Institute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18976FAJournal Article19700101The movement of seawater under tidal force is causing periodic changes on the gravity and position (vertical and horizontal location) of points near the sea, which is known as tidal load effect in geometry and gravity spaces. Besides, the crustal deformation due to tidal load is the source of secondary effect to the gravity at the points near the sea due to the mass redistribution of the Earth. In this paper the aforementioned effects are studied under following two categories: (i) Crustal deformation due to tidal load. (ii) The change of gravity due to redistribution of the masses within the Earth. The used technique is the convolution of the ocean tide models with the Green functions of elastic response of the Earth crust. As the case study, the mentioned technique, is applied at 53 points along the Oman Sea and Persian Gulf at the southern coast of Iran, and the maps of co-range and co-phase of the radial deformations at those 53 points for 4 tidal components namely M2, S2, N2, and K2 based on 4 tide models, i.e. CSR4.0, FES99, GOT00.2, NAO99.b, are computed. According to the numerical results at the test points, maximum radial displacement is equal to 11 mm and is associated with the tidal component M2, and the maximum gravity change at the 53 coastal test points is 4 mGal, again due to M2 tidal component.The movement of seawater under tidal force is causing periodic changes on the gravity and position (vertical and horizontal location) of points near the sea, which is known as tidal load effect in geometry and gravity spaces. Besides, the crustal deformation due to tidal load is the source of secondary effect to the gravity at the points near the sea due to the mass redistribution of the Earth. In this paper the aforementioned effects are studied under following two categories: (i) Crustal deformation due to tidal load. (ii) The change of gravity due to redistribution of the masses within the Earth. The used technique is the convolution of the ocean tide models with the Green functions of elastic response of the Earth crust. As the case study, the mentioned technique, is applied at 53 points along the Oman Sea and Persian Gulf at the southern coast of Iran, and the maps of co-range and co-phase of the radial deformations at those 53 points for 4 tidal components namely M2, S2, N2, and K2 based on 4 tide models, i.e. CSR4.0, FES99, GOT00.2, NAO99.b, are computed. According to the numerical results at the test points, maximum radial displacement is equal to 11 mm and is associated with the tidal component M2, and the maximum gravity change at the 53 coastal test points is 4 mGal, again due to M2 tidal component.https://jesphys.ut.ac.ir/article_18976_a116f35070af8dda29fc3a8288492cc9.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18977FAJournal Article19700101It is very important to estimate the velocity model of the earth with seismic data inversion. Inverse theory concerns the problem of making inferences about physical systems from indirect noisy measurements. Information about the noise in the observations is essential to solve any inverse problem, because in the absence of this information it is impossible to say what mode is better. So in the absence of repeated measurements, it is very important to be able to estimate noise component in the data. In practice, however, one seldom has a direct estimate of noise. Here, we use Tikhonov regularization with L-curve method to construct a reference model of the system. Differences between the data predicted for this reference model and the observations represent an initial estimate of the noise. We then use the resulting noise variance estimate to determine optimally truncated singular value decomposition (OTSVD) and solve inverse problem. We use this method with synthetic examples of downhole data.It is very important to estimate the velocity model of the earth with seismic data inversion. Inverse theory concerns the problem of making inferences about physical systems from indirect noisy measurements. Information about the noise in the observations is essential to solve any inverse problem, because in the absence of this information it is impossible to say what mode is better. So in the absence of repeated measurements, it is very important to be able to estimate noise component in the data. In practice, however, one seldom has a direct estimate of noise. Here, we use Tikhonov regularization with L-curve method to construct a reference model of the system. Differences between the data predicted for this reference model and the observations represent an initial estimate of the noise. We then use the resulting noise variance estimate to determine optimally truncated singular value decomposition (OTSVD) and solve inverse problem. We use this method with synthetic examples of downhole data.https://jesphys.ut.ac.ir/article_18977_99ea5d136d2e83f7193567868d0bbb5a.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18978FAJournal Article19700101The Firozabad-Kojour earthquake occurred on May 28, 2004 with an estimated magnitude of Mw=6.2, 60 Km north of Tehran. The main shock was recorded at 145 accelerograph stations which were installed by Building House Research Center (BHRC).
