Characteristics of dispersion curves for Love channel waves in transversely isotropic media
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Characteristics of dispersion curves for Love channel waves in transversely isotropic media* Ji Guang-Zhong1,2,3, Zhang Ping-Song1,2,3, Guo Li-Quan1,2,3, Yang Si-Tong4, and Ding Ren-Wei4 Abstract: Coal seams have a pronounced bedding structure with developed cracks and exhibit significant anisotropy. However, few studies have examined the frequency dispersion properties of channel waves in anisotropic coal seams. In this study, numerical solutions are calculated using the generalized reflection–transmission coefficient method for the dispersion curves of Love channel waves in vertical transversely isotropic (VTI) and horizontal transversely isotropic (HTI) medium models. Moreover, the frequency dispersion characteristics of Love channel waves in several typical transversely isotropic models are analyzed. We find that the dispersion curves for isotropic and VTI media differ significantly. In addition, the phase and Airy-phase velocities in VTI media are higher than those in isotropic media. Thus, neglecting this difference in practical channel wave detection will result in large detection errors. The dispersion curves for the isotropic and HTI media do not differ significantly, and the Airy-phase velocities of various modes are similar. The group-velocity curve for a coal seam model containing a dirt band is found to be extremely irregular. The fundamental-mode Airy phase is not pronounced, but the first-mode Airy phase can be clearly observed. Hence, first-mode channel waves are suitable for detecting dirt bands. Keywords: Coal seam, transverse isotropy, Love channel wave, dispersion curve, generalized reflection–transmission coefficient
Introduction Small faults and collapsed columns in coal seams can easily cause safety hazards, such as roof collapses and water and gas bursts, which are detrimental to safe mining operations (Yin et al., 2016). In this respect,
channel wave exploration methods (Dresen and Rüter, 1994; Liu et al., 1994) are highly effective in structure detection. Primary structure coals have a pronounced bedding structure and exhibit strong transverse isotropy (TI), whereas tectonic coals contain developed cracks (Chen et al., 2010) and exhibit strong anisotropy (Dong, 2008).
*Manuscript received by the Editor August 20, 2018; revised manuscript received December 27, 2019. 1.State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines, Anhui University of Science and Technology, Huainan 232001, China 2.Key Laboratory of Mine Geological Disaster Prevention and Environment Protection of Anhui Higher Education Institutes, Anhui University of Science and Technology, Huainan 232001, China 3.School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China 4.College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China ♦Corresponding author: Zhang Ping-Song (E-mail: [email protected]) © 2020 Chinese Geophysical Society. All rights reserved.
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Characteristics of dispersion curves for Love cha
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