JOHANNESBURG, March 9 (Xinhuanet) -- A rarely strong earthquake jolted mines and townships about 200 km southwest to Johannesburg on Wednesday morning, forcing evacuation of miners and residents but causing no casualties.

    South Africa's National Seismograph Network said the quake was measured preliminary 5 on the Richter scale, a rare one in South Africa, according to a report of the SAPA news agency.

    The tremor was obviously felt in Johannesburg.

    Ian Saunders, project leader of the National Seismograph Network, said the tremor's epicenter was believed to be around Klerksdorp, the Free State.

    The SAPA report said miners at Durban Roodepoort Deep (DRD) near Stilfontein, which is adjacent to Klerksdorp, were being evacuated early on Wednesday afternoon. And a number of buildings in the mining town were severely damaged and had to be evacuated. Two high schools in the town were also evacuated as the walls weredamaged.

    By early Wednesday afternoon emergency services had received a report of only one minor injury.

    Saunders said such a measure was "quite serious" for South Africa, which is an aseismic (not prone to earthquakes) country. He said the largest earthquake to have hit South Africa, in Ceres in the Western Cape in 1969, had measured 6.1 on the Richter scale.

    It was not yet known whether the Klerksdorp quake was related to mining or due to natural causes.

    An earth tremor occurring also in the Free State on Monday morning killed four gold miners after they were trapped by fallingrocks inside a shaft belonging to Harmony Gold, the world's sixth largest gold mining company. Enditem