Verification of the Load-Unload Response Ratio Theory in the Conditions of Induced Seismicity in the Ostrava-Karvina Coal Basin

摘要

The LURR (load-unload response ratio) theory (Yin et al., 1995) was verified in the Ostrava-Karvina Coal Basin (OKCB) mines. The theory is based on the influence of tidal forces on the rock mass. The rock mass in normal conditions does not show the difference between the seismic activity in the load and unload phases of tidal variations. In the breaking stress conditions, the seismic activity rises much more during the load phase of tidal variations, which leads to the rise of the LURR coefficient value before the main event (Yin et al., 1995). The LURR theory was tested in the areas of coal blocks with a high seismic activity and well-localised foci of seismic events. It was found that the tidal forces influence the seismic activity, but the phase shift varied from coal face to coal face. The phase shift varied in the area of one coal face depending on the height of the seismogenic layer above the mined-out coal seam. Finally it was found that LURR coefficient could not be used in induced seismology in the same manner as in global ― not induced ― seismology because seismic activity depended mainly on the time and intensity of coal excavation, which implied that the LURR coefficient varied according to the shift between excavation and tidal variations cycle. In the conditions of induced seismicity, coefficient b of energy-frequency distribution can be used instead of LURR coefficient. The disadvantage of b coefficient is its variance related to the strength and strain and a high number of events, necessary for its evaluation.