جستجوی مقالات مرتبط با کلیدواژه « tomography » در نشریات گروه « علوم پایه »

The Iranian Plateau is a part of the Alpine–Himalayan orogenic belt located in the western part of Asia. Convergence of the Arabian Plate and Eurasia from the late Cretaceous to the present has generated significant lithospheric deformations such as crustal shortening and thickening in the Plateau and surrounding mountain ranges including the Zagros Fold–Thrust Belt, Alborz and Kopeh Dagh. The convergence across Zagros is accommodated through different mechanisms of diffused shortening and/or thrusting of the Arabian lithosphere beneath Central Iran. This study focuses on the velocity structure of the eastern part of the Iranian Plateau which has not been studied well yet. Our study region also contains Binalud and Kopeh-Dagh deformation domains which were built up by the north-eastern collisional boundary between the Plateau and Eurasia and a small part of the Urumieh-Dokhtar magmatic arc which was the volcanic arc of the past Neotethyan subduction. The lithosphere-asthenosphere system beneath east of Iran is investigated by employing earthquake surface wave tomography. A total of 5862 teleseismic Rayleigh waveforms from 368 events recorded at three permanent networks during a period of three years were used to produce 2-D high-resolution phase velocity maps. We employed a two-plane wave tomography approach to generate phase velocity maps at period ranges of 25–111 s. From a published study of ambient noise tomography, we extracted Rayleigh wave dispersion data at 8–20 s periods to improve resolution in the crust and then inverted them for a 3-D S-wave velocity model. A 3-D velocity model was then constructed by a nonlinear Bayesian Markov chain Monte-Carlo algorithm of local node-wise dispersion data into S-wave velocity models down to a depth of 200 km. The most prominent resolved feature by our 3-D velocity model is a low-velocity asthenospheric channel at 70 and 150 km depths overlaid by a thin lithosphere. We believe that in the lack of an isostatic compensated crustal root in the Iranian Plateau, this feature is supporting high elevation (~1000 m) topography covering the Iranian Plateau. A Moho map for the study region is obtained by mapping the geometry of 4.0 km/s S-wave velocity contour in the 3-D velocity model. It shows that most of the study region is covered by a less deformed crust with a thickness of ~36 km. Two crustal roots are observed, one beneath the Urumieh-Dokhtar magmatic arc and the other beneath the north-eastern part of the study region where an array of the Neotethys suture zones is marked by ophiolite outcrops. Lithospheric scale deformation in a sequence of Neotethys suture zones is high probably responsible for the crustal thickening in NE Iran.

Seismic methods are common techniques that are used in the fields of engineering and exploration. In seismic refraction method the aim is to measure travel times of P-waves from the shot point to the geophones, which are located at known points on the surface. In this method, the first wave arrivals are used to produce time-distance plots, which are then used in the calculation of the depths of refracting interfaces and compressional wave velocity with respect to depth. After gathering and preprocessing of seismic data, the inversion stage is performed to estimate model parameters. Similar to other kind of geophysical data, the inversion of seismic data is also faced to non-uniqueness challenge. In this study to tackle the non-uniqueness of seismic data inversion, a method based on artificial intelligence is proposed. Creating a neural network with the highest possible performance and decreasing the risk and level of error is a major goal in this regard. A large amount of effort is usually spent on fine tuning the network to make sure it provides the best results.However, a single classification or regression model can hardly produce the best results for every sub-section of a complex problem space. Creating multiple neural networks (or any other machine learning model) and combining the results of those networks could potentially improve the performance and decrease the risk and level of error.

