Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Nonstretch NMO by constant NMO correction (CNMO)
1
1
FA
حسام شینی
کیماسی
17459173
عبدالرحیم
جواهریان
86664512
ابوالفضل
مسلمی
28112876
The application of traditional NMO-correction techniques in the processing of seismic data may result in severe distortion. This distortion is observed as a decrease in frequency content (NMO stretch). This may be seen as the source of problems in the processing with stretch. In this paper, CNMO method is applied which doesn't have the `stretching effects' of conventional NMO correction. Unlike conventional NMO, the technique implies constant normal moveout (CNMO) for a finite time interval of a seismic trace. The benefits of the CNMO method in relation to the traditional NMO method include preservation of higher frequencies and reduction of spectral distortions at far offsets. The need for severe muting after the correction is reduced, allowing longer spreads for CMP stack. The CNMO technique has been tested on synthetic and real data. The method may improve the resolution of CMP stack. The only assumption for this stretch-free NMO correction is that all time samples of a reflected wavelet at a particular offset have the same normal moveout
Correction,NMO,NMO stretch,Constant normal moveout (CNMO),Far offsets,CMP stack
https://jesphys.ut.ac.ir/article_19304.html
https://jesphys.ut.ac.ir/article_19304_213f600f5cc5bbe4380693d3d656ec03.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Sensitivity analysis of the GRACE in single satellite mode
1
1
FA
علیرضا آزموده
اردلان
76831981
حسن هاشمی
فراهانی
59353779
یکی از مطالعات ضروری در گرانیسنجی ماهوارهای، " تجزیه و تحلیل طیفی" یا "تجزیه و تحلیل حساسیت" مشاهدات ماهواره نسبت به <br /> طیفهای متفاوت میدان پتانسیل جاذبة زمین است. در این مقاله یک روش آماری برای تجزیه و تحلیل حساسیت ماهوارههای گرانیسنجی در ساختار HL-SST پیشنهاد و برای ماهوارة گرانیسنجی GRACE-1 برحسب مشاهدة از نوع پتانسیل جاذبه از طریق "فن انتگرال انرژی" <br /> با استفاده از 345 روز مشاهدات جاذبی این ماهواره در سال 2004 بهکار برده شده است. با در نظر گرفتن بسط مشاهدات به هارمونیکهای <br /> کروی نرمالیزه تا درجه و مرتبة ، 486743 معادلة مشاهدة خطی برای محاسبة 3721 ضریب هارمونیک کروی نرمالیزه تا <br /> درجه و مرتبة یاد شده در نظر گرفته شد و بر اساس آن ماتریس ضرایب این معادلات (A) و ماتریس وزن مشاهدات (P) تشکیل شد و به <br /> کمک آنها، ماتریس کوواریانس مجهولات با 483022 درجة آزادی برآورد شد. مدل ژئوپتانسیلی EGM96 به مثابه <br /> جامعة آماری و شاخصی برای اندازة ضرایب هارمونیک کروی نرمالیزه در نظر گرفته میشود، و برای تشخیص ضرایبی که ماهوارة <br /> گرانیسنجی به آنها حساس نیست، از طریق آزمون آماری میانگین، مورد استفاده قرار گرفته است. بهکارگیری فن یاد شده برای تک <br /> ماهوارة گرانیسنجی GRACE-1، درجه و مرتبة را درحکم حداکثر درجه و مرتبة بسط هارمونیکهای کروی قابل برآورد با این ماهواره مشخص کرد.
1,Grace,Satellite gravimetry,Sensitivity analysis,Energy integral,Spherical harmonics,Geopotential model
https://jesphys.ut.ac.ir/article_19305.html
https://jesphys.ut.ac.ir/article_19305_565574986a87e71b0a0d4de9c56d706b.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Focal mechanism determination of Zarand Dahyiue earthquake by amplitude spectra and polarity
1
1
FA
محمدرضا
حاتمی
mrhatami@ut.ac.ir
مهرداد
پاکزاد
11356286
نصراله
کمالیان
12169317
نوربخش
میرزایی
62218992
Using amplitude spectra and polarity (ASPO) is a way for determining focal mechanisms of earthquakes. In the paper, the method has been used to determine the focal mechanism of Zarand Dahuiye earthquake dated 22 February 2005. The method uses frequency-wave number approach for calculating Green functions and inverts full waveforms (from P arrival time up to the end of surface waves). At first strike, dip and rake is determined by grid search for different depths, then the optimum solution is chosen according to the minimum of the error values. At the end, correct rake angle is determined by at least one polarity. The input seismograms are from broad band stations of the International Institute of Earthquake Engineering and Seismology (IIEES). The epicentral distances of stations used are from about 91 to 459 km and applied frequency band pass is 0.01-0.08 Hz. In this study the best fit is resulted at depths from 4 to 5 km and the optimum focal mechanism found is 226, 38 and 106, respectively for strike, dip and rake. The results are compared with independent focal mechanism determination for the earthquake.
