@article { author = {Nemati, Majid and Hatzfeld, denis and Gheitanchi, Mohammad Reza and Sadidkhouy, Ahmad and Mirzaei, Noorbakhsh and Moradi, Ali}, title = {Investigation of seismicity of the Astaneh Fault in the East Alborz}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {1-16}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The Alborz mountains, as a folded and faulting region, is the northern region of crust shortening in Iran. Dominant mechanism (Harvard, 2002) of Alborz earthquakes is left-lateral strick-slip paralleled to the range. East Alborz is one of the active regions that plays a significant role in the tectonics of its neighbors like South Casbin Basin. Regarding the geological maps of the area, the faults have clearer outcrops in the east than the west. The strike of mountain range is changed from N110°E in the western part to N80°E in the eastern part. The Astaneh is one of the important faults in the Shahroud fault system in the east Alborz. Astaneh fault, the case study of the local networks, with about 150 km length is clearly seen in satellite pictures especially at the eastern segment. and is about 100 km in length, based on 1:250000 geological map of Semnan (Samadian et al., 1975) and Sari (Vahdati and Saidi, 1990). This fault has made a 30-40 km left lateral pull-apart basin near 53.6°E; this is the same with total left lateral offset, found by reconstructing Cambrian sandstone of the Lalun Formation with the slip rate of 3-5 mm/year. There is 45 (m) left lateral alluvial fan deposit displacement near 54°E (Hollingsworth et al., 2008). The offset dated from the last incision event at about 12 ka in the east (e.g., Regard et al., 2005; Fattahi et. al., 2006). The fault had initially introduced thrust with southward dip (Berberian, et al., 1996) and now is considered as left lateral strike slip (Jackson et al., 2002). The local government responsible say that about 2 million people live in and around the mentioned faults in Semnan, Damghan, Astaneh, Kiasar, Firuzkuh and Veresk cities, which may be affected by the activity of the fault in future. The faults in the Shahroud Fault system were mapped and their surface mechanisms are known, but their related geometry at depth and seismicity are not known. Many important historical earthquakes have occurred in the east Alborz. The most destructive earthquake was historical A.D. 856 Qumes with the estimated magnitude of 7.9 (Ambraseys and Melville, 1982). The distribution of the IGUT recorded earthquakes, because of large station spacing, can not show accurate relationship between seismicity and the faults, also IGUT large station spacing is not appropriate for computation of focal mechanism of the local earthquakes. The master event technique helps increase the accuracy of the teleseismic earthquake location (Engdahl, et al., 1998), but there are only a few events have been relocated in the studied area (small circles in fig.1), because this technique requires large earthquakes with the magnitude greater than 6.5 (Jackson and MacKenzie, 1984). Also the World Wide Seismological Station Network (WWSSN) has just been installed since 1966. Several attempts have been made to solve the earthquakes smaller than 6.5 (Shirkova, 1972; Akasheh and Breckhemer, 1984); but their solutions are not stable, so consequently they could not give a correct explanation because the majority of original data were not available. Therefore the remaining reliable solutions are Centriod Moment Tensor (CMT) at Harvard University (Harvard, 2002) and body waveform modeling (Priestley, et al,. 1994) for the earthquakes with a magnitude greater than 5.5. But there is no earthquake in the studied area with known mechanism except the earthquake of 1990/01/20 with left lateral strike slip mechanism related to the Firuzkuh fault at a longitude of 52.9°E and latitude of 35.8°N (Harvard, 2002). This paper investigates crustal velocity structure and micro-earthquake locations to explain kinematics and seismic activity of the faults in the studied area. We used IGUT network with 10 permanent stations and two local networks each with 10 temporary stations to investigate a selected area in the east Alborz. The duration of the local networks, 2007-2008 network and the 2008 network, was in total months. The temporary stations were visited every week for maintenance, checking their power supplies and internal time against the time of the external GPS of the instruments. First, we estimated the Vp to Vs ratio (1.71) by the Wadati method (Wadati, 1933). Then we determined the crust velocity model using local earthquake arrival times by 1D inversion (Kissling, 1988). Totally 121 events recorded with minimum 8 phases, maximum azimuthal gap of 180°, RMS less than 0.3 s and both horizontal and vertical uncertainties less than 2.0 km were used for computing velocity structure. We processed the inversion in two steps, after testing a few thousand multilayer models, in order to see the convergence of the inversion to a unique velocity model, first 50 random models were tested. These models were stacked with 15 layers of 2.0 km thickness from the surface to 30 km depth, with maximum 0.5 kms-1 velocity change for each layer and with the uniform starting velocity of 6.0 kms-1. Those thin layers allowed us to determine the approximate depth and velocity of the real layers. We suggested a three-layer model with two velocity contrasts located at 4 and 12 km depth over a half space. After merging these layers with a similar velocity then the starting model was repeated with the mentioned layers and the same velocity of the first step. The final selected velocity model is 5.4 and 6.0 km/s for the mentioned layers over a half space with a velocity of 6.3 km/s. Because the majority of the well located events were located shallower than 20 km, we could not determine any layer beneath this depth using inversion. We selected 834 events with a minimum of 6 phases, a RMS less than 0.5 s and a horizontal and vertical uncertainty less than 5.0 km from a total of 1443 events that were recorded by the IGUT network during this period. Regarding the distribution pattern of these earthquakes, the seismic activity is located near Astaneh, Firuzkuh, Mosha, Garmsar, Khazar, North Alborz and North Semnan faults. Also the temporary networks totally recorded 1972 earthquakes during this period. The statistics of the local network earthquakes show that the location error and RMS of about 60% of them are less than 3 km and 0.3 s respectively, but only about 40% of them are inside the networks (with an azimuthal gap less than 180°). We selected 339 earthquakes which were recorded with minimum 6 phases, a RMS value less than 0.3 s and both horizontal and vertical uncertainties less than 3.0 km. For this selection the average of location uncertainties are 1.25 km, depth of seismicity is 8.5 km, the number of the phases read for locating is 12 and RMS of time residuals is 1.4 s. Distribution of these earthquakes shows that the horizontal dimension of the two located clusters with the new model is almost the same as the length of the fault, about 100 km, has good correspondence with the fault and shows the activity of Astaneh two segments. The depth histogram of the earthquakes shows that the majority of the events have been located between 4 and 14 km. To constrain the geometry of the Astaneh fault, we plotted two cross-sections both perpendicular (in section points) to the Alborz range tectonic structures and Astaneh fault. All of the seismicity dips concluded from the depth distribution have high angle and southeast dipping but have more vertically beneath the southwest segment of the Astaneh fault than the east segment. Because of having no earthquake deeper than 23 km, the seismo-genic zone in the area was not greater than 23 km deep. We were also able to estimate the sedimentary cover thickness about 4 km.}, keywords = {Astaneh Fault,Crustal velocity model,East Alborz,Local Networks,Micro-earthquake}, title_fa = {بررسی لرزه‌خیزی گسله آستانه در البرز شرقی}, abstract_fa = {گسله آستانه یکی از گسله‌‌های جنبا در سامانه گسلی شاهرود است که نقش مهمی در زمین‌ساخت البرز شرقی بازی می‌‌کند. در این مقاله لرزه‌خیزی محلی و ناحیه‌‌ای در ناحیه آستانه درالبرز شرقی با برداشت داده خردزمین‌لرزه‌‌ها و پردازش آنها، بررسی شده است. در این بررسی از داده‌‌های دو شبکه محلی که درمجموع به مدت 9 ماه ناپیوسته در طول سال‌‌های 2007 و 2008 نصب شده‌‌اند و نزدیک به دو سال داده‌‌های شبکه موسسه ژئوفیزیک دانشگاه تهران استفاده شده است. پردازش هر دو دسته خردلرزه‌‌های شبکه‌‌های محلی و شبکه ژئوفیزیک در گستره البرز شرقی نشان می‌‌دهد که این زمین‌لرزه‌‌ها پیرامون گسله‌‌های خزر، شمال البرز، گرمسار، مشا، شمال سمنان و به‌ویژه آستانه پراکنده شده‌اند. این پردازش بر جنبایی آنها نیز دلالت دارد. در این ناحیه یک الگوی سرعتی دو لایه‌‌ای موج P روی یک نیم‌‌فضا با سرعت 4/5 کیلومتر بر ثانیه در سطح تا 3/6 کیلومتر بر ثانیه در ژرفای بالاتر ازناپیوستگی موهو، پهنای 4 کیلومتری نهشته‌‌های رویی، پهنای 23 کیلومتری لایه لرزه‌زا و دو شیب تند پراکندگی ژرفی خردلرزه‌ها منطبق با دو قطعه گسله آستانه به‌دست آمده است.}, keywords_fa = {الگوی سرعتی پوسته,خردلرزه,شبکه محلی و البرز شرقی,گسله آستانه}, url = {https://jesphys.ut.ac.ir/article_23083.html}, eprint = {https://jesphys.ut.ac.ir/article_23083_49242334ac3d5f92b93cd05e8f7ae37f.pdf} } @article { author = {Sohbati, reza and Fattahi, Morteza and Fazeli, Hasan and Quigley, Mark and Schmidt, Armin and Azizi, Ghasem and Maghsoudi, Mehran}, title = {Cheskin blind thrust and its probable effect on the missing millennium (Qazvin plain)}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {17-31}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The archaeological investigations of three prehistoric tells (Zagheh, Qabrestan, and Sagzabad) located at a distance of ~2 km from each other in the Qazvin plain (NW Iran) indicates that Tepe Zagheh was occupied in 6th and 5th millennia B.C. But due to unknown reasons life at this site ceased and started in Tepe Qabrestan at the beginning of 4th millennium B.C. This tell was occupied for a millennium, and the abundance of pottery workrooms shows that this site was probably an industrial center with an area of ~10 hectares at the time. However, again due to unknown reasons, Qabrestan was deserted, and for ~1000 years (The Missing Millennium, 3000-2100 B.C) there was no sign of habitation around it until the end of the 3rd millennium B.C when this time Iron Age people settled in Tepe Sagzabad. Among many possibilities from natural reasons such as climate change to human activities like war which could cause the abandonment of Qabrestan, the occurrence of an earthquake is also likely. According to past seismicity and the seismotectonics of the Qazvin region, the occurrence of an earthquake during the Missing Millennium is possible. One of the active faults in the Qazvin region, whose movement could have led to the destruction of Tepe Qabrestan is the Cheskin Blind Thrust. This fault which was previously unknown has a length of at least 12 km and is capable of generating earthquakes with magnitudes of 6. Because of this and the importance of blind thrusts in general, we decided to determine the activity of this fault. We took a sample from the top of a fold from a ridge which was uplifted due to the activity of the Chekin Blind Thrust beneath. The age of this sample was determined by applying the OSL dating method. Using this age, we estimated an uplift rate of 1.9 ± 0.5 mm/yr. Considering a dip angle of 30°, we also estimated a convergence rate of 2.4-4.2 mm/yr and a slip rate of 2.8-4.8 mm/yr for this blind thrust. Using the Scholz’ relationship (1982) which relates the length of the fault to its average displacement per event, the average displacement on this fault is ~0.6 m. Division of this average displacement per event by the estimated slip rate leads to a return period of 125-214 years for the earthquakes on the Cheskin Blind Thrust.