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تفسیر دوبعدی داده‌های مگنتوتلوریک برای پی‌جویی ذخایر عمیق آب‌های شور حاوی ید در منطقۀ شمال آق‌قلا، دشت گلستان | ||
| فیزیک زمین و فضا | ||
| مقاله 9، دوره 43، شماره 2، مرداد 1396، صفحه 355-367 اصل مقاله (514.34 K) | ||
| شناسه دیجیتال (DOI): 10.22059/jesphys.2017.61705 | ||
| نویسندگان | ||
| بهروز اسکوئی* 1؛ سبحان محبوبی2؛ حسین پرنیان3؛ رابعه صداقت3؛ محمد رضا سپهوند4 | ||
| 1دانشیار، گروه فیزیک زمین، مؤسسۀ ژئوفیزیک، دانشگاه تهران، ایران | ||
| 2کارشناس ارشد ژئوفیزیک، گروه ژئوفیزیک، دانشگاه تحصیلات تکمیلی و فناوری پیشرفتۀ کرمان، ایران | ||
| 3کارشناس ارشد ژئوفیزیک، گروه فیزیک زمین، مؤسسۀ ژئوفیزیک، دانشگاه تهران، ایران | ||
| 4استادیار، گروه ژئوفیزیک، دانشگاه تحصیلات تکمیلی و فناوری پیشرفتۀ کرمان، ایران | ||
| چکیده | ||
| برداشت‌های مگنتوتلوریک در بازۀ فرکانسی وسیعی در شمال دشت گلستان به منظور تشخیص چگونگی رسانایی لایه‌های زمین و با هدف بررسی پتانسیل منطقه از لحاظ وجود لایه‌های رسانای الکتریکی که بیانگر وجود ساختارهای آب شور حاوی ید هستند، در پاییز سال 1393 صورت گرفته است. در این تحقیق مؤلفه‌های میدان‌های الکتریکی و مغناطیسی در طول دو پروفیل با فاصلۀ 1500 متر و در 10 ایستگاه با فاصلۀ 900 متر اندازه‌گیری شده است. متعاقباً پردازش یک‌بعدی و دوبعدی داده‌های این منطقه با استفاده از کد اسمیرنف انجام شده است. در این تحقیق داده‌های مقاومت ویژه و فاز امپدانس با استفاده از الگوریتم ریبوک وارون‌سازی شده است. داده‌های مگنتوتلوریک برای دو پروفیل مربوطه در مد دترمینان برای دو مدل اولیۀ همگن و ناهمگن وارون‌سازی شده است. از مد DET یا همان دترمینان داده‌ها در حکم ورودی برای وارون‌سازی داده‌ها برای تفسیر نهایی استفاده شد که میانگینی از همۀ جهت‌های جریان فراهم کرده و همچنین مستقل از جهت امتداد الکترومغناطیسی است. نتایج بیانگر وجود لایه‌هایی بسیار رسانا حاوی آب شور در اعماق بیش از 450 متر در امتداد بعضی از پروفیل‌هاست. | ||
| کلیدواژه‌ها | ||
| رسانایی؛ گلستان؛ مقاومت ویژه؛ مگنتوتلوریک؛ وارون‌سازی؛ ید | ||
| عنوان مقاله [English] | ||
| 2D interpretation of the Magnetotelluric data to prospect deep iodine bearing salt water reservoirs in northern Aqqala, Golestan plain | ||
| نویسندگان [English] | ||
| behrooz oskooi1؛ sobhan mahboubi2؛ hosein parnian3؛ rabee Sedaghat3؛ mohamad reza sepahvand4 | ||
| 1Associate Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Iran | ||
| 2M.Sc. in Geophysics, Department of Geophysics, Graduate University of Advanced Technology of Kerman, Iran | ||
| 3M.Sc. in Geophysics, Department of Earth Physics, Institute of Geophysics, University of Tehran, Iran | ||
| 4Assistant Professor, Department of Geophysics, Graduate University of Advanced Technology of Kerman, Iran | ||
| چکیده [English] | ||
| The Magnetotelluric (MT) method is an electromagnetic geophysical exploration technique that images the electrical conductivity distribution of the Earth crust and upper mantle. The source of energy in the MT method is natural. When the external energy, known as the primary electromagnetic field, reaches the Earth's surface, part of it is reflected, whereas the remainder penetrates into the Earth, which by interaction with the conductors, induces an electric field (known as telluric currents) and at the same time produces a secondary magnetic field which can be measured at the surface and the impedance tensor is calculated. In the fall of 2014 MT measurements were carried out at northern Aqqala of Golestan plain in the northeast of Iran, close to the southeastern shore of the Caspian Sea. It was carried out in a wide frequency range to recognize the Conductive layers in depths of less than 2000 m in the region. Determining the potential of the area in terms of electrically conductive layers which represent the iodine bearing saltwater structures was our objective. The electric and magnetic field components were acquired along two EW profiles (with 1500 meter distance) at 20 stations with a 900 meter distance between stations using GMS05 (Metronix, Germany) systems. Three magnetometers and two pairs of non-polarizable electrodes were connected to this five-channel data logger. The experimental setup included four electrodes distributed at a distance of 100 m in north-south (Ex) and east–west (Ey) directions. In the MT method, conductive structures are ideal targets when located in a considerably resistive host. They produce strong variations in underground electrical resistivity. A robust single site processing followed by the one dimensional and two dimensional modeling that were performed for the MT data along profiles A and B. Analysis of the MT data-set suggests signatures of salt water reservoirs in the area which are distinguished potentially positive to contain iodine. We could recognize the more conductive zones in the less conductive host as layers of saline water. Aqqala of Golestan plain geologically is a part of the Kopeh-Dagh sedimentary basin. Kopeh- Dagh was formed by the last orogeny phase of Alpine and the subsequent erosion. Topography relief is very smooth and basically it is a flat plain consisting of loesses occurring naturally between the Alborz mountain range and the desert of Turkmenistan. Quaternary sediments including clay and evaporates and particularly salt are impenetrable. The MT data were processed using a code from Smirnov (2003) aiming at a robust single site estimate of electromagnetic transfer functions. 