[1] The complexity of volcano-hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work. We use here an integrated multidisciplinary approach, combining geological investigations with hydrogeochemical and soil degassing prospecting, and resistivity surveys, to provide a comprehensive characterization of the shallow structure of the southwestern Ischia's hydrothermal system. We show that the investigated area is characterized by a structural setting that, although Copyright 2011 by the American Geophysical Union 1 of 25 very complex, can be schematized in three sectors, namely, the extra caldera sector (ECS), caldera floor sector (CFS), and resurgent caldera sector (RCS). This contrasted structural setting governs fluid circulation. Geochemical prospecting shows, in fact, that the caldera floor sector, a structural and topographic low, is the area where CO 2 -rich (>40 cm 3 /l) hydrothermally mature (log Mg/Na ratios < −3) waters, of prevalently meteoric origin (d 18 O < −5.5‰), preferentially flow and accumulate. This pervasive hydrothermal circulation within the caldera floor sector, being also the source of significant CO 2 soil degassing (>150 g m −2 d −1 ), is clearly captured by electrical resistivity tomography (ERT) and transient electromagnetic (TEM) surveys as a highly conductive (resistivity < 3 W·m) layer from depths of ∼100 m, and therefore within the Mount Epomeo Green Tuff (MEGT) formation. Our observations indicate, instead, that less-thermalized fluids prevail in the extra caldera and resurgent caldera sectors, where highly conductive seawater-like (total dissolved solid, TDS > 10,000 mg/l) and poorly conductive meteoric-derived (TDS < 4,000 mg/l) waters are observed, respectively. We finally integrate our observations to build a general model for fluid circulation in the shallowest (<0.5 km) part of Ischia's hydrothermal system.
Geophysical surveys are carried out in the coastal area of Petrosino (south-western Sicily) to study the time evolution of seawater contamination of the coastal aquifer, probably increased due to human impact. The overexploitation of the aquifer, due to an intensive agricultural use has affected significantly the natural hydro-geochemical state of the basin. The study is based on a processing and integrated analysis of hydrogeological, geochemical and geophysical data. In particular in the last two years seasonal time-lapse electrical resistivity tomographies (ERT), new TDEM soundings and Multi-Analysis Surface Wave soundings (MASW) have been carried out. The interpretation of the total set of previously existing and new geophysical data made it possible to reconstruct a threedimensional model of the electrical resistivity of the aquifer, aimed at defining the extent and geometry of the seawater intrusion. Furthermore, the execution of a series of high-resolution timelapse electrical tomographies and a correlation analysis between geophysical measures and geochemical, geological and hydrogeological data allowed to discriminate the effects of the salt concentration in the groundwater and the porosity and saturation degree of the rock on the time variations of the measured electrical resistivity. Finally, the average porosity of the rocks forming the reservoir was determined.underground water flows, resulting in a strong degradation of specific coastal wetlands locally called 'Margi'. These very specific environments, characterized by an outcrop of the local piezometric surface, are sensitive ecosystems with a high-conservation value. In addition they are very valuable ecosystems, qualified as special protection areas of the Sicilian region and between the areas of intervention of the European project LIFE-Nature.
Because of its high seismic hazard the urban area of Oliveri has been subject of first level seismic microzonation. The town develops on a large coastal plain made of mixed fluvial/marine sediments, overlapping a complexly deformed substrate. In order to identify points on the area probably suffering relevant site effects and define a preliminary Vs subsurface model for the first level of microzonation, we performed 23 HVSR measurements. A clustering technique of continuous signals has been used to optimize the calculation of the HVSR curves. 42 reliable peaks of the H/V spectra in the frequency range 0.6–10 Hz have been identified. A second clustering technique has been applied to the set of 42 vectors, containing Cartesian coordinates, central frequency and amplitude of each peak to identify subsets which can be attributed to continuous spatial phenomena. The algorithm has identified three main clusters that cover significant parts of the territory of Oliveri. The HVSR data inversion has been constrained by stratigraphic data of a borehole. To map the trend of the roof of the seismic bedrock, from the complete set of model parameters only the depth of the seismic interface that generates peaks fitting those belonging to two clusters characterized by lower frequency has been extracted
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