}, keywords = {Cheskin Blind Thrust,OSL,Qazvin Plain,the Missing Millennium}, title_fa = {راندگی پنهان چسکین و اثر احتمالی آن بر هزارة گمشده (دشت قزوین)}, abstract_fa = {کاوش‌‌های باستان‌‌شناسی در سه محوطة باستانی زاغه، قبرستان و سگزآباد در دشت قزوین در شمال غرب ایران مرکزی نشان می‌‌دهد که تپة باستانی زاغه در هزاره‌‌های ششم و پنجم پیش از میلاد مورد سکونت قرار داشته است. اما به دلایل نامعلومی زندگی در این تپه متوقف شده و با آغاز هزارة چهارم پیش از میلاد، در تپه قبرستان از سر گرفته شده است. زندگی در "قبرستان" برای هزار سال ادامه داشته و با توجه به فراوانی کوره‌‌‌های سفالگری یافت شده در آن، گمان می‌‌رود که این تپه در زمان خود یک مرکز صنعتی پر رونق، با وسعتی در حدود ده هکتار بوده باشد. با‌‌این‌حال معلوم نیست که چرا در آغاز هزارة سوم پیش از میلاد، زندگی در این تپه نیز متوقف شده است و از آن پس نزدیک به هزار سال (هزارة گمشده) نشانی از سکونت در حوالی آن یافت نمی‌‌شود؛ تا اینکه در اواخر هزارة سوم پیش از میلاد، گروهی از مردمان، این بار در تپه سگزآباد ساکن شدند. بررسی پیشینة لرزه‌‌خیزی و لرزه‌‌زمین‌‌ساخت گسترة قزوین نشان می‌دهد که رخداد زمین‌لرزه به‌منزله یکی از دلایل ممکن در ترک سکونت در تپة باستانی قبرستان، کاملاً محتمل است. یکی از گسل‌‌هایی که جنبش روی آن می‌توانسته باعث ویرانی "قبرستان" شود، راندگی پنهان چسکین است که نخستین‌‌بار در این تحقیق معرفی می‌شود. همچنین میزان فعالیت این گسل با استفاده از سن‌‌یابی به شیوة لومینسانس برانگیخته شدة نوری (optically stimulated luminescence)، تعیین شده است.}, keywords_fa = {دشت قزوین,راندگی پنهان چسکین,رخشانی برانگیخته شدة نوری هزارة گمشده}, url = {https://jesphys.ut.ac.ir/article_23084.html}, eprint = {https://jesphys.ut.ac.ir/article_23084_c7720133723df53646c7aefbecf19489.pdf} } @article { author = {Jazayeri Jouneghani, Sajjad and Oskooi, Behrooz}, title = {Depth Estimation of Ground Magnetic Anomalies using Standard Euler Deconvolutionin the Reshm area, Semnan}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {33-43}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {Depth estimation of the top of the bedrock in the sedimentary basins is the main goal in geomagnetic explorations. The depth estimation of this kind of anomalies can be done using different methods, in the cases where the bedrock is magnetized. In this article, we use the standard Euler deconvolution method and its results to interpret the magnetic data from the Reshm region in Semnan province of Iran. The estimated depths of the top of major anomalies in the area are resembled as 100 m and 135 m. In the potential field explorations, both of the depth estimation and the horizontal position detection of the source of anomalies and as a result, the imagination of the source of anomaly is the main purpose of exploration. Some methods can lead us to these purposes such as Euler deconvolution, Peters, Werner deconvolution, Analytical Signal, AN-EUL methods etc. Some methods such as the Analytical Signal can just show the horizontal positions of the anomalies. And some such as the Peters method can show just the depth of anomalies. The standard Euler deconvolution method can provide the estimated depths of anomalies and the horizontal region covering the source of the anomalies. In this paper we used Geosoft Oasis Montaj 6.4.2 software and also a Matlab code written by Durrheim and Cooper. The standard Euler method is based on the Euler equation, and using this method in the depth estimation of magnetic anomalies inserts the geology of the region into the calculations. A drawback of the Euler deconvolution is the scattering of the solutions estimated at different data window positions. We derive the analytical estimators for the horizontal and vertical source positions in 3D Euler deconvolution as a function of the x-, y-, and z-derivatives of the magnetic anomaly within a data window. From these expressions we show that, in the case of noise-corrupted data, the x-, y-, and z-coordinate estimates computed at the anomaly borders are biased toward the respective horizontal coordinate of the data window center regardless of the true or presumed structural indices and regardless of the magnetization inclination and declination. On the other hand, in the central part of the anomaly, the x- and y-coordinate estimates are very close to the respective source horizontal coordinates regardless of the true or presumed structural indices and regardless of the magnetization inclination and declination. This contrasting behavior of the horizontal coordinate estimates may be used to automatically delineate the region associated with the best solutions. Applying the Euler deconvolution operator inside this region would decrease the dispersion of all position estimates, improving source location precision.}, keywords = {anomaly,Euler,geomagnetic method,Reshm area.,structural index,Window Size}, title_fa = {برآورد عمق بی‌هنجاری‌‌های مغناطیسی زمینی با استفاده از روش واهمامیخت اویلر استاندارد در منطقه رشم، استان سمنان}, abstract_fa = {در پردازش و تفسیر داده‌های مغناطیس زمینی، عمق بی‌هنجاری مدفون، از چندین روش، قابل محاسبه است. در این مقاله، برآورد عمق بی‌‌هنجاری‌های مغناطیسی ناشی از پیمایش‌های مغناطیسی در منطقه رشم استان سمنان، با استفاده از روش اویلر مورد بررسی قرار می گیرد. بررسی صورت گرفته در این منطقه شامل دو بی‌هنجاری کمانی‌‌شکل بزرگ در شمال در جنوب منطقه، به ترتیب عمق 135 و 100 متر را برای این بی‌هنجاری ها به‌دست داده که با نتایج برداشت ژئوفیزیکی به روش قطبیدگی القایی انطباق دارد.}, keywords_fa = {اندیس ساختاری,بی‌‌هنجاری,پهنای پنجره,رشم,روش اویلر,مغناطیس}, url = {https://jesphys.ut.ac.ir/article_23085.html}, eprint = {https://jesphys.ut.ac.ir/article_23085_f8e2d327738becee7a6ce8e2ce220a7f.pdf} } @article { author = {Rahimi Zeynal, Asal and Riahi, Mohammad Ali}, title = {Application of seismic inversion and multi attribute analysis to prediction of porosity distribution in an oil field in SW of Iran}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {45-55}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {This paper describes a methodology for the integration of well logs and a series of grid-based attributes extracted from interpreted seismic data for prediction of porosity distributions. The studied area is located in the southwest Iran. Before finding a relationship between the target logs and predicted logs from 3D seismic data, we have interpreted the 3D seismic data in the studied area. Also we matched and combined well data with seismic for forward modeling and seismic inversion. Inversion produces a full band acoustic impedance model of earth which improves the vertical resolution. Then we have checked other different inversion methods such as spare spike and model based. Since the model based method resulted with a better resolution outcome, therefore we decided to apply model based inversion method in the reservoir level. In the next step we applied a linear and a non linear transforms between a group of seismic attributes and porosity logs. Then we obtained a relationship for estimating the porosity at all locations of the seismic volumetric data. Finally we found an improvement in the porosity prediction from linear multi attribute transforms when using neural network methods. Introduction: Nowadays integration of different sources of data and building static and dynamic reservoir models has increased efficiency of exploration and production activities. Seismic reservoir characterization has crucial importance in those activities attributes, their analysis and study form are major field of study in reservoir characterization. Acoustic impedance is one of the attributes that from some years ago has been used extensively for determination of reservoir properties, especially porosity, fluid saturation and clay content. The idea of using multi attribute seismic analysis to estimate log properties was first introduced (Schultz et al., 1994). The integration of well-log and seismic data has been a consistent aim of geoscientists. One type of integration is forward modeling of synthetic seismic data from the logs. A second type of integration is inversion of the logs from the seismic data which is called seismic inversion. The method for finding the statistical relationship between seismic data and well logs has been described by Russell et al. (1997). We used this method in an oil field in the southwest of Iran. The data have been supplied by the National Iranian Oil Company (NIOC) and consist of a 3-D seismic data, which ties 6 wells. In this paper we applied model based seismic inversion method. The Main Description: We interpreted the 3-D seismic data in the studied area by formal Software then depth map were prepared and also appropriate velocity field. Synthetic seismogram method is used for horizon identification. Understanding of reflection characters is essential for tracking of target horizons in the whole area. The 3-D seismic volume was interpreted at different horizons and was reproduced by the model based inversion method. The training data set for each well consist of the real porosity, a single composites seismic trace that was extract from the 3-D seismic volume around the well and the impedance log predicated with the seismic inversion method. The attributes available for the multi attribute analysis was 25 plus external of seismic inversion. The cross plot of the target porosity value against predicted porosity from five seismic attributes (Cosine Instantaneous Phase, 1/Inversion-Result, Filter 25/30-35/40, Derivative Instantaneous Amplitude, Amplitude Weighted Phase) are shown in Figure 5. The normalized correlation is now 0.74 For improving the result we used the radial basis function neural network (RBF) method, the RBFN, described by Powell,1987, and first applied by Ronen et al, 1994, is a feed-forward network where the Gussian bell curve is the basis function. Conclusions: In this study we have focused mainly on 3D seismic interpretation of gas bearing layer by using different seismic inversion and multi attribute transform methods, the acquired results are as follow: 1. The optimum number of attributes in this study was five (Cosine Instantaneous Phase, 1/Inversion-Result, Filter 25/30-35/40 Hz, Derivative Instantaneous Amplitude, and Amplitude Weighted Phase). 