Abstract
AbstractClear VLF electromagnetic (EM) anomalies were detected prior to the Athens earthquake (EQ). We attempt to establish the hypothesis that these emissions were launched from the pre-focal area during micro-fracturing process. The spectral analysis in terms of fractal dynamics reveals that distinquished alterations in the associated scaling parameters emerge as the EQ is approached. These alterations suggests that the evolution of the Earth’s crust towards the “critical point” takes place not only in the seismological sense but also in the pre-fracture EM sense. VAN-signals and space-time TIR-signals were also detected prior to the Athens EQ. These anomalies, as well as the fault modeling of the Athens EQ obtained by interferometric combinations of ERS2 SAR images bring further support for the confidence in the reliability of our conclusions.
Highlights
An outstanding problem in material science and in geophysics is to undrestand, and more importantly to predict, macroscopic defects or shocks
Our main tool is the monitoring of the microfractures, which occur before the final break-up in the prefocal area, by recording their very low frequencies (VLF)-very high frequencies (VHF) EM emissions
Aiming at recording VLF-VHF EM precursors, since 1994 a station was installed at a mountainous site of Zante island (37.76◦N–20.76◦E) in western Greece (Fig. 1) with the following configuration: (i) six loop antennas detecting the three components (EW, NS, and vertical) of the variations of the magnetic field at 3 kHz and 10 kHz respectively; and (ii) three vertical λ/2 electric dipoles detecting the strength of the electric field at 41 MHz, 54 MHz, and 135 MHz respectively
Summary
An outstanding problem in material science and in geophysics is to undrestand, and more importantly to predict, macroscopic defects or shocks. When a heterogeneous material is strained, its evolution toward breaking is characterized by the nucleation and coalescence of micro-cracks before the global instability Both acoustic as well as EM emissions, in a wide frequency spectrum ranging from very low frequencies (VLF) to very high frequencies (VHF), are produced by micro-cracks, which can be considered as the so-called precursors of general fracture. IC bridges both the hypothesis of an underlying self-organized complexity and the occurrence of precursory phenomena (e.g. Huang et al, 1998; Grasso and Sornette, 1998; Hainzl et al, 2000; Newman and Turcotte, 2002; Al-Kindy and Main, 2003) It is a further purpose of this paper to investigate the suggestion that the precursory seismic activity and the pre-fracture EM activity may reveal the “critical” rearrangements that occur as the external field drives the heterogeneous pre-focal area from one meta-stable local free-energy minimum to another towards the global instability
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