@article { author = {Afsari, Nargess and Taghizadeh-Farahmand, Fattaneh and Gheitanchi, Mohammadreza and Solaimani, Azam}, title = {Moho depth variations in the Central Zagros (Shiraz region) using Ps converted phases}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {1-13}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29110}, abstract = {Study crust and upper mantle structure below the surface of Earth is one of the important objectives of geophysics. Teleseismic body waveforms have been used to infer crust and upper mantel structure. The Iranian plateau is part of the Alpine-Himalayan orogenic belt. The Zagros mountain belt in southwestern Iran has resulted from the collision of Arabian Plate with the continental crust of Central Iran after the closure of the Neotethys Ocean. The region referred as central Zagros of Iran in this study includes the area located between 50.9°-54° longitude and 28.1°-30.8° latitude. In this study we use teleseismic receiver function method to determine the Moho depth variations and Vp/Vs ratio beneath Shiraz Telemetry Seismic Network, located in the central Zagros using teleseismic data (30°? ? ?95°, Mb ? 5.5) which have been recorded in five 3C stations short period from 2002-2009. Teleseismic events with relatively high signal-to-noise ratio (>4) have been carefully selected at each station. We considered a time window of 110s, starting 10 s before the P-onset arrival time. Firstly, to broaden the response of short-period instruments into a more useful teleseismic frequency band, the instrument response is denconvolved from the original records. ZNE components are then rotated into the local LQT ray-based coordinate system (using theoretical back azimuth and incidence angle), in which L shows the direction of P wave incident to the surface; Q is perpendicular to L and T is perpendicular to both L and Q forming the third axis of the right-hand LQT system. To isolate the P-to-S conversions on the Q component, the L component is deconvolved from the Q component. A band-pass filter of 2-10s is applied to the P receiver functions (PRFs). They are stacked after move out correction for reference slowness of 6.4 s/°. P-RFs are sorted by increasing back azimuth. A notable feature, which can be observed underneath all stations, is the presence of a significant sedimentary layer at about 0.2-1.2s delay time. The middle crustal layer at about 2.3-4.0s delay time can be also seen beneath all stations. The most coherent conversion is however the conversion at the Moho boundary arriving between 5.6-6.6 s delay time. This conversion can be clearly followed in the individual traces as well as in the stacked traces. The minimum arrival time of the Moho converted phase (5.6s) is observed beneath the station MOK located in the northeastern part of the area. Even though, the largest arrival time (6.6 s) is seen beneath the station PAR located in the northwestern part of the region. Moho depths are obtained by using an average crustal P wave velocity of 6.3 km/s and a Vp/Vs ratio of 1.73. This keeps our depth values independent from possible errors of preliminary shear wave velocity models. However, we estimate the deviation to this model to be less than 5%. Therefore, this procedure results in a ±2 km error in the Moho depth determination. For station KAZ, we couldn’t obtain P-RF because of low signal-to-noise ratio. We have used the arrival times of crustal multiples for determination of crustal thickness (H) and Vp/Vs ratio. This was done using Zhu and Kanamori method, which performs a grid search through the H and Vp/Vs space and searches for the largest amplitudes at the predicted times of direct conversions and multiples. We used weight factors of 0.5, 0.25, 0.25 for the Moho conversion and multiples, respectively. The average Moho depth is 49.5 km and varies between 46.0 km and 56.5km. We observed that Moho depth decrease from north to south. The thinnest crust was found beneath MOK station whereas the deepest crust was observed beneath PAR station. The Shiraz region crust has an average Vp/Vs ratio of 1.73, with higher ratio of 1.74 in MOK station and lower ratio of 1.70 in SHI station. 2D migrated PRF section depth-distance obtained from a profile perpendicular to the strike of Zagros (NE-SW), shows the Moho boundary varies from 45 km to more than 50 km.}, keywords = {Moho discontinuity,Ps converted waves,Teleseismic receiver functions,Zagros}, title_fa = {تغییرات عمق موهو در زیر زاگرس مرکزی (منطقه شیراز) با استفاده از امواج تبدیل‌یافته Ps}, abstract_fa = {تابع‌های گیرنده امروزه به‌نحو گسترده برای به تصویر درآوردن ناپیوستگی‌‌های لرزه‌‌ای در پوسته و گوشته بالایی مورد استفاده قرار می‌گیرند. در این مقاله برای استخراج تغییرات عمق موهو و نسبت Vp/Vs پوسته در زیر شبکه لرزه‌نگاری شیراز که در زاگرس مرکزی قرار دارد، از روش تابع گیرنده دورلرز P استفاده کرده‌ایم. به‌‌همین‌‌منظور از داده‌‌های زمین‌لرزه‌‌هایی که در پنج ایستگاه لرزه‌ای کوتاه‌دوره سه‌مولفه‌ای‌‌ در فاصله رومرکز ?95 > ?> ?30 از مرکز شبکه و بزرگای 5/5 ? Mb که از اواخر سال2002 تا 2009 ثبت شده، استفاده شده است. در این تحقیق به کمک تحلیل تابع گیرنده P و با استفاده از تأخیر زمانی فاز تبدیلی Ps از موهو نسبت به رسید مستقیم P، متوسط عمق موهو برای منطقه برآورد شد. سپس با استفاده از روش برآورد هم‌زمان عمق و نسبت Vp/Vs پوسته و به کمک بازتاب‌‌های چندگانه پوسته (PpPs ,PpSs + PsPs) مقدار متوسط ضخامت و نسبت Vp/Vs پوسته محاسبه شد. عمق موهو برای منطقه شیراز به‌‌طور متوسط 5/49 کیلومتر به‌دست آمد. کمترین ضخامت پوسته را 0/46 کیلومتر در زیر ایستگاه MOK و بیشترین ضخامت پوسته را 5/56 کیلومتر در زیر ایستگاه PAR به‌دست آوردیم. نسبت Vp/Vs به‌‌طور متوسط برای منطقه 73/1 به‌دست آمد و حدود تغییرات Vp/Vs بین 70/1 تا 74/1 است. نتایج به‌دست آمده در این تحقیق با نتایج مطالعات قبلی در این منطقه همخوانی قابل‌‌ قبولی داشته است.}, keywords_fa = {Moho discontinuity,Ps converted waves,Teleseismic receiver functions,Zagros}, url = {https://jesphys.ut.ac.ir/article_29110.html}, eprint = {https://jesphys.ut.ac.ir/article_29110_064fe85fbd6cb9b11e6e64d1fa054bcb.pdf} } @article { author = {Sadidkhouy, Ahmad and Alikhani, Zahra and Sodoudi, Forough}, title = {The variation of Moho depth and VP/VS ratio beneath Isfahan region, using analysis of teleseismic receiver function}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {15-24}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29111}, abstract = {Iran is located in a roughly triangular deforming region, consisting of relatively undeformed shield areas to the southwest (Arabia) and northeast and the more recently deformed, though currently inactive, southwest Afghanistan block in the east. The current geological and tectonic setting of Iran is due to the ongoing convergence between the Arabian and Eurasian Plates, which resulted in the formation of the Iranian plateau, mountain building, extensive deformation and seismicity. The deformation involves intracontinental shortening except where the Oman Sea subducts towards the north beneath the southern east of Iran. The edges of the deformation zone are well defined by the distribution of seismicity and the local topography. It is concentrated in the mountain belts along the SW borders (Zagros), the southern shore of the Caspian Sea (Alborz) and along the NE (Kopeh Dagh) and eastern borders. These belts enclose a series of relatively aseismic and flat blocks. The Isfahan Seismic Network belongs to IGUT (Institute of Geophysics, University of Tehran), consists of 5 stations, which are located in Isfehan province. The short-period seismographs (SS-1) are connected to the central recording station via telemetry. The recording is performed on an event-triggered basis. Teleseismic data between 2000 and 2007 have been used in this study. More than 200 teleseismic events with magnitudes greater than 5.5 at epicentral distances between 30? and 95? have been used for P receiver function analysis. Then we have been processed all of data by using the P receiver function and Zhu and Kanamori (2000) methods to calculate the Moho depth and VP/VS ratio beneath Isfahan region. The teleseismic P receiver function method has become a popular technique to constrain crustal and upper mantle velocity discontinuities under a seismic station (e.g. Langston, 1977; Owens et al., 1984; Kind and Vinnik, 1988; Ammon, 1991; Kosarev et al., 1999; Yuan et al., 2000). Telesismic body waveforms recorded at a three-component seismic station contain a wealth of information on the earthquake source, the earth structure in the vicinity of both source and the receiver, and mantle propagation effects. The resulting receiver function is obtained by removing the effects of source and mantle path. The basic aspect of this method is that a few percent of the incident P wave energy from teleseismic events at significant and relatively sharp velocity discontinuities in the crust and upper mantle will be converted to S wave (Ps), and arrive at the station within the P wave coda directly after the direct P wave. Ps converted waves are best observed at epicentral distances between 30° and 95° and are contained largely on the horizontal components. The amplitude, arrival time, and polarity of the locally generated Ps phases are sensitive to the S-velocity structure beneath the recording station. By calculating the time difference in arrival of the converted Ps phase relative to the the direct P wave, the depth of the discontinuity can be estimated using a reference velocity model (in this paper, the IASP91 reference velocity model is used). After rotating the coordinate system into a local LQT (P-SV-SH) recording system, in which the L component is in the direction of the incident P wave, the Ps energy is mostly observed on the Q component perpendicular to the L component. The Q components (P receiver functions) contain Ps converted waves as well as related S type multiples. To obtain the P receiver function, the following steps are generally used. Restitution, To utilize data recorded at different types of seismometers, the instrument responses have to be deconvolved. Rotation, Firstly, the two horizontal components N and E are rotated to radial (R) and tangential (T) directions. Most of the energy of the direct P and Ps waves are dominating the Z and R components, respectively. To isolate the converted Ps wave from the direct P wave, the ZRT components are rotated into an LQT (P-SV-SH) ray-based coordinate system, in which the L component is in the direction of the incident P wave; the Q component is perpendicular to the L component and is positive away from the source; the T component is the third component of the LQT right hand system. Deconvolution, To eliminate the influence of the source and ray path, an equalization procedure is applied by deconvolving the Q and T component seismograms with the P signal on the L component (Yuan et al., 2000, 2002). The resulting Q component data are named P receiver functions and are mainly composed of the P-to-S converted energy and contain information on the structure beneath a seismic station. The arrival time of the converted Ps phase in receiver functions depends on depth of the discontinuity, whereas the amplitude of the converted phase depends on the S-wave velocity contrast across the discontinuity. Moveout correction (distance equalization), The converted Ps phases are usually weak and of low amplitude. In order to increase signal-to-noise, it is necessary to align and stack receiver functions from different epicentral distances at each station. However, successful alignment and constructive summation of conversion phases requires that the receiver functions be equalized in terms of their ray parameters. Migration, To improve the spatial resolution and convert the delay times into depths, the Ps amplitudes on each receiver function can be back projected along the ray path onto the spatial locations of the conversion points to their true locations in a process similar to migrating in exploration seismology (Kosarev et al., 1999). The ray paths are calculated using a one dimensional global velocity model (IASP91) with assumption that conversions are produced from planar interfaces. Sometimes a spatial smoothing filter is used to improve the spatial correlation so that the space is gridded and back projected amplitudes originating from adjacent boxes are stacked to improve signal to noise ratio. Estimation of crustal thickness and Vp/Vs ratio, The converted Ps phase and crustal multiples (PpPs, PpSs and PsPs) contain a wealth of information concerning the average crustal properties such as the Moho depth and the Vp/Vs ratio. We compute P receiver functions (PRF) for all stations. We rotate the ZNE-component waveforms into the local LQT ray-based coordinate system and deconvolved the L component from the Q component to isolate the P-to-S conversions on the Q component. Individual and summed PRF for PIR station are presented in Fig 2(Up) and VP/VS ratio base on Zhu and Kanamori (2000) method is plotted in Fig 2(Bottem) as an example. P receiver function analysis of recorded events between 2000 and 2007 by 5 short period stations from the Isfehan Seismic Network shows clear conversions from the crust mantle boundary beneath the Isfehan region and VP/VS ratio. We have been able to present clear images from the Moho at depths ranging from 38.5 to 43 km beneath the Isfahan region and VP/VS ratio ranging 1.71 to 1.79. The average Moho depth and Vp/Vs ratio are achieved 40 km and 1.74 which confirmed previous results obtained by other methods.