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Sifelani Tsiko-Environment & Innov Editor
An earth tremor of magnitude 4,3 was felt in Kariba and surrounding areas on Tuesday night this week, the Meteorological Services Department of Zimbabwe reported.
The tremor occurred at 10.03 pm and the Met Department triangulated the epicentre to be about 50km south of Kariba Dam, according to the Zambezi River Authority.
But in a statement, the authority’s chief executive Munyaradzi Munodawafa said there were no casualties or damage, and the infrastructure at Lake Kariba continuing to operate regularly.
“We wish to assure the public and those domiciled in and around the affected areas that tremors of this magnitude are not expected to affect the structural integrity of the Kariba Dam,” he said.
“We further confirm that there were no unusual observations made from the inspections that were carried out on the morning of August 3 nor from the analysis of dam safety data that is collected from several instruments that monitor the behaviour of the dam.”
Over the past 12 months, two tremors of equivalent magnitudes and several others of even smaller magnitudes occurred south of the Kariba Dam. There was a tremor of magniture 4,5 with an epicentre near Binga on August 9 last year and one of magnitude 4,6 on May 24 this year, with an epicentres below the lake.
Kariba and the Zambezi Basin area experience seismic activity attributed to changes in the water levels in Lake Kariba as the huge weight of water rises and falls. These were common when the lake was filling, and some were felt as far away as Harare although the latest ones are too mild for that.
Generally Africa being an old continent made up of a number of ancient cratons has very little seismic activity. Seismology data shows that only four earthquakes with a magnitude greater than 7 have been recorded since 1900, the largest being a magnitude 7.3 event in Tanzania in 1910.
This would be roughly a 1000 times more severe as the Kariba tremor on Tuesday. The magnitude scales work on a log scale, so a magnitude 5 quake is 10 times as severe as a magnitude 4, and a magnitude 6 quake 100 times as severe as the magnitude 4.
The most severe quakes felt in Zimbabwe in recent decades have been in the south-eastern end of the East Africa Rift in Mozambique, but even close to the border caused no significant damage or any injuries although buildings were shaken.
Online Reporter