2. The quality of inverted data (as one of the main input) is very important in multi attribute analysis. 3. We found that correlation coefficient for porosity prediction is improved in RBFN method with respect to multi attribute transform. Acknowledgments: The authors wish to thank NIOC, Exploration Directorate, and Geophysics Department for supporting this study. We are grateful to Research Council of the University of Tehran for providing full support of this study.}, keywords = {Acoustic impedance,Neural Network,Porosity,RBFN,seismic inversion}, title_fa = {کاربرد روش وارون‌سازی لرزه‌ای و بررسی چندنشانگرها در برآورد توزیع تخلخل در میدان نفتی جنوب غربی ایران}, abstract_fa = {در این تحقیق روش ترکیب داده‌های نگار چاه همراه با مجموعه‌ای از نشانگرهای حاصل از داده‌های لرزه‌ای، به‌‌منظور برآورد توزیع تخلخل بررسی شده است. منطقه مورد تحقیق در جنوب غربی ایران واقع است. قبل از پیدا کردن ارتباط بین نگار هدف و نگار به‌دست آمده از داده‌های سه‌بُعدی لرزه‌ای، داده‌های سه‌بُعدی لرزه‌ای حاصل از منطقه موردِنظر تفسیر شد. سپس داده‌های چاه با داده‌های لرزه‌ای به‌‌منظور مدل‌سازی مستقیم و وارون‌سازی لرزه‌ای ترکیب شد. روش وارون‌سازی یک مدل امپدانس صوتی با باند کامل زمین را تهیه می‌کند که باعث افزایش تفکیک‌پذیری لایه‌‌های موردِنظر مخزن می‌شود. سپس روش‌های وارون‌سازی با خارهای پراکنده و وارون‌سازی برمبنای مدل مورد بررسی و استفاده قرار گرفته‌‌اند. به علت اینکه روش وارون‌سازی بر مبنای مدل دارای نتایج بهتری بود، درحکم روش اصلی تحقیق در نظر گرفته شده است. در مرحله بعدی تبدیل خطی و غیرخطی بین گروهی از نشانگرهای لرزه‌ای و نگار تخلخل برای به‌دست آوردن حجم تخلخل منطقه موردِنظر به کار رفته است. درنهایت استفاده از روش شبکه عصبی نسبت به تبدیل خطی چندنشانگر پاسخ بهتری به‌دست داده و روش شبکه عصبی تابع بر مبنای شعاعی (RBFN) برای برآورد توزیع تخلخل در میدان نفتی جنوب غربی ایران به کاربرده شده است.}, keywords_fa = {امپدانس صوتی,تخلخل,شبکه عصبی,نشانگر لرزه‌ای,وارون‌سازی}, url = {https://jesphys.ut.ac.ir/article_23086.html}, eprint = {https://jesphys.ut.ac.ir/article_23086_219de8133cea10db1bfebdb2a859bfe1.pdf} } @article { author = {Ilaghi, Hossein and Yamini-Fard, Farzam and Tatar, Mohammad}, title = {Crustal Velocity Structure In Fin region (Zagros - Iran)}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {57-69}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The NW-SE trending Zagros fold and thrust belt extends for about 1,800 km from a location some 300 km SE of the East Anatolian Fault in NE Turkey to the Strait of Hormuz where the north-south trending Zendan-Minab-Palami fault system (ZMP) separates the Zagros belt from the Makran accretionary prism. The NE limit of the Zagros belt is marked by the Main Zagros Reverse Fault which is rotated about a horizontal axis to form a steeply NE-dipping to sub-vertical reverse fault with a right-lateral component of movement of unknown magnitude (Wellman, 1966; St?cklin, 1974 Berberian, 1995). The extension of the Main Zagros Reverse Fault to the NW of latitude ~33o is referred to as the Main Recent Fault (Tchalenko and Braud, 1974), and is a right-lateral strike-slip fault as indicated by earthquake focal mechanism solutions and field evidence (Talebian and Jackson, 2002; Bachmanov et al., 2004). There is no clear surface boundary to the frontal edge of the Zagros fold and thrust belt where folding is gentle both on land and beneath the Persian Gulf. However, the southern edge of the Zagros deformation front can be defined at different levels by the shape in map view of the oil- and gas fields (Talbot and Alavi, 1996), and also by the seismicity and topography (Jackson and McKenzie, 1984). The deformation within the Zagros fold and thrust belt is due to the relative convergence between Arabia and Eurasia since the Middle-Late Cretaceous period (Falcon, 1974; St?cklin, 1974; Koop and Stoneley, 1982). However, the Zagros fold and thrust belt were formed during the main phase of the Zagros orogeny in the Late Miocene Epoch to recent times (St?cklin, 1968; Stoneley, 1981; Hessami et al., 2001). Current shortening at a rate of about 7 mm/yr (Tatar et al., 2002; Vernant et al., 2004; Hessami et al., 2006) as well as active seismicity indicate that this deformation is still active. A moderate earthquake (MW=5.9) struck the Fin region in Hormozgan Province on March 25, 2006 (07:29 GMT) with a little damage. The main-shock was followed by 3 aftershocks with magnitude greater than 5. After reading seismic phases and initial location of the aftershocks and using 90 selected aftershocks which had reliable accuracy, we obtained a velocity model for the upper crust beneath the studied region. Calculated velocity model for the Fin region showed two discontinuities at 12 and 18 kilometer depths. P wave velocity obtained was 5.65 km/s, 5.9 km/s and 6.25 km/s for the first layer, second layer and half space respectively.}, keywords = {aftershock,fin,Zagros}, title_fa = {تعیین ساختار پوسته فوقانی در ناحیه فین (ایران- زاگرس)}, abstract_fa = {در ساعت 58 :10 روز 5 فروردین 1385 (7:29 UTC)، زمین‌‌لرزه‌‌ای با بزرگای گشتاوری 7/5 در بخش فین استان هرمزگان به وقوع پیوست و باعث ایجاد خسارات جزئی در منطقه شد. زمین‌لرزه اصلی با 4 پس‌لرزه با بزرگای گشتاوری 5/5 (9:55 UTC )، 2/5 (10:00 UTC)، 5 (11:02 UTC)، 9/4 (12:15 UTC)، دنبال شد که سازوکار محاسبه شده برای آنها مشابه زمین‌لرزه اصلی از نوع معکوس است. در این مقاله با استفاده از پس‌‌لرزه‌‌های ثبت شده با شبکه موقت محلی نصب شده در منطقه، نسبت V P/VS برای ناحیه فین 73/1 و ضریب پواسون 25/0 به‌دست آمد و در نهایت ساختار سرعتی پوسته فوقانی به روش برگردان یک‌‌بُعدی، محاسبه شد که نشانگر وجود دو مرز لایه در اعماق 12 و 18 کیلومتر است. ممکن است این دو مرز، مرز پایینی پوشش رسوبی و مرز بین لایه بلورین فوقانی و زیرین باشند.}, keywords_fa = {پس‌لرزه,زاگرس,ساختار پوسته}, url = {https://jesphys.ut.ac.ir/article_23087.html}, eprint = {https://jesphys.ut.ac.ir/article_23087_227f3cb79514fd8511e32b03d7881530.pdf} } @article { author = {Naseri, Jalil and Siahkoohi, Hamid Reza}, title = {Seismic texture recognition in time-frequency domain}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {71-81}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {In seismic exploration studies different types of techniques are used to recognize seismic features in terms of their temporal and spatial spectra. Variations in frequency content are sensitive to subtle changes in reflection information (Castro de matos et al., 2003). In this study the joint time-frequency analysis is used for seismic texture recognition. Discrete wavelet transform (DWT) without decimation is implemented to identify the seismic trace singularities in each geologically oriented segment along a seismic line within a time window. The DWT involves a decimation operation and a down sampling by a factor of two. This process causes DWT not to be invariant to displacement in time and applicable for detecting and characterizing the singularities. To obtain an invariant DWT, the down sampling operation is removed from the process. DWT without decimation, known as wavelet a trous, is a signal convolution with filter bank coefficients with zeros inserted between the samples (Matos, 2007). The mathematical concepts are the basis of detection of singularities in signals. The signal inflection points are associated with the first derivative extremes. A differentiable smoothing function , with integral equal to one, is defined, which converges to zero when tends to . Since the integral of and are zero in the interval of they can be considered as a wavelet. In this way, the WT of a signal , in the scale , can be obtained by convolving the signal with a scaled wavelet; . If the wavelets are substituted by the derivatives of smoothing function into the last equations, they change to; . Hence, the wavelet transforms and are the first and second derivatives of the signal. The local extremes of and zeros of correspond to the inflection points of . The local changes in the seismic event manifest themselves as changes in the extremes, which are the minimum and maximum amplitudes of each decomposition level of seismic traces derived by DWT without decimation. Hence lateral changes to seismic reflections are characterized by the extremes. The extremes obtained from decomposition are used as seismic attributes and classified to define the seismic texture variation. A support vector machine (SVM), a learning machine based on statistical learning theory (Vapnik, 1995), is used to classify the attributes. The concept of SVM is based on finding an optimal separating hyperplane, which could be derived either in the input space or in a more generalized feature space. SVM uses the structural risk minimization principle to construct decision rules that generalize well (Burges, 1998). The SRM method is based on the fact that the test error rate is bounded by the sum of the training error rate and a term which depends on the VC dimension of the learning machine, and generalized by minimizing the summation. For a linear hyperplane the decision function is; . The VC dimension can be controlled by controlling the norm of the weight vector . Giving training data , a separating hyperplane which generalized well can be found by subject to , , . The method can be generalized to a nonlinear decision surface by mapping the input nonlinearly into some high dimension space, and finding the separating hyperplane in the space. This is achieved by using different types of kernel functions, , instead of ordinary scalar product . Consequently, the generalized decision function for a nonlinear input will be; . Classification can be performed in several dimensions using two or more attributes derived from decompositions. In this instance two attributes are used as inputs for the SVM classifier and the hyperplane separates the regions where the seismic reflections are changing. The hyperplane was constructed by half of the selected training data, and then its accuracy was cross checked by the other half. Finally, all test data is used as input to the classifier. For instance, the seismic textures are classified into two types within a time window of a phantom horizon on a 2D seismic section. The color code of green and white indicate different seismic textures on the color band.