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  • عارف زینال پور، رضا قائدرحمتی *، علی مرادزاده، محمدرضا رحمانی
    در این مقاله اکتشاف منابع زمین گرمایی در منطقه بوشلی استان اردبیل با استفاده از داده های مگنتوتلوریک (MT) مورد بررسی قرار گرفته است. این مطالعه بر اساس داده های 60 ایستگاه مگنتوتلوریک در منطقه ای به وسعت 90 کیلومترمربع در بوشلی، جنوب شرقی شهرستان نیر، صورت گرفته است. ابتدا پردازش داده ها با استفاده از الگوریتم هایی مبتنی بر روش های پایدار و مقاوم در برابر نوفه صورت گرفته است. سپس تحلیل ابعادی داده ها بر اساس پارامترهای چولگی، چولگی حساس به فاز، بیضی وارگی و اندیس های وزنی نرمال شده مورد توجه واقع شده است. بر اساس این تحلیل ها امتداد ساختارهای منطقه بیشتر دوبعدی و با جهت شمالی- جنوبی تشخیص داده شد. در مرحله بعد عملیات مدل سازی وارون یک و دوبعدی روی داده ها در طول 12 پروفیل انجام گرفته است. بر اساس مقاطع مقاومت ویژه به دست آمده از این مدل ها و همچنین اطلاعات زمین شناسی، ساختارهای احتمالی منطقه شناسایی و تفسیر شده اند. نتایج مقاطع یک و دوبعدی مقاومت ویژه با تلفیق اطلاعات زمین شناسی، یک سیستم زمین گرمایی را نشان می دهد. موقعیت سه بخش اصلی این سیستم شامل سنگ پوش، مخزن و منبع داغ زمین گرمایی به خوبی نشان داده شده است. بخش فوقانی این سیستم یک منطقه با مقاومت ویژه حدود 10 اهم متر به عنوان پوشش رسی مخزن به خوبی نشان داده شده است. مخزن زمین گرمایی با مقاومت ویژه بیشتر (حدود 100 اهم متر) ، در زیر این پوشش رسی قرار گرفته است. همچنین مقاطع مقاومت ویژه به دست آمده از مدل سازی دوبعدی داده ها، موقعیت منبع داغ زمین گرمایی را در زیر مخزن زمین گرمایی در عمق بیشتر از 3000 متر، به خوبی نشان می دهند. نتایج این مطالعه موقعیت مخزن زمین گرمایی را در منطقه جنوبی محدوده مورد نظر با کشیدگی به سمت جنوب منطقه نشان می دهد.
    کلید واژگان: بوشلی جنوب سبلان، پردازش داده ها، داده های مقاومت ویژه و فاز، روش مگنتوتلوریک، مخزن زمین گرمایی، وارون سازی یک و دوبعدی
    Aref Zainalpour, Reza Ghaedrahmati*, Ali Moradzadeh, Mohamadreza Rahmani
    Summary: The exploration of geothermal resources in the Bushli area of Ardebil Province utilizing magnetotelluric (MT) data is presented in this paper. This study is performed on 60 MT stations in an area surface of 90 square kilometers of Bushli area, located in southeast of Nir district. The data has been processed using algorithms based on robust methods, which are resistant to noise. After that, dimensionality analysis has been applied to the MT data having appropriate limits of frequencies related to all stations. Considering dimensionality analysis results, the regional structures are mostly identified as two-dimensional structures with north - south strike direction. Regional structures have been interpreted following one dimensional (1D) and two dimensional (2D) inverse modeling applied on the data. The results of 1D and 2D inverse modeling integrated with geological data indicate that the upper part of the geothermal reservoir is composed of a low resistivity area at the depth of 500 to 2000 meters. Final results have shown that the location of the geothermal reservoir extends to the southern parts of the study area.
