Instrumental studies of electromagnetic signals linked to geophysical phenomena began early in Italy, during the XIX century thanks to Luigi Palmieri, Michele Stefano de Rossi and Father Alessandro Serpieri. These were meteorological studies and inspired by several observations reported in XVIII century collections of Italian earthquake phenomena (for example see scripts of Giuseppe Vannucci after the Rimini earthquake in 1786).

Recently, the subject of electromagnetic pertuurbations was strongly developed in several countries by magnetic and electromagnetic stations, from ULF to VHF. Also in Italy a subionospheric propagation monitoring system started in Bari. All of them revealed a number of perturbations in occasion of the major earthquakes which still needs of a better understanding.

 

 

Meteorology is strongly connected to atmospheric electricity, our stations reveals strong ELF elctric field activity during the passage of each perturbation. Such activity being strictly connected to rainfall give to us another way to quantify it. The sistem is capable to evaluate lightning activity by intensity and number variation. A further interference appear on the strenght of VLF radio signals when a strong rainfall is near, but not still above, the station.

The electromagnetic signal which appear long time before an earthquake

shows as an irregular spectral label which is characterised by frequency ranging from 60 and 200 Hz. Its occurrence revealed not to be perfectly coinciding with the quakes but its time length and magnitude resulted increased in the period of the main shock. Furthermore, they appeared principally before strong seismic activity with M>5.