@article { author = {Davoudian, Reza and متقی, خلیل and Sobouti, Farhad and Rahimi, Habib and Ghods, Abdolreza}, title = {Inversion of Rayleigh waves group velocity to shear wave velocity structure in the NW Iran}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {1-13}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58922}, abstract = {We determined inter station shear wave structure using data from a temporary network of 23 broadband stations in the north west of Iran. Waveforms were used from 230 tele-seismic and regional earthquakes to obtain inter station dispersion curves of the group velocity of the Rayleigh waves. Events in the epicentral distance range of 250 to 3000 km with magnitudes 3.0 ≤ Mw ≤ 7 were used. The individual dispersion curves of the group velocity of Rayleigh waves for each source-station path have been calculated; Then via double-station method we calculated 20 dispersion curves for inter station paths. The group velocities are available in the range of 6-48 sec; in general it is only possible to resolve the parameters of upper mantle and crust. We divided study area to 5 regions, and then we calculated the average dispersion curve in each region. These curves have been used to determine shear wave structure in each region via non-linear Hedgehog inversion method. We need to initial velocity model to start non-linear inversion process, therefore initial model are calculated via linear inversion method.In additional, the obtained velocity models show that crustal thickness in these 5 regions varies between 40 and 56 km. Also the boundary between Upper and Lower crust changes between 12 and 28 km. The results from the non-linear Hedgehog inversion as applied to derived dispersion curves show a crustal thickness of approximately 40 km in the west part of studied area, 56 km in the middle of studied area and 43 km in the western coast of Caspian Sea.Based on obtained results the Moho depth varies from 56 km to 40 km when you move from the middle of study area to western coast of the Caspian Sea. We propose that under thrusting of Caspian Sea basement beneath the Talesh Mountains impresses Moho depth in Talesh zone. But no geological observation prove the under thrusting of Caspian Sea basement beneath the Talesh Mountains, thereforewe cannot be certain about this propose. In other hand, Talesh zone is located in passive continental margin of Caspian Sea; these kinds of margins have complicated structure. We can assume that observed results in Talesh zone have been created by passive continental margin of Caspian Sea. Also we observed a low velocity and warm (probably) anomaly in range of depth 12-22 km beneath the Sahand volcano. We derived attenuation effects of south Caspian basin when periods bigger than 32 seconds of fundamental mode Rayleigh waves propagate across the south Caspian Basin. We used 20 events in along the Apsheron Sill and calculated dispersion curves of these events at our stations. We collected 172 waveforms from used events; we found only 31 fundamental mode waveforms of Rayleigh waves. In other waveforms energy of fundamental mode was diffused and we cannot specify any trend for dispersion. The South Caspian Basin contains one of the thickest sedimentary deposits in the world. In the South Caspian Basin, based on Priestley et.al. (2001), attenuation of surface waves is largely controlled by sediments in the basin. Therefore we guess that our observations about attenuation of the Rayleigh waves are related to sediments in this basin.}, keywords = {Crust,Rayleigh Waves,Non-linear Inversion,Dispersion curve,Hedgehog}, title_fa = {برگردان سرعت گروه امواج ریلی به ساختار سرعت موج برشی برای منطقه شمال غرب ایران}, abstract_fa = {در این مطالعه تغییرات سرعت موج برشی با استفاده از داده های ثبت شده در 23 ایستگاه باند پهن شبکه موقت دانشگاه تحصیلات تکمیلی علوم پایه زنجان، در منطقه شمال غرب ایران مورد بررسی قرار می گیرد. به همین منظور با استفاده از 230 رخداد منطقه ای و دورلرز منحنی های پاشش سرعت گروه امواج ریلی در مد پایه برای 20 مسیربین ایستگاهی محاسبه می شود. سپس جهت محاسبه ساختار سرعت موج برشی در هر مسیر، برگردان خطی و غیرخطی منحنی های پاشش به ساختار سرعت موج برشی انجام می شود. منحنی های پاشش بین ایستگاهی به روش دو ایستگاهی و ساختارهای سرعت نهایی به روش جستجوی محاسباتی- تصادفی "هجهاگ" محاسبه می شوند. با توجه به بازه دوره تناوبی در منحنی های پاشش محاسبه شده در این مطالعه (بین 5 تا 48 ثانیه) تنها پارامترهای سرعتی در پوسته و گوشته بالایی قابل محاسبه است. ساختارهای سرعت موج برشی نشان دهنده یک ساختار ناهمگن با ضخامت متغیر پوسته در امتدادپروفیل لرزه نگاری است. عمق مرز موهو بین 40 تا 56 کیلومتر و عمق مرز میان پوسته بالایی و پایینی نیز بین 12 تا 28 کیلومتر به دست آمده است. در بازه عمقی 12 تا 22کیلومتر در شمال آتشفشان سهند یک توده کم سرعت و احتمالا گرم مشاهده می شود.همچنین اثر عبور مسیر 20 رخداد منطقه ای بر میرایی امواج ریلی با دوره های زمانی بیش از 32 ثانیه نیز نشان داده می شود و منشاء این میرایی غیر عادی به اثر رسوبات ضخیم حوضه خزر جنوبی نسبت داده می شود.}, keywords_fa = {پوسته,امواج ریلی,برگردان غیرخطی,منحنی پاشش,هجهاگ}, url = {https://jesphys.ut.ac.ir/article_58922.html}, eprint = {https://jesphys.ut.ac.ir/article_58922_c0febf01e013da3f3adb19921d9cdddd.pdf} } @article { author = {Rahimi, Habib and asadi, samane and رضاپور, مهدی and امیری فر, روح اله}, title = {Estimation of earthquake magnitudes using coda duration in Zagros area}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {15-22}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58908}, abstract = {Amplitude and duration of seismic signals depend upon recording distance, propagation path of the wave through different media, and geology at the recording site. In addition, amplitude of recorded signals varies according to the P- and S-wave radiation patterns. Influence of these factors on seismic signals has been considered for magnitude computation in many seismic regions (e. g., Michaelson, 1990 and Eaton, 1992). Estimation of earthquake magnitude is a routine task in all seismological observatories. Several magnitude scales are available, based on amplitude measurement of different seismic phases, and/or on total signal duration. Among them, the duration magnitude (MD) is adopted in many regional networks because it provides a rapid and reliable estimate of the earthquake size through a fairly simple procedure based on the measure of the duration of recorded seismograms. Bisztricany (1958) first demonstrated the existence of a relationship between magnitude and duration, and several authors (e.g., Sole’vev, 1965; Tsumura, 1967; Bakun, 1984; Vidal and Munguía, 2005; Hara, 2007; Colomblli et. al., 2014 and among many others) later discussed the use of duration of the recorded seismograms to measure the event size., Lomax and Michelini (2009) proposed a duration magnitude procedure for the rapid determination of the moment magnitude, based on the P-wave recordings at teleseismic distances, which can be applied for tsunami early warning.In this study, the relationship for estimation of earthquake magnitude was derived using the duration of the coda-waves of recorded signals in the Zagros area. Determination of duration magnitude (MD) is a fast and reliable while in other methods it is difficult to read the correct amplitude. In this method as another advantage is no need to correct signals for instrumental effect. In this study more than 3890 records with magnitude in the range of 2 to 5 with epicentral distances less than 200 km were used. The mentioned data is recorded in IIEES seismic network in the period between 2006 and 2013. Location of earthquakes was in the range of 23.59 to 37 latitude and 43.37 to 61.63 longitude. The aim of this study was to determine the relationship between the magnitudes of the duration using the following equation: M_D=a+b.log_10⁡〖τ+c.R+S_c 〗 In which R is the hypocentral distance, 𝞽 is the signal duration, Sc stands for the station correction, and coefficients of a, b, and c must be determined by analysis of regression. Duration was considered as the time elapsed since the first P-wave arrival to the moment when the noise level is reduced to the coda wave amplitude. By comparing the signal amplitude of the noise before the event, the signal end was determined, our conditions were A_(sign-A_noise )/A_noise}, keywords = {Duration,coda wave,magnitude estimation,estimation relationship magnitude}, title_fa = {برآورد رابطه بزرگای زمین‌لرزه با استفاده از مدت دوام امواج کدا در پهنه زاگرس و جنوب‌غربی ایران مرکزی}, abstract_fa = {در این مطالعه رابطه بزرگای زمین‌لرزه با استفاده از مدت دوام امواج کدا برای پهنه زاگرس و جنوب غربی ایران مرکزی برآورد شده است. بزرگای مدت دوام امواج کدا روشی برای برآورد سریع و قابل اطمینان از اندازه زلزله بوده و با توجه به بکارگیری محتوای زمانی شکل موج‌ها به جای محتوای دامنه آن‌ها، روشی قابل اعتمادتر و سریع‌تر خواهد بود. برای برآورد بزرگا در روش‌های معمول مانند بزرگای محلی یا امواج حجمی، در اغلب موارد خواندن صحیح دامنه با توجه به اثرات دستگاهی، اثرات مسیر روی دامنه و ... دشوار بوده و با خطای زیادی همراه است. در مطالعه حاضر از 3890 نگاشت با بزرگی بین 2 تا 5 و با فاصله‌های رومرکزی کمتر از 200 کیلومتر استفاده شده است. در این مطالعه از داده‌های ایستگاه‌های باند پهن شبکه لرزه‌ای در بازه‌ی زمانی بین سال‌های 2006 تا 2013 استفاده شده است. در این بررسی مدت دوام ، به عنوان زمان سپری شده از اولین رسید موج P تا لحظه‌ای که دامنه موج کدا به سطح نویز کاهش پیدا ‌کند، در نظر گرفته ‌می‌شود. برای بدست آوردن نقطه انتهایی سیگنال، دامنه سیگنال با دامنه نویز قبل از رخداد مقایسه شده و زمان انتهایی پنجره محاسبه گردید. بعد از محاسبه پارامتر مدت دوام و داشتن فاصله و بزرگای محلی، با استفاده از رگرسیون سه بعدی رابطه مطلوب محاسبه شد. در ادامه، به منظور سنجش صحت تخمین بزرگی، ضرایب تصحیح ایستگاهی برآورد گردیده و برای ایستگاه‌های مختلف با زمین‌شناسی و اثرات ساختگاه آنها مقایسه گردید.