Investigation of the inhomogeneity of subsurface structures at various VES points at Samaru-Zaria, Northern-Nigeria

Abstract

Vertical electrical sounding (VES) data was carried out at Samaru-Zaria,
Sabongari Local government area of Kaduna State, Nigeria. This was
aimed to investigate the inhomogeneity of the subsurface structures as it
varies from one location to the other. The groundwater potential and the
geologic characteristics of the overburden of the area were also
delineated. The VES curves were interpreted using IPI2Win resistivity
computer software. The survey area is dominated by mainly four layers,
namely: Overburden (topsoil), weathered layers, fractured layers and
Fresh basement. Five subsurface layers were noticed at VES 09, 12 and
30. The overburden consists of indurated laterites, clay and sandy soil.
VES Points 01, 02, 03, 04, 07, 13, 15, 25, 26, 27, 28, 29, 31 and 32 has
topsoil resistivity values ranging from 200 ohm-m to 370 ohm-m, this is
taken to be indurated laterites.VES Points 06, 08, 14, 18, 20 and 23 has
topsoil resistivity values ranging from 28 ohm-m to 98 ohm-m which is
taken to be clay. While VES Points 05, 10, 11, 12, 17, 19, 21, 22 and 30
has topsoil resistivity values of 100 ohm-m to 190 ohm-m which is taken
to be Sandy Soil. Generally, the thickness of the topsoil ranges from
0.34m to 5.54m with the highest thickness at VES 19 and the lowest at
VES 13. The aquifer thickness varies from 6m to 20m with the highest
value at VES 11. There is variation in the topsoil thickness from one
place to another within the survey Area, which is an indication of the
inhomogeneity of the subsurface structures. VES Points where the
thickness of the topsoil is large also have large aquifer thickness and
vice-versa. There is also correlation between the topsoil thickness and
depth to basement; Areas where the topsoil thickness is low have low
depth to basement.