GNGTS 2015 - Atti del 34° Convegno Nazionale

12 GNGTS 2015 S essione 2.1 Station. Likewise, the Avigliano Umbro Station recorded the epicentre to be about 10 km east of the station in June 2013. Two shocks with magnitudes M = 3.1 struck the same area seven days later on April 2, 2014. The seismic swarm migrated to the Colfiorito area on April 15, 2014, with a shock of M = 3.3 and had other smaller seismic events (Bina Observatory, 2014). Clear signals were detected in 2014 at the Perugia Station before many moderate earthquakes in Pietralunga. While the Avigliano Umbro Station detected strong signals a few hours before the two strongest shocks occurring in Massa Martana on March 2014. The day before the moderate shock of M = 3.3 in the Colfiorito area, a signal of -55 dB was recorded at the Perugia Station along the E-W electrode. ELF electric versus magnetic signals and meteorology. From November 2014, a magnetic loop was installed at the Avigliano Umbro Station in order to detect magnetic components of electric perturbations at locations where frequent ELF anomalies had been recorded. In fact, two magnetic loops had already been recording near two other CIEN electrodes in the Chieti and Città di Castello stations; no magnetic signals have been recorded up to now simultaneously at ELF electric perturbations. The magnetic signals have been amplified to be registered using a sound card as well as electric signals. The magnetic field variations have been recorded and analysed in the same way as electric ones and have been reported on spectrograms together. This has been done to render a comparison more legible. For this analysis, no magnetic field variations were recorded during the numerous electric signals recorded at the Avigliano Umbro Station. This behaviour can be explained by the model proposed for the source of the ELF electric perturbations (Fidani and Martinelli, 2015). In this model, rough spherical charge distributions could have formed in the atmosphere by expelled charged gases from the ground. The balancing electrostatic forces, due to air ions of net zero charge and external pressure, could be responsible for spheroidal confined structures which are stable and oscillates (Tennakone, 2011). But such symmetric structures, which oscillate radially, also create very small magnetic fields at a certain distance, due to the symmetry (Heller et al. , 2004). In a perfectly spherical symmetric charge Fig. 1 – CIEN stations in Italy as shown on a google map from the Bina Observatory at http://www.binapg.it/.