Seismic hazard estimate based on the extracted deposit volume and bimodal character of seismic activity

Main assumptions of the stochastic model of seismic activity in the rockmass, leading to bimodal distribution of shocks, are discussed. An analysis of energy-frequency distribution of shocks from longwall No. 4 3765 in the mine Doubrava in the Ostrava-Karviná Coal Field showed that the bimodal model fits observations very well. The results of the analysis indicate that shocks with energies exceeding 10 6 J ihave their origin in a greater area than the region directly associated with mining works. The results of the study of bimodal distribution were taken into account in equations for the relationship between seismic energy and the extracted deposit amount. With the obtained equations, we calculated the seismic hazard of the longwali in the period under study. The majority of shocks with energy greater than 5 · 10 6 J and the accompanying roekbursts were preceded by high (P > 0.7) probability for the occurrence of energy greater than 10 6 J. A high accumulation of energy for as long as a few months was observed as well.