Journal of Earth Sciences and Geotechnical Engineering

Seismic Refraction Investigation of Fracture Zones and Bedrock Configuration for Geohydrologic and Geotechnical Studies in part of Nigeria’s Capital City, Abuja

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• Abstract 
  
  
  Seismic refraction surveys have been in use for over 40 years in petroleum, geohydrology and geotechnical studies. The present survey was carried out to determine the subsurface nature (thickness, bedrock configuration and fracture zones), in Karshi part of Nigeria’s Federal Capital City (FCT) Abuja, North Central Nigeria which lies between latitudes 80521 – 80551N and longitudes 70291 - 70321E and underlain by basement rocks that form part of the Nigerian Basement Complex. A 48 channel GeodeTM seismic system was used with a geophone spacing of 2m, giving a total spread length of about 96m. Elastically accelerated weight drop (50kg) energy source was used, with minimum of three number shots stacked per location. The quality of the recorded data was generally good, which shows clear direct arrival, 1st and 2nd refracted arrivals from the water bearing fractured basement and fresh basement interface. Analysis of the data revealed that, the layers are dipping and undulating with dip angles of -0.3 (down dip) and 0.79 (up dip) respectively. The results obtained suggests that, the upper slow velocity (283±0.16m/s) layer is loose overburden materials having a thickness ranges from 1.3m – 2.05m, the second layer (1572±0.004m/s) represent a water bearing fractured zones having a thickness ranges from 18.7m – 21.4m respectively, and finally the third layer (3385±0.002 m/s) represent the crystalline fresh basement rock. The thick fractured zones of the second layer are potential target for groundwater exploration and would require remediation treatment for engineering purpose.
  
  
  Keywords: Seismic refraction, Bedrock configuration, Fracture Zones, Geohydrology and Velocity