The strong motion records have been used to estimate attenuation of coda wave by using the single back scattering method (Aki, 1975).
The frequency dependence attenuation has been obtained in the Alborz according to four regions introduced by Tchalenko (1974) as follow:
1. Northwest Qc=92×f 1.14
2. Northeast Qc=188×f 0.79
3. Southwest Qc=157.5×f 0.93
4. Southeast Qc=132.5×f 0.87
for recorded stations of main shock and in frequency range of f=1~32Hz respectively, and studied manner changes Q-1 in difference stations and relation of tectonic and seismtectonicThe Firozabad-Kojour earthquake occurred on May 28, 2004 with an estimated magnitude of Mw=6.2, 60 Km north of Tehran. The main shock was recorded at 145 accelerograph stations which were installed by Building House Research Center (BHRC).
The strong motion records have been used to estimate attenuation of coda wave by using the single back scattering method (Aki, 1975).
The frequency dependence attenuation has been obtained in the Alborz according to four regions introduced by Tchalenko (1974) as follow:
1. Northwest Qc=92×f 1.14
2. Northeast Qc=188×f 0.79
3. Southwest Qc=157.5×f 0.93
4. Southeast Qc=132.5×f 0.87
for recorded stations of main shock and in frequency range of f=1~32Hz respectively, and studied manner changes Q-1 in difference stations and relation of tectonic and seismtectonichttps://jesphys.ut.ac.ir/article_18978_0efb5314d77485bd2d100ff35d730482.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18979FAJournal Article19700101In seismic data acquisition, source and receiver array is used for attenuation of surface waves caused by the source. To further attenuate surface waves it necessary to optimize arrays.
One of the ways to optimize source and receiver arrays is spatial convolution. In this method each complex array consists of several simple arrays which make a large array when joined together. By using simple arrays of 2 and 3 elements and putting notch points of these arrays in side lobes of the final response of the array, the side lobes can be reduced.In seismic data acquisition, source and receiver array is used for attenuation of surface waves caused by the source. To further attenuate surface waves it necessary to optimize arrays.
One of the ways to optimize source and receiver arrays is spatial convolution. In this method each complex array consists of several simple arrays which make a large array when joined together. By using simple arrays of 2 and 3 elements and putting notch points of these arrays in side lobes of the final response of the array, the side lobes can be reduced.https://jesphys.ut.ac.ir/article_18979_9588bb02faadc6c6ffcacb116d9dac87.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18980FAJournal Article19700101Spectral induced polarization (SIP) technique is widely used in environmental and engineering geophysical prospecting, as well as mineral exploration, oil, gas and coal exploration. The SIP method can provide measurements of multifrequency complex apparent resistivity at ultra low frequencies,(10-2- 102 Hz), to determine spectral parameters and spatial distributions of buried geologic structures. Since the method measures complex apparent resistivities, it is also called the complex resistivity (CR) method. In the theory of SIP data interpretation, defined as the inversion of three spectral induced polarization parameters (m, and c), the main task in SIP technique is using the Cole- Cole model. This paper shows the application of SIP method to oil and gas exploration on the Dehdasht oil reservoir.
Results showed that the averages of the apparent SIP parameters in the anomalous section are useful for discriminating the source of the anomaly.Spectral induced polarization (SIP) technique is widely used in environmental and engineering geophysical prospecting, as well as mineral exploration, oil, gas and coal exploration. The SIP method can provide measurements of multifrequency complex apparent resistivity at ultra low frequencies,(10-2- 102 Hz), to determine spectral parameters and spatial distributions of buried geologic structures. Since the method measures complex apparent resistivities, it is also called the complex resistivity (CR) method. In the theory of SIP data interpretation, defined as the inversion of three spectral induced polarization parameters (m, and c), the main task in SIP technique is using the Cole- Cole model. This paper shows the application of SIP method to oil and gas exploration on the Dehdasht oil reservoir.