}, keywords_fa = {مدت دوام,امواج کدا,بزرگی,برآورد رابطه بزرگا}, url = {https://jesphys.ut.ac.ir/article_58908.html}, eprint = {https://jesphys.ut.ac.ir/article_58908_faf734027745835a7772a25570f99ba2.pdf} } @article { author = {Karimi Vahed, Homeyra and Heidari, Reza}, title = {Investigating The Probabilistic Warning Times for The Earthquake Early Warning System (EEWS) On The North Tabriz Fault}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {23-32}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.60285}, abstract = {In this study the first step toward establishing an earthquake early warning system in the northwestern of Iran has been studied. The area includes populated cities such an Tabriz, Ahar and Khoy. Due to heavy toll in recent years, great economic and social vulnerability of urban areas to earthquake hazards has been important and particularly noticeable. However, there has been little and few progress made in reduce and minimizing the impact of this natural and destructive disaster. While predicting the earthquake with precision is beyond our current knowledge and ability, in order to tackle the potential casualties as a result of destructive earthquakes, an Earthquake Early Warning System can significantly reduce and minimize the possible death toll. Using CDF (Probability Cumulative Distribution Function) this study aims at investigating the extent to which this Earthquake Early Warning System is implemented for the North Tabriz Fault so as to predict the time of On-Site warning time and Regional warning time in a probabilistic manner. To find out the areas and cities subject to risks of earthquakes, earthquake simulation by using stochastic method, the peak ground motion of the earth (PGA), were calculated for the cities of northwest Iran, as a result of these calculations, high- priority areas examined in the study, 15 of the top priorities in terms of seismicity on the basis of strong ground motion (PGA) nature cities such as Khoy, Varzaqan, Sarab, Tabriz, Qarah Zia od Din, Amand, Tekmeh Dash, Osku, Damirchi, Bostan abad, Sufian, Heris, Avin and Khvajeh has been considered and these cities were based of our study. The result of this study shows that the maximum Regional warning time in the cities of Khoy, Qarah Zia od Din, Avin, Bostan abad, Heris, Khvajeh, Sarab, Tekmeh Dash, Varzaqan, Damirchi, Tabriz was calculated 19, 20, 21, 13, 17, 12, 19, 14, 15, 18, 10 seconds respectively. Due to the fact that for the stations close to the epicenter of the earthquake, the creation of Regional warning time only for distant and far objects is possible and implementable; The On-Site warning time for earthquakes close to the targets was measured, as already was clear it is not possible to establish considerable On-Site warning time by for high-risk areas for North Tabriz Fault. It seems that this amount of time (Regional warning time) to set up Earthquake Early Warning Systems in the city of Tabriz where is the fourth largest city of Iran and comprises about 1.4 million inhabitants and one of the largest Iranian industrial cities that the Regional warning time is under 10 seconds, in terms of economy, cost, time and energy, according to the existing station arrangement will not be economical and vital. It has to be mentioned that the warning times were calculated using the existing seismic network geometry in the region. We calculated the warning times to at least some of the affected population and cities 15 of the top priorities in terms of seismicity on the basis of strong ground motion) in damaging and destructive earthquakes.}, keywords = {Earthquake Early Warning Systems,Onsite Warning and Regional Warning,Peak Ground Motion of the earth,Probability Cumulative Distribution Function (CDF)}, title_fa = {بررسی زمان هشدار احتمالاتی برای سامانه هشدار سریع زمین لرزه بر روی گسل شمال تبریز}, abstract_fa = {با توجه به اینکه پیش‌بینی دقیق زمین‌لرزه با دانش فعلی بشر امکان‌پذیر نمی‌باشد؛ بنابراین، یک سامانه هشدار سریع زمین‌لرزه می‌تواند نقش پراهمیتی در کاستن تلفات و خسارات زمینلرزه‌ها داشته باشد. در این مطالعه با استفاده از تعریف تابع احتمالاتی، میزان اجرایی بودن سامانه هشدار سریع زمین‌لرزه برای گسل شمال تبریز در شمال‌غرب ایران بررسی و زمان هشدارهای در سایت و ناحیه‌ای مناطق و شهر-های در معرض خطر که شامل 15شهر با اولویت بالا شامل: خوی، ورزقان، سراب، تبریز، قره‌ضیاءالدین، آمند، تیکمه‌داش، اسکو، دمیرچی، بستان‌آباد، صوفیان، هریس، اهر، خواجه و میانه می‌باشد؛ به شکل احتمالاتی ارزیابی گردد. اولویت‌بندی خطرپذیری شهر‌های ذکر شده در این مطالعه بر اساس شبیه‌سازی جنبش نیرومند زمین با استفاده از روش تصادفی برای 22 زمینلرزه محتمل سناریو انجام شده است. نتایج حاصل از این مطالعه نشان می‌دهد که حداکثر زما‌ن‌های هشدار ناحیه‌ای برای شهر‌های خوی، قره‌ضیا‌الدین، میانه، بستان‌آباد، هریس، خواجه، سراب، تیکمه‌داش، ورزقان، دمیرچی و تبریز به ترتیب 19، 20، 21، 13، 17، 12، 19، 14، 15، 18 و 10 ثانیه است. این زمان‌های هشدار به عنوان یک فرصت مناسب قبل از رسیدن امواج سهمگین و نیرومند زمینلرزه، تا حد بسیار زیادی می‌تواند از تلفات و خسارات ناشی از وقوع زمینلرزه‌ها بکاهد. با توجه به این موضوع که برای ایستگاه‌های نزدیک به کانون زمینلرزه، امکان ایجاد هشدار ناحیه‌ای صرفاً برای اهداف دورتر میسر است؛ میزان هشدار‌های درسایت برای زمینلرزه‌های نزدیک به اهداف (زمینلرزه‌های تاثیرگذار)، بررسی گردید که همانطوری که انتظار می‌رود؛ میزان هشدار درسایت قابل توجهی ایجاد نمی‌شود.}, keywords_fa = {سامانه هشدر سریع زمینلرزه,هشدار در سایت و هشدار ناحیه‌ای,بیشینه شتاب جنبش نیرومند زمین,نمودارهای تابع تجمعی احتمالاتی}, url = {https://jesphys.ut.ac.ir/article_60285.html}, eprint = {https://jesphys.ut.ac.ir/article_60285_f6dd5f7b310befbfa261b00204802df2.pdf} } @article { author = {روفیان نایینی, مهدی and عرب صاحبی, رضا}, title = {the effects of large Earthquake on the excitation of polar motion and the change in length of day}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {33-51}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.60280}, abstract = {In this study, the effects of Earthquake on the excitation of polar motion and the changes in the length of day are investigated. To do so, at first the deformation resulting from Earthquake is computed and then, its effects on the polar motion and length of day are derived. The geodynamic model which determines the crustal deformation is Dahlen's model in which the effects of Earthquake deformation coupled with the rotational motion of the Earth. For this purpose, it is assumed that the Earth is a spherical symmetric, isotropic, elastic and homogeneous media and the Earthquake is caused by the dislocation discontinuities on fault surface. In this case, the solution of the corresponding boundary value problem determines the deformations of the Earth due to Earthquake. On the other hand, the rotational motion of the Earth as a deformable body is governed by the Liouville equation, which determines the motion of polar axis under the applied external torque. Since the polar motion is investigated, only the homogeneous solution of the latter equation must be determines. In this case the solution of Liouville equation is only dependent on the moment of inertia of the Earth. Since, the components of the Inertia tensor of the Earth are dependent on the shape of the earth and its density distribution, and in this case, the Earth undergoes a shape change, therefore, its moments of inertial are no longer constant and depend on the deformation of the Earth. By computing the deformation results from the Earthquake as discussed at the first step, one may derive shape change and changes in the density distribution of the Earth from which, the changes in the component of inertia tensor may be obtained. Finally, the changes in the inertial tensor through Liouville equation can lead to the excitation of polar motion or the variations in the length of day, which determine by the solution of the corresponding equation. The simulated problems in two cases of strike-slip and dip-slip faults reveal that the amplitude of excitation due to strike-slip fault is maximum at equator and decrease toward poles and it is zero at pol. However, in the dip-slip fault, the amplitude at mid-latitude regions is maximum and is zero at both equator and poles. The variation in the length of day is zero at poles and is maximum at equator for strike-slip fault. For dip-slip fault, it is zero at both equator and poles and is maximum over the mid-latitude regions. Moreover, using the geometric parameters of the large Earthquakes from Harvard Earthquake Catalogue, occurred during the period of 1976 to 2014, their effects on the polar motion and length of day are studied within the adapted geodynamical model. The results show that among the selected Earthquakes, the 2011 Japan Earthquake had had the most significant effects on the motion of polar axis and the length of day .This excitation is in westward direction. The combined impact of all Earthquakes is also computed which clarifies that the polar excitation is increasing in the X direction (prime vertical component) and decreasing in the direction of Y (meridian component). For the validation of our results, we use the data of IERS (International Earth Rotation Service) which shows a relatively good agreement.}, keywords = {Deformation,dislocation theory,Dahlen's model,Polar motion,Large earthquake}, title_fa = {بررسی اثر زلزله‌های بزرگ جهان (1976 تا 2014 ) در تهییج حرکت قطبی و تغییرات طول روز}, abstract_fa = {در این تحقیق، به کمک تئوری دالن، اثر زلزله بر روی تهییج حرکت قطبی و تغییر طول روز مورد بررسی قرار گرفته است. برای این منظور، نخست تغییر شکل زمین در اثر زلزله محاسبه و سپس اثرات این تغییر شکل بر تغییر مولفه‌های تانسور اینرسی و حرکت قطبی مطالعه گردید. نتایج این تحقیق در مورد دو مسئله شبیه‌سازی که رخداد زلزله را در دو حالت با گسل‌های امتداد لغز و شیب‌لغز نمایش داده‌اند، حاکی از آن است که دامنه تهییج حرکت قطبی در اثر گسل امتدادلغز در استوا بیشترین مقدار بوده و هرچه به طرف قطبین پیش می‌رویم این اثر کاهش یافته تا اینکه در قطبین به صفر می‌رسد. در مقابل، در گسل شیب‌لغز دامنه در عرض‌های متوسط ماکزیمم و در استوا و قطبین صفر است. پارامتر تغییر طول روز در اثر گسل امتدادلغز در قطبین صفر و در استوا بیشترین و در گسل شیب‌لغز در قطبین و استوا صفر و در عرضهای متوسط ماکزیمم است. در ادامه، با استفاده از پارامترهای زلزله‌های بزرگ از سال 1976 تا 2014، برگرفته از کاتالوگ زلزله هاروارد، و مبتنی بر تئوری تشریح شده اثرات زلزله‌های فوق بر تهییج حرکت قطبی مورد مطالعه قرار گرفت}, keywords_fa = {تغییر شکل,تئوری نابجایی,مدل دالن,حرکت قطبی,تغییر طول روز,زلزه های بزرگ}, url = {https://jesphys.ut.ac.ir/article_60280.html}, eprint = {https://jesphys.ut.ac.ir/article_60280_77e0a5653a8b6f792605abd42c9fd36a.pdf} } @article { author = {Nikrouz, Ramin and Siabeghodsy, َAliasghar and حسنعلی زاده, پروین}, title = {Detective of stratigraphic trap of Sarvak formation using petrophysical logs and seismic attributes in one of the oil fields in the south west of Iran}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {53-69}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.59029}, abstract = {Nowadays there are many attempts to exploring stratigraphic traps all over the world. Because of existing Sarvak reservoir rock Formation in central Persian Gulf which consists of carbonate with various lateral changes in the terms of lithology, there is high probability to form of these stratigraphic