Mapping the subsurface structure of the suevite deposit in the north of the Bosumtwi impact crater using electrical resistivity and seismic refraction tomographies

Abstract

Electrical resistivity imaging and seismic refraction methods have been used to map the subsurface structure of the suevites north of the Bosumtwi impact crater in Ghana to determine the depth extent and in-situ resistivity and P-wave velocity of the suevites. Seven electrical resistivity and two seismic refraction profiles were surveyed. The lengths of the profiles varied between 160 and 600 m. The multi-electrode system was combined with roll along techniques for the resistivity data collection using the gradient array. The data was acquired in 2D where the electrodes separation of 4 m was the same as the geophones spacing, while the shooting interval was 8 m. The data was processed with Res2DInv and ReflexW for the resistivity and seismic refraction respectively. Electrical resistivity and seismic refraction tomographies identified the suevite deposits which were observed within 12 m depth. The resistivity of the northern Bosumtwi suevites varies between 1.56 and 25 Ω𝑚, and the P-wave velocity ranges from 3 to 3,9 𝑘𝑚/𝑠. The results also showed that the subsurface is made up of either two or three layers: an unconsolidated topsoil, clayey soil, and fractured claystone. The seismic velocities and the electrical resistivities of the northern Bosumtwi suevites compare very well with those found for suevites at the Ries impact crater Germany and other impact craters.