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.
#1L. M. Slifkin(UNC: University of North Carolina at Chapel Hill)H-Index: 13
Abstract One possible mechanism for the generation of seismic electric signals is the displacement of segments of charged dislocations, responding to changes in the applied stress. Using information available from the study of simpler ionic crystals, a crude estimate is made of the voltage that could be generated from large blocks of the Earth's crust during a pre-earthquake stress adjustment. Within the many uncertainties of critical parameters, the results are consistent with the magnitudes of...
#1Panayiotis A. Varotsos(UoA: National and Kapodistrian University of Athens)H-Index: 65
#2K. Alexopoulos(UoA: National and Kapodistrian University of Athens)H-Index: 22
Last. M. S. Lazaridou(UoA: National and Kapodistrian University of Athens)H-Index: 20
view all 3 authors...
Varotsos, P. and Lazaridou, M., 1991. Latest aspects of earthquake prediction in Greece based on seismic electric signals, Tectonophysics, 188: 321-347. Since 1983, continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in Greece. The basic physical properties of the transient changes-seismic electric signals (SES)-in the electrotelluric field that are forerunners of earthquakes were first described six years ago. Sin...
Abstract A long distance (200 km) electromagnetic signal occured at Keratea (near Athens), few days prior to the September 13th 1986, Kalamata earthquake. We suggest an explanation based on the fact that long range stress occuring before an earthquake should create local electrical potential gradients in heterogeneous ground at great distances. This could be a general explanation for the origin of electrical telluric signals appearing before an earthquake.
Abstract It is shown that line tension, phonon damping and charge-cloud interactions all contribute to amplitude-independent mechanical damping, while depinning and charge-cloud stretching both contribute to amplitude dependence. A theory is developed for the complete model, specifically recognizing that, following depinning, repinning does not occur later in the stress cycle. The ultrasonic composite oscillator technique is used to measure mechanical damping and phase angle in KCI single crysta...
#1Panayiotis A. Varotsos(UoA: National and Kapodistrian University of Athens)H-Index: 65
#2K. Alexopoulos(UoA: National and Kapodistrian University of Athens)H-Index: 22
Varotsos, P. and Alexopoulos, K., 1984. Physical properties of the variations of the electric field of the earth preceding earthquakes. II. Determination of epicenter and magnitude. Tectonophysics, 110: 99-125. As reported in the preceding paper, a transient change of the electric field of the earth (seismic electric signal), hereafter called SES. appears many hours before an earthquake (EQ). By measuring this change in a given direction and dividing it with a suitable relative effective resisti...
#1Panayiotis A. Varotsos(UoA: National and Kapodistrian University of Athens)H-Index: 65
#2K. Alexopoulos(UoA: National and Kapodistrian University of Athens)H-Index: 22
Abstract In an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field. The present letter clarifies a few points that were not properly emphasized in our previous publications. Furthermore, recent results—like that of the destructive Kalamata earthquake on September 13, 1986—indicate that the duration of a preseismic electric signal may reach considerably high values, lasting up to several hours.
A theory for the strain‐amplitude‐independent damping due to electrically charged dislocations oscillating within their surrounding charge clouds and for the strain‐amplitude‐dependent damping caused by the dislocations ``breaking away'' from their charge clouds is discussed. Damping experiments on single crystals of KCl [〈100〉, 〈111〉, and 〈110〉 orientations] at temperatures of 450° to 760°C, frequencies ranging from 40 to 200 kc/sec, and strain amplitudes from 2.1×10−8 to 1.7×10−4 are reported....
Abstract If the energies required to form positive and negative ion vacancies in an ionic crystal are unequal, then in thermal equilibrium dislocations in the crystal will be electrically charged and surrounded by a Debye-Huckel cloud of vacancies. If the vacancy cloud is immobile a finite force is required to separate the dislocation from the cloud, and so the crystal will possess a yield stress below which plastic flow will not occur. The presence of divalent impurities modifies the magnitude ...
A quantitative theory of damping and modulus changes due to dislocations is developed. It is found that the model used by Koehler of a pinned dislocation loop oscillating under the influence of an applied stress leads to two kinds of loss, one frequency dependent and the other not. The frequency dependent loss is found to have a maximum in the high megacycle range. The second type of loss is a hysteresis loss which proves to be independent of frequency over a wide frequency range which includes ...
