تحلیل مخاطرات لرزه ای حوضه آبریز تالار و بابل رود بر اساس ارزیابی شاخص های مورفوتکتونیک

علمی که تاثیر تکتونیک فعال را با استفاده از شاخص های ژئومورفیک به عنوان سنجش و توصیف کمّی اشکال و چشم اندازهای زمین مشخص نماید، مورفوتکتونیک نامیده می شود؛ اندازه گیری های کمی شرایطی را فراهم می آورد تا با استفاده از آن ها به شناسایی وضعیت مناطق دارای زمین ساخت فعال پرداخته شود. در این مطالعه با استفاده از شاخص های کمی ریخت سنجی بخشی از البرز مرکزی که در محدوده حوضه های آبریز تالار و بابل رود قرار دارد مورد بررسی قرار گرفته است و 5 شاخص ناهنجاری سلسله مراتبی (∆a)، انشعابات (r)، شکل حوضه (ff)، تراکم زهکشی (dd) و برجستگی نسبی (bh) در 15 حوضه زهکشی در محیط نرم افزاری arc gis به منظور تعیین کمی میزان تکتونیک فعال این منطقه محاسبه شده است. نتایج به دست آمده از محاسبه شاخص های فوق بیان گر آن است که در محل تقاطع گسل های شمال البرز و خطیرکوه و هم چنین گسل هایی که در دامنه شمالی البرز در اثر فعالیت این گسل های بزرگ شکل گرفته اند مقادیر به دست آمده از شاخص های یادشده، بالا بوده که بیانگر وجود فعالیت تکتونیکی بالا و بسیار بالا در آن نواحی است. در اثر بالا بودن این مقادیر انتظار می رود که ریسک لرزه خیزی منطقه نیز در اثر گسیختگی گسل ها افزایش یابد.

Seismic Hazard in Babolrud and Talar Basins based on Morphometric Indices

IntroductionTectonic geomorphology is a knowledge that can determine the effect of active tectonic using the geomorphic indices as a quantitative description of the rivers form. Accordingly, quantitative measurements provide conditions that allow them to identify the status of active tectonics areas. Active tectonic processes can affect the shape and performance of rivers. The extraction of geomorphic indices using digital elevation map (DEM) in the GIS in the past two decades has been a fast and accurate method for drainage basin analysis so that these indices are used for quick evaluation of recent tectonic activities in a particular region. Base on a natural theory, rivers are the first environmental forms that show a relatively rapid response to changes in the bedding or changes in the outflow of the bed. Regarding the proved reactions of rivers to the occurrence of normal changes, it is possible to analyze them by using geomorphic indices as the result of the effects of tectonic on the river 's route. Geomorphic indices are especially used for active tectonic studies. With the study of topographic landforms and the model of drainage systems using geomorphic indices and the geological structure of each area, it is possible to evaluate the active tectonic performance and to determine the absence of active tectonic movements. The quantitative measurements provide conditions that allow them to identify the status of active tectonics areas. Along with the advancement of tectonic science of geomorphology, scientists have found that active tectonic processes can affect the shape and function of rivers being one of the most important observations that occur rapidly. Consistently in respond to deformation caused by active tectonics at the surface reflecting minor changes in topography, thus examining drainage pattern and river diversion provides important information on structural expansion and evolution of the area. The study area is classified into four categories of very high, high, medium and low tectonic activities. Alborz mountain range is the result of two orogenic movements. One of them is Precambrian ores (Acinitic), the course of which is essentially a metamorphism that leads to the interconnection and hardening of the paving stones in the Precambrian, The second one is the Alpine orogeny movements that happens in Mesozoic and Cenozoic periods. This mountain range is approximately 600 kilometers long and 100 kilometers wide along the south side of the Caspian Sea. The northern margin of the Alborz line is usually sloping. General trend of study area is NESW. & nbsp;Materials and MethodsIn this research, with using the Arc GIS software and 1:100000 Geological maps, at first, rivers and basins shapes of the area were extracted using STRAHLER method using 30 m accuracy digital elevation model in Arc GIS software. Then the necessary modifications to the wells and extraction basins were carried out using topographic maps and satellite images and finally a part of central Alborz at Talar and BabolRud area was divided into 19 catchments. 5 morphotectonic indices such as hierarchical anomalies (Δa), Bifurcation (R), Form factor (Ff), drainage density (Dd) and Relative relief (Bh) were calculated in drainage basins. Using the Relative Active Tectonic (IAT) index, the study area was classified into 4 categories. Category 1 indicates a very high tectonic activity. Category 2 is the high tectonic activity. Category 3 shows the average geological activity and category 4 activities are low relative construction. A tectonic activity zoning map was prepared for each indicator in the study area and the results of the indices were analyzedResults and DiscussionBased on studies of hierarchical anomaly indices in subbasins associated with North Alborz and Khatirkuh faults, this index increases and shows very high and high rates. Intersection between these faults and the subbasins waterway has caused anomalies in the connection of lowgrade waterways to several degrees higher. In subbasins 11, 12, 13 and 14 which are dominated by the abovementioned faults, the bifurcation index and the elevation changes are due to the activity of these faults are high.ConclusionStudies in this section of the Alborz mountain range using morphometric indices such as hierarchical anomalies (Δa), Bifurcation (R), Form factor (Ff), drainage density (Dd) and Relative relief (Bh) and using the IAT Index in this area, shows that recent tectonic activity is generally due to the faults activity in the region such as North Alborz and Khatirkuh faults are in a high and very high categories. Based on these studies, it was found that some other minor faults formed due to high tectonic activity and caused by major faults such as North Alborz, Khatirkuh and other major faults in the area affect the indices numbers. Tectonic impacts show that about 33.3% of the subbasins associated with the major and minor faults