RECONNAISSANCE OF A HIGH-TEMPERATURE (100-150C) GEOTHERMAL RESOURCE.
A geophysical reconnaissance based on seismic refraction profiling has been carried out in the region of Olot (northeast of Spain), the youngest Quaternary volcanic area of the Iberian Peninsula. The methodology designed to provide the structure of the upper crust under the volcanic zone (VZ) and its lateral variations has been tested in this study. A global model coherent for the profiles covering the axis of volcanism shows low seismic velocities (V) for P-waves, less than 4 km/s in the first 400 m under the VZ. In the surrounding Eocene sediments higher values are measured, differing from east (5.3 km/s) to west (4.6 km/s). Comparable variations of electrical resistivityhave been obtained in a complementary survey. The basement was located at about 2 km depth, deepening from east to west and from north to south, and higher velocities, 6.6 to 6.7 km/s, were correlated below an horizon at 5 km depth. The S-waves analysis from individual 3-component stations provided independant structural constraints. High Vp/Vs values were obtained at small depths. The polarizations derived from particle motions showed several converted P-S phases, originated mainly on top of the basement. The area beyond eastern boundary of the VZ displays anomalous high energetic arrivals and complex particle motions corresponding to local effects that should be further investigated from denser seismic measurements.
THE AIM IS TO DETERMINE THE STRUCTURE OF THE UPPER CRUST THROUGH THE FIRST 10 KM UNDER THE OLOT QUARTERNARY VOLCANIC ZONE (SPAIN) USING SEISMIC REFRACTION TECHNIQUES BASED ON EXPANDING SEISMIC PROFILES (ESP), AND IN PARTICULAR DETERMINING THE LOCATION AND LATERAL VARIATIONS OF AN INTERCRUSTAL REFLECTOR ALREADY IDENTIFIED, WHICH COULD BE AN ESSENTIAL ELEMENT IN THE GEOTHERMAL RESOURCES OF THIS REGION.