@article { author = {Rahimi Bahoosh, Hoda and Hamzehloo, Hossein}, title = {Simulation of strong ground motion for the 2004 Firozabad Kojoor earthquake in northern Iran}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {1-13}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {In recent years, seismologists have attempted to develop quantitative models of the earthquake rupture process with the ultimate goal of predicting strong ground motion. Simulation procedures provide a means of including specific information about the earthquake source, the wave propagation path between the source and the site and local site response in an estimation of ground motion. Simulation procedures also provide a means of estimating the dependence of strong ground motions on variations in specific fault parameters. Several different methods for simulating strong ground motions are available in the literature. A number of possible methods that could be used to generate synthetic records include the following: (i) deterministic methods, (ii) stochastic methods, (iii) empirical Green’s function, (iv) semi-empirical methods, (v) composite source models, and (vi) hybrid methods. The Firozabad Kojoor earthquake occurred on May 18, 2004, with a magnitude of 6.2 in the central Alborz region. We have used the empirical Green’s function and stochastic finite fault modeling to study the source parameters and rupture propagation and make a comparison between the observed and simulated records. The empirical Green’s function method synthesizes the ground motion from a large earthquake (target) by exploiting actual small-event ground motions as the Green’s functions of the earth. It is based on the concept of self-similarity, a notion that assumes a constant stress drop for earthquakes of all magnitudes and provides scaling values for determining related faulting parameters of earthquakes of varying size. The simulation of the ground motion from the target event is expressed as a superposition of contributions from the subfaults separated by a time difference that depends on (1) the location of the particular sub-element on the fault relative to the rupture initiation point and (2) the rupture propagation characteristics. It assumes that the rupture propagates radially from the rupture initiation point at a constant fraction of the shear wave velocity. This study also employs the modified stochastic finite fault modeling of Motazedian and Atkinson (2005), which is based on the dynamic corner frequency. In this method, a large fault is divided into N subfaults, where each subfault is considered as a small point source. The ground motions of subfaults are summed with a proper time delay in the time domain to estimate acceleration time history. The comparison shows that the length and width of the rupture plane is 15 × 15 km. The coordinate of the nucleation point is estimated as 36.33 oN, 51.60 oE and 29 km depth, and rupture was determined to have propagated from east toward the west. The estimated focal mechanism is reverse with a minor left-lateral strike slip component. The strike, dip and rake have been estimated as 110o, 34o and 71o, respectively.    }, keywords = {Simulation,stochastic finite fault,empirical Green’s function,Firozabad Kojoor earthquake}, title_fa = {شبیه‌سازی جنبش نیرومند زمین برای زمین‌لرزه 1383 فیروزآباد-کجور، شمال ایران}, abstract_fa = {در تاریخ 8 خرداد 1383 زمین‌لرزه فیروزآباد کجور با بزرگای 2/6 در منطقه البرز مرکزی به وقوع پیوست. به منظور برآورد پارامترهای چشمه و نحوه انتشار گسیختگی شتاب‌نگاشت‌های حاصل از این زمین‌لرزه با استفاده از دو روش شبیه‌سازی تابع تجربی گرین و کاتوره‌‌ای گسل محدود شبیه‌سازی و مقایسه شد. این مقایسه نشان می‌دهد که طول و عرض صفحه گسیختگی km15 در km15 و مختصات نقطه شروع گسیختگی60/51، 33/36 و در عمق km29 است. انتشار گسیختگی روی صفحه گسل به صورت یک‌‌طرفه از شرق به سمت غرب منتشر شده است. سازوکار کانونی به‌دست آمده معکوس با مولفه کوچک چپ‌گرد است. راستا و شیب و ریک صفحه گسل به ترتیب 110،34 و71 درجه برآورد شده است. نتایج به‌دست آمده از شبیه‌سازی تابع تجربی گرین و کاتوره‌‌ای گسل محدود به ترتیب برای ایستگاه‌‌هایی که در آنها رویداد کوچک (پس‌لرزه) موجود بوده و ایستگاه‌‌هایی که رویداد کوچک در آنها ثبت نشده است، همخوانی مناسبی با رکوردهای مشاهده شده نشان می‌‌دهد.}, keywords_fa = {شبیه‌سازی,کاتوره‌‌ای گسل محدود,تابع تجربی گرین,زمین‌لرزه فیروز آباد کجور}, url = {https://www.ijgeophysics.ir/article_40745.html}, eprint = {https://www.ijgeophysics.ir/article_40745_f66b531061a502a52c601132170b20e6.pdf} } @article { author = {Amini, Hamideh and Fattahi, Morteza and Ghassemi, Mohammad Reza}, title = {Determination of the slip rate in the Shesh-Taraz river on the Doruneh fault using histogram and minimum age OSL methods}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {14-29}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Having a left lateral strike slip, the Doruneh fault is located in the northeast of Iran. It is thesecond longest fault system (~700 km), after the Main Zagros Recent Fault system, in Iran. This fault is the response of the convergence between the Arabian and Eurasian plates in the regional tectonic map. Despite high potential seismicity, only two historical earthquakes with magnitudes greater than 7 more than, and no instrumental earthquakes with greater than 6, have been recorded for this fault. Therefore, it is necessary to determine the hazard of this fault in the area. One way to conduct the Earthquake Hazard Assessment is to calculate the slip rate, and one method for calculating the slip rate is measuring the displacement by the fault and dividing it by the period during which this displacement has occurred. Optically Stimulated Luminescence (OSL) is one of the best methods for determining sediment age in arid and semi-arid zones such as Iran. Displacements of quaternary geological evidence (e.g., river beds) by the Doruneh fault also suggest this fault is active.  In this study, the Shesh-Taraz area was selected because it is near populated areas, including Kashmar, Bardaskan, Khalilabd, Ali mardankhan, and Chenar. Fattahi et al. (2006) collected Optically Stimulated Luminescence (OSL) samples from the Shesh-Taraz and employed the weighted mean Infrared Stimulated Luminescence (IRSL) from the feldspar for slip rate determination. This investigation used similar samples but calculated the ages of both quartz and feldspar fragments using a different OSL method.   The samples were processed under subdued red light. A portion of the sample was taken by dry and wet sieving. The quartz and feldspar fragments were purified and separated by chemical treatment. The separated quartz and feldspar were mounted as monolayers on the 10 mm diameter Al discs for the single aliquot analysis using a silicon spray as an adhesive.  The Equivalent Doses (De) of quartz and feldspar of each sample were calculated using the Minimum Age and Histogram Methods for which the Analyst program was used.  By dividing the calculated Equivalent Dose by the Total Dose Rate, the ages of these samples were calculated. The estimated ages for T1, T1a and T2, from the quartz samples using the Minimum Age Method were 3.49±0.75, 7.67±0.95, and 4.57±1.34 ka, respectively, and employing the Histogram Method were 3.88±3.15, 10.99±10.5, and 7.99±4.45 ka, respectively.  