Microseismic investigation of mining-induced brittle fault activation in a Chinese coal mine

The process whereby a brittle fault was activated by mining is not only significant for disaster prediction, but also for earthquake prediction. Thus, it was necessary to study their activation process. In this study, stress state, AE (acoustic emission)/MS (microseismic) activities during brittle fault activation, stages of brittle fault activation, and the relation between AE/MS activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults, determine their parameters and activation process based on MS monitoring. The No. 22517 working face in the Dongjiahe Coalmine was taken as an example. Firstly, a buried brittle fault was identified in No. 22517 working face by the MS monitoring method. Secondly, the buried brittle fault parameters were determined. Its azimuth angle was 307.5° in the orbital roadway and 357.5° on the haulage roadway. Its dip angle was 73° and it was a reverse fault. Thirdly, the activation process of the buried brittle fault was determined. The buried brittle fault was not affected by the mining activities when the distance (from mining activities to the buried brittle fault) was over 300 m, the ‘disturbance stage’ was from 300 m to 80 m, and the ‘local activation stage’ from 100 m to 30 m, and the ‘whole activation stage’ around 30 m. The b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage; it was concluded that these changes are related to the stress distribution around the brittle fault. The results demonstrated that MS monitoring technology can detect small buried brittle faults ahead of the working face, and is also an effective method to study the process and mechanism of brittle fault activation.