The seismicity of east Africa

Abstract

A preliminary investigation of seismic recordings made by the Durham University array station at Kaptagat, Kenya, for the period July 1970 until May 1971 has been made, A map has been produced indicating the epicentral location of earthquakes recorded within East Africa during this period. The work has shown that the majority of earthquakes recorded occurred associated with the major tectonic features of the East African rifts. The areas from which the largest numbers of earthquakes have been recorded were the western rift and the Kavirondo rift. An empirical preliminary magnitude scale has been devised for earthquakes recorded at Kaptagat, Magnitude frequency plots for areas within East Africa indicate a difference in the strength between the underlying rocks of the western and eastern rifts. The western rift exhibits the large bursts of energy release normally associated with more elastic material failure of the crust. The eastern rift shows earthquake magnitude and frequency characteristics that are indicative of the lower maximum stresses possibly associated with semi plastic flow rather than more elastic failure. This is taken as confirmation that the western rift has a structure possibly close to normal crust with significant spreading having not yet occurred. The eastern rift on the other hand, is seen as a zone of more plastic material failure and crustal spreading, identifying it as a plate boundary.