The estimated ages for the feldspar samples with the Minimum Age Method were 6.23±0.48, 7.40±2.23, and 4.96±0.25 ka, respectively, and with the Histogram Method were 7.61±1.22, 9.40±1.79, and 8.07±2.43 thousand years, respectively.    The displacement of geomorphologic evidence was measured by satellite images (Landsat and Quick Bird Image). Because of high accuracy of the field-measured displacement, in comparison to the satellite image displacement measurements, we calculated the slip rate by dividing the values calculated using the former method of displacement by OSL ages into the newly estimated ages.   The estimated slip rates for T1, T1a and T2, using quartz samples with the Minimum Age Method were 6.30±1.39, 3.26±0.43, and 1.75 ±0.56 mm.yr-1, respectively, and with the Histogram Method were 5.67 ±4.61, 2.28±2.18, and 1±0.57mm.yr-1, respectively.  The estimated slip rates for T1, T1a and T2, using the feldspar samples with the Minimum Age Method were 3.53±0.31, 3.38±1.03, and 1.61±0.22 mm.yr-1, respectively, and with the Histogram Method were 2.89 ±0.48, 2.66 ±0.52, and 0.99 ±0.32 mm.yr-1, respectively.  Comparative studies of the luminescence signals of quartz and feldspar showed that the results of feldspar are more reliable. The range of the slip rates calculated in this study includes the range of slip rates determined by previous studies. Therefore, additional studies in this region are required.    }, keywords = {Doruneh fault,Shesh-Taraz River,Optical Simulated Luminescence (OSL),Slip Rate}, title_fa = {محاسبه نرخ‌لغزش در منطقه شش‌تراز گسل درونه به روش هیستوگرام و حداقل سن با استفاده از لومینسانس برانگیخته شده با نور}, abstract_fa = {گسل درونه در شمال‌شرق ایران، از گسل‌هایی است که با وجود طویل بودن، قرار‌گیری در محل همگرایی دو صفحه عربستان-اوراسیا و دارا‌ بودن پتانسیل بالای لرزه‌خیزی، فقط یک زمین‌لرزه تاریخی با بزر‌گای 7 (زمین‌لرزه 1619، دوغ آباد (آمبرسیز و ملویل، 1982)) و دو زمین‌لرزه دستگاهی با بزرگای بیش از حدود 6 (زمین‌لرزه‌های 1933 با بزرگای 6 و 1940 با بزرگای 5/6، در حوالی این گسل (چالنکو و همکاران، 1973)) داشته است؛ بنابراین، تحلیل‌خطرلرزه‌ای روی این گسل ضروری است.  یکی از روش‌های تحلیل‌خطر در یک منطقه، محاسبه نرخ‌لغزش است.  از بهترین روش‌های تعیین نرخ‌لغزش، استفاده از سن‌یابی رسوبات، با به‌کارگیری لومینسانس (لومینسانس) برانگیخته‌شده با نور (OSL) است. در این بررسی، نرخ‌دُز‌معادل‌دُز‌طبیعی (De) ذرات کوارتز و فلدسپار نمونه‌های برداشت‌شده از منطقه شش‌تراز، با تحلیل داده‌ها در برنامه Analyst به روش هیستوگرام (هیستوگرام) محاسبه شد.  با توجه به آنکه در رسوبات منطقه، احتمال صفر نشدن کامل سیگنال‌های لومینسانس نمونه‌ها وجود دارد، نتایج حاصل به روش حداقل سن نیز محاسبه شد.  با استفاده از مقادیر De، سن ذرات کوارتز نمونه‌های T1، T1a و T2، به روش حداقل سن به‌‌ترتیب 75/0±49/3 و 95/0 ± 67/7 و 34/1±57/4 هزار سال و به روش هیستوگرام، به‌ترتیب 15/3±88/3 و 5/10±99/10 و 45/4±99/7 هزار سال برآورد شد و سن ذرات فلدسپار این نمونه‌ها نیز، به روش حداقل سن، به‌‌ترتیب 48/0±23/6 و 23/2±40/7 و 25/0±96/4 هزار سال و به روش هیستوگرام، به‌‌ترتیب 22/1±61/7 و 79/1±40/9 و 43/2±07/8 هزار سال برآورد شد.  با استفاده از جابه‌جایی‌های اندازه‌گیری‌شده طی عملیات صحرایی در منطقه شش‌تراز، بر پایه داده‌های ذرات کوارتز و فلدسپار، نرخ‌لغزش ذرات کوارتز نمونه‌ها T1، T1a و T2، به روش حداقل سن به‌‌ترتیب 39/1±30/6 و 43/0±26/3 و 56/0±75/1 میلی‌متر بر سال و به روش هیستوگرام، به‌ترتیب 61/4±67/5 و 18/2±28/2 و 57/0±1 میلی‌متر بر سال برآورد شد و نرخ‌لغزش ذرات فلدسپار این نمونه‌ها، به روش حداقل سن به‌ترتیب 31/0±53/3 و 03/1±38/3 و 22/0±61/1 میلی‌متر بر سال و به روش هیستوگرام، به‌ترتیب 48/0±89/2 و 52/0±66/2 و 32/0±99/0 میلی‌متر بر سال برآورد شد. مقایسه سیگنال درخشایی (لومینانس) ذرات کوارتز و فلدسپار روشن ساخت که سن‌های به‌دست آمده از ذرات فلدسپار، قابل قبول‌تر از ذرات کوارتز است. محدوده نرخ‌لغزش‌های به‌دست آمده در تحقیق حاضر، وسیع‌تر از محدوده به‌دست آمده در تحقیقات قبلی است، لذا تحقیقات  بیشتر، ضرورت دارد.}, keywords_fa = {گسل درونه,رودخانه شش‌تراز,لومینسانس برانگیخته شده با نور (OSL),نرخ‌لغزش}, url = {https://www.ijgeophysics.ir/article_40746.html}, eprint = {https://www.ijgeophysics.ir/article_40746_857e9ef372bca9e3b250f9a35b41e16b.pdf} } @article { author = {Sabziparvar, Ali Akbar and Olyaie, Ehsan}, title = {Evaluation of the performance of artificial neural networks (ANN) in predicting the daily global solar radiation and comparison with results from the Angström model (case study: Tabriz synoptic station)}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {30-41}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Global Solar Radiation (GSR) is one of the most widely used parameters in many fields of agriculture engineering, meteorology, and hydrology. To design a reliable solar energy system, knowledge of the radiation data is essential. Because of high costs of maintenance, calibration, and measurement of global solar radiation, the application of commonly used radiation methods such as Angström models has become popular. In spite of the simplicity and advantages of Angström models, there are many weaknesses in this simple model which may result in unreliable predictions. For instance, Angström models ignore some important factors such as site elevation, relative humidity, and atmospheric turbidity. Since 1924, many attempts have been made for solving such difficulties.  During recent years, numerous works have attempted to develop statistical methods, physical approaches (Sabziparvar, 2008), empirical relations, and artificial neural network (ANN) models to predict global solar radiation around the world. Sozen et al. (2005) simulated GSR in different sites in Turkey with an error of less than 10%. Using air temperature and relative humidity data, Rehman & Mohandes (2008) predicted GSR using an ANN method. Jiang (2009) compared the GSR as predicted by empirical approaches with the GSR as simulated by ANN methods in different sites in China. They showed that ANN results are more accurate than empirical methods.  In the semi-arid region of Ahwaz, Rahimikhoob (2010) predicted GSR using air temperature and the ANN method. In the present study, an ANN model was constructed to predict global solar radiation and the results were compared to the results of an Angström model. For this purpose, daily meteorological and climatic parameters (relative humidity, mean temperature, maximum temperature, minimum temperature, soil ground temperature, sunshine duration, global solar radiation, cloud cover, and vapor pressure) which affect solar radiation at the Tabriz Synoptic Station during a period of five years (2001-2005) were selected as the input of the neural network method. Three statistical criteria including the mean bias error (MBE), root mean square error (RMSE), and correlation coefficient (r) were applied. The results showed that the best model performance is a 9-11-1 structure and the sigmoid function based on the back propagation training algorithm. The minimum error was obtained by using 10,000 iterations for the training stage and 11 neurons in hidden layers. This study used the trial and error method to find the optimum number of hidden layers. Changing the number of neurons from one to eight in a hidden layer led to larger errors. The application of 9 to 12 neurons improved the results significantly, but higher numbers of neurons (n>13) resulted in error divergence. Generally, the comparison of neural network performance results and Angström model results versus actual measured values revealed a significant superiority of the neural network model compared to the conventional Angström method. Therefore, the proposed method can be a useful tool for the estimation of daily global solar radiation in areas where direct measurement of radiation is not available. The suggested ANN method can be a good candidate instead of the commonly used Angström method. Due to the sensitivity of weather parameters to climate conditions, different ANN methods have to be tested for prediction of global solar radiation for other climates.    }, keywords = {prediction,Global Solar Radiation,Artificial Neural Networks,Angström Model,Tabriz}, title_fa = {ارزیابی عملکرد شبکه عصبی مصنوعی در پیش‌بینی تابش خورشیدی کل روزانه و مقایسه آن با نتایج مدل آنگستروم (مطالعه موردی: ایستگاه همدیدی تبریز)}, abstract_fa = {تابش خورشیدی جهانی (GSR) یکی از پرکاربردترین کنش‌گرها در بسیاری از زمینه‌های مهندسی کشاورزی،‌ هواشناسی و آب‌شناسی است. در این پژوهش، از یک مدل شبکه عصبی مصنوعی برای برآورد تابش خورشیدی کل رسیده استفاده شد و یافته‌های برآمده از آن با یافته‌‌های مدل آنگستروم به‌منزلة یکی از فراگیر ترین روش‌های برآورد تابش خورشیدی مقایسه مورد سنجش قرار گرفت. برای این کار داده‌های روزانه برخی متغیرهای اقلیمی و هواشناسی بنیادین و نشان‌‌گذار بر تابش خورشیدی ایستگاه همدیدی (سینوپتیک) تبریز در دوره آماری 5 ساله (1380- 1384) درحکم پارامترهای درون داد شبکه عصبی به‌کار گرفته شد. دست‌‌آوردها نشان داد که اندازه RMSE، MBE و rبرای ساختار 1-11-9 برپایه الگوریتم آموزشی پخشیدگی به پس، یکی پس از دیگری، برابر 3/3 ژول بر سانتی‌‌متر مربع بر روز، 134 ژول بر سانتی‌‌متر مربع بر روز و 905/0 به‌دست آمد. روی‌‌هم‌‌رفته، سنجش دست‌‌آوردهای شبکه عصبی با دست‌‌آوردهای مدل آنگستروم و داده‌‌های دیده‌‌بانی شده، نشانگر برتری معنی‌‌دار مدل شبکه عصبی نسبت به روش آنگستروم است. لذا، برای برآورد تابش کل خورشیدی، روش پیشنهادی می‌تواند جایگزین درخوری برای روش‌هایی مانند مدل آنگستروم باشد. }, keywords_fa = {پیش‌بینی,تابش خورشیدی کل,شبکه‌های عصبی مصنوعی,مدل آنگستروم,تبریز}, url = {https://www.ijgeophysics.ir/article_40747.html}, eprint = {https://www.ijgeophysics.ir/article_40747_04cb465ae115bdce109a8e033f3d54fa.pdf} } @article { author = {Razavi Rad, Fatemeh and Ghorbani, Ahmad and Falsafin, Zahra}, title = {Identifying excavation damaged zones using2D electrical resistivity tomography modeling}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {42-54}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Underground excavations provoke in their vicinity a region where the rock is disturbed, i.e., loosened due to micro as well as macro fractures. The shapes, dimensions, and properties of such so-called excavation damaged zones (EDZ) are of increasing importance for the planning and construction of geotechnical barriers in underground repositories for toxic and problematic wastes. Dynamic stability assessment of rocks after underground excavation is important. Mechanical changes related to an excavation damage zone (EDZs) leads to changes the physical properties of rocks. In fractured and unsaturated materials, resistivity is sensitive not only to the matrix electrical properties but also to the saturation of the water phase and to the density and orientation of cracks. Recent studies show that electrical resistivity tomography (ERT) and induced polarization (IP) methods are capable of monitoring the mechanical behaviour of EDZs. ERT and IP methods are performed in the galleries which are excavated in clay-rocks of the Tournemire test site located in the south of France. The aim of these geophysical investigations is the characterization of EDZ zones and hydro-mechanical behaviour. ERT is performed for an arc profile on the walls of the gallery, with 43 electrodes arranged on the floor and wall with a distance of 20 cm between them. Non-polarizing electrodes of Cu/CuSO4 were used. Interpretation of the ERT section on the straight line profile, carried out on the floor of the tunnel, confirmed the existence of a high electrical resistivity zone near the surface (a fractured and partially saturated zone with a depth of 50 cm). A 2D electrical resistivity model was developed to perform a tomography survey for the arc profiles on the walls of the underground excavations (horseshoe section). All the Wenner, dipole-dipole, and Schlumberger electrode arrays can be used for ERT surveying. Current and potential electrodes can be arranged on the floor, walls and ceiling of the tunnel, with equal intervals. A finite element method was performed in order to solve the Poisson equation for all points of the model space with respect to boundary conditions. The finite element approach involves solving a discretized form of the weak formulation of the Poison equation. For each quadripole (two current and two measured electrodes), the code is run once and the electrical resistance can be calculated. The geometric factor of electrical array can be calculated when the code is run for a homogeneous electrical conductivity earth around the tunnel. The space model surrounding the gallery (up to 10 times the distance to the tunnel diameter) is divided into quadrilaterals whose conductivity can be changed. The Neumann boundary condition is considered for the inner and outer surface of the tunnel wall. The outer surface is far from the walls of the gallery. The code (Forward model) is programmed in COMSOL Script software using Matlab language. An input file was used that determines the location of each quadripole for each electrode array according data acquisition. Eventually, the apparent resistivity pseudo-section is calculated from the code. An interpreted cross-section, obtained from manual inverse modelling using the code, shows good conformity with the results of the tomography obtained from the straight profile taken on the floor of the tunnel. The results also show that ERT is capable of investigating the resistivity changes near the surface of tunnel walls. The depth of the investigation is up to the tunnel radius.