In order to perform the inversion of travel times of seismic refracted waves using artificial neural networks, different synthetic models having different thicknesses and P-wave velocities were produced for the purpose of training the neural networks. Moreover, 20% of generated data (synthetic models) were considered as test (unseen) data for evaluation of the proposed inversion method. Many networks with different structures were tested using cross- correlation method (i.e. K-fold method). Then, networks with better performance or lower prediction error were selected. This is equal to assigning larger weights to better performing networks while assigning very small weights to those with large errors. Then, the output results of the individual networks were combined using linear averaging method. Finally, the proposed inversion algorithm was run on an actual dataset. In order to further investigate the proposed neural network based inversion algorithm, the actual dataset was additionally inverted using tomography method. The results of the two methods were then compared.

In this study, a new inversion algorithm based on artificial intelligence is introduced. Then, the capability of the proposed inversion algorithm was evaluated using a test data and an actual dataset. The results show that the applied method is a fast and powerful technique in automatic inversion of seismic refraction data. Furthermore, the performance of the applied inversion algorithm was compared with tomography inversion method. The results show that the introduced inversion algorithm, which is based on neural networks, is capable of automatically estimating model parameters, including the number of layers, thicknesses and P-wave velocities of the layers without having auxiliary data. Furthermore, the inversion of the experimental data using the proposed inversion algorithm resulted in a two-layer model, which had a good correlation with the geological and seismic evidence of the study area. The models produced from the inversion of the synthetic MT data and the Bushli MT field data set using the adaptive regularization, MGCV, and ACB methods are almost similar. The constructed model from using adaptive regularization is slightly better than the model obtained from MGCV and ACB methods. therefore, with respect to the results obtained from 2D inversion of the synthetic MT data and the Bushli (Nir) MT field data, the adaptive regularization metho provides a more accurate solution especially in estimating the conductive layer and reservoir boundaries. In addition, this method, compared to the MGCV and ACB methods, is faster and requires less memory in the inversion process. Hence, this method can be considered as the most reliable method for selection of the optimal regularization parameter in the inversion of large 2D and 3D magnetotelluric data sets.

Tabriz city with 1.6 m population is located in the NW Iran. Estimation of empirical attenuation relations for the region is a key for realistic seismic hazard assessments. Recently, Motaghi et al. (2016) have employed microseismicity of the region to estimate an attenuation relationship for the NW Iran. Their regression has left significant amplitude residuals at different stations where neighboring stations have similar average residuals confirming important lateral structural variations ignored in the attenuation estimations. For instance, stations located around the NTF have systematic negative residuals consistent with location of a thick sedimentary basin in the region. Such systematic residual patterns have been reported before in Canada and North America by Atkinson (2004) or in Alborz Mountains, north Iran, by Motaghi and Ghods (2012). These observations have inspired us to conduct 2-D amplitude residual tomography similar to widely used local travel time tomography (e.g., Rawlinson and Sambridge, 2003). We assume that attenuation variations are only affected by anelastic coefficient variations generated by change of rock properties. Thus, we have discretized the study region and considered anelastic attenuation coefficient (inverse of quality factor) as an unknown parameter for the inversion procedure. 

Methodology and Approaches:

We formulized a linear relationship between the amplitude residual (as datum) and anelastic coefficient variation (as unknown parameter), and then, we analyzed seismograms recorded from 943 local earthquakes with magnitudes between 1.6 and 5.2, and azimuthal gap less than 250o . The data were gathered by 35 seismic stations located in the NW Iran to carry out the inversion. We used a weighted damped least squares approach (e.g. Menke, 1989) in which weight matrices for the data and model parameters were used. The weights for the data come from the signal to noise ratio calculated for each signal. The weights for the model parameters come from the number of rays per block. This helps to exclude model parameters associated with blocks not crossed by rays. An optimal damping value of 23 was selected from the trade-off curve between the total residuals and the weighted model variances. The inversion procedure estimated variations of intrinsic attenuation coefficient relative to the average value (0.0012). We converted the obtained values into change of quality factor, ΔQ, which was more usual in the literature.

