Landslide Susceptibility Analysis with Emphasis on Earthquake Impacts (Case Study: Karand to Sarpolzahab Corridor)

Document Type : Research Article

Authors

Hamid Ganjaeian ¹

Milad Firozeh ²

Ali Mirakhorli ³

Toktam Yazdani ⁴

¹ Ph.D. in Geomorphology, University of Tehran, Tehran, Iran

² M.Sc. in Urban Engineering, Urban Planning Major, Allameh Tabatabaei University, Tehran, Iran

³ Ph.D. Student in Geomorphology, University of Tehran, Tehran, Iran

⁴ Ph.D. in Geomorphology, University of Tabriz, Tabriz, Iran

10.22067/geoeh.2025.94360.1591

Abstract

Landslides are among the most significant hazards threatening many mountainous regions. One such high risk area, due to its geomorphological and tectonic characteristics, is the transport corridor between Karand and Sarpolzahab in Kermanshah Province. In this study, Sentinel-1 radar imagery, MODIS satellite images, the 1:100,000 digital geological map of the area, and the 12.5 m ALOS PALSAR Digital Elevation Model were used as the primary data sources. The main analytical tools applied included GMTSAR, Google Earth Engine, and ArcGIS. Using relative weight coefficient methods, fuzzy logic, and radar interferometry, landslide-prone areas were identified while considering the impacts of the Ezgaleh earthquake. Results indicate that vertical ground displacements in the study area ranged from −5 to 334 mm. Given that such displacements can significantly contribute to slope instability and trigger landslides, zones exhibiting both high susceptibility to landslides and vertical displacements exceeding 100 mm were classified as areas with the greatest landslide risk. Accordingly, mid-slope areas and those adjacent to Sarpolzahab city, owing to both their environmental susceptibility and substantial vertical displacements, were identified as the most hazardous zones in terms of landslide occurrence.
Introduction
Landslides are among the most destructive geomorphological hazards, involving the sudden or gradual movement of soil, rock or debris downslope under the influence of gravity. This phenomenon is particularly common in mountainous and steep terrains and can result in severe consequences, including infrastructure damage, loss of agricultural land, human casualties and disruption of transportation and communication networks. Landslide occurrence is influenced by both natural and anthropogenic factors. Natural triggers include intense rainfall, earthquakes, snowmelt, erosion processes and geological conditions, while human activities such as unplanned road construction, deforestation, landuse change, and construction on steep slopes can significantly increase landslide susceptibility. The impacts of landslides are not limited to physical damage but also extend to economic, social, and environmental dimensions. Economically, they impose substantial reconstruction costs and lead to the destruction of farmlands and infrastructure. Socially, landslides may cause fatalities, displacement, forced migration and a decline in quality of life. Environmentally, they contribute to vegetation loss, habitat destruction, and the formation of landslide dams. Therefore, landslides represent a multidimensional hazard that threatens both human security and environmental sustainability. Due to variations in geological, geomorphological, hydrological and topographic conditions, different regions exhibit varying levels of landslide susceptibility. Iran’s geographical setting has made large parts of the country prone to landslide hazards, particularly the western regions of Kermanshah Province within the Zagros mountainous belt. This area is characterized by steep slopes, high elevations, extensive transportation networks, and intense human activities, resulting in high vulnerability to landslides. Moreover, the active tectonic setting and frequent earthquakes, including the Mw 7.3 Azgaleh earthquake in 2017, have played a crucial role in slope destabilization. Beyond their immediate impacts, such earthquakes induce subtle changes that weaken slope stability and increase landslide potential. Accordingly, this study aims to identify landslide-prone areas along the transportation corridor between Kerend and Sarpol-e Zahab cities, with a particular emphasis on tectonic factors.
Material and Methods
This study utilized Sentinel-1 radar images acquired before (07/11/2017) and after (19/11/2017) the Azgaleh earthquake, MODIS satellite imagery from 2020 to 2024, 1:100,000 geological maps of the Kerend and Sarpol-e Zahab sheets, and a 12.5 m resolution ALOS PALSAR digital elevation model as the primary datasets. The main analytical tools included GMTSAR (version 6.0) for interferometric processing and ArcGIS for data standardization and map production. The research was conducted in three main stages. First, landslide susceptibility was assessed using eight parameters: distance to roads, distance to rivers, elevation, slope, aspect, lithology, distance to faults, and vegetation cover. All layers were standardized to a common scale ranging from 0 to 1. Weights were assigned to each parameter based on expert judgment from ten geomorphology specialists using the relative weighting method. In the second stage, the effects of the 2017 Azgaleh earthquake were evaluated using Differential Interferometric Synthetic Aperture Radar (DInSAR). Sentinel-1 images acquired before and after the earthquake were processed to calculate vertical ground displacement over a 12 day period. In the final stage, the landslide susceptibility map was integrated with the vertical displacement map. Areas exhibiting both high displacement and high susceptibility were identified as zones exposed to landslide hazard.
