The effect of lithology and tectonic on the landslide occurrence and hazard zonation in the Dalanpar mountains, Zagros orogenic belt

The Dalanpar Mountains, located in the northwestern part of the Zagros Mountains, are highly active in terms of orogeny and morphology. Various types of landslides, such as successive landslides, rock falls, earth flows, and debris flows occur in this region. To assess the occurrence of landslides in this area, a combination of field geology and satellite imagery was utilized to identify landslides and perform susceptibility analysis based on the density area and the Landslide Numerical Risk Factor (LNRF) methods. Landslide hazard zonation maps indicate that the majority of landslides in the Dalanpar Mountains are in the high and very high hazard classes, and that geology, slope, slope aspect, precipitation, and land use factors have played significant roles in landslide occurrence. The high percentage of area under the success rate curves (AUC) for density area (72%) and LNRF (68%) methods demonstrates that both methods have accurately predicted the landslide susceptibility zonation map of the study area. Field observations indicate that lithological and structural factors are significant contributors to slope instability. Both field observations and landslide susceptibility analysis show that serpentinization plays a crucial role in slope instability, with most landslides occurring on serpentinite units. Reverse and strike-slip faults have significantly impacted the occurrence of landslides and increased the serpentinization process. Field observations reveal that large landslides have resulted in planar surfaces and depressions, where water has accumulated in some cases, creating seasonal and permanent lakes. The high activity rate and persistence of activity in the Dalanpar landslides indicate that, in addition to the usual factors affecting landslides such as slope and precipitation, they are strongly influenced by the behavior of the serpentinite units and fault effects in the diapirism system with the positive flower structure in the dextral strike-slip fault mechanism.