Abstract
Acoustic emission (AE) signals were obtained during deformation by uniaxial compression of specimens of various geomaterials. Experiments on uniaxial compression were carried out on a low-noise lever setup with water leakage, where the maximum load on the sample does not exceed 250 kN. The received signals were digitized by an 8-channel USB 3000 ADC unit with a width of 14 bits and a maximum sampling rate of 3 MHz. The energy distribution functions of AE signals are considered. The maximum amplitude of the AE waveform was selected as the energy characteristic of the AE signal. The flow of AE events is considered from the viewpoint of nonequilibrium thermodynamics using the Tsallis statistics. To describe the energy distribution function of the AE signals, we used a modified model of a stick-slip earthquake source -”discontinuous sliding” of two plates over each other along a fault in the presence of friction and the principle of maximum entropy. The model is used to quantify long-range correlations arising in the flow of earthquakes. It is shown that the AE signal flow is a system with memory and longrange correlations. The analysis of the behavior of the Tsallis parameter was carried out throughout the experiment.
Highlights
The similarity of the processes occurring in geological structures in the Crust, and deformation that in the rocks tested in laboratory experiments [1 - 6], creates a prerequisite to study the deep geostraing processes using the method of physical modeling on rocks specimens
For rejection of Acoustic emission (AE) signals, the algorithm [45] was implemented, consisting of two stages: 1selection of a useful signal in the amplitude-frequency spectrum in the operating range of the sensor according to its calibration curve; 2- analysis of the amplitude-frequency spectrum of signals, in which the ratios of the sums of the amplitudefrequency spectrum were calculated in the range from the lower limit of sensor sensitivity (200 kHz) to the Nyquist frequency, based on the ADC sampling limit (1.5 MHz) to the sum of amplitudes in the spectrum of the entire signal.In the array of AE signal waveforms formed in this way, the maximum amplitude of the AE waveform was selected as the energy characteristic, and a catalog of AE events was formed
The calculated values of the Tsallis parameters q and a, the errors in determining these values, and the number of AE signals for different experimental sessions are given in the table
Summary
The similarity of the processes occurring in geological structures in the Crust, and deformation that in the rocks tested in laboratory experiments [1 - 6], creates a prerequisite to study the deep geostraing processes using the method of physical modeling on rocks specimens. The revealed patterns in the signal sequence, reflecting and accompanying changes in the state of the material during fracturing, are transferred to the full-scale geophysical (seismological) scale The adequacy of this schematically presented approach was confirmed already by the results of the first works [17 - 19], devoted to the destruction of homogeneous or inhomogeneous materials under uniaxial compression. Subsequent studies of acoustic emission, carried out with the use of more advanced technical means for recording AE, again demonstrated the possibility of obtaining results adequate to the conditions in seismogenic zones [20 - 23] Taking this into account, it is quite natural to use continuous AE measurements when studying the process of rock cracking, which is caused by uniaxial mechanical compression, and by the additional effect of model sources of vibrations and electromagnetic fields
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