}, keywords = {seismic interpretation,SVM classification,Texture analysis,Wavelet transform}, title_fa = {شناسایی بافت‌های لرزه‌ای در حوزه زمان- بسامد}, abstract_fa = {هدف از این تحقیق شناسایی تغییر بافت‌های لرزه‌ای با استفاده از تبدیل زمان-بسامد (مقیاس) سیگنال‌‌های لرزه‌‌ای است. شناسایی گستره بافت‌‌های لرزه‌‌ای می‌تواند در تفسیر داده‌‌های لرزه‌‌ای کمک شایانی در تهیه مدل‌‌های زمین‌شناسی داشته باشد. تبدیل موجک که تصویری از سیگنال در مقیاس‌‌های گوناگون را عرضه می‌کند در شناسایی بافت‌‌های لرزه‌‌ای می‌تواند مفید باشد. انتخاب مناسب تابع موجک در شناسایی نحوه تغییر خواص سیگنال لرزه‌ای (که در اینجا ناشی از تغییر در بافت لرزه‌ای است) در امتداد خط لرزه‌‌نگاری و در یک بازه زمانی مشخص، نقش بسزایی دارد. بیشینه و کمینه دامنه ‌ضرایب موجک به‌دست آمده از تجزیه سیگنال با به‌کارگیری تبدیل موجک گسسته پایا (بدون کاهش تعداد نمونه)، منطبق بر نقاط عطف در دو سوی رویداد لرزه‌ای مورد‌‌ِنظر است. در این تحقیق این بیشینه و کمینه‌‌ها درحکم نشانگرهایی (Seismic attribute) به‌کار می‌روند که می‌توانند تغییرات بافت لرزه‌ای (Seismic texture) را نمایان سازند. برای تعیین گستره تغییرات و دسته‌‌بندی نشانگرهای به‌دست آمده در حوزه زمان–بسامد، از ابزار ریاضی بنام ماشین پایه‌برداری استفاده شده است. ماشین پایه‌برداری بر خلاف روش‌‌های مرسوم دیگر (مانند شبکه عصبی) که سعی در کمینه ساختن خطای آموزش دارند، این روش سعی در کمینه کردن حد بالایی خطای تعمیم برای بیشینه‌‌سازی حاشیه بین صفحه جدایش چند‌بُعدی و داده‌‌ها دارد (اسکالکوپف و همکاران، 1996). ما از ماشین پایه‌برداری برای دسته‌‌بندی نشانگرهای به‌دست آمده از تبدیل موجک استفاده کردیم که احتمال می‌رود بافت لرزه‌‌ای در آنها تغییر کرده باشد.}, keywords_fa = {تبدیل موجک,تحلیل بافت‌های لرزه‌ای,تفسیر مقاطع لرزه‌ای}, url = {https://jesphys.ut.ac.ir/article_23088.html}, eprint = {https://jesphys.ut.ac.ir/article_23088_a5589c0db1053569fa749c71dedf91f1.pdf} } @article { author = {Vajedian, Sanaz and Sarajian, Mohammad Reza and Mansouri, Babak}, title = {Derivation of the complete (3d) displacement field using interferometric Synthetic Aperture Radar (SAR) technique; Case Study on the Bam fault}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {83-96}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {Investigation and monitoring of the displacement field derived from deformation is among the important studies in earth science and geophysics topics, which plays a main role in the prevention and praxeology of natural disasters such as earthquake, subsidence, land slide et cetera. Here we can mention the several methods in geodetic measurement and deformation monitoring such as spirit leveling, the positioning systems like (SLR, Satellite laser range finding), (VLBI, Very long baseline interferometer) and (GPS, Global positioning system), and Interferometric Synthetic aperture Radar (InSAR) technique. Of the above methods, the InSAR technique with the ability to generate large, continual and contiguous ground overlays, so with high spatial and temporal resolution it turns out to be one of the important techniques. The goal of this study is derivation of a continual map for three orthogonal components of the co-seismic surface displacement field with InSAR data. The displacement components observed with radar are in the direction of satellite line of sight. The satellite LOS displacement vector has a lower sensitivity to north displacements than to the other two components of a surface displacement, i.e. east and up, due to the near-polar satellite orbits. This act caused a reduction in the accuracy of the calculated deformation components. There are several solutions to this problem and in this paper, the azimuth offset data of ascending and descending passes is used solve this problem. So as regards efficacy of atmosphere errors on radar imaging, the calculation of displacement components is relative, so with far field data derived from coherence images, the necessary shift to converting the relative values to absolute was calculated with the detrending process and reduced from the calculated deformation components. The case study of this research is on the 2003 Bam earthquake using co-seismic and pre-seismic pairs of Envisat radar images in ascending and descending orbits. The images were processed with Doris Software in Linux systems. Finally the 3D reconstruction process was accomplished with Matlab software in Windows. The derived results in this study have compared well with other publications.}, keywords = {Ascending,Azimuth Offset,Co seismic,Descending,Differential Interferometry,Pre seismic,Synthetic Aperture Radar (SAR)}, title_fa = {استخراج میدان جابه‌جایی سه‌بُعدی با استفاده از فن تداخل‌سنجی رادار با دریچه مصنوعی (SAR)؛ بررسی موردی گسل بم}, abstract_fa = {هدف این تحقیق استخراج سه مؤلفه اورتوگونال میدان جابه‌جایی هم‌لرزه‌ای سطح، با استفاده از تداخل‌سنجی راداری (InSAR, Interferometric Synthetic aperture radar) است. تصویربرداری راداری، مؤلفه‌های مشاهداتی جابه‌جایی را در راستای دید ماهواره و در دو عبور بالارو (Ascending) و پایین‌رو (Descending) به‌دست می‌دهد. با توجه به نزدیک به قطبی بودن (Near polar) مدار ماهواره، حساسیت مؤلفه‌های جابه‌‌جایی حاصل به راستای شمالی-جنوبی کم است که این امر باعث کم شدن دقت مؤلفه دگرشکلی (Deformation) محاسبه شده می‌شود. برای رفع این مشکل راهکارهای متعددی وجود دارد. در این تحقیق از تصاویر سَمت-دوراُفت (آزیموت-دوراُفت (Azimuth offset)) عبور پایین‌رو استفاده شد. همچنین با توجه به تأثیر خطاهای جوی روی تصویربرداری راداری، مؤلفه‌های دگرشکلی به صورت نسبی تعیین شد و سپس با استفاده از داده‌های فرامیدانی (Far field) حاصل از تصویر هم‌چسبی، انتقال لازم برای تبدیل مقادیر نسبی به مطلق، به‌واسطه فرایندی به نام detrending محاسبه و از مؤلفه‌های محاسباتی کسر شد. بررسی موردی این تحقیق روی زلزله بهمن ماه 1383 شهر بم صورت گرفته است. در این تحقیق زوج تصاویر راداری پیش‌لرزه‌ای (Pre seismic) و هم‌لرزه‌ای (Co seismic) ماهواره Envisat در عبورهای بالارو و پایین‌رو مورد بررسی قرار گرفت و تصاویر با استفاده از نرم‌افزار DORIS در محیط لینوکس پردازش شد. در پایان بازسازی میدان جابه‌جایی در محیط ویندوز با نرم‌افزار Matlab صورت پذیرفت و نتایج به‌دست آمده در این تحقیق با سایر گزارش های منتشر شده مقایسه شد.}, keywords_fa = {آزیموت- دوراُفت,بالارو,پایین رو,پیش لرزه ای,تداخلسنجی,رادار با دریچه مصنوعی,هم لرزه ای}, url = {https://jesphys.ut.ac.ir/article_23089.html}, eprint = {https://jesphys.ut.ac.ir/article_23089_0dea889ca05cd541f4393d636134433e.pdf} } @article { author = {Rezaeifarahabadi, Mahbobeh and Riahi, Mohammad-Ali and Mishinchi, Mir Sattar}, title = {Aliasing in ?-? domain and attenuation of aliased linear noise in this domain}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {97-110}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {One of the common problems in reflective seismic records is the existence of coherent linear and random noises which cause covering of the most important parts of reflective signals; therefore, it is necessary to attenuate them by processing methods. Several processing techniques have been devised for attenuation of coherent linear noises and linear radon or ?-? transform is a powerful technique for attenuation of these noises. In this method, by doing slant stack (summing amplitudes in the offset domain along slanted paths), data will transform to ?-? domain and least square method is used for this transform. p: Ray parameter ?: Zero offset intercept h: Offset In this domain, reflectors and coherent linear noises map separate points. Then, after elimination of coherent linear noises in this domain, data reconstructs are employed to offset domain by using inverse ?-? transform. Aliasing in this domain appears as: aliasing in ?, aliasing in P and spatial aliasing. If there is spatial aliasing in data, by using following methods, aliasing affects will be eliminated: 1- High cut filter: By applying this filter alias artifacts will be eliminated. 2- LMO correction: in order to prevent aliasing of the noise trends to be attenuated, LMO may be applied around the ?-? transform. 3- interpolation in h direction: In this method data will be interpolated in h direction and then transform to ?-? domain and linear noise will be eliminated. By comparing these three methods, it is clear that the result of the interpolation method is the best. In this study, linear ?-? transform has been tested on several aliased synthetics and real data and acceptable results have been provided. By comparing this method with F-K filter results, it is clear that the results of these two methods are nearly similar but in some seismic data, F-K filter was not a good method for aliased surface wave attenuation and attenuated little energy of reflectors. Therefore, when the reservoir study is the case, ?-? transform is preferred to F-K filter.}, keywords = {Aliasing,FK filter,interpolation,?-? transform}, title_fa = {اثر دگرنامی در تبدیل ?-p وچگونگی تضعیف نوفه‌‌های لرزه‌‌‌ای خطی دگرنامی شده در این تبدیل}, abstract_fa = {روش تبدیل ?-p یکی از روش‌های تضعیف نوفه‌‌های خطی در داده‌های لرزه‌‌‌ای بازتابی، است. با انتقال این داده‌‌ها به حوزه p ?- و اِعمال فیلتر در آن حوزه می‌‌توان نوفه‌های خطی را تضعیف کرد. دگرنامی (Aliasing) در این حوزه به سه صورت دگرنامی در ?، دگرنامی در p و دگرنامی مکانی (Spitial Aliasing) پدیدار می‌‌شود. در جاهایی که یک پدیده دچار دگرنامی مکانی شود با به‌کاربردن روش‌هایی مثل اِعمال فیلتر پایین‌‌گذر، تصحیح LMO و درون‌یابی در جهت h می‌‌توان اثرات دگرنامی را کاهش داد.}, keywords_fa = {تبدیل ?