چکیده:
زلزله از جمله پدیده هایی است که بیشترین آسیب را به سازهها و شریانهای حیاتی وارد میسازد. براساس گزارشات موجود بخش اعظم خطوط اصلی موجود در شبکه راه آهن کشور ایران در مناطقی با خطر نسبی زیاد زمین لرزه قرار گرفتهاند. مسیر خطوط ریلی مورد مطالعه بین دو شهر اصفهان و اهواز قرار گرفته است و هنوز احداث نشده است و در مرحله مطالعه است. در سالهای بین 2011-1050، بیش از350 زلزله در محدوده مورد بررسی رخ داده که زلزله سال 1384با بزرگای 8/6 ریشتر بیشترین مقدار را داشته است. همچنین در این محدوده 615 گسل وجود دارد . بنابراین خطر پذیری مسیر انتخابی آن در مقابل زلزله مورد بررسی قرار گرفته است. در این پژوهش با استفاده از داده های توپوگرافی ، نقشه های زمینشناسی ، تصاویر ماهواره ای IRS LISS III ، آمار و اطلاعات زلزلههای تاریخی و دستگاهی و روشهای تحلیل واریوگرافی، درون یابی و توابع فازی، پهنه بندی خطر پذیری خطوط ریلی در 4 کلاس بدون خطر، خطر متوسط، خطر زیاد و خطر خیلی زیاد تهیه گردید. نتایج مطالعات نشان داد که دو بازه طولانی و یک بازه کوتاه از خطوط ریلی بر محدوده های با حداکثر خطر پذیری انطباق دارند. بررسی نتایج خاطرنشان ساخت که محدوده مورد مطالعه از نظر توپوگرافی، جنس زمین و سیستم گسلهها و درزها و شکستگیها دارای تنوع فوقالعادهای می باشد و این تنوع سبب شده است که آسیبهای وارده از رخداد زلزلهها متفاوت باشد. به بیان دیگر زلزلهای با بزرگای ثابت میتواند از شدتهای تخریب متفاوتی در خطوط ریلی اصفهان- اهواز برخوردار باشد.
Introduction
The earthquake is a natural disaster, causing the most damage to structures and lifeline. For this reason, in structures and lifeline, estimates of damages caused by the earthquake are considered and designed in the plan. The earthquake in Iran has a dominant risk among natural disasters. During the past century, Iran experienced an earthquake of magnitude 7.5 magnitudes and more. The center of most historical and recorded earthquakes is located along two hilly and young belt bays (Kopet Dagh and Alborz Mountains) and southern (Zagros Mountains with the north-west-south-east trend). The focal point of most historical and recorded earthquakes is located along two chain belt of northern (Kopet Dagh and Alborz mountains) and southern (Zagros Mountains with the northwest-southeast trend). The classification of the relative risk of earthquakes in different regions of the country in the 2800 bylaw indicates that about 73% of the country's railways network are located in areas with a high risk of earthquakes and mountainous areas, especially the Zagros chain, are at increased risk of seismicity. Construction of railway lines between Isfahan and Ahvaz is at the study stage and in this study, the risk of the railways has been investigated against earthquake.This railway passes through the Zagros mountains and has bridges, tunnels and bends. The earthquake is a natural disaster that most damage to structure and lifeline. For this reason the structures and lifeline, earthquake loads shall estimate and in order to provide its design. It should be noted that Iran in recent years, an earthquake with a magnitude of 7.5 Richter scale or more frequently experienced. Focus most historical and instrumental earthquake is located along the northern margin of two young belts (Kope-Dagh and Alborz Mountain) and south (Zagros Mountains to the northwest - southeast). The relative risk of different regions in the 2800 earthquake building and Housing Research Center Indicate that is about 73 percent of the main railway network in the regions with high relative risk and especially the Zagros mountain areas are the greater risk of earthquake. This research has studied construction of railway between Isfahan and Ahvaz against earthquake risk. This path also passes through Zagros Mountain and included bridges, tunnels and numerous curves.
