Induced gravity anomalies and seismic energy as a basis for prediction of mining tremors

Abstract

The results of prediction of occurrence of mining tremors and bursts in the course of the exploitation of the remaining part of the hard coal in seam 510 of the mine “Pstrowski”, Upper Silesia, have been presented in the paper. The exploitation has taken place under extremely difficult conditions hazardous for the mining crew.

To predict the occurrence of mining tremors, bursts and direction of migration of increased elastic strain in the rock mass, the microgravity method has been applied.

The microgravity observations were carried out in the measurement points located at mutual distances equal 20 m in three profiles of the lengths 700 m, 760 m and 260 m respectively. The profiles were located in mining workings in the vicinity of the exploited part of the bed. In the course of exploitation, lasting 25 months, 29 series of measurements including 3600 individual microgravity observations were carried out. Microgravity observations were made with a Worden-Master gravimeter.

The observed time changes of gravity microanomalies were essential for prediction. Local negative changes of gravity microanomalies signalled the approaching mining tremor. The tremor would cover an area of the radius 60 m to 100 m. The regional time changes of the gravity microanomalies appearing as linear trends of these anomalies signalled the development of the fields of elastic strain in the whole investigated area and the approaching violent release of elastic strain energy from the rock mass.

The values of the amplitudes AMP of the above-mentioned trend were the measure of this hazard. In the course of the investigations each shock was preceded by considerably increased values of AMP.