In the present paper we report the results of almost three years of measurements of the electromagnetic variations in 3 and 10 kHz, 41 and 53 MHz. The data are collected using a telemetric network installed along the island of Crete, i.e. in the central segment of the South Hellenic Arc. The experiment indicates that electromagnetic perturbations occur prior to seismic activity and supports previous observations that the time sequence of the variations appears in an invariant pattern.