Results and Conclusions

Our tomogram for the NW Iran showed a lower quality anomaly for Neogene sedimentary basin around the North Tabriz Fault in contact with high quality Cretaceous volcanic and Cambrian metamorphic basement outcrops in the north of the region. Such clear consistency between our tomogram and lithology variations at the surface disappeared in the eastern part of the tomogram where deep (depth = 20–45 km) events occurring in the oceanic-like crust of the South Caspian Basin are observed. Comparing our eastern anomalies with a teleseismic tomography across the same region, we found that low and high quality patches in eastern part of our tomogram are probably generated by thermal effects of Sabalan volcano and oceanic like crust of the South Caspian Basin, respectively. Good consistency between our results and previously reported features confirms that the amplitude residuals are proper data set to detect structural heterogeneities responsible for large amplitude variations in active seismic regions.

Water extraction from groundwater resources has been increasing in recent decades. Qaleh Tol plain is one of the critical plains in Iran, located in Khuzestan province, that is necessary to determine the groundwater potential in the plain to meet the water needs of the region. Also, in spite of the regional decline in groundwater level in the plain in recent years, the drop of water level in some observation wells in special areas, is lower than other plain areas. Accordingly, it was necessary to carry out deep geoelectrical exploration in Qaleh Tol plain for the purpose of detection of buried formations under the alluvium and determining the hydrogeological heterogeneities of the plain. Therefore, a combination of hydrogeological and geoelectrical studies in Qaleh Tol plain was carried out. Vertical Electrical Sounding (VES) using Schlumberger array was carried out at 86 VES stations in six profiles. 1-D interpretation have been performed using IPI2WIN to determine the types and depths of subsurface layers and geoelectrical tomography of subsurface was done by RES2DINV. In order to provide an appropriate image of underground the electrical resistivity tomography maps (ERT) were prepared. In the tomography sections, the investigation depth over than 450 meters has been able to accurately determine the bedrock of Qaleh Tol plain. The results showed that the bedrock of Qaleh Tol plain are composed of limestone of Asmari Formation, conglomerate of Bakhtiari formation and shale of Pabdeh formation. The Asmari limestone strip shaped bedrock in deeper parts of the aquifer with high groundwater potential along the plain is the cause of hydrogeological heterogeneities in the Qaleh Tol plain, which has led to very different hydrogeological behaviors in neighborhood water wells.

The images of dental CBCT imaging systems used in conic shaped beams, stored in the DICOM format, have various applications in the dentistry, including bone density estimation to select the location of the orthodontic implant, bone loss detection and etc. In these systems, unlike CT imaging systems, the resulting images exhibit gray-scale non-uniformity in each of the different axis in FOV. This specification along with the inability of the CBCT to display the CT numbers accurately, makes it difficult to obtain bone density information, so diagnosing of dental complications using a quantitative information from the images cannot obtained accurately. In this regard, in order to be able to use the quantitative information of the images of these systems to assess more precisely the bone density, the gray scale changes in the images of several different CBCT systems were studied. The results showed that the process of gray scale changes for each system in each direction is unique for the each system, and it can be concluded that in each system, changes in the gray scale of images in each direction have a roughly constant trend. One of the most important results is that the gray scale changes of the images for all systems along the axis of the body (Z axis) have a steady trend and It has the lowest standard deviation. One of the most important results is that the gray scale changes of the images for the Scanora 3D and  New Tom GIANO systems in the axis of the body (Z axis) have a stable trend and the lowest standard deviation (0.54 ± 0.009) And (0.18 ± 0.004) respectively.

