İstanbul Avcılar Heyelanı Üzerinde VLF ve ERT Yer İletkenlik Modellerinin Kıyaslanması

Abstract

VLF and ERT methods are widely used for investigating the resistivity distribution in the first few ten meters of the earth. VLF method provides rapid and low-cost measurements; however, the low frequency count and the relatively narrow frequency band provide a lower depth of investigation, compared to that of the ERT method. Hence, ERT is amongst the most employed methods in the landslides areas where sharp resistivity contrasts are generally observed. To investigate the performance of the 2D inversion results of the VLF data on landslide areas, VLF-EM and ERT measurements are acquired on two parallel profiles. Besides, VLF-R measurements are performed on the northeastern end of the VLF-EM profile. The measured data are modeled and interpreted individually, using 2D smooth inversion algorithms. The results suggest that conductive zones and the sliding surface of the landslide are delineated using the VLF method. Accordingly, conductive clays of the Gürpınar formation, consisting of the sliding surface, are delineated between 15-20 m depth. Due to the sensitivity of the VLF-EM data to the horizontal conductivity differences, the conductive alluvium cover is not delineated from the VLF-EM data. In the northeastern part of the study area, clays of the Gürpınar formation are observed to be approaching to the surface, detected from both VLF-EM and ERT models. In the northeasternmost part of the study area, VLF-EM model failed to detect the alluvium cover separately from the conductive clays at ~3-10 m depth. However, due to the higher vertical resolution obtained from the VLF-R measurements, these conductors are successfully identified by the VLF-R model.