-p,درون‌یابی,دگرنامی,فیلتر F-K}, url = {https://jesphys.ut.ac.ir/article_23090.html}, eprint = {https://jesphys.ut.ac.ir/article_23090_b0e1333e3620854c38b1238e31c074d5.pdf} } @article { author = {Doulati Ardejani, Faramarz and Moradzadeh, Ali and Yaghobipour, Mohammad and Tabatabaie, S. Hashem}, title = {A study of the capability of the finite element method in gravity anomalies separation of oil traps}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {111-125}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {This paper attempts to investigate the capability of the numerical finite element method for the removal of the regional effects from the observed gravity data from the Dehnow anticline. From a geological point of view, the Dehnow area is a part of the Fars sedimentary basin south-east Iran. The Khamy formation and Bangestan group are the oldest geological structures in the area that have outcrops. Younger structures consist of Aghajary, Mokhtari, Mishan, Gachsaran and Asmary. The dominant structural trend in the area is northwest-southeast. The Dehnow anticline is located between the Hendurabi and Razak faults. These faults are almost perpendicular to the Dehnow anticline. The presence of these two series of perpendicular faults has been well proved by the detailed geological investigations carried out in the area. The first type of the faults with a northwest-southeast direction has formed oil seeps due to the extension of these types of faults to the dipper layers. The second types of faults in the salt layers of the Hormoz formation at the base of the Dehnow anticline may be related to the salt intrusion. The evidence of the salt outcrops can be recognized at two points from the Dehnow anticline. The Dehnow anticline is surrounded by Ashkenan, Ahal, Boochir, Hamiran, Hashniz and Kemeshck towns. The Tabnack gas structure is located in the west of this district. The anticline can be accessed through Asalouie-Bandarlengeh and Lamard-Ashkenan- Gavbandy roads. The area has a very harsh topography with numerous mountains and valleys. The region is very warm and wet in the summer. It has a mild winter. A careful geological study of the area, a detail investigation of structural features such as faults associated with the Dehnow anticline and application of the proper geophysical techniques and other exploration methods is necessary to investigate its subsurface extension and to further identify salt plug intrusion into this anticline. Furthermore, the information obtained by the various exploration techniques can help to design a cost management program related to any further investigation in the area. The gravity method has been used in the past in many applications related to petroleum exploration studies as a way of investigating oil traps and exploring the impact of faults and intrusions in particular salt into such geological structures. This method together with other geophysical methods including magnetic and Magnetotelluric (MT) have been used in the study area to achieve the above objectives. Anomaly separation using appropriate techniques is noted to be an important stage in the interpretation of gravity data in order to accurately detect the subsurface oil traps. The literature review has shown that despite the conventional separation methods such as first and second vertical derivatives, upward and downward continuations, weighting average and trend surface analysis that have been used during the past few decades in the separation of gravity anomalies in the exploration of oils and ore deposits, the application of the finite element method related to anomaly separation has not been widely reported so far. Using new techniques in the regional-residual anomalies separation of the observed gravity data is a crucial demand in gravity interpretation. In this paper, the finite element approximation method was used to remove regional effects from the measured gravity data of the Dehnow anticline. For regional gravity approximation, four nodes element, eight nodes isoparametric quadratic element and twelve nodes cubic element were used. The necessary computations were performed on a non-dimensional space, ranging between -1 and 1 and subsequently translated to the real x-y space. The capability of the finite element method in regional-residual separation of the gravity data was evaluated using the conventional separation techniques including the trend surface method. The residual map obtained using the finite element method indicates the presence of two anticlines and three syncline structures with a northwest – southeast strike. The anticlines identify the Dehnow structure. The results of the finite element method are in close agreement with those results obtained from the conventional methods; confirming that the finite element approximation technique is a capable method for computation of the regional gravity anomaly free from residual effects.}, keywords = {anomaly separation,Dehno area,Finite element,Gravity data,oil trap}, title_fa = {بررسی قابلیت روش اجزاء محدود در جداسازی بی‌هنجاری‌‌های گرانی ساختمان‌‌های نفتی}, abstract_fa = {استفاده از روش‌‌های مناسب تفکیک بی‌هنجاری‌ها در تعیین وضعیت دقیق ساختمانی تله‌‌های نفتی یکی از مسائل مهم در تفسیر داده‌‌های گرانی است. اگرچه روش‌‌های متداول تفکیک بی‌هنجاری‌ها از قبیل مشتقات اول و دوم، گسترش بی‌هنجاری‌ها به سمت بالا و پایین، متوسط‌‌گیری وزنی و روند سطحی طی سالیان متمادی به‌منظور تفکیک بی‌هنجاری‌های گرانی در اکتشاف منابع نفتی و کانسارها به کار گرفته شده است بااین‌حال ضرورت استفاده از روش‌‌های جدید در تفسیر داده‌‌های گرانی هنوز احساس می‌شود. در این مقاله از توانمندی‌‌های روش عددی اجزاء محدود به منظور حذف اثرات ناحیه‌‌ای داده‌‌های گرانی منطقه دهنو استان فارس استفاده‌یمی‌‌شود. برای برآورد گرانی ناحیه‌‌ای، از اِلمان‌‌های چهار گره‌‌ای، هشت گره‌‌ای با تابع درون‌‌یاب درجه دو و اِلمان دوازده گره‌ای با تابع درون‌یاب درجه سه ستفاده شد. محاسبات مورد نیاز در فضای بدون بُعد ، در فاصله 1- و 1 صورت گرفت و سپس مجدداً به فضای واقعی ??? برگردانده شد. با استفاده از روش‌‌های متداول، قابلیت و توانمندی، روش اجزاء محدود در جداسازی بی‌هنجاری‌‌های ناحیه‌‌ای و محلی مورد ارزیابی قرار گرفت. نقشه باقی‌مانده حاصل از روش اجزاء محدود دو بی‌هنجاری تاقدیسی و سه بی‌هنجاری ناودیسی را مشخص کرد. بی‌هنجاری‌‌های تاقدیسی منطبق بر ساختمان دهنو هستند. نتایج حاصل از روش اجزاء محدود در تطابق نسبتاً خوبی با نتایج سایر روش‌‌های تفکیک بی‌هنجاری‌ها است که این موضوع خود قابلیت استفاده از روش اجزاء محدود را برای حذف اثرات ناحیه‌‌ای از مقادیر گرانی برداشت شده به اثبات می‌‌رساند.}, keywords_fa = {اجزاء محدود,تفکیک بی‌هنجاری‌ها,تله نفتی,داده‌‌های گرانی,منطقه دهنو}, url = {https://jesphys.ut.ac.ir/article_23091.html}, eprint = {https://jesphys.ut.ac.ir/article_23091_86742d7cb1adfc996b8076dfc3d95956.pdf} } @article { author = {Seif, Mohammad Reza and Sharifi, Mohammad Ali and Najafi Alamdari, Mehdi}, title = {Fast Dynamic Orbit Determination of LEO Satellites using the Legendre Polynomial Approximation}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {127-138}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The Low Earth Orbiting (LEO) satellites are widely used for geosciences applications. For most applications, precise orbital information of the satellites is required. A Combination of the in suite observations and dynamic orbit yields the optimum solution. In order to obtain the combined optimal solution, one needs to analytically or numerically propagate the state vector epoch by an epoch based on dynamic force models. In the analytical propagation, the dynamic model simplification leads to a biased solution. On the other hand, the numerical solution is a highly time- consuming computational task. Among all computation parts, computation of the Legendre Polynomials is the most time- consuming. Vectorization could effectively reduce computation time of the polynomials for the gravity field modeling. However, it cannot be implemented for the orbit determination because of the point-to-point computation in orbit propagation. In this article, we propose a new method for effective computation of the Legendre polynomials. The proposed method is based on the approximation of the polynomials at any arbitrary point using pre-computed values of the polynomials on evenly-spaced grid points (i.e., mesh points). Moreover, the first- and second-order derivatives of the polynomials are simultaneously computed using the recurrence relations at the mesh points. Therefore, the polynomials can be approximated using the Hermite approximation algorithm between the mesh points. In other words, employing the Legendre polynomial derivatives for estimating the best approximating function efficiently prevents the approximating oscillations of polynomials between the mesh points. Consequently, the approximating function perfectly follows the Legendre polynomials between the mesh points. Of course, a few methods have been proposed for fast computation of dynamic orbits by other researchers. They are mostly based on the computation of the gravitational acceleration on the mesh points and approximation of the acceleration between the mesh points. Our proposed method leads to higher accuracy since both the Legendre polynomials and their derivatives are used for approximation. In order to show numerical performance, the proposed method has been implemented for a CHAMP-type LEO satellite orbit propagation. Sub-millimeter approximation error can be achieved for a two-week propagated orbit.}, keywords = {Hermite Interpolation.,Legendre Polynomials,LEO satellites,Orbit propagation,Polynomial approximation}, title_fa = {تعیین سریع مدار دینامیکی ماهواره‌های LEO با استفاده از تقریب چندجمله‌ای‌های لژاندر}, abstract_fa = {مسئله تعیین مدار دینامیکی یک ماهواره چیزی جز حل یک معادله دیفرانسیل مرتبه دو نیست که امروزه این معادله به علت دقت زیاد روش‌های عددی، به‌صورت عددی حل می‌شود. علی‌رغم پیشرفت رایانه‌ها و فنون محاسباتی، انتگرال‌گیری مدار همچنان از فرایندهای زمان‌بر در ژئودزی ماهواره‌ای به حساب می‌آید. علت این مسئله لزوم محاسبه شتاب به صورت نقطه‌‌به‌‌نقطه است. اگرچه می‌توان با استفاده از فنون برداری‌‌سازی (Vectorize) در محاسبه شتاب، سرعت اجرای برنامه را تا حد زیادی بهبود داد، اما امکان استفاده از این فن برای محاسبه چندجمله‌ای‌های لژاندر، به‌دلیل وجود رابطه بازگشتی بین آنها و لزوم محاسبه مرحله‌‌به‌‌مرحله وجود نخواهد داشت. در این مقاله نشان داده خواهد شد که با استفاده از روش‌های تقریب می‌توان به برآورد دقیقی از چندجمله‌ای‌های لژاندر در نقاط دلخواه دست پیدا کرد و با استفاده از این چندجمله‌ای‌های تقریب زده شده در فرایند انتگرال‌گیری سرعت برنامه را چندین برابر افزایش داد. برای تقریب توابع لژاندر در بازه‌های کوتاه می‌توان از چندجمله‌ای‌های مرتبه پایین‌تر استفاده کرد که برای یافتن ضرایب این چندجمله‌ای مرتبه پایین می‌توان علاوه بر مقدار چندجمله‌ای‌های لژاندر، در نقاط معلوم از مشتقات مرتبه اول و دوم آن نیز استفاده کرد. با ورود مشتقات چندجمله‌ای‌های لژاندر به مسئله، دقت روش تقریب انتگرال‌گیری مدار ماهواره‌های کم‌‌ارتفاع (LEO) که دارای بیشترین اغتشاش هستند در یک بازه زمانی دو هفته‌ای زیر یک میلی‌متر خواهد بود.