Application of Morphotectonic Indices in Landslide Hazard Evaluation of Lorestan Railway

Landslides are among the natural hazards that cause the greatest damage to vital transportation networks, including rail lines, and after the events such as the departure of the train from the rails and the destruction of the infrastructure, they have the most financial losses dedicated. This factor has always caused the problem of the operation of the rail transport system and reduced the reliability of its customers. Therefore, the identification of predisposing factors, and areas with potential landslide hazard can help to secure and reduce the risks posed by this phenomenon. In addition to lithology, morphology and climatic conditions, the tectonic activity and seismicity are considered as one of the most important triggering factors of landslides. In this regard, a large number of studies were conducted around the world indicated that landslides occur frequently in tectonically active areas. In fact, many geomorphologic landforms are very sensitive to active tectonic movements and change concurrent with them. Thus, recognizing the tectonic characteristics of a region contributes to a better understanding of geomorphic processes. The Lorestan Railway is part of the north-south railway of Iran that is 215 km long. It extends from the Momenabad Station in Markazi province to the Tang-e-Haft Station in Khuzestan province and goes across high Zagros Mountains located in the geographical coordinates of 48°, 15' to 49°, 05 ' E, and the latitudes of 32°, 25' to 33°, 30' N. This region has specific characteristics in terms of slope instability and related geomorphological phenomena due to local and region al characteristic of the active Zagros orogenic belt.
The data of this research included topographic maps with 1: 25000 scale received from the National Cartographic Center, 30 meters’ digital elevation model (DEM) achieved from USGS, geological map of 1: 1000000 scale of Lorestan province, field survey from the studied area in 2019, and 35 samples have been taken. The research methodology includes tectonic indicators that show the region's activity in terms of tectonics and the correlation between the occurrence of landslide phenomena, and tectonic activity. The tectonic indices used include the hypersonic and integral hysterometric (HI) curves, drainage asymmetry (AF), topographic symmetry (T), stream length gradient (SL), valley floor width-valley height ratio (VF) The V ratio index and basin shape index (BS) are calculated for each sub-basin. The classification of the indices was also carried out according to Hamdoni et al. Classification. The land status of the region was determined using the tectonic activity (lat) partial evaluation index. Then, the indices were standardized by Z-score method due to lack of homogeneity in the scale. A quantitative relationship between observed slides and tectonic indices in sub-basins was calculated by analysis of variance.
The activity of the sub-basins was tectonically investigated using the Iat index. According to the classification of Hamdoni et al., ​​the study area, were divided into three tectonic activity classes (3-2-1). The number 1 represents the highest neo-tectonic activity, and the number 2 is neo-tectonic, semi-active and moderate, and the number 3 is low and inactive. According to the results obtained from this indicator, in basin number 12, 3 ,1 the tectonic activity is high and in the rest of the basins, tectonic activity is high to moderate. In the basins above the 3rd index, field observations with slip samples are not found. According to field observations, more than 80 percent of the total landslide in the region between the Dorood to Tang-7 stations lies in the range of tectonic activity to a large extent, which indicates the effect of land-based construction on the frequency of landslides in the area. Most field observations have been observed around railways in basins 12 and 5, while field observations are considered in basins 12.3 and 5, which can be concluded that the construction of railroad slopes and slopes of the Slide potential range in Basin 5 has increased and the condition of crossing the railways of Basin 3 is more appropriate. The basin covers 12 major parts of the Cham - sengr station - the country and the basin - covering a large part of the Qaron-Bizeh stations that are also involved with the flood issue every year. Variance analysis was used to establish a quantitative relationship between the observed landslides and tectonic indices in the sub basins. Due to the lack of homogeneity of the indices in the number range, the Z scale was standardized and to establish a relationship between indices and perceptions you know, its linear regression model was calculated.
The results of this study showed that the studied area is young in terms of neotectonics activity, but the activity level is not the same in all places, so that basins number 12, 3 and 1 have the highest tectonic activity, and basins number 13, 11, 10 and 9 have relatively less activity. The maximum landslide occurrence has been observed around railways in the 12th and 5th basins, but field surveys have shown more specimens in the 12.3 and 5 basins, which may have increased rail slots and slopes in the basin area 5 And the railways in the basin 3 have better conditions. In general, based on the morphological indices, field evidence and the regression model of the slide and tectonic relationship, it is suggested that sufficient attention be paid to the slopes and ditches.