Geophysical exploration for geothermal low enthalpy resources in Lipari Island, Italy P.P.G. Bruno a, * , V. Paoletti b , M. Grimaldi b , A. Rapolla b a Osservatorio Vesuviano-Centro di Sorveglianza, Via Diocleziano, 328, 80124 Naples,Italy b Dipartimento di Geofisica e Vulcanologia, Universita ` di Napoli Federico II, Largo S. Marcellino, 10, 80138 Naples,Italy Received 22 June 1999; received in revised form 15 November 1999; accepted 15 November 1999 Abstract Integrated geophysical surveys were performed in two sites, Fossa di Fuardo and Terme di San Calogero in Lipari Island, Southern Italy with the intent of the exploration of low-enthalpy geothermal fluids. Both sites show strong geochemical and geologic evidences of hydrothermal activity. The geophysical methods consist of two microgravimetric surveys, two 2D geoelectric profiles, a seismic reflection profile and a five seismic refraction profiles. The seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships. The gravity field was used to constraint the seismic discontinuities, while the electric prospecting let discriminate more conductive areas, which could correspond to an increase in thermal fluid circulation in the investigated sites. The results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo- structural model of the subsurface setting of the two investigated areas. A low-enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at Fossa del Fuardo. The reservoir is intersected by some sub-vertical faults/fractures that probably play an important role in convoying the thermal water up to the surface. At the other site, Terme di S. Calogero, the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area. This circulation concentrates along a ENE-trending fault located at a little distance from the thermal resort. The hot fluids may upraise along the fault if the width of the ascent area is smaller than 20 m.  2000 Elsevier Science B.V. All rights reserved. Keywords: Aeolian island; Lipari; geoelectric; seismic reflection; seismic refraction; gravimetry; low enthalpy geothermal exploration 1. Introduction Lipari is the largest of seven islands constituting the Aeolian archipelago, located in the south-eastern margin of the Tyrrhenian sea (Fig. 1) and interpreted as a volcanic arc sitting about 250 km above the Tyrrhenian Benioff zone (Anderson and Jackson, 1987). The genesis of this area is strictly connected to the ensuing fragmentation, dispersion and sub- sidence of a formerly continuous lithospheric segment during Miocene to Pliocene. These have led to the formation of the western Mediterranean and the Tyrrhenian basins (Alvarez et al., 1974; Alvarez, 1976; Biji-Duval et al., 1987). The peri-Tyrrhenian margin of Italy is the site of present-day volcanism. On the northeastern border the recent activities occur on mainland Italy and adjacent islands. On the southeastern border, the volcanic Journal of Volcanology and Geothermal Research 98 (2000) 173–188 0377-0273/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0377-0273(99)00183-3 www.elsevier.nl/locate/jvolgeores * Corresponding author. Tel.: + 39-81-6108-437; fax: + 39-81- 6100-811. E-mail address: piebruno@cds.unina.it (P.P.G. Bruno).