THE SELF-POTENTIAL METHOD IN THE GEOTHERMAL-EXPLORATION OF GREECE

Self-potential (SP) anomalies are generated by flows of fluid, heat, a nd ions in the earth. SP investigations have been used to locate and d elineate sources associated with such flows in three areas of geotherm al interest in Greece-Lesvos Island, Loutra Hypatis (central Greece), and Nisyros Island. A combination of geophysical methods, with SP bein g the primary method, has been applied in these areas. The SP method i s adversely influenced by various sources of noise. Field procedures h ave been suggested to minimize their effects by monitoring electrode p olarization and telluric activity. The interpretation of SP contour ma ps is preferred to using profile data. A procedure was adopted for SP interpretation, and the results were satisfactory. However, this model is based on thermoelectric sources only and is not related directly t o hot fluid movement. In all three survey areas, the geothermal zones delimited by the SP interpretation in combination with data acquired b y other geophysical methods result in an integrated interpretation of the geothermal system. Since SP and very-low-frequency (VLF) anomalies can be generated by the same geological source (i.e., geothermal, hig hly conductive zone), the corresponding results are compared to provid e a strong indication of the presence of geothermal zones. The activit y of geothermal zones affects the conductivity of the surrounding medi um, which also can be detected by de resistivity and audio-magnetotell uric (AMT) methods. In addition, geothermal zones can be related to va rious interfaces or tectonic features that can be detected by gravity or seismic methods.