GNGTS 2022 - Atti del 40° Convegno Nazionale

526 GNGTS 2022 Sessione 3.3 DEFINING THE BEST PROCESSING PROCEDURE FOR THE EVALUATION OF SEISMO-ELECTROMAGNETIC SIGNALS (SES) MEASURED DURING AN ACTIVE SEISMIC EXPERIMENT I. Ventola 1 , G. Romano 1 , A. Siniscalchi 1 , M. Balasco 2 , S. Tripaldi 1 1 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari Aldo Moro, Italy 2 CNR - Istituto di Metodologie per l’Analisi Ambientale, Potenza, Italy Seismic-electromagnetic signals (SES) consist of transient electromagnetic signals that originate in response to a mechanical perturbation in the subsoil (Gao and Hu, 2010). Several mechanisms have been proposed in order to explain the phenomenology (e.g. Thompson and Gist, 1993; Pride, 1994; Haarsten and Pride, 1996; Honkura et al., 2004; Gao and Hu, 2010). In all cases it is attributed to the interaction between elastic waves and porous media containing fluids, which play a key-role in the generation of these signals and influence their features. The study of SES could thus be a useful tool for characterizing the subsoil and, in a broader scenario, could provide clues about the role of fluids in the generation of earthquakes (Romano et al. , 2018). In the literature referring to the last two decades, studies reporting the observation of such signals in association with seismic phenomena are increasingly frequent (e.g. Matsushima et al. , 2002; Zlotnicki et al. , 2006; Johnston et al. , 2006, Balasco et al. , 2014, Balasco et al. , 2015). However, there are no ad-hoc instruments for their detection, and they are generally recorded accidentally during surveys using magnetotelluric (e.g. Balasco et al. , 2014), a geophysical method that acquires natural electromagnetic fields to characterize the subsoil in terms of electrical properties. In this case, the generated transients are added to the signal due to the natural electromagnetic field which varies over time. When this last is particularly intense, it is difficult to recognize these contributions generated by the passage of seismic waves. In this study we present the results arising out of the analysis of seismic-electromagnetic signals recorded during an active seismic experiment carried out in the Solfatara crater (Campi Flegrei, Southern Italy). We analyzed data collected during the RICEN (Repeated InduCed Earthquakes and Noise) campaign where were performed a two-dimensional active seismic profile with NNE-SSW direction and a three-dimensional active seismic experiment on a dense regular grid of 90 m × 115 m (Serra et al. , 2016). The vibroseis truck was the seismic source and the electromagnetic field was acquired by placing three magnetotelluric stations close to the experiments mentioned above. With the aim of extracting as much information as possible from SES has been necessary to isolate them, minimizing the background variability of the MT signal as well as removing the effects of the seismic source. First, we applied a frequency deconvolution to remove the instrumental response; then we evaluated the spectra of the natural electromagnetic field comparing the signals of two different stations. In the absence of SES, these spectra were similar, permitting the subtraction in the frequency domain. The correspondent signal in time was then analyzed with typical seismic approaches like vibroseis deconvolution (Brittle et al. , 2001). Finally, for each shot the Green’s function was estimated. References Balasco, M., Lapenna, V., Romano, G., Siniscalchi, A., Stabile, T., & Telesca, L. (2014). Electric and magnetic field changes observed during a seismic swarm in Pollino area (southern Italy). Bull. Seismol. Soc. Am., 104 , 1289- 1298. Balasco, M., Lapenna, V., Romano, G., Siniscalchi, A., Stabile, T., & Telesca, L. (2015). The Pollino 429 2011-2012 seismic swarm (southern Italy): first results of the ML=3.6 aftershock recorded by co- 430 located electromagnetic and seismic stations. Bolletino di Geofisica Teorica e Applicata Vol. 56, n.2 , 203-2010.