Investigation of layer differences with DC resistivity method

ABSTRACT Properties of the Five-Electrode Configuration which is formed through using the combination of Half and Full Schlumberger configurations, were investigated, and the economical aspects were also analysed for the geophysical electrical investigations with respect to minimum cost and maximum productivity through carrying out lateral and vertical measurements at the same time. It was also compared with the dipole electrode configuration that has been used widely for lateral variation investigations. Information could be obtained about the location, position and situation of the structure from the shape of anomaly with the help of maximum and minimum points for the lateral investigations (Profile measurements). Information could be obtained about the layer thicknesses and resistivities from vertical electrical soundings by using the transformation properties between resistivity transform function and apparent resistivity function. All the apparent resistivity values obtained from the lateral and vertical electrical measurements, are the averages between the current electrodes affected by the total field. Differences between the apparent and real resistivity values increase as the averaged area being larger. In order to reduce this difference, the investigation should be increased as well as the area being narrowed. Measurement intervals must be made small too. These affect the measurement time and costs. Two lateral and one vertical measurements could be taken together with this electrode configuration at one point. Three different apparent resistivity values could be obtained at the same point. Lateral and vertical resistivity variations of the medium could be investigated in details through the mathematical evaluations. According to the image techniques, certain special conditions should be fulfilled in order to determine the location and properties of the structure exactly obtained fromthe theoretical studies about the lateral investigations. Electrode spacing and measurement interval selections must be observed very well in order to obtain the best anomaly describing the body. These spacings must be less than the structure depths and widths. In order to obtain the parameters of depths and resistivities determined from the vertical electrical soundings with the minimum level error, the averaged area affecting the apparent resistivity values should be small. Half Schlumberger configuration should be used instead of the full Schlumberger configuration to reduce the area under consideration for these kinds of works. Here, the medium parameters were also obtained from the evaluation of the Half Schlumberger vertical electrical soundings. Five-electrode configuration that has been used for lateral and vertical investigations was tested initially on the theoretical model structures. After these tests, the important parameters were found to be electrode spacing, measurement interval and profile length affecting the measurements. Electrode spacing and measurement interval should be chosen smaller than the structure width, whereas the profile length must be longer. In this study, there are three different field-work to test theoretical results. Kösemtuğ Tûmûlüsü-B ANDIRMA which is known before the structural charateristic of it, Dutlimam-B ANDIRMA, Şoförler Sitesi - ÖDEMİŞ which is lasted now. In conclusion, Five Electrode Configuration supported all of our prescience therefore this configuration is convenient to use.