Some discriminatory characteristics of earthquakes near the Kariba, Kremasta, and Koyna artificial lakes

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Abstract
The behavior of earthquakes near the artificial lakes at Kariba, Kremasta, and Koyna, where earthquakes of magnitude exceeding 6 have occurred, is examined. Foreshock-aftershock patterns of these earthquake sequences correspond with Mogi's type II model, whereas the normal earthquakes of these regions belong to type I. Three similar relations could be fitted in the time distribution of aftershocks of the main earthquakes. Quite contrary to normal earthquakes, foreshock b values are found to be comparable with the aftershock b values in the frequency-magnitude relations. Focal mechanisms of the largest earthquakes of these sequences have been determined and compared. Dip-slip components of the motion are such that the lakes are situated on the downthrown blocks. These regions are characterized by a volcanic past and the presence of rocks such as limestones and red boles which are easily affected by water. These findings are useful in distinguishing the reservoir-associated earthquakes from normal earthquakes and suggest that the artificial lakes are responsible for changing the mechanical properties of the strata and releasing the accumulated strains.

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