THE CQU REGIONAL SEISMIC NETWORK AND APPLICATIONS TO UNDERGROUND MINING IN CENTRAL QUEENSLAND, AUSTRALIA

The Central Queensland University (CQU) Regional Seismic Network is made up of an array of six short-period seismometer and two strong motion accelerometer stations. The array has an aperture of about 50 km. CQU is able to resolve epicentral co-ordinates to about +/-2 kilometres, with a sample rate of 100 per second, and an absolute time accuracy of 100 milliseconds. This resolution is achieved by using triaxial seismometers which allow better secondary phase identification of shear, converted and depth phases. The network covers an area of above average seismic risk in continental Australia. The area has been affected in 1918 by one of the largest earthquakes ever recorded along the eastern seaboard of Australia. The network also monitors a large number of blasts carried out by the coal mines and hard rock quarries in the region, and these are being used in a long-term study to determine the structure of the Crust and Upper Mantle in Central Queensland. Techniques for monitoring rockbursts and longwall caving in mines are similar to those used for monitoring local earthquakes. CQU has successfully used a single triaxial seismometer to record seismic events produced by the strata failure and roof falls of a longwall coal mine. The case history presented shows that the initial fall under massive roof conditions appears to be predicted by a simple trend plot of microseismic event magnitude and longwall production rate. Extension of this technique to a closely spaced array of both surface and in-seam triaxial seismometers is required for a more detailed appraisal to be undertaken. Adequate resolution of event location requires a higher sample rate (up to 1000 Hz) and more accurate timing (about 1 millisecond) than for earthquake monitoring. An appropriate stratigraphic model is also required, as is the case for earthquake location.