Focal mechanism,Zarand Dahyiue,ASPO
https://jesphys.ut.ac.ir/article_19306.html
https://jesphys.ut.ac.ir/article_19306_d22d6f3c4405dea2c5daf4b5225524fa.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Determination of improved velocity model for the north west Iran region, using simultaneous inversion of local earthquake travel times
1
1
FA
اسماعیل
بایرامنژاد
ebayram@ut.ac.ir
محمود
میرزایی
13658147
محمدرضا
قیطانچی
57329365
Earthquakes travel times inversion for determination of velocity structure of crust is one of the most important objectives in seismology. In the simultaneous inversion method, the parameters of earthquakes and velocity model are determined initially and are improved during inversion steps. <br />In this study, we have used more than 22000 calculated travel times for first arrivals of 6000 earthquakes, which occurred in north west Iran (bounded 36°N-40°N & 44°E-50°E) to estimate P wave velocities and thickness of the crust in this region. This information has been used to determine several initial models. First, we selected 181 events with magnitudes 4 or above that were well located. Then, the simultaneous inversion method was used to obtain the best initial and final improved model. The obtained model was tested again with the travel times of 2940 earthquakes with magnitudes greater than 2.5 in six independent sets. The results were in good agreement, specially for depths greater than 8 km. The results show two low velocity shallow layers with thicknesses of 3 km and 2 km and with a corresponding average velocity of 4.8 and 5.4 km.s-1 for P wave. Also, a sharp change of velocity was detected in depth 23 km, where the P wave velocity increased from 6.1 km.s-1 to 6.6 km.s-1. The depth of Moho was found to be 45 km while the P wave velocity in the upper mantle was evaluated <br />at 8.0 km.s-1.
https://jesphys.ut.ac.ir/article_19307.html
https://jesphys.ut.ac.ir/article_19307_15d0a35f4d15c7f707435a92ac8277e5.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Interpretation of aeromagnetic data in the Khorramabad region using improved integrated Analytic signal and Euler
1
1
FA
محسن
اویسیمؤخر
41362697
وحید
قاسمی
25375455
حسین شاهنظری
اول
55165393
In this paper, an improved method (Improved AN-EUL) is presented. This method is based on the combination of the analytical signal and the Euler deconvolution method. Two important parameters such as location and approximate geometry of a magnetic source can be obtained using the conventional AN-EUL method. Altitude of ground and height in upward continuation has been considered for depth determination. Due to the intrinsic nature of the magnetic data, the analytic signal curve of an anomaly is not exactly above the anomaly. Therefore, the previous AN-EUL method cannot give a good estimation of depth and structural index of an anomaly. In this method, reduction to pole filter is applied on the data before the analytic signal filter application. Then, the problem of curve displacement of an anomaly is prevented. <br />This method is applied on the airborne magnetic data of the Khorramabad area.
https://jesphys.ut.ac.ir/article_19308.html
https://jesphys.ut.ac.ir/article_19308_d6d2eb7385473eb6e0eb84cb8e5e4e6c.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
31 March 2006 Darbe Astaneh Silakhor earthquake, focal mechanism determination
1
1
FA
مهرداد
پاکزاد
11356286
نوربخش
میرزایی
62218992
One of the methods for the determination of focal mechanisms of earthquakes is the linear inversion of moment tensor in time domain. That method is used here for determining of the focal mechanisms the Darbe Astaneh Silakhor earthquake of 31 March 2006 and two of its foreshocks and six aftershocks with local magnitude more than 4. The data of six broadband stations of the International Institute of Earthquake Engineering (IIEES) in epicentral distances less than 375 km are used. The focal mechanism obtained for the main shock is strike slip right lateral. The location of the main shock and the aftershocks and focal mechanisms show the Doroud fault as the cause of the earthquake. The variations of focal mechanisms of six aftershocks primarily indicate the local change in faulting and secondly the location of the aftershock with mainly normal mechanism can suggest the activity of the Qaleh Hatam fault. In this paper the main focus is on the main shock. Its centroid is obtained and the effect of frequency range in focal mechanism is studied by the inversion in nine small frequency bands and the optimum focal mechanism is found. Rupture length is also calculated. The uncertainty analysis confirms the acquired solutions.