    Introduction
    MT method is an electromagnetic (EM) method that uses natural EM fields, generated from Earth's magnetosphere for mapping deep subsurface structures. This method plots the electrical conductivity distribution beneath the earth surface by recording vertical and horizontal components of magnetic and electric fields from ground surface. High penetration depth of EM fields in MT method has made it applicable to deep target explorations such as geothermal and hydrocarbon resources. Hence, due to these options, this method has special status among other geophysical methods. Preliminary studies on the geology of Bushli area, which is located in southwest of Nir and Sareyn hot springs, have shown a relatively good potential for geothermal resources in this area that could be a preferred alternative for fossil fuels and future energy supply. Methodology and Approaches : MT method is widely utilized for surveying geothermal areas. In thermal areas, the electrical resistivity is extremely lower than that of areas with colder subsurface temperature. The selected MT survey lines are located in the area crossing over the hydrothermally altered zones and different geological structures. The data was acquired along 12 survey lines crossing the Bushli hot springs with a total of 60 MT stations in a frequency range of 1000 Hz to 0.001 Hz. Spacing between MT stations was almost considered 500 m constantly, for a better resolution. At first, 60 MT sounding time series data were reviewed. Then, the acquired raw data were analyzed using methods resistant to noise (i.e. robust methods), and also, outlier elimination method in order to achieve high quality apparent resistivity and phase data at each desired frequency. Specialized software was utilized for this purpose such as Mapros for processing and WinGLink for 1-D and 2-D smooth inverse modeling. Mapros has plenty of different robust methods for processing, and the preferred processing procedure, used in this paper, was to use least squares weighted functions. The Rodi and Mackie computer code and Occam smoothing algorithm were also used for 2D inversion and forward modeling, respectively. This algorithm seeks the minimum possible structure model subjected to an appropriate fit for the data, and it uses a code for 2D inversion from Rodi and Mackie (2001) in a way that this algorithm searches simultaneously for the model with the lowest overall RMS misfit and the smallest lateral and vertical conductivity gradients respectively. Apparent resistivity and phase data of TE+TM (joint) mode along each survey line were modeled in this study. Results and Conclusions: Considering the results obtained from 2D inversion and the geological information, the following conclusions were acquired: the thick surface layer with resistivity of 100-500 ohm-m along the north-south survey lines was also observable along the west-east survey lines. In some stations, a very conductive layer was seen on top of the surface that could be interpreted as the top soil saturated by penetrated water. Below this layer, there was a decline of resistivity with depth observable along the whole survey lines. This conductive layer (<10 ohm-m), showing variable thicknesses along the profile, was most naturally interpreted as the limestone, related to late Permian, of Ruteh formation acting as system reservoir. Below this conductor, a very resistive zone (>250-300 ohm-m) was observed. This resistive and intrusive mass was interpreted as the bed rock zone and a heat source that was mostly formed from granite and granodiorite related to first age of geology with high enthalpy. According to the models and electrical vertical sections and also horizontal resistivity maps at different depths, the geothermal reservoir was designated at a depth of 2500 to 3000 meters. Furthermore, resistivity map showed that the location of the geothermal reservoir continued to the south of the area. This was probably due to the significant properties of eastern parts of the area like the existence of many faults as well as low height of this part of the area compared to neighboring parts that caused the appearance of numerous hot springs in the area.
    Keywords: Bushli Area Sabalan, Data Processing, Apparent Resistivity, Phase Data, Magnetotelluric Method, Geothermal Reservoir, One-, Two-Dimensional Inversion
  • مسعود حسینی، ابوالقاسم کامکار روحانی، مهدی محمدی ویژه، سعید پرنو*
    شمار کابل ها و لوله های مدفون زیر سطح زمین در مناطق شهری، طی سال های گذشته به شدت افزایش یافته است. فقدان نقشه های دقیق زیر سطحی، باعث آسیب رسیدن به این خطوط در طی عملیات مختلف عمرانی می شود؛ بنابراین استفاده از یک روش غیر مخرب برای آشکار سازی این گونه اهداف زیرسطحی کاملا ضروری است. روش رادار نفوذی به زمین روشی غیر مخرب، سریع و کم هزینه با قدرت تفکیک بالا برای بررسی های نزدیک به سطح زمین است. در مقاطع GPR اهداف استوانه ای (لوله، کابل و غیره) و نقطه ای به صورت هذلولی نمایش داده می شوند. لذا تمایز بین این اهداف از اهمیت ویژه ای برخوردار است. در این پژوهش با برداشت سه بعدی یا شبکه ای، به وسیله ی دستگاه Noggin Plus با آنتن پوششی با فرکانس مرکزی 250 مگاهرتز، توانایی و عملکرد روش GPR در آشکارسازی تجهیزات زیرسطحی در یک منطقه شهری با شبکه نسبتا پیچیده ای از تاسیسات زیرسطحی مورد بررسی قرار گرفته است. این شبکه زیرسطحی متشکل از لوله های فلزی و غیرفلزی، کابل ها و کانال های زیرسطحی انتقال آب است. بعد از انجام پردازش های مناسب بر روی داده های شبکه ای، نقشه ها و مقاطع مختلف دوبعدی و سه بعدی GPR دارای مختصات افقی و عمقی با دقت بالا تهیه شده؛ که در این مقاطع ساختارهای زیرسطحی آشکارسازی شده است. علاوه بر این تخمین قطر لوله های غیر فلزی محتوی آب با دقت حدود یک سانتیمتر امکان پذیر شده است. با برداشت شبکه ای، پردازش های مناسب و به دنبال آن نقشه ها و مقاطع تهیه شده، اطلاعات مفید و دقیقی از اهداف زیرسطحی مدفون در منطقه برداشت به دست آمده است.
