GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.1 291 stations while the lower parts of LF radio waves were sampled at 8/15 CIEN stations. The Fermo Station was able to sample radio broadcast up to 50 kHz but the only radio transmitter which sub-ionospheric channel goes near the Amatrice epicentre was Niscemi, Sicily, at about 45 kHz. The variations in wave amplitude for the Niscemi transmitter are reported in Fig. 3 bottom, from about two weeks before the main shock in Amatrice. This type of monitoring was recently made uninfluenced from meteorological activity by a special algorithm running at the Fermo and Perugia Stations before being used in all the other stations. Two weeks of data preceding the Amatrice earthquake, (Fig. 2) bottom, evidenced a strong amplitude depletion on the night between August 21 and 22, 2016, and a minor amplitude depletion on the night between August 14 and 15, 2016. Moreover, perturbed amplitudes appeared between August 17 and 19, 2016. A model has been proposed to explain ELF signatures (Fidani and Martinelli, 2015). This model is made up of a rough spherical charge distributions which could have formed into 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 have been responsible for spheroidal confined structures which were stable and oscillating. At the same time, such symmetric structures, which oscillate radially, also create no electric fields beyond a certain distance and infinitely small magnetic fields out of the structures, due to the symmetry (Fidani, 2015). Furthermore, regarding high charge concentrations, corona discharges in the space between the separated charges can render the object luminous, therefore explaining the occurrence of spheroidal earthquake lights. A statistical correlation between ELF signals and earthquakes was calculated. Finally, a probability of earthquake occurrence based upon ELF activity was estimated including a reliability parameter (Fidani, 2015). The meteorological processes can generate spurius anomalies that create a noise factor. This factor can be quantified by the reliability parameter, which is defined by the ratio: genuine anomaly numbers / the total Fig. 2 – Vertical conductivity variations, fifth power distribution harmonic and Niscemi radio wave recorded at the Fermo Station after August 10, 2016.