Focal mechanism,Silakhor earthquake,Darbe Astaneh,ISOLA
https://jesphys.ut.ac.ir/article_19309.html
https://jesphys.ut.ac.ir/article_19309_9e3f57d3a5861be0cfb18d09b8897702.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
An experimental study of turbulent mixing near a density interface
1
1
FA
عباسعلی
علیاکبریبیدختی
32845411
فاطمه
مالکیفرد
91925475
مسعود
خوشسیما
16921215
The entrainment of a stably stratified layer into a turbulent mixed layer in a confined region has been studied in the laboratory for different Richardson numbers, Ri. The results include direct observation of turbulent characteristics and density measurements using two high precision salinity meters. The measurements include turbulence intensity, scale of eddies near the interface and energy spectrum of turbulence. For the step density profile we found a Ri-1 dependence for entrainment speed which is in accordance with the result of others. This changes to Ri-1.3 when the bottom layer has a linear density profile. In this case the internal waves generated at the interface propagate into the stratified fluid that may influence the entrainment process. In these experiments we find that the modal structure of these waves appears to interact with the turbulence processes near the interface creating a non-uniform entrainment rate usually in steps. This may be related to the vertical wave number of the dominant wave which is dependent on the depth of the stratified layer as well as the horizontal cross section of the tank. These are effects that have been considered for the first time here.
turbulence,Richardson number,instability,Stably stratified fluid,Entrainment
https://jesphys.ut.ac.ir/article_19310.html
https://jesphys.ut.ac.ir/article_19310_d9f058667ebdbaea14d349de11f91fc0.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Total ozone variation and the effect of SO2 on the total ozone values measured by the Dobson instrument at the Institute of Geophysics of the University of Tehran
1
1
FA
زهرا
شرعیپور
38283637
مجید مزرعه
فراهانی
43966463
It has been proved that pollutant gases have a remarkable effect on the amount of total ozone measurements by the Dobson instrument. Among these gases SO2 and NO2 are the most influential pollutants on the ozone and have attracted the attention of scientists. <br />In this study we make a general survey of the total ozone in the 4 year period, 2002-2005 measured in the Institute of Geophysics of the University of Tehran by the Dobson instrument D109. <br />A correlational study has also been made using SO2 pollutant values and unrefined total ozone data. The results show that the SO2 makes a fluctuation on the total ozone magnitude and this varies between 0.2% -1.4% in winter and 0.1% - 0.7% in summer. It has also been found that Maximum variability of ozone value happens in winter and early spring. The Maximum value in the spring is experiencing a moderate growth. The largest value of monthly averaged total ozone happened in 2005 and the least value is for 2003 in our data. <br />A comparative study between the Dobson unit and satellite data reveals that the differences between these two groups of data have decreased in recent years.
Total ozone,SO2 pollutant,Correction of SO2 pollutant,Dobson instrument
https://jesphys.ut.ac.ir/article_19311.html
https://jesphys.ut.ac.ir/article_19311_0687e22de2b1e3871cec8652379afb21.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Investigation of Rossby and inertia gravity waves based on proper orthogonal decomposition (POD) in beta plain
1
1
FA
خسرو
اشرفی
83334455
وحید
اصفهانیان
51632678
In the present work properties of Rossby and inertia gravity waves are investigated based on proper orthogonal decomposition (POD) functions. The POD functions are constructed using analytical, experimental or numerical data recorded as snapshots. The POD basis can be carried out to make a reduced order model by Galerkin projection of governing equations onto these functions. In this paper, the analytical solutions of Rossby and inertia gravity waves obtained from linearized shallow water equations (SWEs) are applied to form the POD basis. In order to analyse Rossby and gravity waves based on POD functions, the linearized SWEs are projected onto the POD basis and as a result the partial differential equations are converted to few ordinary differential equations. This reduced order model makes a framework to study the behaviour of Rossby and gravity waves. It was discovered that, in order to capture the dynamics of a Rossby wave 2 POD modes are needed, whereas to capture an inertia gravity wave, 4 POD modes are required. Furthermore, one can predict one Rossby wave accurately up to 120 h using a reduced order model formed by 100 recorded snapshots during 5 h or 24 h of beginning of integration time. However, to predict an inertia gravity wave accurately up to 96 h, 400 snapshots during 0.1 h are needed.