}, keywords_fa = {انتگرال‌گیری مدار,تقریب چندجمله‌ای,چندجمله‌ای‌های لژاندر,چندجمله‌ای هرمیت,ماهواره‌های کم‌ارتفاع}, url = {https://jesphys.ut.ac.ir/article_23092.html}, eprint = {https://jesphys.ut.ac.ir/article_23092_3621fb81c8bdaaa277447dd1532e61f1.pdf} } @article { author = {Abd-e-etedal, Mahsa and Gheitanchi, Mohammad Reza}, title = {Investigation of one dimensional upper crust velocity structure in northeast Khorasan by the travel time inversion of P waves}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {139-152}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {North-East Khorasan is one of the most active regions in the world because of is setting on the Alpine-Himalayan belt. Historical and geological backgrounds suggest that this region has experienced many destructive earthquakes throughout history. Compared with the historical background, the seismicity of the region, in the present century, is better known both from the macroseismic and instrumental point of view. The instrumentally located earthquakes suggest that seismic activity in the present century has increased remarkably. A better understanding of crustal velocity model could help to improve the location of earthquakes and to find out the active faults and the tectonic evolution in the region. In this study we used the travel times of local earthquakes recorded by the seismic networks of Quchan and Mashad operated by the Institute of Geophysics, University of Tehran, to investigate the crustal velocity structure in the Khorasan region. In this study, among all recorded data during 1997-2006, we selected and used the records of 103 earthquakes that were recorded by at least four seismic stations. For these selected earthquakes, the azimuth coverage was less than 270 degrees; RMS less than 1 second and the location error was less than 5 km. The travel times obtained from these earthquakes were used to find out an appropriate velocity model. First we applied the VELEST method and used the travel time data to obtain the one dimensional velocity model. We applied random velocity variations of about ±0.5 Km/s in each crustal layer and produced fifty preliminary models. We selected those models that indicated acceptable convergence during the inversion process. Then, by inversion, we obtained a preliminary three layer model. Next, we used this model as initial value to find out the appropriate velocity model. The final result indicated a simple two layer model. This model contains a first layer having a thickness about 10 km and a velocity of 4.5 km/s over the second layer that has a velocity of 6.2 km/s. As we used local data and the earthquakes had shallow depths, we could investigate the structure down to 20 km. This result is in good agreement with the results of other studies in this region In general, the one dimensional inversion of travel time data for crustal velocity structure is sensitive to the number of seismic stations and the distance between the successive two stations. The results of this study indicate that if a good data set is available, the one dimensional inversion of travel time data is an appropriate method for the study of crustal velocity structure.}, keywords = {Crustal Structure,inversion,Khorasan}, title_fa = {بررسی ساختار سرعتی پوسته فوقانی و میانی در شمال شرقی استان خراسان به روش برگردان یک‌بُعدی زمان رسید امواج مستقیم P}, abstract_fa = {برای تعیین ساختار سرعتی پوسته در استان خراسان زمین‌‌لرزه‌‌های رخ داده در این منطقه که با شبکه‌‌های لرزه‌نگاری قوچان و مشهد وابسته به مؤسسه ژئوفیزیک دانشگاه تهران به‌دست آمده بود پردازش شد. از میان همه داده‌‌های ثبت شده در این شبکه، تعداد 103 زمین‌لرزه مورد استفاده قرار گرفت. آنها زمین‌لرزه‌‌هایی بودند که حداقل در چهار ایستگاه ثبت شده بودند، حداقل 12 قرائت P داشتند، جدایش سَمتی آنها کمتر از 270 درجه بود، RMS کمتر از 1 ثانیه داشتند و خطای تعیین محل (در سطح و عمق) آنها کمتر از پنج کیلومتر بود. از این زمین‌لرزه‌‌های انتخابی برای اجرای آزمون‌‌های گوناگون و پیدا کردن مدل سرعتی مناسب استفاده شد. ابتدا زمان رسید‌‌های این زمین‌لرزه‌‌ها برای پیدا کردن مدل یک‌بُعدی سرعتی با استفاده از روش ولست (کیسلینگ،1998) وارون شد. با اِعمال تغییر سرعت در هر لایه از مدل اولیه (به‌‌صورت تصادفی و به میزان 5/0± کیلومتر بر ثانیه)،50 مدل اولیه تولید شد.فقط مدل‌‌هایی درحکم نتیجه انتخاب شد که حاصل برگردان یک‌بُعدی آنها همگرایی قابل‌‌ِقبولی را نشان می‌‌داد. از نتایج برگردان صورت گرفته در مرحله اول که یک مدل سه‌‌لایه بود درحکم مدل آغازی در مرحله دوم برای پیدا کردن مدل سرعتی مناسب استفاده شد. نتیجه نهایی مدل ساده دولایه تا عمق 20 کیلومتری متشکل از لایه‌‌ای به ضخامت 10 کیلومتر و سرعت 5/4 کیلومتر بر ثانیه است که روی یک لایه با سرعت 2/6 کیلومتر بر ثانیه قرار گرفته است. به دلیل استفاده از داده‌‌های محلی، تهیه مدل سرعتی برای پوسته فوقانی و پوسته میانی تا عمق 20 کیلومتری امکان‌‌پذیر بوده است.}, keywords_fa = {خراسان,ساختار پوسته,وارون‌سازی}, url = {https://jesphys.ut.ac.ir/article_23093.html}, eprint = {https://jesphys.ut.ac.ir/article_23093_fd140cb9989b66ef09a5f0e56f909059.pdf} } @article { author = {Shad Manaman, Navid and Shomali, Zaher Hosein and Mirzaei, Noorbakhsh}, title = {3-D S-velocity structure of upper mantle and Moho depth variations in the Makran subduction zone}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {153-169}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The Makran subduction zone in southeastern Iran and southern Pakistan is where the oceanic crust of the Arabian plate (Oman Sea) is subducting beneath Eurasia. Compared to other subduction zones in the world, the Makran subduction zone has some unusual features, including different seismicity patterns in its eastern and western parts. Also, the Quaternary volcanoes in the eastern part of Makran are located far from its foreland comparing to the western part of Makran. The very low seismicity of western Makran causes two different viewpoints about its current situation; i.e., whether the subducted plate is undergoing aseismicity or has been locked strongly. The Partitioned Waveform Inversion (PWI) method is used here to image the S-velocity structure of the upper-mantle and Moho-depth variations of Makran subduction zone and explore the relationship of the Makran seismic structure with the seismicity and the volcanic arc in the region. For this purpose, we used the vertical components of the seismograms recorded by the National Iranian Seismic Network with high signal to noise ratio from the earthquakes with magnitudes of 5.5 to 7.7. Despite the limited number of stations around the Makran region, choosing proper earthquakes enables us to improve the azimuthal and path coverage and apply the PWI method in the region. Our tomography data show that the Moho depth across the Makran subduction zone is increasing from the Oman seafloor and Makran forearc setting to the volcanic arc. Generally, the crust in the western Makran is thicker than its eastern part and the maximum crustal thickness in the Makran region reaches to 50±2 km below the Taftan volcano. The Moho map clearly depicts the western edge of the Makran subduction zone, where the Minab fault (representing the eastern edge of the Hormuz Straits) marks the boundary between the thick continental crust of the Arabian plate and the thin oceanic crust of the Oman Sea. Our results show clearly that the high-velocity slab of the Arabian plate subducts northwards beneath the low-velocity overriding lithosphere of Lut block in the western Makran and Helmand block in the eastern Makran. We found that the slab in the western Makran starts with a gentle dip (about 8?) and increases to about 55?, where it plunges into the asthenosphere beneath the volcanic arc. In eastern Makran, the slab is subducting with a low dip angle of about 8? and reaches approximately 20?below the volcanic arc. We found that the bending of the subducted plate occurs with relatively low dip and much farther beneath eastern Makran than in the western part which may explain the different volcanic arc offsets across the Makran subduction zone.}, keywords = {Makran,Moho depth,Subduction,S-Velocity,upper mantle,Waveform Tomography}, title_fa = {بررسی ساختار سه‌بُعدی سرعت برشی در گوشته بالایی و تغییرات عمق موهو در منطقه مکران}, abstract_fa = {زون مکران در حاشیه جنوب شرقی ایران و جنوب پاکستان، محل فرورانش پوسته اقیانوسی صفحه عربستان (در دریای عمان) به زیر صفحه اوراسیا است. این زون فرورانش از دیدگاه‌های متفاوتی رفتار غیرعادی از خود نشان می‌‌دهد. از جمله اینکه بخش‌های شرقی و غربی آن الگوی لرزه‌خیزی بسیار متفاوتی دارند. همچنین، آتشفشان‌های کواترنری در بخش شرقی مکران دورافت (offset) بیشتری از پیش‌‌کمان خود نسبت به بخش غربی دارند. درک این موضوع که آیا فرایند فرورانش در غرب مکران با لرزه‌خیزی همراه است و یا اینکه قفل‌شدگی (lock) شدید بین صفحات فرورانش عامل نبود زمین‌لرزه‌‌های بزرگ بین‌‌صفحه‌‌ای در غرب مکران است، همواره از چالش‌های بزرگ در لرزه‌‌زمین‌ساخت این منطقه است. در این تحقیق سعی می‌‌شود که با استفاده از روش وارون‌‌سازی افرازی شکل موج (PWI, Partitioned Waveform Inversion)، تصاویر دقیق‌تری از ساختار سرعت موج برشی گوشته بالایی در زون فرورانش مکران به‌دست آید و ارتباط آن با لرزه‌خیزی و کمان‌های آتشفشانی موجود در منطقه مورد بررسی قرار گیرد. برای این منظور، از همه شکل‌‌موج‌های مولفه قائم ثبت شده در ایستگاه‌های باندپهن ایران با نسبت سیگنال به نوفه زیاد از زمین‌لرزه‌هایی با بزرگی 5.5 تا 7.7 استفاده شده است. علی‌‌رغم پوشش ایستگاهی بسیار محدود در اطراف منطقه مکران، توانایی روش PWI این امکان را به ما می‌دهد که با گزینش زمین‌لرزه‌‌های مناسب، پوشش آزیموتی و در نتیجه تلاقی‌‌های مسیر(paths crossing) را افزایش دهیم. نتایج ما نشان‌دهنده افزایش تدریجی ضخامت پوسته از جنوب به شمال در عرض زون مکران است که این افزایش تدریجی تا محل خمش صفحه فرورونده در زیر کمان‌های آتشفشانی ادامه می‌‌یابد. به‌طورِکلی پوسته در غرب مکران ضخیم تر از شرق آن‌ است و بیشینه مقدار آن (2±50 کیلومتر) در منطقه مکران در زیر آتشفشان تفتان قرار دارد. گسل میناب به‌منزلة حاشیه غربی منطقه مکران، پوسته ضخیم تنگه هرمز را از پوسته کم‌‌ضخامت پیش‌‌کمان مکران جدا کرده است. این کاهش شدید و تغییرات ناگهانی در ضخامت پوسته از تنگه هرمز به سمت مکران ناشی از تغییر جنس پوسته صفحه عربستان از قاره‌‌ای ضخیم به اقیانوسی نازک دانست که گسل میناب حدفاصل این تغییرات است. بررسی ساختار سرعت برشی گوشته بالایی در زون مکران با استفاده از روش PWI نشان می‌‌دهد که فرورانش در بخش غربی با زاویه شیب کم از حدود 8 درجه آغاز شده و سپس با افزایش تدریجی به بیشنه مقدار خود در حدود 55 درجه در صفحه فرورونده به درون سست‌‌کره در زیر دشت لوت می‌‌رود، می‌‌رسد. در شرق مکران، صفحه فرورونده با زاویه شیب کم در حدود 8 درجه در حال فرورانش است و به‌تدریج این شیب افزایش می‌یابد تا اینکه در صفحه فرورونده به درون سست‌‌کره در زیر کمان آتشفشانی خمیده می‌‌شود، مقدار شیب حدود 20 درجه است. بهرحال، روشن است که خمیدگی صفحه فرورانش با شیب کمتر و در فاصله دورتری از ساحل شرقی مکران در مقایسه با ساحل غربی آن رخ می‌‌دهد که این امر می‌‌تواند دلیل دورافت‌های متفاوت در کمان آتشفشانی در امتداد زون فرورانش مکران را توضیح دهد.}, keywords_fa = {زون فرورانش,سرعت برشی,عمق موهو,گوشته بالایی,مکران,وارون‌سازی افرازی شکل موج}, url = {https://jesphys.ut.ac.ir/article_23094.html}, eprint = {https://jesphys.ut.ac.ir/article_23094_5106bf798fb4b1faa56f7c3e68b35f34.pdf} } @article { author = {Ghader, Sarmad and Ali-Akbari Bidokhti, Abbas-Ali and Falahat, Saeed}, title = {Numerical solution of conservative form of two-dimensional compressible and non-hydrostatic equations of the atmosphere using second-order MacCormack method}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {171-191}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {This work reports the results of the application of the second-order MacCormack method for numerical solution of‎ the conservative form of two-dimensional non-hydrostatic and fully compressible Navier-Stokes equations governing an inviscid and adiabatic atmosphere‎. Various aspects of the computational approach such as discretization of the governing equations for the interior and boundary points‎, ‎the details of implementation of boundary conditions for different boundary types, i.e., ‎rigid and open boundaries‎, ‎time step‎, ‎grid resolution and dissipation are presented‎. In addition, it is shown that application of the second-order MacCormack scheme to spatial discretization of the source term in the vertical momentum equation of two-dimensional non-hydrostatic and fully compressible Navier-Stokes equations ‎needs special treatment‎. ‎In other words‎, ‎the spatial discretization of this source term should be consistent with the hydrostatic equation and must not degrade its balance‎. ‎The details of the procedure to reach the discretized version of the vertical momentum equation are also presented. ‎Several well known test cases including evolution of a warm bubble in a neutral atmosphere (in domains with rigid and open boundary conditions), evolution of a cold bubble in a neutral atmosphere (density current benchmark proposed by Straka et al. (1993)) and a gravity current, ‎are used for numerical experiments. Qualitative and quantitative comparisons indicate the validity of the results and show that the results of the second-order MacCormack scheme are in good agreement with the published results for the evolution of the warm bubble and the reference solution presented by Straka et al.