While mining-induced earthquakes in the deep gold mines of South Africa pose a risk to mines, mineworkers, and the public, they also provide an unusual opportunity to study the physics of earthquakes. The source zone of a M5.5 earthquake that occurred near Orkney, South Africa on 5 August 2014 was well-defined by tens of thousands of aftershocks recorded by instruments deployed as part of a Japanese - South African research project. The upper edge of the M5.5 rupture is located several hundred metres below the mining horizon. A proposal to drill into the M5.5 source zone, as well as several other active faults in other deep mines, was approved by the International Continental scientific Drilling Programme (ICDP) in August 2016. Here we describe the scope and objectives of the project, and the selection and preparation of the principal drilling sites. In addition to the studies of earthquake phenomena, some of the holes will be used by geomicrobiologists to investigate deep microbiological activity fuelled by hydrogen released by seismic rupture to address questions about early life on planet Earth.

INTRODUCTION

Gold-bearing quartz pebble conglomerates were discovered near present-day Johannesburg in 1886. As mining operations followed the orebody, the dipping ‘reefs’ were found to persist to great depths. Mining-induced seismicity and its hazardous manifestation, rockbursts, were first encountered in the early 1900s, when extensive stopes, supported solely by small reef pillars, reached depths of several hundred metres.

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