B. Toro

Volcano–tectonic structures, gravity and helium in geothermal areas of Tuscany and Latium (Vulsini volcanic district), Italy

Abstract Since the early 1980s, geological and structural mapping, gravity, and helium soil–gas studies have been performed in the eastern sector of the Vulsini Volcanic District (Roman Magmatic Province) in an attempt to locate potential geothermal reservoirs. This area is characterised by an anomalous geothermal gradient of >100°C/km, and by widespread hydrothermal mineralization, thermal springs, high gas fluxes, and fossil and current travertine deposits. The results of these surveys indicate the existence of a number of fault systems, with N–S and E–W structures that appear to be superimposed on older NW–SE and NE–SW features. Comparison of the results of the various studies also reveals differences in permeability and potential reservoir structures at depth.

Gravity and elevation changes in the Travale geothermal field (Tuscany) Italy

The results of precise levelling measurements on a specially constructed network of benchmarks in the Travale geothermal area (Tuscany, Italy) revealed the subsidence of the central part of this area, at an average rate of 20 mm/year in the period 1978 – 1980. Two sets of gravity measurements over the same time-interval, using two Lacoste — Romberg gravimeters, have an average standard error of 2–4 μGal for the main network, and 4–8 μGal for the auxiliary network. The observed g variations fall within the error range in most of the stations. The variations noted in the stations in the south-western area of the field clearly fall outside the confidence interval, and cannot entirely be attributed to changes in elevation. An absolute gravity station was set up at Palazzo at Piano (Siena), where measurements were made by the IMGC absolute gravimeter, to detect any long-term gravity variations induced by geodynamic events.

Crustal deformation and gravity changes during the first ten years of exploitation of the new Travale-Radicondoli geothermal field, Italy

Abstract The results of precise levelling measurements on a specially constructed network of benchmarks in the Travale geothermal area (Tuscany, Italy) revealed that the central part of this area is subsiding and that the average rate of subsidence in the period 1973–1983 was 20–25 mm/year. Three series of horizontal distance measurements were carried out (1980, 1981, 1982) to monitor variations in the coordinates of the bases of a horizontal control net. The variations noted in this time interval range between 13 and 36 mm, slightly exceeding the semi-axis values of their error ellipses. A series of gravity measurements was carried out annually between 1979 and 1982 on a network of gravity benchmarks coinciding with part of the topographic benchmarks. The g variations observed reached a maximum of 40 μGal. A tentative correlation of these data with field exploitation data indicates a possible means of interpreting the variations observed during these surveys.

Gravity monitoring of Nisyros volcano activity: 2001-2003 preliminary results

Abstract Topographic monitoring of gravity benchmarks, based on a differential-mode, dual-frequency GPS, started in 2002 on Nisyros volcano. A monitoring network was installed in June 2001. The sites were selected in parts of the island experiencing different seismic-tectonic processes, in order to detect their relative movements. In June 2002, monitoring with the microgravity network was repeated for the first time. The comparison of the resulting values with those recorded in 2001 showed a maximum variation of +0.034 mGal in the active volcanic area, with an increasing trend towards South. In 2003, the monitoring was repeated. The resulting G variations were comparable to those observed in 2001-2002. However, with the installation of a new station in 2002, the G variations proved to be confined to the most active volcanic areas. The extent of the variations recorded between 2001 and 2003 largely exceeded the measuring errors, suggesting that such variations are to be ascribed to mass variations of the volcanic complex.

Gravity Variations in Microgravity Networks in Central Italy

In the period from 1980 to 1994, the geodynamically-active and highly-seismic area of Central Italy was investigated by means of three microgravity networks, aimed at recording gravitational field changes

GEOPHYSICAL CONTRIBUTION TO THE STUDY OF BRACCIANO LAKE

Abstract A Uniboom survey was carried out in Bracciano Lake (Northern Latium) in order to obtain further information about its structural and morphological features. The authors give an updated geophysical interpretation of the lake by combining the findings of the seismic survey with those from gravity and magnetometric prospecting. Through seismic sections, obtained by developing a new bathymetric map, some sedimentary and volcanic structures were identified.

Recent Tectonics in the Origin and Evolution of Gran Bajo del Gualicho, Argentina

The results of an interdisciplinary research program on the Gran Bajo del Gualicho (Rio Negro, Argentina) are reported. Geological, morphological, gravimetric, and geochemical studies provide the basis for a reconstruction of the possible origin and evolution of this endorheic depression. On the basis of the available data, the hypothesis is advanced that the depression had a tectonic origin (according to NNW-SSE and ENE-WSW tectonic lines) and subsequently was shaped by exogenous forces that obscured the original fault scarps and caused the depression to assume its present characteristics.