Introduction

Mass movements are a particular type of natural and formative phenomena within the domain of geomorphological, hydrological, and local geological conditions. Among mass movements, landslides and rockfalls are of special significance due to their extensive nature. Landslides represent the most important type of slope hazards, involving the downslope movement or relatively rapid displacement of sediments along slopes or sliding surfaces. Over the years, various techniques and methods have been developed for mapping landslide susceptibility and have been utilized in the literature. Landslide susceptibility maps can be prepared using quantitative or qualitative approaches.The Pataq Pass, serving as a transportation axis between Kerend and Sar-e Pol-e Zahab in Kermanshah province, is prone to mass movements such as landslides and rockfalls. During the 7.3 magnitude earthquake on November 11, 2017, in Ezgele, Kermanshah triggered by the seismic activity, landslides and rockfalls occurred in the region, blocking the transportation axis between Kerend and Sar-e Pol-e Zahab (Pataq Pass). This event posed challenges for providing assistance to urban and rural areas. Hence, it is deemed highly necessary to identify areas susceptible to mass movements to prevent risks and mitigate financial, human, and environmental damages through protective and preventative measures. Therefore, this current research aims to investigate and map the areas prone to mass movements, including landslides and rockfalls, along the transportation axis of Pataq Pass. The preparation of landslide and rockfall zoning maps will be conducted using the Weighted Linear Combination (WLC) method and GIS technique. The objective of this study is to create landslide and rockfall susceptibility maps to develop appropriate strategies for reducing the hazards of landslides and rockfalls. The findings of this research will assist residents/local communities at risk, urban planners, and engineers in reducing present and future damages caused by existing and potential landslides.

Methodology

In this study, various criteria have been used for the zoning of landslide and rockfall hazards. These criteria include slope, aspect, curvature index, geographic latitude, distance from roads, and distance from faults, land use, and geology. Considering that some of these criteria have a direct relationship and others have an inverse relationship with the research output, the data layers have been transformed to an appropriate scale to be able to be integrated. After standardizing the data, the Analytic Hierarchy Process (AHP) model and binary comparison matrix, along with the opinions of experienced university professors, have been used to determine the influence and importance of each criterion on the research output. Subsequently, using ExpertChoice11 software, the final weights of each criterion have been calculated. Finally, for the zoning of the study area, the Weighted Linear Combination (WLC) method has been employed. This method, by assigning weights to the criteria, helps in achieving a higher accuracy in determining the hazard zones for landslides and rockfalls. These analyses and their resulting outcomes serve as an effective tool in making appropriate decisions for reducing the risks of landslides and rockfalls in the study area.

Results

Based on the results of zoning the landslide hazard in the slopes overlooking the Pataq Pass in the central and northwestern areas of the study area, it is characterized by a very high risk of landslides. According to results, approximately 42.96 square kilometers (17.89%) of the area is covered by areas with a very high risk of landslides. The largest area belongs to the moderate hazard category, accounting for 91.43 square kilometers (38.08%). In terms of rockfall occurrence, a small percentage of the study area, around 0.01 square kilometers (0.01%), is located in areas with very low risk, while the majority falls within areas with moderate risk, covering an area of approximately 102.21 square kilometers (43.63%). The areas with a very high risk encompass the central regions along the Pataq Pass in the study area. Furthermore, we observe more severe destruction in areas located on separate quaternary units compared to areas situated on harder units like limestone formations. As evidenced by the earthquake on November 12, 2017, in Ezgele, Kermanshah Province, regions with separate quaternary units experienced greater damage due to their lower resistance and the intensity of seismic waves, leading to landslides and collapses in the area. The consequences of this earthquake and the varying resistance levels of geological units, steep slopes, mountainous terrain, sparse vegetation cover, and active faults confirm the necessity of conducting extensive studies on mass movements in the region.
 

Discussion

Based on the zoning results of the study area according to the Weighted Linear Combination (WLC) model and the earthquake reports of November 12, 2017, in Ezgele, Kermanshah, the Pataq Pass is prone to landslides and rockfalls, and the occurrence of this hazard has caused damage and losses to the region; thus, it requires serious attention from officials and the implementation of fundamental and control measures to reduce the frequency and resulting damages. Among these measures, identifying and zoning areas at risk of slope movements using modern methods along with employing geographic information systems and remote sensing, implementing biological and mechanical measures in high-risk areas can be highlighted.
 

Conclusion

The results of this study indicate that in areas with high elevation and rough topography, steep slopes, and sparse vegetation cover, the potential for landslide hazard is higher. In the Aghajari geological units, especially in the northern-facing slopes or northern domains, the occurrence of landslides increases. The presence of gypsum-bearing marls in this formation has made it susceptible to erosion. Additionally, in Quaternary sediments that cover parts of the northwestern areas within the Sarpol-e Zahab region, in areas with steep slopes and roughness, the potential for landslides increases. Given the mountainous nature of the region, phenomena such as freezing and expansion of rocks and weathering exist, which create conditions for the formation of fractures and rock fissures on the slopes. In the event of seismic shaking from an earthquake, the likelihood of rockfall occurring in these areas increases.