}, keywords = {Moho depth,Receiver function,Teleseismic Waves,VP/VS}, title_fa = {تغییرات عمق موهو و نسبت VP/VS در گستره اصفهان با استفاده از تحلیل تابع انتقال گیرنده}, abstract_fa = {تابع‌های انتقال گیرنده، سری‌های زمانی هستند که از واهمامیخت مؤلفه قائم و مؤلفه شعاعی (مؤلفه افقی چرخش‌‌یافته در راستای چشمه زلزله) لرزه‌نگاشت‌‌ دورلرز به‌دست می‏آیند و بیانگر پاسخ نسبی ساختار زمین درمحل گیرنده لرزه‏ای هستند. به‌‌منظور به‌دست آوردن تابع‌های انتقال گیرنده ابتدا سه مؤلفه Z، N و E لرزه‌‌نگاشت‌‌های دورلرزه (30 تا 95 درجه) و بزرگای 5/5 و بالاتر در بازه زمانی 2000 تا 2007 را انتخاب و بعد از حذف منحنی پاسخ لرزه‌‌نگار، تحت زاویه آزیموت پشتی و زاویه ورودی موج دوران می‌‌‌دهیم تا مؤلفه‌‌های L، Q و T به‌دست آید. سپس با واهمامیخت در حوزه بسامد مؤلفه L از دو مؤلفه Q و T، اثر چشمه و مسیر از لرزه نگاشت‌ها برداشته می‌‌‌شود و با تبدیل معکوس فوریه تابع‌های واهمامیخت شده، آنچه روی مؤلفه Q باقی می‌‌‌ماند همان تابع انتقال گیرنده موج P است که شامل انرژی تبدیل شده P به S (PS) و حاوی اطلاعاتی در مورد ساختار زیر ایستگاه است. زمان رسید فاز تبدیلی Ps اولیه در تابع انتقال گیرنده نشان‌‌دهنده عمق ناپیوستگی موهو و دامنه فاز تبدیلی، اختلاف آکوستیک‌‌ امپدانس محیط را نشان می‌دهد. در این مقاله با استفاده از روش تابع انتقال گیرنده موج P و استفاده از 200 لرزه‌‌نگاشت کوتاه‌دوره دورلرز ثبت شده در 5 ایستگاه شبکه لرزه‌نگاری اصفهان، وابسته به مؤسسه ژئوفیزیک دانشگاه تهران، عمق موهو و نسبت VP/VS در گستره اصفهان تعیین شد. تحقیقات گرانی‌سنجی نشان می‌دهد که ضخامت پوسته در نوار سنندج- سیرجان که بخش جنوب غربی ایران مرکزی را تشکیل می‌دهد حدود 50 تا 55 کیلومتر است و همچنین براساس این تحقیقات عمق موهو در گستره اصفهان بین 5/38 تا 43 کیلومتر به‌دست آمد. در این تحقیق نقشه تغییرات عمق موهو در گستره اصفهان به‌دست آمده است. با استفاده از فازهای تکراری پوسته (PpPs , PpSs + PsPs) و رسم نمودار ضخامت پوسته برحسب VP/VS برای 5 ایستگاه لرزه‌نگاری در گستره اصفهان نسبت VP/VS بین 71/1 تا 79/1 به‌دست آمد؛ بنابر این در این گستره میانگین عمق موهو 40 کیلومتر و میانگین نسبت VP/VS ، 74/1 به‌دست آمد.}, keywords_fa = {Moho depth,Receiver function,Teleseismic Waves,VP/VS}, url = {https://jesphys.ut.ac.ir/article_29111.html}, eprint = {https://jesphys.ut.ac.ir/article_29111_9c8be9fd798861372b962857516be039.pdf} } @article { author = {Javan-Mehri, Mostafa and Bayramnejad, Esmaeil and Gheitanchi, Mohammadreza and Azhari, Mahmoud}, title = {Crustal seismic velocity structure study in Kope Dagh using simultaneous inversion modeling}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {25-37}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29112}, abstract = {Crustal Velocity Structure Model has a significant role in truly understanding of seismicity and also in relocating earthquakes. On the other hand, it can be used for recognizing major and potential seismic sources which is very critical for seismicity and earthquake hazard assessment studies. Seismic parameters simultaneous inversion modeling is one of the most prevalent methods in the study of seismic velocity structure. This approach optimizes the coordinate parameters, time of the events and the velocity structures simultaneously by processing the initially assumed values. The resulted velocity model can be used for relocating the seismic events, registered on the local seismic network, and locating future seismic events as well as establishing the future seismic tomography studies. In this study, the simultaneous inversion modeling and VELEST software were used in order to find an optimum crustal velocity model. located in east of Caspian Sea, north east of Iran and south of Touran plate tectonics, the Kope Dagh region lies within a broad zone of deformation and forms part of Alpine-Himalayan orogenic belt which is actually the conjunction zone of Touran and Iran plates. This region is separated from Touran plate by Main Kope Dagh Fault from the north, and its southern boundary is assumed Sabzevar Reverse Fault and Mayamey Reverse Fault. Our study area covers Sabzevar, Mashhad, Shirvan and Quchan cities. Quchan is located in the central Kope Dagh region and has experienced four destructive earthquakes in the past centuries (1851, 1871, 1893 and 1895). These earthquakes caused widespread devastation and heavy human loss in Quchan and many surrounding villages. To estimate the layer configuration, velocities and thicknesses; we used first arrival travel times. More than 14000 first arrival data related to 2200 seismic events, registered by the local seismic network, were considered. They are all registered in the stations located less than 400 meters of epicenters. First arrival times were plotted versus their distances. The chart suggests three major layers; therefore we decided to fit three lines on three sections of the chart which are 50-100 meters, 120-180 meters and 190-350 meters, using least square method. By inversing the slopes of these three lines, we calculated the mean velocities for the three layers which are 6.01, 6.36 and 8.10 km/sec related to 0-20 km, 20-46 km and more than 46 km respectively. The second anomaly is corresponding to Moho Depth so it shows thickness of the crust in the study area. We used this resulted information as an initial velocity model to prepare numerous models needed for VELEST software runs. In the next step of our work, in order to improve resulted velocity model, we used VELEST for seven run groups, each containing 20 independent runs using 20 initial models. These initial models are created by a FORTRAN program in a way that 20 initial models have all same thickness but different velocities which are restricted in defined intervals. We considered the convergence of the resulted models in each group to select one as the best run and then to determine a proper velocity model and Moho Depth as well. Hence the third group was selected as the best run group and therefore the related Moho Depth is 46. It is exactly the same as Moho Depth resulted from the first arrival travel times. In the final step, we used the resulted velocity models in the previous step and calculated their mean values as the mean velocity model. This model was used as another initial model for the final run of VELEST program, but in this run we added several layers to initial model so that their velocities increase regularly. The calculated model, by the VELEST, is very similar to the mean resulted model of the second step. We determined this three layers model as an optimum velocity model for the study area in which the thicknesses of layers are 5, 10 and 31 and velocities of P-wave in these layers are 5.95, 6.1 and 7.97 km/sec respectively. Quchan station is determined as our origin station, therefore its time correction was assumed zero. The most time correction resulted by the final VELEST run is related to Moghan Station.}, keywords = {Crustal seismic velocity model,Kope Dagh,Simultaneous inversion,VELEST}, title_fa = {بررسی ساختار سرعتی پوسته در زیر شبکه لرزه‌نگاری قوچان با استفاده از برگردان زمان سیر امواج زمین‌لرزه‌‌های محلی}, abstract_fa = {روش مدل‏سازی وارون هم‌زمان پارامترهای زمین‌لرزه‌ای یکی از روش‌های متداول در تحقیقات ساختار سرعتی پوسته زمین است. در این روش، پارامترهای مکانی و زمانی زمین‌لرزه‌ها و ساختار سرعتی پوسته، طی مراحل مدل‏سازی وارون به‌طور هم‌زمان بهینه می‌شوند. در این تحقیق برای تعیین مدل سرعتی بهینه پوسته در ناحیه کپه‌داغ از روش مدل‏سازی وارون هم‌زمان و نرم‏افزار ولست استفاده شده است. ناحیه کپه‌داغ، قسمتی از کمربند کوه‌زایی آلپ-هیمالیا است که در شمال شرق ایران و روی حاشیه جنوب غربی پوسته قاره‌‌ای توران قرار دارد. شهر قوچان که در مرکز این ناحیه واقع شده، از 1870 تا به حال، بارها با زمین‌لرزه‌های بزرگ و مخرب ویران شده است. این زمین‌لرزه‌ها از بزرگ‌ترین زمین‌لرزه‌هایی بودند که در طول 160 سال اخیر در منطقه کپه‌داغ رخ داده‌اند و تلفات و خسارات بسیاری در شهر قوچان و دهکده‏های اطراف آن برجای گذاشته‌اند. در ابتدا برای برآورد مدل یک‌بُعدی اولیه از نمودار زمان‏سیر اولین فازهای رسیده برحسب فاصله استفاده شده است و از نتیجه آن در مراحل بعدی برای تهیه تعدادی مدل اولیه مورد نیاز در نرم‌افزار ولست استفاده شد. سپس با به‌‌کارگیری نرم‌افزار ولست مدل پوسته نهایی محاسبه شد که بر وجود سه لایه با سرعت‌های 95/5 تا عمق 5 کیلومتری، 1/6 تا عمق 15 کیلو متری و 97/7 اعماق بیش از 46 کیلومتر دلالت می‌کند.}, keywords_fa = {Crustal seismic velocity model,Kope Dagh,Simultaneous inversion,VELEST}, url = {https://jesphys.ut.ac.ir/article_29112.html}, eprint = {https://jesphys.ut.ac.ir/article_29112_69589f32b84b8c8e9cc269b2d26e9db1.pdf} } @article { author = {Azhari, Mahmoud and Rezapour, Mahdi and Javan-Mehri, Mostafa}, title = {Determination of velocity of seismic waves and upper crustal velocity model in Shiraz seismological network}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {39-52}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29113}, abstract = {Iran is located between two lithospheric plates (Euroasia, Arabian) and these two plates converge toward each other with a velocity of 25 mm/yr rate. Shortening that produced from this convergence with Makran subductin shows faulting and folding in Zagros orogenic belt, Alborz and Kopedagh in north and sliding in sum strike slip faults with north-south trend in central Iran. The NW-SE trending Zagros fold and thrust belt, extends for about 1800 km from a southeast of the East Anatolian Fault in northeastern of Turkey to the Strait of Hormuz, where the north-south trending Zendan-Minab-Palami fault system separates the Zagros belt from the Makran accretionary prism. The Zagros range currently accommodates almost half of NS shortening between the Arabia and Eurasia. This active fold and thrust belt is subdivided into five morphotectonic units: the High Zagros Thrust Belt, the simple Fold Belt, the Zagros Fordeep, the Zagros Coastal Plain and the Persian Gulf-Mesopotamian lowland. The studied region in this paper located in Fars province, in the High Zagros Thrust Belt, north Eastern part of this region is Abarkuh desert that located in central Iran is less active than the other border region around studied region. The west and southeastern part of this region is located in Zagros seismotectonic province that a lot of earthquakes were seen. For study of velocity of seismic waves and upper crustal velocity model in Shiraz region the recorded data by Shiraz seismic network during 2002 to 2009 were used and for seismicity, International Seismological Centre (ISC) catalog, Harvard Centroid Moment Tensor (CMT) catalog and historical earthquakes catalog (Ambraseys and Melville, 1982) were used. Crustal structure of this region is a particular issue that is not yet resolved in the studied region. In order to study the crustal structure of studied region, we use Shiraz network that have 5 stations, To assesse the velocity model, subset of 78 events was selected that recorded by minimum of 4 stations, with an azimuthal gap less than 270?, residual RMS less than 0.3s and uncertainties in epicenter less than 6 km and depth less than 10 km. Consequently using these events, a crustal velocity model obtained with VELEST software for the upper crustal velocity model beneath studied region. The calculated velocity model for the studied region showed three discontinuities in 6, 10 and 14 kilometer depths. P wave velocity has been obtained 5.68 km/s, 5.88 km/s, 6.54 km/s and 6/66 for the first layer, second layer third layer and half space, respectively. Plotting Tsj-Tsi (S arrival time to stations i and j respectively for same event) versus Tpj-Tpi (P arrival time to stations I and j respectively for same event) for all events and all stations, Vp /Vs ratio was computed about 1.77 with 908 arrival times. Comparison of obtained VP/VS value with other research results shows that there is not a significant difference between them. Also, local velocity curves for Pg, Pn, Sg, and Sn phases are obtained in the study area by using the data base 2002 through 2009. The slopes of these curves give crustal P and S velocities of 6.16±0.02 and 3.71±0.02 kms-1, and Moho P and S velocities of 7.8±0.1 and 4.78±0.04 kms-1, respectively.}, keywords = {compressional wave,Crustal velocity model,seismicity,Shiraz seismic network,VELEST}, title_fa = {تعیین سرعت امواج لرزه‌ای و مدل سرعتی پوسته فوقانی در ناحیه شبکه لرزه‌نگاری شیراز}, abstract_fa = {کشور ایران در میان دو صفحه سنگ‌سپهری (لیتوسفری) اوراسیا و عربستان قرار دارد که با آهنگی حدود mm/yr 25 هم‌گرا می‌شوند. کوتاه‏شدگی ناشی از این هم‌گرایی با فرورانش در مکران، چین‌خوردگی‌‌ و گسلش تراستی در کمربند کوهستانی زاگرس در جنوب، البرز و کپه‌داغ در شمال و نیز با لغزش در تعدادی گسل‌های امتداد‏‏لغز مهم (اغلب با روند شمال-جنوب) در ایران مرکزی، آشکار می‌شود. همین‌طور صفحه ایران یک ناحیه پهناور فشارشی در طول کمربند فعال کوه‌زایی آلپ-هیمالیا است که در بین صفحه عربی در جنوب غرب و سپر پایدار اوراسیا در شمال شرق قرار گرفته است. از این‌رو ایران یکی از نواحی فعال لرزه‏خیز جهان محسوب می‌شود. در این میان، ناحیه شیراز به‌سبب قرارگیری در نوار لرزه‏خیز جنوب ایران (ایالت لرزه‏زمین‌ساختی زاگرس) درخور توجه است. به‌منظور بررسی و تعیین نسبت سرعت امواج لرزه‏‏ای Vp/Vs و سرعت انتشار فازهای متفاوت، داده‏های زمین‌لرزه‌‌‏هایی که از 2002 تا 2009 در ایستگاه‏های شبکه لرزه‏نگاری شیراز ثبت شده بود، مورد بررسی قرار گرفت. در این تحقیق با رسم منحنی زمان-سیر فاز‏های ثبت شده برای یک منطقه به مرکزیت شیراز و شعاع تقریبا 150 کیلومتر سرعت فازهای متفاوت Pg، Pn، Sg و Sn ‏به‌ترتیب برابر با 02/0 ± 16/6Vpg = ، 02/0 ± 71/3Vsg = ، 1/0±8/7Vpn = و04/0 ± 77/4Vsn = تعیین شد. همچنین با استفاده از زمان‌‌‌‌‌‌سیر و زمان رسید امواج لرزه‏ای ثبت شده در شبکه لرزه‌نگاری شیراز، متوسط نسبت سرعتی VP/VS برابر با 77/1 به‌دست آمد. درضمن در این تحقیق 78 زمین‌لرزه‌‌ از مجموع زمین‌لرزه‌‌‏های ثبت شده در این منطقه که دقت مناسبی داشتند، انتخاب شد و با استفاده از داده‏های 78 زمین‌لرزه‌‌ موردنظر، با به‌کارگیری نرم‌افزار ولست، ساختار سرعتی در ناحیه مورد بررسی تعیین ‏شد. نتایج به‌دست آمده حاکی از وجود سه ناپیوستگی در عمق‌‌های 6، 10 و14 کیلومتر است، همچنین سرعت امواج تراکمی در لایه اول 68/5 کیلومتر بر ثانیه، لایه دوم 88/5 کیلومتر بر ثانیه لایه سوم 54/6 کیلومتر برثانیه و نیم فضا 66/6 کیلومتر بر ثانیه به‌دست آمد.