A possible explanation for electric perturbations recorded by the Italian CIEN stations before the 2012 Emilia earthquakes

A network of Extremely Low Frequency (ELF) electromagnetic detectors consisting of identical instruments that continuously record the electrical component of the electromagnetic field, ranging from a few Hz to tens of kHz has been operating in central Italy for several years. These signals are analysed in real time, their power spectrum contents and time/frequency data are saved for further analysis. The spectral contents have evidenced very distinct power spectrum signatures that increase in intensity when strong seismic activity occurs near the stations. During the Emilia seismic sequence in 2012, the network consisted of nine stations, seven in central Italy and two in northern Italy, at Zocca (Modena province) and at Torre Pellice (Turin province). Data recorded by the Zocca station, near Modena, at about 60 km from the Emilia epicentres were analysed. Data analysis shows the existence of several ELF oscillations of the horizontal electric field started on April 2012 and lasted up to the end of June 2012. Recorded ELF oscillations were similar to those recorded before and after the L\'Aquila earthquake in 2009. However, since May 2012 was interested by significant rainfall close to the station, it is possible that the selected signals were linked to it. A theoretical model which could explain recorded ELF oscillations in concomitance with seismic and rain events is proposed.