Seismic and Magnetic Studies to Characterize the Foundation Layer of the Future Kalehiwot University Site, Debrezeit Area
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Date
2014-06-06
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Addis Ababa University
Abstract
Ground geophysical study was conducted at the future Kalehiwot university site, Kuriftu, Debre
zeit, Ethiopia, using an integrated approach of seismic refraction and magnetic survey techniques
in order to image the near subsurface in terms of main geological and geophysical properties
covering the study area for construction purpose.
Kuriftu is located in the south end of Northern Main Ethiopia Rift (NMER), more specifically
northeast of Debrezeit town. The main objective of the study has been to characterize the
foundation layer of the future Kalehiwot University site with seismic refraction and magnetic
methods. Seismic refraction method is based on the first arrival time information of seismic
waves propagating through the subsurface, whereas magnetic method is based on the magnetic
susceptibility contrast of the geology. Data enhancement techniques such as analytic signal and
upward continuation were used to filter the magnetic data and clearly image the area anomaly.
Seismograph, geophones, as well as proton precision magnetometer was the instruments used in
seismic refraction and magnetic survey respectively. The seismic refraction data were processed
using SeisImager software, facilitates construction of time-distance plots and velocity model.
The travel time curves were inverted using tomographic inversion techniques and reveal the
velocity model of the area. Likewise the magnetic data was processed using Geosoft (oasis
montage) software and different anomaly map and magnetic model was produced.
From the result of the velocity and magnetic models, the foundation layer was characterized. The
area of study is covered by soil deposits with maximum thickness of 10 m.Volcanic origin
phreatomagmatic materials underlie the soil deposit. This volcanic material originated from the
interaction of hot magma with the ground water and it is located about 5-10m depth. The seismic
velocity of this material is 1.5Km/s. The bedrock of the area is located about depth of 20-30 m; it
is slightly weathered pyroclastic rock type. The seismic velocity of this layer is 2.5Km/s, reveals
that it is relatively hard rock type. The rest of the lithologies underlie are welded pyroclastic and
basalt.
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Keywords
Seismic, Magnetic Studies, Characterize, Foundation Layer, Future Kalehiwot University Site, Debrezeit Area