Passive Seismic Tomography as a Tool of Rock Burst Hazard Prognosis in Copper Ore Mine in Poland

Abstract

In Poland, underground mines of copper ores, which belong to KGHM Polish Copper JSC, have been struggling with seismic dynamic events such as tremors and rock bursts since almost the first years of exploitation i.e. the 70s of the twentieth century. Mining activities infringe the original stress balance and make the rock mass accumulate energy and then release it, which triggers seismic hazard even far away from a tremor epicentre. Therefore, prediction of the position, time and energy of tremors plays a significant role in mining operation especially in work safety. For this purpose, many observation methods including seismology, seismic, geotechnical-geological monitoring, are used; unfortunately, most of them help describe the state of the rock mass after but not prior to the occurrence of the seismic phenomena. Only passive seismic tomography is promising since it can be used to forecast, to some extent, the location of places of seismic energy excessive accumulation. In this method, on the basis of seismic events recorded in a given period, zones of high and low seismic wave velocity are determined (calculated), which in the near future may pose areas of increased seismic activity. The phenomenon of the increase of seismic longitudinal wave velocity with the increase of stress in rocks makes the ground of tomography calculations. The prime purpose of the paper is to assess passive seismic tomography as a means for forecasting and evaluation of seismic and rock burst hazard. To accomplish this, the analysis of seismic activity and archival seismic tomography results (seismic wave velocity zones and seismic anomaly zones) with reference to seismic phenomena, their energy, number and location were carried out. On the basis of obtained the results, the effectiveness of seismic hazard forecast with the use of passive seismic tomography was assessed. The research was carried out for one mining division of the Polkowice-Sieroszowice mine and covered ten years. This division was selected due to its high seismic activity and the permanent use of the passive seismic tomography to assess the seismic risk. Linear correlation and determination coefficients between seismic activity characteristics and seismic anomaly as well as longitudinal wave velocity were calculated. It was found that in the study area the effectiveness of passive seismic tomography in forecasting the seismic hazard is relatively satisfying since about half of the tremors were located within zones of high seismic activity (substantial velocity of P-waves and seismic positive anomalies)..