| dc.description.abstract | The Kiserian-Matathia area is prone to subsequent tectonic movements which are related to
the formation of the Great Rift Valley. These activities have dominated the geological history
of the area since Miocene times and have contributed to the Geology and Structures in the
area. Ground geophysical and hydrogeological investigations have been carried out in order to
evaluate the significance of the rift activities on the geology and hydrogeology of the area.
Faults have been delineated and mapped through the analysis and interpretation of aerial
photographs. Inversion of ground resistivity soundings have revealed resistivities and
thicknesses that are consistent with the geology. The area is underlain by volcanic rocks
estimated to be of Tertiary age. The fractured and weathered trachytes and basalts, the sands
and sediments comprise the aquifer formations in the area. Tuffs act as aquifers only when
fractured. However, their aquifer characteristics are limited because they are generally
impervious. The lithological stratigraphy in most of the area where resistivity soundings were
carried out is represented, from the surface, by: soils and laterites; trachytes; and basalts with a
. varied degree of fracturing and weathering. Sands and sediments occur, in most cases, at the
contact zones between any two formations or intercalated within the formations. Fractured
and weathered formations are excellent aquifers, and their resistivities range between 3 and 35
Q.m. Compact formations with resistivities ranging between 100 and 170 Q.m are aquifers
only when fractured. Faults influence the borehole yield and the flow direction of
groundwater. Boreholes with the highest yield are those located in areas immediately
recharged by faults. The groundwater flows in lateral (E-W) and longitudinal (N-S) directions.
The longitudinal flow is due to the influence of faults. | en |
