Geophysical Investigation of the Near Surface Structure and Determination of Subsurface Lithology, Using High Resolution Seismic Method in Otuoke and Its Environs

Author:Chiemeke C. C., Ibe S. O. and Onyedim G.

published date:2017-Feb-06

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Abstract

High resolution seismic method has recently been carried out in Otuoke and Its Environs with the aim of investigating the near surface geological structure and the determination of the lithology which is very crucial for infrastructural development. To achieve this, seismic tomography was used for the survey. The results revealed that, the thickness of overburden (highly weathered layer) in the survey area ranges between 28 m to 50 m, with an average of value of 37 m, with the thickest overburden covers occurring in regions with less infrastructural development. The result of the velocity analysis from the surface, down to a depth of 60 m, revealed the velocities within 5 m depth from the surface, range between 660 m/s to 1160 m/s, which falls within the velocity of sandy clay. The velocity distributions gave an indication that, it is highest within the residential area, and has the least velocity values in the undeveloped regions, where thickest overburden was delineated. It connotes that, more sand filling, and remedial engineering work are needed in most area that are not yet developed within the survey area, before putting up any structure. The velocity distribution at a depth of 30 m, which ranges from 1200 m/s to 2100 m/s falls within the velocity of the aquifer zone, of velocity 1400 m/s and saturated sand. Meaning, any borehole drilled within this region should be drilled down to a depth of 30 m. From the 3D velocity distribution, the North-East section of the survey area, has better aquifer distribution located within sand layer. The velocity distribution at a depth of 60 m ranges from 2000 m/s to 2500 m/s which represents a more evenly distribution of seismic velocity within a consolidated sandy layer.

Keywords: Near Surface Structure, Subsurface Lithology, High Resolution seismic, Otuoke,

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