    کلید واژگان: رادار نفوذی به زمین (GPR)، لوله های فلزی و غیر فلزی، پردازش و تفسیر داده ها، مدل سازی دوبعدی و سه بعدی، دانشگاه صنعتی شاهرود
    Masoud Hosseini, Abolghasem Kamkar Rouhani, Mahdi Mohammadi Vizheh, Saeed Parnow*
    Summary Geophysical methods can effectively be used for delineation and maintenance of man-made subsurface installations. These installations are suitable targets for detection by ground penetrating radar (GPR) method. In this non-invasive method, high frequency electromagnetic (EM) waves in the frequency range 10 to 1000 MHz are used for detection, demonstration and investigation of shallow subsurface structures. The most important advantage of this method over other geophysical methods its high resolution, high speed of survey and nondestructiveness. In urban areas where the ground surface is covered by asphalt and also noise level is high, it not possible to use other geophysical methods while obtain high resolution data without destruction of the asphalt. However, the GPR method with shielded antenna acts well in urban areas. This method can present a three-dimensional (3-D) picture from the subsurface in which an accurate estimation of the subsurface structures can be made. In this method, EM waves, generated by the GPR transmitter, are sent into the ground and the reflections from the subsurface structures are received by the GPR receiver. The GPR waves are intensively attenuated in high conductive subsurface media and hence, the depth of penetration of GPR waves in this method is limited. In this research work, the depth of penetration of the GPR waves in the study area decreases to less than 2 meters. In this research, an urban survey area where various metallic and non-metallic pipes have been buried is selected, and then, GPR survey is performed on a grid in the area. As a result of processing and interpretation of the acquired GPR data, the subsurface targets at different depths are detected with relatively good accuracy and resolution.
    Introduction Nowadays, transmission of fuels, water and other energy resources by buried pipes, tanks and cables in urban areas is a substantial necessity for human beings. This leads to creation of huge and costly underground networks. Following creation of such networks, a very important matter is the maintenance of these man-made installations to prevent them from possible destructions. These destructions to the installations are not normally observable at the ground surface as the installations are located in the subsurface areas. These destructions that can occur due to different reasons can cause considerable financial losses and also irreparable environmental contaminations. In this regard, geophysical methods can be used for delineation and maintenance of these installations. Often there is a sufficient physical contrast between these installations and their surrounding media. Thus, these installations are suitable targets for detection by GPR method. In this method, high frequency EM waves in the frequency range 10 to 1000 MHz are used for detection, demonstration and investigation of shallow subsurface structures.
    Methodology and Approaches In this research work, GPR method has been used in an urban survey area where various metallic and non-metallic pipes have been buried. The GPR survey has been performed on a grid in the area, and then, the GPR data have been acquired using 250 MHz Noggin Plus GPR system with shielded antenna. Following processing and interpretation of the GPR acquired data, two-dimensional (2-D) and 3-D maps and depth cross-sections are obtained. As a result of this GPR survey, the subsurface targets at different depths in the 3-D maps have been detected with relatively good accuracy and resolution. These 3-D maps can considerably help the interpreter to interpret the GPR data reliably and accurately. Moreover, significant and relatively comprehensive information from these 3-D maps is obtained. 3-D presentation of the GPR data is very useful in the 3-D visualization of the subsurface, and thus, can indicate the targets more precisely.
    Results and Conclusions In this research work, the depth of penetration of the GPR waves in the study area was less than 2 meters. 2-D and 3-D GPR maps and depth cross-sections were obtained as a result of processing and interpretation of the GPR acquired data. Moreover, the subsurface targets at different depths in the 3-D maps were well detected with relatively good accuracy and resolution. 3-D presentation of the GPR data is very useful in the 3-D visualization of the subsurface, and thus, can indicate the targets more precisely. The results of this research indicate that non-invasive, fast and cheap GPR method has considerable advantages over other geophysical methods in civil engineering applications.
