A new look at South African seismicity using a temporary network of seismometers : research article

Earthquake activity in South Africa is dominated by events induced by deep gold mining on the periphery of the Witwatersrand basin. Between April 1997 and April 1999, a dense network of seismometers (Kaapvaal network) was deployed across southern Africa. This network supplemented recordings of seismic activity made by the South African national network, thereby contributing to improved definition of seismicity over a 25-month period. Localized networks of seismic instruments are also deployed within individual gold mines or across mining areas, providing magnitudes and accurate locations of many events not located by the national network. Comparison of catalogues of seismic events of magnitude greater than 2, located by both the national and mine seismic networks, enabled 1577 common events to be identified. A database of waveforms of those mining-induced events recorded by the Kaapvaal network that were located by the national network allowed a comparison of the location accuracy of the two networks (average errors of 1.56 + 0.10 km and 9.50 + 0.36 km for the Kaapvaal and national networks, respectively). The database has also assisted in defining new regional reference travel-time curves to improve earthquake location procedures, in studying the deep geology of the Kaapvaal craton, and is contributing to a better understanding of the physics of earthquake sources.