نوع مقاله : مقاله پژوهشی

نویسندگان

1 تکتونیک، دانشگاه خوارزمی، تهران

2 آب شناسی، دانشگاه خوارزمی، تهران

چکیده

در این مطالعه، ارتباط بین گسل‌های فعال در کواترنری با وضعیت فراوانی  چشمه‌ها و آبدهی چاه‌ها در بخشی از زاگرس مرکزی مورد بررسی واقع شده است. به این منظور، گسل‌ها، چشمه‌ها و چاه‌های منطقه مورد نظر با مطالعه دقیق نقشه‌های زمین‌شناسی، تصاویر ماهواره‌ای و برداشت‌های میدانی مورد بررسی قرار گرفته و در محیط نرم افزار  GIS10.1  تحت تفسیر واقع گردیده‌اند. نتایج این تحقیق حاکی از آن است که بسیاری از چشمه‌های منطقه از نوع گسلی بوده و یا در شکل گیری آن‌ها گسل‌های دارای فعالیت عهد حاضر نقش اصلی را ایفا نموده‌اند. همخوانی مکانی موقعیت این چشمه‌ها با راستای گسل‌های مهمی همچون پهنه گسلی سروستان و سبزپوشان و همچنین اختلاف فاحش آبدهی چاه‌ها در  پهنه‌های گسلی نسبت به سایر چاه‌ها از جمله شواهد این مدعا است. علاوه بر این، نتایج نشان می‌دهد که ارتباط نزدیکی بین فراوانی منابع آب با عناصر ساختاری در منطقه مورد مطالعه وجود دارد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Quaternary active faults effect on the abundance of underground water resources in Maharlu Basin, Central Zagros

نویسندگان [English]

  • Maryam Deh Bozorgi 1
  • Mohsen Rezaei 2

1 Tectonics, Khwarazmi University, Tehran

2 Hydrology, Khwarazmi University, Tehran

چکیده [English]

Introduction: The assessment of major faults to identify the effect of their recent activity on the tectonic evolution of the hydrogeological characteristics of drainage basins is essential. The number of springs as well as the amount of wells discharge often change corresponding to the distribution of fault zones. The 78 km long Sarvestan fault zone is the most typical case according to the distribution of springs. The fault zone, cutting across the fold-thrust belt of Zagros, is dominated by strike-slip (Berberian, 1995), and has deformed some of the previously formed folds. Furthermore, The Sabz-Pushan is an active strike-slip fault zone with length of 220 km, extended along the Zagros fold-thrust belt from northwest of the Shiraz toward the southeast. Since class 1 of Iat, indicative of the most active tectonics, and class 2 of  Iat corresponding to highly active tectonics, occurs mainly in the southwestern part of the study area along the Sabz-Pushan fault zone and also the Sarvestan fault zone, in this research, the relation between these large scale faults which are active in quaternary and the abundance of water resources (spring and well) have been studied.
Materials and methods: In this research, using geological maps, satellite images and field studies, we have analyzed the faults, the springs and the wells of study area through GIS 10.1. The study area, covering an area of 9732 (km^2), is located along a simply folded belt of southeastern Zagros. It is underlain by Phanerozoic sedimentary sequences in elongated, doubly-plunging, box-shaped anticlines, and the synclines are partly buried by younger Quaternary alluvium. The SW–NE oriented contraction that initiated in the Late Cretaceous and strengthened during the Early Miocene due to the collision of the Arabian and Eurasian plates, has led to the development of NW–SE trending, SW-verging folds, and NE-dipping thrusts in the Phanerozoic sedimentary strata covering the Afro-Arabian basement, above a detachment zone of the Infracambrian–Cambrian Hormuz evaporite (Kadinsky-Cade and Barzangi, 1982; Alavi, 1994). In this research, Firstly, all available information for the area of interest was collected and compiled by using geological and topographic maps, satellite images as well as fieldwork. Then, all data were converted to digital format and consequently different layers were created, such as tectonic elements, lithology, slope, elevation and drainage density. The relationship between the number of springs and distance from structural elements is generated by cross operation between springs layer and structural elements layer using buffer and distance operation in the GIS environment. In order to identify the relationship between the amount of slope and the number of springs, the topo-spring layer was crossed with the slope map in the GIS. Springs layer was, also, crossed with 400 m altitude zones of a DEM (digital elevation model) to present the relationship between the elevation levels and the number of springs.
Results and discussion:  The springs at large distance from the main structural elements can be explained by local geologic conditions, including fracturing not mapped at the scale used. The result of topo-spring layer on the the slope map is showing that there is a good correlation between slope class and the frequency of springs located in each class and represent that the number of springs is a function of slope. The output of the existence of springs on different elevation levels clears that the vast majority of springs are in 1400-2200 meter. Springs at high altitude indicate local geologic control. Drainage density has been measured as total stream length per unit area of each basin. The results reveal that high drainage density is correspondent with impermeable sub surface units and mountainous relief, whereas, the low drainage density reveals that the subsurface material are permeable and low relief which results in more infiltration capacity in the basins.
Conclusion: According to the results, there is a tendency for springs to occur at short distances from structural elements. It can be concluded that many of tectonic elements, are conduits of water. However, the water surface is not necessarily on the element itself.  Most of the springs are either faulted ones or identified with major faults through the study area. It has been proved not only by correspondence between the location of springs and the trend of main faults such as Sabz Pushan and Sarvestan, but also by the huge differences in the amount of wells’ discharge. Furthermore, it is concluded that there exists an entwined relationship between the abundance of water resources and structural elements.
 