To obtain the distribution of the Love wave group velocities in northwest Iran and its surrounding areas for 7, 10, 20 and 25 second periods, the waveform of 241 local and regional events used in a dispersion curve tomography of the Love waves. The evnets occurred within NW Iran and surrounding areas between 2005 and 2015 and were recorded by 39 permanent and temporary medium and broad band seismic stations belonging to national and international seismic networks. In order to reduce the effect of non-uniform distribution of events, we selected the more uniform list of events out of an initial number of 1734 non-uniform distributed events. We applied the Frequency-Time Analysis method to each event-station path for estimation of Love wave group velocities, then we used a tomographic method to compute the distribution of local group velocities throughout the region. From the analysis of the surface wave tomography, we concluded that crustal structure in the South Caspian Basin and the Kura Depression is almost the same, but it is significantly different from that of the northwest Iran. In the presence of thick and low shear velocity sediments in the South Caspian Basin, we observed low velocity anomalies at periods less than 10 seconds that are surrounded by relatively higher velocities along Alborz, Talesh and Lesser Caucasus. In the “Eastern Anatolian Accretionary Complex” where volcanic activities are much higher than in rest of the region, less group velocities were observed for periods less than 25 seconds. The main reason for this observation can be related to the presence of partial melting zones inside the crust as a result of intensive volcanic activities in this region. In Zagros, for the periods of 7 and 10 seconds, a relatively high velocity anomaly along the “Sanandaj-Sirjan” metamorphic zone was observed, which was trapped by two low velocities along the “Zagros Folding and Thrust Belt” in one side and “Urmieh-Dokhtar Magmatic Arc” in another side. The active and broken crust, reverse, active and shallow thrust faults and high seismicity of Zagros Folding and Thrust Belt is characterized by low group velocities in our results for periods of less than 25 seconds. In most areas of central Iran and Urmieh-Dokhtar Magmatic Arc, local sedimentary basins are characterized by low velocities for periods of 7 and 10 seconds. Our results indicate that crustal structure in the northwest of Iran is almost uniform and has the minimum changes, but it is completely different from the crustal structure in the South Caspian Basin, eastern Turkey, and the Zagros mountains.

The crustal structure study based on ambient noise measurements has become a popular, fast and reliable method in earthquake seismology in recent years around the world. Generally, not only in seismology but also in other applications which deal with signals, accept noise as an undesired component of the signal. It is believed that noise obscures data and does not contain useful information. Ambient noise measurements promise significant improvements in the resolution and accuracy of crustal and upper mantle images. Traditional dispersion analysis, however, does not yield reliable estimates of the structure in the shallow crust because of strong scattering at short-periods (T

In recent years, fuzzy partitioning cluster algorithms have become more popular. Similar to crisp partitioning clustering, fuzzy algorithms can be used to integrate multiple models into a single zonal multiparameter model by grouping samples in a multidimensional space into clusters. The concept of partial cluster memberships integrates the structural heterogeneity of all input models and describes it in a fuzzy sense. In this study, the electrical resistivity data inversion is made by Gauss-Newton least squares method using RES2DINV software and also, the first arrival or break times are calculated using PickWin software, and moreover, the refraction seismic tomography data inversion is carried out using GeotTom CG software. Then, the data results have been clustered by three K-Means, FCM and Gustafson-Kessel FCM. Using Dunn index to optimize the number of clusters, the number of optimal clusters has been obtained equal to 12 that is a suitable number of clusters by considering the obtained electrical resistivity and refraction seismic tomography maps. Furthermore, considering the studies made in the dam site, alluvial basin and bedrock as well as bedding, it seems that Gustafson-Kessel FCM clustering method has shown better results. By starting Gustafson-Kessel algorithm and obtaining the results of running FCM, we see that the number of iterations is reduced and the speed of convergence is increased. The clustering algorithm computations in this research work have been made using programming in MATLAB software.

Seismotectonic Zone of Zagros is one of the most active seismic areas in Iran. Therefore, in this study, the tectonic structure of the area was investigated using seismographic stations around the Seymare dam in Ilam province. Mormori earthquake with magnitude of 6.1 occurred in August 2014, 77 km south-east of the dam site and well recorded at local stations. All data collected from seismic stations around Seymare Dam from 2014 to 2016 was collected. By seismic tomography, the velocity of seismic waves was calculated by one-dimensional inversion. Using the calculated velocity model, location was coded using hypoDD method and distribution of center and depth sections were reviewed which is in good agreement with the fault processes of the area. The Vp / Vs ratio was calculated to be 1.65 Which is different from the previous results of the Mormori earthquake in the area. This indicates tectonic changes after the earthquake in the region.

