Abstract
The evolution characteristics of high-energy and low-energy microfracture events play an important role in the brittle failure mechanism of rock and reasonable microseismic (MS) monitoring and acoustic emission (AE) monitoring. The bimodal distribution (BMD) model is commonly used to observe the evolution characteristics of high-energy and low-energy MS events; however, its precise mechanism remains unclear. The evolution characteristics of high-energy and low-energy microfracture events are assessed in this study based on a BMD model. MS monitoring results from the No. 22517 working face of the Dongjiahe Coal Mine are studied, and AE monitoring results of a biaxial compression experiment of a granite specimen are analyzed. High-energy MS events in the No. 22517 working face are found to be generated by an increase in the failure scale of the overlying rock mass upon exiting the insufficient mining stage and entering the sufficient mining stage. The change characteristics of the high-energy AE hits are positively correlated with crack evolution characteristics in the granite specimen and negatively correlated with changes in the Gutenberg-Richter b value. A precise high-energy and low-energy AE hit evolution mechanism is analyzed based on the microscopic structure of the granite specimen. Similarities and differences between high-energy MS events and low-energy AE hits are determined based on these results. Both are found to have bimodal characteristics; an increase in the failure scale is identified as the root cause of the high-energy component. The bimodal distribution of AE hits is far less obvious than that of MS events.
Highlights
In a study on the recurrence of large seismic events in Polish mines, Gibowicz and Kijko [1] found that the pattern of empirical distributions of the largest seismic events is more complex than expected based on the most general theoretical considerations (e.g., Gumbel distributions) [2]
Washington, in May 1980 obeyed the bimodal distribution (BMD) as confirmed by the distribution of characteristic periods in the maximum amplitude signals and by the frequency-magnitude relations [3]. Another striking example of BMD was found in New Madrid, Missouri, and interpreted as a result of the superposition of two distinct seismogenic source types observed in the area [4]
Li et al [18] showed that when the stress increases to 78.2% of the peak loading value, critical cracks initiate in the tensile stress concentration zones under uniaxial loading conditions; similar results were reached by Zhong et al [41]
Summary
In a study on the recurrence of large seismic events in Polish mines, Gibowicz and Kijko [1] found that the pattern of empirical distributions of the largest seismic events is more complex than expected based on the most general theoretical considerations (e.g., Gumbel distributions) [2]. The observed distributions possess bimodal distribution (BMD) characteristics, as shown in Figure 1 BMD has been observed in the underground coal mines of Upper Silesia, Poland, at the Doubrava coal mine of the Ostrava-Karvina Coal Field, Czechoslovakia, and in the copper ore mines of Lubin Copper Basin, Poland [1]. The seismicity associated with the eruption of Mount St. Helens, Washington, in May 1980 obeyed the BMD as confirmed by the distribution of characteristic periods in the maximum amplitude signals and by the frequency-magnitude relations [3]. Washington, in May 1980 obeyed the BMD as confirmed by the distribution of characteristic periods in the maximum amplitude signals and by the frequency-magnitude relations [3] Another striking example of BMD was found in New Madrid, Missouri, and interpreted as a result of the superposition of two distinct seismogenic source types observed in the area [4].
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