Integrated geophysics for investigation of landslide-affected site located near to Alemketema town, Central Ethiopia

Abstract

The Central Ethiopian highlands are known for recurrent landslides that pose major challenges to development of infrastructure. In 2021 a landslide was occurred about 4 km northwest of Alemketema town following the construction of the Alemketema-Wereilu highway. Therefore, to map the landslide area, elucidate the causes and triggering factors, and thereby propose plausible mitigation measures, geophysical studies were carried out applying electrical resistivity and seismic refraction methods. Data interpretation revealed three contrasting lithologies, namely the upper colluvium-eluvium deposit (with 10–101 Ω-m and < 526 m/s), in the middle a highly altered (decomposed) basalt containing considerable moisture, and a relatively resistive (>180 Ω-m) and dense (1280-1580 m/s) weathered and fractured basalt at the bottom. These results are compared with geological log data obtained from nearby borehole and found to be in good correlation. In addition, the main slip surfaces and weak tectonic features are indicated which directly and indirectly destabilize the slopes and affect the road's foundation. The presence of physically weak lithologies covering steep terrain, poor agricultural and earth work practices are the main factors exposing the area for sever landslide that usually triggered by intense rainfall, Therefore, the development of alternative road design should properly considers these subsurface characteristics, and incorporate surface and shallow groundwater management, slope area stabilization measures, and improve earthwork practices to reduce their impacts.