The explanation of the elastic, or velocity structure of the Earth has long been a goal of the world’s seismologists. For the first few decades of seismological research, the investigation on velocity structure was restricted to the determination of one-dimensional models of the solid Earth and of various regions within it. Seismologists are currently obtaining three dimensional velocity models and are working to resolve finer and finer features in the Earth. The knowledge of seismic velocity structure of the crust and the upper mantle is important for several reasons: these include accurate location of earthquakes, determination of the composition and origin of the outer layers of the Earth, improvement of our ability to discriminate nuclear explosions from earthquake, interpretation of large-scale tectonics and reliable assessment of earthquake hazard. The Iranian part of the Alpine-Himalayan collision zone consists of an assemblage of lithospheric blocks, features a complex tectonic setting, which results from the collision and convergence of the Arabian plate towards Eurasia, thus investigation of the structure of the lithosphere and the asthenosphere of the Iranian plateau is of great interest.
The North West of Iran is affected by important seismic activity concentrated along the North Tabriz Fault. In recent centuries, more than five successive and destructive seismic events have occurred along the North Tabriz Fault. The North West of Iran is particularly rich in geological and Most of NW Iran is located in a volcanic arc zone of Cenozoic age, including the Quaternary. Some of the main geological features in the North western of Iranian plateau include the Sahand Volcano, the Urmia Lake, salt deposits, travertine deposits, springs, limestone caves, tectonic structures and Cenozoic vertebrate fossils. Sahand and Sabalan peaks are the most prominent geological as well as topographic feature in the region.
The aim of this study is to obtain two dimensional tomographic maps of Rayleigh wave group velocity of the Northwest part of Iran plateau. To do this, the local earthquakes data during the period 2006 to 2013, recorded at 10 broadband stations of the International Institute of Earthquake Engineering and Seismology (IIEES) were used. firstly, Rayleigh wave fundamental mode dispersion curves using single-station method were estimated. In single-station method after the preliminary correction, Rayleigh wave group velocity for each source-station using time-frequency analysis (FTAN) were estimated. After estimating group velocity dispersion curves, using a 2D-linear inversion procedure, the group velocity tomographic maps for the period 2-50 s were obtained. Each tomographic map has been discretized with a grid of 0.5° of latitude per 0.5° of longitude. The results at period 5 s show a low velocity anomaly beneath the Sabalan volcano, whereas beneath the Sahand volcano a high velocity anomaly is observed. At period 10 s the results are different. Beneath the Sabalan volcano a high velocity anomaly is observed, whereas beneath the Sahand volcano and also along the Urumieh-Dokhtar Magmatic Arc a low velocity anomaly are observed. At period 20 s in most of the study area, a low velocity anomaly is observed. The results at period 40 s are different, so that a low velocity anomaly in the southern part and a high velocity anomaly in the northern part are observed.

Hydro-geoelectric properties of the Asmari and Ilam-Sarvak formations in Susan Syncline (located in Middle Karoon Basin), North of Izeh, were investigated to recognize electrical resistivity ranges of dry and wet limestone, karstification, and fractures and determine the areas with high potential for groundwater exploitation. For this purpose, the resistivity data were collected in 245 vertical geoelectric sounding (VES) using Schlumberger array in the contact of limestone and adjacent alluvium. The resistivity data were interpreted as one-dimensional and two-dimensional tomography (using RES2DINV software). The resistivity curves of VES in the Asmari Formation have lower value and ranges of resistivity than the Ilam-Sarvak Formation which can be understood by high yield of the aquifers from the smooth descending VES curves. Interpretation of two-dimensional geoelectrical tomography revealed that the Ilam - Sarvak Formations have considerable potential groundwater in crushed zones but the karst development and cavities in them are less than the Asmari limestone. The spring discharges from the Ilam-Sravak Formations in Susan area is in relation with the contact of compact limestone and water bearing fractured zones. Despite the lack of major springs in the Susan Syncline,the results of the hydro-geoelectrical investigation showed the Asmari limestone aquifer, has a high groundwater potential. The electrical resistivity of the Asmari Formation is lower than the Ilam-Sravak ones because of the higher porosity of limestone matrix in the former.

