A perspective electric earthquake precursor observed in the Apennines

We present the data on particular electric signals in the frequency band around 8 kHz emitted by various types of rocks that are subject to pressure and fracture in the laboratory and recorded in the surrounding air. A similar type of electric signal was recorded as an electric precursor of the earthquake with magnitude 5.0 that occurred on September 14, 2003 at 22h 42m 50s in the Tosco-Emiliano Apennines (lat. 44.22^o N, long. 11.35^o E). The precursor was recorded with an instrument called radio-geophone installed in an experimental station located near Cascia (PG) (lat. 42.8^o N; long. 13.1^oE; 900 m a.s.l.).