Results showed that the averages of the apparent SIP parameters in the anomalous section are useful for discriminating the source of the anomaly.https://jesphys.ut.ac.ir/article_18980_1d86704644d9018238d8b63c8959dcac.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18981FAJournal Article19700101Magnetotelluric (MT) method is an important passive surface geophysical method which uses the Earth’s natural electromagnetic fields to investigate the electrical resistivity structure of the subsurface. The depth of investigation of MT is much higher than that of other electromagnetic (EM) methods. This paper includes an MT survey on the Inche-Boroon area located in the north of Golestan province, Iran to study subsurface electrical conductivity down to 1300 m.
As a result, two conductive layers were distinguished from 95 to 190 m and 250 to 660 m. These two layers are interpreted as the layers which consist of salt water and probably Iodine constructions.
An exploration borehole is located at 25 km SW of the area. 1D modeling of the MT data on the MT-site closeby the borehole shows reasonably a confirmation of a deep conductor.Magnetotelluric (MT) method is an important passive surface geophysical method which uses the Earth’s natural electromagnetic fields to investigate the electrical resistivity structure of the subsurface. The depth of investigation of MT is much higher than that of other electromagnetic (EM) methods. This paper includes an MT survey on the Inche-Boroon area located in the north of Golestan province, Iran to study subsurface electrical conductivity down to 1300 m.
As a result, two conductive layers were distinguished from 95 to 190 m and 250 to 660 m. These two layers are interpreted as the layers which consist of salt water and probably Iodine constructions.
An exploration borehole is located at 25 km SW of the area. 1D modeling of the MT data on the MT-site closeby the borehole shows reasonably a confirmation of a deep conductor.https://jesphys.ut.ac.ir/article_18981_22d282b435f03aea6e3a22e6be6bbee3.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18982FAJournal Article19700101The goal of this work is to determine the directions of fissures that contain water around the well drilled at a distance of 1930m along the main road to Tochal telecabin. To investigate this problem, a geoelectrical survey was conducted combining dipole-dipole and Schlumberger arrays. At the beginning of the survey, Schlumberger array profile carried out along the road. The electrical tomography obtained from the 2D inversion of the data showed anomaly with low resistivity between 7m to 30m of depth. Then one dipole-dipole array profile overlaying on the Schlumberger array profile crossing the well was carried out. To improve the inverse model using the vertical resolution of Schlumberger array and the horizontal resolution of dipole-dipole array, we performed a joint inversion of Schlumberger and dipole-dipole data. We conclude that the joint inversion improves the resolution of section obtained from each array separately.The goal of this work is to determine the directions of fissures that contain water around the well drilled at a distance of 1930m along the main road to Tochal telecabin. To investigate this problem, a geoelectrical survey was conducted combining dipole-dipole and Schlumberger arrays. At the beginning of the survey, Schlumberger array profile carried out along the road. The electrical tomography obtained from the 2D inversion of the data showed anomaly with low resistivity between 7m to 30m of depth. Then one dipole-dipole array profile overlaying on the Schlumberger array profile crossing the well was carried out. To improve the inverse model using the vertical resolution of Schlumberger array and the horizontal resolution of dipole-dipole array, we performed a joint inversion of Schlumberger and dipole-dipole data. We conclude that the joint inversion improves the resolution of section obtained from each array separately.https://jesphys.ut.ac.ir/article_18982_8187918cf174552f083259b0ff825b00.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18983FAJournal Article19700101The capability of analytic signal to determine the edges and consequently the width of the gravity anomalies is discussed. Several synthetic models are applied and finally we found that this method is suitable for anomalies where the ratio of the depth to width is less than 0/3. Meanwhile the calculated width is usually equal or less than the actual width.The capability of analytic signal to determine the edges and consequently the width of the gravity anomalies is discussed. Several synthetic models are applied and finally we found that this method is suitable for anomalies where the ratio of the depth to width is less than 0/3. Meanwhile the calculated width is usually equal or less than the actual width.https://jesphys.ut.ac.ir/article_18983_de7aba30e6119dba1144632bacce60e5.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18984FAJournal Article19700101The recent satellite missions dedicated to measuring the Earth’s magnetic field have increased the amount of magnetic field data considerably. With the new high quality data, the understanding of the Earth’s magnetic field is improving rapidly and new and better descriptions of the magnetic field models are continuously being developed. The resolution of magnetic field models of the crustal field is now approaching a level, where it becomes possible to use them for geological and geophysical interpretation.
