Landslides are one of the most common geological hazards worldwide, with the characteristics of wide distribution, high frequency, fast movement speed, and serious natural disaster casualties. Out of 40 different types of natural disasters experienced in different parts of the world, about 31 types of natural disasters have been identified in Iran, including frequent severe earthquakes, floods, droughts, landslides, etc. Desertification, deforestation, storms, and the like have been recorded. Due to the abundance, diversity, frequency, intensity, and environmental disturbances, Iran is among the top ten countries facing natural disasters with an average of four events per year, according to global estimates. Landslides are acute natural disasters such as earthquakes, volcanic eruptions, and floods. They cause significant damage to the areas affected every year .

Methodology

In the first step, data from land points were collected and examined using historical documents, field studies, and Google Earth software, which recorded a total of 129 landslide points in the Shahid Abbaspour Dam catchment area, 27 landslide points in the northern Deh Sheikh basin, and 102 landslide points in the southern Deh Sheikh basin. In the next step, as can be seen in the flowchart of, 15 environmental parameters were selected to identify factors affecting the occurrence of landslide risk, including altitude, slope, slope direction, geology, land use, soil texture, distance from fault, road, and river, topographic moisture index, slope curvature, river erosion index, average annual precipitation, and NDVI. The altitude, slope, slope direction, and slope curvature indices were prepared using the ASTERGDEM digital elevation map with a spatial resolution of 30 meters in ARCGIS 10.8 software.

MaxEnt or Maximum Entropy is a machine learning model that quantitatively calculates the probability of landslide occurrence using Bayesian law based on geological environment indicators - educational landslide . The specific calculation principle of this algorithm is based on the fact that the study area is divided into a finite pixel set X, assuming that x represents each computational unit. Then, x∈X in the study area and π(x) represents the probability value of the landslide occurrence distribution in each computational unit 0<P(x) < 1. The sum of the probability values of all computational units is equal to 1. The calculated grid slip value is taken as the response variable 1, otherwise the response variable is y, otherwise, it is the unit y. Therefore, the conditional probability distribution of landslide P(y|x) can be expressed as

P(y=1|x)= (P(x│y=1)P(y=1))/(P(x)) ̧



Results and Discussion

After preparing the landslide impact indices in ArcGIS software, the layers in ASCII format and the landslide length and width points in Excel file format in SVC format were entered into MaxEnt software, finally the results of the percentage of participation and importance of each parameter in the model were examined. (Figure 3). The Shahid Abbaspour Dam catchment area has a uniform rainfall (28.41) percent in the range between (2000 and 2200 mm) and does not have much effect on the drift. However, in the range (2600 mm) the landslide is high and after this range it decreases and again in the range of rainfall (3200 mm) the landslide impact increases. Geological formations (20.99) percent, the response curve shows the highest Quaternary and Gachsaran sediments and the lowest role in landslides. Distance from the road (13.93) percent, distance from the fault (9.37) percent, the trend of the curve at distances less than (5000) meters, the landslide reaches its peak and the greater the distance from the landslide(5000 <) the landslide decreases.

In order, the highest percentage of participation and response curve of the parameters of the northern Deh Sheikh watershed are land use (14.07)percent, residential areas index, uncovered land bed, water areas, agriculture have the greatest impact on the risk of landslides, and pastures and forests have the least impact on the occurrence of this phenomenon. Distance from the road (13.88) percent, distance from the river(12.39), the trend of the response curve at distances less than (5000) meters, the landslide is greater. The erosive power of the river is(11.09) percent, the response curve is located in the range near (1) and has an increasing trend, and gradually after the range(1) it has a decreasing trend and increases with the increase in the landslide phenomenon. The southern Deh Sheikh basin has the highest percentage of participation and the response curve of the geological formations parameter (24.99) percent, and the response curve shows the highest Quaternary sediments and Gachsaran and the Bakhtiari Formation respectively, and the greatest role in landslides. Distance from the road (19.93) percent, distance from the river(10.40), the curve trend increases at distances less than(5000) meters, the landslide increases.Precipitation (10.39), in the range (2600 and 3200 mm) landslides increase.

Conclusion

By producing and classifying the landslide zoning map of the studied basins, it was concluded that the highest landslide hazard class of the Shahid Abbaspour basin is the high hazard class With an area of (78.08) square kilometers and (30.19) percent, High landslide hazard is mainly distributed in the southern and central parts of the basin near villages that have experienced heavy human activities and the construction of roads and tunnels is mostly on soft and vulnerable Quaternary and Gachsaran sediments. The northern Dehsheikh basin has a medium hazard class With an area of (79.55) square kilometers and (40.21) percent, This basin has less vulnerable formations than the other two basins. However, the location of Karun Dam I as a result of land use change, especially near the upper valley, has intensified landslides. And the southern Dehsheikh basin has the highest landslide area in the very high risk class with With an area of (79.84) square kilometers and (33.21) percent. The southern Dehsheikh basin has the most vulnerable formations (Quaternary, Gachsaran) compared to the northern Dehsheikh basin. The location of Karun Dam 2 to 4 and the numerous tunnels built near Karun Dam (4), the concentration of residential areas and especially the many communication roads, especially compared to the northern Dehsheikh basin, have caused the landslide risk to be in the very high risk class.