    Keywords: Ground, Penetrating Radar (GPR), Metallic, Non-Metallic Pipes, Data Processing, Interpretation, Two, Dimensional (2, D), Three, Dimensional (3, D), Modeling, Shahrood University of Technology
  • حبیب الله عشقی، ابوالقاسم کامکار روحانی*
    در این مطالعه که بر روی رسوبات حاشیه جنوب شرقی دریاچه خزر انجام شده، سعی بر آن بوده که با اعمال پردازش های مختلف بر روی داده های رادار نفوذی به زمین (GPR)، اثر هر یک از پردازشها بر روی داده های مذکور مورد بررسی قرار گیرد. با توجه به تعداد بالای پروفیل های GPR برداشتی در این تحقیق و امکان استفاده از هر یک از پردازش ها در جای مناسب خود، امکان درک شهودی نحوه پردازش داده ها برای شرایط و اهداف متفاوت فراهم شده است. به علاوه در این مطالعه ضمن بررسی نحوه اثر هر یک از پردازش ها و سازوکار عمل هر یک از عملگرها بر روی داده های GPR، با انتخاب پارامترها و روندهای پردازش مناسب سعی بر بازسازی و ترسیم بهترین مقطع ممکن بوده است؛ ضمن این که با بررسی مقاطع GPR، ردهای جداگانه، میانگین طیف بسامد و میانگین دامنه بر حسب زمان، به درک صحیحی از موفقیت و یا عدم موفقیت یک روند پردازشی می توان رسید.
    کلید واژگان: رادار نفوذی به زمینGPR، رسوبات زیرسطحی، پردازش و تفسیر داده ها، گذردهی نسبی الکتریکی، دریاچه خزر
    Habibolah Eshghi, Abolghasem Kamkar Rouhani*
    Ground penetrating radar (GPR) method as a high-resolution non-destructive geophysical method acts based on the transmission of relatively high-frequency electromagnetic waves inside the ground and recording the reflected waves from the interfaces between the subsurface layers. As the method uses electromagnetic waves in the frequency ranges of 12.5 megahertz to 1 gigahertz (called GPR waves), it can only be used for shallow subsurface investigations. As a result of fast and dense data measurements in this method, continuous images of the reflections of GPR waves from the interfaces of subsurface media with different electrical or electromagnetic properties are obtained. These properties comprising of dielectric constant (or relative permittivity), electrical conductivity and magnetic permeability play key roles in GPR responses. The GPR equipment measures the travel time of the waves. Thus, the preliminary display of the acquired GPR data is in the form of a time section in which the vertical axis indicates the two-way time taken from the transmission of the GPR wave by the transmitter into the ground until its reflection and receipt by the receiver. GPR method has been successfully used in a variety of applications including hydrogeological investigations, mapping of bedrock surfaces, and detection of subsurface targets such as buried pipes, cavities, foundations, subsurface contaminations, waste deposits, water tables, soil horizons and other subsurface interfaces or targets. In this research, GPR method has been used to examine the subsurface sediments in southeast margin of the Caspian Sea. After acquiring the GPR data along a large number of relatively long survey lines in the study area, effort has been made to apply various processing techniques to the acquired GPR data in order to investigate the effect of each of processing techniques on the data enhancement. Considering the collection of vast GPR datasets along different long survey lines in the study area containing various subsurface targets with different depths and sizes, the results or performances of applying each of the processing techniques to the GPR data have not been similar. Due to the low distance between the GPR transmitter and receiver as well as the electrical properties, especially the conductivity of the ground, and also, to remove the unwanted low-frequency signals or reflections while preserving the highfrequency signals, the dewow filter has been applied before any other processing to all the GPR datasets. The short time intervals between the transmitted GPR pulses and the pulses received directly from the air-ground surface, and also, the existence of reflections from the shallow subsurface targets, cause signal saturation in the receiver. For this, the dewow filter is applied to the GPR data to correct for signal saturation or wow in the data. Different types of gain are also among the processing methods applied to the data to reduce the attenuating effect of the GPR waves as the depth increases. To demonstrate the effects of different gains and to select the optimum gain, we have applied different gains to the GPR data. To convert the trace from a wavelet with both positive and negative components (i.e., sine or cosine nature) to a monopulse wavelet with all positives, we have used the envelope filter. This process removes the oscillatory nature of the radar wavelet and shows the data in its true resolution, making it easier to interpret. To determine the locations of the GPR events, the GPR time section should be converted to its corresponding GPR depth section in which the vertical axis shows the depth. To do this, it is necessary to know the velocity of the GPR wave in the subsurface structures of the area under study. This research indicates that using the characteristics of GPR waves in the GPR sections, we can detect the subsurface targets and discriminate the coarse-grained sediments from the fine-grained sediments, and also determine the electrical properties of subsurface layers with high success. High resolution of the GPR data has enabled us to characterize most of the subsurface sediments. Furthermore, the shallow subsurface bedding can be easily observed in the GPR sections obtained. High moisture, salinity, clay and silt contents of the shallow subsurface sediments cause high conductivity of the ground in the area, and thus, cause the depth of penetration of the GPR waves to be mostly less than 1 meter.
    Keywords: Ground penetrating radar (GPR), subsurface sediments, data processing, interpretation, relative electrical permittivity, Caspian Sea
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