}, keywords = {Atmosphere,Compressible,Finite difference,MacCormack Scheme,Non-hydrostatic}, title_fa = {حل عددی شکل پایستار معادلات تراکم‌پذیر دوبُعدی و غیرهیدروستاتیک جو با استفاده از روش مک‌کورمک مرتبه دوم}, abstract_fa = {در پاره‌ای از پدیده‌های جوی اثرات تراکم‌پذیری دارای اهمیت است و همچنین گرادیان‌های شدید همراه با این پدیده‌ها، بررسی دقیق‌ آنها را با درنظر گرفتن حالت غیرهیدروستاتیک امکان‌پذیر می‌کند. کار حاضر به حل عددی شکل پایستار معادلات دوبُعدی، غیرهیدروستاتیک و تراکم‌پذیر جو با استفاده از روش مک‌کورمک مرتبه دوم می‌پردازد. جزئیات مربوط به نحوه گسسته‌سازی معادلات، اعمال شرایط مرزی نابازتابی و مرز سخت و نحوه آغازگری معادلات عرضه شده است. به‌علاوه در کار حاضر یک روش کلی برای گسسته‌سازی بخش‌های دربرگیرنده جملات توازن هیدروستاتیک در معادلات با تعریف یک ضریب جدید آورده شده است. با به‌کارگیری آزمون‌های موردی موجود نتایج حل عددی برای شبیه‌سازی تکامل حباب سرد و گرم و همچنین شبیه‌سازی یک جریان گرانی عرضه می‌شود. نتایج عددی به‌دست آمده و مقایسه کیفی آنها با نتایج موجود مربوط به سایر محققان گویای این مطلب است که روش مک‌کورمک مرتبه دوم، عملکرد مناسبی در شبیه‌سازی معادلات دوبُعدی و تراکم‌پذیر جو، همانند پدیده‌های همرفت عمیق دارد.}, keywords_fa = {تکامل یک ترمال در جو خنثی,روش مک‌کورمک مرتبه دوم,معادلات غیرهیدروستاتیک و تراکم‌پذیر}, url = {https://jesphys.ut.ac.ir/article_23095.html}, eprint = {https://jesphys.ut.ac.ir/article_23095_98626d26e9dc900d7784f80a7e833613.pdf} } @article { author = {Ghorbani Taleghani, Mehdi and Golshani, Ali Asghar}, title = {Study of wave climate in amir abad port using setup of local model and semi-analytical methods}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {193-210}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {Wave prediction is useful for safety and effective management of vessel navigation or construction of offshore structures. Since human activity mainly takes place in nearshore regions, accurate wave prediction is necessary there. However, nearshore waves are not easy to predict compared with ocean waves, because not only the waves but also the wind, which is the energy source of the waves, changes locally due to the complex terrain around the shore. During the past 50 years, wave forecasting using numerical models according to wave energy balance equation has become widespread. These models also change significantly when new generation of spectral wave models such as Mike21-SW are suggested as the most advanced wave forecasting models. These models using formulation of basic physical wave generation by wind, wave transport and special processes of shallow waters e.g depth-induced wave breaking and bottom friction present reasonable results. Shallow-water wave transformation strongly depends on coastal geomorphology and bottom sediment characteristics. Accurate prediction of wave parameters is vital for the coastal infrastructure developments and other activities. MIKE 21 SW is a new generation wind wave model based on unstructured meshes. The model simulates the growth, decay and transformation of wind generated waves and swell in offshore and coastal areas. In this study, some semi-analytical methods and numerical model Mike21-SW at the Amir Abad port were wied to predict the wind wanes, with results that has strongest agreement with buoy data. To study and assess the semi-analytical method results, wave height and wave period are determined by SMB, SPM ,CEM, JONSWAP methods and compared with Amir Abad buoy data.Wind data which is used in semi-analytical methods are extracted from Babolsar synoptic station. Because of the importance of Babolsar port, an unstructured application to the mesh file SW model was constructed covering 53.2 to 53.6 E and 36.8 to 37.2 N and mesh size in this area (which is uniform) is 0.005 degree( 500m). Boundaries in the north, east and west are open and in the south there is a closed boundary. The boundary condition of the local SW model is extracted as a parametric module from Iranian Sea Waves Modeling Project (ISWM) over 12 years from 1992 to 2004.These parameters are significant wave height, peak wave period, mean wave direction and spreading directional index. Amir Abad buoy data was used for local SW model callibration. Comparsion which was made between the semi-analytical methods and buoy data shows that the SPM method has the best correlation with Amir Abad buoy data within the semi-analytical methods. Over 12 years (from 1992 to 2004) wave climate in study area was assessed and compared with rose wave calculated by local model and with NEKA buoy data. Results shows that wave growth condition in Amir Abad area is a duration limited condition and only in few cases fully developed conditions occur. In general , there is not good agreement between semi-analytical methods and buoy data and there is large error in using these methods. Semi-analytical methods predict values typically lower than observations. Results show that the local SW model is the best method for wave condition prediction as is expected. Because in Local SW Model all phenomena associated with energy transport and with all frequencies and directions are included completely and any presupposition is not included. The Root-Mean-Squired Error of SPM method in wave height forecasting is 0.45m, in wave period is 1.2 s . In semi-analytical methods, SPM method has good agreement in wave parameters forecasting. The rose wave acquired by the local model indicates that dominant wave direction in Amir Abad Port is NW and another dominant wave direction is N. Numerical model forecast for wave direction is more accurate than semi- analytical methods and the wave rose acquired by the local model has good agreement with the buoy data. The study suggests that another local model with smaller mesh should be tried in this zone.}, keywords = {Amir abad Port,Mike21-SW Model,Semi-Analytical wave prediction methods}, title_fa = {بررسی اقلیم موج در بندر امیرآباد با اجرای مدل محلی Mike21-SW و روش‌‌های نیمه‌‌تجربی}, abstract_fa = {پیش‌بینی امواج در پنج دهه اخیر با به کارگیری مدل‌‌های ریاضی مبتنی بر معادله پایستگی انرژی، شاهد پیشرفت‌های چشمگیری بوده است. این مدل‌‌ها نیز به نوبه خود دستخوش تغییرات بسیاری شده‌‌اند که پیشرفته‌‌ترین آنها مدل‌‌های طیفی نسل سوم نظیر Mike21-SW (توسعه یافته از سوی موسسه هیدرولیک دانمارکDanish Hydraulic Institue ) هستند. این مدل‌‌ها با فرمول‌‌بندی مبانی فیزیکی تولید، انتشار امواج ناشی از باد و فرایندهای خاص آب کم‌عمق نظیر شکست ناشی از عمق و اثر بستر، نتایج قابل اطمینانی را عرضه می‌‌کنند. در این مقاله ابتدا با استفاده از روش‌‌های نیمه‌‌تجربی SMB, SPM ,CEM , JONSWAP مشخصات موج در آب‌‌های دور از ساحل بندر امیرآباد محاسبه شده و سپس با داده‌‌های بویه بندر امیرآباد و بویه نکا مقایسه شده‌ است. با توجه به اهمیت راهبردی منطقه دریایی بندر امیرآباد در دریای خزر، با استفاده از مدل SW از بسته نرم‌‌افزاری مایک 21 اقدام به شبیه‌سازی امواج در این منطقه شد. برای این کار ناحیه اطراف بندر با استفاده از مش‌‌های نامنظم به ابعاد 500 متر شبکه‌‌بندی می‌‌شود و شرایط اولیه برای این مدل از داده‌‌های طرح مدل‌سازی امواج دریاهای ایران وارد می‌‌شود. برای واسنجیدن (کالیبره کردن) مدل نیاز به داده‌‌های اندازه گیری موج است که بدین‌‌منظور از داده‌‌های بویه امیرآباد و بویه نکا استفاده می‌‌شود . با مقایسه ضریب همبستگی بین داده‌‌های بویه و روش‌‌های نیمه‌‌تجربی و مدل عددی SW مشخص می‌‌شود که مدل محلیSW بهترین روش برای پیش‌بینی امواج منطقه است. سپس با استفاده از نرم‌افزار MIKEZeroگل‌موج حاصل از روش‌‌های نیمه‌‌تجربی و مدل عددی ترسیم شد و از این طریق مشخص شد که جهت غالب موج در منطقه غربی است. و روش SPM ارتفاع موج غالب را 185/0 متر و مدل محلی ارتفاع موج غالب را 485/0 متر پیش‌بینی کردند.}, keywords_fa = {بندر امیرآباد,روش‌‌های نیمه‌تجربی پیش‌بینی موج,مدل Mike21-SW}, url = {https://jesphys.ut.ac.ir/article_23096.html}, eprint = {https://jesphys.ut.ac.ir/article_23096_b602b92aabfc0324794235a87fd83e46.pdf} } @article { author = {MirRokni, S. Majid and Mohebol-Hojeh, Alireza}, title = {Analysis of the polar vortex oscillations in a shallow water model of the Stratosphere using Eulerian diagnostics}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {211-223}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The internal variability of the stratosphere, in particular the vacillation of the polar vortex, in a shallow-water model is investigated. The combined effects of mechanical forcing and thermal forcing are the major factors involved in the vacillation of the polar vortex in the shallow water (SW) model examined here. Mechanical forcing is provided by a time-independent topography mimicking tropospheric excitation of the stratosphere. Thermal forcing is provided by a linear relaxation of the mass field to a time-independent equilibrium state mimicking the radiative relaxation taking place in the stratosphere. In this way, the setup of the problem is such that the barotropic effects arising from the horizontal structure of PV on the polar vortex in the real atmosphere can be examined. The SW equations in potential vorticity (PV), velocity divergence and acceleration divergence representation are solved for a range of resolutions using the "diabatic contour-advective semi-Lagrangian" (DCASL) algorithm and a standard pure semi-Lagrangian (SL) algorithm. Using different numerical algorithms enables us to address the issues related to numerical sensitivity of the zonal vacillations in the SW model of the stratosphere. The equations for velocity and acceleration divergence are solved using spectral transform in longitude and compact fourth-order finite differencing in latitude. The spatial resolution is indicated by M?N, M and N being the number of grid points in the longitudinal and latitudinal directions, respectively. As a first step in understanding the nature and robustness of the zonal wind vacillations in the SW for the stratosphere, the Eulerian diagnostics based on the terms of the zonal mean zonal momentum equation are calculated and analyzed. To this end, the results for the pure SL algorithm with spatial resolution of 256?256, 512?512, and 1024?1024 are presented and compared with the corresponding results for the DCASL algorithm with spatial resolution of 256?256. The results for all of the resolutions and algorithms indicate that the topographic forcing, the divergence of horizontal momentum flux and the Coriolis torque are the dominant factors determining the zonal mean zonal momentum time evolution. From the Eulerian perspective, overall, the zonal wind vacillations can be attributed to the out-of-phase variations of the topographic forcing, the divergence of horizontal momentum flux and the Coriolis torque. However, the irregularity of the cycles of the vacillations in the results for the PV-based algorithms in all of the resolutions examined is in clear contrast with the regular vacillations reported at T42 resolution by Rong and Waugh in 2004, where spectral transform algorithm used to solve the SW equations in vorticity, divergence, mass and dissipation is provided by explicitly damping vorticity using hyperdiffusion. Regarding the irregularity of the vacillations and the statistical difference between the results for the SL and DCASL, on the one hand, and between the various resolutions of the SL, on the other hand, further diagnostics to study the geometry of the vortex and its time evolution as well as additional numerical experiments are needed to assess the polar vortex oscillations.