The magnetic crust is that part of the crust that can sustain a magnetic field. Its upper boundary is the bedrock surface, thus it does not include sediments or ice sheets. The lower boundary of the magnetic crust is given the depth to Curie temperature of the crustal rocks. In this paper, it is first explained how satellite magnetic field models are prepared for interpretation. Then the equivalent source magnetic dipole method (ESMD) is introduced and it is explained how we can use it to derive magnetic crustal thickness from the data.The recent satellite missions dedicated to measuring the Earth’s magnetic field have increased the amount of magnetic field data considerably. With the new high quality data, the understanding of the Earth’s magnetic field is improving rapidly and new and better descriptions of the magnetic field models are continuously being developed. The resolution of magnetic field models of the crustal field is now approaching a level, where it becomes possible to use them for geological and geophysical interpretation.
The magnetic crust is that part of the crust that can sustain a magnetic field. Its upper boundary is the bedrock surface, thus it does not include sediments or ice sheets. The lower boundary of the magnetic crust is given the depth to Curie temperature of the crustal rocks. In this paper, it is first explained how satellite magnetic field models are prepared for interpretation. Then the equivalent source magnetic dipole method (ESMD) is introduced and it is explained how we can use it to derive magnetic crustal thickness from the data.https://jesphys.ut.ac.ir/article_18984_2ac99ae9e56969ce0edbb3f870fe1dd2.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18985FAJournal Article19700101The S transform is a type of time-frequency analysis transform composed of some concepts of short time Fourier transforms (STFT) and wavelet transform. To localize time-frequency spectrum in this method, a scalable Gaussian window is used. The scalable Gaussian window provides time-frequency resolution while maintaining a direct relationship with the Fourier spectrum. In this study, after introducing the S transform, generalized S transform is introduced and its application in first arrival time estimation of noisy seismic records is presented.The S transform is a type of time-frequency analysis transform composed of some concepts of short time Fourier transforms (STFT) and wavelet transform. To localize time-frequency spectrum in this method, a scalable Gaussian window is used. The scalable Gaussian window provides time-frequency resolution while maintaining a direct relationship with the Fourier spectrum. In this study, after introducing the S transform, generalized S transform is introduced and its application in first arrival time estimation of noisy seismic records is presented.https://jesphys.ut.ac.ir/article_18985_d5ca8568d019dd3727714fd763ca6230.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18986FAJournal Article19700101Variations in the intensity of solar radiation and solar zenith angle related to the earth's surface during the daytime, night-time and also during a year cause some variations in ionospheric electron densities.
In this study, the effect of solar radiation on the ionospheric F2 layer in one day is studied and the direct relation of ion production with solar variation is proved. Besides, ionospheric variations during a year, that are due to thermospheric circulation and atmospheric composition changes, are studied. Moreover, the relation between the 11 year sunspot cycle and long period variation in the ionosphere is proved.Variations in the intensity of solar radiation and solar zenith angle related to the earth's surface during the daytime, night-time and also during a year cause some variations in ionospheric electron densities.
