Cross-Correlations Between Moderate Earthquakes and ELF Electric Oscillations Detected by the CIEN Station of Avigliano Umbro, Terni, Italy

Abstract

(1) Background: The issue of providing evidence for some electromagnetic phenomena occurring with strong earthquakes has not yet received a conclusive response. Here, long-term continuous monitoring of electromagnetic signals detected by the Central Italy Electromagnetic Network in the atmosphere was reported, and data from the Avigliano Umbro station from the beginning of October 2013 to early January 2015 were analysed. (2) Methods: Spectrogram recordings of extremely low-frequency electric fluctuations were analysed for frequency-time well-defined structures. Electrical oscillations with intensities exceeding a threshold were extracted and compared with moderate earthquakes using Pearson correlations. (3) Results: The cross-correlation between the electric activity of non-meteorological origin and the seismic activity observed within 70 km around the station during the same period was calculated. A correlation peak at +7 days emerged, suggesting that the electric phenomenon occurs mainly 7 days before earthquakes, which has a probability < 1% of being due to chance. (4) Conclusions: The electric oscillation phenomenon is concluded to have a relationship with moderate seismic activity. They show moderate predictive skill. A possible interpretation relates to fluids escaping from the ground. These results are useful for risk mitigation by enabling the computation of the conditional occurrence probability of a seismic event.