}, keywords = {electrical resistivity tomography (ERT),Finite element method (FEM),Poisson equation}, title_fa = {شناسایی منطقه آسیب دیده در اثر حفاری تونل‌‌ها با استفاده از مدل‌‌سازی دوبُعدی توموگرافی مقاومت ویژه الکتریکی}, abstract_fa = {حفاری‌های زیرزمینی باعث تحریک محیط اطراف می‌شوند و این مسئله ایجاد درز و شکاف‌هایی در سنگ‌های سست شده را در پی دارد. شکل، ابعاد و ویژگی‌های این منطقة آسیب دیده در اثر حفاری، در طراحی و ساخت سدهای ژئوتکنیکی و در مخازن زیرزمینی برای نگهداری زباله‌های سمی اهمیت بسزایی دارد. تغییرات مکانیکی منطقة اغتشاش تنش‌های القایی در اثر حفاری، منجر به تغییر در خواص الکتریکی آنها می‌شود. تحقیقات اخیر نشان می‌دهد که روش‌های توموگرافی مقاومت ویژة الکتریکی و قطبش (پلاریزاسیون) القایی  قادر به پایش و اندازه‌گیری رفتار مکانیکی این منطقة آسیب دیده در اثر حفاری هستند. یک مدل دوبُعدی مقاومت ویژه الکتریکی برای برداشت‌های توموگرافی مقاومت ویژه الکتریکی روی یک نیم‌رخ کمانی از دیوارة گالری‌ها با شکل مقطع متفاوت (نعل اسبی، دایره‌‌ای) و آرایش‌های‌ الکترودی گوناگون (ونرآلفا، دوقطبی- دوقطبی، شولمبرگر) توسعه داده شد. در این مدل فضای اطراف گالری به چهارضلعی‌هایی تقسیم شده که مقدار هدایت الکتریکی آنها قابل تغییر است. معادلة پواسون برای همة نقاط فضای مدل، با توجه شرایط مرزی از روش اجزای محدود حل می‌شود، و پتانسیل الکتریکی به‌دست می‌‌آید. برای هر تزریق جریان در دو الکترود، یک‌بار برنامه اجرا و مقاومت الکتریکی محاسبه می‌شود. شرط مرزی نیومن برای سطح درونی و بیرونی در نظر گرفته شده است. سطح بیرونی دورتر از دیوارة گالری است. مدل‌سازی (مدل پیش‌رو) ذکر شده با استفاده از نرم‌‌افزار کمسول اسکریپت صورت گرفته و کدهای مورد نیاز در محیط «مطلب» نوشته شده است. در طول مدل‌سازی از یک فایل ورودی که محل قرارگیری هر چهار الکترود را برای هر آرایش الکترودی طبق برداشت تعیین می‌کند، استفاده شده است. سرانجام با استفاده از این برنامه‌، شبه‌مقطع مقاومت ویژة ظاهری محاسبه می‌شود. مدل پیش‌گفته برای برداشت های مقاومت ویژه الکتریکی روی یک نیم‌رخ کمانی با 43 الکترود (با فواصل مساوی 20 سانتی‌متر) چیده شده بر کف و دیواره‌های گالری در سازند رُسی در سایت آزمایشگاهی تورنمیر واقع در جنوب فرانسه به‌کار گرفته شد. نتایج به دست آمده از مدل‌‌سازی نشان می‌‌دهد که، مقطع تفسیر شده حاصل از مدل‌‌سازی معکوس دستی، با نتایج برداشت توموگرافی از روی نیم‌رخ خطی برداشت شده از کف تونل، انطباق خوبی دارد (وجود یک منطقه‌ با مقاومت ویژة زیاد، ضخامت کمتر از 50 سانتی‌متر). نتایج نشان می‌‌دهد که، توموگرافی مقاومت ویژه قادر به تشخیص تغییرات مقاومت ویژه در اعماق نزدیک به سطح گالری است و عمق بررسی به شعاع گالری بستگی دارد و بیشترین مقدار آن با شعاع گالری برابر است.}, keywords_fa = {مقاومت ویژة الکتریکی,توموگرافی الکتریکی,اجزای محدود,معادلة پواسون}, url = {https://www.ijgeophysics.ir/article_40748.html}, eprint = {https://www.ijgeophysics.ir/article_40748_da9c42d67a2013a994da22c26d0d5696.pdf} } @article { author = {Ahmadi, Muhammad Ali and Ebrshimzadeh Ardestani, Vahid and Baniamerian, Jamaledin}, title = {The use of two-dimensional discrete wavelet transform in theboundary estimation of gravity sources}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {55-66}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Wavelet transform is one of the new methods in potential data interpretation. This transform can be applied in both continuous and discrete forms. As the gravity data are discrete, the wavelet discrete transform is used to interpret the data. Moreover, this transform can be used in two- and three3-dimensional forms depending on the nature of the anomalies. The two-dimensional transform is applicable when the length of the anomaly is approximately more than 10 times its width. For this kind of anomaly, the discrete transform can be used along the profile perpendicular to the strike of the linear anomalies. These perpendicular profiles can also be used for three-dimensional interpretation of the anomalies. The variety of the methods in wavelet transform provide widespread potential for estimating the unknown parameters in gravity interpretation, such as depth and shape. The results can also be tested with several routine algorithms. On the other hand, the toolboxes prepared in Matlab can facilitate the process. The two-dimensional discrete wavelet transform has different uses in analyzing and processing potential fields. This paper describes attempts to use this method in estimating boundaries of gravity potential fields and the attenuating effect of noise in gravity data. According to the theory of the method, the detail coefficient values of the wavelet transform correspond to the maximum or minimum boundaries of the source; consequently, horizontal boundaries (long direction), vertical boundaries (width direction), and corners of the sources are estimated by calculating and reconstructing the horizontal, vertical, and diagonal detail coefficients. To study the resolution of the method, it was applied on both synthetic and real data and the results were compared with those of the Enhanced Horizontal Derivative (EHD) method. Calculations show that the resolution of the method is more accurate than that of the EHD method. Moreover, data analysis at special levels makes it possible to mute high frequency properties of the signal (caused by the effects of existing noise in the data). Hence, corresponding to the amplitude of noise, the noisy synthetic data (%1 ratio of random noise) and real data were analyzed in the second and third levels, respectively. The following observations can be considered as the advantages of this method in preference to the EHD method: 1. The boundary estimation of sources is more accurate than that of EHD method. 2. The corners of sources are estimated. 3. The stability of this method against noise is higher than the stability of the EHD method because the magnitude of maximum amplitude of noise is %4 in the wavelet transform method whereas it is only %1 in the EHD method.    }, keywords = {gravity data,two-dimensional wavelet transform,Edge detection}, title_fa = {کاربرد تبدیل موجک گسسته دوبُعدی در برآورد مرز چشمه‌‌های گرانی}, abstract_fa = {تبدیل موجک گسسته دوبُعدی کاربردهای متعددی در تحلیل و پردازش میدان‌های پتانسیل دارد. در این مقاله سعی کرده‌ایم، از روش تبدیل موجک گسسته دوبُعدی در برآورد مرزهای چشمه‌های میدان‌های پتانسیل گرانی و تضعیف اثر نوفه در داده‌های گرانی استفاده شود.  براساس این روش، مقادیر ضرایب جزئی تبدیل موجک متناظر با مرزهای چشمه، بیشینه یا کمینه می‌شود، بنابراین، با محاسبه و بازسازی ضرایب جزئی افقی، قائم و قطری، به ترتیب، مرزهای افقی (در راستای طول)، قائم (در راستای عرض) و گوشه‌های چشمه‌ها برآورد می‌شود.  به منظور بررسی دقت، روش فوق بر داده‌های مصنوعی و واقعی اِعمال، و همچنین با روش مشتق افقی بهبود یافته، EHD ،مقایسه شده است که در آن، نتایج حاصل از تحلیل به روش تبدیل موجک، دقیق‌تر از روشEHD بوده است. علاوه‌‌براین، این امکان وجود دارد که با تحلیل داده‌ها در ترازهای خاصی بخش بسامد زیاد سیگنال (ناشی از اثر نوفه موجود در داده‌ها) را میرا کرد. بنابراین، با توجه به دامنه نوفه، به ترتیب، داده‌های مصنوعی همراه با نوفه(نوفه تصادفی به نسبت 1%) و داده‌های واقعی در ترازهای دوم و سوم تحلیل شده است. در ادامه، مزایای این روش در مقایسه با روش EHD چنین لحاظ شده است: 1- برآورد مرز چشمه‌ها نسبت به روش EHD دقیق‌تر بوده است. 2- گوشه‌های چشمه‌ها برآورد شده است. 3- پایداری نسبت به نوفه در این روش نسبت به روش EHD بیشتر است، زیرا آستانه شدت نوفه در روش تبدیل موجک 4% ولی در روش EHD، 1% است.