GNGTS 2013 - Atti del 32° Convegno Nazionale

A new type of sensor has been recently installed at the Perugia Station, that measures air and rain electricity, along with vertical electric fields. It was activated on the top of the “A. Bina” Observatory at the beginning of April, 2013. It recorded a clear signal from about 30 minutes to 5 minutes before the Ancona shock, then the signal suddenly disappeared, see Fig. 2 on the right. The new sensor recorded an electric oscillation which had probably stated under 10 Hz and increased up to 200 Hz, with a frequency width of about 50 Hz. The electric vibration power intensity reached a signal to noise ratio of about 15-20 dB in the 50-100 Hz range. Disappearing, the signal covered the whole range of 10 - 200 Hz in a few seconds. VLF observations. VLF signals from transmitters (Loudet, 2011) in Novosibirsk, Krasnodar and Khabarovsk, Russia of the Alpha 500 kW radio navigation system, at 11.905 kHz, 12.649 kHz and 14.881 kHz; 400 kW in Rosnay, France at 15.1 kHz and 21.75 kHz; 100 kW in Matotchkinchar, Russia at 18.1 kHz; 400 kW in Anthorn/Skelton, England at 19.6 kHz and 22.1 kHz; 400 kW in Saint-Assise, France at 20.9 kHz; 800 kW in Rhauderfehn, Germany at 23.4 kHz; 1,000 kW in Culter, Maine at 24.0 kHz and 192 kW in Seattle, Washington at 24.6 kHz, were analysed from the Fermo, Chieti and Perugia Stations before and after the shock time, to verify if any signals had had a depletion in their carrier waves. Depletions appeared in the signal from Anthorn transmitter at 19.6 kHz, at Fermo, Perugia and Chieti Stations, occurring hours before and after the recorded time of shock. Especially at Fermo, where the power loss was about 10 dB, see Fig. 3 at the top. The sub-ionospheric channel between Fermo and Anthorn overhang the earthquake epicenter. Natural VLF signals were also monitored at this time. The vertical signatures appearing in the VLF spectrogram represent distant lightning origins, which fill a large band intensity modulate by the ionosphere altitude and diffusion, following the day/night cycle. The intensity of this band is modulated by lightning activity, and its frequencies are also selected by the ionosphere altitude and diffusion. An increased activity was observed in the band intensity hours before the earthquake, showing two maximums, at the Fermo, Chieti and Perugia Stations. However this variation was completely normal following the long time observation of the frequency band. It might have been due to normal ionospheric fluctuations. LF observations. The Fermo, Torre Pellice and Chieti Stations had already been modified to produce LF spectrogram (Fidani, 2011): Fermo and Torre Pellice Stations from 25 kHz to 50 kHz while the Chieti Station from 25 kHz to 100 kHz. Specifically, the Chieti Station receives LF signals from (Loudet, 2011): Bafa, Turkey, 26.7 kHz; Kaliningrad, Russia, 30.3 kHz; Niscemi, Italy, 45.9 kHz; Maraton, Greece, 49.0 kHz; Irkutsk, Russia, 50.0 kHz; Anthorn, England, 60.0 kHz; La Règine, France, 62.6 kHz; Kerlouan, France, 65.8 kHz; Moscow, Russia, 66.6 kHz; Lintong, China, 68.5 kHz; Prangings, Switzerland, 75.0 kHz; Mainflingen, Fig. 2 – The ELF signals recorded at the Avigliano Umbro Station on July 19, 2013, N-S antenna, on the left; the electric signal observed by the new instrument at the Perugia Station a few minutes before the shock. 68 GNGTS 2013 S essione 2.1