https://jesphys.ut.ac.ir/article_19312.html
https://jesphys.ut.ac.ir/article_19312_3f8c489c5f845c1805e5d87cce0f1d8f.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
Determining the synoptic pattern of autumn heavy and extreme precipitations on the southern coast of the Caspian Sea
1
1
FA
عباس
مفیدی
47547985
آذر
زرّین
73865724
غلامرضا جانباز
قبادی
62955198
In order to determine the synoptic pattern of heavy and extreme precipitations on the southern coast of the Caspian Sea, precipitation characteristics of the Caspian region were investigated by the use of eight synoptic stations data. Considering the percentage thresholds, the days with heavy and extreme precipitations were determined for a 10 year period (1994-2003). Since more than 75% of days with heavy precipitation were concentrated in autumn, the threshold of 10% of autumn precipitation values (52.8mm) were considered and 28 days with heavy precipitation were determined in the 10 year period. The 6-hour and daily mean NCEP/NCAR 2.5×2.5 reanalysis data of pressure, vertical velocity, specific humidity and zonal and meridional wind components at different levels and outgoing longwave radiation(OLR) from two days before of precipitation days were employed. <br />The results revealed that all the heavy and extreme precipitations of the southern coast of the Caspian Sea can be classified into three main patterns including High pressure, Low pressure and Coupling. 16 days (57.1%) out of 28 days with heavy precipitation were the result of the existence of high pressure pattern and negative vorticity related to the influence of a high pressure tongue on the southern coast of the Caspian Sea. In contrast, there were only 6 days (21.4%) with low pressure pattern. 6 days with heavy (21.4%) precipitations belonged to the coupling pattern which included a high pressure center over the west-northwest of the Caspian Sea and a low pressure center over the east of it. The southern half of the Caspian Sea has mainly negative vorticity due to the influence of anticyclonic circulation in this pattern, However, the precipitation was the result of convergence of cyclonic and anticyclonic flows over the Caspian Sea. <br />The results indicated that the main mechanism of precipitations was the local convection occurrence at the southern extremity of the Caspian Sea in both high pressure and coupling patterns, whereas, the existence of a Cyclone was the main mechanism of precipitation in Low pressure pattern. However, the maximum ascend (highest negative omega) in both High Pressure and Coupling patterns occurs in the lower troposphere, while in Low Pressure pattern it occurs in a thick layer in mid-troposphere. The existence of a high pressure center over the west of the Caspian Sea and a negative vorticity over the sea at lower levels, associated with the strong and prevailing north-south flows are the main factors causing heavy and extreme autumn precipitation in all synoptic patterns.
https://jesphys.ut.ac.ir/article_19313.html
https://jesphys.ut.ac.ir/article_19313_7d3a5ea74b658c7ff81780959ca017c9.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
2-D Euler de-convolution through DST of gravity data
1
1
FA
وحید ابراهیمزاده
اردستانی
25239262
The Different Similarity Transformation (DST) technique (Stavrev, 1997) utilizes a powerful and fully automatic tool for depth estimation of a point source through Euler de-convolution. Stavrev (1997) showed the results for the magnetic data of simple 2-D sources and aeromagnetic data along profiles. We apply the technique for the gravity data of 2-D rectangular models and real gravity data which has not been considered by Stavrev (1997).
Convolution,Gravity,depth estimation,Euler de
https://jesphys.ut.ac.ir/article_19314.html
https://jesphys.ut.ac.ir/article_19314_1dbe7eda1a2758ba583f386fbfa90694.pdf
Institute of Geophysics, University of Tehran
Journal of the Earth and Space Physics
2538-371X
2538-3906
33
3
2007
10
23
3-Dimensional upper mantle velocity structure for Iranian Plateau revealed by Pn and Sn tomography
1
1
FA
شادی طباطبایی
میر
95627944
اریک
برگمن
61717333
محمدرضا
قیطانچی
57329365
Studying crustal and upper mantel structures has been limited in the Iranian Plateau and there has been little work done in this field. In this paper we have a primary motive to map Pn and Sn velocities beneath most of the Iranian Plateau in order to test 3-D mantle models and to develop and test a method to produce Pn and Sn travel time correction surfaces that are the 3-D analogue of travel time curves for a 1-D model. To the new data set that we have relocated using HDC method which we have published in another paper; we apply the tomographic method of Barmin et al., augmented to include station and event corrections and an epicentral distance correction. The Pn and Sn maps are estimated on a 2o x 2o grid thoughout the Iranian Plateau. We define the phases Pn and Sn as arriving between epicentral distances of 3o and 15o. After selection, the resulting data set consists of 42,368 Pn and 10,897 Sn travel times distributed in-homogeneously across the Iranian Plateau. We used CRUST 5.1 as the starting Model. The Pn and Sn maps compare favorably with recent 3-D models of P and S in the uppermost mantle. The RMS misfit to the entire Iranian data set from the Pn and Sn model increases nearly linearly with distance and averages about 1.5 s for Pn and 3.1 s for Sn. Comparing with the starting model we have a better detail map of the region. Getting the vertical velocity derivative right may be more important in predicting regional travel times than mapping lateral variations. Recent models are providing new information about the vertical velocity gradient in the uppermost mantle which controls the depth of penetration. Further research remains to determine if these results improve regional location capabilities.
Iranian plateau,Crustal velocity model,upper mantle,Tomography,Pn and Sn velocities
https://jesphys.ut.ac.ir/article_19315.html
https://jesphys.ut.ac.ir/article_19315_88fb838e2d462abf2ec902b590939cac.pdf