Source Parameters and Source Mechanism of Seismic Events Occurring in Sequencesat a Polish Copper Mine and South African Gold Mine: Search for Possible Time Variations

摘要

This report results from a contract tasking Polish Academy of Sciences asfollows: Investigate the swarm-like behavior of seismic events from Polish and South African mines. The investigation conducted under this contract is focused on a search for possible time variations of source parameters and mechanism of seismic events occurring in sequences at Polkowice copper mine in Poland and Western Deep Levels (WDL) gold mine in South Africa. The results of this study are described for WDL in Part I and for Polkowice mine in Part II of this report. A swarm-like seismic sequence, composed of four main shock-aftershock type sequences, occurred in April 1993 at the WDL mine. Altogether 199 events with moment magnitude from -0.5 to 3.1 were located by the local seismic network. The first sequence lasted 179 hours and the second sequence lasted only 13 hours and was interrupted by the third sequence which lasted 33 hours and was in turn interrupted by the fourth sequence. The parameter p, describing the rate of occurrence of aftershocks, ranges from 0.7 to 1. The parameter b from the frequency-magnitude relation has the value of 0.6 for the whole series. The fractal dimension D has the lowest value of D=1.75 for the first sequence and the highest value of D=2.4 for the second sequence.