A landslide research at Northeastern Turkey using 2D electrical resistivity method

Landslides are an earthflow that may occur in areas with heavy rainfall, on the banks of rivers and on mountain slopes. They may be defined as a sudden or gradual rupture of rocks or soils and their following movements down slope by power of gravity. Landslides endanger engineering structures, properties and human lives. The most important causes of landslides in northeastern Turkey are generally morphology of slopes, heavy rainfall, excavation, decomposed rocks and existence of underground water in soil material. In the study area, structurally complex volcanic and sedimentary sequences, occurred limestone, marl, claystone and tuffite, were observed. The geological units are weathered due to heavy rainfall, surface and underground waters. The weathered units as a result of increase in water movements in landslide area caused the reduction in slope stability, and hence the earthflow by power of gravity occurred. The landslide located in 7 km south from the province of Trabzon in northeastern Turkey is investigated using the two dimensional dipole dipole electrical resistivity method. The resistivity imaging produces significant results to characterize the landslides. The resistivity survey is the definition lateral extension and thickness of landslide body, the determination of a potential sliding surface, and the detection of the movement of groundwater flow and its distribution within the slip mass. The landslide having about 17° slope is approximately 120 m long, about 100 m wide, and in an environment with an altitude ranging from 150 m to 200 m. The highway and buildings in the landslide area have been largely damaged due to the landslide. The resistivity pseudosections with a dipole spacing varying from 5 to 30 m over eight profiles with the length of 100 m, five of which were oriented transversely to the landslide body, carried out during the field study. The field apparent resistivity pseudosections were inverted to obtain a true resistivity structure using an algorithm based on the finite element forward and the least-squares inversion methods. The subsurface is divided in to rectangular blocks, the number of which is less than the number of resistivity data. The inversion method adjusts the resistivity model trying to iteratively reduce the difference between the calculated and observed apparent resistivity values. A parameter mesh for the case of 21 electrodes and n-separation of 6 for the used array is used. The number of parameter layers is set equal to the maximum n-separation of the measured data set and the thickness of each layer is set as 0.5 of the inter electrode spacing for array used. The number of parameters in every layer is eleven. Note also that the side and bottom parameters were set to be large to simulate infinite boundaries. The inverted resistivity sections show that the landslide body has different degrees of an altered material and a high degree of saturation. The sliding surface is at a depth of about 10 m, with 2.5 m of soil material overlying 7.5 m of landslide material. The landslide body has different degrees of an altered material and a high degree of saturation, and the sliding surface is at a depth of about 10 m. The relatively high resistivity values at the bottom of the sliding surface correspond to the marl layer.