}, keywords_fa = {compressional wave,Crustal velocity model,seismicity,Shiraz seismic network,VELEST}, url = {https://jesphys.ut.ac.ir/article_29113.html}, eprint = {https://jesphys.ut.ac.ir/article_29113_e08a9bde552b467904bfbc2b5af5d6ff.pdf} } @article { author = {Hojjatnia, Parisa and Riahi, Mohammadali}, title = {Pore pressure prediction from seismic reflection data in an oil field}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {53-61}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29114}, abstract = {Pore pressure is an important parameter, in exploration and production of hydrocarbon resources. Lack of accurate knowledge about pore pressure, before drilling phase, leads to serious dangers in drilling process. Accurate knowledge about distribution of pore pressure in a field, leads to reduce risks in drilling, improve well planning and mud weight calculations. During burial, normally pressured formations are able to maintain hydraulic communication with the surface. Pore pressure or formation pressure is defined as the pressure acting on the fluids in the pore space of a formation. So, this pore fluid pressure equals the hydrostatic pressure of a column of formation water extending to the surface and is also commonly termed as normal pressure. Hydrostatic pressure is controlled by the density of the fluid saturating the formation. As the pore water becomes saline, or other dissolved solids are added, the hydrostatic pressure gradient will increase. Also, sonic velocity, density and resistivity of a normal pressured formation will generally increase with depth of burial and the way such rock properties vary with burial under normal pore pressure conditions is termed its normal compaction trend. Pore pressure gradient is defined as the ratio of the formation pressure to the depth and is usually displayed in units of psi/ft or equivalent mud weight units in pounds per gallon (ppg). Overburden pressure at any depth is the pressure that results from the combined weight of the rock matrix and the fluids in the pore space overlying the formation of interest. Overburden pressure increases with depth and is also called the vertical stress. Effective pressure is defined as the pressure acting on the solid rock framework. Terzaghi defined it as the difference between the overburden pressure and the pore pressure. Effective pressure thus controls the compaction that takes place in porous granular media including sedimentary rocks and this has been confirmed by laboratory studies. The only method for predrill predicting pore pressure is based on the use of 3D seismic data. In this study, seismic velocity obtained from processing methods, will be calibrated with regard to sonic velocities measured at wells. Then using the relation between effective pressure and velocity the effective pressure is calculated. In order to distribute the velocity and pressure quantities in the whole field, we use geostatistical estimation methods (krigging or co-krigging). For using co-krigging we need to have more than one variable. We use acoustic impedance as the second variable. For this purpose firstly the 3D seismic volume was inverted to obtain an acoustic impedance. Usage of multi-variable estimation will consider lithologic and geologic variations of the layers and we have a better estimation in comparsion with one-variable estimate. The 3D pore pressure cube was constructed using these calibrated velocities. The validation of the results illustrates a successful pore pressure prediction in this carbonate field. We also include some of definitions here for convenience.}, keywords = {Acoustic impedance,Multi-variable estimation,Pore Pressure,seismic inversion,Seismic velocity}, title_fa = {برآورد فشار منفذی با استفاده از داده‌های لرزه‌ای بازتابی در یک میدان نفتی}, abstract_fa = {فشار منفذی یکی از مهم‌ترین پارامتر‌های مخازن هیدروکربوری است. بی‌اطلاعی از چگونگی توزیع این فشار در نقاط گوناگون میدان در حین حفاری ممکن است سبب بروز خطرات جدی جانی و مالی بسیار شدیدی شود. استفاده از داده‌های لرزه‌ای بازتابی تنها راهی است که می‌تواند فشار منفذی را قبل از حفاری پیش‌‌بینی کند. در این تحقیق ابتدا سرعتی که از پردازش داده‌های لرزه‌ای به‌دست آمده است، به کمک نمودارهای صوتی موجود در چاه‌های منطقه تصحیح و سپس با استفاده از رابطه موجود بین سرعت و فشار موثر، فشار موثر در منطقه محاسبه شد. با محاسبه فشار روباره و استفاده از رابطه بنیادی ترزاقی، فشار منفذی در منطقه به‌دست آمد. به‌‌منظور پراکنده کردن اطلاعات موجود در چاه‌ها (سرعت یا فشار) در کل منطقه، از روش‌های برآورد زمین‌آماری (یک یا چند‌متغیره) استفاده شد. برای استفاده از روش برآورد چند‌متغیره (کوکریجینگ) لازم است تا متغیر دیگری علاوه بر سرعت یا فشار در نقاط گوناگون میدان در دسترس باشد. در این تحقیق، مقاومت صوتی درحکم متغیر دوم انتخاب شد. این تحقیق روشن ساخت که در مناطقی که پدیده فشار زیاد و مشکل فشار وجود ندارد، با دقت خوبی می‌توان فشار منفذی را با استفاده از رابطه باورز معمولی و رابطه بنیادی ترزاقی به‌دست آورد. از این مکعب به‌دست آمده می‌توان در بررسی‌هایی مانند طراحی مسیر چاه، طراحی وزن گل، تعیین محل نصب لوله جداری استفاده کرد.}, keywords_fa = {Acoustic impedance,Multi-variable estimation,Pore Pressure,seismic inversion,Seismic velocity}, url = {https://jesphys.ut.ac.ir/article_29114.html}, eprint = {https://jesphys.ut.ac.ir/article_29114_dc05166c2cb2a4c2cb34ef123c406883.pdf} } @article { author = {Roshandel Kahoo, Amin and Siahkoohi, Hamidreza}, title = {Mixed-phase seismic wavelet estimation by analyzing the zeros of autocorrelation function in Z-domain}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {63-72}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29115}, abstract = {A seismic section which is very close to the true model of the earth is the goal of reflection seismology. Because raw seismic data are affected by the various ingredients such as geometry, noise and, etc., we are not able to use them for interpretation. Therefore, a processing flow must be applied on the raw seismic data to remove the effects of undesirable ingredients. Deconvolution is one of the most important stages in seismic data processing removed source signature from seismic trace to improve the temporal resolution. Inverse filtering and spiking deconvolution are usual methods in seismic deconvolution. If the seismic source wavelet is known, it can be removed from seismic trace, easily. But in most cases, the source signature is unknown and there is only an approximation of the source wavelet autocorrelation function. The usual deconvolution methods work well when the seismic source is of minimum-phase wavelet. Often, the seismic source wavelet is mixed-phase, thus estimation of mixed-phase wavelet is important for deconvolution of seismic data. Moreover, the efficiency of the inversion of seismic data depends on the correlation of the real and synthetic seismic data near the well position. A good estimation of seismic source wavelet can improve the correlation of real and synthetic seismic traces. In this paper, we estimate the mixed-phase seismic source wavelet by analyzing the zeros of estimated seismic source autocorrelation function. This method is very simple and efficient. We tested the efficiency of mentioned method on both real and synthetic seismic data. It can estimate all of seismic source wavelet type, but given the importance of mixed-phase seismic source wavelet estimation; this paper deals with this issue. In the most seismic deconvolution methods, the reflection series of the earth is considered as a random series. With this assumption, we can estimate the autocorrelation of source wavelet from seismic trace. Autocorrelation of a signal is equivalent to the convolution of signal with reversed version of it. The reversing effect of a signal simply reciprocates its zeros. Thus, the zeros of autocorrelation function of a signal contain the zeros of original signal combined with zeros of reversed version of it. Let us call the zeros of reversed version of signal as "image" zeros. Because, the image zeros are the complex conjugate of the zeros of original signal, the autocorrelation function is a zero-phase series. To estimate the original seismic source wavelet, we must find a way to distinguish between the original zeros and its images between the zeros of autocorrelation function. We use a second autocorrelation function calculated from the signal multiplied by exponential, decaying or expanding. Multiplying the original data with an expanding exponential will cause original zeros to move toward the origin along their radials. However, image zeros, being reciprocals of original zeros, will move in the opposite direction away from the origin. Thus, as we observe the movement of the original roots of the autocorrelation function with the expanding exponential multiplication, we see some of the roots move in the expected direction. Therefore, they are the seismic source wavelet roots. Now we can define a process by which the roots of the wavelet Z-transform can be determined uniquely. This will, in turn, define the wavelet phase function. We tested the efficiency of the proposed algorithm for mixed-phase seismic source wavelet estimation on both synthetic and real seismic data. In the case of synthetic seismic data, first the algorithm was tested on the free noise trace. The estimated mixed-phase wavelet was very similar to that used in the generation of synthetic seismic trace. To investigate the algorithm sensitivity to noise, Gaussian random noise with different signal to noise ratios were added to synthetic trace and mixed-phase wavelet were estimated. We saw that the algorithm can estimate the source wavelet with good accuracy in the presence of random noise with SNR greater than 20 dB. For investigation of efficiency of algorithm on real seismic data, we selected a part of common-midpoint gather with 75 traces and 4 ms sampling interval. We applied the mentioned methods on various traces of CMP. The theory and obtained results in both synthetic an real seismic data show that: (1) The method has a simple theory, (2) The uncomplicated theory of this method caused it to have low cost of computations and (3) The method has a good efficiency in existence of noise. Therefore, autocorrelation function zeros analysis method for seismic source wavelet estimation is a suitable an efficient algorithm.}, keywords = {Autocorrelation function,Deconvolution,Mixed phase,Wavelet estimation,Z transform}, title_fa = {برآورد موجک لرزه‌‌ای با فاز مرکب با استفاده از تحلیل صفرهای تابع خودهمبستگی در حوزه Z}, abstract_fa = {هدف از لرزه‌شناسی بازتابی رسیدن به مقطعی لرزه‌‌ای است که تا حد ممکن به مدل واقعی زمین نزدیک باشد. اما محدود بودن باند بسامدی داده‌‌های ثبت شده و اثر جذب در زمین مانع از رسیدن به این هدف می‌‌‌‌شود و بایستی مراحل گوناگون پردازشی روی داده‌‌ها اِعمال شود. از مراحل اصلی در پردازش داده‌‌های لرزه‌‌ای بازتابی برای نیل به این هدف می‌‌‌توان به واهمامیخت اشاره کرد. این مرحله به‌‌منظور حذف اثر همامیختی موجک با سری بازتاب زمین صورت می‌‌‌گیرد. متداول‌ترین روش‌‌ها در واهمیخت داده‌‌های لرزه‌‌ای فرض می‌‌‌کنند که موجک چشمه دارای فاز کمینه باشد. در‌حالی‌‌که در اکثر موارد موجک چشمه دارای فاز مرکب است، بنابراین امکان برآورد موجک با فاز مرکب اهمیت بسیار زیادی در پردازش داده‌‌های لرزه‌‌ای بازتابی دارد. در این مقاله با استفاده از تحلیل صفرهای برآورد تابع خودهمبستگی موجک و خواص تبدیل Z، موجک چشمه لرزه‌‌ای با فاز مرکب برآورد می‌شود. این روش بسیار ساده و درعین‌‌حال کارآمد است. کارایی آن روی داده‌‌های لرزه‌‌ای مصنوعی و واقعی مورد بررسی قرار گرفت و نتایج به‌دست آمده نشان داد که این روش با دقت خوبی موجک چشمه با فاز مرکب را برآورد کرده و از طرفی در مقابل نوفه نیز دارای حساسیت کمی است.}, keywords_fa = {Autocorrelation function,Deconvolution,Mixed phase,Wavelet estimation,Z transform}, url = {https://jesphys.ut.ac.ir/article_29115.html}, eprint = {https://jesphys.ut.ac.ir/article_29115_ffbdeab59613c02df64ec709a4706fa5.pdf} } @article { author = {Mohammadabadi, Hamed and Edalat, Ali and Siahkoohi, Hamidreza}, title = {Applying horizon-based attributes to detect faults/fractures}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {73-84}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29116}, abstract = {Faults/fractures detection is an essential step of the full field study in hydrocarbon reservoir. Definition of exact location of these structural events is a critical step to optimize location of the development wells. Despite of the fast development of the geo science technology and oil industry in recent years, detection of the small geological events such as faults and fractures in some of the situations is still problematic. There are some methods to identify the faults. One of these methods is direct interpretation of the faults on seismic sections. Considering most of the faults/fractures in carbonate reservoirs are too small to identify by conventional faults interpretation and are smaller than seismic resolution, this method could not specify all of the reservoir fractures. One of the new methods for distinguishing the faults and fractures which has been developed recently is used to seismic attributes which allows us to detect sub-seismic faults/fractures. In this study we try to interpret faults/fractures in Kangan- Dalan reservoir formations with Upper Permian–Lower Triassic age in one of the hydrocarbon reservoirs in Persian Gulf. These layers were divided to five zones namely K1, K2, K3, K4 and K5. Total thickness of the reservoir layers varies from 400 meters to 600 meters and these formations including of sequences of Calcite, Dolomite and Anhydrite. The geophysical data which have been used in the study consist of 3D seismic post- migrated data and interpreted time horizons in the study area. The seismic data have 25*6.25 m grid size with two second length of seismic traces and four milliseconds sampling rate. Petrel software has been also used foe seismic attribute generation and comparing them. In the first step of the study, 3D seismic data as well as interpreted time horizons of the top and base of the reservoir were loaded in the mentioned software. Then, in order to detect the faults, some horizon- based Root Mean Square (RMS) amplitude, dip, azimuth and curvature attributes were generated using Top Kangan time map and 3D seismic data. In this regards, the suitable parameters were selected by performing some tests and quality control of the results. Then generated seismic attribute maps were evaluated and fault/ fractures patterns of the reservoir layer were determined and compared with each other using these maps. In this step, the resulted seimic attribute in fault/ fractures demonstration in reservoir level was investigated. Finally, it was found that in the study reservoir curvature attribute and root mean square (RMS) of amplitude are the best seismic attributes for faults/fractures detection. The results of this study shows ability of the curvature attribute groups to detect sub-seismic faults/fractures. Moreover it shows using only one attribute could not be detect all of the fault/fractures in the reservoir; so some seismic attributes should be generated and results of the all attributes should be compared to find an accurate fault pattern.