traps in this region. The main aim of this research is to recognize the oil and gas stratigraphy traps by using seismic attributes and petrophysical and geological logs in the Bahregansar oil field, NW of Persian Gulf basin. In order to reconnaissance these regions, petrophysical logs (density, acoustic, neutron and gamma) and seismic reflection data from three wells have been studied. On the other hand, the obtained data have been interpreted with some seismic volume attributes such as momentary frequency, domain and acoustic impedance, reflection coefficient, normalized amplitude and envelope amplitude attributes to show the situation of hydrocarbon basin in the study area. By using seismic attributes and compare with geological information we can infer reliable interpretation because of some reasons. The first reason is seismic velocity allow us to understand the situation of lithology, fluid content and abnormal pressure or temperature. The second reason is lateral amplitude changes permit the inference of geological situation such as changes in porosity, existence of hydrocarbon and thickness of lithology. The third reason is seismic trace morphologies or interpretation sections allow us to recognize depositional environments or faults and fractures. Finally, changes in measurements direction permit to deduce velocity anisotropy, or fracture orientation. The software which used in this study was Petrel. Density log is creating with using neural network method by application of well No.3 in this oil field. The petrophysical study of gamma log shows well identity of formation boundaries in sections. Also the use of cross plot graph of density-neutron logs applied to well recognized of the efficient zones in Gurpi-Ilam, Sarvak and Kazhdumi-sand Formation. The Turonian epirogenic event is caused erosion of top of the Sarvak Formation and on the other hand Santonian epirogenic is caused hiatus stratigraphic trace in the lower part of Gurpi and Ilam Formation. By seismic volume attributes interpretation a number of the stratigraphy traps detected over some seismic sections. Furthermore, recognizing a main fault which exists in the western part of Hendijan oil field has main role in the changing of lithological effect in continuity quality of seismic reflection. In order to increase interpretation accuracy, some seismic inversion has been made on considered sections and the obtained data have been compared with petrophysical logs and seismic attributes. By doing this research and interpretation of sections two type of stratigraphic traps recognized. The first type is oil trap related to the top of Turonian unconformity (truncation) which exists in the eastern part of fault. The second is relation to narrowing part which is belonging to the above of the reservoir layer (pinch out) under Turonian unconformity in the western part of seismic section. Meanwhile the study shows that there is an oil trap as hydrocarbon accumulation in the upper part of Kazhdumi sand formation seismic subunit acting like stratigraphy trap in the above unconformity. In general, all of oil traps recognized in this study were composed of anticline structural dip and on the other hand existence of faults has a main role of geological structure in this region. The obtained results clearly demonstrated the shape and the geological situation of the existing structural traps in the studied area.}, keywords = {seismic attributes,Sarvak Formation,Petrophysical logs,Petrel software,Stratigraphic trap,Unconformity}, title_fa = {شناسایی تله های چینه ای سازند سروک با استفاده از لاگ های پتروفیزیکی و نشانگرهای لرزه ای در یکی از میادین نفتی جنوب غرب ایران}, abstract_fa = {امروزه تلاش زیادی در راستای اکتشاف نفتگیرهای چینه ای صورت می گیرد و از آنجایی که در خلیج فارس مرکزی سنگ مخزن سازند سروک می باشد لذا احتمال بسیاری وجود دارد که نفتگیرهای چینه ای در این ناحیه تشکیل شده باشند. به منظور شناسایی این مناطق، در این مطالعه به بررسی لاگ های پتروفیزیکی چگالی، صوتی، نوترون و گاما پرداخته شده و از آنجایی که حضور هیدروکربن تاثیر خاصی بر روی داده های لرزه ای می گذارد، نتایج حاصل از بررسی لاگ ها با نشانگرهای لرزه ای امپدانس صوتی، پوش دامنه و فرکانس لحظه ای تلفیق داده شده است. نشانگرهای حجمی به کار گرفته شده جهت نیل به اهداف مورد نظر شامل نشانگرهای ضریب امپدانس صوتی، کسینوس فاز لحظه ای، نشانگر پوش دامنه، فرکانس لحظه ای و فاز لحظه ای می باشند. داده ها با استفاده از نرم افزار پترل (Petrel) مورد تجزیه و تحلیل قرار گرفته شده است. با مطالعات انجام شده دو نوع تله چینه ای در قسمت های بالای سازند سروک شناسایی گردید. با توجه به برگردان لرزه ای تعدادی از مقاطع، تغییرات لیتولوژی و مرز سازندهای مورد مطالعه به خوبی تفسیر شدند. نتایج حاصل از فرکانس رنگ ها نشان داد که کربنات های متراکم بیشترین فرکانس رنگی (بنفش) و رسوبات آواری کمترین فرکانس رنگی (قرمز) را نشان میدهند. حضور هیدروکربن یکی از عوامل افت فرکانس می‌باشد. در این مطالعه نشان داده شد که تجمع هیدروکربن در بخش بالایی زیر واحد لرزه ای ماسه کژدمی به عنوان یک تله چینه ای در بالای ناپیوستگی عمل نموده است.}, keywords_fa = {نشانگرهای لرزه ای,لاگ های پتروفیزیکی,سازند سروک,نرم افزار پترل,تله چینه ای,ناپیوستگی}, url = {https://jesphys.ut.ac.ir/article_59029.html}, eprint = {https://jesphys.ut.ac.ir/article_59029_20ae56a80f55d46a383d52c4b2dad17a.pdf} } @article { author = {برازش, محمد and Motavalli Anbaran, Seyed Hani}, title = {Improvement In Depth And Structural Index Estimation Of Potential Field Sources By Using Curvature Attributes}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {71-86}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.57739}, abstract = {Interpretation of potential field data generally is quantitative or qualitative. An important factor in the issue of interpretation is how much interpreter is confident on data that provides the information needed to achieve the objectives of the study. Reliance on interpretation can be increased by the use of effective methods for parameters determination of causative sources. Although in most of methods not required to know the density or susceptibility contrast, but these methods are based on the assumption that the source is a certain type (horizontal slab, vertical dykes, etc.) and in two-dimension. By selecting the wrong type of sources, large errors may occur. Despite all these problems, numerous automatic techniques are designed that can be applied over the magnetic or gravity anomalies to quickly estimate the depth of sources.Curvature method is used to analyze and interpretation of potential field anomalies. Potential field anomalies can be transformed into special functions that formed peaks and ridges over isolated sources. All of these special functions have a mathematical form over sources that lead to a common equation to estimate the depth of the source from the peak value and curvature at the peak. Curvature attributes that used at this case called most negative curvature. Special functions are divided into two categories: Model-specific special functions and Model-independent special functions. Model-specific special functions usually are calculated from a transformed potential field for locating of specific sources such as a vertical magnetic contact, vertical density contact, etc. The horizontal gradient magnitude (HGM) and observed potential field (absolute value) are two types of model-specific special functions that formed ridges over specific sources. Model-independent special functions are used to calculate locations for various types of sources from the observational or modified potential field. Total gradient (TG), also called the analytic signal, and local wavenumber (LW) fall into this group.Usually, special functions need that the potential field undergoes a transformation, such as reduction-to-pole and vertical derivative. For gridded data, eigenvalues of the curvature matrix associated with quadratic surface is fitted to a special function within 3×3 window, to locate and estimate the depth of sources. Another curvature attributes is shape index that quantitatively stated the local shape in terms of bowl, valley, flat, ridge and dome. Shape index attribute (SHI) and Geometry factor provide a way to easily reject some of invalid estimations.In this study, method of curvature attributes has been applied on noisy and noise free synthetic data by using Model-specific (HGM and absolute value) and Model-independent special functions (Total gradient and local wavenumber). Finally, this method was tested on real data from Mobrun massive sulfide ore of Canada by using special functions of two models and was estimated a structural index (SI) from local wavenumber special function for the mine. The results of estimating the depth by this method had a good match with the results of the boreholes. Finally, the depth results of this method were compared with Euler deconvolution method which shows that method of using curvature attributes is more accurate in depth estimation.}, keywords = {Potential Field,Curvature,Special function,Quadratic surface,depth estimation}, title_fa = {بهبود تخمین عمق و اندیس ساختاری چشمه میدان پتانسیل با استفاده از نشانگرهای انحنا}, abstract_fa = {انحنا یکی از مشخصه‌های یک منحنی است که در هر نقطه مقدار انحراف آن را از یک خط راست تعیین می‌کند. در تعمیم این خصوصیت به سه بعد ما با یک سطح روبرو هستیم که با توجه به تقاطع صفحه با سطح، بی نهایت منحنی و در نتیجه انحنا در یک نقطه مشخص خواهیم داشت. مناسب‌ترین انحناها آن‌هایی هستند که که از تقاطع یک صفحه‌ی عمود به سطح بدست می‌آیند و انحناهای نرمال نام دارند. منفی‌ترین انحنا یکی از انحناهای نرمال است که در تحلیل و تفسیر کمی آنومالی‌های میدان پتانسیل استفاده می‌شود.آنومالی‌های میدان پتانسیل برروی منابع وابسته به مقدار تباین خصوصیت فیزیکی موردنظر دارای بیشینه هستند. آنومالی‌ها را می‌توان با یک رابطه ریاضیاتی بیان کرد که این امکان را فراهم می‌کند تا بتوانیم عمق چشمه را از مقدار پیک و مقدار انحنا در پیک بیابیم. این آنومالی‌ها را وابسته به اینکه نوع چشمه از قبل برای ما مشخص باشد یا خیر می‌توان به دودسته‌ که توابع ویژه وابسته به مدلی خاص و مستقل از مدل نامیده می‌شوند، تقسیم‌بندی کرد. ابتدا توابع ویژه از میدان پتانسیل تبدیل یافته محاسبه شوند و انحنا سطح این توابع ویژه، مکان و نوع چشمه را تخمین زد.روش آنالیز تخمین عمق با استفاده از نشانگرهای انحنا بر روی‌داده‌های مصنوعی بدون نوفه و همراه با نوفه به‌کاربرده شد. درنهایت این روش بر روی‌داده‌های واقعی از معدن سولفیدی موبرون کانادا با استفاده از توابع ویژه آزمایش شد و با استفاده از عدد موج محلی یک اندیس ساختاری برای این معدن تخمین زده‌ شد.