In this study, the effect of solar radiation on the ionospheric F2 layer in one day is studied and the direct relation of ion production with solar variation is proved. Besides, ionospheric variations during a year, that are due to thermospheric circulation and atmospheric composition changes, are studied. Moreover, the relation between the 11 year sunspot cycle and long period variation in the ionosphere is proved.https://jesphys.ut.ac.ir/article_18986_1bd6a1ec18b9f967e377d253ca1f1459.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X33220070622--18987FAJournal Article19700101This research investigates the evolution of middle-and upper-level fronts in three frontal cyclones. The first case occurred over the northern Mediterranean in February 2005 and the other cases were located over the Middle-East region and Iran during November and December 2004. The version 5 of the meso - scale model (MM5) was run for the all cases, with 75 km × 75 km horizontal resolution. The boundary conditions were determined from the (United States) National Center for Environmental Prediction (NCEP) – National Center for Atmospheric Research (NCAR) reanalysis. Using the model outputs, including wind and temperature fields, the vector frontogenesis was calculated for each grid point in the different levels. Then, the changes in the magnitude and direction of the horizontal potential temperature gradient along the three upper-level fronts were diagnosed. The vector frontogenesis has two rotational and scalar components. The scalar component comprises three terms related to divergence, deformation, and tilting, whereas the rotational component comprises three terms related to vorticity, deformation, and tilting.
Results of the calculations for scalar component of vector frontogenesis show that divergence term is smaller than deformation term in the all cases. Both terms are positive in the first and third cases, leading to frontogenesis, but they caused frontolysis in the second case. Besides, the tilting term leads to frontogenesis in the second and third cases, and is dominated along the front in the region of active frontogenesis. Against, the tilting term is negative in the first case, indicating that the total frontogenesis is primarily a result of the deformation term.
The analysis of the rotational component of vector frontogenesis reveals that the tilting term is negative in the all cases, leading to anticyclonic rotation of the isentropes. The vorticity term is positive and the dominant one in all the cases, coincident with the region of positive vorticity. It results in the cyclonic rotation of the isentropes relative to the mean flow, thereby initiating cold advection along the front. The deformation term is positive (negative) on the upstream (downstream) side of the front.This research investigates the evolution of middle-and upper-level fronts in three frontal cyclones. The first case occurred over the northern Mediterranean in February 2005 and the other cases were located over the Middle-East region and Iran during November and December 2004. The version 5 of the meso - scale model (MM5) was run for the all cases, with 75 km × 75 km horizontal resolution. The boundary conditions were determined from the (United States) National Center for Environmental Prediction (NCEP) – National Center for Atmospheric Research (NCAR) reanalysis. Using the model outputs, including wind and temperature fields, the vector frontogenesis was calculated for each grid point in the different levels. Then, the changes in the magnitude and direction of the horizontal potential temperature gradient along the three upper-level fronts were diagnosed. The vector frontogenesis has two rotational and scalar components. The scalar component comprises three terms related to divergence, deformation, and tilting, whereas the rotational component comprises three terms related to vorticity, deformation, and tilting.
Results of the calculations for scalar component of vector frontogenesis show that divergence term is smaller than deformation term in the all cases. Both terms are positive in the first and third cases, leading to frontogenesis, but they caused frontolysis in the second case. Besides, the tilting term leads to frontogenesis in the second and third cases, and is dominated along the front in the region of active frontogenesis. Against, the tilting term is negative in the first case, indicating that the total frontogenesis is primarily a result of the deformation term.
The analysis of the rotational component of vector frontogenesis reveals that the tilting term is negative in the all cases, leading to anticyclonic rotation of the isentropes. The vorticity term is positive and the dominant one in all the cases, coincident with the region of positive vorticity. It results in the cyclonic rotation of the isentropes relative to the mean flow, thereby initiating cold advection along the front. The deformation term is positive (negative) on the upstream (downstream) side of the front.https://jesphys.ut.ac.ir/article_18987_edafabeb0a67c0e51f1387fe30ae6fdd.pdf