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 SA measures four earthquakes

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PosOnderwerp: SA measures four earthquakes   Fri Apr 23, 2010 10:08 pm

2010-04-22 20:03

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Johannesburg - Four earthquakes were recorded around Gauteng, the North West province and Limpopo on Wednesday, the Council for Geosciences reported on Thursday.

The first was at 13:28 in the Gamoep area of Limpopo and measured 2.4 on the Richter scale, with a depth of 5km.

The second earthquake was at 19:.34 in Gauteng, along the Roodepoort mining belt, west of Johannesburg. It measured 2.4 on the Richter scale and was recorded with a depth of 2km.

Patrick Malaza, chief financial officer at Rand Central Gold mines said they felt nothing and operations had not been affected.

"I didn't even spill my coffee," he quipped.

However, that quake solicited a number of calls to the council by worried residents around Johannesburg wanting to know what was happening.

A third earthquake was recorded in the area of the West Rand gold mines in the North West at 23:42, measuring 2.9 with a depth of 2km.

A fourth was recorded at 23:49 in the same area, measuring 2.9 with a depth of 2km.

Increase in quakes

Michelle Grobbelaar, manager of the seismology unit at the council said on Thursday there had been an increase in quakes in the Johannesburg region, which they are trying to get to the bottom of.

"We have been noticing it not just through our measuring, but also through the public phoning us to tell us about them," said Grobbelaar.

Grobbelaar said the council is trying to increase the number of seismograph stations in the Johannesburg area, and encourage the public to fill in their online questionnaire to let them know about an event.

Their initial feeling is that the quakes are related to mining activity and the number of abandoned mines in Johannesburg. Eighty percent of the region's quakes occur in gold mining areas.

The build up of stresses in the earth's crust needs to be released along a weak point and where areas have been excavated, there are empty spaces where there used to be rock.

"If you have excavated all that solid rock and have empty spaces, the earth has to accommodate for that," said Grobbelaar.

Earthquakes could also occur in areas where dams or reservoirs have built on spaces where there was originally nothing, putting tons of water onto the land mass.

"This creates stresses and lubricates the faults, now we have faults that can move."

Records

Equipment to measure earthquakes was only installed in South Africa in the 70s so researchers are trying to find ways of gathering older written records like journals to find out whether they are getting bigger or smaller in South Africa.

With the tragic images of the Haiti earthquake still fresh, Grobbelaar said that South Africans should not panic about a similar occurrence here.

"Generally, a 2.8 shouldn't cause any structural damage. But in the 3's you can expect more structural damage."

"In gold mines if the guys are down there, that's pretty serious."

Spokespeople for other mines in the quake areas were not immediately available to say if they had been affected, but during parliamentary questions, Mineral Resources Minister Susan Shabangu said "fall-of-ground" accidents remained the predominant cause of deaths in the industry.

Grobbelaar said South Africa was blessed with "modest" seismicity compared with countries like Japan or Chile.

Asked whether Wednesday night's quakes could be a predictor of something more serious she said: "I don't think people should be worried. We are looking into the Johannesburg ones though, because there is an increase."

"The others are running their normal course, it's to be expected."

To report an earthquake in your area contact the council at 012-841-1911 or complete a questionnaire on their website.
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