Mapping lateral extent of suevites at northern part of Lake Bosumtwi using resistivity and seismic refraction methods.

Abstract

Electrical resistivity imaging and seismic refraction method have been used to map the lateral extent of suevites in northern lake of Bosumtwi. Seven electrical resistivity tomography and two seismic refraction pro les were surveyed. The lengths of the pro les varied between 160 and 600 m. The multi electrode system was combined with roll along techniques for resistivity data collection using gradient array. Roll along was also executed for the seismic refraction survey where two geophones were overlapped to extend the survey length. The data was acquired in 2D where 4 m as electrodes separation was also equal to geophones spacing, while shooting interval was 8 m. Depth of investigation for resistivity and seismic refraction surveys are 25 m and 26 m respectively. Data was processed with Res2dinv and ReexW for the resistivity and seismic refraction respectively. Electrical resistivity and seismic refraction tomography identi ed fractured zones as well as suevite deposits which were observed within 12 m depth. Resistivity of northern Bosumtwi suevites varies between 1.56 and 25 m, and the P wave velocity ranges from 3000 to 3900 m/s. The results also showed that the subsurface is made up of either two or three layers: unconsolidated top soil and moist clay, soil with moisture content or clayey soil and fractured claystone. The seismic refraction tomography and the electrical resistivity tomography agree well in revealing subsurface geological units based on their velocity and resistivity values.