The study area is located in the northeastern part of Isfahan province, within the Na’in county, between the Khur and Bayabanak regions, and Ardistan, on the 1:100,000 Anarak geological map sheet. It lies between geographical longitudes ‘30°53’ to ‘54’ and latitudes ‘30°33’ to ‘33’.
The study was conducted using satellite image processing techniques with Landsat 7 (Enhanced Thematic Mapper Plus - ETM+) and Landsat 8 (Operational Land Imager - OLI and Thermal Infrared Sensor - TIRS) sensors. The following techniques were employed:
1. Band Ratio: Used to mitigate topographic and shadow effects and enhance mineral visibility.
2. Normalized Difference Vegetation Index (NDVI): Highlighted vegetation in the area.
3. RGB Color Combination: Separated lithological units based on color.
4. Filter Applications (Sunangle, Highpass, Edges): Enhanced fault lines, boundaries, and sharp edges.
5. Digital Elevation Model (DEM): Utilized ASTER DEM at a 1:10,000 scale to create a 3D model of the region, enhancing visibility in valleys through shadow creation.
6. Principal Component Analysis (PCA): Reduced data dimensions while preserving information. This method was used for identifying geological faults using seismic or magnetic data.
7. Aerial Geophysical Data: Analyzed 7.5-kilometer data to examine the total magnetic field intensity map, determine the location and subsurface status of magnetic bodies, and identify magnetic lineaments and both visible and concealed faults.
8. GIS Layer Evaluation: Assessed and evaluated information layers obtained in the Geographic Information System (GIS).
9. Field Survey: Conducted field visits to familiarize with the study area, correlate available information with field observations, and accurately identify and differentiate lithological units and their relationships, especially fault zones.
Geological investigations, remote sensing, aerial geophysics in the GIS environment, and field operations within the study area revealed that the density map of fault lineaments significantly influences the erosion-deposition trend in the southeastern part of the region, particularly in areas of faulting. Further analysis of regional tectonics indicated that the final thrust faults control the regional tectonics.
Based on geological investigations, remote sensing, aerial geophysics in the Geographic Information System (GIS) environment, and field operations within the study area, it has been determined that the lineament density map significantly influences the trend of land loss in the southeastern part of the region. This map is particularly indicative of substantial variations in fault lineament density, especially in the faulted regions.
After examining the tectonics of the area, it was found that the final emplacement of faults controls the regional tectonics. According to calculations of fault slip potential, in each section of the regional faults, two faults—Shurab and Doldol—have the highest slip potential. In other words, the northeastern segment of the Doldol fault exhibits a higher seismic rate compared to other sections. Remarkably, recent seismic activities in the region have occurred primarily near the major fault zones.
The seismic rate gradually increases toward the northern terminus of the Jombay faults, while conversely, in the southeastern part of the region, the maximum slip potential is observed for the Turkmeni-Arba’id, Kuh-e Pol Khavand, and Baybank faults. Additionally, the Anarak fault experiences an elevated seismic rate toward its northern-southwestern terminus.
The active fault trends in the study area reveal a northwest-southeast pattern, consistent with data obtained from field surveys. Considering the average slip rates of regional faults in recent years and results from previous studies, the northern-southwestern segment of the Anarak fault (from Anarak to the Shurab fault in the Talmasi section) has been identified as an area with the highest likelihood of future sliding. The northern-southwestern half of the study area is associated with the most significant fault slip potential, and tectonic structures in the northwestern-southeastern regions represent the youngest neotectonic activities. Remote sensing data were effectively utilized to display lithological and structural alterations.
In the studied area, which includes 198 lineaments (from remote sensing studies) and 18 digital faults from the geological map of Anarak, with a length of over ten kilometers, as well as 9 probable magnetic faults, the majority of these lineaments are observed in the southwest region. However, these lineaments do not correspond to any fault features on the geological maps. The magnetic lineaments are well-aligned with the structural faults on the geological map, except for lineaments F-586, F-416, F-417, F-698, and F-701, which do not have any equivalent fault representation on the existing maps.
All 198 lineaments require field studies, and most of them are associated with alluvial deposits. These lineaments could potentially represent new geological features. A very high correlation was observed after overlaying the lithology map with the geological map.