}, keywords = {Eulerian diagnostics,oscillation cycles,polar vortex,Potential vorticity,shallow water model}, title_fa = {تحلیل چرخه‌های نوسان تاوه قطبی در یک مدل آب کم‌عمق برای پوش‌سپهر با استفاده از فرایافت‌های اویلری}, abstract_fa = {در این تحقیق، برای تعیین سازوکارهای موثر در چرخه‌های نوسان (vacillation) تاوه قطبی و به‌طورخاص بررسی چرخه‌های نوسان بادمداری، مدل آب کم‌عمق روی کره با بهره‌گیری از چندین الگوریتم متفاوت به‌کار گرفته می‌شود. عامل اصلی در چرخه‌های نوسان تاوه قطبی، اثر ترکیبی واداشت‌های موجی و گرمایی است. برای آشکارسازی نقش پوش‌سپهر در ایجاد تغییرپذیری، واداشت موجی مستقل از زمان توسط عامل کوهساری (topography) و واداشت تابشی نیز به‌صورت یک فرایند واهلش گرمایی در معادله پیوستگی جرم وارد شده است. در الگوریتم‌های عددی مورد استفاده، معادلات آب کم‌عمق در نمایش (تاوایی پتانسیلی، واگرایی سرعت، واگرایی شتاب) با استفاده از تعمیم روش فرابرد پربندی نیمه‌لاگرانژی به معادلات دررو و نیز روش نیمه‌لاگرانژی محض در تفکیک‌های فضایی متوسط تا زیاد حل ‌شده‌اند. با استفاده از داده‌های بلندمدت مدل آب کم‌عمق، مجموعه‌ای از فرایافت‌های اویلری حاصل از محاسبه جملات معادلة میانگین مداری مؤلفه مداری تکانه برای بررسی نوسان‌های تاوه قطبی و استواری (robustness) یا نا استواری آن، محاسبه و تحلیل ‌شده است. محاسبات نشان می‌دهد در معادلة فوق جملات گرایش باد مداری، واداشت کوهساری، واگرایی شار تکانه افقی و گشتاور کوریولیس سهم اصلی را در تعیین تحول زمانی چرخه‌های نوسان تاوه قطبی دارند. با توجه به مقادیر ناچیز جمله‌های انتقال پیچکی جرم و چشمة جرم، چرخه‌های نوسان تاوه قطبی را می‌توان حاصل تغییرات ناهم‌فاز سه جملة واداشت کوهساری، واگرایی شار تکانه افقی و گشتاور کوریولیس دانست.}, keywords_fa = {تاوایی پتانسیلی,تاوه قطبی,چرخه‌های نوسان,فرایافت‌های اویلری,مدل آب کم‌عمق}, url = {https://jesphys.ut.ac.ir/article_23097.html}, eprint = {https://jesphys.ut.ac.ir/article_23097_e874ec42c01bb29ca33a942e8c6b970a.pdf} } @article { author = {Raziei, Tayeb and Fatahi, Ebrahim}, title = {Evaluation of the applicability of the NCEP/NCAR precipitation dataset for drought monitoring in Iran}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {225-247}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {Drought monitoring, which is a crucial component of drought management, aims to provide information that enables and supports people and organizations to take actions to reduce potential drought-related impact and damage. We usually tend to focus on drought when it is occurring and to react when crises strike. However, recent experiences and developments on drought knowledge are encouraging societies to shift from the traditional crisis-based management to a risk management approach. While some developed countries enjoy drought monitoring and early warning systems, the lack of updated and reliable meteorological data is still the major limitation in establishing such useful tools in many developing countries like Iran. On the other hand, while the existence of reliable dataset in a given country is essential for drought monitoring, the organizations responsible for collecting meteorological data in Iran delay publishing the updated data. So, the lack of updated data is one of the most important obstacles for drought monitoring in Iran. In this research, the possibility of using NCEP/NCAR grided precipitation dataset for drought monitoring in Iran was assessed. To this end, the NCEP/NCAR monthly precipitation rate corresponding to 52 grid points distributed all over Iran in a spatial resolution of 1.9 × 1.9 degree geographical longitude by latitude was utilized for the period 1951-2005. Moreover, monthly precipitation associated with 32 leading synoptic stations for the same period was also used for comparison purposes. The SPI time series for the 6 and 12 month time scales were calculated for all 52 grid points and 32 observations distributed across Iran. This index which is based only on precipitation is widely used in drought monitoring centers and it is in fact a useful tool for capturing the climate variability associated with water shortage or surplus in different areas. Furthermore, in analyzing the spatial and temporal variability of drought across Iran, we applied the Principal Component Analysis (PCA) coupled with Varimax rotation to the SPI field of SPI-6 and SPI-12 for both NCEP/NCAR and observational datasets. Therefore, the S-mode PCA was separately applied on the SPI time series for both time scales associated with each dataset in order to identify the modes of time and spatial variability of the SPI over the country. Finally, the extreme drought of 2008 was given more attention in this analysis due to its importance considering the severity and areal extent. Applying PCA coupled with Varimax rotation to the SPI fields corresponding to both datasets have regionalized Iran into four distinctive sub-regions considering the time variability of SPI in both time scales used here. In order to verify the results, the Varimax rotated PC score time series obtained from NCEP/NCAR dataset was compared with their counterparts obtained from observational dataset. The results show that the spatial patterns of PC loadings obtained from both datasets are noticeably in agreement and their corresponding rotated PC score time series and are significantly correlated with each other; especially from 1970 onward. Furthermore, comparison of the anomaly maps of precipitation of the cold season of 2008, obtained from both NCEP/NCAR and observational dataset showed a considerable spatial co-variability among them. As a conclusion, it can be said that the NCEP/NCAR dataset detects well the spatial and temporal pattern of precipitation deficit and surplus across Iran and can be used to complement the information provided by observations for drought monitoring in Iran.}, keywords = {Drought Monitoring,Iran,NCEP/NCAR,precipitation,SPI}, title_fa = {ارزیابی کاربرد داده‌‌های بارش NCEP/NCAR در پایش خشک‌سالی ایران}, abstract_fa = {اساس پایش خشک‌سالی در هر کشور وجود داده‌‌های مطمئن و به هنگام است. داده‌‌های هواشناسی موجود در ایران اغلب با تاخیر انتشار می‌یابند که این مسئله امکان پایش بهنگام خشک‌سالی در کشور را با مشکل روبه‌رو می‌کند. ازاین‌رو در این پژوهش امکان استفاده از داده‌‌های شبکه‌بندی شده بارش NCEP/NCAR به منظور استفاده در پایش خشک‌سالی ایران مورد ارزیابی قرار گرفت. برای این منظور داده‌‌های بارش ماهانه 52 یاخته (Grid) از شبکه داده‌‌های NCEP/NCAR که کشور ایران را پوشش می‌دهند به همراه داده‌‌های بارش ماهانه 32 ایستگاه سینوپتیک کشور برای دوره آماری 2005-1951 مورد استفاده قرار گرفت و سری‌های زمانی SPI شش و دوازده ماهه آنها محاسبه شد. سپس آرایه S تحلیل مولفه‌‌های اصلی به همراه چرخش وریمکس (Varimax) روی سری‌های زمانی SPI شش و 12 ماهه داده‌‌های NCEP/NCAR وداده‌‌های مشاهده‌‌ای به طور جداگانه صورت گرفت و مدهای اصلی تغییرپذیری SPI در سطح کشور شناسایی شد. نتیجه تحلیل مولفه‌‌های اصلی روی سری‌های زمانی SPI شش و 12 ماهه هر دو منبع اطلاعاتی نشان داد که ایران را می‌توان از نظر تغییرات زمانی SPI در هر دو مقیاس زمانی به چهار منطقه متمایز تقسیم کرد. سری‌های زمانی نمره استاندارد مولفه‌‌های چرخش یافته به‌دست آمده از داده‌‌های NCEP/NCAR با سری‌های زمانی نمره استاندارد مولفه‌‌های متناظر با آنها در داده‌‌های مشاهده‌‌ای مورد مقایسه قرار گرفت و مشخص شد که در اغلب موارد هماهنگی خوبی میان آنها، به‌‌ویژه در دوره 1970- 2005 وجود دارد. همچنین نقشه‌‌های ناهنجاری بارش 2008 براساس داده‌‌های NCEP/NCAR و داده‌‌های مشاهده‌‌ای تهیه شد و مورد مقایسه قرار گرفت. این مقایسه نیز روشن ساخت که داده‌‌های NCEP/NCAR روند تغییرات زمانی و مکانی بارش در ایران را به‌خوبی نشان می‌دهد و می‌تواند برای پایش بهنگام خشک‌سالی در کشور مورد استفاده قرار گیرد.}, keywords_fa = {ایران,بارش,پایش خشک‌سالی}, url = {https://jesphys.ut.ac.ir/article_23098.html}, eprint = {https://jesphys.ut.ac.ir/article_23098_28e577addee39d15a8512ba5919d0a7a.pdf} } @article { author = {Hajian, Ali Reza and Ebrahim Zadeh Ardestani, Vahid and Lucas, Car}, title = {Depth estimation of gravity anomalies using Hopfield Neural Networks}, journal = {Journal of the Earth and Space Physics}, volume = {37}, number = {2}, pages = {-}, year = {2011}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {}, abstract = {The method of Artificial Neural Network is used as a suitable tool for intelligent interpretation of gravity data in this paper. We have designed a Hopfield Neural Network to estimate the gravity source depth. The designed network was tested by both synthetic and real data. As real data, this Artificial Neural Network was used to estimate the depth of a Qanat (an underground channel) located at north entrance of the Institute of Geophysics and the result was very near to the real value of the depth.}, keywords = {Artificial Neural Network,depth estimation,Gravity,Hopfield}, title_fa = {تخمین عمق بی هنجاریهای گرانی با استفاده از شبکه های عصبی هاپفیلد}, abstract_fa = {در این مقاله روش شبکه عصبی هاپفیلد برای تفسیر هوشمند داده های گرانی استفاده شده است. یک شبکه عصبی هاپفیلد برای تخمین عمق چشمه گرانی طراحی شده است. این شبکه طراحی شده برای داده های مصنوعی و واقعی آزمایش شده اند. در مورد داده های واقعی این شبکه برای تخمین عمق یک تونل قنات واقع در موسسه ژئوفیزیک به کار برده شده و نتایج حاصله به مقادیر واقعی عمق بسیار نزدیک است.}, keywords_fa = {تخمین عمق,شبکه عصبی,گرانی,هاپفیلد}, url = {https://jesphys.ut.ac.ir/article_23099.html}, eprint = {https://jesphys.ut.ac.ir/article_23099_f3c7de783c732fc03cebe2860a20ad41.pdf} }