We examine the precursory behavior of geoelectric signals before large earthquakes by means of a previously published algorithm including an alarm-based model and binary classification [H.-J. Chen, C.-C. Chen, Nat. Hazards 84, 877 (2016)]. The original method has been improved by removing a time parameter used for coarse-graining of earthquake occurrences, as well as by extending the single-station method into a joint-stations method. Analyzing the filtered geoelectric data with different freque...
Landslides are one of the many catastrophic events which result in massive destruction and loss of lives across the globe. Hence, an appropriate forecasting technique is essential in order to predict such potential weak slip planes which may eventually lead to landslides. Here, we present a study where Fracture Induced Electromagnetic Radiation (FEMR) technique has been used to identify such regions of potential “activity” in a study area around IISER Bhopal Hill, India, stretched along a length...
Last. Yang Tao(North China Institute of Science and Technology)H-Index: 2
view all 5 authors...
Abstract In this paper, the characteristics and mechanism of the surface potential of coal containing gas for different loading modes (uniaxial compression, cyclic and graded loading) are investigated using an experimental surface potential testing system. Coal can produce a surface potential signal during gas adsorption. This signal increases with the adsorption time and exhibits a memory effect; that is, when the adsorbed gas pressure is increased, the surface potential increases. The coal con...
Last. Yue Niu(CUMT: China University of Mining and Technology)H-Index: 7
view all 6 authors...
Coal rock would emit the electromagnetic radiation (EMR) while deformation and fracture, and there exists structural body in the coal rock because of mining and geological structure. In this paper, we conducted an experimental test the EMR characteristics of cracked rock under loading. Results show that crack appears firstly in the prefabricated crack tip then grows stably parallel to the maximum principal stress, and the coal rock buckling failure is caused by the wing crack tension. Besides, t...
Last. Ilias Stavrakas(UWest: University of the West)H-Index: 6
view all 3 authors...
Abstract Pressure Stimulated Currents (PSCs) are emitted while brittle materials of high electrical resistivity are subjected to mechanical loading. The PSCs are related to the generation of cracks and the consequent evolution of cracks’ network in the bulk of the specimen. In the experimental protocol described here cement-mortar beams of rectangular cross-section were subjected to Three-Point Bending (3PB) repetitive loading/unloading loops. The qualitative and quantitative characteristics of ...
Geoelectric precursors are considered to be predictors of earthquakes, but this issue is still under debate. The objective of this research is to statistically test the relationship between the geoelectric system and earthquakes. We observed that anomalies of skewness and kurtosis of geoelectric fields may precede large earthquakes. Next, we developed an alarm model of time of increased probability to quantitatively determine their relationship. Performing binary classification and C1–F1 analysi...
#1Dazhao Song(CUMT: China University of Mining and Technology)H-Index: 6
#2Enyuan Wang(CUMT: China University of Mining and Technology)H-Index: 35
Last. Liming Qiu(CUMT: China University of Mining and Technology)H-Index: 11
view all 5 authors...
To understand the relationship between the frequency of electromagnetic radiation (EMR) emitted from loaded coal rock and the micro-crack structures inside it, and assess the stress state and the stability of coal rock by analyzing frequency changes in characteristics of its emitted EMR, we first experimentally studied the changes in time sequence and the frequency spectrum characteristics of EMR during uniaxial compression, then theoretically derived the relationship between the principal frequ...
This paper presents a new method for assessing the three-point-bending (3PB) strength of mortar beams in a non-destructive manner, based on neural network (NN) models. The models are based on the radial basis function (RBF) architecture and the fuzzy means algorithm is employed for training, in order to boost the prediction accuracy. Data for training the models were collected based on a series of experiments, where the cement mortar beams were subjected to various bending mechanical loads and t...
#1Guang-Jian Liu(CUMT: China University of Mining and Technology)H-Index: 6
#2Cai-Ping Lu(CUMT: China University of Mining and Technology)H-Index: 10
Last. Yang Liu(CUMT: China University of Mining and Technology)H-Index: 8
view all 5 authors...
Electromagnetic radiation (EMR) can reflect the stress state and deformation level of coal, yet its warning indexes correlated with coal properties and roof caving is poorly understood. The laboratory observations of EMR effects of coal samples bursting failure and in situ investigations in the process of roof caving are presented in this paper. EMR peak with increasing stress is discussed when the failure of coal samples happens, which provides an explanation to EMR signals positively correlate...
