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In this paper, we performed experiments of uniaxial compression of granite samples and recorded time series of electromagnetic pulses during the evolution of the catastrophic fracturing process. The cumulative energy release of the electromagnetic emission (EME) up to the critical point at the moment of rupture was then calculated. It was shown, that the validity of the proposed hierarchy models for the catastrophic fracturing process of composite materials, in analogy to critical phenomena, can be experimentally established not only via acoustic emission data, but via electromagnetic emission data as well. The above conclusion could be a useful tool for the improvement of the earthquake prediction method, based on precursory electromagnetic signals. [ABSTRACT FROM AUTHOR] more...

The electromagnetic (EM) activity observed before earthquakes has received a lot of attention of the scientific community. Various aspects have been proposed in order to interpret these observed EM phenomena, and the most plausible interpretation is based on the microfracturing electrification. The scope of this paper is the laboratory investigation of this aspect by carrying out laboratory experiments for the detection of EM emission from rock samples and other crystalline materials under uniaxial compression. This paper reveals physical processes that occur in the compressed material, in the microscopic scale, resulting in the observed macroscopic EM phenomena. It was experimentally verified that (a) an abrupt microcracking event generates temporally varying EM field, not only in piezoelectric materials but in non-piezoelectric ionic crystals as well. This implies that the EM generation mechanism is not necessarily of piezoelectric origin. (b) In the presence of a large number of microfractures, each one of them essentially acts as an elementary emission source and thus the resulting spectrum is correlated to the spectral content of each individual pulse and (c) the microcracking process might display criticality. [Copyright &y& Elsevier] more...

It is known that during uniaxial compression of dielectric crystalline materials, acoustic and electromagnetic (EM) emission is detected. Such emissions are of particular interest, since they are related to the physical processes taking place during the preparation stage of an earthquake. In this letter, we report recent experimental results on the memory effects observed in the EM emission during successive cyclic mechanical loading-unloading of LiF crystal samples in a similar fashion, as it has been described by the so-called "Kaiser effect," i.e., the memory effect for the acoustic emission, and we discuss on a conceptual explanation. [ABSTRACT FROM PUBLISHER] more...