New experimental data reveal possible relation of chaotic behavior of the long-term geoelectric potential difference to seismic activity in Western Greece

In this paper, observations of the long-term geoelectric potential difference are presented based on data collected during a six-year (1998-2003) investigating period. Moreover, this paper constitutes a continuation of a previously published work with five-year (1993-1997) experimental data. For data logging purposes, an automatic system for collection of geoelectric measurements operates at the Seismological Laboratory of the University of Patras. The analysis of these data using Lyapunov exponents and Takens estimator confirm their quite chaotic behavior. The Lyapunov exponents have also been calculated for short periods of fifteen days, ten days before and five days after the earthquakes occurred during this six-year period. By thorough examination of the resulting Lyapunov spectrums, it seems that these are subject to possible changes prior to an earthquake.