Active Stress Field in the Geothermal Areas of Latium and Tuscany

Abstract

We have investigated the present-day stress field in the Tyrrhenian border of Latium and Tuscany using borehole breakout from deep geothermal wells, fault plane solutions of shallow earthquakes, and surface mesostructural data. The study region is a NW-SE elongated belt (200 km by SO km) bordering the western side of the Apennines, that includes a suite of volcanoes active during Quaternary times. The breakouts have been observed on four-arm caliper dipmeter data, indicating a horizontal minimum stress direction (Sh) that varies from NE to ENE. The earthquake focal mechanisms show normal or to a lesser extent strike-slip faulting, with T (tensional) axes predominantly oriented NE-SW. Field studies of fractures and faults also indicate NE extension. These data suggest that the whole area is presently extending in a direction perpendicular to the Apenninic chain, where a similar, probably faster extension, is documented by focal mechanisms of strong recent earthquakes and young geologic data.