بررسي ژئومورفولوژي چينهاي فعال محدوده شمال شهر يزد

Study of the Active Folds in North of Yazd

مطالعه مخاطرات طبيعي يكي از مهم‌ترين اصول اوليه براي توسعه شهرهاي درحال‌توسعه و گسترش تأسيسات زيربنايي است. ارزيابي فعاليتهاي ژئوديناميكي با استفاده از داده هاي ريخت شناسي يكي از روشهاي مهم و كاربردي در اين راستا تلقي ميشوند. در اين مقاله سعي شده با استفاده از داده هاي سنجش‌ازدور، مطالعات صحرايي نسبت به شناسايي چينه اي فعال در شهرستان يزد اقدام و براي اولين بار چينه اي فعال منطقه شناسايي شوند. بررسي ها نشان ميدهد در محدوده شرق تا شمالشرق اين شهر باستاني تعداد حداقل 5 چين فعال وجود دارد كه به‌عنوان مخاطرات جدي براي منطقه محسوب ميشوند. مقايسه موقعيت اين چين ها با فعاليتهاي لرزه، حاكي از انطباق برخي كانونهاي زمين لرزهاي در اين منطقه است. بديهي است عبور هرگونه تأسيسات و شريانهاي حياتي ازجمله راههاي مواصلاتي، خطوط گاز، آب و يا ساير زيرساختهاي شهري در اين منطقه نيازمند تمهيدات ويژه ميباشد

Abstract The study of natural disasters is one of the most important primary principles for the growth of developing cities and the development of infrastructures. To this end, evaluating geodynamic activities using morphological data is considered one of the most pivotal applied methods. In this study, it was tried to detect active faults in Yazd province using desert studies and remote sensing data. The results showed that there are at least five active faults along the eastern to north-eastern part of this ancient city. These faults are considered as serious hazards for this area. A comparison of the position of these faults with seismic activities is indicative of the seismic correspondence in this area. It goes without saying that the passage of any kind of main arteries and structures including road ways of gas, electricity and water lines or other urban infrastructures require specific arrangements. Introduction Active faults are those types of faults which are the result of rock plastic deformation. This type of deformation occurs without breakage of the rock and affects the whole faulted rock unevenly. This phenomena is closely related to the earth’ internal order to achieve stable equilibrium. In most cases, faults are the source of surface fracture. One of the pivotal tools for detecting these dynamic phenomena is to use earth morphological young deformations. Yazd city is deemed to be one the inactive areas of Iran by most people. In this study, it is tried to investigate Yazd city in terms of active faults. Yazd city is a located in Central desert, 667 km far from Tehran. According to UTM coordinates. The geographic coordinates of the Yazd Province is limited by the eastern longitude 54◦19'56'' to 54◦23'36'' from Grinvich meridian and 31◦55'21'' to 31◦52'18'' of northen latitude from Equator. This area is between eastern 815187 to 821009 of eastern and northern 3530575 to 3536800. Yazd city is the capital city of Yazd Province. The study tectonic area The location of Iran plate among the Arabian plate in the east-south, Indian plate in the south-east, Afghan plate in the East and Turan plate in the noth-east has led to the creatiomn of a convergent area. Convergent, compressive forces has led to faulting and inverse folding in Iran’s crust. In the study area along Bahabad, Anar, Chapduni and Dehshir the old faults are activated. The movement of Quaternary alluvium proves this fact. The frequency of the Quaternary activities is indicative of the continuation of these movements in the area. The evidence which exists in the Iran’s Central Plateu is a manifestation of the removement of the thrust faults. To this end, satellite images and common geodectic methods are used to study this phenomenon and its behavior in the suburban areas. The results of the study showed that in north eastern part of Yazd four active areas whose activities have been formed in the Quaternary era. This gainsays the tectonic inactivity of Yazd city. The study of Fault positions Faults are wavelike structures which are the results of the deformation of the layers and other plate surfaces in rocks. Faults existing in the nature vary from microscopic to macroscopic scales of several kilometers length. From morphological point of view, faults have different shapes, including anticline, dome and deformation of layers, plunging faults and asymmetric faults. In order to study faults, we must first determine the type of the target fault. Surface faults Hidden faults Active faults The investigation of the faults of the study area was carried out by using ETM++ Landsat satellite images, geological maps and desert tours. Regarding the magnifying capability of the Google Earth pictures, they were also used for final control and investigation of large scale facies. Faulting is the most obvious manifestation of earth crust deformation. This phenomenon is strongly dependent on the internal earth order in order to reach stable equilibrium. Moreover, they are closely related to folding and surface fractures and in most cases, faults are the source of surface fractures. These changes are quite manifest in alluvial trace and uplifting of the earth in every area. The foldings in an area may sometimes create faults. Then, due to their gradual and continuous activities, some of these faults remain hidden under the surface. Conclusion Detecting morphological phenomena plays a very important role in evaluating the seismicity of an area. Recent studies showed that the eastern part of Yazd city is surrounded by many active faults. These faults have moved the quaternary sediments and have even created Holocene sediments. Moreover, recorded data have shown the occurrence of various earthquakes some of which are up to magnitude of 5. In this study, ETM++ Landsat satellite images were used to carry out the morphologic study of the area. According to the results, contrary to the belief that Yazd is a safe city, the findings are indicative of the fact that Yazd has an active regime. Based on the analysis of the satellite images, there are four faults with NW-SE trend in the north-eastern part of Yazd city. These folds have cut Holocene sediments and have outcrops and are considered active faults of the area. The detected folds have led to morphogical changes of the earth, in a way that in the area around the fold (1) with a N48W trend, a tectonic pool has come into existence. The other detected folds have cut the trend and moved the upper and lower stream due to the uplifting and changes in the topography of the area. The fold with a N39W trend is located near Yazd city in the form of an anticline. It can be a threatening factor for Yazd city. This fold has moved the southern alluvial fans in the southern cline with a dip of 9. The third fold which is composed of a series of consecutive anticline and syncline have strongly affected Neogene and Quaternary sediments is one of the most important threatening zones for Yazd city in terms of tectonic activities. Moreover, the earthquakes which have occurred in the margin of these folds can be directly accounted for by these young movements which are one of the most important reasons for activity of