Abstract

The Itezhi‐Tezhi reservoir area in the Republic of Zambia, located in the East African rift (EAR) zone, is characterized by significant potential for natural tectonic activity. The highest known magnitude of 5.7 occurred on 15 May 1968 at a distance of 22.1 km from the dam site. Analysis of the spatial distribution of local seismicity recorded by a microearthquake (MEQ) network during March 1981–December 1992 and its correlation with water level changes of the lake indicates five different episodes of enhanced local seismicity of triggered nature within and in close proximity of the reservoir. The triggered nature of these episodes of seismicity is also corroborated by hydraulic diffusivity analysis. The reservoir was first impounded in 1977, but emptied shortly after for inspection of the bottom. The refilling of the reservoir started in 1978, and the first episode of swarm type of local seismic activity occurred in 1981, after about three years. The second episode, which had the highest frequency of earthquakes and a maximum magnitude of 4.0, occurred during April 1982–September 1983. Another episode, also of swarm type of activity but with a relatively lower frequency of earthquakes, occurred from July 1986–January 1987. The remaining two episodes in 1984 and 1991 were short lived and of localized and isolated nature, with a relatively higher number of large magnitudes compared with the smaller episodes. The episode of 1984 includes a maximum magnitude of 4.4 on 26 October, which is the highest triggered magnitude during the complete period of study. Thus the region of Itezhi‐Tezhi reservoir, which is known to have high potential for natural seismicity during both pre‐ and postimpounding periods, has exhibited triggered seismicity close to the reservoir in the form of increased frequency of micro and small magnitudes of earthquakes during the period of present study.

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