ارزيابي خطر پذيري مسير انتخابي احداث راه آهن حد فاصل اصفهان و اهواز در مقابل زلزله

Risk Assessment of Selected Path Railway between Isfahan and Ahvaz against Earthquake

زلزله از جمله پديده هايي است كه بيشترين آسيب را به سازه ها و شريان هاي حياتي وارد مي سازد. براساس گزارشات موجود بخش اعظم خطوط اصلي موجود در شبكه راه آهن كشور ايران در مناطقي با خطر نسبي زياد زمين لرزه قرار گرفته اند. مسير خطوط ريلي مورد مطالعه بين دو شهر اصفهان و اهواز قرار گرفته است و هنوز احداث نشده است و در مرحله مطالعه است. در سالهاي بين 2011-1050، بيش از350 زلزله در محدوده مورد بررسي رخ داده كه زلزله سال 1384با بزرگاي 6/8 ريشتر بيشترين مقدار را داشته است. همچنين در اين محدوده 615 گسل وجود دارد . بنابراين خطر پذيري مسير انتخابي آن در مقابل زلزله مورد بررسي قرار گرفته است. در اين پژوهش با استفاده از داده هاي توپوگرافي ، نقشه هاي زمين شناسي ، تصاوير ماهواره اي IRS LISS III ، آمار و اطلاعات زلزله هاي تاريخي و دستگاهي و روشهاي تحليل واريوگرافي، درون يابي و توابع فازي، پهنه بندي خطر پذيري خطوط ريلي در 4 كلاس بدون خطر، خطر متوسط، خطر زياد و خطر خيلي زياد تهيه گرديد. نتايج مطالعات نشان داد كه دو بازه طولاني و يك بازه كوتاه از خطوط ريلي بر محدوده هاي با حداكثر خطر پذيري انطباق دارند. بررسي نتايج خاطرنشان ساخت كه محدوده مورد مطالعه از نظر توپوگرافي، جنس زمين و سيستم گسله ها و درزها و شكستگي ها داراي تنوع فوق العاده اي مي باشد و اين تنوع سبب شده است كه آسيب هاي وارده از رخداد زلزله ها متفاوت باشد. به بيان ديگر زلزله اي با بزرگاي ثابت مي تواند از شدت هاي تخريب متفاوتي در خطوط ريلي 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 Iran’s 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.