Abstract
A network of low frequency electromagnetic detectors has been operating in Central Italy for more than three years, consisting of identical instruments that continuously record the electrical components of the electromagnetic field, ranging from a few Hz to tens of kHz. These signals are analyzed in real time and their power spectrum contents and time/frequency data are available online. To date, specific interest has been devoted to searching for any possible electromagnetic features which correlate with seismic activity in the same region. In this study, spectral analysis has evidenced very distinct power spectrum signatures that increased in intensity when strong seismic activity occurred near the stations of the 2009 L'Aquila earthquake. These signatures have revealed horizontally oriented electric fields, between 20 Hz to 400 Hz, lasting from several minutes to up to two hours. Their power intensities have been found to be about 1 μV/m. Moreover, a large number of man-made signals and meteorologic electric perturbations were recorded. Anthropogenic signatures have come from power line disturbances at 50 Hz and higher harmonics up to several kHz, while radio transmissions have influenced the higher kHz spectrum. Reception from low frequency transmitters is also provided in relation to seismic activity. Meteorologic signatures cover the lower frequency band through phenomena such as spherics, Schumann resonances and rain electrical perturbations. All of these phenomena are useful teaching tools for introducing students to this invisible electromagnetic world.
Highlights
Instrumental studies of earthquake electric phenomena began in the 1800s in Italy [1,2]
Many inventors ceased to proceed because their studies were founded on the recently rooted and not yet fully applied Electromagnetic (EM) theory, which contrasted with the nascent science of seismology founded on the existing inertial theory [9]
Carrier waves of LF transmitters are indicated by white arrows and the power spectrum intensity scale is shown on the bottom left; (b) The set of monitored sub-ionospheric channels, Very Low Frequency (VLF) in yellow and LF in red, from the Chieti Station with the transmitters are depicted on a Google Map [31]
Summary
Instrumental studies of earthquake electric phenomena began in the 1800s in Italy [1,2]. Given that recent magnetic recordings have not provided definitive confirmation of an earthquake link, the CIEN has chosen to record the EM field via its electric component. A particular and intense type of signal was recorded on the occasion of the 2009 L'Aquila earthquake; the strongest quake in Italy since CIEN began operating. This signal is analyzed to illustrate the CIEN capacity. Because a single sensor is capable of detecting electric fields at several frequency bands, different types of electromagnetic perturbations observed with earthquakes [23] must be considered in this paper. Is devoted to summarizing, even if not statistically significant yet, the characteristics of the recorded signals and natural or anthropogenic phenomena
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