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محمدعلى
ریاحى
author
فرهاد
عبدالهى
author
text
article
2003
per
In this paper, an attempt was made to calculate normalized depth of investigation characteristics (NDIC) for the CRP array. For this purpose the concept of depth of investigation in a homogeneous anisotropic half-space with inclined stratification was investigated. The potential difference distribution function for this case was derived and then used for calculation of NDIC in two and three dimensions using the Gauss-Legendre integration method. A computer code was developed to model a homogeneous anisotropic half-space with varying parameters such as coefficient of anisotropy, stratification dip, orientation, spacing of the array and depth of layers. Using this code, the calculations of required parameters were carried out for different models, and accurate results were obtained. In this step, the maximum depth was calculated for stratification dip between 0 and 17 degrees. Then NDIC values were drawn against relative depth of investigation, and maximum value of NDIC was obtained. The depth of investigation decreases with increase of anisotropy and increases with increase of the dip of layers. To test the obtained results for the NDIC study, pseudo sections of electrical receptivity data obtained from the CRP measurement at Behesht Abad dam site were used and improved
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10836_56fd592c4235f21d0c8a04e12d81707f.pdf
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محمدعلى
ریاحى
author
رضا
نظریان
author
text
article
2003
per
In this paper reflection data obtained from a seismic line located in the south of Gheshm Island in the Persian Gulf region were processed. Seismic section showed weak amplitudes for deeper reflectors due to energy decay of reflections. To retrieve the weak amplitudes to their true values, the AVO attributes were applied. For this purpose, CDP angle gathers in the incident angle domain were performed. To suppress multiples and noises with high amplitudes, mute windows with different incident angles in the x-t domain were applied. Mute windows with the angles between30 and 35 degrees resulted considerable effects on the noise elimination. To study the amplitude variations versus offset, the AVO gradient section of reflection data was performed. In this stage a negative gradient anomaly was determined in the middle part (1600 — 1800 ms TWT) of the seismic section. The mentioned anomaly with due attention to the geological information was attributed to a gas reservoir. In this study, application of the AVO attributes on seismic data showed that, amplitude due to energy decay that was not present on the routine seismic section could be simulated.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10837_19bd648c145eb14bfcdf979a3624d9ed.pdf
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عبدالرحیم
جواهریان
author
احمد
سدیدخوى
author
مصطفى نقى
زاده
author
مازیار
حقیقى
author
text
article
2003
per
Remote yield estimation of the underground nuclear explosions is possible by the inspection of different seismic phases. In order to estimate unknown yields, it is necessary to obtain relationships between seismic parameters and known yields of underground nuclear explosions. In this regard, the most important seismic parameters are the amplitude, body wave and surface wave magnitudes. Since the Pakistan nuclear explosion of May 28, 1998, was the first explosion in this country, there was not any relevant information. Therefore, to estimate the yield of the Pakistan explosion we need to find the necessary relationships. In Iran, only Iranian Long Period Array (ILPA) has recorded the Pakistan explosion. The methodology we used here is first to derive several relationships for Semipalatinsk Test Site (STS) east Kazakhstan, and then to employ these relationships for estimating the yield of Pakistan explosion. In this paper, different methods have been used to derive relationships between the recorded seismic parameters by the seismograms at ILPA and the known yields of STS. These methods include: the amplitude of P-wave with a period of one second, the body wave magnitude, mb, the surface wave (Rayleigh) magnitude in the time domain and in the frequency domain, Mf. The derived equations are as follows:
log(Y)=1.21 log(A)+ 2.80
mb = 1.05 log(Y)± 3.90
Mst=0.69 log (Y)+2.36
Msf= 0.80 log (Y) + 2.68
where, A is the amplitude of P-wave in micron and Y is the yield in kilotons TNT. Using above equations. the yield of Pakistan nuclear explosion has been estimated for five possible media which may affect the explosion test sites. These media were dry alluvium, water saturated alluvium, tuff, salt and granite. The yield average of this explosion is estimated to be 14 kt TNT with an error of± 20%.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10838_27ab38b9047a40b4b6ea9fceb427fc70.pdf
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غلام جوان
دولویى
author
text
article
2003
per
Teleseismic waveform modeling based on receiver function analysis is becoming a common method of examining crust and uppermost mantle structure. The purpose of this paper is to discuss and investigate the shear wave splitting and to calculate the orientation and degree of anisotropy using teleseismic P-waveform receiver functions. In addition to analytical calculations, the geological aspects of the anisotropic material within the crust and upper mantle are briefly discussed. Finally, the particle motion monitoring technique is applied to Ps converted phases that were recorded at the MAIO station. The result of this investigation would suggest N17°E orientation for the fast motion of shear wave in crustal structure of Mashhad (the center of Khorasan in the northeastern part of Iran) area.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10839_210e738a0736d94d2b395583ed802f27.pdf
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علیر ضا صادقى
حسینى
author
آتوسا فر دوسیان نجف
آبادى
author
text
article
2003
per
