تحليل ناپايداري بافت هاي شهري و پهنه بندي ميزان آسيب پذيري در برابر زلزله با استفاده از GIS&AHP ، نمونه موردي: بخشي از هسته مركزي شهر سنندج

Analysis of Urban Instability and Vulnerability in Old Texture by Using GIS & AHP, Case Study: Sanandaj City

شهر سنندج در گذشته دور براساس مقتضيات معماري و اقليم و تا اندازه اي ضروريات اقتصادي- اجتماعي تكوين يافته و به مقاوم سازي آن توجه نشده است. ريزدانگي قطعات، استفاده از مصالح نامرغوب در ساخت ابنيه، فرسوده بودن اغلب ساختمان ها و كمبود فضاهاي عمومي و كمبود سرانه فضاي سبز، عرض كم معابر و پيچ د رپيچ بودن آن ها و عدم رعايت اصول فني و شهرسازي و آيين نامه 2800 در خصوص اين بافت، سبب آسيب پذيري بالاي اين بافت شده و اين امر طبيعي است كه آنچه در رودبار و منجيل و بم اتفاق افتاده به شكل مشابه مي تواند براي سنندج نيز اتفاق افتد. هدف اصلي از اين پژوهش، ارايه روشي براي تحليل آسيب پذيري لرزه اي بافت هاي قديمي با استفاده از شاخص هاي آسيب پذيري لرزه اي به منظور كارآمد نمودن فرآيند مديريت بحران زلزله در بخشي از هسته مركزي و قديمي شهر سنندج است. در اين مقاله تلاش شده كه مدلي براساس تحليل فضايي براي بررسي ميزان آسيب پذيري در اثر زلزله با استفاده از توابع تحليل فضايي GIS ارايه شود كه بتواند معياري براي ميزان خطرپذيري ناشي از زلزله در هسته مركزي شهر سنندج باشد. بدين منظور با تركيب فرآيند تحليل سلسله مراتبي (AHP )و روش فازي به سنجش ميزان آسيب پذيري محدوده مورد مطالعه پرداخته شده است. سپس به تحليل آماري نقشه هاي آسيب پذيري و متغيرهاي تحقيق به كمك نرم افزار SPSS پرداخته شده است. نتايج تحقيق نشان مي دهد كه درصد بالايي از قطعات موجود در محدوده مورد مطالعه با آسيب پذيري بالايي در برابر زلزله روبرو هستند و اين امر لزوم برنامه ريزي صحيح جهت ساماندهي بافت مذكور را نمايان مي سازد.

Urban vulnerability is a widespread and multidimensional phenomenon that covers all the factors of the city which is rapidly increasing due to the factors’ interdependencies. Therefore, urban earthquake vulnerability has been studied from different perspectives and this research has tried to examine all the factors affecting vulnerability. It also has been tried to provide a model based on spatial analysis to investigate the earthquake vulnerability level, using GIS spatial analysis functions that can be considered as a criterion to determine the earthquake vulnerability level in Sanandaj downtown. Earthquake danger width map is made in three steps. The main maps that are effective in the destruction resulting from earthquakes, are ranked and rated based on their importance in the first step. These maps the second step, are turned into Fuzzy ones using Fuzzy function. In the third step, these Fuzzy maps are merged according to each using Fuzzy functions. In the third step, these Fuzzy maps are merged according to each map’s score based on hierarchy analysis method. It should be mentioned that maps related to the distance between users, open spaces and clinics are made using pathway axes and network analysis extensions. In this way, the real distance between any given places and neighboring usages can be calculated. Finally, main vulnerability factors and variables are analyzed statistically. According to the statistical analysis using SPSS software, it becomes evident that there is a meaningful correlation (R= 0.926, n= 1711) between the overall vulnerability of the being studied contexture and its physical vulnerability and also there is a direct and average relationship between overall vulnerability and access vulnerability. The relation between overall vulnerability and socio-economical vulnerability and the relation between physical vulnerability and access are direct and weak. The next table contains plural R values that measure the variability ratio of the dependent variable and also R square (determining coefficient) which is the value of development variable that is determined by the independent variables. For instance, according to the value of 0.861 for the determining coefficient physical vulnerability, this variable determines 86.1 percent of the changes of dependent variable (overall vulnerability). The results show that 90 percent of the contexture has average or over-average earthquake vulnerability, 42 percent of the pieces in the being studied district are high earthquake vulnerable and only 10 percent of the contexture of the being studied district are low earthquake vulnerable to. Parts with high earthquake vulnerable are not, generally, in a good condition from the viewpoint of all factors. In fact, high population density, high structure density, the pieced small narrow pathways and blind alleys, lack of access to open spaces and clinics, old buildings, low earthquake resistance structures, and high level of earthquake vulnerable for people are among some characteristics of these areas. Statistical analysis of the vulnerability maps and variables shows that the main factor of earthquake vulnerability of Sanandaj downtown is a physical factor. The main vulnerability factors including structures’ quality and skeleton, show the necessity of the paying more attention to the reforming of physical indexes of the Sanandaj contexture. Keywords: Vulnerability, Earthquake, Sanandaj Central Core, Fuzzy Logic, AHP.