}, keywords_fa = {میدان پتانسیل,انحنا,تابع ویژه,سطح درجه‌دوم,تخمین عمق}, url = {https://jesphys.ut.ac.ir/article_57739.html}, eprint = {https://jesphys.ut.ac.ir/article_57739_9b68b92a6893f2cd06132df1952cb74a.pdf} } @article { author = {Javadi Azar, Rahim and Voosoghi, Behzad and Ghaffari Razin, Mir Reza}, title = {Novozhilov Mean Rotation as a scalar earth surface deformation measure in local scale (Case study: N-W of Iran)}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {87-99}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.60281}, abstract = {The regions of northwestern Iran, eastern Turkey and Caucasus are one of the most intriguing regions of the Arabia-Eurasia collision. It is a pure intercontinental collision zone with the highest elevation in western Asia. This region is known for a spatial separation of sub-parallel thrusts and strike-slip faults. Iranian plateau includes two major mountain belts, hence Alborz in the north and Zagros in the south and west of Iran. Azerbaijan includes Alborz mountains, Talesh and Lesser Caucasus along with mountains in the Azerbaijan plateau. Azerbaijan is between great mountains of Caucasus in the north and Alborz in the east and distance away from Zagros in the south. A lot number of faults including Tabriz fault and Aras fault meet in the west of the study area. One of the most fundamental and important a new area of research in geodesy is earth surface deformation modeling at local and global scales. Also, check out the effective factors in deformation, and offers various computation methods in order to determine the movement of the earth's crust are considered as a recent development in geodesy. In recent years, space geodetic techniques with high precision and reliability have provided new sources of information to determine the geodetic positions. This information used for the detection and quantification of surface deformations. In this paper, Novozhilov method has been studied for mean rotation calculation with finite difference approach on earth surface in N-W of Iran especially north Tabriz fault. To achieve this goal, linear strain and rotation tensors on earth surface based on shell theory in continuum mechanics will be calculated using finite difference approach and then the mean rotation is extracted using linear strain and rotation tensors. Finite difference method is numerical methods based on mathematical discretization of the equations of boundary problems. By using this method, continuous process is studied in a finite number of sufficiently small time intervals. So it is possible, in these small intervals, the function approximated by approximate expressions. In each elementary interval is the integration, with the results of integration in the previous interval are taken as initial for the next time interval.In the fourth decade of the 20th century Novozhilov obtained a measure of the mean rotation by modifying a previous definition produced by Cauchy. In the literature, this measure has been named Novozhilov's mean rotation measure ever since. The measure introduced by Novozhilov for the mean rotation indicates the importance of the infinitesimal rotation tensors. The results obtained from linear strain and rotation tensors that computed using geodetic observations (GPS) in 2005, have good agreement with the results of previous work. The results of Novozhilov’s mean rotation criteria in the part of the Azerbaijan plateau shows that the highest right turn rotation is related to YKKZ station (2.975±0.631deg/Myr). An important feature of Novozhilov’s mean rotation analysis on earth surface than analysis of this parameter in Cartesian system is that the results of this measure on earth surface is very close to the results of previous studies on blocks rotation in different areas in Iran. Accuracy of this measure on earth surface is acceptable in most parts of the case study.}, keywords = {Earth surface deformation analysis,Strain tensor,Rotation tensor,Mean Rotation (Novozhilov),Finite difference}, title_fa = {معیار دوران متوسط نووژیلو بعنوان یک پارامتر اسکالر تغییر شکل سطح زمین در مقیاس محلی (مطالعه موردی: شمالغرب ایران)}, abstract_fa = {در این مقاله به بررسی یک معیار عددی جدید بنام نووژیلو جهت محاسبه دوران متوسط به‌کمک روش تفاضل محدود در فضای پوسته زمین و در محدوده شمالغرب ایران به‌ویژه شمال گسل تبریز پرداخته شده است. برای رسیدن به این هدف ابتدا تنسورهای استرین و دوران خطی، روی سطح پوسته زمین بر مبنای نظریه پوسته در مکانیک محیط‌های پیوسته، با استفاده از روش تفاضل محدود محاسبه شده و سپس معیار دوران متوسط نووژیلو با استفاده از مؤلفه‌های تنسورهای استرین و دوران خطی استخراج می-شود. نتایج بدست آمده از تنسورهای استرین و دوران خطی در فضای پوسته با استفاده از مشاهدات ژئودتیکی (GPS) سال 2005 ایران سراسری، تطابق خوبی با نتایج کارهای قبلی دارد. نتایج بدست آمده از معیار دوران متوسط نووژیلو در فضای پوسته بخشی از فلات آذربایجان، نشان‌دهنده آن است که بیشترین دوران راستگرد در منطقه مربوط به ایستگاه YKKZ به مقدار ( deg/Myr631/. ± 975/2) می‌باشد. ویژگی مهم بررسی معیار دوران متوسط نووژیلو روی پوسته زمین نسبت به بررسی این معیار در سیستم مختصات کارتزین، این است که نتایج بدست آمده روی پوسته زمین بسیار نزدیک به نتایج مطالعات قبلی که روی دوران بلوک‌ها در مناطق مختلف آذربایجان صورت گرفته، می‌باشد. دقت بدست آمده برای این معیار در فضای پوسته در اکثر ایستگاهها قابل قبول می‌باشد.}, keywords_fa = {تغییرشکل پوسته زمین,فلات آذربایجان,تنسور استرین خطی,تنسور دوران خطی,دوران متوسط نووژیلو}, url = {https://jesphys.ut.ac.ir/article_60281.html}, eprint = {https://jesphys.ut.ac.ir/article_60281_df5e7e004cd50f657280864e6d184772.pdf} } @article { author = {شاهوردی, محبوبه and نمکی, لقمان and منتهایی, منصوره and مصباحی, فاطمه and بساوند, مهدی}, title = {Interpretation of Magnetic Data, based on Tilt Derivative Methods and Enhancement of Total Horizontal Gradient, A Case Study of Zanjan Depesion}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {101-113}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58910}, abstract = {Magnetic survey data are generally used to map faults, geologic contacts and magnetic ore bodies. The spatial distribution of magnetic sources will be determined during the mapping process. Variation in depth, magnetization and geometrical parameters generate magnetic anomaly waveform. Direction of the remanent and induced magnetization vector will also affect the shape of these waveforms. A magnetic anomaly waveform includes amplitude, phase and wavelength. Putting these parameters altogether makes the interpretation of the magnetic data a difficult task. There are different useful methods for interpretation of a magnetic map. Generally, these methods are based on reduction data to a simpler form, so that the edges and center of the causative bodies will be determined easily. In recent years many methods have been used to balance the difference between various anomaly amplitudes. Each method is designed to determine a specific parameter of the magnetic anomalies. Local phase filters are commonly used in potential field data interpretation. They are high-pass filters based on horizontal and vertical derivatives, such as total horizontal derivative, tilt angle, theta map, etc.Edge detection of a magnetic structure is one of the most important issues in the interpretation of magnetic data. In the present study we have used two local phase filters for this purpose: Tilt angle (TDR) and Total Gradient of Tilt angle (TAHG). Although the tilt angle filter is used to determine the boundary of anomaly sources, but it is relatively less sensitive to the source depth, so it can resolve shallow and deep sources as well. As the tilt angle is a function of vertical derivatives normalized by horizontal derivatives of magnetic field intensity (THDR), it does not contain information on the strength of the geomagnetic field nor the susceptibility of the causative bodies. The tilt angle amplitudes depend strongly on magnetic field inclination. Their maximum occurs at the center of the magnetic sources and they disappear over the anomaly edges.Another enhancing method employed in this study to determine the structure boundaries, is the tilt derivative of horizontal gradient. It is defined by taking the arctangent of the vertical derivative of the THDR, divided by the modulus of the horizontal gradient of THDR:TAHG=arctan⁡〖((∂THDR/∂z)/√(〖(∂THDR/∂x)〗^2+〖(∂THDR/∂y)〗^2 ))〗TAHG equalizes the signals obtained from shallow and deep sources. This method has two notable features: I- it produces maximum amplitudes over the edges of the sources, II- it gives suitable resolution and is less dependent on the structure depths. However, like the TDR, this method depends on the inclination of magnetic field.We applied these methods for synthetic noise-free and noisy data. Magnetic responses of synthetic models as well as calculations of different edge detection methods have all been done in MATLAB. In comparison with common methods like horizontal gradient and analytic signal, it delineates the edges of sources more efficiently and accurately. Furthermore the TAHG method has better resolution in determining the boundaries of deeper sources than TDR method. We applied the TAHG method for the aeromagnetic dataset from Zanjan region. The Zanjan depression is a narrow and continuous igneous basin, located in the north western Zanjan province. There are many young active and basement faults in the study area. Total magnetic anomaly map of the region, shows two major structural trends in NW-SE and NE-SW, respectively. Applying different edge detection algorithms we obtained the hidden boundaries of the basement which is not detectable in the geological maps because of the thick sedimentary covers. The results show that TAHG method is suitable for determining the basement faults and boundaries, as well as mapping the contacts of magnetic units.}, keywords = {Potential Field,Magnetic Anomaly,Tilt Angle of Horizontal Gradient,Vertical Gradient,Edge detection}, title_fa = {تفسیر داده‌های مغناطیسی براساس محاسبه زاویه تیلت و بهبود گرادیان افقی، مطالعه موردی: فروافتادگی زنجان}, abstract_fa = {جهتگیری متفاوت مغناطیدگی‌های القایی و بازماند در ‌یک توده بی‌هنجار مغناطیسی و همچنین اثر تداخلی بی‌هنجاری‌های مختلفی که با خصوصیات هندسی و فیزیکی متفاوت دراعماق مختلف قرار گرفته‌اند، تفسیر نقشه‌های مغناطیسی به منظور شناسایی گسل‌ها، مرزهای بین لایه‌ای و بی‌هنجار‌های مغناطیسی پراکنده در پوسته زمین را پیچیده و دشوار ساخته‌اند. با اعمال فیلترهایی نظیر فیلترهای فاز محلی می‌توان این پیچیدگی‌ها را برطرف کرد.. در این مقاله برای تشخیص لبه‌های بی‌هنجاری از دو فیلتر فاز محلی، زاویه تیلت (TDR) و زاویه تیلت گرادیان افقی (TAHG)، استفاده شده است. این فیلترها در واقع ترکیبی از گرادیان افقی و قائم میدان پتانسیل می‌باشند. کارایی این روش‌ها بر روی مدل مصنوعی H شکل در دو حالت، نوفه‌دار و عاری از نوفه، آزموده شده است. نتایج، حاکی از توانایی بالای این روش‌ها در تعیین مرز توده‌های مغناطیسی نسبت به روش‌های معمول گرادیان افقی، سیگنال تحلیلی و ... است. علاوه بر این، روش TAHG تفکیک‌پذیری عمقی بهتری نسبت به روش TDR دارد. اعمال روش TAHG بر یک مجموعه داده مغناطیسی هوابرد مربوط به ناحیه فروافتاده زنجان، نشان داد که این روش قادر است تا گسل‌های پی‌سنگی و پی‌سنگ این ناحیه را توصیف و لبه‌های آن‌ها را با دقت بالایی ترسیم کند. مدل‌های مصنوعی و الگوریتم روش‌های مورد بررسی، در محیط متلب تهیه شده‌اند.