More tremors could hit SA, Moz, Swazi

Thursday, May 31, 2012

Mbombela - People living in South Africa, Swaziland and Mozambique can expect more mild earthquakes as water settles in Maguga Dam in northern Swaziland.

On Thursday, seismic expert Professor Raymond Durrheim, from the University of the Witwatersrand, said mild tremors were common when big dams fill with water after construction.

This followed the earth tremor that measured 4.0 on the Richter scale that hit the parts of Swaziland, Mpumalanga and southern Mozambique on Sunday.

"Mild earthquakes like this can be felt months or years after a specific dam was completed," said Durrheim.

Durrheim said similar mild tremors were recorded near dams like Kariba in Zimbabwe, the Gariep in the Northern Cape and the Katse dam in Lesotho after they were built.

"Some tremors can even be felt 20 years after a dam was completed as the crust of the earth settles and re-adjusts under the pressure of the dam's water," said Durrheim.

South Africa's last large earthquake was recorded in 1969 when the Western Cape's towns of Ceres and Tulbagh were rattled by an earthquake that measured 6.3 on the Richter scale.

However, in 2006 an earthquake measuring 7.0 on the Richter scale was recorded on the banks of the Save river, south of Beira in Mozambique.

Durrheim said this was felt as far as Pretoria and Durban in South Africa.

Director of the Department of Geology at the ministry of natural resources Simon Maphanga said the recent tremor was one of the largest recorded in Swaziland with minor property damage reported. There were no injuries.

Mbombela resident Liz Bayford said she felt the tremor while watching television on Sunday.
"The doors and the windows rattled but nothing was damaged. It was the first time I felt a tremor," she said.

Maguga dam was completed in 2001 during a joint project between South Africa and Swaziland.

South Africa owns rights to half the dam's 332 million cubic metres of water.

Maphanga said the dam has taken years to fill up due to dry seasons in its catchment areas.
Mpumalanga and Swaziland recorded good rainfall this year due to several tropical storms that passed over land from the Indian Oceans.

Wits seismic expert Hlompho Malephane, who has worked in Lesotho on the highlands water project, said the tremor in Swaziland this past week may be described as a delayed seismic response.

"Water may have seeped through an old fault line and increased pressure may have reactivated it causing this tremor long after the dam was completed," said Malephane.

Malephane said an earth tremor in Lesotho was recorded soon after the Katse dam was completed and caused some damage to traditionally built buildings.

Nkomazi local municipality spokesman Cyril Ripinga said no damage to houses in the communities along the Swaziland borders were recorded by the municipality.

"In the case of a disaster we can provide food parcels, tents and shelter if a more serious incident is recorded," Ripinga said.

Geologists are uncertain when the next tremor will occur, or how long the settling process will last.

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