Two earth tremors or earthquakes with magnitude 4.0 were recorded in the Zambezi Valley around Kariba Dam on the 1st and 2nd April 2020 at 19.29 hours and at 17.31 hours respectively. The epicentres of the earthquakes in relation to the dam are shown in the map.
The epicentre of the April 1st earthquake was approximately 3 km south-west of the Spurwing Island Lodge or 27 km south of the Kariba Dam and the epicentre of the April 2nd earthquake was approximately 65 km east of the Kariba Dam wall.
These tremors are a common occurrence in the area around the Kariba Dam. The tremors are referred to as load induced tremors or specifically reservoir induced tremors in the case of the Kariba Dam and are a result of the earth crust’s response to the water load or weight of water given the size of the dam. These reservoir induced tremors have been occurring since 1963 when the Kariba Dam started filling. Over 1000 tremors of magnitude 4.0 as the most recent tremors occurred since filling of the dam in 1963.
The 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. The dam was inspected on the 2nd and 3rd April 2020 and the dam instrumentation data was analysed. Analysis of instrumentation data showed that the dam was not affected which was also corroborated by the visual inspections of the dam and its appurtenant structures which showed no structural damage to the dam and its related structures.