JOHANNESBURG (miningweekly.com) – Historical research by the Council for Geoscience (CGS) has placed almost beyond doubt that it is the gold mining sector that is solely responsible for causing seismic events in and around Johannesburg.
Gold mining has, however, amplified the number and magnitude of seismic events, delegates at this year’s CGS conference, in Pretoria, were told on Friday.
Following a 5.5-magnitude earthquake with its epicentre in Orkney, a gold mining town in the Klerksdorp district, in North West, in August 2014, it was thought that historical mining activities had compromised the stability of the fault lines which the town overlays.
However, CGS seismicity researcher Nicolette Flint explained that seismic events in the former Transvaal, particularly in Johannesburg, had been recorded prior to the Witwatersrand Gold Rush, which kicked off in 1886, suggesting that seismicity and earthquakes in Johannesburg have had natural causes.
She noted that records of the first alleged mining-related seismic events date back to 1898 albeit only one or two tremors reported each year. By 1906, the frequency of tremor and rock burst reports increased dramatically becoming “a fact of life” for Johannesburg residents.
Following the government decreed installation of a seismograph, in Ophirton, in 1910, seismic events were given greater prominence in the press, with each tremor having been reported between 1908 and 1918.
Prior to the installation of the seismograph at Ophirton, seismicity reports had no scientifically recordable mechanism against which they could be verified; therefore, no accurate sources exist for determining what the scale and magnitude of those seismic events in Johannesburg was, however.
Flint’s research found that between September 1840 and 1949 about 199 earthquakes were recorded across South Africa. Between November 1907 and December 1950 about 700 tremors were recorded in the Johannesburg area alone.