Application fo geophysical methods for the evaluation of thermal centers and their structural controls in Boku, Nazareth, main Ethiopian rift

The Boku thermal centres are located in the tectonically active axial part of the East African Rift system where the east and west rift margins are the narrowest. More specifically, in the part of the rift system known as the Main Ethiopian Rift (MER) where acidic and central volcanoes are erupted along NE-SW tectonic lines forming a region interspersed with fault scarps, volcanic scoria cones and collapsed segments (Figure 1). The topography is dominated by sunken strips of land between a series of normal faults forming part of the so called Wonji Fault Belt system. The area is also characterised by high geothermal gradient and thermal anomaly associated with the acidic volcanic centres. Steam temperatures as high as 72 °C has been recorded at the currently active thermal centre, although the steam temperatures has also been observed to show variations within a given day. Studies conducted in the area earlier specially in Aluto volcanic centres, which are currently being developed for power generation, and adjoining areas within the rift have shown that pyroclastc deposits are the major thermal aquifers. The main geological feature in the area, called the Boku caldera and its surroundings represent a typical example of central eruption from where peralkaline acidic and pyroclastic deposits have been erupted. The caldera shows rims of irregular geometry, indistinct at some places but well marked on the eastern side of the Boku. The prominent topographic high in the area is the Boku ridge which rises to an elevation of 1875 meters a.m.s.l. in the centre of the region. In a few places in the area, manifestations of steam of very high temperatures from the ground have rendered the area to be usable as a traditional steam bath centre. The major area currently used for the purpose, the Boku, has a small scale infrastructure connected to Nazareth town by gravel road and serving the local population as a bath/healing centre. Due to its geographic location connecting parts of Ethiopia between Addis Ababa and the large sections of the country in the east, Nazareth town is one of the fast growing urban centres of Ethiopia with future potential to be the centre of economic and industrial growth. It has recently shown large growth in population and has a future which will make it a trade and economic centre. The potential of the Boku to be involved in the future development of the town both as a source of recreational and healing centre and in the future for the supply of hot water to the town and the surroundings is therefore apparent.