WED EqUATION DATUMING APPLIED TO CRUSTAL LAND DATA: REPROCESSING OF CROP PROFILES ACROSS THE GEOTHERMAL PROVINCE OF TUSCANY

Introduction. Reflection seismic profiles, programmed within the Italian CROP (CROsta Profonda) project for the investigation of the deep crust, where acquired across the two main structural domes and geothermal fields of Larderello and Mt. Amiata during 1993-1995. The transect CROP-18, split into two lines, identified as CROP 18-A and CROP 18-B, was designed to study the continuity of crustal structures from the Larderello to the Mt. Amiata areas, following a NW-SE direction roughly parallel to the Apennine structural trends. CROP03 was recorded across the Northern Apennine Arc, with nearly E-W direction, from Tyrrhenian to the Adriatic Seas. The profiles allowed exploring the crust to understand the origin of the main heath flow anomalies, looking also for hidden resources and new exploitable geothermal reservoirs (i.e., Della Vedova et al., 2008). The first processing of these lines was focused on illuminating the deep crustal features (Accaino et al., 2005, 2006), starting from the major reflector that characterizes the geothermal fields, the K-horizon, based on previous seismic surveys (Batini et al., 1978; Liotta et al., 1998; Brogi et al., 2003, 2005). On the contrary, our purpose was to reprocess the first 4 s reflection times (6 s for the profile CROP-03), with the aim of better highlighting the upper crust and getting images directly comparable with the drilling information and the industrial seismic profiles, which are of limited extension and designed to inspect specific objectives (Cameli et al., 1993, 2000). In order to reach the above-mentioned goals, we applied advanced techniques improving signal/noise ratio and extracting information previously hidden by approximate static corrections and near surface noise. In fact, the seismic acquisition did not included techniques to better resolve the shallow subsurface, such as down-hole velocity measurements or refraction profiles, and the group distance of 60 m was chosen to detect reflected energy from deep interfaces ignoring the near surface complexities. Moreover, near surface high-velocity formations, alternate to sub-basins filled with Neogene and Quaternary deposits, did not favor the penetration and the focusing of the seismic energy. Surprisingly, in contrast with the non-reflective and dispersive, or not resolved upper highly deformed nappes, the area turns out to be characterized by the occurrence of high amplitude reflecting horizons with good lateral continuity in the deeper parts. The reflectivity was attributed by several authors to the degree of metamorphism and to thermal alterations. The origin of possible presence of fluids is still debated and it can be of great importance for the recovery of geothermal fluids of industrial interest.