Strong electromagnetic (EM) anomalies have been detected, from MHz to kHz, prior to the three destructive earthquakes occurred during 1995--1999 in Greece. The observed sequence of EM anomalies before the Kozani-Grevena earthquake (K-G) of Ms = 6.6 on May 13, 1995 showed some important characteristics: (i) an increasing electromagnetic emission rate; (ii) an emergence of lower kHz frequencies with large amplitudes at the tail of the MHz electromagnetic anomaly; (iii) an electromagnetic quiescence approximately a few hours before the earthquake and (iv) a total absence of EM anomalies during the aftershock period. All these features are compatible with those reported by other authors. This sequence of the field observed EM signals revealed, in terms of emission pattern, similarities to the laboratory acoustic (AE) emissions during different stages of failure preparation process in rocks.