Despite many successes in the field of freezing nucleation during the last two decades, there are still uncertainties and questions that have been of special interest to cloud physicists. Due to the wide variety of nucleation processes, most of the concepts expressed to describe the subject, could not bring forward comprehensive explanations. Using cold plate and fishing line apparatus, the immersion freezing nucleation rates of some natural materials such as, distilled water, smog, clay and leaf would have been studied. The seeding efficiency of natural material solutions have been studied through spraying them over the drops of distilled water suspended on the fishing line. The experimental results confirm the time-temperature dependence of freezing rate due to heterogeneous nucleation. They also show that a good cloud seeding agent can be easily produced from bacterial biogenetic nuclei as effective nucleation materials. By deduction the effect of contact freezing, the biogenetic nuclei are found to have maximum activity at -5°C and their seeding efficiency is about 80% at -9°C. These results are more acceptable than those of mineral substances such as Silver Iodide. The performance of these experiments in a clean weather or the use of the bacteria incubation method, leads to more accurate and reliable results. Performing such low-cost experiments, not only could bring out a better understanding of the freezing nucleation process, but it is also possible to decrease the expences of cloud seeding projects as well as the dangers of airplane accidents inside the clouds.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10840_d50b5f36b549516bc699c72c46daa7ba.pdf
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مهدى
رضاپور
author
text
article
2003
per
To record the local earthquakes, Tehran digital seismic network comprises 12 three-component seismic stations installed in southern margin of Alborz. This array started its operation in January 1995. In the central office of this array the extracted data after processing of recorded waveforms are archived similar to other seismological centers. The archived database contains information on date of shocks, origin time, location coordinates, magnitude as well as station information such as epicentral distance and amplitude of measured P-wave. In this article, the completeness of database and the bias in the magnitude values which have been determined in this array are investigated. Investigation of database showed that some essential station information such as epicentral distance and amplitude of measured phase, which are necessary for magnitude determination, have not been completely stored in database especially in the period of 1997 to 2000. Therefore, recovering these parameters for any purpose requires analyzing waveform data. Investigation of archived magnitude values showed that magnitude values in the database have not been calculated by using a single formula or a specific method. Comparison of magnitude values in database with those values that have been published in ISC and NEIC Bulletins shows that in Tehran network, magnitude values are underestimated. By using local magnitude values and corresponding mt’ values, ML scale is calibrated to mb scale and the formula ML = log(V / 4r) + 2.5 log(A) — 1.8 is derived. For distances grater than 106 km, using this formula gives a better estimate for the magnitude of earthquake in comparison with the formula that currently is being used in this array.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10841_a7c9206a79f3bf38de1b66955316ead9.pdf
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فرهنگ احمدى
کبری
author
محمدعلى
نصراصفهانى.
author
text
article
2003
per
A mean diagnostics analysis for a period of one year (July 2001-July 2002) of Mediterranean cyclones and their impacts on the Middle East weather is carried out. The diagnostic tools used in this study are the monthly mean geopotential height and relative vorticity at 850 and 500 hPa as well as the monthly mean 1000-850 hPa thickness. In addition, using an objective method about 30 cyclones were identified that occurred in the Mediterranean region during the period of one year. The characteristics of each cyclone, such as duration, intensity, path, source region and its dynamic were examined. The results show that the strength and the number of cyclones in the whole Mediterranean region are significantly decreased during the period of early June until the end of September, largely due to the movement of the subtropical high to the higher latitudes. Also, the Persian Gulf pressure trough, which is an extension of the southwest Asia monsoon, acts to weaken the intensity of cyclones and slow down their eastward movement in the eastern Mediterranean region. During early October until the end of January, as the effect of subtropical high is weaken in the northern Mediterranean, cyclogenesis activity increases over the Aegean Sea and the Gulf of Genoa. Since these cyclones move northwards, their effects are rather weak in the Middle East weather. From February to May, the cyclonic occurrences in the northern Africa increase, mainly due to the strong temperature gradient between the North Africa coast and the southern Mediterranean. As these cyclones move over the Saudi Arabia and the Red Sea, the Middle East weather is affected.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10842_ae6171f242cb2475b81f532d7c6dacc3.pdf
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مجید مزرعه لی
فراهانى
author
محمد على
ئقفى
author
text
article
2003
per
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10843_29865b1d20cf113c79595e1308ea2f73.pdf
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محمدرضا
قیطانچى
author
اسماعیل بایرام
نژاد
author
احمد سدید
خوی
author
text
article
2003
per
Northwest Iran is one of seismically active regions in Iranian plateau and has experienced many destructive earthquakes in the past centuries. Since 1996, the Institute of Geophysics, University of Tehran has deployed a telemetric seismic network in northwest Iran. The main purpose of the network is the acquisition of seismic data originated in a set of eight remote seismological stations, and investigation of the origin of processes that cause earthquakes in this region. The data is transmitted from each remote station through telemetric link to a central station located at Fatabad near Tabriz city where all the information is processed. In this paper, an overview of the northwest seismological network in Iran is presented and the instrument response is calculated by applying a synthetic signal (sine wave) which consists of different frequencies with uniform amplitude (unit volt) to the system as input. The new seismological network has been oriented towards forecasting and warning capabilities concerning earthquakes. It is to study the spatial and temporal seismic distribution to identify seismogenic sources, its mechanism and geometry; and to create public awareness about the causes, effects and mitigation of natural hazards.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
29
v.
2
no.
2003
https://jesphys.ut.ac.ir/article_10844_d3aed2b9401818ffe622e31b0b75abd6.pdf