The delineation of the elastic, or velocity, structures of the Earth has long been a goal of the world's seismologists. In the first few decades of seismological research, the investigation of velocity structures was restricted to the determination of one-dimensional models of the solid Earth and various regions within it. Seismologists are currently working on three-dimensional velocity models, and they are trying to resolve finer and finer features in the Earth. The knowledge of seismic velocity structure of the crust and the upper mantle is important for several reasons: It includes the accurate location of the earthquakes, it is used in the determination of the composition and origin of the outer layers of the Earth, it improves our ability to discriminate nuclear explosions from earthquakes, it helps to interpret the large-scale tectonics as well as a reliable assessment of earthquake hazards. In this study, we used highfrequency dispersion curves to estimate the elastic properties of Tehran and the suburbs. Tehran city is located in the Alborz major seismic tectonic zone. The Alborz is an arcuate chain of mountains in the Northern Iran that wraps around the Southern side of the South Caspian basin; the boundary is roughly the present shoreline of the Caspian Sea. The range is actively deforming on range-parallel thrusts and left lateral strike-slip faults. The thrusts dip inward toward the interior of the range from both its northern and southern sides, and the GPS-derived shortening across the range is 5 ± 2 mm/yr at the longitude of Tehran (Vernant et al., 2004b). Most are parallel to the range and accommodate the present-day oblique convergence across the mountain belt. Recent large earthquakes occurring in this region suggest that the seismicity is connected with major faults of the recent age that cut across the regional Quaternary Lineaments. In this study, in order to estimate the upper crust elastic structure, we conducted a tomographic inversion of the Love wave dispersion to obtain two-dimensional Love wave group velocity tomographic images in a period range from 2 s to 5 s for the city of Tehran and the suburbs. We used two databases to derive dispersion curves for different paths. In the first dataset, continuous ambient noise in ten stations located in and around the city of Tehran and installed by the Tehran Disaster Mitigation and Management Organization network was used to explore the inter-station Green’s Functions. In the second database, forty seven earthquakes recoded by the Parsian stations were prepressed and rotated to be used as single station records to estimate the Love wave group velocity. In the next step, the inter-station Green functions and single-station records were used to estimate the Love wave dispersion curves by applying a multiple filtering technique. All dispersion curves were used to estimate the two-dimensional Love wave group velocity models. For this purpose, Tehran region was divided into 0.1° × 0.1° cells. According to the ray coverage, the minimum dimension of distinct heterogeneity was 6 km. In our study, topographical features and near-surface known geological structures were two main criteria to assess the credibility of the estimated Love wave group velocity variations. There was a strong correlation between the estimated group velocities and topographical features. The prominent surface geology units at the mountain range consisted of varying structures including sand-stone, siltstone, claystone, and massive limestone.