}, keywords_fa = {میدان پتانسیل,بی‌هنجاری مغناطیسی,زاویه تیلت- مشتق افقی,مشتق قائم,تشخیص مرز}, url = {https://jesphys.ut.ac.ir/article_58910.html}, eprint = {https://jesphys.ut.ac.ir/article_58910_36c0fef1acee4c1395a698df3c1e06c8.pdf} } @article { author = {Ghasemiannia, Ramin and Oskooi, Behrooz}, title = {Estimation of depth, location and structure index of magnetic anomalies by enhanced local wavenumber method}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {115-131}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58909}, abstract = {A reliable analysis of magnetic data is the correct estimation of the causative sources to plan for drilling to achieve the targets. This paper presents enhanced local wave number (ELW) method for interpretation of the magnetic data. ELW method has been proposed during the previous decades and is based on analytic signal to estimate the location and depth of the anomalies without having any knowledge about the geometry and magnetic susceptibility of the source. Final equation in this technique, is based on the depth and position and is independent of the structural index. The solution of normal this equation is obtained by assigning ELW kx and kz (the local wave number with respect to x and z) for different values of x and heights of continuation, z within a window centred with the peak of the analytic signal amplitude. A problem of over determined unknown parameters can be solved through a standard technique, using the least squares approach, therefore, the Golub algorithm is used to solve a set of linear equations. The ELW technique requires computation of horizontal and vertical derivatives of the first and second orders. Due to this characteristic, any high frequency noise present in the data gets substantially enhanced, masking the response from a target. To restrict the high frequency response, a window function is designed on the basis of the maximum frequency computed from Agrawal and Lal (1972). After finding these quantities the method can approximate the structure index. Although, an appropriate Matlab code for the method is introduced and tested on two dimensional synthetic data before and after adding noises. There is a peak in the curves of analytic signal and kx of ELW and also a turning point in the curve of kz of ELW witch shows the position of anomaly. Existence of these features shows that final responses of ELW method are correct. Synthetic data produced from a dyke like body with dip, magnetization, declination, inclination, depth and thickness are 45º, 1( ), 90º, 64º, 10m and 15m respectively. The ELW method has had reasonable responses for noises with different amplitudes up to 20nT and for noises with amplitude more than 20nT, ELW method looses its efficiency. Then, the method is tested by applying on the real data of Golbelaghi area in Zanjan, and ok compared with the results obtained from Model vision software. To do this a 525m profile is used. At the end, the depth and structure index are obtained about 4m and 0.8, respectively, using ELW method and the depth is estimated about 4.4m using model vision software. It is worthy to note that the depth of anomaly has been reported 4.5m by drilling. The parameters obtained from the introduced method for the anomalies show that the enhanced local wavenumber method and its introduced Matlab code can be a powerful tool in the studies of local anomalies. Because this method is automatic and quick, it can be used for large data sets like vast area or airborne data. This method is used on airborne data of Damghan region in another paper.}, keywords = {Analytic signal,Enhanced Local Wavenumber,Golbelaghi region,Zanjan}, title_fa = {تخمین عمق، مکان و هندسه بی‌هنجاری‌های مغناطیسی به روش عددموج محلی بهبودیافته}, abstract_fa = {لازمه تحلیل صحیح داده‌های مغناطیسی، یک تخمین عمق واقعی از منبع بی‌هنجاری مغناطیسی به‌منظور تعیین نقاط حفاری و رسیدن به هدف مغناطیسی می‌باشد. روش عدد موج محلی بهبودیافته بر پایه معادلات سیگنال تحلیلی شکل گرفته است و می‌تواند مکان افقی و عمق بی‌هنجاری را بدون نیاز به آگاهی از هندسه و خودپذیری مغناطیسی منبع مشخص کند. پس از مشخص شدن این کمیت‌ها تقریبی از ضریب ساختار نیز قابل تخمین است. در این تحقیق، کد این روش برای اعمال بر روی بی‌هنجاری‌های دوبعدی در محیط متلب نوشته شده و توانایی آن بر روی داده‌های مصنوعی بدون نوفه و همراه نوفه آزمایش شده است. در قسمت داده-های مصنوعی از دایکی با شیب 45 درجه و مغناطیدگی یک آمپر بر متر ، زاویه انحراف 10 درجه و زاویه میل 64 درجه استفاده شده است. روش عددموج محلی بهبودیافته بر روی این دایک، بدون حضور نوفه و همچنین آلوده به نوفه با دامنه‌های مختلف، اعمال شده است. در ادامه این روش بر روی داده‌های میدانی منطقه گل‌بلاغی واقع در شهرستان زنجان اعمال شده و جواب‌های آن با جواب‌های به دست آمده از نرم‌افزار مدل‌ویژن مقایسه گردیده است. برای این بررسی از یک پروفیل به طول 525 متر با فواصل نمونه‌برداری یک متر استفاده شده است. پارامترهای توده بی‌هنجاری که به‌وسیله این روش به‌دست آمده با نتایج حاصل از نرم‌افزار مدل‌ویژن مطابقت دارد. روش عدد موج محلی و کد متلب نوشته شده، می‌تواند ابزار توانمندی برای بررسی بی‌هنجاری-های دوبعدی باشد.}, keywords_fa = {زنجان,سیگنال تحلیلی,عدد موج محلی بهبودیافته,منطقه گل بلاغی}, url = {https://jesphys.ut.ac.ir/article_58909.html}, eprint = {https://jesphys.ut.ac.ir/article_58909_83562631be3b5219af65dbac74349fd6.pdf} } @article { author = {Raziei, Tayeb and Sotoudeh, Fatemeh}, title = {Investigation of the accuracy of the European Center for Medium Range Weather Forecast (ECMWF) in forecasting observed precipitation in different climates of Iran}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {133-147}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.57958}, abstract = {The lack of reliable and updated precipitation datasets is the most important limiting factor in studying many climatological and hydrological topics including climate change and temporal variability of precipitation in many data sparse areas around the globe. This is particularly valid for Iran that encompasses vast deserts and un-settled hyper-arid climate areas (central-eastern Iran) that hinders establishing an adequate network of rain-gauge stations required for climatological studies. Similarly, the high elevation areas of mountainous regions of western and northern Iran suffer from limited representative stations. Using the gridded or reanalysis precipitation datasets could be one of the possible solutions to overcome this obstacle; knowing that the representativeness of these datasets has been already proved for many different parts of the world. Amongst many available gridded precipitation datasets are the Global Precipitation Climatology Center (GPCC) and the Tropical Rainfall Measuring Mission (TRMM) that have been widely used in many researches; indicating their accurate estimation of precipitation values and intra-annual variation for the regions studied. The reanalysis precipitation dataset which is a product of the Numerical Weather Prediction (NWP) models is an alternative source of precipitation data that is widely used in the literature and many authors have pointed to the relatively accurate precipitation prediction of reanalysis for many parts of the word. The two widely used reanalysis datasets are NCEP/NCAR and different products of ECMWF, namely ERA-15, ERA-40 and ERA-Interim reanalysis. ERA-Interim which is used in the present study is produced at T255 spectral resolution (about 80 km) and covers the period from January 1979 to present, with product updates at approximately 1 month delay from real-time (Dee et al., 2011; Balsamo et al., 2015). The ERA-Interim atmospheric reanalysis is built upon a consistent assimilation of an extensive set of observations (typically tens of millions daily) distributed worldwide (from satellite remote sensing, in situ, radio sounding, profilers, etc.). To develop the reanalysis, the analysis step combines the observations with a prior estimate of the atmospheric state (first-guess fields) produced with a global forecast model in a statistically optimal manner (Balsamo et al., 2015).The representativeness and performance of ERA-Interim in forecasting precipitation amount at 45 Iranian synoptic stations distributed across the country is herein examined. Spatial resolution of ERA-Interim dataset used in this study is 0.125 × 0.125 in latitude and longitude. For each station, the closest grid point of ERA-Interim to the station coordinates was chosen for a statistical comparison analysis. To evaluate the performance of the considered dataset when compared to the observed precipitation records at the considered locations we have used R squared, the Nash–Sutcliffe model efficiency coefficient (EF), RMSE, Bias, B slope of the regression and the standardized RMSE indicators. The performance of the dataset was also graphically represented through scatter plots of the established regression between ERA-Interim and observation at the selected stations. The results of the statistical indicators were represented through plotting the indicators over the map of Iran to ease displaying spatial tendency of the indicators and explaining the possible geographical role in controlling the spatial variation of the indicators. The results indicate that the ERA-Interim performs well in majority of the studied stations with strong correlation coefficient. However, it was found that the ERA-Interim underestimates precipitation in most of the stations located in the coastal areas of the Caspian Sea as well as in some stations along the Persian Gulf and the Oman Sea, suggesting that ERA-Interim is somewhat inefficient in adequately forecasting precipitation in the coastal areas; very likely due to not properly taking into account the complex topography of the region in its model parameterization or not being able to adequately differentiate between land and sea characteristics for the stations very close to the sea. It should be noted that the ERA-Interim is less efficient in accurately forecasting extreme precipitation in the Caspian Sea region. Nevertheless, we found very high agreement between observations and ERA-Interim in this region when some extreme precipitation events were excluded from the analysis. Contrarily, the results suggest an over-estimation for most of the stations located in northwestern and northeastern mountainous areas of the country; once again due to perhaps improper representation of topography of these regions in the model.