تاثيرات مورفوژنتيكي تكتونيك فعال بر زمين لغزش در حوضه جاجرود

Morphogenetic Effects of Active Tectonics on Landslide in Jajrood Basin

زمين لغزش به عنوان يك مخاطره طبيعي، همواره خسارات فراواني ر ا به همراه داشته است. شناسايي عوامل موثر در وقوع اين پديده و پهنه بندي خطرآن ، يكي از روش­هاي اساسي وكاربردي جهت دستيابي به راهكارهاي كنترل و پايش آن مي باشد. دراين پژوهش هدف بررسي ارتباط تكتونيك فعال و پتانسيل وقوع زمين لغزش درحوضه آبريزجاجرود به عنوان يكي از حوضه هاي كوهستاني كشور مي باشد. ابزارهاي اصلي پژوهش را شاخص هاي مورفوتكتونيكي تشكيل داده اند. اين شاخص ها به تفكيك در 39 زير حوضه جاجرود مورد بررسي قرارگرفته اند. نسبت تعداد زمين لغزش ها به تعداد زيرحوضه ها براي هرطبقه از IAT به دست آمد . پس از آن درجه سطح خطراحتمالي از كلاس هاي IATشناسايي شد. در نهايت ، خطر زمين لغزش براي هر زير حوضه بر اساس اثر تركيبي از سطح خطر احتمالي و فركانس وقوع زمين لغزش مورد بررسي قرار گرفت . نتايج نشان مي دهد كه تطابق خوبي بين كلاسIAT و نسبت تعداد زمين لغزش ها به تعداد زيرحوضه ها وجود دارد . حدود 85٪ از زير حوضه ها كه زمين لغزش در آنها رخداده در سطح زياد و بسيار زياد خطر قرار دارند ، در حالي كه از 27 زيرحوضه بدون زمين لغزش ، حدود 33 درصد در سطوح بالا و بسيار بالاي خطر قرار دارند . به‌ منظور صحت سنجي و ارزيابي دقت مدل از دوشاخص به نام‌هاي مجموع كيفيت (QS) و دقت روش (P)استفاده شد . مقدار مجموع كيفيت (QS) 97/0 و دقت روش (P) براي كلاس هاي خطر زياد و خيلي زياد 79/0 بدست آمد . مجموع كيفيت و دقت روش نشان‌ دهنده صحت يا مطلوبيت عملكرد روش در پيش‌بيني خطر زمين‌لغزش است . يافته ها نشان دادند كه حوضه جاجرود از نظرتكتونيكي بسيار فعال بوده و اين موضوع استعداد روانگرايي دامنه اي و زمين لغزش را به نسبت افزايش داده است.

Landslide as a natural hazard has always caused a lot of damage. Identifying the effective factors in the occurrence of this phenomenon and its risk zoning is one of the basic and practical methods for achieving its control strategies. The geomorphic setting of Alborz Mountain is a result of complex interactions involving neo-tectonic movements and processes of erosion and deposition. In this research, the aim of the study is to investigate the relationship between active tectonics and the potential of landslide occurrence in the Jajrood watershed as one of the mountainous regions of the country. The main research tools are Morphotectonic Indicators. Based on 10m-resolution DEM data, a total of 39 basins were extracted using ArcGIS . The Jajrood basin is up to the Latian dam with a total area of 949 km2, located between the latitudes 51 °,22ˊ),( 51 °, 51ˊ) East and the latitudes( 35 °,45ˊ),( 36 °,50ˊ) Is located . Geological and lithologic features of Jajrood basin and important fault systems such as Mesha-Fashem fault and North Tehran fault in this area, as part of the complex tectonic system of the southern Alborz, have caused the proposed basin to be a suitable place for evaluation of tectonic indices Be active. A total of 28 landslide were visually interpreted from satellite images and published documents. Seven geomorphic indices were calculated for each basin including the relief amplitude,(RA), hypsometric integral,(HI), stream length gradient,(SL), basin shape indices,(BS), fractal dimension, (FD),asymmetry factor,(AF), and ratio of valley floor width to height,(VF). These geomorphic indices were divided into five classes and the ratio of the number of the landslide to the number of the basins for each geomorphic index was computed and analyzed for every class. Average class values of the seven indices were used to derive an index of relative active tectonics (IAT). IAT values range from 0/64 to 5/79 with an average of 63/2 and a standard deviation of 1/07 is relatively active tectonic indication. Deviation from the relatively low benchmark shows that the tectonic activity in the study area is less affected. The ratio of the number of the landslide to the number of the basins was computed for every class of IAT. The landslide ratio to drainage basins for classes 4 and 5 is clearly has a relatively high frequency. The degree of probable risk level was then defined from the IAT classes. The degree of likelihood of a landslide hazard is generally high across sub-basins. Areas with a much higher probability degree are primarily distributed in the north and in the central region.Finally, the landslide hazard was evaluated for each drainage basin based on the combined effect of probable risk level and occurrence frequency of the landslides. The results show that there is a good agreement between the IAT class and the number of landslides to the number of sub-basins. About 85% of the sub-basins where landslides are occurring at high and very high levels, while Of the 27 sub-basins without landslides, about 33% are at high and very high levels. In order to validate and evaluate the accuracy of the model, two factors were used: total quality (QS) and accuracy (P). The total quality (QS) value was 0.97 and the accuracy of the method (P) for high risk and very high risk classes was 0.79. The sum of the quality and accuracy of the method indicates the correctness or usefulness of the method for predicting landslide hazard. The findings showed that the Jajrood basin was very active from tectonic viewpoint and this has increased the talent of landslide. These results indicate that the geomorphology conditions by active tectonics provide an important basis for studying the landslide hazard, although other factors also affect the occurrence of landslide.