One of the most important purposes in seismology is determination of crustal velocity using earthquakes data that have been recorded by regional and local seismic stations. The more precise the process is carried out، the better shall be the results reached in various studies in the area including earthquake locating، seismicity of area، seismic zone mapping or the determination of the plane of faults causing earthquakes Imaging velocity structure of Earth''s interior using travel times inversion commonly called seismic tomography which is usually done two or three-dimensionally.. This method has extensively been used in recent decades by researchers. Since the seismic waves are associated with valuable information about direction of propagation and environmental properties، using earthquakes as natural seismic sources are very useful in seismic tomography as well as the artificial sources such as limited and controlled explosions، air guns and bore-hole sources.. The seismic tomography characterizes the size، geometry and extent of velocity anomalies. In this method subsurface structure is modeled initially by several parameters and improved by the inversion of seismic travel times data. In this study the crustal velocity structure was determined using three-dimensional inversion of local earthquakes travel times recorded by seismic networks of Institute of Geophysics University of Tehran (IGUT) occurred within the period from 2000 and 2012 in the study area. The study area is bounded within 31oE to 34oE and 50oN to 53oN. We used the VELEST software in one-dimensional modeling section. The procedure of study is minimizing the differences between observed and calculated travel time by applying the initial obtained model. This software simultaneously optimizes the earthquake locations، crustal velocity model and station corrections using the Joint-Hypocenter-Determination (JHD) method. The initial estimates for P waves velocity and crust thickness of the region are achieved using the travel-time curve of primary phases of all earthquakes occurred in the area. Then the larger relative earthquakes are selected and the best crustal one-dimensional model was derived by simultaneously inverse modeling method using this data set and VELEST algorithm. This method can be considered as one of the useful methods in study of 1D crust structure. The results proposed a 4 layers model of crust in which the P wave velocity is equal to 5. 4 km/s for depths less than 5 km، 6. 0 km/s for depths from 5 km to 20 km، 6. 2 km/s for depths of 20 km to 32 km and finally 6. 9 km/s for depths of 32 km to 47 km. The thickness of crust and Pn velocity are respectively obtained 47 km and 7. 9 km/s. The aim of this work is obtaining an optimal crust model that can aid to improve seismic data and can be used to determine the next earthquake locating. Then the obtained crustal model is used as an initial model to study of three-dimensional inverse modeling of crust in the region by using FAST algorithm. All the earthquakes relocated using new obtained model. In this study a data set recorded by the 8 seismic stations of Isfahan and Shahrekord networks were used. The resolution of final solution of 3D model was investigated using synthetic dataset (checkerboard model) that shows fair resolution for various depths. The lateral variations of the main resolved structures in the model obtained are highly correlated with the faulting systems in the region.

In this study, applying a tomography method to local earthquakes, a three-dimensional (3D) image of the crust of central Alborz is obtained. The result is not only consistent with the tectonics features in the region but also abale to interpret the tomography of Moho and crustal structure beneath the volcanic mountain of Damavand. More than 11000 local earthquakes, with a magnitude of 1.7 or higher, recorded by three-component short-period seismic stations of Tehran, Mazandaran, and Semnan networks between 1996 and 2006, bounded by 34-37N and 39.7-54E, were used to image the crust in central Alborz. These raw pieces of data, on one hand, were used as input for the 1D inversion method to obtain the variation of Vp and plot the velocity versus depth diagram whose rms was smaller than 0.15. On the other hand, they were used in a relocation process and when their locations were improved, a 3D model was generated based on them. After determining the preliminary 3D and forward models using the finite-difference method, the refracted and wide-angle reflected travel times were inverted and the horizontal and vertical sub-structures in our determined region were investigated. Based on these results, the discontinuities of the crust and Moho were mapped and analyzed. The final outputs showed that the resulted crust model is consistent with some of the recent geological studies. These outputs illustrat that the upper layer is thicker than the middle and lower ones as these two layers become thinner and even disappear below Alborz. It seems that the upper layer fills some hollows in the other ones. The depth of Moho increases below Damavand mountain; also, the area around the volcanic conduit of Damavand, between 6km and 18km depths, has a high velocity and is colder than the other areas.The P-velocity model resulted by using 1D tomography facility of Velest with RMS values less than 0.15, are compatible with the previous models. The resulted depth is 45 ± 2 km for the Moho and 7 km for the sediment layer. Frequency and distribution diagrams of the earthquakes show that about 75% of earthquakes have happened in depths less than 24 km and consequently the most seismogenic layer of the crust is estimated to be located at this depth. The 3D tomography, performed through the Zelt routines, has acceptable results with less than 2.5% error. Although an enough number of earthquakes overcome the problem of scarcity of the stations, the high depths of earthquakes cause a low resolution in shallow layers. However, this problem can be solved by increasing the density of stations.

