بررسی ویژگی های زمین ساخت فعال در گستره رودبار با نگرش ویژه بر زمین لغزش های منطقه

منطقه پرجمعیت رودبار در شمال ایران، بدلیل شیب های تند توپوگرافی، مصالح سست پوشاننده شیب‌ها، فازهای تکتونیکی فعال، ساخت وساز جاده و راه آهن، ازمناطق مستعد رخداد زمین‌لغزش است. در این پژوهش، درفاز اول براساس پیمایش های زمینی، نقشه زمین‌شناسی درمقیاس1:25000، تصاویر ماهواره‌ای و دیگر داده‌های منطقه رودبار،محدوده و وضعیت زمین‌لغزش‌های منطقه شناسایی شد؛ عوامل ساختاری و وزنی( باربرداری شیب) بیشترین تاثیر در وقوع این رخداد را داشته و محرک اصلی در بیشترآنها، عامل ساختاری است. این مهم نیاز به تعیین و چگونگی فعالیت‌های تکتونیکی برای پیش‌بینی و کنترل پدیده‌ زمین‌لغزش در زیرساخت‌های عمرانی و زیست‌محیطی منطقه رودبار را ضروری می نماید. از این رو درفاز دوم پژوهش، از شاخص‌های ژئومورفیک سینوزیته جبهه کوهستان(smf)، نسبت پهنای دره به ارتفاع دره(vf)،شیب طولی رودخانه(sl)، شکل حوضه(bs) و عدم تقارن حوضه زهکشی(af) استفاده شد. سپس نتایج شاخص‌ها، به صورت شاخص فعالیت تکتونیک نسبی(lat)نشان داد که بیشتر زیرحوضه‌‌ها دارای فعالیت تکتونیکی شدید و متوسط است.از نظر گستردگی، طبقه‌ شدید با مساحت 198/05 کیلومتر مربع (67/21 درصد) ازکل مساحت منطقه را دربر می‌گیرد. تلفیق مکانی پهنه‌های زمین‌لغزش‌ های شناسایی شده در بخش اول پژوهش با پهنه‌های تکتونیکی استخراج شده در بخش دوم پژوهش، انطباق این پهنه‌ها در دو طبقه نشان می‌دهد. پهنه‌های رخداد زمین‌لغزش‌های فتلک، لویه، رودبار، فیلده، در پهنه‌هایی با فعالیت تکتونیکی شدید قرار گرفته و زمین‌لغزش‌های دشتگان، طلابر، تکلیم، نصفی، دولت‌آباد، هرزویل در پهنه‌های فعال تکتونیکی متوسط واقع شده است. برای جلوگیری ازخسارات آتی رخداد زمین لغزش و ارایه گزارش‌های دقیق تر برای هرگونه فعالیت عمرانی و زیست‌محیطی درمنطقه رودبار باید مطالعات تفصیلی مهندسی و زمین‌شناسی درمقیاس‌های بزرگ‌تر انجام گیرد. 

active tectonics of the roudbar region: with special reference to the landslides of the area

active tectonics of the roudbar region: with special reference to the landslides of the area tayebeh kiani, assistant prof. in geomorphology, kharazmi universitytayebeh.kiani@gmail.com hyrdad nadim, msc in environmental geology, geological hazards trends, geological survey & mineral exporation of iranhirad.nadim@gmail.com parastoo ghaforpur anbaran, ph.d student in geomorphology, kharazmi universityparastooghaforpur@yahoo.com   extended abstract:introduction: due to its specific morphology and extensive tectonic activities, roudbar rigion has always been affected by various geological hazards such as earthquakes, floods, biological pollution and landslides, which landslide is one of the most active phenomena in the region of this vast and mountainous area. within the roudbar geological sheet, 11 large and small landslides have been recorded with different yields and properties, some of which have catastrophic consequences, including the roudbar and fatalak landslides, which occurred as a result of the earthquake of june 31, 1990 has caused devastating events in the roudbar area and resulted in casualties and financial losses. extreme performance of tectonic phases, which enact a major role in landslides, construction factors, road and rail, steep slopes of topography, sloping loose materials, are a various factors in the occurrence of such landslides. due to the fact that landslide is predictive, preventive and sustainable, it is important to identify and zoning in the country and province and perform basic geological studies in prone araes to landslides with a large scale. due to the high potential of the region for the subsequent landslides and the properties of the intact areas with the old landslide areas, in present research, it is necessary to determine the most important factor in landslide occurrence in roudbar area through field investigations and based on that, plan management will happen for controlling landslide phenomenon. eventually, using geomorphic indices, the tectonic activity status of the roudbar region is determined, and with the adaptation of the location of landslides and faults with the tectonic activity zones map, relationship between tectonic and landslide are investigated. also, the risk zone, where there is a probability of landslide instability, is determined.method: the study area is located at 45 ° 36 ’to 30 ’45 ° 36’ north latitude and 30 ’22 ° 49’ to 49 ° 49 ’east longitude. roudbar is one of the southern cities of gilan province, which has a reputation for having olive gardens, and is named after its seasonal and permanent rivers. roudbar city leads to from north to rasht, south to roudbar alamut (from qazvin province), from east to lahijan and from west to fomen city. in the first phase, based on ground surveys and laboratory studies, the geological map in the scale of 1: 25,000 and other required data, limited area and condition landslides are identified on aerial photos and satellite imagery. in the second phase of this research, geomorphic indicators the mountain front sinuosity index (smf), the ratio of width to depth valley floor (vf), stream length index (sl), basin shape (bs), asymmetry factor (af) are used. then, the results of the indicators are presented as a tectonic activity index (lat).conclusion: based on ground surveys and laboratory studies, the geological map in the scale of 1: 25000 and other required data, limited area and condition landslides are identified on aerial photographs and satellite imagery. based on this, it was found that roudbar landslides were more affected by structural factors and weight (slope loading) has taken place. it seems structural factors hidden in most of the landslides in the region. based on the results of the tectonic activity relative index (lat), most sub-basins have high and moderate tectonic activity. in term of width, the intense class includes with 195.55 square kilometers (67.21%) of the total area. the integration of different tectonic zones with the location of the landslide zones of the region, the close relationship between the zones with intense and moderate tectonic activity with the landslide zones designated in the first part of this study shows that the zones with fatalak, lavie, roudbar, filde landslides are in areas with intense tectonic activity and the landslides of dashtgan, talabar, taklim, nesfi, dolatabad, herzavil are located in the moderate tectonic activity zone. based on ground surveys, the results of calculations of geomorphic indices indicate the relation between the activity of the land area and the landslide hazard. considering the inevitability of the faults’ activity and the resulting hazards, it is suggested that, in order to improve the country’s substructure development, more detailed and larger scales on the landslide mechanism introduced in this research (including determination of gradient safety factors (fs), calculation of the risk of slipping region and applying slope stability and safety methods, etc.), be done systematicly and in coordination with organizations and related departments.keywords: active tectonic, geographic information system, geomorphic indices, landslide, roudbar.