}, keywords = {"Precipitation","ECMWF"," ERA-Interim","statistical indicators","Iran"}, title_fa = {بررسی دقت مرکز اروپایی پیش‌بینی‌های میان مدت جوی (ECMWF) در پیش بینی بارش مناطق گوناگون اقلیمی ایران}, abstract_fa = {به منظور بررسی میزان خطای مرکز اروپایی پیش‌بینی‌های میان مدت جوی (ECMWF) در پیش‌بینی بارش مناطق مختلف ایران، داده‌های بارش ماهانه 45 ایستگاه‌ همدیدی پراکنده در سطح کشور با داده‌های بارش ماهانه ERA-Interim در نزدیک‌ترین نقطه به هر ایستگاه مورد مقایسه آماری قرار گرفت. برای این منظور از آماره‌هایی مانند ضریب تعین (R2)، مجذور میانگین مربع خطا (Rmse)، شیب خط (B Slope)، اریبی (Bias) و ضریب کارایی مدل (EF) برای مقایسه آماری داده‌های ERA-interim در برابر داده‌های مشاهده‌ای ایستگاه‌های مورد مطالعه استفاده شده است. نتیجه این بررسی نشان داد که ERA-Interim از دقت بسیار بالایی در پیش‌بینی بارش بسیاری از نقاط کشور برخوردار است و میزان خطای آن در بیش از 70 درصد از ایستگاه‌های مورد مطالعه اندک و قابل چشم پوشی است. همچنین مشخص شد که ERA-Interim بارش ایستگاه‌های ناحیه ساحلی خزر و برخی ایستگاه‌های ناحیه ساحلی خلیج فارس را کم‌تر از مقدار واقعی پیش‌بینی می‌کند. کم برآورد کردن بارش در ایستگاه‌های ناحیه خزری عمدتا به علت ناتوانی ERA-Interim در پیش‌بینی درست برخی بارش‌های فرین این ناحیه می‌باشد. اگرچه بین بارش ERA-Interim و بارش مشاهده‌ای در منطقه شمال غرب و شمال شرق کشور همبستگی بسیار قوی دیده می‌شود ولی مقدار بارش پیش‌بینی شده ERA-Interim برای اکثر ایستگاه‌های این مناطق نیز بیش‌تر از مقدار واقعی برآورد می‌شود.}, keywords_fa = {"بارش","مقایسه آماری",پ"یش‌بینی عددی","ECMWF","ERA-Interim","ایران"}, url = {https://jesphys.ut.ac.ir/article_57958.html}, eprint = {https://jesphys.ut.ac.ir/article_57958_7ac45d1266a9ec55b595cc05e33aa3be.pdf} } @article { author = {محب الحجه, علیرضا and علی زاده, زکیه and احمدی گیوی, فرهنگ}, title = {Study of the climate anomaly of Iran in Aban 1390 (23rd Oct. to 21st Nov. 2011) from the perspective of the large-scale dynamics}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {149-164}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58906}, abstract = {Based on the report by Islamic Republic of Iran Meteorological Organization (IRIMO) published as part of a greater report on the state of the world climate in 2011 by the American Meteorological Society (Blunden and Arndt, 2012), large parts of Iran, from central to northern and northeastern areas, have experienced significant negative anomalies of surface temperature together with positive anomalies of precipitation in autumn 2011. The temperature and precipitation anomalies have been determined with respect to the climatological mean values over the period 1960 to 2010. As the establishment of a prolonged period of cold weather in Aban 1390 (23rd Oct. to 21st of Nov. 2011) together with abundant precipitation in the form of both rain and snow played a great role in shaping the climate anomalies of autumn 2011 in Iran, this study aims to investigate the large-scale dynamical processes involved in the climate anomalies of this period. Such studies are particularly important, when the increase in the frequency of extreme climate anomalies in recent years and its possible link with global warming is noted. To this end, the NCEP/NCAR reanalysis data are used for the concerned period and the long-term mean fields (from 1950 to 2010). The main analysis tools used are the analysis of the anomalies of geopotential height and temperature in the lower and middle troposphere, jet speed and relative vorticity in the upper troposphere, the computation of the blocking index (BI) introduced by Wiedenmann et al. in 2002, and the energy diagnostics. The latter includes the eddy kinetic energy, ageostrophic geopotential flux and its convergence, total flux and its convergence, baroclinic generation, baroclinic conversion, and barotropic conversion. The results for the year 2011 indicate the action of two consecutive blocking systems, which extended their central ridges over Europe with their troughs stretched over the North Atlantic and the west of Asia. The two blocking systems were peaked in the 3rd and 21st of Aban 1390, with respectively moderate and high intensities as measured by BI. In addition, the obtained results show that a branch of Siberian high-pressure system extended to the west of Asia associated with a positive relative vorticity anomaly in the north of Iran, lead to vigorous cold air advection to the North and Northwest of Iran. The increase in eddy kinetic energy over a band stretched from the North Atlantic to the Mediterranean and Black Seas in Aban 1390 was associated with an increase in the strength as well as the zonal and meridional extensions of the subtropical jet. Concerning energy diagnostics, the positive anomalies of the ageostrophic and total flux convergence over Iran indicate that the country was a favorable region for receiving large amounts of energy. Also, the flux vectors demonstrate that the main passage of this energy to Iran was through a north–south extent that included an emission area over the Black Sea. This was further confirmed by the analysis of baroclinic generation, which showed a positive anomaly over the Black Sea. The analysis also shows that the low-frequency phenomena and teleconnection patterns, including the positive phases of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO), and the positive phase of the East Atlantic–West Russia (EA–WR) may have played a part in shaping the climate anomaly over Iran in Aban 1390.}, keywords = {Large-scale dynamics,anomaly,Blocking,baroclinic generation,ageostrophic flux,total flux}, title_fa = {بررسی بی هنجاری اقلیمی ایران در آبان‌ماه 1390 از دیدگاه دینامیک بزرگ‌مقیاس}, abstract_fa = {بر اساس آمارهای سازمان هواشناسی ایران به نقل از گزارش انجمن هواشناسی آمریکا در بررسی وضعیت اقلیم جهان در سال 2011، بخش بزرگی از کشور در پاییز 2011 دارای مقادیر چشم‌گیر بی‌هنجاری منفی دما همراه با بی‌هنجاری مثبت بارش نسبت به میانگین‌های اقلیم‌شناختی در دوره 1960 تا 2010 میلادی بوده است. سهم عمده در شکل‌گیری این بی‌هنجاری‌ها را حاکمیت یک دوره بلند سرما همراه با بارش در بخش‌های گسترده‌ای از کشور در آبان‌ماه 1390 داشته است. با استفاده از داده‌های بازتحلیل روزانه NCEP/NCAR، میانگین برخی کمیت‌های هواشناختی مهم و هم‌چنین جمله‌های معادله انرژی جنبشی پیچکی در این ماه با میانگین‌های اقلیم‌شناختی متناظر برای دوره بلندمدت 2010-1950 مقایسه شده است. نتایج نشان از حاکمیت دو بندال پی‌درپی در دوره مورد مطالعه، هر کدام با پشته مرکزی روی اروپا و ناوه‌هایی روی اطلس و غرب آسیا دارد. قوی-تر شدن و گسترش مداری و نصف‌النهاری جت جنب‌حاره‌ای و هم‌راستایی آن با جت مسیر توفان اطلس در این دوره نیز سبب افزایش انرژی جنبشی پیچکی در منطقه اطلس، شمال آفریقا و ایران شده است. از دیدگاه انرژی، وجود بی‌هنجاری منفی تولید و تبدیل کژفشار و بی‌هنجاری مثبت همگرایی شار کل و شار آزمینگرد روی منطقه ایران نشان‌دهنده آن است که در آبان‌ماه 1390 ایران گیرنده قوی انرژی جنبشی پیچکی گسیل شده از سوی دریاهای مدیترانه و سرخ بوده است.}, keywords_fa = {دینامیک بزرگ‌مقیاس,بی‌هنجاری,بندال,تولید کژفشار,همگرایی شار کل,شار آزمینگرد}, url = {https://jesphys.ut.ac.ir/article_58906.html}, eprint = {https://jesphys.ut.ac.ir/article_58906_aa7cb29397bbadc51f49299bbd435b9a.pdf} } @article { author = {amiri-Simkooei, alireza and parvazi, kamal and عسگری, جمال}, title = {Extracting tidal frequencies of the Persian Gulf and Oman Sea using multivariate least square harmonic estimation of sea level coastal height observations time series}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {165-180}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.60304}, abstract = {Tidal observations have been widely used for a variety of applications. Realistic functional and stochastic models of tidal observation are then required. The functional model is complete if one knows the tide characteristics such as tidal frequencies (M2 and S2 for instance). The stochastic model is complete if we know noise characteristics of tidal observations. There is always a prediction error between the predicted values and the observed tide heights. This can be investigated when taking the noise characteristics of tidal time series observations. Functional model identification is however the subject of discussion in the present contribution. Tide data are frequently used for different applications such as safe navigation. Real tide gauge data can be expressed by their tidal constituents (frequencies) and a noise structure. Using tidal frequencies and tidal observations one can employ the functional model to predict tide. Therefore identifying tidal frequencies is an important issue for tidal analysis. So far, most of the available methods to determine tidal frequencies have been based on the theory, and sea level height observations have not seriously been used to extract tidal frequencies. The theory-based methods usually apply the ephemeris of Moon, Sun and other planets to extract tidal frequencies without the use of tidal observations. Following-up the study by Amiri-Simkooei et al. (2014), we further focus on extracting tidal frequencies using tidal observations. For this purpose, we apply the least squares harmonic estimation (LS-HE) to the multivariate tidal time series. As a generalization of the Fourier spectral analysis, LS-HE is neither limited to evenly spaced data nor to integer frequencies. We may also note that the main tidal constituents may change from one area to another area. In this contribution, we use the data sets of eight coastal tide gauge stations in Persian Gulf and Oman Sea between 1999 and 2010 with a sampling rate of 30 min using a multivariate analysis. In multivariate analysis, the frequencies contributed in tide structure are more obvious than in the univariate analysis. Such signals can thus simply be detected in the multivariate analysis. Using the above-mentioned data, 414 main tidal constituents have been extracted. Our extracted lists of frequencies (of the Persian Gulf and Oman Sea) are compared with the two lists of frequencies consisting of 50 and 121 frequencies by the study of Amiri-Simkooei et al. (2014), which was applied to UK tide gauge stations. In the present contribution, new frequencies that belong to the tide gauge stations of the Persian Gulf and Oman Sea have been identified. Finally, a six-month prediction is performed for all stations using the two lists of main frequencies obtained in the two studies. The prediction results of the two studies are then compared using the estimated root mean squared error (RMSE). The RMSE difference of our predicted data show a reduction ranging from 2 cm to 7 cm compared to that predicted using the frequency lists of Amiri-Simkooei et al. (2014). The estimated RMSE of tide prediction using the frequencies obtained in this study ranges from 9 to 16 cm.