}, keywords_fa = {تبدیل موجک گسسته دوبُعدی,مشتق افقی بهبود یافته,برآورد مرز,داده گرانی}, url = {https://www.ijgeophysics.ir/article_40749.html}, eprint = {https://www.ijgeophysics.ir/article_40749_74509bf97c36d56b780e1a5b81672684.pdf} } @article { author = {Habibi, Farideh and Mazraeh Frahani, Majied and Moshiri, Behzad and Nohegar, Ahmad and Kalhor, Ahmad}, title = {Improvement the tropical cyclone forecasting process with effective features selection}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {67-82}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {The selection of adequate features for studying and forecasting of each atmospheric quantity regarding the meteorological ‎phenomena (for example, a tropical cyclone) is one of the basic challenges in system recognition and modeling concepts. This study uses various methods of feature extraction including sequential forward selection, sequential backward ‎selection, mutual information, principal components analysis (PCA) and principal factor analysis (PFA) to extract quantities ‎ considering the wind speed at 10 meters above surface for a tropical cyclone activity period. This work studies 45 ‎various quantities of a Guno tropical cyclone activity domain which occurred in early June 2007 over the Arabian ‎Sea, the Gulf of Fars, and the OmanSea regions which caused significant damage to the region due to storm surges. These ‎quantities were initially selected from 286 quantities of the atmosphere which were determined in the global network of 1‎ by ‎1 ‎degree under the standard conditions including standard pressure levels (1000 mb to 10 mb), surface land ‎temperature (SLT), and surface sea temperature (SST). Due to the fact that the activity of the ‎interesting phenomena (i.e. Guno tropical storm) concentrates at the low and medial troposphere, it is possible to exclude ‎quantities of the upper atmosphere. As a rule, the employment of neural network and fuzzy logic methods requires that the data be tested and validated. As a result, the Yemyin tropical ‎cyclone data was considered as testing data (it happened exactly 8 days after the Guno storm in the west of India, and, after ‎traveling over India, then entered into the southeast of Iran and, subsequently, into the northwest of Pakistan). The Nargis tropical cyclone data which occurred in May 2008 at the Bay of Bangal was considered as validation data because there ‎is currently no valid and acceptable data regarding the history of the old Guno tropical storm which occurred in this region approximately 35 ‎years ago.‎ The features extracted from the three first methods were tested using an adaptive network-based fuzzy inference system (ANFIS) approach. ‎Of course, 44 features were considered as inputs and a speed of 10 meters of surface was considered as output. The Guno storm data was considered for ‎training the network but the Yemyin storm data was used for testing the network and the Nargis storm data was used for the purpose of network validation. Due to the fact that the KMO parameter for all three storms was greater than 0.80, the PCA method was used with high ‎confidence for data mining. The results show that the first 18 new components of the storms Guno and Yemyin are greater ‎than the others and they include more than 95% of existing information regarding 45 variables; consequently, the remaining components can be eliminated. However, this is true for the Nargis storm with the first 20 new components.‎ The results show that the computation time of the sequential backward selection method is very high in comparison with the sequential ‎forward selection method. The results show that the corresponding accuracy for sequential backward selection is also high. The results of an ANFIS test for a different epoch show that the features extracted from the forward selection method have ‎minimum errors within three epochs.‎ The study of coefficient components shows the basic part of the second component is related to wind speeds of 10 meters height ‎over the surface and wind speeds in the layer 30 mb above the surface. Therefore, these components can be utilized as output for neural networks and ‎fuzzy systems such as the ones used in the ANFIS method.‎    }, keywords = {Features selection,Adaptive Network-based Fuzzy Inference System (ANFIS),Tropical Cyclone,Sequential Forward Selection (SFS),Mutual Information}, title_fa = {اصلاح پیش‌بینی فرایند توفان حاره‌ای با انتخاب ویژگی‌‌‌های موثر}, abstract_fa = {انتخاب ویژگی‌های مناسب برای بررسی و پیش‌بینی هر کمیت جوًی مرتبط با یک پدیده هواشناسی از قبیل وقوع توفان حاره‌ای یکی از چالش‌های اساسی شناسایی سامانه و مدل‌سازی آن است. در این تحقیق روش‌های گوناگون استخراج ویژگی از قبیل جست‌وجوی پی‌در‌پی پیشرو، پسرو، معیار همبستگی متقابل، تحلیل مولفه‌های اصلی و تحلیل عامل‌های اصلی برای استخراج کمیت‌های مرتبط با سرعت باد در ارتفاع 10 متری از سطح زمین در زمان وقوع پدیده توفان حاره‌ای اعمال شده است. در این بررسی فقط داده‌های 45 متغیر متفاوت در محدوده فعالیت توفان حاره‌ای گونو که در اوایل ماه ژوئن 2007 منطقه دریای عرب، دریای عمان و خلیج فارس را در نوردید و خسارت زیادی را به جنوب و جنوب‌شرقی ایران، شرق کشور عمان وارد ساخت پردازش ‌شده‌ است. ازآنجاکه برای استفاده از شبکه عصبی و منطق فازی نیاز به داده‌های آزمون و اعتبار‌سنجی است از داده‌های توفان حاره‌ای یمین که در اواخر ماه ژوئن همان سال در خلیج بنگال و خلیج فارس شکل گرفت درحکم داده آزمون و از داده‌های توفان حاره‌ای نرجس که در اوایل ماه مه 2008 در خلیج بنگال رخ داده بود به‌منزله داده اعتبار‌سنجی استفاده شده است. کمیت‌های انتخابی نهایی بعد از استخراج ویژگی درحکم ورودی به شبکه استنباط فازی-عصبی تطبیقی(ANFIS) که خروجی آن سرعت باد در ارتفاع 10 متری از سطح زمین است داده شد و مقدار شاخص خطا در حالت‌های متفاوت آموزش شبکه تعیین و در داخل جدولی آورده شده است.      }, keywords_fa = {استخراج ویژگی,شبکه استنباط فازی-عصبی تطبیقی (ANFIS),توفان حاره‌ای,جست‌وجوی پی‌در‌پی پیشرو (SFS),معیار همبستگی متقابل}, url = {https://www.ijgeophysics.ir/article_40751.html}, eprint = {https://www.ijgeophysics.ir/article_40751_d8bd2fbe412cc71b090068b371f6a49a.pdf} } @article { author = {Yari, Mostafa and Mohebian, Reza and Riahi, Mohammad Ali}, title = {Single-frequency seismic attribute obtained from continuous-wavelet transform and matching pursuit methods}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {83-93}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Seismic data, being non-stationary in nature, have varying frequency content across time. Time-frequency decomposition(also called spectral decomposition) of a seismic signal aims to characterize the time-dependent frequency response of subsurface rocks and reservoirs. Castagna et al. (2003) use matching-pursuit decomposition for instantaneous spectral analysis to detect low-frequency shadows beneath hydrocarbon reservoirs. A case history of using spectral decomposition and coherency to interpret incised valleys is shown by Peyton et al. (1998). Partyka et al. (1999) use windowed spectral analysis to produce discrete-frequency energy cubes for applications in reservoir characterization. Continuous wavelet transform (CWT) was introduced by Morlet et al. (1982). In CWT, time frequency atoms are chosen in such a way that their time support changes for different frequencies according to Heisenberg’s uncertainty principle (Mallat, 1999; Daubechies, 1992). This study used the Morlet wavelet, which provides an easy interpretation from scale to frequency. Time-frequency CWT (TFCWT; Sinha, 2005) analysis provides high-frequencyresolution at low frequencies and high time resolution at high frequencies. This optimal time-frequency resolution property of the TFCWT makes it useful in seismic data analysis. Computing the TFCWT in the Fourier domain is a fast process. Furthermore, TFCWT is an invertible process such that the inverse Fourier transform of the time summation of the TFCWT reconstructs the original signal, provided the inverse wavelet transform exists. The purposes of this study require only the forward transform; reproducibility is