DR. MULWA JOSPHAT KYALO

Arus-Bogoria geothermal prospect, located in the central Kenya rift valley (KRV), encompasses several features of geological significance that are indicators of possible geothermal potential. These include surface manifestations, such as fumaroles, steam jets, mud pools, hot springs, spouting geysers, and high rate of micro-seismic activity of about 500 earthquakes recorded within a period of three months in comparison to other geothermal fields and prospects along the Kenya rift valley (KRV).

A comparison of the results of gravity survey, undertaken between 2005 and 2006 for geothermal resource evaluation of Arus and Lake Bogoria geothermal prospects, to results of micro-seismic monitoring undertaken in 1985 during the Kenya Rift International Seismic Project (KRISP 85) was undertaken to map the existence of heat source(s), presumably due to dyking, and define the brittle-ductile transition zone. The results indicate that the heat source is due to a series of north-south trending dyke injections occurring at depths of ~3 – 6 km in the vicinity of the Arus steam jets. The geothermal prospect is seismically active and approximately 95% of the seismic activity is probably associated with tectonic activity due to reactivation of north-south trending faults.

Further, only ~5% of micro-earthquakes can be correlated with the geothermal activity such as dyking, as mapped using gravity data, and hydrothermal processes. The change in seismic activity at Arus-Bogoria geothermal prospect occurs at a depth of 8 – 15 km with a peak in micro-seismic activity at 12.5 km depth. We therefore conclude that 8-15 km represents the brittle-ductile transition zone in Arus-Bogoria geothermal prospect.