Understanding the fracture phenomena in inhomogeneous rock samples and ionic crystals, by monitoring the electromagnetic emission during their deformation

Abstract

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.