}, keywords = {"Least square harmonic estimation (LS-HE) ","Tidal frequencies","multivariate tidal time series analysis","coastal tide gauge","tide prediction","Persian Gulf and Oman sea}, title_fa = {استخراج فرکانس‌های جزر و مدی منطقه خلیج فارس و دریای عمان به روش برآورد هارمونیک کمترین مربعات چند متغیره سری‌های زمانی مشاهدات ارتفاع‌سنجی ساحلی سطح دریا}, abstract_fa = {تاکنون، اکثر روش‌های ارائه شده جهت تعیین فرکانس‌های جزر و مدی، بر اساس مبانی تئوری بوده‌ و مشاهدات جزر و مدی نقشی در یافتن این فرکانس‌ها نداشته‌اند. این تحقیق، در ادامه تحقیق انجام شده توسط امیری سیمکویی و همکاران (2014) به استخراج فرکانس‌های جزر و مد از طریق آنالیز مشاهدات جزر و مد می‌پردازد. بدین منظور، با استفاده از روش برآورد هارمونیک کمترین مربعات (LS-HE)، سری‌های‌ زمانی مشاهدات جزر و مد مورد بررسی قرار گرفته و فرکانس‌های جزر و مدی استخراج می‌گردند. در این تحقیق از داده‌های 8 ایستگاه تاید-گیج در منطقه خلیج فارس و دریای عمان بین سال‌های 1999 تا 2010 استفاده شده است. 414 فرکانس موثر در این ایستگاه‌ها بدست آمده است. مقایسه‌ای بین دو لیست فرکانسی شامل 50 و 121 فرکانس اصلی حاصل از تحقیق امیری سیمکویی و همکاران (2014) برای تاید-گیج‌های کشور انگلستان، با فرکانس‌های استخراجی در این تحقیق(منطقه خلیج فارس و دریای عمان) انجام گردیده است. فرکانس‌های جدیدی که به ایستگاه‌های منطقه خلیج فارس و دریای عمان اختصاص دارد استخراج شده‌ است. در پایان پیش‌بینی‌ جزر و مد به مدت شش ماه برای تمام ایستگاه‌ها با استفاده از، دو لیست از فرکانس‌های مهم استخراجی حاصل از دو تحقیق انجام شده و نتایج با هم مقایسه گردیده ‌است. اختلاف RMSE داده‌های پیش‌بینی شده در این مقایسه بین 2 تا 7 سانتیمتر بوده و دقت ارائه شده برای پیش‌بینی جزر و مد با استفاده از فرکانس‌های بدست آمده در این تحقیق برای ایستگاه-های تاید-گیج منطقه خلیج فارس و دریای عمان بین 9 تا 16 سانتیمتر می‌باشد.}, keywords_fa = {"برآورد هارمونیک کمترین مربعات(LS-HE)," "فرکانس‌های جزر و مد","آنالیز سری‌ زمانی چند‌متغیره","تاید-گیج‌های ساحلی","پیش‌بینی جزر و مد"," خلیج فارس و دریای عمان"}, url = {https://jesphys.ut.ac.ir/article_60304.html}, eprint = {https://jesphys.ut.ac.ir/article_60304_2d9e8b555eb08b8a4026fb3335f512d0.pdf} } @article { author = {Deldar, Hamed and علی اکبری بیدختی, عباسعلی and چگینی, وحید and اکبری نسب, محمد}, title = {A laboratory study of the effect of internal waves on acoustic propagation}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {181-192}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.60299}, abstract = {For calculating the acoustic pressure due to sound propagation at sea using usual methods (pressure variations signals), knowing the density distribution and consequently, changes the speed of sound in the environment is very important. Many environmental factors affect the distribution of the density at sea, depending on environmental conditions and geographical location and the weaknesses of each of them are different. One of them is internal waves which usually cause temporal and spatial changes and consequently affect the acoustic wave propagation in the ocean. Internal waves can be generated by tidal currents over sea floor sloping that is very common in the stratified oceans. Results of study in the some researches showed that internal waves can effected on sound waves in two ways: 1-Internal waves can be decrease sound level up to 25 dB due to sound mode coupling in an exact frequency. 2- Internal waves can fuscous and defocus sound waves because of sound speed fluctuation.The purpose of this study is a laboratory investigation of internal waves caused by fluctuation of a cylinder in a stratified glass channel with 3 meters long, 0.5 meter width and 1 meter height, on the sound waves propagation. In this study, using the double bucket and filling box method for generating stratification that stratification can be measured by one pair of salinity and temperature meters fixed on a rail moved up and down. Using the usual methods of setting up internal waves and using acoustical transducers in 53 KHz frequency, internal wave's effects on the propagation of sound waves, were investigated. In this study with usual optical method (Synthetic Schlieren) internal waves generated in the tank can be detected. In this method Internal wave generated in the glass tank change optical index of water layers and cased deviation of Straight lines designed on the back of tank. Laboratory results showed that sound waves can be focused and defocused due to the normal modes of internal waves. Some 9 experiments were done mainly in cases withvertical linear density stratified fluid. As the modal structure of internal waves in the water tank change due to the waves, constant density surfaces change slopes, hence changing the sound ray's paths and the amount of signals reaching the receivers. Similar results of numerical simulation also show similar behavior in the strength of the acoustic signal. Numerical simulation modeled by AcTUP v2.2L software that use KERAKENC method based on normal mode method. The acoustic signal can be weakened up to 54 per cent depending on the degree of sound ray divergence. We can conclusion that in the laboratory tank in this study internal waves effects on sound waves by focusing and defocusing and not by mode coupling. Similar behaviors can be expected in the open ocean as the existence of internal waves is ubiquitous. For this goal dimensionless numbers should be use. Bowen (1993) showed that for simulating a sound waves interaction with a phenomenon in laboratory scale we can use ka = k'a'. With this formula we can compare laboratory results with real results on oceans.}, keywords = {Internal waves,propagation of sound waves,focusing and defocusing of sound waves}, title_fa = {مطالعه آزمایشگاهی تاثیر امواج درونی بر روی انتشار امواج صوتی}, abstract_fa = {برای محاسبه‌ی فشار اکوستیکی در دریا با استفاده از روش‌های معمول، دانستن نحوه‌ی توزیع میدان چگالی و به تبع آن نحوه‌ی تغییرات سرعت صوت در محیط بسیار مهم است. عوامل محیطی بسیاری بر توزیع میدان چگالی در دریا تاثیرگذارند که بسته به شرایط محیطی و جغرافیایی شدت و ضعف هر یک از آن‌ها متفاوت می‌باشد. یکی از این عوامل امواج درونیاست که ساختار آنباعث تغییرات زمانی مکانی میدان چگالی و به تبع اثر گذاری روی نحوی انتشار امواج صوتی در اقیانوس می شود.هدف از این مطالعه بررسی آزمایشگاهی تاثیر امواج درونی ناشی از نوسان یک استوانه در یک کانال چینه بندیشده، بر روی انتشار امواج صوتی می-باشد. در این مطالعه ابتدا با استفاده از روش‌های معمول امواج درونی در محیط تشکیل داده شد و با استفاده از فرستنده و گیرنده صوتی تاثیر امواج درونی بر روی انتشار امواج صوتی بررسی شد. همچنین علاوه بر نتایج عملی شبیه سازی با یک نرم افزار انتشار صوتی صورت گرفت که نتایج آن مطابقت خوبی با نتایج آزمایشگاهی داشت. نتایج آزمایشگاهی نشان داد که امواج درونی در حالاتی باعث جمع‌شدگی و پراکندگی پرتوهای امواج صوتی می شود و در حالاتی قدرت سیگنال صوتی تا 54 درصد را کاهش دهد. در محیطهای دریایی نیز به دلیل وجود این امواج تغییرات سیگنال صوتی می تواند رخ دهد.}, keywords_fa = {امواج درونی,انتشار امواج صوتی,جمع شدگی و پراکندگی امواج صوتی,شبیه سازی صوتی}, url = {https://jesphys.ut.ac.ir/article_60299.html}, eprint = {https://jesphys.ut.ac.ir/article_60299_184c7c53ab8801701e199f9ef547f543.pdf} } @article { author = {Oji, Ruhollah and Farajzadeh, M. and Ghavidel Rahimi, Y. and Massah Bavani, A.}, title = {An evaluation of single-site and multi-site statistical downscaling of SDSM–DC in terms of indices of climate extremes (Case study: Midwest of Iran)}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {193-208}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.57734}, abstract = {Two single and multi-site statistical downscaling methods of Statistical Downscaling Model–Decision Centric (SDSM–DC) for daily temperature and precipitation are evaluated at nine stations located in the mountainous region of Iran’s Midwest. SDSM is best described as a single-site model, but it can be extended to multi-site applications via conditional resampling (CR-SDSM, Wilby et al. 2003; Harpham and Wilby 2005). SDSM–DC (Wilby and Dawson 2013) is a hybrid of the stochastic weather generator and transfer function methods. Predictor selection is based on empirical relationships between GCM-scale predictors and single-site predictand variables. (Farajzadeh et al. 2015). Applying SDSM to multi-site daily rainfall downscaling includes two steps: (1) the daily rainfall and temperature at a “marker” site (in this study, the area average amounts) is first downscaled by the single-site SDSM; (2) Daily rainfall amounts are then “resampled from the empirical distribution of area averages, conditional on the large-scale atmospheric forcing and the stochastic error term. The actual daily rainfall is determined by mapping the modeled normal cumulative distribution value onto the observed cumulative distribution of amounts at the marker site” (Wilby et al. 2003; Liu et al. 2013). Ultimately, the marker site rainfall is resampled to the constituent amount falling on the same day from each station in the multi-sites array (Harpham and Wilby 2005). Thus, if the marker series is based on an unweighted average of all sites, the conditional resampling will preserve both the areal average of the marker series and the spatial covariance of the multi-site rainfall (Wilby et al. 2003). Additionally, using area average, instead of individual sites as the marker series, reduces the risk of employing a nonhomogeneous/non-representative record and increases the signal to noise ratio of the predictand (Wilby et al. 2003; Liu et al. 2013). To downscale temperature, the same steps are applied but unconditionally using transfer function methods.For statistical downscaling, two sets of data are generally required: (1) observational data for model calibration and validation, as predictands; and (2) synoptic-scale climate data from GCM and/or reanalysis, as predictors. In order for a better assessment of climate variability and change on local and regional scale, long-term time series of reliable climate data at fine-scale resolution are