Geoelectrical integrated models for determining the geometry of karstic cavities in the Zarrinabad area, west of Iran: combination of fuzzy logic, C-A fractal model and hybrid AHP-TOPSIS procedure

Abstract

The main aim of this study is to determine the location of the cave and cavities in Zarrinabad area, Lorestan province, west of Iran. For this purpose, a combination of hybrid AHP-TOPSIS procedure and content-area (C-A) fractal method has been conducted on three types of geoelectrical data derived from electrical resistivity, self-potential and mise-a-la-masse methods to detect karstic zones and determining the geometry of the cavities. Initially, the raw values of the data were transformed to [0–1] domain using the MSlarge fuzzy function, and then the fuzzified values were discretized applying C-A fractal model to separate different geological populations (e.g., conglomerate and limestone layers as well as the geometry of the cave). Subsequently, the analytical hierarchy process (AHP) as the most widely used multiple criteria decision making (MCDM) technique was applied for calculating meaningful weights and then assigning them to different fractal-based classes of investigation criteria (here, triple geoelectrical data) based on the expert knowledge. A decision matrix based on the calculated weights were constructed and TOPSIS as another well-known MCDM technique was then employed for generating cave potential model of AHP-TOPSIS procedure. In addition, a fuzzy Gamma model (gamma = 0.9) based on three fuzzified electrical layers is implemented to assess the AHP-TOPSIS model. Finally, for the evaluation of generated models, electrical resistivity sections along profile 1, 2 and 3 were prepared. The results exhibit a strong spatial association between final prospectivity models, electrical resistivity sections and the outcrop of the cave on the surface. According to the obtained results, a cave with dimensions of several meters (for example, its length in one direction is up to 100 m) is appeared to be expanded from the north of the study area to the south. Besides, it is possible that the karstic zones contain a number of small cavities which are linked together like a beehive. Thus, this area can be considered as a good source of underground water due to the presence of these holes which often contain fresh water. In addition, this area is prone to convert into a tourism area in the future as this cave contains high level water especially in rainy seasons.