ارزیابی خطر زمین‌لغزش با استفاده از نظریه دمپستر شیفر (مطالعه موردی: بخشی از حوزه آبخیز تالار)

زمین ‌لغزش یکی از انواع ناپایداری های دامنه ای است که هر ساله خسارت های مالی وتلفات جانی فراوانی را بر زندگی انسان ها وارد می کند و از جنبه های مختلف ژئومورفولوژی ، فرسایش و رسوب در حوزه های آبخیز مهم تلقی می شود. در این تحقیق عوامل موثر بر وقوع زمین لغزش از قبیل شیب، شکل شیب، ارتفاع، کاربری اراضی، سنگ ‌شناسی، فاصله از جاده، فاصله از آبراهه، فاصله از گسل، شاخص حمل رسوب و شاخص رطوبت توپوگرافی منطقه بررسی شد. سپس با استفاده از تئوری دمپستر شیفر، نقشه ی خطر زمین ‌لغزش در بخشی از حوزه آبخیز رودخانه تالار تهیه شد. به منظور ارزیابی روش دمپستر شیفر نیز از منحنی roc استفاده شد. نتایج نشان داد که بیشترین درصد حساسیت به زمین ‌لغزش ‌ها در طبقه شیب 155 در جهت های غرب، جنوب و جنوب ‌غرب در ارتفاع 1000-500 و کاربری جنگل و در فاصله کم از جاده، آبراهه و گسل صورت گرفته است. همچنین بیشترین درصد زمین لغزش، مربوط به کلاس 0.3-0.1 شاخص ndvi است. شاخص‌ های طول شیب و رطوبت توپوگرافی نیز روند مشخصی نشان ندادند. در نهایت، نقشه حساسیت خطر زمین ‌لغزش در منطقه نیز به ترتیب در کلاس های حساسیت کم 16.53 درصد، متوسط 33.33 درصد، زیاد 33.94 درصد وخیلی زیاد 16.18 درصد قرار گرفته‌ است.

Landslide Hazard Assessment Using Dempster-Shafer Model (Case study; part of Talar watershed)

Extended abstract1 IntroductionLandslides are natural hazards that destroy nature and often cause severe damage to natural resources and loss of life and human property (Intaravichin and Dasananda, 2010; Feyzzadeh et al., 2013). Despite significant advances in risk analysis and landslide risk management, this natural hazard remains a real threat to the lives and property of people in mountainous areas (Getz et al., 2011). Natural factors affecting landslides can be rainfall, lithology, slope, and the like (Talebi and Niazi, 1390). Among the natural factors affecting the occurrence of landslides, we can mention factors such as rainfall, lithology, slope, and the like (Talebi and Niazi, 1390). In general, Iran is considered a highrisk country due to favorable geographical conditions, lack of comprehensive environmental management, and noncompliance with environmental thresholds. Approximately 38 hazards have been identified and recorded in Iran, and due to the multiplicity, diversity, recurrence, and severity of natural hazards and environmental unrest are among the ten most prosperous countries in the world (Mohammadi et al., 2004). Considering landslide hazard zoning map is essential for a proper understanding of its mechanisms in recent research (Sun, 2014).2 MethodologyIn order to prepare a landslide susceptibility map using DempsterSchiffer theory, first, using the landslide database, the General Department of Natural Resources of Mazandaran province, and field studies, landslide points in the region were identified. During the field observations, the accuracy of the collected information was evaluated, and the position of the landslide points was checked using the Global Positioning System (GPS), and 26 new landslides were recorded. A total of 134 slide points were examined. In this research, 12 information layers including altitude map, slope direction, slope degree, slope shape, distance from fault, distance from road, land use, geology, distance from waterway, Slope length or sediment transport index (STI), topographic moisture index (TWI) and vegetation were prepared and classified using ArcMap and ENVI software using 1: 50,000 topographic maps, 1: 100,000 geology, geology and satellite imagery, IRS for 2012. In order to evaluate the DempsterSchaefer theory in landslide risk analysis, the relative performance curve of the relative efficiency of variables (ROC) is used. ROC curve analysis is used to determine the accuracy and efficiency of the model (Egan, 1975; Soots, 1988; Williams et al., 1999). This curve is one of the most efficient methods in providing diagnostic properties, probability identification, and prediction systems that quantitatively estimate the modelchr('39')s accuracy (Soots, 1988). The area under the ROC curve represents the prediction value of the system by describing its ability to accurately estimate its occurrence events (landslide occurrence) and its nonoccurrence events (nonlandslide occurrence). Therefore, the area of ​​the curve is used as a measure of the accuracy of the model. In this study, out of 134 slip points, several points were used for modeling, and part of it was used to evaluate the model (with a ratio of about 70 to 30%) (Matthew et al., 2007; Pourghasemi et al., 2009; Constantine et al., 2010).3 Discussion ConclusionsThe study of the slope factor shows that although the highest percentage of landslides is related to the class of 1530 degrees with 52.127 percent, which is consistent with the views (Moradi et al., 2010). However, the highest weight is related to the class of 515 degrees, which can be attributed to road construction and unprincipled constructions that have caused the slope to be cut in the region. No landslides have been observed or recorded in areas with a slope above 50 degrees, which can be due to the rocky outcrop and the lack of soil layer in the high slopes. According to the results of this study, the western and southern slopes with 19.15% and 18.1%, respectively, had the highest percentage of landslides in the region, which with the results of studies (Pour Ghasemi et al., 2009) and (Lee, 2007) corresponds. The study of altitude factors indicates that the altitude class of 1000500 with 56.38% of landslides, the highest number of landslides, and the altitude class of 0500 have the highest weight, also, with increasing altitude in the study area, the sensitivity to landslides decreases, which is consistent with the studies of Moradi et al. (2010) and Pourghasemi et al. (2011). At altitudes above 2000 m, no landslides have been observed or recorded, which indicates a decrease in sensitivity to landslides with increasing altitude (Moradi et al., 2010). The highest weight for the geological factor belongs to group 1, which includes deposits and unhardened alluvial deposits of the Quaternary period, while the highest percentage of landslides occurred in the units. The lithology of the Shemshak Formation is located at 37.23%, which is consistent with the views (Naji, 2006), (Shadfar et al., 2008), (Pourghasemi et al., 2011). The study of the linear element of the distance from the waterway has shown that because the highest percentage of landslides occurred at a distance of more than 400 meters at the rate of 31.915%. However, the highest weight in calculations by class is allocated 0100 meters, which is in accordance with the opinions (Pourghasemi et al., 2009), (Dokota et al., 2013). Investigation of the distance from the road showed that the highest percentage of landslides occurred at a distance of more than 500 meters (30.85%); however, the highest weight in the calculations to the class 0100 for the distance from the road is allocated which is consistent with the results of studies of Mazouki et al. (2011), Pourghasemi et al. (2009, 2012).