}, keywords = {Curvature,faults,Seismic attribute,Time horizons}, title_fa = {استفاده از نشانگر‌‌های لرزه‌‌ای مبتنی بر افق در تعیین گسل‌‌ها و شکستگی‌‌ها}, abstract_fa = {نیاز به تعیین محل گسل‌‌ها و شکستگی‌‌ها در تحقیقات جامع مخازن هیدروکربنی، گامی مهم و اجتناب‌ناپذیر است. تعیین دقیق محل‌‌ این ویژگی‌‌های ساختمانی، ابزاری بسیار موثر در شناسایی محل بهینه چاه‌‌های تولیدی است. در‌‌ این تحقیق با استفاده از نشانگرهای مبتنی بر افق، سعی در تفسیر گسل‌‌ها و شکستگی‌‌ها در لایه مخزنی کنگان در یکی از میادین هیدروکربنی واقع در خلیج فارس شده است. اطلاعات پایه‌‌ای مورد استفاده شامل داده‌لرزه‌‌ای سه‌بُعدی مهاجرت یافته و افق‌‌های زمانی در محدوده مورد بررسی است. به‌منظور تشخیص گسل‌ها در محدوده مخزن، چند نشانگر بر پایه افق شامل نشانگرهای با استفاده از اطلاعات لرزه‌نگاری و افق زمانی سرسازند کنگان تولید شد. سپس نقشه‌‌های نشانگری منتجه مورد ارزیابی قرار گرفت و الگوی گسلش با استفاده از آنها تعیین شد. نتایج‌‌ این تحقیق بیانگر توانایی زیاد گروه نشانگرهای انحنا در تعیین شکستگی‌‌های کوچک‌تر از قدرت تفکیک اطلاعات لرزه‌نگاری است.}, keywords_fa = {Curvature,faults,Seismic attribute,Time horizons}, url = {https://jesphys.ut.ac.ir/article_29116.html}, eprint = {https://jesphys.ut.ac.ir/article_29116_3c495f6cf31f1dfcd85e897ab8dbebd0.pdf} } @article { author = {Hashemi, Hossein and Maazallahi, Mahdiyeh}, title = {Comparison of SSR and H/V microtremor data analysis techniques}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {85-92}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29117}, abstract = {The destructions caused by many recent earthquakes shows that the subsurface structure directly affects the ground motions. Especially in areas with possible seismic hazard expectation, expansion of cities has come up with detailed vulnerability analysis. Therefore, site response investigation is a key step in every microzonation study. One of the best approaches for understanding the geological structure is to observe the seismic ground motions on the ground surface. Although mostly qualitative measures are presented, the relationship between the destruction caused by earthquakes and site effect has been proven by many researchers. So, it is widely known that the site response is the most important information needed in site evaluation. So, there is a great need to evaluate the dynamic site response characteristics such as resonant frequency and amplification factor efficiently and cost-effectively. These data are not only useful for earthquake engineers but geotechnical engineers and seismologists. Nowadays, microtremors are being used in site effect and microzonation studies. Microtremors are the ubiquitous, weak, low amplitude vibrations which may be recorded on the surface of the earth. Microtremors are used as passive seismic methods which are cost effective, so t¬¬hey are being used increasingly. Studies by many scientists (e.g. Aki, 1957; Nakamura, 1989; Lachet and Bard, 1994; Lermo and Chavez-Garcia, 1994) about nature of microtremor sources and effect on ground identify the atmospheric disturbances and meteorological phenomena over the land or the sea as well as human activities as generators of microtremors. The relationship between local geological structure of surface layers and microtremor spectral characteristics has been proven by the above mentioned scientists. The most commonly used methods to quantify this relationship, are the well known Standard Spectral Ratio technique which requires the simultaneous measurement of local and remote reference data on bedrock (Borcherdt and Gibbs, 1976) and the more recent Horizontal to Vertical Spectral Ratio (Nakamura, 1989), each of which has its own advantages and disadvantages. A difficulty of SSR technique is selection of an appropriate reference site on the outcrop of bedrock, which is also free of topographic effects. The last mentioned point is vital for analyzing and interpreting data. The H/V technique assumes that the vertical component is not amplified by the local geology. In the present paper microtremor data has been analyzed using Standard Spectral Ratio (SSR) and horizontal to vertical Spectral ratio (H/V) techniques using FFT spectral analysis method, in Kamyaran city using a developed code in Matlab software. Kamyaran city is located in Kordestan province in west of Iran with an area of 2950 square kilometers and its elevation from sea level is 1400 meter. It is located in the longitude of 34.793 and the latitude 46.936. Due to the high seismicity of Kamyaran city,a national project was carried out in order to measure the microtremors and evaluate site response and estimate the relation between ground motions and geological structure i.e. amplification level and resonant frequencies. In other words, quantifying and comprehending the local geology and ground motions in Kamyaran City is a main task of this project. Using geological and seismological approaches, we can achieve such a task. In order to carry out this, two cost effective seismological techniques were used; Horizontal to vertical ratio (H/V)(Nakamura, 1989; Lachet and Bard, 1994; Lermo and Chaez- Garcia, 1994) and Standard Spectral ratio (SSR)(e.g. Borcherdt and Gibbs, 1976;) for processing the recorded microtremor data in studied area. Also, a comparison is made between the results of the two techniques. Ambient noise data were collected using SSR1 sensor in Kamyaran city; ten appropriate stations were selected among all recorded stations for site effect evaluation. The H/V technique should be more concentrated, because powerful near field noise causes amplification of both the horizontal and vertical components similarly. Practically, it results in underestimation of real H/V ratio, because of the distortion caused by leakage. In coincidence of the noise and real ground resonant frequencies, these effects are more noticeable. At the end for better interpretation the geological and geotechnical data are used. H/V technique appears to be more useful in site response evaluation, because it yields precise resonant frequency and amplification factor and it has a greater correspondence with the available geological information. On the other hand, SSR technique (with respect to a reference rock-site station) appears to be useful in sites close to the reference site and it can be used in H/V calibration. As mentioned before, generally, the results obtained from both techniques are relatively similar in many sites of the studied area. Detailed comparison yields that H/V techniques shows a greater consistency to the available geological data (not mentioned here) than SSR technique. On the other hand, in sites with a close distance to the reference site, SSR technique yields data similar to H/V technique. This result demonstrates the advantage of application of the SSR in interpretation of the obtained H/V ratios. Also, a good way to solve the problems of these methods is applying both techniques and interpretation of the results together, which has been proved by other authors as well.}, keywords = {H/V technique,Kamyaran,Microtremor,Microzonation,SSR technique}, title_fa = {مقایسه روش‌‌‌های SSR و H/V در تحلیل داده‌‌‌های مایکروترمور منطقه کامیاران}, abstract_fa = {امروزه مایکروترمورها به‌نحو روز‌افزون در تحقیقات ریز‌پهنه‌بندی و تعیین اثر ساختگاه به کار برده می‌شوند. در این مقاله با استفاده از موارد ثبت شده مایکروترمور به بررسی اثرات ساختگاه پرداخته‌ایم. در ابتدا روش‌‌‌های آنالیز داده‌‌‌های مایکروترمور مورد بررسی قرار گرفت. برای این منظور داده‌‌‌های مایکروترمور با استفاده از دو روش متداول نسبت طیفی مولفه افقی به قائم (H/V) و نسبت طیفی استاندارد (SSR)، با استفاده از طیف فوریه FFT، تحلیل شد. در صورت استفاده از فیلترهای مناسب قله به دست آمده در طیف های دامنه حاصل از روش H/V به خوبی می تواند فرکانس غالب و میزان تشدید یک رخداد لرزه ای را نشان دهد. روش نسبت طیفی مولفه افقی به قائم، به‌خوبی مقادیر بسامد غالب و ضریب تقویت را نشان می‌‌دهد و روش نسبت طیفی استاندارد فقط در جاهایی کارآمد است که فاصله ساختگاه مورد بررسی تا ساختگاه مرجع مناسب باشد. این روش همچنین برای واسنجی کردن روش نسبت طیفی مولفه افقی به قائم نیز مناسب است. نتایج حاصل از این مقاله کمک شایانی به مطالعات ریز پهنه بندی لرزه ای خواهد کرد.}, keywords_fa = {H/V technique,Kamyaran,Microtremor,Microzonation,SSR technique}, url = {https://jesphys.ut.ac.ir/article_29117.html}, eprint = {https://jesphys.ut.ac.ir/article_29117_3874b7c090095287bca8066face45094.pdf} } @article { author = {Askari, Abdolrahim and Feizeabady, Baratali and E.Ardestani, Vahid}, title = {Crustal and isostasic model for the Gulf of Oman using gravity data}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {93-98}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29118}, abstract = {The mapping of the crust-mantle boundary surface is an important geophysical task, which the method of seismic profiling has dealt with profitably. There are, however, areas where the crustal structure is not known up to the present, and where the Moho has as yet not been determined by geophysical sounding. In such areas the isostatic theory may be applied to give a first estimate of the depths of the crust-mantle boundary. However, young orogenic regions are not necessarily in isostatic equilibrium. Therefore the isostatically calculated crust mantle boundary must be corrected. In our method, the long wavelength observed gravity anomalies are inverted in an iterative process to model the crust-mantle boundary, assuming thus that the mass responsible for the observed gravity anomalies is located at the level of the crust-mantle boundary. As in all gravity-inversion problems, the ambiguity inherent in the underlying mass distributions implies the choice of a particular starting model, defining the crustal equilibrium thickness, and the crust and mantle densities. This may be done adopting a standard crustal model, where mean values found in the literature are used. In cases where these are available, further geophysical knowledge on the crustal thickness from other sources, particularly seismic, gives a means to anchor the crustal equilibrium depth. Thickness of the crust is mostly determined using seismic data provided by recorded earthquakes. The gravity data also can be a very useful source for this purpose. In this paper, authors have estimated a new crust model in The Oman Sea using the new database. The study region is extended between latitude and . The estimated thickness of the crust is compared with the A-H model of Isostasy. According to Airy, the mountains are floating on a fluid lava of higher density, so that the higher the mountain, the deeper it sinks. (Airy Isostasy: constant density materials, topography underlain by roots, depressed Moho depth). Airy proposed this model, and Heiskanen gave it a precise formulation for geodetic purposes and applied it extensively. The gravity model computed by Bhaskara Rao et al., formula (1990) and is compared with the observed gravity dataset. To investigate subsurface structure from potential data such as gravity and magnetic data, various methods have been developed. Blakely (1995) divided them into three categories of forward method, inverse method, and data enhancement and display. Since the algorithm that allows the Fourier transform quite fast had developed, there have been many attempts to apply it to geophysical data processing, and one of the most important works in potential field was done by Parker (1973). He derived mathematical expansions and showed how a series of Fourier transforms could be used to compute the gravity anomaly caused by an uneven, non-uniform layer of material. Shortly after his work, Oldenburg (1974) deduced a method to compute the density contrast topography from the gravity anomaly reversely in two-dimensional Cartesian coordinate system by intuition from the Parker's formula. anomaly. The inversion method used here is that proposed by Oldenburg (1974), in which the topography of a density interface generating a certain gravity anomaly is estimated using the equation described by Parker (1973). To do this, we need to know both the mean depth of the interface and the density contrast between the bodies separated by this interface. According to Parker (1973), the Fourier transform of the gravity anomaly and the sum of Fourier transforms of the topography causing such a gravity anomaly are related.