-During mining activity, the natural equilibrium of the rock mass gets altered resulting in increase in stress causing sudden, violent failure of rock mass. The stress increases with increase in the depth of mining. The dynamic stress changes caused due to release of strain energy from within the rock mass in the form of seismic signals are termed as seismic events. The occurrence of seismic events has been a regular phenomenon in and around the abandoned mines of Kolar Gold Fields causing damage to the surface structures and inducing apprehension about the safety and stability of mining areas. Among the abandoned mines, one of them had reached mining depth as deep as 3200m. In this sensitive mining area, there has been occurrence of many seismic events that were monitored by a dedicated seismic monitoring system from time to time. The monitoring system was used to determine the location of seismic events and used as an indicator of precaution from future events. In the background of this monitoring history, an attempt has been made here to assess the overall scenario of seismic hazard due to the seismic events observed over one decade. This study focuses on assessing the current probable seismic hazard for the abandoned mining region by using the estimated source parameters such as source radius, seismic magnitude obtained from the data of strong motion accelerometer supported by data from existing broad band seismometer.

Active deep hard rock metal mines with long mining history come with inherent problems of stability and mining induced issues. These hard rock mines once closed, still pose even greater environmental risks and stability concerns. The issues of post-mining impact on environment are usually undervalued and disregarded. It is very essential to give utmost importance to these mines by following standard mine closure methods and remediations using post-mining management plans for long-term monitoring and risk assessments associated with the mine for the safety of life and structures above. The area identified for the study is Kolar Gold Fields mine located in Karnataka, India. The mine was completely closed in 2000. The underground mine has been posing post-mining induced seismicity even today. Due to the complexity of the underground mine and the inaccessibility to the mine post closure, the Finite Element Method of approach has been used. The approach is developed to simulate a model similar to actual field conditions, subjecting them to the seismic loads, varying the parameters which play a significant role, assessing the entire Kolar Gold Fields mines for vulnerable zones subjected to post-mining induced effects and finally making it possible to evaluate the stability conditions of the deep hard rock underground metal mine. The simulations were carried out for the three cases with varying the peak ground acceleration (PGA) for a low PGA of 0.06g, for an intermediate PGA of 0.1g and high value of 0.2g. It can be inferred that as the acceleration is increased from 0.06g to 0.22g, there is a corresponding increase in ground acceleration observed at the ground surface for each case. The maximum acceleration for PGA of 0.06g is 0.071g, for PGA of 0.10g, it is 0.170g and for PGA of 0.22g it is 0.266g. The results were validated with the field observations (data of seismicity from installed seismic monitoring systems). The Finite Element Method of approach has aided in quick assessment of stability of the underground closed mine.