required (Vincent et al 2002; Mekis and Vincent 2011; Menne et al 2012). As mentioned before, for the Midwest of Iran, we selected nine synoptic stations with nearly complete data coverage for 1981–2010.We used station data from two decades (1981–2000) for calibration and from one decade (2001–2010) for validation of daily values of minimum and maximum temperature, and total daily precipitation. To assess the accuracy and homogeneity of the observational data, we used different methods for quality control: the R packages RHtestsV3 (Wang and Feng 2010) and RHtests_dlyPrcp (Wang et al. 2010), based on penalized maximal t and F tests (Wang et al. 2007; Wang 2008b) that are embedded in a recursive testing algorithm (Wang 2008a); the R package Climatol (Guijarro 2012), which applies a type II linear regression model; and SDSM (Wilby and Dawson 2012, 2013) based on reanalysis predictor variables. Missing values are filled in by using the sequential k-nearest neighbor imputation method (Kim and Yi 2008) and homogeneity tests are applied both before and after infilling to assess infilling performance.Predictor fields are extracted from the National Centers for Environmental Prediction (NCEP) Reanalysis (Kalnay et al. 1996) archives at resolutions of 2.5°×2.5°. As mentioned earlier, SDSM has its own methodology for predictor selection in which EOFs of NCEP reanalysis data over the domain (30° N, 42° E) and (40° N, 52° E) are screened separately for temperature and for precipitation. (Farajzadeh et al. 2015)Results indicated that the methods are of widely varying complexity, with input requirements that range from single point predictors of temperature and precipitation to multivariate synoptic-scale fields. The period 1981-2000 is used for model calibration and 2001–2010 for validation, with performance assessed in terms of 27 Climate Extremes Indices (CLIMDEX). The sensitivity of the methods to large-scale anomalies and their ability to replicate the observed data distribution in the validation period are separately tested for each index by Pearson correlation and Kolmogorov–Smirnov (KS) tests, respectively. Combined tests are used to assess overall model performances. Single (multi)-site method of SDSM, passing 76%(81%), 16%(7%) and 14% (5%) of the Kolmogorov–Smirnov (KS), the Pearson correlation and the combined tests, performed well in terms of temperature and precipitation downscaling. Single-site method performed better than multi-site one at single sites; however, multisite method performance is better at regional downscaling. Correlation tests were passed less frequently than KS tests. Both methods downscaled temperature indices better than precipitation indices. Some indices, notably R20, R25, SDII, CWD, and TNx, were not successfully simulated by any of the methods. Model performance varied widely across the study region.}, keywords = {"Single-site and multi-site downscaling","SDSM","climate extremes","Pearson correlation and Kolmogorov–Smirnov (KS) tests","Iran’s Midwest"}, title_fa = {ارزیابی ریزگردانی تک ایستگاهی و چند ایستگاهی مدل آماری اس‌دی‌اس‌ام با استفاده از شاخص های حدی دما و بارش (مطالعه موردی: غرب میانی ایران)}, abstract_fa = {دو روش تک ایستگاهی و چند ایستگاهی مدل ریزگردانی آماری اس‌دی‌اس‌ام-دی سی به منظور ریزگردانی مقادیر حدی دما و بارش، در 9 ایستگاه سینوپتیک واقع در منطقه کوهستانی غرب میانی ایران طی سالهای آماری 2010-1981 مورد ارزیابی قرار گرفتند. دوره آماری 2000-1981 بمنظور کالیبراسیون مدل و 2010-2001 برای اعتبار سنجی آن، با بکارگیری 27 شاخص حدی اقلیمی، عملکرد مدل را مورد سنجش قرار داد. حساسیت روشها به ناهنجاریهای بزرگ مقیاس جوی و نیز توانمندی آنها در بازنمونه برداری توزیع داده‌های مشاهداتی در دوره اعتبار سنجی، بطور جداگانه برای هر شاخص، به ترتبیب با استفاده از آزمونهای همبستگی پیرسن و کمولوگراف-سیمونوف، مورد آزمون قرار گرفت. بمنظور ارزیابی کلی مدل، از روش ترکیبی استفاده شد. روش ریزگردانی تک ایستگاهی(چند ایستگاهی) با گذراندن به ترتیب 76(81)، 16(7) و 14(5) درصد از آزمونهای کلموگراف-سیمرنف، همبستگی پیرسن و نیز آزمون ترکیبی، نتایج قابل قبولی را ارائه دادند. بنحوی که می توان گفت؛ روش تک ایستگاهی، جهت ریزگردانی مقادیر حدی در هر تک ایستگاه بهتر از روش چند ایستگاهی بوده ولی برای ریزگردانی مقادیر حدی درکل منطقه مورد مطالعه(یعنی در مجموع ایستگاهها)، روش چند ایستگاهی نتایج بهتری را ارائه داد. هر دو روش، شاخص‌های دما را بهتر از شاخص‌های بارش، ریزگردانی کردند. درحالیکه، بعضی از شاخص ها از جمله روزهای دارای بارش بیش از 25 میلی متر، شاخص ساده روزانه بارش، روزهای مرطوب متوالی و حدکثر دمای حداقل با هیچ یک از روشهای فوق به خوبی تولید نشدند. در حالت کلی، عملکرد مدل از ایستگاهی به ایستگاهی دیگر متغیر بود.}, keywords_fa = {"ریزگردانی تک ایستگاهی و چند ایستگاهی","اس‌دی‌اس‌ام","مقادیر حدی اقلیمی","آزمونهای پیرسن و کلموگراف-سیمرنف","غرب میانی ایران"}, url = {https://jesphys.ut.ac.ir/article_57734.html}, eprint = {https://jesphys.ut.ac.ir/article_57734_1e25641f495050f03992ff628b89bce5.pdf} } @article { author = {Mirzaei-Shiri, Rasoul and قادر, سرمد and مزرعه فراهانی, مجید and علی اکبری بیدختی, عباسعلی}, title = {Numerical solution of the shallow water equations using fourth-order compact MacCormack scheme}, journal = {Journal of the Earth and Space Physics}, volume = {43}, number = {1}, pages = {209-228}, year = {2017}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.58911}, abstract = {Shallow water equations are a model to present the behavior of a single-layer fluid with constant density, that the hydrostatic approximation has been applied. These equations for the motion of a dry and inviscid atmosphere with constant density include the momentum and the continuity equations. In addition, the shallow water equations are often used as a testbed to assess the performance of new numerical algorithms.In recent years, the trend toward increasing the accuracy of the numerical simulations of the atmospheric and oceanic motions has increased due to the inherent complexity in these motions. In recent researches, the compact schemes have been noticed because of their remarkable performance in the numerical simulation of fluid flows in other branches of fluid dynamics.This work is devoted to the application of the fourth-order compact MacCormack scheme to numerical solution of the conservative form of the two dimensional shallow water equations. The compact MacCormack method is formulated in form of a two-point scheme. Two versions of the fourth-order compact MacCormack scheme have been introduced and called as 4/2 and 4/4. The first order spatial derivative operators have implicit forms in both schemes (4/2 and 4/4), for one-sided forward and backward operators. The MacCormack scheme uses two time-marching methods: The first is the original two-stage method and the other one is the Runge-Kutta-type (RK2, RK4 and LDDRK4-6) method.In the present work first, we solve a simple linear (advection) equation with an analytical solution, using the second-order and the fourth-order compact MacCormack-type schemes (with the original and the Runge-Kutta time-marching methods) and compare their global errors. The results show that when the fourth-order compact MacCormack schemes with the original time-marching are used, the 4/2 formulation has better results than the 4/4 formulation, but when these schemes use the Runge-Kutta time-marching, the results of the 4/4 formulation are better than those in the 4/2 formulation. According to these results and the magnitude of the global errors, we used four MacCormack-type methods to solve the shallow water equations. The methods are the second-order scheme with the original time-marching, the 4/2 type of fourth order compact scheme with both the original and the RK4 time-marching, and the 4/4 type of fourth order compact scheme with the RK4 time-marching.In the following, we solved the conservative form of the one-dimensional shallow water equations with those four mentioned schemes. The results were compared with a test case with known analytical solution.At last, we solved the conservative form of the two-dimensional shallow water equations. To perform the simulations two well know test cases are used. To assess the numerical accuracy, we estimated conservative quantities such as energy, enstrophy and mass along the simulation process in all time steps. The estimated results indicate that the fourth-order compact MacCormack schemes retain the conservation of these quantities better than the second-order MacCormack scheme. In comparison with the other applied schemes in this work, while the 4/4 formulation with the RK4 time-marching shows more accurate results, the numerical stability condition of this scheme is less than the other schemes. In the second test case, we point out that the computational time of the code for each numerical solution, which utilizes the fourth-order compact schemes, is longer than the computational time of the solution using second-order scheme; but their implementation is reasonable because their numerical accuracy is higher than that of the second-order scheme.}, keywords = {Shallow water equations,Compact MacCormack scheme,Numerical accuracy,Runge-Kutta}, title_fa = {حل عددی معادلات آب کم‌عمق با روش مک‌کورمک فشرده مرتبه چهارم}, abstract_fa = {کار حاضر، به اعمال روش مک‌کورمک فشرده مرتبه چهارم برای حل عددی شکل پایستار معادلات آب کم‌عمق، می‌پردازد. گسسته‌سازی مکانی روش مک‌کورمک فشرده مرتبه چهارم با دو طرحواره به نام‌های 2/4 و 4/4 و پیمایش زمانی این روش نیز، با روش-های اصلی و رونگ-کوتا معرفی می‌شوند. یک معادله ساده خطی، یعنی، معادله فرارفت یک‌بعدی که دارای حل تحلیلی می‌باشد، با استفاده از روش‌های مک‌کورمک مرتبه دوم و مک‌کورمک فشرده مرتبه چهارم با طرحواره‌های 2/4 و 4/4، با پیمایش‌های زمانی اصلی و رونگ-کوتا حل شده و مقادیر خطای کلی آنها، با استفاده از نُرم‌های قدرمطلق، مربع و بی‌نهایت، با یکدیگر مقایسه می‌شود. این مقایسه، برتری روش‌های فشرده مرتبه چهارم را از نظر دقت عددی، نسبت به روش مرتبه دوم نشان می‌دهد. درادامه شکل پایستار این معادلات در حالت دوبعدی و غیرخطی، با استفاده از این روش‌ها، حل شده و نتایج آن نیز برای دو آزمون موردی که توسط محققان دیگر، با روش‌های دیگر، به‌طور عددی حل شده‌اند، مقایسه می‌شود. مقایسه کمی و کیفی نتایج به‌‌دست آمده نشان از عملکرد مناسب روش مک‌کورمک فشرده مرتبه چهارم دارد. همچنین نتایج نشان می‌‌دهند که پیمایش زمانی رونگ-کوتای مرتبه چهارم در طرحواره 4/4 روش مک‌کورمک فشرده مرتبه چهارم، نسبت به بقیه روش‌های اعمال‌شده در این کار، پاسخ‌های مناسب‌تری دارد.}, keywords_fa = {معادلات آب کم‌عمق,روش مک‌کورمک فشرده,دقت عددی,رونگ-کوتا}, url = {https://jesphys.ut.ac.ir/article_58911.html}, eprint = {https://jesphys.ut.ac.ir/article_58911_eae5a90775ac4732862a54cfe30d4388.pdf} }