Robust analysis for the characterization of the Seismo-Electromagnetic Signals observed in Southern Italy

Gerardo Romano,Anna Eliana Pastoressa,Marianna Balasco,Vincenzo Lapenna,Agata Siniscalchi

doi:10.4401/ag-7811

Abstract

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 on the role of fluids in the earthquake generation and seismic waves propagation. A systematic study on the SES and on the related data analysis techniques is fundamental in order 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 were also recorded in correspondence to earthquakes distant from the MT stations over 800km. In this paper, we present a procedure aimed to improve the SES detectability and to gather the maximum information possible on these signals. The procedure is especially tuned for the analysis of MT time series and it is based on the application of the Continuous Wavelet Transform and frequency filters. As it will be shown, the operational scheme allows to minimize the background variability of the MT signal facilitating the detection and the characterization of SES in terms of amplitude and duration.

Highlights

The occurrence of seismo-electromagnetic signals (SES) associated with the generation and propagation of mechanical perturbation in the subsoil is a matter of fact
The most reliable hypothesis concerning the origin of the coupled seismic and electromagnetic wave propagation is the electrokinetic theory that assumes the existence of an electrochemical double layer along the solidgrain/fluid-electrolyte boundaries of porous media
The first is related to SE signals generated by a regional earthquake and for which a certain ambiguity in the estimation of the arrival time and amplitude is present

Summary

Introduction

The occurrence of seismo-electromagnetic signals (SES) associated with the generation and propagation of mechanical perturbation in the subsoil is a matter of fact. Starting from the pioneering work by Frenkel (1944), in which the author postulated equations that estimated the amount of relative fluid motion induced by a seismic wave, several authors developed physical models to explain the growing number of experimental evidence [i.e. The most reliable hypothesis concerning the origin of the coupled seismic and electromagnetic wave propagation is the electrokinetic theory that assumes the existence of an electrochemical double layer along the solidgrain/fluid-electrolyte boundaries of porous media. Within the double layer the charge is redistributed, creating an excess of electrical charge in the fluid along the boundary. Maxwell’s equations of electrodynamics in fully saturated porous media One of the most complete and rigorous physical and mathematical formulations of the equations controlling such phenomena can be found in Pride [1994], in which Biot’s poro-elastodynamic equations are coupled to ROMANO ET AL.

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Conclusion