}, keywords = {3-D gravity modeling,Crust isostasy model,gravity anomaly,inversion,Oman Gulf,Thickness crust}, title_fa = {استفاده از تحلیل داده‌های گرانی در تعیین مدل پوسته و مقایسه با مدل هم‌ایستایی ایری- هیسکانن در دریای عمان}, abstract_fa = {برای تحقیق ساختار پوسته در دریای عمان ، از بی‌‌هنجاری‌های گرانی و مدل هم‌ایستایی ایری- هیسکانن، استفاده کرده و ضخامت پوسته را به‌دست آورده‌ایم. نقشه بی‎هنجارى هم‎ایستایى ایران که بر پایه مدل تعدیل شده هم‌ایستایی ایری- هیسکانن تهیه شده است، نشان می‎دهد که چگالى بلندی‎ها 67/2، چگالى میانگین پوسته 75/2، چگالى ریشه کوه‎ها 85/2، چگالى گوشته بالایى 35/3 گرم بر سانتی‌متر مکعب و ضخامت عادى پوسته 30 کیلومتر است. طبق مدل ایری- هیسکانن، چگالی پوسته ثابت است و تعادل هم‌ایستایی با تغییر در ضخامت پوسته در محل ارتفاعات (ریشه‌‌های عمیق) و گودی‌ها (پادریشه‌‌‌ها) صورت می‌گیرد. قاره‌‌ها از کف اقیانوس‌‌ها به دلیل داشتن چگالی بیشتر و نیز ضخامت بزرگ‌تر، بالاتر هستند. بی‌‌هنجاری‌‌های گرانی بوگه از داده‌های ارتفاع‌سنجی ماهواره‌ای روی اقیانوس‌ها محاسبه شده است.قدرت تفکیک مکانی این داده‌ها 5 کیلومتر است. در این تحقیق مدل پوسته و هم‌ایستایی ایری-هیسکانن جدیدی برای منطقه مورد بررسی براساس روش معکوس به روش پارکر تعیین شده است ناحیه مورد بررسی در عرض جغرافیایی 20= تا 5/25= و طول جغرافیایی 60= تا 5/66= درجه که کلاً پوشیده از آب است، قرار دارد. برای محاسبه ضخامت مقادیر گرانی و عمق، به‌صورت یک شبکه کیلومتر در آمده و برای محاسبات در هر دو روش از این قدرت تفکیک استفاده شده است. تفاوت مشاهده شده در تعیین ضخامت پوسته حاکی از آن است که منطقه به‌لحاظ هم‌ایستایی، جبران نشده است.}, keywords_fa = {3-D gravity modeling,Crust isostasy model,gravity anomaly,inversion,Oman Gulf,Thickness crust}, url = {https://jesphys.ut.ac.ir/article_29118.html}, eprint = {https://jesphys.ut.ac.ir/article_29118_1c064099f8ef275a4d7823f682d31044.pdf} } @article { author = {Goli, Mehdi and Najafi-Alamdari, Mahdi and Vanícek, Petr}, title = {Downward continuation of Helmert gravity anomaly to precise determination of geoid in Iran}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {99-109}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29119}, abstract = {The use of Stokes boundary values problems for the determination of the geoid requires that gravity anomalies (as boundary values) are known on geoid (as boundary). While, the gravity observations are measured on the Earth's surface, to obtain boundary data, the surface gravity anomalies does are downward from the terrain onto geoid. For downward continuation (DWC) of surface gravity anomalies, the Poisson integral can be used if the disturbing potential corresponding to gravity anomalies have harmonics everywhere above the geoid. But free-air gravity anomalies are non harmonics due to presence of (topographical+athmospherical) masses above the geoid. In the geoid accounting for the topography was first suggested by Helmert put in practice for example by Martinec and Van??ek (1994), and ultimately applied in the Stokes-Helmert scheme (Van??ek et. al, 1999). The second condensation method proposed by Helmert, involves the condensation of the topographic and atmospheric masses outside the geoid onto the geoid in the form of a surface layer. As the Helmert disturbing potential is harmonic above the geoid, we use the Poisson solution formulated for harmonic functions. A critical and unavoidable problem encountered in the DWC is the implementation of discretization of the Poisson integral. Several discretization schemes have been proposed by, e.g., Matrince (1996), Van??ek et al. (1996) and Sun and Van??ek (1998). In mean-mean model the mean values on the surface are transformed to the corresponding mean values on the geoid by doubly averaged Poisson kernel. The point-point model transformed point surface values to point geoid values. The in point-mean the mean values of geoid are obtained from the point values on the Earth's surface by averaged Poisson kernel. Normally, mean anomalies are evaluated from several/many point values on the Earth's surface on the regular grid. Also the finite element method of evaluation of Stokes integral needs that mean anomaly to be given on the geoid. Therefore we have to use the mean-mean model of discretization of Poisson integral. But In Iran, the distribution of observed point gravity data are very spars and it involves the big gaps in Alborz and Zagros mountainous areas as well as in deserts and sea. The gaps usually are filled by the high resolution satellite geopotential model. Therefore in most cells, the mean gravity anomalies are predicted/computed from few point values or geopotential model. In this case, the mean values tend to point values. We employed both point-mean and mean-mean models of DWC in Stokes-Helmert method to precise determination of geoid in Iran. The long wavelengths part of geoid up to degree and order 180/180 is determined using the EGM08 model. As external evidence, the two geoids were compared to the GPS solution at 213 points into the national height network. The RMS of differences between two geoids and GPS-levelling data are 46cm without any applying correction surface. The RMS of difference between two geoid models is about 4cm and it can be reached up to 35cm in mountainous area. As a result, we cannot able to decide to suitable discretization model of Poisson integral due to very poor distribution of gravity data in Iran.}, keywords = {Discretization model,Downward continuation,Helmert gravity anomaly,Precise geoid determination,Stokes-Helmert}, title_fa = {انتقال رو به پایین بی‌هنجاری‌‌های گرانی هلمرت برای تعیین دقیق ژئویید در ایران}, abstract_fa = {روش استوکس برای حل مسئله‌‌ مقدار مرزی نیاز به حذف اثر گرانی توپوگرافی بالای ژئویید دارد. فضای هلمرت یک مدل مناسب برای حل مسئله‌‌ مقدار مرزی ژئویید است. هدف این تحقیق تعیین دقیق ژئویید به‌روش استوکس– هلمرت در منطقه ایران با تاکید بر نحوه گسسته‌سازی انتگرال پواسون است. در این تحقیق از گسسته‌سازی نقطه-متوسط و متوسط-متوسط برای تعیین بی‌هنجاری‌‌های متوسط در سطح ژئویید استفاده شده است. محاسبات ما نشان می‌‌دهد که اختلاف بین این دو مدل گسسته‌سازی انتگرال پواسون در ارتفاع ژئویید در منطقه آزمون در حدود دسی‌متر است. بااین‌‌حال در مقایسه با 213 نقطهGPS-Leveling دقت مطلق و نسبی ژئویید گرانی هر دو مدل متوسط و نقطه‌‌ای در منطقه آزمون در حدود 46 سانتی‌متر است.}, keywords_fa = {Discretization model,Downward continuation,Helmert gravity anomaly,Precise geoid determination,Stokes-Helmert}, url = {https://jesphys.ut.ac.ir/article_29119.html}, eprint = {https://jesphys.ut.ac.ir/article_29119_53cd71ec8c6497f9c35601d16d543b1d.pdf} } @article { author = {Kamkar-Rohani, Abolghasem and Shokri, Dariush and Moradzadeh, Ali}, title = {Determination of the dips, and segregation, of geological units from airborne magnetic data}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {111-127}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29120}, abstract = {Various geological units in an area often exhibit different magnetic properties. Due to this distinction in magnetic properties of the geological units, a correlation between the type of a geological unit and its magnetic response can be established. To determine the lateral and vertical extents of geological units from the magnetic data in a survey area, a number of filters for processing magnetic data can be used. Magnetic responses of deep anomalies are generally obtained by applying upward continuation filter on the magnetic data. If the upward continuation filter in contact between two layers having different magnetic properties is applied, the magnetic profiles with increasing height are displaced laterally. This displacement is carried out in the direction of the dip between two layers. By combining the upward continuation processing results in the form of a three-component combination image (RGB), we can obtain the dips of geological layers from the magnetic data or map. In this regard, airborne magnetic data acquired from Kalateh-Reshm area, Damghan, have been used and a map indicating the dips of geological layers for the area has been derived. To determine the interface between two adjacent geological units, ZS-Edgezone filter, developed by Zhiqun Shi, have been applied. By analysis of the results of applying the ZS-Edgezone filter on the upward continuation processed magnetic data, we can quite well determine the directions of the dips of geological units, and also distinguish the geological units having low dips from those having high dips. This is due to the fact that a geological unit having a low dip indicate a relatively high horizontal displacement as we increase the height in the upward continuation process. However, a relatively low horizontal displacement can be seen for a geological unit having a relatively higher dip as the height in the upward continuation process is increased to the same amount as in the previous case of the low dip geological unit. The above-mentioned method has been used in this paper to determine the dips of geological units from airborne magnetic data in Kalateh-Reshm area, located at 120 kilometers south of Damghan city. The aeromagneic data have been acquired by Geological Survey of Iran (GSI) in 2004. In general, the survey area geologically consists of metamorphosed carbonated units and volcanic rocks. To determine the dips of geological units from the airborne magnetic data in the survey area, first we have applied reduction to the pole (RTP) processing filter on the magnetic data. Then, upward continuation filter on the RTP processed magnetic data, and finally, ZS-Edgezone filter on the obtained RTP and upward continuation processed magnetic data have been applied. All these processed magnetic data and maps have been obtained using “Profile Analyst” software, developed by Encom geophysical company. The magnetic field variations in the area are mainly attributed to the changes in the primary and/or secondary magnetite contents of the rocks. As a result of some kinds of alterations in the rocks, the secondary magnetite is occurred while the primary magnetite is origininally occurred in the rocks when they are just formed. The obtained map of the dips of units has been shown by three main colours, i.e. red, green and blue (RGB). Where these three colours in the map are well separated, the dip is considered to be low. However, for the case of high dip, the separation of these three colours in the map is is less made. In other words, in the case of high dip, these three colours in the map have more overlapping than in the case of low dip. Based on this procedure and the results of applying the above processing methods on the magnetic data from the area, presented in the form of RGB colour map, we conclude that the dips of the geological units in central parts of the survey area are comparatively higher. Also, in northeastern parts of the area, the dips are intended towards northeast while in southwestern parts of the area, the dips are seen towards south. Also, two anticlines and a syncline are observed in the central and northern parts of the area. Also, an anticline structure can be seen in the centrer towards south of the area. The obtained results are in good agreement with the geological map information of the area, and indicate the significance of the method in determination of the dips, and segregation, of the geological units of the extensive study area covered by airborne magnetic surveys.}, keywords = {Aeromagnetic data,anomaly,Dip,Upward continuation}, title_fa = {تعیین شیب و تفکیک واحدهای زمین‌شناسی از روی داده‌های مغناطیس هوایی}, abstract_fa = {به‌طورکلی با اِّعمال فیلتر ادامه فراسو، پاسخ مغناطیسی مشاهده شده از توده‌های عمیق‌تر ناشی می‌شود. در نتیجه با اِعمال فیلتر ادامه فراسو در مرز بین دو لایه شیب‌دار با خواص مغناطیسی متفاوت، به سادگی می‌توان دید که مکان قرارگیری بی‌هنجاری مغناطیسی ناشی از مرز بین دو لایه روی نیم‌رخ‌‌‌های مغناطیسی با افزایش ارتفاع به طور جانبی جابه‌جا می‌شوند که این جابه‌جایی در جهت شیب بین دو لایه صورت می‌گیرد. با ترکیب نتایج پردازش حاصل از اعمال فیلتر ادامه فراسو به‌صورت یک تصویر ترکیبی سه‌‌تایی (RGB) می‌توان جهت شیب لایه‌ها را از روی داده‌های مغناطیسی به‌دست آورد. در این تحقیق، داده‌های مغناطیس هوایی از منطقه کلاته-رشم دامغان مورد استفاده قرار گرفته و تفکیک لایه‌ها و تعیین شیب لایه‌ها از روی داده‌های مغناطیسی برای این منطقه صورت گرفته است. نتایج به‌دست آمده به‌‌خوبی با نتایج موجود روی نقشه زمین‌شناسی مطابقت دارد و اهمیت روش مورد استفاده را با توجه به وسعت زیاد منطقه برداشت داده‌های مغناطیس هوایی نشان می‌دهد.