Data and
Method
The Railway between is located between Isfahan and Ahvaz cities. More than 350 earthquakes occurred in the area during 1050- 2011 years. The biggest earthquake with a magnitude of 6.8 Richter took a place in 1384. There are 615 faults in this area and the biggest reverse fault zone of Zagros is perpendicular to that direction. The important characteristics of this zone are that they consist of various geomorphologic units including high Zagross (Lordegan - Brojen), Zagross folded (Baghmalek - Lordeghan) and Khuzestan plain (Ramhormoz - Ahvaz), in addition they covered from different geological units. The beginning and end of the railway in Ahvaz passes out the young sedimentary soils and not consolidate and in the Zagros that most of the diversity of geological sedimentary formations have been broken by numerous faults. In this research considered vulnerability of the railway in the seismic zone. In this research Geological maps 1:100000, LISS III images of IRS satellite, recorded and historical earthquakes and path of railway were used. In the first stages of investigation the earthquakes based on semivariogram model and Kriging interpolation method converted to seismic map. Then the Fault lines have extracted of geological maps. Slope, Curvature, Profile and Hypsometric diagram were calculated based on digital elevation model of Aster data. Lineaments, landforms, landuse and vegetation cover were prepared from LISS III images of IRS satellite. The layers were standard by fuzzy membership. Then, they have combined based on Gaussian fuzzy membership function. Final integration was done by 0.7, 0.8, 0.9 and 0.95 gamma and the result was asseted by zonal statistics method.
Result and
Discussion
Seismic zones on the basis of semivariogram model and Kriging interpolation method showed that railway in three reaches is facing to earthquake with about 4 Richter. Whereas the earthquakes greater than 4.5 Richter are located on quaternary alluvial deposits, in addition the maximum magnitude of earthquakes on faults and lineaments as well as on the difference formations. The case study is Irans biggest fault zones and more than 350 earthquakes occurred during 1000 years. The fault, earthquakes and also historical earthquakes layers, indicates active seismic region. Density of vegetation, landuse, seismic layer, slope, Curvature, Profile, faults and lineaments and drainage density layers, combined using overlapping functions and 0.8gamma. The zonation of risk was done in 4 classes included low risk, medium risk, high risk and very high risk. The result was shown two long part and a short part l of railway were placed at the maximum risk.
Conclusion
There are a great variety of topography, geology and system faults in this area. Due to that diversity, the damage of the earthquake are differently. In other words the severity of an earthquake with a constant magnitude is different. The diversity of lithology and outcrops are in two fault systems that railway pass through them, one of the Shareza to Ardekan and other the Ramhormoz to Baghmalek. So magnitude of the earthquake will be changed in path of railway.The beginning and end of the railway are most vulnerable because they passes of young alluvial sediments and isfahan and Ahvaz areas. The presence of sediments around the Gandman as well as in the railway in Izeh will be encountered with increasing mass movement by earthquake. The existence of convex domains from Dizjan to Izeh shows the severity of the earthquake in sensitive and vulnerable areas. Seismic records of more than 5 magnitudes and low depths have little effect on the risk outcomes that need to be considered as evidence of potential risk.
خلاصه ماشینی:
در این پژوهش با استفاده از داده های توپوگرافی ، نقشه های زمین شناسی ، تصاویر ماهواره ای IRS LISS III ، آمار و اطلاعات زلزله های تاریخی و دستگاهی و روشهای تحلیل واریوگرافی، درون یابی و توابع فازی، پهنه بندی خطر پذیری خطوط ریلی در ٤ کلاس بدون خطر، خطر متوسط ، خطر زیاد و خطر خیلی زیاد تهیه گردید.
همچنین آسیب پذیری خطوط راه آهن را بر اثر وقوع زمین لرزه در ژاپن و آمریکا با استفاده از بررسی شدت و عمق زلزله های گذشته و میزان آسیب وارده آنها و شرایط زمین شناسی بررسی شده است و مسیرهای در معرض خطر زمین لرزه تعیین شده (٢٠٠٤,William and Byers) .
در خصوص خطر زمین لرزه در راه آهن ایران مطالعاتی در خصوص درجه بندی خطر پذیری آن صورت گرفته است در تحقیقی از تصاویر ماهواره ای و نقشه های زمین شناسی و عکس های هوایی استفاده شده است و نتایج به دست آمده نشان داده است که ٧٣ درصد از خطوط ریلی در معرض آسیب ناشی از زلزله قرار دارند (مختاری، ١٣٨٥).
از توابع فازی در ارزیابی آسیب پذیری و خطر پذیری بویژه هنگامی که عوامل تاثیر گذار در ترکیب با هم نقش ویژه ای دارند، مورد استفاده محققین قرار گرفته است ((٢٠٠٦ ,Sabuya and pinto ٢٠٠٣ ,Murat and Candan ,٢٠٠٧,Lee ,٢٠١١,Mohammadi and Meech) .
احداث خطوط ریلی بین اصفهان و اهواز در مرحله مطالعه است که در این پژوهش خطر پذیری مسیر انتخابی آن در مقابل زلزله مورد بررسی قرار گرفته است .