Robust analysis for the characterization of the seismo-electromagnetic signals observed in southern Italy

Seismo‐electromagnetic signals (SES) are anomalous electromagnetic signals generated as a response to the propagation of a mechanical perturbation within the subsoil. Fluid presence plays a key role in determining SES generation and characteristics, therefore SES study could be useful for subsoil characterization. In a more general framework, it can give insight about the role of fluids in the earthquake generation and seismic wave propagation. A systematic study on SES and the related data analysis techniques is fundamental to define the characteristics of these signals which are superimposed to the natural electromagnetic field induced by the external variable magnetic field. To this aim, the Pollino seismic swarm was a great opportunity because continuous MagnetoTelluric (MT) data were recorded in a period in which numerous seismic events of various magnitudes occurred. During the observational period, SES have also been recorded in correspondence to earthquakes far from the MT stations over 800km. In this paper, we present a procedure aimed to improve the SES detectability and gather as much information as possible on these signals. The procedure is especially tuned for the analysis of MT time series and is based on the application of the Continuous Wavelet Transform (CWT) and frequency filters. As will be shown, the operational scheme allows minimizing the background variability of the MT signal facilitating SES detection and the characterization in terms of amplitude and duration.