An integrated geophysical study of the northern Kenya rift crustal structure: Implications for geothermal energy prospecting for Menengai area

Nicholas O Mariita, University of Texas at El Paso

Abstract

In this study, seismic refraction data gathered and interpreted by the Kenya Rift International Seismic Project (KRISP) group has been used as a constraint for the construction of gravity models for the crustal structure of the northern sector of the Kenya rift valley. The gravity data were obtained from the University of Texas at El Paso's (UTEP) database. Additional data were also obtained for the southern Ethiopia and Turkana areas. The analysis and interpretation presented, therefore, takes advantage of this new compilation which has not been incorporated in earlier studies. The other new data set analyzed was an aeromagnetic survey flown in 1987 for the National Oil Corporation of Kenya (NOCK). Maps prepared from these data have been used to corroborate the gravity interpretation for a qualitative assessment of the shapes and trends of the anomalies, in conjunction with the geologic map of Kenya. Therefore, use of integrated methods incorporating well data, KRISP and published industry seismic lines make the presented models better constrained than previous studies. ^ In this study, variations in crustal thickness and upper-mantle structure have been modeled along with evidence for major magmatic modification of the upper crust along the axis of the northern sector of the rift. Results show the following: (1) a decrease in the crustal thickness from about 35 km in the south to 20 km in the north, due to a northward increase in extension, as noted in earlier studies; (2) the gravity highs observed along the axis have been modeled and interpreted as resulting from main magmatic centers underlain by discrete mafic bodies; (3) the axis of the rift is marked by a series of high amplitude magnetic anomalies whose wavelengths are less than 2.5 km, with the positive anomalies coinciding closely with known Quaternary volcanoes; (4) the character of the magnetic field in the southern section of the Kenya rift is significantly different from that of the northern section as shown by a transition zone located just south of Baringo-Bogoria basin. This zone is about 20 km wide and is bounded by pronounced east-west trending faults. ^ In addition to regional analysis of rift structure, a detailed study of the Menengai volcano area was conducted using over 100 DC resistivity soundings. Resistivity anomalies have been highlighted by contouring the apparent resistivity values from the soundings at various depths and investigating how they vary with depth and how they compare with those from the Olkaria geothermal field. The resistivity and gravity signatures suggest the presence of a heat source and a geothermal reservoir hosted within the fractured/faulted brittle trachytic lavas of the rift floor to the north and northeast of Menengai caldera. It is hoped that this analysis will be used in future exploration efforts. (Abstract shortened by UMI.)^

Subject Area

Geophysics|Environmental Sciences|Energy

Recommended Citation

Mariita, Nicholas O, "An integrated geophysical study of the northern Kenya rift crustal structure: Implications for geothermal energy prospecting for Menengai area" (2003). ETD Collection for University of Texas, El Paso. AAI3118500.
http://digitalcommons.utep.edu/dissertations/AAI3118500

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