Integrated Geophysical Investigations at Gemeto Thermal Springs, Awassa, Main Ethiopian Rift
No Thumbnail Available
Date
2007-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
In this thesis work three integrated geophysical investigations namely; gravity magnetic
and electrical resistivity sounding have been carried out over Gemeto thermal springs.
The area is situated in the central sector of the main Ethiopian rift at a close proximity to
the SE of Awassa town.
The study aims at investigating all the necessary geothermal characteristics in the area
based on the thermal manifestations. To achieve the objectives of the research, the
required data for each of the geophysical method applied in this study are collected,
processed, and interpreted .Based on the results obtained from the data analyzed using
standard softwares; interpretations and concluding remarks are also given.
Results from gravity survey indicate two interesting features; the first one is the heat
source for the Gemeto thermal springs has been characterized. Small area near the springs
has shown uniquely the lowest negative Bouguer anomaly values. In principle, lowest
Bouguer anomaly values are indicatives of either high cliffs or high density materials.
Our study area is inside the Awassa caldera where high density volcanic rocks are
common with the lowest topography in the area. Therefore, the lowest Bouguer anomaly
values in the area are interpreted as densities of rocks in the area are lowered due to
thermal expansion. The second one is the regional structural trend extending NE-SW that
is clearly shown on the Bouguer and regional anomaly map. Interpreted as an extension
and integral structure of the eastern escarpment of the rift.
From the magnetic anomaly map, the area proposed by the gravity method to be the
possible heat is also characterized by the lowest total magnetic field response. This is
interpreted as rock units in that area are forced to lose their elements with magnetic
properties due to high temperature. The method has also shown different major shallow fault structures mainly lying in NNE-SSW and N-S directions. The 2-D magnetic models
prepared along two profiles also confirm these results.
Results from vertical electrical soundings along one profile show that the first top layer
up to 10m has resistivity values of 2-24Wm which is indicative of alluvium soil deposits
in the area and the second layer of thickness between 20 to 60m, the resistivity value
varies from 12-37Wm which is interpreted as coarse clay materials. In both geoelectric
and pseudosection diagram shallow structure between VES3 and VES4 is observed
which is interpreted as one of the major shallow structures identified by magnetic
method. These shallow structures identified by magnetic and electrical methods are
possible structures that recharge the area.
Based on the joint analysis of these geophysical methods and thermal manifestation, the
area has the potential for small scale development such as center for recreation and
thermal therapy. Besides, additional geophysical methods are proposed to further
reinforce the outcome of the study.
Description
Keywords
Gemeto thermal springs