}, keywords_fa = {Aeromagnetic data,anomaly,Dip,Upward continuation}, url = {https://jesphys.ut.ac.ir/article_29120.html}, eprint = {https://jesphys.ut.ac.ir/article_29120_da2b591c47f71cb0cf2f418896cf6f5a.pdf} } @article { author = {Jahandari, Hormoz and Oskooi, Behrooz and E.Ardestani, Vahid}, title = {3-D inversion of magnetic data from Sorkheh-Dizej region, Zanjan, using the nonlinear Marquardt-Levenberg algorithm}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {129-146}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29121}, abstract = {The aim of this study is 3-D inversion of magnetic data acquired from the Sorkheh-Dizej iron-bearing region in Zanjan province, Iran, in order to determine the geometrical distribution of the buried magnetic sources. For this purpose, our program discretizes the subsurface region into vertical right rectangular prisms and uses the nonlinear Marquardt-Levenberg algorithm to optimize the unknown parameters of the model, iteratively. To evaluate the applicability of the method, it has been first applied to modeling the synthetic data with added noise. The nonlinear inversion of potential field data has long been used for determining the unknown parameters of the source bodies. One of the major applications of this method is to determine the topography of the basement relief (see, e.g., Bott, 1960; Pedersen, 1977; Bhattacharayya, 1980). In this study, we use a similar approach for modeling the magnetic sources with complicated geological shapes. To do this, the region is discretized into vertical right rectangular prisms. As a result, the unknown geometrical parameters will be the depth to the top and depth to the bottom of each prism. The only other unknown parameter is magnetization which is constant for each prism A right rectangular prism is a widely used geometrical model for 3-D interpretation of magnetic source bodies. Bhattacharayya (1964) presented equations for computing the total field magnetic anomaly due to prismatic models. Kunaratnam (1981) simplified the logarithmic and arctangent terms in these equations using complex notation. The program used in this study uses these simplified expressions for forward modeling of magnetic data. To obtain the body parameters that best describe the observed data, our program uses the Marquardt-Levenberg optimization algorithm (Marquardt, 1963) in an iterative way to minimize the difference between the observed and calculated anomalies. The objective function to be minimized is the sum of the square-roots of the errors at all the data points (equation 1). Marquardt-Levenberg algorithm can be regarded as an interpolation between the Gauss-Newton and Steepest Descent methods. At points distant from the solution, this algorithm acts like the Steepest Descent method (for being faster), but as it approaches the solution it acts more like a Gauss-Newton technique, for being more accurate. This behavior is controlled by a damping factor which is automatically adjusted at each iteration according to the success or failure of the iteration in reducing the objective function. The program that is used in this study is the modified version of the FORTRAN-77 program presented by Rao and Babu (1993). For forming the Jacobian matrices, the program uses the expressions for derivatives from Rao and Babu (1991) and it uses the Cholesky decomposition technique for the factorization of the coefficient matrix (matrix D in equation 4). The input data to the program are the observed magnetic data and the magnetic properties of the region (i.e., magnetic declination and inclination and the regional constant). The program then generates an initial model of adjacent vertical prisms with similar upper and lower depths. There should be one data point above each prism on the surface of the earth. The goodness of fit between the observed data and calculated data is computed and then solving the inverse problem (equation 3) the increments that should be added to each body parameter to gain a smaller objective function in the next iteration are obtained. The iterations are continued until the desired objective function is reached or this residual is negligible. The geometrical configuration of the collection of the prisms at the end of the inversion shows the distribution of the magnetic source body. In order to evaluate the applicability of the method, first we apply it to modeling the synthetic data. The synthetic model consists of three separate rectangular blocks which represent a complex geological configuration (Fig. 1). The blocks have the same magnetization intensity (10 A/m) and the declination and inclination of the magnetization are assumed to be zero and 45 degrees, respectively. In order to make the generated synthetic data resemble the realistic field data, random noise with zero mean and standard deviation of 5 percent of each datum magnitude has been added to the data set. The terrain is discretized into a grid of 10x10 prisms, each with a surface data centered above it. The magnetization is supposed to be known and constant throughout the body. The result of the inversion after 100 iterations has a good similarity to the original model although it can be seen that the accuracy reduces with increasing depth (Fig. 3). We apply the inversion scheme to model the real field magnetic data from Sorkheh-Dizej region in Zanjan province, Iran. The shape of the anomaly map (the region isolated by the rectangle in Fig. 4) is typical of a large tabular body. As non-uniqueness is one of the major concerns in the inversion of potential field data, it is useful to limit the possible solutions by devising constraints on the variation of magnetization during the inversion procedure. The source body is completely buried with no outcrops, but the existence of several iron mines very close to the survey area, and the high amplitude of the anomaly intensity, suggest a similar genesis for the magnetic bodies of the region. Therefore, we performed magnetization intensity measurements on 15 core samples from the region which resulted in a range of 5-15 A/m for this parameter. We assume no remanent magnetization is present and the magnetization is only due to induction. The terrain is divided into a 17x15 grid of prisms and inversion performed for 100 iterations. Fig. 7 shows a view of the result body from East. The vertical extension of this dyke-like body is interpreted between -10 and -210 meters, and the average dip-angle of the body is 70 degrees towards North. The results have been compared with the results of the 3-D compact inversion of pseudo-gravity data. The good agreement between the two models shows the efficiency of the algorithm that is employed for the inversion of geomagnetic data in this study.}, keywords = {3-D modeling,Geomagnetism,inversion,Marquardt-Levenberg}, title_fa = {وارون‌سازی سه‌بُعدی داده‌های مغناطیسی منطقۀ آهن‌دار سرخه-دیزج زنجان با استفاده از الگوریتم غیرخطی مارکوارت-لونبرگ}, abstract_fa = {هدف از تدوین مقال? حاضر، وارون‌سازی سه‌بُعدی داده‌های مغناطیسی منطق? آهن‌دار سرخه-دیزج در استان زنجان با استفاده از الگوریتم غیرخطی مارکوارت-لونبرگ و عرضة یک مدل زمین‌شناسی به‌منزلة منشأ این داده‌‌ها است. برنام? فرترن مورد استفاده، محدود? مورد بررسی را به شبکه‌ای منظم از توده‌های منشوری قائم تقسیم می‌کند و با استفاده از یک مدل اولیه و با یک فرایند تکراری، پارامترهای مجهول هریک از منشورها را می‌یابد. توزیع هندسی مجموع? این منشورها شکل سه‌بُعدی تود? زیرزمینی را تعیین می‌کند. رهیافت استفاده شده در این تحقیق، قرار دادن عمق سطح فوقانی و سطح تحتانی منشورها درحکم متغیر برای ارزیابی میزان کارآمد بودن این رهیافت، ابتدا از این روش در مدل‌سازی داده‌های مصنوعی همراه با نوفه استفاده شده است. به‌منظور اِعمال محدودیت در تغییرات پارامتر مغناطیدگی توده در فرایند وارون‌سازی، از نقاط متفاوت محدود? مورد بررسی، نمونه‌گیری و با اجرای آزمایش‌های مغناطیس سنگ، طیف مجاز تغییرات مغناطیدگی تعیین شد. فرض ما در وارون‌سازی داده‌های واقعی، یکنواخت بودن مغناطیدگی در کل توده و همین‌طور حاضر نبودن مغناطیس بازماند است. نتایج به‌دست آمده از مدل‌سازی سه‌بُعدی داده‌های مغناطیسی، یک دایک را نمایش می‌دهد. این نتایج با مدل حاصل از وارون‌سازی سه‌بُعدی داده‌های شبه‌گرانی همین محدوده که با روش وارون‌سازی فشرده صورت گرفته، مقایسه شده است. نتایج مقایسه با روش گرانی، مناسب بودن به‌کارگیری این روش را در این تحقیق روشن می‌سازد.}, keywords_fa = {3-D modeling,Geomagnetism,inversion,Marquardt-Levenberg}, url = {https://jesphys.ut.ac.ir/article_29121.html}, eprint = {https://jesphys.ut.ac.ir/article_29121_85ffd99718f6c9b02c2bef03d4b3d652.pdf} } @article { author = {Goli, Mahdi and Najafi-Alamdari, Mahdi and Vanícek, Petr}, title = {Formulation of Stokes-Helmert boundary value problem using no topography space}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {147-159}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29122}, abstract = {To solve the geodetic boundary-value problem the gravity anomalies have to be continued from the Earth's surface down onto the geoid surface. Helmert’s gravity anomalies (multiplied by the geocentric radius) are harmonic above the geoid. It is thus possible to use them in the Poisson solution of the inverse Dirichlet boundary value problem to get their values on the geoid. The downward continuation (DWC) of Helmert gravity anomalies has raised some criticism, however, originating from the suspicion that the anomalies, even though they are smoother than free-air and Faye anomalies, are still too rough to yield a reasonably good solution particularly for denser grid of gravity anomalies. No topography (NT) space is the gravity Earth's field after the removal of the gravitational effect of the all masses above geoid. Van??ek et al., 2003 proposed the Spherical Complete Bouguer Anomaly (SCBA) as a 3D solid gravity anomaly that is suitable for DWC. The SCBA is a harmonic and smooth function that conforms to an accurate and stable downward continuation. The topography above the geoid contributes toward the high frequency portion of the free-air gravity anomaly on the Earth surface. By contrast, the SCBA is a smooth function because it is already corrected for the topographical effect. Hence, the Bouguer anomaly, especially the SCBA, is much smoother with attenuated high frequency content, compared to the Helmert anomaly. By the nature of the Downward Continuation (DWC) process, which amplifies high frequencies, the SCBA is better suited (Heck, 2003). However, in contrast to the Helmert anomaly (a free-air type), the SCBA involves the disturbed isostasic equilibrium of the crust on the mantle because of the removal of the topographical effect. This phenomenon results in a powerful low frequency content in the SCBA and a large indirect effect (PITE), ultimately amounting to a few hundred meters which is detrimental to the accuracy of the geoid solution. To reduce the large effect to a few decimeters, the SCBA on the geoid is transformed back to the Helmert space. In this paper we formulate the Stokes-Helmert BVP using No topographical space and SCBA in a three space scenario. 1. transforming the observed gravity anomaly on the terrain to the NT space on the same position, 2. downward continuation of the SCBA anomalies from the observation positions to the geoid level, 3. transforming the SCBA on the geoid to the Helmert space, 4. evaluation of the co-geoid using the generalized Stokes integral, 5. transforming the co-geoid back to the geoid. i.e., from Helmert’s space to the real space by applying the PITE. In theory, all different reductions yield the same result in geoid determination. We compared the geoid by NT deduced Stokes-Helmert method and geoid by Stokes-Helmert method in Iran. The long wavelengths part of geoid up to degree and order 180/180 is determined using the EGM08 model. As external evidence, the two gravimetric geoids were compared to the geometric GPS-levelling solution at 213 points. The RMS of differences between two geoids and GPS-levelling data are 46cm without any applying correction surface. However, the RMS of difference between two geoid models is about 4cm and it can be reached up to 1.67meter in mountainous area.}, keywords = {Bouguer,Downward continuation,No topography space,Precise geoid determination,Stokes-Helmert}, title_fa = {استفاده از فضای بدون توپوگرافی برای حل مسئله مقدار مرزی استوکس–هلمرت}, abstract_fa = {تعیین ژئوئید به‌روش استوکس نیازمند انتقال رو به پایین بی‌هنجاری‌‌های جاذبی به سطح ژئوئید دارد. در غیاب جرم‌های بالای ژئوئید انتقال رو به پایین بی‌هنجاری‌‌های جاذبی با انتگرال پواسون میسر است. استفاده از تحکیم توپوگرافی و جوّ روی ژئوئید یک روش مناسب برای حذف توده بالای ژئوئید است. بااین‌حال به‌علت ایجاد لایه با چگالی بسیار سنگین سطحی روی ژئوئید این فضا نرم نیست و بی‌هنجاری‌‌های جاذبی هلمرت حاوی بسامد‌‌های زیاد ناشی از تراکم توپوگرافی‌‌اند. در این تحقیق استفاده از فضای بدون توپوگرافی (مدل اصلی بوگه) و مسئله‌ مقدار مرزی متناظر با آن طرح شده است. همچنین برای گریز از اثرات غیرمستقیم بزرگ ناشی از به‌هم خوردن تعادل هم‌ایستایی پوسته زمین، بعد از انتقال رو به پایین از حل مسئله‌ مقدار مرزی استوکس-هلمرت استفاده شده است. نتایج ما در تعیین ژئوئید در ایران در مقایسه با ژئوئید حاصل از GPS-levelling نشان می‌د‌هد که استفاده از فضای بدون توپوگرافی، روش هلمرت را بهبود می‌‌بخشد. دقت نسبی و مطلق حاصل از ژئوئید به‌روش استوکس-هلمرت برابر 46 سانتی‌متر و برای روش استوکس هلمرت با استفاده از فضای بدون توپوگرافی برابر با 45 سانتی‌متر است.}, keywords_fa = {Bouguer,Downward continuation,No topography space,Precise geoid determination,Stokes-Helmert}, url = {https://jesphys.ut.ac.ir/article_29122.html}, eprint = {https://jesphys.ut.ac.ir/article_29122_f7cc3f1fe5365f18360b5996ecd4327e.pdf} } @article { author = {Oskooi, Behrooz and Sayyadi, Mostafa and Omidian, Safiyeh}, title = {Study of Mosha fault structure (South of the Central Alborz) using magnetotelluric method}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {161-174}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29123}, abstract = {Magnetotellurics (MT) is an electromagnetic geophysical method of imaging the earth's subsurface by measuring natural variations of the electrical and magnetic fields at the Earth's surface. Investigation depth ranges from 300m below ground by recording higher frequencies down to 10,000m or deeper with long-period soundings. Research applications include experimentation to further develop the MT technique, long-period deep crustal exploration, and earthquake precursor prediction research. Also, Magnetotelluric method is a powerful tool for deep crustal studies of tectonically active mountainous regions such as the Himalaya, where logistic constraints severely limit the use of other artificial source electrical and electromagnetic methods. Topographic variations in mountainous regions distort apparent resistivity curves and thus lead to artifacts in interpreted models. The results of the magnetotelluric soundings provide new insights on the geological structure and tectonics of the mountainous areas. Magnetotelluric method (MT) offers opportunity to detect crustal fluids along faults due to their high conductivity anomaly. Supposing that fluids deposited minerals in the conductive fractures (faults, dykes) decreasing the resistivity, the high seismicity in the area can be explained by the presence of the fluids. Mosha Fault in northern part of Iran is located in an E-W trend and act as a separator for Alborz mountain chain from Central Iran. This fault is interesting to investigate, because Tehran city (Capital of Iran) has a risk of an earthquake occurrence so that understanding the fault