Changes of chaotic behavior of the long-term geoelectric potential difference observed during a five-year investigation and its possible relation to seismic activity in Western Greece

Observations of the long-term geoelectric potential (LTGP) difference are presented in this paper. The data have been collected during a five-year (1993–1997) experimental investigation. For the creation of these data, an automatic system for collection, transfer and processing of geoelectric measurements operates at the Seismological Laboratory of the University of Patras. The analysis of the data using the Lyapunov exponents has shown a quite chaotic behavior. The Lyapunov exponents have also been calculated for short periods of 20 days, i.e. 10 days before and 10 days after the earthquakes occurred during this five-year period. The resulting Lyapunov spectrums have been compared with corresponding spectrums of periods that none earthquake has been occurred. The comparison leads to a possible change of the Lyapunov spectrum prior to an earthquake. A theoretical explanation of the above result is also given.