Results and Discussion
The results of this study indicate that the 2017 Azgaleh earthquake played a significant role in intensifying slope instability and increasing landslide susceptibility within the study area. The analysis of Differential Interferometric Synthetic Aperture Radar (DInSAR) data demonstrates that, beyond its immediate and visible impacts, the earthquake induced subtle but highly influential changes in slope structures. One of the most critical of these changes is the substantial vertical ground displacement, which can be considered a key factor in weakening the geomechanical equilibrium of slopes. Based on the vertical displacement map derived from Sentinel-1 imagery, ground surface deformation within the study area ranged from −5 to 334 mm. This wide range of displacement values reflects the heterogeneous response of different geological units and slope conditions to seismic stress. In particular, areas characterized by weaker lithological units, moderate to steep slopes, and proximity to active faults experienced the highest levels of vertical displacement. These findings are consistent with previous studies conducted in the seismically active Zagros region, which emphasize that earthquakes can alter slope structures and significantly increase the likelihood of subsequent landslides over short to medium-term periods. In this research, areas exhibiting vertical displacement greater than 100 mm were classified as unstable zones. The integration of these zones with the landslide susceptibility map revealed a strong spatial correspondence between areas of high landslide potential and zones affected by intense seismic-induced displacement. This overlap is especially pronounced in the midslope sections of the region and in the vicinity of Sarpol-e Zahab city. These areas are characterized not only by favorable geomorphological conditions for landsliding such as appropriate slope gradients, unstable lithologies, and sparse vegetation cover but also by direct exposure to earthquake-induced stress and deformation.
Conclusion
The results of this study demonstrate that integrating radar remote sensing data with multi criteria decision making models is an effective approach for identifying and zoning landslide prone areas in mountainous and seismically active regions. The application of the fuzzy gamma method for combining environmental information layers such as slope, lithology, elevation, distance to faults, and vegetation cover enabled the simultaneous analysis of multiple contributing factors while reducing uncertainty inherent in spatial data. The findings indicate that the central sections of the Kerend–Sarpol-e Zahab transportation corridor exhibit the highest landslide susceptibility due to their specific geological and geomorphological characteristics. The analysis of the 2017 Azgaleh earthquake using the DInSAR technique revealed that this seismic event played a decisive role in exacerbating slope instability. Significant vertical displacements, exceeding 100 mm in several locations and reaching much higher values in certain areas, highlight the profound impact of the earthquake on slope structures and stability. Although such deformations may not immediately result in landslide occurrence, they substantially increase slope vulnerability and predispose hillslopes to failure under subsequent triggering factors such as intense rainfall or smaller seismic events. One of the key contributions of this research is the demonstration of the importance of incorporating indirect and subtle seismic effects into landslide hazard assessments. The results show that areas experiencing vertical displacement greater than 100 mm particularly around Sarpol-e Zahab city and within the mid-slope zones fall into high and very high hazard classes. This spatial coincidence between environmental susceptibility factors and earthquake-induced deformation emphasizes the need to move beyond static landslide models toward dynamic, multi-source hazard assessment frameworks. Overall, the findings of this study provide a valuable scientific basis for landuse planning, infrastructure development, and disaster risk management in seismically active regions. The produced landslide susceptibility and hazard maps offer practical tools for decision makers to identify high risk areas and implement preventive measures such as slope stabilization, route realignment, and restrictions on construction activities in hazardous zones.

Keywords

Landslide Susceptibility

Earthquake

Earthquake-induced landslide

Remote Sensing

Slope Stability

Subjects

• Road hazards

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©2025 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

 

 

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