GNGTS 2014 - Atti del 33° Convegno Nazionale

88 GNGTS 2014 S essione 2.1 Several shocks of M > 3 occurred near the same epicentre over the following years and, at the same time, many ELF oscillations were recorded by the Perugia instruments. Being that the earthquake distances and the magnitudes were compatible with the Dobrovolsky condition (Dobrovolsky, 1979), an analysis was carried out looking for a possible correlation between ELF electrical oscillations and moderate seismic activity. The recently installed CIEN stations in Città di Castello and Gubbio contributed to this analysis, though, a thorough verification needs to be performed on the signals recorded by the two new stations. Electrical oscillations, such as those reported in connection with the 2009 L’Aquila earthquake (Fidani, 2011) were also detected at the Perugia station during moderate seismic activity. Specifically, electrical oscillations were recorded on many occasions where M = 2.8 – 3.7 in the Pietralunga territory. The pattern recorded from the S-N electrode lasted from a of few minutes up to two hours, and concerned electrical oscillations between 40 Hz and 350 Hz. The electrical oscillation intensities observed during moderate seismic activity near the Perugia station ranged between -70 dB and -55 dB. To verify if observed electrical oscillations could have been influenced by the meteorological precipitation, data from the meteorological stations in Perugia were retrieved. Precipitation events were also recorded in ELF data at the Perugia Fig. 1 – The geographical positions of the 13 CIEN stations are indicated by red circles.