not a strict requirement. Seismic data analysts sometimes observe low-frequency shadows in association with hydrocarbon reservoirs. The shadow is probably caused by attenuation of high-frequency energy in the reservoir itself. Matching pursuit decomposition involves the cross-correlation of a wavelet dictionary against the seismic trace. The projection of the best correlating wavelet on the seismic trace is then subtracted from that trace. The wavelet dictionary is then cross-correlated against the residual, and again the best correlating wavelet projection is subtracted. The process is repeated iteratively until the energy remaining in the residual falls below some acceptable threshold. As long as the wavelet dictionary meets simple admissibility conditions, the process will converge. Most importantly, the wavelets need not be orthogonal. The output of the process is a list of wavelets with their respective arrival times and amplitudes for each seismic trace. The inverse transform is accomplished simply by summing the wavelet list and the residual, thus reconstructing the original trace. The wavelet list is readily converted to a time-frequency analysis by superposition of the wavelet frequency spectra. The CWT dilates and compresses wavelets to provide a time-scale spectrum instead of a time-frequency spectrum. Converting a scalogram into a time-frequency spectrum using the center frequency of a scale gives an erroneous attenuation in the spectrum. The TFCWT overcomes this problem and gives a more robust technique of time-frequency localization. Since TFCWT is fundamentally derived from the continuous-wavelet transform, wavelet dilation and compression effectively provides the optimal window length, depending upon the frequency content of the signal. Thus, it eliminates the subjective choice of a window length and provides an optimal time-frequency spectrum with an absence of erroneous attenuation effect for a non-stationary signal. It has high-frequency resolution at low frequencies and high time resolution at high frequencies, whereas the spectrogram has fixed time-frequency resolution throughout. Matching Pursuit Decomposition (MPD) requires no windowing of the seismic data and thus has the best combination of temporal and spectral resolution in comparison to TFCWT and the continuous wavelet transform. Most hydrocarbon reservoirs have a seismic response, but sometimes this is expressed only in certain spectral ranges, hidden within the broadband data. Gas-bearing layers have been an interesting area of research for geophysicists, especially spectral decomposition researchers, since they have a very specific spectral attribute: low-frequency gas shadows. This paper presents an investigation of the application and efficiency of Time-Frequency Continuous Wavelet Transform and Matching Pursuit method in time-frequency analysis of seismic sections to delineate and detect low-frequency gas shadows on real data from an Iranian gas reservoir. The results from the MPD are compared with those of the CWT and TFCWT applying single frequency seismic sections at frequencies of 15 Hz and 25 Hz with the expectation that low-frequency gas shadows will be observable in this range of frequencies.    }, keywords = {Time-frequency resolution,time-frequency continuous wavelet transform,matching pursuit,time-frequency spectrum,non-stationary signal,low-frequency shadow}, title_fa = {نشانگر لرزه‌‌ای تک‌بسامد به‌‌دست آمده از روش‌‌های تبدیل موجک پیوسته و تعقیب تطابق}, abstract_fa = {تبدیل فوریه امکان بررسی محتوای بسامدی سیگنال‌های پایا را فراهم می‌کند، اما، برای سیگنال‌های ناپایا که محتوای بسامدی آنها با زمان تغییر می‌کند تبدیل یک‌‌بُعدی به فضای بسامد کافی نیست. یکی از روش‌‌هایی که برای تحلیل یک سیگنال ناپایا مورد استفاده قرار می‌‌گیرد روش تبدیل موجک پیوسته است. در این روش یک طیف زمان-مقیاس به طیف زمان–بسامد تبدیل می‌شود که این امر باعث ایجاد مجموعه‌ای از تضعیف‌‌های ناخواسته روی مقطع لرزه‌‌ای خواهد شد. برای حل این مشکل از روش تبدیل موجک پیوسته زمان-بسامد استفاده می‌‌شود که طیف زمان-بسامد با تفکیک‌‌پذیری بهتری به دست خواهد داد. روش تعقیب تطابق  نیز به‌علت بررسی هر جز از سیگنال و استفاده از الگوریتم تکرار، یک نقشه زمان-بسامد با تفکیک‌پذیری زمان- بسامدی بهتر نسبت به دو روش پیش‌گفته به دست می‌دهد. هدف از این تحقیق، به‌‌کارگیری روش‌های تحلیل زمان-بسامد برای آشکارسازی سایه‌های کم‌‌بسامد ناشی از مخازن هیدروکربن است.      }, keywords_fa = {سیگنال­های ناپایا,طیف زمان-بسامد,تبدیل موجک پیوسته زمان-بسامد,سایه­های کم‌‌بسامد,تعقیب تطابق,تفکیک­پذیری زمان-بسامدی}, url = {https://www.ijgeophysics.ir/article_40752.html}, eprint = {https://www.ijgeophysics.ir/article_40752_17d060d95ba88f81f8608b9835a53899.pdf} } @article { author = {Askari, Abdolrahim and Ebrahimzadeh Ardestani, Vahid}, title = {Interpretation of gravity data using the finiteelement method in the Chabahar Plain}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {94-101}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {In view of the numerous publications, there is clear interest in the application of the Finite Element Method (FEM) to compute the regional gravity anomaly involving only 8 nodes on the periphery of a rectangular map. Geophysical data processing methods, such as trend analysis, analytical continuation and filtering can reveal the general structural properties of a region. Although, there were improvements in distinguishing the regional and residual gravity anomalies, no progress has been made in trend analysis, filtering or analytical continuation methods. With improvements in scientific computing, high degree trend analysis and filtering methods have been used more efficiently for 2-D data. On the other hand, computed regional anomalies still contain residual anomaly effects. For this reason, the finite element method (FEM) might be used to eliminate the residual anomaly effects on the regional anomalies. A brief description of the theory of FEM is presented for the sake of completeness. The gravity map in real space is superimposed by a weighted sum of discrete gravity values at eight stations coinciding with the eight nodes of a second-order iso-parametric element to compute the regional anomalies on the finite elements in the FEM application. For each node coordinate and field variable, the element can be defined by the same shape functions. Due to this feature, it could be named an isoparametric element. The observed gravity values for each node are obtained from the map. The non-dimensional reference plane, which is related to the real plane, was described by using the shape function to perform an easy computation. Eight observed gravity values on quadratic isoparametric elements, which were superimposed onto the gravity map, are needed to compute regional anomolies. Other observed gravity data are unnecessary. Gravity anomalies always include the total effects (combination of the structures which have different densities and depths) of the study area and beyond. Moreover, the well-known non-uniqueness of potential field modeling may lead to very different interpretation results. FEM is here applied in order to determine the regional anomalies. The method has advantages over