Stress induced polarization currents and electromagnetic emission from rocks and ionic crystals, accompanying their deformation

International audienceA crucial question of the scientific community nowadays, concerns the existence of electric signals preceding earthquakes. In order to give a plausible answer to this question, we carried out two kinds of laboratory experiments of uniaxial deformation of ionic crystals and rock samples: a) In the first kind, stress induced polarization currents are detected and recorded. Our experimental results showed not only the existence of stress induced polarization currents before the fracture of the samples, but the possibility of the propagation of these signals, as well, through conductive channels, for distances much longer than the source dimensions. b) In the second, acoustic and electromagnetic signals are detected and recorded in the frequency range from 1KHz to some MHz. The mechanism of generation of these signals is shown to be different for those emitted from piezoelectric and from non-piezoelectric materials. A plausible model is also suggested, on the compatibility of our laboratory results with the processes occurring in the earth during the earthquake preparatory stage

Electrical precursors of earthquakes in Aegean Sea during the last decade (1997?2007)

International audienceThe purpose of this study is to investigate some properties of the Seismic Electric Signals (SES) that preceded large earthquakes which occurred in the Aegean Sea (24?27)° E, (37?40)° N, during the last decade. Our main interest is focused on the important parameter of the lead time ?t, which is the time difference between the occurrence of the earthquake and the detection of the associated SES signal. Two groups of lead times, a short (i.e. ?t~ some weeks) and a long one (?t~ some months) have been observed. We examine whether this difference could be related to the regional tectonics. Furthermore the property of SES selectivity is discussed

Experimental evidence of the compatibility of the cumulative electromagnetic energy release data, with the hierarchical models for the catastrophic fracturing process

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

Transient electric signals prior to rock failure under uniaxial compression

Transient variations of the electric field are detected, prior to the failure of a rock sample which is subjected to uniaxial compression at a variable rate. These precursory electric signals are attributed to the stress induced polarization of the sample and seem to have a form similar to the so called Seismic Electric Signals (SES), which are detected in Greece by the VAN network, prior to earthquakes. The emitted electric signals seem to follow in form the variations of the first time derivative of the externally applied stress. A tentative model for the origin of these signals is also discussed. Copyright 1994 by the American Geophysical Union

Electrical precursors of earthquakes in Aegean Sea during the last decade (1997-2007)

The purpose of this study is to investigate some properties of the Seismic Electric Signals (SES) that preceded large earthquakes which occurred in the Aegean Sea (24-27)° E, (37-40)° N, during the last decade. Our main interest is focused on the important parameter of the lead time Δt, which is the time difference between the occurrence of the earthquake and the detection of the associated SES signal. Two groups of lead times, a short (i.e. Δt∼ some weeks) and a long one (Δt∼t∼ some months) have been observed. We examine whether this difference could be related to the regional tectonics. Furthermore the property of SES selectivity is discussed

Stress induced polarization currents and electromagnetic emission from rocks and ionic crystals, accompanying their deformation

A crucial question of the scientific community nowadays, concerns the existence of electric signals preceding earthquakes. In order to give a plausible answer to this question, we carried out two kinds of laboratory experiments of uniaxial deformation of ionic crystals and rock samples: a) In the first kind, stress induced polarization currents are detected and recorded. Our experimental results showed not only the existence of stress induced polarization currents before the fracture of the samples, but the possibility of the propagation of these signals, as well, through conductive channels, for distances much longer than the source dimensions. b) In the second, acoustic and electromagnetic signals are detected and recorded in the frequency range from 1 KHz to some MHz. The mechanism of generation of these signals is shown to be different for those emitted from piezoelectric and from non-piezoelectric materials. A plausible model is also suggested, on the compatibility of our laboratory results with the processes occuring in the earth during the earthquake preparatory stage. © European Geosciences Union 2004

Electric signals emitted by LiF ionic crystals during their deformation

During the uniaxial compression of LiF crystals, transient polarization electric currents are recorded, with density of the order of some nA/cm2 which are attributed to the movement of segments of charged dislocations relative to their Debye-Huckel cloud, consisting of point defects. On the other hand, during the microfracturing regime of the deformation process, near field electromagnetic disturbances in the frequency band of some KHz to some MHz are detected, which are attributed to the electrical phenomena accompanying the microcrack opening. Furthermore, experiments with γ-irradiated LiF crystals were carried out. A careful consideration of the aforementioned experimental results could support the more plausible interpretation concerning the origin of the electrical phenomena preceding fracture

Memory effects in EM emission during uniaxial deformation of dielectric crystalline materials

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. © 2005 IEEE