Introduction: The assessment of major faults to identify the effect of their recent activity on the tectonic evolution of the hydrogeological characteristics of drainage basins is essential. The number of springs as well as the amount of wells discharge often change corresponding to the distribution of fault zones. The 78 km long Sarvestan fault zone is the most typical case according to the distribution of springs. The fault zone, cutting across the fold-thrust belt of Zagros, is dominated by strike-slip (Berberian, 1995), and has deformed some of the previously formed folds. Furthermore, The Sabz-Pushan is an active strike-slip fault zone with length of 220 km, extended along the Zagros fold-thrust belt from northwest of the Shiraz toward the southeast. Since class 1 of Iat, indicative of the most active tectonics, and class 2 of  Iat corresponding to highly active tectonics, occurs mainly in the southwestern part of the study area along the Sabz-Pushan fault zone and also the Sarvestan fault zone, in this research, the relation between these large scale faults which are active in quaternary and the abundance of water resources (spring and well) have been studied.
Materials and methods: In this research, using geological maps, satellite images and field studies, we have analyzed the faults, the springs and the wells of study area through GIS 10.1. The study area, covering an area of 9732 (km^2), is located along a simply folded belt of southeastern Zagros. It is underlain by Phanerozoic sedimentary sequences in elongated, doubly-plunging, box-shaped anticlines, and the synclines are partly buried by younger Quaternary alluvium. The SW–NE oriented contraction that initiated in the Late Cretaceous and strengthened during the Early Miocene due to the collision of the Arabian and Eurasian plates, has led to the development of NW–SE trending, SW-verging folds, and NE-dipping thrusts in the Phanerozoic sedimentary strata covering the Afro-Arabian basement, above a detachment zone of the Infracambrian–Cambrian Hormuz evaporite (Kadinsky-Cade and Barzangi, 1982; Alavi, 1994). In this research, Firstly, all available information for the area of interest was collected and compiled by using geological and topographic maps, satellite images as well as fieldwork. Then, all data were converted to digital format and consequently different layers were created, such as tectonic elements, lithology, slope, elevation and drainage density. The relationship between the number of springs and distance from structural elements is generated by cross operation between springs layer and structural elements layer using buffer and distance operation in the GIS environment. In order to identify the relationship between the amount of slope and the number of springs, the topo-spring layer was crossed with the slope map in the GIS. Springs layer was, also, crossed with 400 m altitude zones of a DEM (digital elevation model) to present the relationship between the elevation levels and the number of springs.
Results and discussion:  The springs at large distance from the main structural elements can be explained by local geologic conditions, including fracturing not mapped at the scale used. The result of topo-spring layer on the the slope map is showing that there is a good correlation between slope class and the frequency of springs located in each class and represent that the number of springs is a function of slope. The output of the existence of springs on different elevation levels clears that the vast majority of springs are in 1400-2200 meter. Springs at high altitude indicate local geologic control. Drainage density has been measured as total stream length per unit area of each basin. The results reveal that high drainage density is correspondent with impermeable sub surface units and mountainous relief, whereas, the low drainage density reveals that the subsurface material are permeable and low relief which results in more infiltration capacity in the basins.
Conclusion: According to the results, there is a tendency for springs to occur at short distances from structural elements. It can be concluded that many of tectonic elements, are conduits of water. However, the water surface is not necessarily on the element itself.  Most of the springs are either faulted ones or identified with major faults through the study area. It has been proved not only by correspondence between the location of springs and the trend of main faults such as Sabz Pushan and Sarvestan, but also by the huge differences in the amount of wells’ discharge. Furthermore, it is concluded that there exists an entwined relationship between the abundance of water resources and structural elements.

کلیدواژه‌ها [English]

  • Faults
  • Quaternary
  • Spring
  • Well
  • Zagros