characteristics is very important. Mosha Fault Zone is also an interesting structure due to its key character of mysterious structural relation to the mechanism of the fault zone. Mosha fault has the most complicated tectonic structure in Alborz zone due to big changes that have affected the region basically. These ambiguities come from the increase with new studies about process and work parts of great faults in the area. Central Alborz inclusive structures are reverse faults with nearly East- West crackled dipping towards north. This can be a result due to continuous compression of the Arabian plate to the Iranian plate with N10-20E direction. Latter studies showed that some of the faults recently show tensional behavior or the dip is changing towards to the south, generally. Based on the seismic and GPS studies, the Uplift, south Caspian subsidence and subsequent folding, reversal of Alborz strike-slip (from dextral to sinistral) and eastward extrusion of central Iran, coarse Zagros molasse deposition, Dead Sea transform reorganization, Red Sea oceanic spreading, and North and East Anatolian fault slip, all apparently began ca. 5 ± 2 Ma, suggesting a widespread tectonic event that was a response to buoyant Arabian lithosphere choking the Neo-Tethyan subduction zone. Basically, some researchers believe that the westward rotation of the stable Caspian block at this time is started and it cause the change of the dextral strike-slip faults mechanism to the sinistral strike-slip one which cause to making pull-apart system in some part and also in the development of new normal faults with a change in dip direction and block motion of pre-existing faults. In this study, MT measurements were carried out in the period range 0.001- 420 s crossing Mosha fault along a 2.5k m profile with 8 MT sites. In these work we detect geo-electrical resistivity anomalies of the Earth’s crust and link them to local seismic activities. And also the fault location on the geological map is investigated. Surprisingly, fault dip changes from 75-80 degrees in depths to nearly vertical (90 degrees), at the surface. With attention to the geological map and occurrence of this kind of variations in resistive parts, it is not as a sign of geological units differences. We strongly believe that the fault plan is rotating from north toward south. It means that the new block movement would be a normal displacement and not reverse type. For completion and supporting up the results, more profiles in both directions -perpendicular and parallel to the fault tenor- would be necessary to be done. The place of two remarkable drainages system in the studied area and along the profile is compatible with two linear near surface trend of low resistance anomalies. The root of Karaj formation is distinguished at depth of 2500m with having 2.2 to 2.4 ohm meter resistivity. It is shown geophysically below the number four completely and in corner of stations number 3 and 5. It seems that in depth, Mosha fault and Karaj formation have the same trend and dip direction. It would be a key point to understand and decipher the mysterious about the place and circumstance of Karaj pyroclastics emission. We suggest that they are emitted from faulted structures during Eocene. From this point, we will expand our study to a three-dimensional analysis including the complete data set in order to reveal the detailed features of the electrical structure around the focal regions where the great earthquakes maybe threaten the metropolis.}, keywords = {Determinant data,Dimensional analysis,magnetotelluric,Mosha fault}, title_fa = {بررسی ساختار گسل مشا (جنوب البرز مرکزی) با استفاده از روش مگنتوتلوریک}, abstract_fa = {بررسی پدیده‌‌های زمین‌‌شناسی و زمین‌ساختی البرز و تحلیل چگونگی روند و منشا این پدیده‌‌ها همواره به‌منزلة یکی از جذابیت‌های البرز مورد ‌توجه بوده است. البرز مرکزی به دلیل برهم‌کنش‌های متعدد ساختاری و پیچیدگی‌های زمین‌ساختی، چالش‌های بیشتری را دربر داشته است. با بررسی‌های جدید در مورد روند و عملکرد بخش‌‌هایی از گسل‌‌های بزرگ و توانمند این منطقه ابهامات فراوانی به‌وجود آمده است. البرز مرکزی به دلیل فشارش مداوم صفحه عربی به صفحه ایران با جهت N10-20E دارای ساختارهای شدیداً گُسلیده فشاری و چین‌خورده تقریباً شرقی- غربی و با شیب رو به شمال است. اخیراً در مورد برخی از گسل‌ها روشن شده است که دارای حرکات کششی با شیب رو به جنوب هستند. در این تحقیق با استفاده از روش مگنتوتلوریک، در امتداد یک نیم‌رخ‌‌ 5/2 کیلومتری عمود بر گسل مشا و در جنوب شرق آتشفشان دماوند محل دقیق گسل، منطبق با نقشه زمین‌‌شناسی شناسایی شده است. از سوی دیگر تغییرات شیب گسل از 75 تا80 درجه به سمت شمال در اعماق، به حالت تقریباً قائم در نزدیکی سطح رسیده است. که با توجه به تغییر روند مشهود در مدل‌‌های حاصل از وارون‌سازی، عملکرد گسل در جابه‌جایی واحدهای دارای مقاومت یکسان با در نظر گرفتن شیب گسل به طرف شمال، نرمال است. عملکرد شاخه‌‌های فرعی گسل و همچنین آبراهه‌‌های گسلی نیز در این تحقیق در زیر بعضی از ایستگاه‌ها شناسایی شد که نشان از وجود زون‌‌های خُرد شده با مقاومت کم دارد. تغییر شیب صفحه اصلی گسل از نتایج اساسی و بحث‌انگیز تحقیق حاضر و با توجه به پیشینه زمین‌ساختی البرز مرکزی طراحی نیم‌رخ‌‌‌‌های موازی و عمود بر امتداد گسل در این منطقه برای تأیید صحت نتایج فوق پیشنهاد می‌شود.}, keywords_fa = {Determinant data,Dimensional analysis,magnetotelluric,Mosha fault}, url = {https://jesphys.ut.ac.ir/article_29123.html}, eprint = {https://jesphys.ut.ac.ir/article_29123_4dc2085fdec6b58a0af6656f6d0e7627.pdf} } @article { author = {Kamal, Alireza and Massah Bavani, Alireza}, title = {Comparison of future uncertainty of AOGCM-TAR and AOGCM-AR4 models in the projection of runoff basin}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {175-188}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29124}, abstract = {Increased concentration of greenhouse gases is expected to alter the radiative balance of atmosphere, causing increases in temperature and changes in precipitation patterns and other climatic variables. These changes are associated with the changes in hydrological systems globally and at the basin scale. These changes include: precipitation patterns and extremes; the amount and generation of river flow; the frequency and intensity of flood and drought. At present, coupled Atmospheric -Oceanic General Circulation Models (AOGCMs) are the most frequently used models for projection of different climatic change scenarios. These scenarios can finally simulate other changes, such as water resources changes in the future. The basis of these models consists of describing the physical processes taking place in the climate system and the dynamics of climate variables as a function of different internal or external changes. Up to now IPCC has released 4 different versions of AOGCM models including: First Assessment Report models (FAR) in 1990, Second Assessment Report models (SAR) in 1996, Third Assessment Report models (TAR) in 2001 and Fourth Assessment Report models (AR4) in 2007. In this paper we evaluate the uncertainty of using different TAR and AR4 AOGCM models on the projection of runoff of a basin. At first we used temperature and precipitation variables of 7 TAR models including CCSR, CGCM2, CSIRO-MK2, ECHAM4, GFDL-R30, HadCM3, NCAR-DOE PCM and 9 AR4 models including; CCSM3, GCM3, CSIRO Mk3, GFDL CM2.1, GISS E-R, HadCM3, ECHAM5, MIROC-med, PCM for the 2040-2069 periods under A2 emission scenario. The A2 scenario corresponds to pessimistic future with higher population growth, lower GDP growth, and fragmented and slower technological change. A conceptual rainfall-runoff model (SYMHYD) was calibrated and verified for the Gharesu basin in baseline period (1971-2000). SIMHYD simulates daily runoff (Surface runoff and base flow) using daily precipitation and potential evapotranspiration (PET) as input data. Gharesu basin is located in North West of great Karkheh River Basin, west of Iran. Historical data in this study are daily temperature (T), precipitation (P) and runoff (R) for thirty years period (1971 to 2000). These data were acquired from different sources and stations. Temperature records of Kermanshah synoptic station, Outflow measurements of Qarehbaghestan hydrometric station, and daily precipitation records of eleven rain gauge stations were used in this study. The climate variables (monthly temperature and precipitation) of 16 AOGCMs were downscaled to Gharesu basin. Downscaling is a procedure that derives local or regional scale information from larger scale data like AOGCM outputs. In this study, change factor downscaling techniques was employed to generate monthly precipitation and temperature values for Gharesu basin scale in future period (2040-2069). Results show that in all months the temperature of the basin will increase by an average of 2.5°C. On the other hand the increasing of temperature simulated by TAR models are more than AR4 models. Both AR4 and TAR models simulate precipitation in a same manner, reduction for winter and spring and increase for autumn. Finally the ranges of precipitation and temperature change of the period 2040-2069 simulated by both models introduced to SYMHYD rainfall-runoff model and the monthly runoff changes of the basin were simulated for the period 2040-2069 relative to the period 1971-2000. Results show that runoff change of the basin due to AR4 models are less than TAR models for most of the months. On the other hand the runoff will increase in winter by 20-60% and by 20-40% in summer and decrease in autumn up to 40% and up to 60% in spring. Finally it can be concluded that although the number of AR4 models used in this study is more than TAR models, the range of uncertainty of AR4 is less than TAR. The final results showed that the projections of AR4 models are more reliable than TAR models.}, keywords = {AOGCM -AR4 models,AOGCM-TAR,climate change,Rainfall-runoff,SimHyd}, title_fa = {مقایسه عدم قطعیت مدل‌های تغییر اقلیم AOGCM-TARو AOGCM-AR4 در تاثیر بر رواناب حوضه در دوره آتی}, abstract_fa = {استفاده از خروجی مدل‌‌های گردش کلی جوّ - اقیانوس (AOGCMs) به‌منزلة معتبرترین ابزار در تحقیقات تغییر اقلیم، در حال افزایش است. تاکنون نسخه‌های گوناگونی از مدل‌های AOGCM عرضه شده است که از آن جمله می‌توان به مدل‌های اولین گزارش ارزیابی هیئت بین‌المللی تغییر اقلیم (IPCC) تحت عنوانFAR(1990) ، مدل‌های دومین گزارش با عنوان SAR(1996)، مدل‌های سومین گزارش با عنوان TAR(2001) و مدل‌های چهارمین گزارش ارزیابی با عنوان AR4(2007) اشاره کرد. هدف از این تحقیق مقایسه عدم قطعیت مدل‌های TAR و AR4 درتاثیر بر رواناب حوضه قره‌سو در دوره 2069-2040 است . برای این کار از خروجی‌های هفت مدل TAR شامل CCSR، CGCM2، CSIRO-MK2، ECHAM4، GFDL-R30، HadCM3، NCAR-DOE PCM و نه مدل منتخب از AR4 شامل CCSM3، CGCM3، CSIRO Mk3، GFDL CM2.1، GISS E-R، HadCM3، ECHAM5، MIROC-med، PCM تحت سناریو انتشار A2 استفاده شد. در ابتدا مدل مفهومی بارش- رواناب SIMHYD در دوره پایه 2000-1971 برای حوضه قره‌سو مورد واسنجی و راستی‌آزمایی قرار گرفت. سپس با مقیاس‌کاهی داده‌های اقلیمی مدل‌های ذکر شده TAR و AR4 برای منطقه تحقیقاتی با روش تناسبی و معرفی آنها به مدل SIMHYD، بازه تفاوت بین مدل‌‌ها در برآورد رواناب حوضه قره‌سو در دوره 2040-2069 تحت دو گروه از مدل‌های TAR و AR4 مورد مقایسه قرار گرفت. هرچند درحال‌‌حاضر از هر دو گروه از این مدل‌ها در بررسی اثرات تغییر اقلیم استفاده می‌شود، نتایج این تحقیق نشان می‌دهد که استفاده از مدل‌های AR4 ضمن مدیریت بیشتر عدم قطعیت نتایج کاربردی‌تری نسبت به مدل‌های TAR به‌همراه خواهد داشت.}, keywords_fa = {AOGCM -AR4 models,AOGCM-TAR,climate change,Rainfall-runoff,SimHyd}, url = {https://jesphys.ut.ac.ir/article_29124.html}, eprint = {https://jesphys.ut.ac.ir/article_29124_41d507ed45b8aa9116c5d974f1c522e6.pdf} } @article { author = {Joghataei, Mohammad and Mohebalhojeh, Alireza and Aliakbari-Bidokhti, A.Ali}, title = {Balance and inertia–gravity waves in a two-layer baroclinic model}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {189-201}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29125}, abstract = {Balance, breakdown of balance, and generation of inertia–gravity waves in vortical flows are fundamental topics of prime importance in geophysical fluid dynamics. This research aims to find the optimum balance relation as well as the Rossby-number variation of the spontaneous generation of inertia–gravity waves in a baroclinic, two-layer, Boussinesq model on a doubly-periodic f-plane geometry for a range of Rossby numbers between 0.07 and 0.79. The setup of the experiments is an initially axisymmetric vortex in each layer formed by a circular contour of Rossby–Ertel potential vorticity (PV) surrounded by a background, uniform PV of the same magnitude in the two layers. The strength of the uniform PV within the upper-layer (lower-layer) vortex is stronger (weaker) with respect to the background PV. Alternatively, the PV anomaly is positive (negative) in the upper (lower) layer. This setup is amenable to baroclinic instability, which is triggered by inserting random noise of very small magnitude on the contour representation of the vortices in the two layers. The initial distribution of PV is inverted by means of the first three members of the , , and hierarchies of balance relations, comprising nine PV inversion procedures and thus nine ways of determining imbalance through wave–vortex decomposition. For each regime of flow, nine experiments are carried out using one of the nine balance relations to construct the initial conditions. The onset of instability leads to breakdown of symmetry, generation of Rossby waves around the vortices, complex vortex –vortex, wave–vortex, and wave–wave interactions. The focus is, however, on the spontaneous generation of imbalance. For each of the nine experiments, PV inversion by means of the same balance relation employed to construct the initial conditions is used to determine the amount of imbalance. The minimum imbalance is then sought over the nine balance relations. The energy spectra of imbalance as obtained using various balance relations are also investigated in order to gain insight into the nature of imbalance. Fluctuations on the spectra appear to be related to wave–vortex and wave–wave interactions. The relation between the spectra and the evolution of linear available energy of imbalance is also studied. As the most important outcome of the present research, the relation between the amplitude of inertia–gravity waves generated during the evolution of unstable, vortical flows and the Rossby number is obtained by spanning the parameter space by changing the strength of the PV anomaly and the nondimensional acceleration due to gravity. The results obtained agree with an exponentially-small functional relation between the amplitude of the inertia–gravity waves and the Rossby number. While this exponentially-small relation agrees with the asymptotic theories available, it is in sharp contrast with the linear relation obtained by Williams et. al, (2008) using their laboratory two-layer experiments.