Seismic Hazard Prediction Using Passive Seismic Tomography in Polkowice-Sieroszowice Copper Ore Mine, SW Poland

Abstract

Rock bursts pose the prime threat in underground copper ore mines in Poland. The rock mass, whose initial mechanical balance is disturbed by exploitation works, accumulates energy and then releases it rapidly. As a consequence, spontaneous seismic events are induced, which are hazardous. Therefore, the forecasting of seismic hazard is crucial for work safety. Many methods are used to assess this threat. Unfortunately, they can describe only the situation after seismic events. Passive seismic tomography allows to predict, to some extent, the location of energy accumulation. On the basis of seismic events occurring in a given period, it is possible to determine zones, which during the future mining, may comprise increased seismic activity. It has been found that hypocenters of strong shocks are most often associated with high velocity of P wave. However, in low seismicity zones, low velocity is observed. The aim of the study is to determine the effectiveness of the passive seismic tomography in the prediction of seismic hazard. The results of the tomography were analyzed in relation to the energy, number and location of seismic events which occurred several months after tomographic calculations. The key term here is the prediction, which is understood as the forecast of the place, time and strength of a seismic event. The accuracy of predicting the stress distribution by means of the seismic wave velocity and seismic anomalies was assessed. The increase in seismic wave velocity means the increase in the strain of rock mass and seismic hazard. The calculated distribution of the P wave velocity allows one to identify seismic hazard zones and monitor their changes. The effectiveness of seismic hazard forecasting was assessed for one mine division of the Polkowice–Sieroszowice mine in 10 years and the relationship between seismic activity and seismic anomaly as well as P wave velocity was determined.