Quantitative Analysis of Seismic Refraction Data to Delineate the Weathering Structures in Parts of Delta State

International Journal of Applied Physics

© 2018 by SSRG - IJAP Journal

Volume 5 Issue 2

Year of Publication : 2018

Authors : Uwadiegwu Promise, Nwankwo C.N, Eze S.U

10.14445/23500301/IJAP-V5I2P106

How to Cite?

Uwadiegwu Promise, Nwankwo C.N, Eze S.U, "Quantitative Analysis of Seismic Refraction Data to Delineate the Weathering Structures in Parts of Delta State," SSRG International Journal of Applied Physics, vol. 5,  no. 2, pp. 19-24, 2018. Crossref, https://doi.org/10.14445/23500301/IJAP-V5I2P106

Abstract:

Seismic refraction shooting have been carried out at a site located in Osubi Township within Effurun metropolis Delta state Nigeria, to establish a database on the subsurface geology and weathering structures in the area for engineering studies. Twenty (20) seismic refraction data using forward and reverse shooting methods of lateral distance 2m along each shot points were acquired within the study area. The data was analyzed using Microsoft Excel and Strata-4 software; and the results indicate the presence of three seismic refraction layers with the first layer having velocity 150-366m/s and thickness 1.0-3.3m, representing topsoil. The second refraction layer is composed of lateritic clay with thickness 4.5-10.5m and velocity 578-878m/s. The third refraction layer consists of sandy clay with velocity 1000-2500m/s. 2D geologic sections were drawn from seismic velocities showed that within the subsurface exists low permeable material (sandy clay) within the third layer. Clay is expansive with respect to moisture content, and this causes differential settlement which results in structural failure. 3D velocity model computed within the second and third layers for shot points 6 to 20 showed discontinuities in velocities at about 7-15m of the subsurface. Abrupt changes in velocity is diagnostic to presence of faults or fault like structures within the subsurface. Faults are plains of weakness where the subsurface geologic materials have lost cohesion (shear strength), therefore the study area has the existence of near surface weak materials (sandy clay) for foundation and engineering structures. Thus it is recommended that further geophysical investigation should be carried out such as resistivity tomography (2D or 3D) to quantify the vertical and lateral extent of the weak zones, so that further geotechnical decisions can be taken.

Keywords:

Seismic refraction, Seismic velocity, Geologic section, Velocity model.

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