}, keywords = {Balance relation,Energy spectrum,Potential vorticity,vortical flow,Wave-vortex decomposition}, title_fa = {توازن و امواج گرانی– لختی در یک مدل کژفشار دولایه‌ای}, abstract_fa = {از جمله مسائل بنیادین در دینامیک جو، اقیانوس و شاره‌های ژئوفیزیکی به طور کل بررسی میزان برقراری "توازن"، وجود و ساختار توازن‌های از مرتبه دلبخواه، شکست توازن و تولید امواج گرانی-لختی در تحول زمانی شارش‌های تاواری (vortical) است. در مدل کژفشار دولایه‌ای روی صفحه f ، با آزمایش عددی و استفاده از تجزیه موج – تاوه، رابطه توازن بهینه یا نزدیک به بهینه در اعداد راسبی کوچک در گستره بین 07/0 تا 79/0 تحقیق می‌شود. در این آزمایش عددی همچنین طیف انرژی روابط توازن با طیف انرژی تلاطم دوبُعدی در ابعاد گوناگون مقایسه می‌شود. افت‌وخیز روی طیف انرژی (حاصل از امواج گرانی– لختی) به برهم‌کنش موج– موج یا موج– تاوه نسبت داده می‌شو‌د. در افت‌وخیز روی طیف انرژی نسبت طول موج تحریک شده به شعاع تغییرشکل راسبی بین نیم تا یک تغییر می‌کند. ارتباط بین طیف انرژی و روند انرژی دردسترس خطی‌شده نامتوازن بررسی می‌شود. در روابط توازن بهینه، یک شکست در آبشار وارونه طیف انرژی در بزرگ‌مقیاس وجود دارد. در آزمایش عددی پیش‌گفته، ارتباط بین بیشینه انرژی امواج گرانی– لختی با بیشینه عدد راسبی در حین تحول زمانی شارش، در رابطه توازنی بهینه در هشت سامانة شارشی بررسی می‌شود. نتایج، یک ارتباط نمایی بین دامنه امواج گرانی– لختی با عدد راسبی را نشان می‌دهد. نتایج حاصل با نظریه‌های دینامیکی موجود حاصل از بسط مجانبی معادلات بسیط کاملاً هم‌خوانی‌ و با تحلیل صورت گرفته بر مبنای نتایج آزمایش دولایه‌ای ویلیامز و همکاران (2008) مغایرت دارد.}, keywords_fa = {Balance relation,Energy spectrum,Potential vorticity,vortical flow,Wave-vortex decomposition}, url = {https://jesphys.ut.ac.ir/article_29125.html}, eprint = {https://jesphys.ut.ac.ir/article_29125_7d8807fc6264326309a890a1c63fb693.pdf} } @article { author = {Azadi, Majid and Vashani, Saeed and Hajjam, Sohrab}, title = {Probabilistic precipitation forecast using post processing of output of ensemble forecasting system}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {203-216}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29126}, abstract = {Accurate quantitative precipitation forecasts (QPFs) have been always a demanding and challenging job in numerical weather prediction (NWP). The outputs of ensemble prediction systems (EPSs) in the form of probability forecasts provide a valuable tool for probabilistic quantitative precipitation forecasts (PQPFs). In this research, different configurations of WRF and MM5 meso-scale models form our eight member ensemble prediction system. The initial and boundary conditions come from the operational 1200 UTC runs of global forecasting system (GFS) of NCEP (National Center for Environmental Prediction). The integration period goes from first November 2008 to 30 April 2009 (182 days). Both WRF and MM5 are used with non-hydrostatic option and were run with two nested domains, with the larger domain covering the south-west Middle East from 10° to 51°north and from 20° to 80° east. The smaller domain covers Iran from 23° to 41° north and from 42° to 65° east. The spatial resolutions are 45-and 15-km for the coarser and finer domains respectively. Forecasts out to +72 hour ahead from the inner domains have been used to form the raw ensemble forecasts. The ensemble forecasts assessed in this study are as follows: raw ensemble forecasts, ensemble forecasts formed by post processing of each member in the raw ensemble forecasts using artificial neural network (ANN), ensemble forecasts formed using rank-histogram calibration technique of Hamill and Cloucci (1998) on the raw ensemble forecasts and ensemble forecasts formed by using both ANN and rank-histogram calibration methods on the raw ensemble forecasts. This research shows that ANN could decrease the error of raw ensemble so that the MAE for the first day of forecast achieves less than 1.5 mm and for second and third forecast days is about 2.5 mm. And all members errors are similar for all forecast days, but it seems that the members related to the MM5 model (members 6, 7, 8) produce slightly better forecasts, while after using the post processing methods the result of MAE are nearly similar. BS was calculated for raw ensemble forecasts, ensemble forecasts formed by post processing of each member in the raw ensemble forecasts using ANN, ensemble forecasts formed using rank-histogram calibration technique of Hamill and Cloucci (1998) on the raw ensemble forecasts and ensemble forecasts formed by using both ANN and rank-histogram calibration methods for mentioned thresholds from forecast days1-3. Having performed ANN method, the forecast quality increased significantly. for example, the amount of BS for raw ensemble 0.42 decreased to 0.32 for post processed ensemble using ANN method for the first forecast day in precipitation less than 0.1 mm. also the BS calculated before and after using rank histogram method proposed by Hamill and Cloucci (1998) shows the increasing of probabilistic forecast quality such that the amount of BS for raw ensemble 0.42 decreased to 0.29 for post processed ensemble using both ANN and method proposed by Hamill and Cloucci (1998) for the second forecast day in precipitation less than 0.1 mm. The Brier Skill Score (BSS) was 0.3 for post-processed ensemble using ANN method and 0.1 for post-processed ensemble using method proposed by Hamill and Cloucci (1998) for all three thresholds in the first day of forecast. Briefly the selection of different configurations does not have much effect on decreasing the error and difference between observation and DMO increases from the first to the third forecast days in all members. The ANN and method proposed by Hamill and Cloucci (1998) as two post processing methods can significantly decrease the systematic error of DMO, but the ANN method can remove systematic error better than the method proposed by Hamill and Cloucci (1998). We can produce more accurate probabilistic forecast using ANN for raw ensemble output and the calibrating the post processed output using method proposed by Hamill and Cloucci (1998).}, keywords = {Artificial Neural Network,Ensemble forecasts,Precipitation forecasts,Probabilistic quantitative,Rank-histogram calibration technique}, title_fa = {پیش‌بینی احتمالاتی بارش با استفاده از پس‌پردازش (post processing) برون‌داد یک سامانه همادی}, abstract_fa = {در پژوهش حاضر یک سامانه همادی با استفاده از مدل‌های میان‌مقیاسMM5 و WRF با پیکربندی‌های گوناگون و تغییر در فیزیک آنها ساخته شد. سپس برون‌داد هر عضو (به‌صورت جداگانه) درسامانه همادی برای کمیت بارش با استفاده از یک شبکه عصبی مصنوعی مورد پس‌پردازش (post processing) قرار گرفت و در نهایت با استفاده از روش بافت‌نگار رتبه‌ای پیش‌بینی‌های احتمالاتی بارش برای آستانه‌های گوناگون بارش برای منطقه شمال ایران محاسبه و واسنجی شد. میانگین خطای مطلق به‌دست آمده برای روز اول کمتر از mm 5/1 و در روزهای دوم و سوم پیش‌بینی حدود mm 2/2 به‌دست آمد که نسبت به برون‌داد مستقیم اعضای سامانه به‌ترتیب حدود mm 2/0 و mm 4/0 کمتر شده است .محاسبه سنجه راستی‌آزمایی امتیاز بریر برای قبل و بعد از واسنجی به روش بافت‌نگار رتبه‌ای، نشان‌دهنده بهبود پیش‌بینی‌های احتمالاتی واسنجیده شده است؛ به‌گونه‌ای که در روز اول پیش‌بینی، امتیاز مهارتی بریر برای شبکه عصبی مصنوعی حدود 3/0 و برای روش بافت‌نگار رتبه‌ای کمتر از 1/0 برای هر سه آستانه به‌دست آمد.}, keywords_fa = {Artificial Neural Network,Ensemble forecasts,Precipitation forecasts,Probabilistic quantitative,Rank-histogram calibration technique}, url = {https://jesphys.ut.ac.ir/article_29126.html}, eprint = {https://jesphys.ut.ac.ir/article_29126_651812c41483061261866da002d34e90.pdf} } @article { author = {Rahimi, Habib and Javan-Doloei, Gholam}, title = {Estimation of the kinematic source parameters and frequency dependent shear wave attenuation coefficient of the 18th June, 2007 Kahak-Qom earthquake in north central Iran}, journal = {Journal of the Earth and Space Physics}, volume = {38}, number = {3}, pages = {1-16}, year = {2012}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2012.29127}, abstract = {In this study, analysis is presented in two steps. In the first step, the theoretical S-wave displacement spectra, conditioned by frequency-independent Q, was fitted with the observed displacement spectra. Therefore corner frequency, moment magnitude and frequency-independent Q for each record were estimated simultaneously and the estimate of error is given in the root-mean-square sense over all the frequencies. In the second step, the corrected observed displacement from source effect was fitted with path term of Brune’s source model to estimate frequency dependent shear wave Quality factor. For comparison, Frequency dependent shear wave quality factor also is estimated from spectral decay method. The earthquake in Qom, 18 June 2007 (Ml=5.7), was the largest earthquake in the south of Tehran that recorded on strong motion acceleration stations. The data represented more than 40 accelerograms recorded from Kahak-Qom earthquake in the hypocentral distance range from 18 to 170 km. The source term obtained from inversion was analyzed to estimate various source parameters. Thereby, we estimated seismic moment (1.86*1024 dyne-cm), corner frequency (0.72 Hz ), source radius (2.33 Km), fault slip (38 cm), source duration (1.5 sec), stress drop (12.3 bars) and moment magnitude (5.4), which are found to be consistent with the corresponding values reported in published studies. The path average value of Q is in the range Q=161 to 1652. The anelastic attenuation coefficient for the region as a whole is estimated in step 2 is Qs= 47f 0.71 in frequency range of 1 to 32 Hz. The frequency-independence attenuation for the study region shows that, in general, a Q value is significantly similar to the entire frequency range used than those found in other tectonic areas.}, keywords = {Generalized inversion,Kahak-Qom earthquake,quality factor,Source parameters}, title_fa = {برآورد پارامترهای کینماتیکی چشمه و بستگی بسامدی ضریب تضعیف موج بُرشی زمین‌لرزه‌‌ 28 خرداد 1386 کهک- قم}, abstract_fa = {در این تحقیق تحلیل داده با تاکید بر دو مرحله صورت گرفته است. در مرحله نخست طیف جابه‌جایی موج بُرشی مستقل از بسامد با طیف جابه‌جایی تجربی مطابقت داده شده است. البته برای هر بسامد، انحراف معیار محاسبه و عرضه شده است. در مرحله دوم، طیف جابه‌جایی با لحاظ کردن تصحیح اثر چشمه زمین‌لرزه‌‌ مطابق مدل براون برای محاسبه وابستگی بسامدی فاکتور کیفیت به‌کار گرفته شده است. برای فراهم شدن زمینه ارزیابی نتایج، فاکتور کیفیت وابسته به بسامد موج بُرشی از روش تضعیف طیفی نیز محاسبه شده است. طیف جابه‌جایی یک زمین‌لرزه‌‌ حاوی اطلاعات ارزشمندی از ویژگی‌‌های چشمه زمین‌لرزه‌‌ و خصوصیات محیط مسیر انتشار موج لرزه‌‌ای است. طیف چشمه زمین‌لرزه‌‌ را می‌‌توان از طریق مجذور بسامد، ?2 مطابق مدل براون (1970) برآورد کرد. در این مدل، تضعیف به صورت ?2 برای بسامد‌‌های بیش از بسامد گوشه رخ می‌‌دهد. در این راستا طیف جابه‌جایی چشمه از تبدیل فوریه نگاشت رویداد پس از اجرای فرایند تصحیحات اولیه و تضعیف ناکشسانی محاسبه شده است. تضعیف ناکشسانی موج‌‌های لرزه‌‌ای از طریق یک کمیت بدون بُعد تحت عنوان فاکتور کیفیت برآورد می‌‌شود. تاکنون تحقیقات اندکی برای برآورد فاکتور کیفیت براساس تضعیف ناکشسانی موج‌‌های لرزه‌‌ای در گستره فلات ایران صورت گرفته است. در این تحقیق سعی شده است تا با استفاده از مدل‌‌سازی معکوس تعمیم یافته و روش حداقل مربعات، پارامترهای چشمه زمین‌لرزه‌‌ و تضعیف ناکشسانی موج بُرشی ناشی از زمین‌لرزه‌‌ 28 خرداد 1386 تا فاصله 170 کیلومتری از کانون آن محاسبه شود. شایان ذکر است زمین‌لرزه‌‌ 28 خرداد 1386 با بزرگی M = 5.7 بزرگ‌ترین زمین‌لرزه‌‌ جنوب تهران است که به‌‌صورت رقومی در چندین ایستگاه شتاب‌نگاری وابسته به مرکز تحقیقات ساختمان و مسکن ثبت شده است. بنابراین، بررسی تضعیف ناکشسانی موج بُرشی این زمین‌لرزه‌‌ به‌خاطر نزدیکی به مراکز پُرجمعیت مانند قم ، تهران و کرج اهمیت زیادی دارد. در این تحقیق علی‌رغم وجود حدود پنجاه شتاب‌نگاشت سه مولفه‌‌ای از زمین‌لرزه‌‌ قم– کهک، برای افزایش دقت محاسبه پارامترها چشمه فاکتور کیفیت، تنها از چهل شتاب‌نگاشت با کیفیت بسیار خوب استفاده شده است. شکل (1) مقایسه‌‌ای از سطح نوفه با سیگنال اصلی موج لرزه‌‌ای را نشان داده است. مولفه‌‌های افقی هر شتاب‌نگاشت با اِعمال صافی پایین‌‌گذر 25 هرتز و چرخش آنها حول زاویه پیش سمت به‌‌منظور بیشینه کردن دامنه موج بُرشی SH برای اجرای فرایند الگوریتم کینوشیتا (1994) آماده‌سازی شده است. پس از تکمیل مراحل پردازش پارامتر‌‌های چشمه زمین‌لرزه‌‌ محاسبه شدند که عبارت‌اند از: (1) مقدارگشتاور لرزه‌‌ای 1.86*1024 dyne-cm ؛ (2) بسامد گوشه 0.72 Hz؛ (3) شعاع چشمه 2.33 Km؛ (4) میزان لغزش گسل 38 cm؛ (5) میزان دوام چشمه 1.5 sec؛ (5) اُفت تنش 12.3 bars؛ (6) بزرگی گشتاوری 5.4. علاوه برآن ضریب تضعیف ناکشسانی موج بُرشی به‌‌صورت رابطه Qs= 47f 0.71 برای فاصله 18 تا 170 کیلومتری اطراف چشمه زمین‌لرزه‌‌ حاصل شد که محدوده قم، تهران، کرج و کاشان را پوشش می‌دهد.}, keywords_fa = {Generalized inversion,Kahak-Qom earthquake,quality factor,Source parameters}, url = {https://jesphys.ut.ac.ir/article_29127.html}, eprint = {https://jesphys.ut.ac.ir/article_29127_3e695b3c79cc3265a37fe4fdd50f1b9a.pdf} }