Integrated Geophysical Investigations at Sodere Thermal Springs, Main Ethiopian Rift
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Date
2008-07
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Addis Ababa Universty
Abstract
In this thesis work two integrated geophysical surveys namely magnetic and electrical
resistivity sounding have been carried out over the Sodere thermal springs area. The area is
located within the Main Ethiopian Rift (MER), close to Nazareth town and is accessible on an
all weather asphalt road on a detour from Nazareth-Assela main road. The Sodere thermal
waters are one of the famous and relatively well-utilized centers in the country, which is being
used for both recreational and healing purposes.
Total magnetic field surveys at station spacing of 25 m well distributed and covering the
thermal area were carried out. About 300 magnetic data points were obtained. Further, a total
of ten VES stations, distributed to lie on three convenient traverses were measured using the
Schlumberger symmetrical array. Maximum current electrode separation (AB/2) of up to
500m was used for the sounding survey. The results of the magnetic survey were presented in
terms of profile plots and also contour maps which were later continued upward to remove
near surface effects. The resistivity survey data were used to construct apparent resistivity
pseudosections and the data were further interpreted and plotted to obtain geoelectric sections.
From the magnetic anomaly map of the magnetic survey, the heat source is characterized by
the lowest magnetic anomaly response interpreted as resulting from rock units that are forced
to lose their magnetization due high temperature. Such areas with low magnetic anomaly and
weak zones have been outlined. From the electrical survey, areas of low resistivity (typically
< 20Wm) observed on the pseudo- and geoelectric sections along Profiles-1and -2 are
interpreted as hydro thermally altered zone and the overall low resistivity observed along
Profile-3 is interpreted as highly water saturated region of the area because of the close
proximity of the profile to the Awash river and the absence of structures that act as a barriers
for ground water movement. Based on the analysis of the two geophysical methods and thermal manifestation, the area has
geothermal potential for further development from central to northwest of the study area.
Considering the limitations in depth of the electrical methods employed, further geophysical
investigations are proposed to reinforce the outcome of the IV study.