Are There Pre-Seismic Electromagnetic Precursors? A Multidisciplinary Approach

Abstract

11www.intechopen.com 2 Will-be-set-by-IN-TECH spectrum ranging from kHz to MHz are produced by opening cracks, which can be considered as the so-called precursors of general fracture. The radiated EM precursors are detectable both at a laboratory [8][9][10][11][12][13][14][15][16] and geological scale .Data collection: Since 1994, a station has been installed and operated at a mountainous site of Zante island (37.76 o N − 20.76 o E) in the Ionian Sea (western Greece). The main aim of this station is the detection of kHz-MHz EM precursors. Six loop antennas detect the three components (EW, NS, and vertical) of the variations of the magnetic field at 3 kHz and 10 kHz respectively; three vertical λ/2 electric dipoles detect the electric field variations at 41, 54 MHz, and 135 MHz respectively. These frequencies were selected in order to minimize the effects of the sources of man-made noise in the mountain area of the Zante Island. Moreover, two Short Thin Wire Antennas, oriented at EW and NS directions of length of 100 m, respectively, have been also installed. The aim of the last installation is the detection of ultra-low-frequency (< 1Hz) EM precursors rooted in a preseismic lithosphere-atmosphere-ionosphere-coupling. All the EM time series were sampled at 1 Hz. Such an experimental setup helps to specify not only whether or not a single EM anomaly is preseismic in itself, but also whether a sequence of EM disturbances at different frequencies, which are emerged one after the other in a short time period, could be characterized as preseismic one. Clear such EM precursors have been detected over periods ranging from approximately a week to a few hours prior to catastrophic EQs that occurred in Greece or Italy (e.g., [21,22,[25][26][27][28][29][30][31][32][33][34][35][36][37]). We emphasize that the detected precursors were associated with EQs: (i) occurred in land (or near coast-line); (ii) were strong, i.e., with magnitude 6 or larger; and (iii) were shallow. Recent results indicate that the recorded EM precursors contain information characteristic of an ensuing seismic event (e.g., [21,22,[25][26][27][28][29][30][31][32][33][34][35][36][37]).An important feature, observed both at laboratory and geophysical scale, is that it the MHz radiation precedes the kHz one [25,[27][28][29]35,36]. Studies on the small (laboratory) scale reveal that the kHz EM emission is launched in the tail of pre-fracture EM emission from 97% up to 100% of the corresponding failure strength [25 and references therein]. At the geophysical scale the kHz EM precursors are emerged from a few days up to a few hours before the EQ occurrence. The association of MHz, kHz EM precursors with the last stages of EQ generation is justified.The origin of EM emissions. The origin of EM emissions from fracture is not completely clear, and different attempts have been made in order to explain it [8, 32 and references therein]. A relevant attempt is related to the "capacitor model" [32]. In many materials, emission of photons, electrons, ions and neutral p...

Statistical Mechanics and Information-Theoretic Perspectives on Complexity in the Earth System

“…These findings led to the hypothesis that any EM emissions related to EQ preparation should present specific characteristics, like fractal scaling, criticality, phase transition characteristics, symmetry breaking, frequency-size laws, universal structural patterns of fracture and faulting, complexity characteristics, long-range correlations, memory, etc., depending on the phase of the EQ preparation process to which they are related. A number of analyses in field-recorded preseismic EM signals have verified this hypothesis (e.g., [18,[136][137][138]148,[153][154][155][156][157][158][159] and references therein).…”

On the puzzling feature of the silence of precursory electromagnetic emissions

“…This feature permits the real-time, step-by-step monitoring of the damage evolution of the heterogeneous component in the focal area during mechanical loading. Indeed, our analysis reveals the following consecutive rupture process epochs as the EQ approaches (Contoyiannis et al, 2005;Eftaxias, 2012):…”

“…More precisely, we have introduced the following two-stage model ( Fig. 1) (Kapiris et al, 2004;Contoyiannis et al, 2005;Contoyiannis and Eftaxias, 2008;Papadimitriou et al, 2008;Eftaxias et al, 2007Eftaxias et al, , 2010Eftaxias, 2012, and references therein):…”

“…This is a question debated in the science community (Eftaxias, 2012). Despite fairly abundant evidence, EM precursors have not been adequately accepted as real physical quantities (Morgounov and Shakhraman'yan, 1996;Uyeda et al, 2009;Hayakawa and Hobara, 2010).…”

“…Recently, improvements in the MHz-kHz EME technique have permitted a real-time monitoring of the fracture process (Fukui et al, 2005;Kumar and Misra, 2007;Chauhan and Ashok Misra, 2008;Baddari et al, 1999Baddari et al, , 2011Baddari and Frolov, 2010;Lacidogna et al, 2010;Schiavi et al, 2011;Carpinteri et al, 2012). However, the MHz-kHz electromagnetic (EM) precursors are detectable not only at the laboratory but also at the geological scale; a stressed rock behaves like a stress-EM transducer (Sadovski, 1982;Hayakawa and Fujinawa, 1994;Gokhberg et al, 1995;Hayakawa, 1999Hayakawa, , 2009Hayakawa and Molchanov, 2002;Eftaxias et al, 2007Eftaxias et al, , 2011Eftaxias, 2012;Molchanov and Hayakawa, 2008). The idea that the fracture-induced MHz-kHz EM fields should also permit the monitoring of the gradual damage of stressed materials in the Earth's crust, as happens in the laboratory experiments, in real time and step by step, seems to be justified: the aspect of self-affine nature of faulting and fracture is well documented.…”