A detailed characterization o f the physical properties o f a granitic pluton, as w ell as a three dimensional reconstruction o f the fractures network and its surrounding are obtained by high resolution seism ic tomography. The input travel times were p icked from offset and azimuth variable seism ic profile (OVSP) acquired in a 500 m deep vertical borehole. The three-component seism ic data sets recorded allow ed to test the methodology for P- and S-waves and to compare the velocity models derived from the first arrivals tomographic inversion o f the two different kind of seism ic waves. Furthermore, the combination o f the two velocity models (P- and S-waves) provides a 3D Poisson's ratio diagram o f the rock massif. This coefficient allows to differentiate volumes o f fractured and altered granite from fresh rock. Poisson's ratios close to 0.3 mean fractured areas and correlate with fracture index (FI) and sonic logs, otherwise Poisson's ratio close to 0.25 is related to unaltered and unfractured rock.

Este estudio ha sido financiado por ENRESA. También parte de la financiación ha sido proporcionada por el Ministerio de Ciencia y Tecnología (becas BTE 2000-0583-C02- 01, REN 2001-4230) y la Generalitat de Catalunya (beca 2001-SGR-00339).