K. Eftaxias, S. M. Potirakis
Fracture-induced electromagnetic emissions (EME) in a wide frequency range are sensitive to the micro-structural chances. Thus, their study constitutes a nondestructive monitoring method of the evolution of damage process at the laboratory scale. A field experimental network has been installed using the same instrumentation as in laboratory experiments for the recording of the fracture-induced EME during the earthquake (EQ) preparation process. The expectation was that experiments by means of EME at the large, geophysical, scale would probably reveal features of the last stages of failure process not clearly observable at the small, laboratory, scale, allowing thus the monitoring in real-time and step-by-step of the EQ generation. The obtained results indicate that the recorded EM precursors at the geophysical scale contain richer information for the last stages of an ensuing fracture / seismic event in comparison to the laboratory ones. A shift in thinking towards the basic science findings relative to plastic flow, phase transitions and self-affinity notion of fracture process, as these have been accumulated by recent high quality laboratory studies, theoretical model and numerical simulations is proposed. Strict criteria have been established for the definition of an emerged EM anomaly as a preseismic one. The proposed three stages model of EQ generation by means of the EM precursors is strongly supported by recent laboratory and numerical studies of granular packings, micron-scale plastic flow, and concepts drawn from phase transitions, interface depinning, fracture size effects, self-affine notion of fracture and faulting process, and universal features of fracture surfaces. Precursory EM features, considered as paradoxes, are explained. The claim that the observed EM precursors may permit a real-time and step-by-step monitoring of the EQ generation is tested.
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http://arxiv.org/abs/1301.1045
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