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Conrad Mupesa Mashonaland West Bureau
THE Zambezi River Authority (ZRA) has confirmed that a series of earthquakes in the Kariba and surrounding areas have had less impact on the dam wall.
In a press statement this morning, ZRA chief executive officer Engineer Munyaradzi Munodawafa said the earthquakes in Kariba and surrounding areas including Hurungwe in Zimbabwe and Siavonga in Zambia of varying magnitudes of between 4.1 to 4.9 on Richter Scale were as a result of decreasing dam water levels.
Inspections and analysis of data from the various monitoring instruments after the earthquakes did not reveal any unusual observations and the dam continued to exhibit normal behaviour consistent with prevailing loading conditions.
“The authority further wishes to inform its stakeholders and the public at large that in the interest of dam safety, it does not focus on the magnitudes of the earthquakes, but the ground accelerations or vibrations that are generated from the event,” read the statement.
“The vibrations/shacking are further influenced by such characteristics as distance and depth of the epicentre. Therefore, an earthquake with a smaller magnitude but with its epicentre closer to the dam wall could be more damaging than a large earthquake with an epicentre located far away from the dam wall.
“Within this context, the earthquakes that have been experienced in Kariba, Siavonga and surrounding areas since the construction of the Kariba Dam are relatively small and have not generated large ground accelerations or vibrations as to cause concern regarding the safety of the dam wall.”
The area experienced seven earthquakes this month, the most recent one with a magnitude of 4.9 occurring at 5:39 am this Monday.
Its epicentre was triangulated to approximately 19km in the South-South East direction from Kariba Dam, at a depth of 10km within the Kariba reservoir, directly behind Antelope Island in Zimbabwe.
He added that earthquakes were primarily reservoir-induced seismic (RIS) activities that are triggered by not only the presence but also the water level fluctuations from the drawing down of the Kariba reservoir.
Similar experiences have been reported from the filling and subsequent operation of several other large dams and reservoirs worldwide.
Online Reporter