profiles intersect fault zones in Kissamos. Five ERT profiles were conducted in Paleohora and three significant faults were identified. The results indicated the continuation of previously mapped faults as well as revealing unreported faults. The coastline of Paleohora and Grammeno can be associated with a system of fault zone striking almost E–W. We propose that the ERT method is a reliable and economic method at identifying buried fault zones in populated areas. Considering the proximity of the revealed fault zones in densely populated areas and the high seismic activity of the region the determination of the identified fault zones could contribute in earthquake hazard assessment studies for future seismic mitigation and urban planning strategies in the two areas for western Crete.