What is the seismic risk of mine flooding?

Abstract

Increased levels of seismicity are known to occur when water enters cracks in the Earth’s surface. This so-called “fluid-induced seismicity” is a phenomenon that has been observed in many non-mining settings (e.g. filling of dams and fluid injection). In South Africa some gold mines are already flooding and many more will fill with groundwater when they close. Preliminary investigations have shown that flooding of mines has already generated increased levels of seismicity. This paper aims to create awareness that fluid-induced seismicity will become increasingly important in South Africa when closed mines are allowed to flood. The flooding of mines could lead to potentially disastrous seismicity, which poses a safety risk for neighbouring mines and surface communities. However, the seismicity associated with flooding of deep mines has not been thoroughly researched. There is an urgent need to research the potential relationships between flooding and the magnitude and frequency of triggered and induced seismicity resulting from mine flooding. A thorough understanding of the interaction between flooding and seismicity needs to be obtained so that the impact of mine flooding on safety can be quantified. In particular, the maximum credible earthquake size resulting from the flooding of deep gold mines in South Africa needs to be determined. The identified risks will, in turn, allow appropriate mitigating strategies to be developed. Such strategies will influence South African mine closure policies.