the traditional methods. For instance, only a few observation points on a Bouguer gravity map are needed to compute the regional gravity anomaly. The FEM can be applied for any size of gravity map. In addition, it will be shown that the computed regional anomaly contains minimal residual anomaly effects. The FEM, which has been used in potential field interpretation for decades, allows complex problems to be solved easily and accurately. The first step of FEM is to identify the elements and then to identify the boundary of the solution space. In this step, the solution space is divided into elements. After determination of the geometrical structure of the solution space, the most suitable elements should be selected for this geometrical structure. The agreement between the geometry and the elements is quite important for the convergence to the best possible solution. FEM has been successfully applied to different modeling problems in the scientific world including in geophysics for decades. In this study, it was used to distinguish the regional and residual anomalies by using the necessary shape functions. These shape functions play quite an important role in changing the reference plane. After the method was applied, it was seen that it produced better results than those produced by the existing traditional methods. In addition to that, fewer gravity values were needed. For instance, only eight nodes with the shape functions were used to compute the regional anomaly.    }, keywords = {Finite element method,regional-residual separation, Chabahar,depth of Moho}, title_fa = {استفاده ازروش اجزاء محدود به‌منظور تفسیر داده‌‌های گرانی در دشت چابهار}, abstract_fa = {بر پایه اکثر مقالات منتشر شده، کاربرد روش اجزاء محدود، صرفا شامل به‌کارگیری تعدادی گره، روی محیط یک نقشه راست‌گوشه گرانی برای محاسبه بی‌هنجاری منطقه‌ای است. خلاصه‌ای از این روش در متن توصیف شده است. بی‌هنجاری‌های گرانی همواره شامل اثرات کل ناحیه‌ مورد بررسی و فراتر از آن است. منحصربه‌فرد نبودن مدل‌سازی میدان پتانسیل، ممکن است به نتایج تفسیری بسیار متفاوتی منتهی شود. روش اجزاء محدود که مدت‌ها در تفسیر میدان پتانسیل به کار می‌رفته است، حل مسائل پیچیده را به‌راحتی و با دقت برای ما ممکن می‌سازد. در روش اجزاء محدود، ابتدا، باید اجزاء‌ها را تعیین کنیم. سپس، برای مشخص ساختن مرز منطقه‌ای که باید مسئله موردنظر در آنجا مورد بررسی قرار گیرد، تصمیم‌‌گیری کنیم. در این مقاله بی‌هنجاری گرانی بوگه در منطقه چابهار به این روش مورد بررسی قرار گرفته است.      }, keywords_fa = {روش اجزاء‌های محدود,جدایش منطقه‌ای‌باقی‌مانده,دشت چابهار,عمق موهو}, url = {https://www.ijgeophysics.ir/article_40753.html}, eprint = {https://www.ijgeophysics.ir/article_40753_6f7f390e5eb7bd265252a7b089d2f2b3.pdf} } @article { author = {Badrzadeh, Yasaman and Ghorbani, Ahmad and Ansari, Abdolhamid and Fatehi Maraji, Mohammad}, title = {Study of the electrical resistivity changes in soils during consolidation testing}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {102-110}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {Determination of the quality and amount of soil settlement due to compression of the underground soil strata are the most important stages in the establishment of stable structures. Soil compressive settlement is induced gradually as a function of time and can be considered as a source of substantial hazards. When a saturated soil stratum is affected by augmented stress, pore water pressure increases significantly. In sandy soil with high permeability, drainage due to pore water pressure is completed rapidly. Pore water drainage occurs as a consequence of a reduction in the soil volume, resulting a settlement termed consolidation settlement. Additionally, in sandy soil, because of rapid drainage of the pore water, instantaneous and consolidation settlements occur simultaneously. In contrast, when a saturated clayey soil is affected by augmented stress, instantaneous settlement occurs in a preliminary process. Due to the low permeability coefficient of clayey soils with respect to sandy ones, the water drainage in clayey soil progresses gradually and over a relatively longer time period in which consolidation settlement follows instantaneous settlement. In order to investigate consolidation settlement and its degree and speed, knowledge of the existence of the clayey strata, their thicknesses, porosity and compressive indices are necessary. Such information is usually obtained from drilled boreholes and samples taken from them. In this regard, borehole drilling is time and cost-consuming, and the very processes involved in the preparation of the samples restricts the efficiency of such geotechnical methods.   Soil structure is determined mainly by its physical properties (especially hydrodynamic and mechanical properties). Conventional methods for determining soil structures are usually spatial and they rarely incorporate changes in location and time. This study uses the non-destructive method of the electrical resistivity measurement to examine the soil structure. The main reasons for this settlement are compressive displacements, dislocations of the soil particles, and the gradual expulsion of air and water through the voids of the soil. On the other hand, the displacements of the soil particles and the expulsions of air and water affect the electrical resistivity of the soils. In this research, four soil samples (in disturbed and homogenized form) are tested in a standard ASTM Odometer which was specially designed and improved for simultaneous measurement of the soil electrical resistivity during the consolidation test. During the recording of soil settlement, the simultaneous changes in the electrical resistivity of the soil were also recorded. All tests were conducted on saturated soils. The measured results show that electrical resistivity is related to the physical state of the soil. Low electrical resistivity of soil samples is due to salt traces in the soil which may cause variations of up to 50 percent in the value of the resistivity during the consolidation test. Generally, during the consolidation period the electrical resistivity increases. The full logarithmic curves of porosity-resistivity show two distinct lines with different slopes in which the slope of the line related to the beginning of the consolidation process is lower. The similarity between the consolidation behavior and electrical resistivity of soil shows the potential of the electrical resistivity method for the possible study of the in situ and long-term consolidation of soils.    }, keywords = {Consolidation,resistivity method,soil structure,odometer}, title_fa = {بررسی تغییرات مقاومت ویژه الکتریکی خاک‌ها در حین آزمایش تحکیم}, abstract_fa = {ساختار خاک مشخص‌‌کننده خواص فیزیکی آن، به‌ویژه خواص مکانیکی و هیدرودینامیکی، است. روش‌های کلاسیک تعیین خواص ساختاری خاک معمولا نقطه‌‌ای هستند و کمتر برای بررسی تغییرات مکانی و زمانی ساختار خاک سازگار شده‌‌اند. تحقیق حاضر روی استفاده از روش غیر تخریبی مقاومت ویژه الکتریکی برای تعیین خواص ساختاری خاک‌ها صورت گرفته است. نشست ناشی از تحکیم لایه‌‌های رُسی، به علت ماهیت تدریجی و طولانی آن، می‌‌تواند خطر بزرگی برای سازه‌‌های بنا شده روی این خاک‌ها محسوب شود. علت این نشست تغییرشکل فشاری و جا‌به‌‌جایی ذرات خاک، رانده شدن هوا و آب از حفره‌های خاک و عوامل دیگر است. از طرفی جابه‌‌جایی ذرات خاک و آب‌‌و‌هوا می‌‌تواند روی مقاومت ویژه الکتریکی خاک نیز تاثیر گذار باشد. در این تحقیق چهار نمونه خاک دست خورده در درون دستگاه ائودومتر استاندارد آزمایش تحکیم، سازگار شد و مورد اندازه گیری هم‌زمان مقاومت ویژه الکتریکی قرار گرفت. در حین ثبت نشست خاک، تغییرات مقاومت ویژه نیز ثبت شد. همه آزمایش‌های تحکیم و مقاومت ویژه الکتریکی، در حالت اشباع کامل خاک صورت پذیرفته است. نتایج حاصل نشان می‌‌دهد که مقاومت ویژه الکتریکی به حالت فیزیکی خاک وابسته است (ثبت مقادیر مقاومت ویژه کم به‌دلیل وجود نمک در خاک و تغییرات 50 درصدی مقاومت ویژه الکتریکی در طول آزمایش‌ها است). به‌طورکلی در طول زمان تحکیم، مقاومت ویژه الکتریکی افزایش می‌‌یابد. منحنی‌‌های لگاریتمی کامل تخلخل- مقاومت ویژه الکتریکی وجود دو خط با شیب‌های متفاوت را نشان می‌‌دهد. شیب خط مربوط به مرحله ابتدای فرایند تحکیم، کمتر است. به‌طورکلی شباهت رفتاری مقاومت ویژه و تحکیم خاک، توانایی روش مقاومت ویژه الکتریکی برای بررسی‌‌های طولانی مدت و بر جای تحکیم خاک را نشان می‌‌دهد.}, keywords_fa = {ساختارخاک,تحکیم,نشست,مقاومت ویژه الکتریکی,ائودومتر}, url = {https://www.ijgeophysics.ir/article_40754.html}, eprint = {https://www.ijgeophysics.ir/article_40754_f2ec346a0fac0c8f5bff01e7ca408043.pdf} } @article { author = {Hejrani, Babak and Hatami, Mohammad Reza and Shomali, Zaher Hossein}, title = {Focal mechanisms of moderate earthquakes with complex sources}, journal = {Iranian Journal of Geophysics}, volume = {5}, number = {3}, pages = {111-134}, year = {2016}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {}, abstract = {It is widely believed that the moment tensor (MT) solution of an earthquake with a non- double couple moment tensor gives significant information about the source mechanism. An interesting topic in non-DC source studies is the relationship among non-DC events, multiple DC events, and complexity in fault segmentations. This study presents a non-DC tectonic earthquake (forward modeling). This means that in the modeled moment tensor, there are no volumetric components. This model was made by adding the seismograms of the two 100% double couple event close lying, thus their seismograms overlap with each other. Then, an investigation is made of the seismic moment of the second subevent, frequency band used in the inversion and also the temporal and spacial separation between two subevents on the result of the inversion. This study focuses on the spacial complex source with Mw ~ 5. Based on empirical relations between moment magnitude and ruptured area (Somerville et al, 1999), the fault plane of an earthquake could not be larger than 11 km2, which could not be “seen” in our MT analysis (our MT inversion was run at frequency bands between 0.02-0.1 Hz). Thus, this inversion was not a pure DC MT inversion for two subevents at the same point but allowed their time separation to vary. The results show that the mechanism of the second subevent is dependent on the frequency band use and its accuracy is related to the higher frequencies  used in the MT inversion (> 0.09). It must be noted that the DC percentage of the moment tensor is dependent on the separation between subevents. The investigation shows that, by increasing the separation between two subevents, the DC percentage reaches higher values, perhaps because of fewer overlaps of the seismograms. We used the ISOLA package developed by Zahradnik et al, (2005) for the MT inversion, centroid location and time. This package is based on the Kikuchi and Kanamori, (1991) method for the teleseismic study of large earthquakes. ISOLA was developed for local and regional distances. For forward modeling of the complex source, we used the CPS package developed by R.B Herrmann in Saint Louis University. Finally, we attempt to model the real data. The 2005/05/01 Mw 5 Central Iran earthquake is investigated based on the results of the synthetic test conducted in the first part. A waveform inversion is performed at near-regional stations at frequencies 0.02–0.07 Hz to search for the optimum 3D location and time of the centroid, using broadband station waveforms from the IIEES network. For calculating the Green function, two crustal velocity models were used, namely Ghods et al, (2010) and Walter, (2000). The Ghods et al, (2010) provides a higher correlation between observed and synthetic data. The optimum depth for centroid is 7 km. The stability of the MT inversion was investigated by the jackknifing method, and, finally, those stations which had low correlation between the observed and synthetic data were eliminated. The DC percentage of the moment tensor during the inversion was changed from 7 to 50%, which made this event a candidate for source complexity in order to study whether this earthquake could be interpreted as having two point sources lying close to each other. MT inversions were executed in frequency ranges from 0.02-0.07 to 0.02-0.13 Hz by adding 0.01 in each run. The second subevent had no significant impact on the waveform matches (about 2%). The mechanism of the first subevent was stable during the inversion and made the same correlation as the deviatoric MT inversion, but the mechanism of the second subevent changed considerably as a result of the changes in the frequency band of the inversion. The time separation between two subevents was about 6 to 8 seconds in different runs, which is unacceptable for earthquakes with magnitudes of approximately ~ 5, for which the fault area is approximately 11 km2. Thus, the two point sources model for this earthquake seems not to be a better model than the one point source. We also endeavored to model the Mw 5.7, 2006/03/25 Fin earthquake in southern Iran. The pure DC source model (for frequencies higher than 0.1 Hz) for this earthquake shows two subevents with a 10 km separation from each other.  }, keywords = {focal mechanism,complex earthquakes,Moment tensor,Fin earthquake}, title_fa = {تعیین سازوکار زمین‌‌لرزه‌های پیچیده با بزرگی متوسط}, abstract_fa = {در این تحقیق، در ابتدا، با حاصل‌جمع لرزه‌‌نگاشت‌های دو رویداد دو زوج نیروی خالص یک چشمه زمین‌ساختی با درصد غیر دو زوج نیروی بالا را مدل‌سازی می‌‌کنیم. در مرحله بعد به وارون‌سازی خطی لرزه‌نگاشت‌های این چشمه در حوزه زمان خواهیم پرداخت. نتایج نشان می‌‌دهد که با افزایش ممان لرزه‌‌ای رویداد دوم و کاهش فاصله دو رویداد، درصد دو زوج نیروی تانسور ممان کم می‌‌شود. همچنین، نتایج وارون‌سازی در حالت دو زوج نیرو نشان داد که باند بسامدی مورد استفاده در وارون‌سازی نقش مهمی در تعیین صحیح سازوکار رویدادهای اول و دوم در یک لرزه‌نگاشت پیچیده دارد. نتایج این تحقیق برای زمین‌‌لرزه مورخ 01/05/2005 و زمین‌لرزه اصلی فین 25/03/2006 که به ترتیب در ایران مرکزی و زاگرس رخ داده‌‌اند، به کار گرفته شد. وارون‌سازی شکل موج زمین‌لرزه فین در بسامدهای بیشتر از 1/0 هرتز نشان‌‌دهنده وجود دو رویداد در چشمه این زمین‌لرزه است. اما، چشمه زمین‌لرزه مورخ 01/05/2005 با یک رویداد دو زوج نیروی خالص تفسیر شد و وجود رویداد دوم در چشمه آن بعید به نظر می‌‌رسد.}, keywords_fa = {سازوکار زمین‌لرزه,زمین‌لرزه‌‌های پیچیده,تانسور ممان,زمین‌لرزه فین}, url = {https://www.ijgeophysics.ir/article_40755.html}, eprint = {https://www.ijgeophysics.ir/article_40755_6660ddf5b894da421436d3e2698b4019.pdf} }