Seismicity of the northern part of the Kenya Rift Valley

Abstract

During the first eight months of 1981 earthquake data were recorded during a passive seismic experiment (KRISP 81) in northern Kenya. An eight station, small aperture, short period seismic array was located on the eastern margin of the Rift at 1.7°N, 37.3°E. Two single-point, three component stations were also located north and west of the array, forming a triangular network with approximately 150 km length sides. 2329 events were recorded during the 231 days of recording. A preliminary micro-earthquake seismicity map of the central and northern parts of the country has been produced, using a uniform half space velocity model derived from the analysis of apparent velocities, azimuths and P-S times of event arrivals at the small aperture array. Events located within the Rift show a marked north-south linearity extending from Lakes Bogoria and Baringo in the south, into the Sugata Valley to the north. Around the southern part of Lake Turkana the seismicity becomes more diffuse. However, there is little seismic activity associated with the broad zone of splay faulting that exists in northern Kenya. The seismicity observed along the axis of the Rift suggests a continuation to about 2.5°N of the tectonic style observed over the apex of the Kenya dome. A relatively quiet zone separates the activity within the Rift from a second, diffuse, north-south zone of seismicity approximately 150 km further to the east.