By Leonard Ncube
Areas around Kariba Dam were hit by five earthquakes in the first week of this month, the Zambezi River Authority (ZRA) and Meteorological Services Department (MSD) have said.
Two of the earthquakes on 1 and 2 April measured 4.0 on the Richter scale while the other three were minor ranging from 3.0 to 3.5 in magnitude.
They were all only felt around Kariba with the epicentre around Kariba Dam and no human injury or infrastructure damage were reported.
The ZRA said in a statement that it inspected Kariba Dam on 2 and 3 April and analysis of data confirmed the two moderate tremors.
ZRA said such reservoir-induced tremors are common in Kariba where more than 1 000 have occurred since 1963 when the water body filled up.
“Two earth tremors or earthquakes with a magnitude of 4.0 were recorded in the Zambezi Valley around Kariba Dam on the 1st and 2nd of April at 7.29PM and 5.31PM respectively,” said ZRA.
The river authority which is jointly owned by Zambia and Zimbabwe to manage Zambezi and Kariba, said the epicentre of the April 1 earthquake was approximately 3km south-west of the Spurwing Island Lodge or 27km south of the Kariba Dam while the epicentre of the April 2 earthquake was approximately 65km east of the Kariba Dam wall.
“These tremors are a common occurrence in the area around Kariba Dam. The tremors are referred to as load-induced tremors or reservoir-induced tremors in the case of the Kariba Dam and are a result of the earth crust’s response to water load or weight given the size of the dam,” read the statement.
The reservoir-induced tremors have been occurring since 1963 when the Kariba Dam started filling up and over 1 000 of them, with a magnitude of 4.0 as the most recent, have occurred since then, the ZRA added.
“Tremors of this magnitude do not affect the structural integrity of the dam. However, as a precaution the Kariba Dam is inspected after each event and the instruments records analysed for any anomalous behaviour irrespective of the magnitude.
“An analysis of the instrumentation data shows that the dam was not affected which was also corroborated by the visual inspections of the dam appurtenant structures which showed no structural damage to the dam and its related structures,” added ZRA. The Chronicle