Introduction

The slopes overlooking the metropolitan area of Tabriz are at high risk of landslides due to a combination of natural factors, including the presence of weak formations such as marl, steep slopes, and sufficient rainfall, as well as human factors such as urban development and road construction on unstable slopes. This phenomenon can lead to disastrous consequences, including casualties, extensive financial losses, and damage to infrastructure. Therefore, the main objective of this research is to prepare a landslide susceptibility zoning map for the slopes overlooking the metropolitan area of Tabriz using the MEREC (Method based on the Removal Effects of Criteria) multi-criteria decision-making method within a Geographic Information System (GIS) environment. This study aims to identify and prioritize areas with high potential for landslide occurrence by considering key effective criteria, including geological formations (especially weak marls), slope, rainfall, distance from faults and rivers, as well as human development indicators such as distance from roads and land use. The results of this research provide essential and necessary information for risk management, sustainable urban development planning, and the implementation of landslide mitigation measures in this sensitive region.

Methodology

The study area of the present research is the slopes overlooking the metropolis of Tabriz. The study area is located at latitudes between 38° 02΄ and 38° 10΄ North, and at longitudes between 46° 11΄ and 46° 23΄ East.

The present study was conducted with the aim of preparing a landslide susceptibility zonation map for the slopes overlooking the metropolitan city of Tabriz, using the MEREC method and GIS. To this end, twelve effective criteria were employed, including lithology, slope, aspect, elevation, precipitation, land use, vegetation cover, distance from fault, distance from road, distance from river, Stream Power Index (SPI), and Topographic Wetness Index (TWI). The data were extracted from various sources such as the Digital Elevation Model (DEM), geological maps, Landsat 8 satellite imagery, and precipitation data, and were prepared in the form of information layers.



Results and Discussion

The results of the criteria weighting process indicate that the lithology criterion, with a relative weight of 0.164, is the most determining factor in slope instability and the occurrence of landslides in the region. Subsequently, the criteria of distance from road (0.124), mean annual precipitation (0.118), and slope (0.112) were ranked. In contrast, the aspect and stream power index criteria were identified as the least influential factors in this analysis. To produce the final landslide susceptibility map, the effective informational layers, after being assigned relative weights for each criterion, were integrated within the Geographic Information System (ArcGIS) environment. Based on the final map analysis, the northern slopes of Tabriz, particularly the Einali highlands, fall within the high and very high-risk categories. This situation is attributed to the presence of weak and unstable formations, such as marls in these zones, coupled with the steep slope gradients, which have significantly reduced the natural stability of the land. On the other hand, human activities have also played a significant role in increasing the landslide risk. The construction of the Pasdaran Highway at the foot of these slopes has caused a loss of slope equilibrium and intensified instability along its path.



Conclusion

The results indicated that weak formations such as marls, the steep slopes of northern Tabriz, and human activities including road construction are among the most important factors of instability in this region. Analyses performed on twelve key criteria clearly revealed the prominent role of geological and human factors in the instability of the region's slopes. The most significant finding of this study was the identification of lithology as the most influential criterion (with a weight of 0.164). The presence of weak and erodible formations, particularly marls on the northern slopes of Tabriz, has provided the primary foundation for landslide occurrence. Subsequently, the criteria of distance from roads (0.124), precipitation (0.118), and slope (0.112) were ranked next, indicating the combined influence of construction activities and natural factors in exacerbating this hazard. The construction of roads and highways such as the Pasdaran Highway has disrupted slope equilibrium by creating slope cuts and altering the natural drainage pattern. On the other hand, regional precipitation acts as a triggering factor; by infiltrating weak subsurface layers, it increases pore water pressure and reduces slope stability. The final susceptibility map clearly revealed the spatial distribution of high-risk areas. The concentration of high and very high hazard zones in the northern highlands of the city, particularly in the Einali (Aun-bin-Ali) Mountain range, poses a serious warning for the future development of the city and the safety of residents in these areas. The significant concordance between recorded historical landslides (such as those along the Pasdaran Highway) and the high-risk zones identified in this research strongly confirms the accuracy and validity of the presented model.