An approach to assessment of post mining-induced seismic hazard in kolar gold fields mines – a review

Abstract

A common challenge faced in underground hardrock mines worldwide is post mining-induced seismicity, as the events have been quite disastrous, causing risk to the structures and lives. In the recent years, many of the worked out mining areas are slowly getting populated and in due course of time shall be posing environmental threat to the people residing above and to the surface structures like sudden void formations or sudden ground collapse becoming visible on the surface. Worked out or closed mines have most of the time shown existence of post mining-induced seismicity signatures. Some of the closed mines showing post mining induced seismicity in Korea, South Africa, Sweden and India are being discussed. Post mining induced seismicity observed in Kolar Gold Fields worked out mine still being felt since closure of deeper levels is discussed. As mining depth increases especially in hard rock mines, magnitude of stress increases, hence, the occurrence and severity of post-mining induced seismicity also increases. The problem becomes more serious if proper fund allocation is not done to investigate these areas, may be due to the absence of economic interest once the mine site has been abandoned and in many cases, direct investigations inside the mines may not be possible due to stability problems or due to the ingress of water into the void spaces of the mining area. Several approaches and techniques adopted by researcher’s world over are being discussed in this paper, with a view to gaining insight into the techniques of evaluation of seismic hazard. Seismic vulnerability assessment should integrate the effects of all the seismic events occurring at different locations of mining area during mining and post mining, along with their uncertainties also being considered. Based on the recorded data and some of the derived parameters from previous years, an attempt should be made to evaluate the existing risk prone areas. The past records of induced seismicity due to mining should be used as a precursor for identification of impending future events and their expected probable locations of occurrence. The methods discussed here for assessment of seismic hazard are based on direct waveform and seismic source parameters, parameters from indirect waveform methods, frequency-magnitude relationship based, and frequency content analysis based. From the assessment it is found that the choice of method that can be used depends on the period of monitoring (short-term monitoring, intermediate-term or long-term monitoring) and the objective of the study required to be achieved, this varies on site-to-site basis. The main focus is to show the importance and need to install a micro seismic monitoring system for long term assessment of seismic risk especially in abandoned/worked out mines showing post mining-induced seismicity.