GNGTS 2013 - Atti del 32° Convegno Nazionale

street light but smaller than the Moon. This luminous sphere was a faded white color. This light quickly moved from the west to the east, forming an arc downwards and disappearing behind houses. This event lasted 2 seconds. Furthermore, gas bubbles appeared in the sea around the port of Numana days after the quake. From 2011, the necessity to better understand the sources of some signals has been supported by the idea that a number of different measurements at each CIEN site should be increased. Thus, the Fermo and Torre Pellice Stations have been recently equipped with Geiger counters for atmospheric radioactivity, as well as meteorological stations which record temperature, humidity, wind speed and direction, atmospheric pressure and rainfall. The Fermo Station has also been equipped with an underground thermometer to measure ground temperature and an LF radio receiver at 150 kHz to record amplitude modulation. The Torre Pellice Station had already been equipped with a magnetometer, a Radon meter and a compass to check the direction of the geomagnetic field. Recently, this station has been equipped with an sub-sound detector to investigate for the origin of animal responses to earthquakes (De Liso, 2013). The Perugia Station has been recently equipped with a new electromagnetic sensor, sensitive to electric charges and vertical electric fields. The same station has always measured for meteorological parameters and seismological activity through the “A. Bina” Observatory. ELF observations. An example signal, recorded by the N-S antenna in Avigliano Umbro on July 19, 2013, at about 1:00LT, is shown in Fig. 2 on the left. Its oscillation covers a similar frequency range as those already reported in other publications (Fidani, 2011); between 50 and 100 Hz. Moreover, the duration of the signal was about 7 min, as well, other traces of it appeared hours before and after it. The frequencies of these signals increased at the beginning, but de- creased towards the end. However, no time correspondence was observed between the signals recorded at all of the stations, indicating that they were of local origin. Additionally, their times did not coincide with the earthquake time. Moreover, the signatures almost always appeared on only one antenna of each station and when appearing on both antennas, the two signatures were always different. Strong ELF signals were also record- ed by the Fermo and Perugia Stations during the weeks pri- or to the July 21, 2013, Ancona earthquake. These oscillations had frequencies ranging be- tween 40 and 200 Hz, they also often started and ended at low- er frequencies. Moreover, the durations of the signals ranged from few minutes to several hours. The strongest intensities were recorded on the days be- fore and after the main shock, with amplitudes greater than 1 μV/m. Fig. 1 – The positions of the 11 CIEN stations are indicated by small red circles and the Ancona, July 21, 2013, M w = 5, earthquake epicenter is indicated by a yellow circle. 67 GNGTS 2013 S essione 2.1