1D and 2D inversions were conducted to resolve the conductive structures. 1D inversion of the determinant (DET) data using the code of Pedersen (2004) as well as the 2D inversion of DET mode data using a code from Siripunvaraporn and Egbert (2000) were performed. The data were calculated as apparent resistivity and phases. The determinant mod provides a useful average of the impedance for all current directions. Since the quality of the determinant data was acceptable, 2D modeling of the determinant data would be expected to provide a more reasonable approximation of the true subsurface structure. Therefore, we used the model obtained from the DET mode data as a final interpretation model The purpose of this study is to evaluate the possibility of using surface MT measurements on the very conductive sediments to monitor the underground salt water bearing layers or bodies. In this study one and two dimensional interpretations for recognizing conductivity structures were performed. The resistivity sections showed a clear picture of the resistivity changes both laterally and with depth. The inversion results revealed a highly conductive layers iodine bearing saltwater structures which are at the depths of over 450 meters along some profiles. One of the sites was proposed for exploratory excavations. | ||
| کلیدواژه‌ها [English] | ||
| conductivity, golestan, inversion, iodine, magnetotelluric, resistivity | ||
| مراجع | ||
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آقانباتی، ع. (آذرماه 1385): زمین‌شناسی ایران، ناشر: سازمان زمین‌شناسی و اکتشافات معدنی ایران. سازمان زمین‌شناسی و اکتشافات معدنی کشور(سازمان زمین‌شناسی و اکتشافات معدنی کشور). نقشه 1:250000. Chave, A. D. and Jones, A. G., 2012, the magnetotelluric method Theory and practice, Cambridge University Press، chapter 6. Groom, R. W. and Bailey, R. C., 1989, Decomposition of the magnetotelluric impedance tensor in the presence of local three-dimensional galvanic distortion. Journal of Geophysical Research 94, 1913–1925. Martı, A., Queralt, P. and Ledo, J. 2009, WALDIM: A code for the dimensionality analysis of magnetotelluric data using the rotational invariants of the magnetotelluric tensor. Oskooi, B., 2004, "A broad view on the interpretation of electromagnetic data (VLF, RMT, MT, CSTMT)". PhD Thesis, Uppsala University, Sweden. Pedersen, L. B. and Engels, M., 2005, Routine 2D inversion of magnetotelluric data using the determinant of the impedance tensor, Geophysics, 70, G33-G41. Pedersen, L. B., 2004, “Determination of the regularization level of truncated singular-valubhe decomposition inversion”, The case of 1D inversion of MT data: Geophys. Prospect, 52, 261-270. Reddy, I. K., Rankin, D. and Phillips, R. J, 1977, “Three-dimensional modeling in magnetotelluric and magnetic variational sounding” Geophysics Journal of the Royal Astronomical Society, Vol. 51, p. 313-325. Siripunvaraporn, W. and Egbert, G., 2000, “An efficient data-subspace inversion method for 2-D magnetotelluric data”, Geophysics, 65, 791-803. Smirnov, M. Yu., 2003, ” Magnetotelluric data processing with a robust statistical procedure having a high breakdown point”. Geophysics. J. Int, 152, 1-7. Smith, J. T., 1995, Understanding telluric distortion matrices. Geophysical Journal International 122, 219–226. Swift, C. M., 1967, "A magnetotelluric investigation of electrical conductivity anomaly in the southwestern United States" .PhD Thesis Massachusetts Institute of Technology, Cambridge, MA. Vozoff, K., 1991, "The magnetotelluric method, in Electromagnetic methods in applied geophysics.". M. N. Nabighian, Ed., Society of Exploration Geophysicists, Tulsa, Oklahoma, 2(B), 641-711. Weaver, J. T., Agarwal, A. K. and Lilley, F. E. M., 2000, Characterisation of the magnetotelluric tensor in terms of its invariants. Geophysical Journal International 141, 321–336. | ||
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