To determine the ground water potential of the karst aquifers، in the southwest of Izeh، three profiles and 62 vertical electrical sounding (VES) conducted by Schlumberger array، eight profiles were performed using dipole-dipole configuration، and 3-D configuration applied in two sites. However، Schlumberger tomography with high investigation depth (about 180 m) may be shows the different zone of karst aquifer but because of 50-100 m of VES spacing has not the detectability of cavities with lower than 50 m diameter. The results show that Ilam-Sarvak limestone is similar to hard rocks while Asmari formation has been identified as developed karst with high matrix porosity. The results in the 2-D geoelectrical tomography using a dipole-dipole configuration، shows that، compared to an electrode spacing of 5 m، an electrode spacing of 1 or 2 m has a higher ability to delineate karst voids. Because of the higher depth of the investigation، however، the longer electrode spacing allowed obtaining a comprehensive insight of different parts of karst regions. The high resolution 3-D electrical tomography has a good ability to detection of geological features and karst voids. The geoelectric results and interpretation of tomograms have been asserted by drilling success of four wells with high yield at Asmari formation and two wells with moderate yield at Ilam-Sarvak formation.

Teleseismic body wave tomography beneath a profile of portable seismic stations using the ACH method (named after authors Aki, Christoffersson, and Husebye) is generally based on relative residual data from teleseismic earthquakes. The relative residuals are inverted to retrieve the two dimensional structure of the velocity perturbation relative to a spherical reference Earth model (for example, IASP91) in the structure of interest beneath the profile. This method tries to minimize the influence of extraneous factors, such as errors in earthquake location or origin time and ray paths from the source to the base of the target volume, by subtracting the mean of the arrival-time residuals for each event, since only the velocity deviations in the target model are investigated. The data are then corrected for crustal travel-time variations a perior inversion. Because travel time perturbation reflects the velocity perturbation integrated along the ray path, some perturbations in the target model may be caused by deeper structures in the upper mantle. This paper intends to study whether the de-meaning process used in the ACH method can remove the effects of deeper mantle anomalies (especially those located directly underneath the target region) or deeper heterogeneities that may leak into the velocity structure of the region of interest. Therefore, considering some different hypothetical velocity structures, including positive and negative anomalies (with relatively high and low velocities, respectively), this study targets an area approximately 1% immediately underneath the base of the model at a depth of 460 to 660 km in an attempt to determine how the velocity structure of the upper mantle beneath a profile would be affected by the presence of possible anomalies in greater depths. Hypothetical tests were applied using teleseismic data recorded in a profile across the Zagros collision zone. The Zagros seismic experiment comprised 66 short-period, medium- and broad-band stations deployed along a NE-SW transect from Bushehr to Posht-e-badam in the southwestern part of Central Iran between November 2000 to April 2001. The profile is believed to be almost perpendicular to the main tectonic units of the Zagros collision zone. For the target model, a simplified P-wave structure to a depth of 460 km based on the tectonic observations and previous tomographic results consisting of two relatively high and low velocity anomalies of approximately 3% at depths of 120 to 300 km, respectively, beneath the Zagros zone and Central Iran were embedded within the reference Earth model. These two anomalies were separated by a sharp sub-vertical transition. Using the target model structure and postulating different anomalies underneath the base of the model, the relative residuals were inverted. The results indicate that these hypothetical heterogeneities in the mantle below the base of the model leads to some effects in the velocity structure of depths lower than 300 km, which have lower resolution. These effects could be attributable to insufficient resolution of the target model at these depths due to a low number of criss-crossing rays. Moreover, there are some deviations in depths of 120 km up to Moho. However, all models retrieve the major features (including transitions and major blocks) available in the hypothetical model, albeit with underestimated amplitude due to the regularization parameters and model parameterization.