JOURNAL OF RESEARCH ON APPLIED GEOPHYSICS
Year:2018 | Volume:4 | Issue:1 |Papers Count:12

Summary: A variety of methods has been presented to invert arrival time of seismic waves for velocity distribution over the survey area. In real world, the velocity distribution model consists of blocky structures as well as smooth varying parts. In such cases, implementation of Tikhonov regularization will recover the smooth varying portion of the velocity model; while the Total Variation (TV) regularization is capable of recovering the blocky varying parts of the velocity model. In this research, a technique for solving inverse problems based on a combination of second order Tikhonov and TV regularizations is proposed. The methods are tested on both synthetic and real arrival times and the results are presented. ...

Summary: Deconvolution problems involve estimating an unknown input when the signal and the response of an LTI system are known and lead to wavelet compression and increase the temporal resolution. However, in practice, the output signal is noisy. For some systems, the deconvolution problem is simple, but for the non-invertible or almost non-invertible systems, the problem is more complex. The use of the exact inverse of the systems leads to the amplification of the noise. The reflectivity sequence is the representation of the layers of the earth. The resulted compression leads to a high-resolution image of the earth. The outcomes exhibit that the reflection coefficient significantly improves after application of the MM algorithm on synthetic and real data, compared to the least squares and the frequency spectrum methods after the application of the algorithm. ...

Summary: In this paper, by combination of seismic data and well log data, the effective porosity in the space between wells is estimated. One of the important petroleum reservoir features is effective porosity that engineers are always looking to find an appropriate model for distribution of this parameter in the reservoir. The petrophysical properties of petroleum reservoirs are very complex. In the last few decades, the effective porosity estimation procedures have become one of the hot topics in the industry to evaluate these procedures or methods. In the current research, by integration of petrophysical, seismic data and seismic attributes classification using Adaboost algorithm, it is tried to estimate the effective porosity in a twodimensional seismic cross section of the block F3 Dutch sector of the North Sea. ...

Summary: We have computed P receiver functions to investigate the upper mantle discontinuity beneath northewest of Zagros in Iran. We have selected data from teleseismic events (Mb ≥ 5. 5, 30 ˚ > > 95˚ ) that have been recorded since 2004 to 2016 at three-component short period and broadband stations from Kermanshah and Khoramabad telemetry seismic network and threecomponent broadband stations in Sanandaj area. The P to S converted phases from 410 and 660 km discontinuities are observed. The results show that the thickness of the upper mantle transition zone in the study area is not the same as that in the entire region, and it is shown a little deviation rather than IASP91 model and appears to be depressed under the Urumieh-Dokhtar zone having northwest-southeast direction. The maximum temperature anomaly is equal to 180˚ C and 450˚ C for 410 and 660 km discontinuities, respectively. ...

Summary: Crosshole seismic travel-time tomography is often applied to image the velocity structure of an inter-well medium and involves in finding a velocity model that minimizes the error energy between the measured and the theoretical travel times. Travel-time tomography is a non-linear inverse problem because the ray paths depend on the unknown velocity field. Linearized techniques are usually employed to reconstruct the velocity field in an iterative manner. A limitation, inherent to deterministic methods, is the strong relation between the starting model and local minima entrapment. Global optimization methods such as particle swarm optimization (PSO) can be applied to such problems. Regardless of the starting model, global optimization ideally finds the region of the solution space containing global minima without calculating derivatives. In this paper, the regularized PSO approach to seismic travel-time tomography is described, and is tested on synthetic as well as real seismic data, and is also compared with a local optimization method that is Levenberg-Marquart (LM) algorithm. The results show that the proposed method estimates the velocity model better than LM, especially in the absence of good prior information. ...

Summary Today, geophysical methods are one of the most feasible means for exploration, detection and localization of underground targets. One of the most used geophysical methods is ground penetration radar (GPR). In this method, based on the depth, shape and electromagnetic properties of the target and surrounding environment, electromagnetic waves with different central frequencies are propagated through the medium. In this paper, first, the theory of GPR, and then, forward modeling of GPR data using finite difference time domain (FDTD) method with consideration of convolutional perfectly matched layer (CPML) absorbing condition are presented. Finally, forward modeling of a buried tunnel in different geological environments is presented and the results are assessed. A schematic model of a tunnel in Tehran-Pardis highway is also constructed and the results of the simulation of the tunnel are compared with the field data. ...

Summary: The effect of blast-induced ground vibrations on mines and on adjacent structures and facilities is an example of the adverse consequences of the mining cycle. In order to control the vibrations, and also, managing the adverse effects, the measurement and modeling of the concerned wave attenuation are necessary. Normally, by implementing several trial blasts and analyzing corresponding ground vibrations, we can determine the related attenuation model for different sites and mines. Usually, the modeling of the peak particle velocity (PPV) damping is performed based on the distance between blast-face and monitoring station and maximum charge used per delay. In this research, using different empirical models, the PPV equation is determined for blasting in the Sungun copper mine. Moreover, imperialist competitive algorithm (ICA) has been employed to develop prediction model for ground vibrations. A comparison of the results obtained from different models are made based on several statistical tests between monitored and predicted values of PPV. According to these statistical tests, fairly good performance of the ICA-based model in the forecasting of PPV is proved. Introduction Drilling and blasting are typical methods of rock excavation. The ground vibrations are an adverse effect of blasting that cannot be completely eliminated; but certainly can be minimized up to permissible level to avoid possible damages to surrounding structures. Ground vibration is directly related to the maximum charge per delay and distance between blast face and monitoring station. To predict ground vibration, several empirical models have been developed by various investigators. In the most of these models, the PPV is the parameter of concern. Methodology and Approaches In this paper, the ICA was proposed to get an appropriate equation for forecasting the PPV in the Sungun copper mine. For comparison purposes, three well-known empirical models were also used. To evaluate the performance of PPV models, the correlation between the predicted and real measured values of PPV was determined. Standard statistical evaluation criteria were used to evaluate the performances of different PPV predictor models. Results and Conclusions Considering the calculated statistical error between the forecasted and real measured values of PPV, the ICA-based model has the lowest values of MAE, VARE and RMSE, while it has the highest value of VAF, in comparison with the empirical models.

Summary: Continental convergence between Arabia and Eurasia is taken up by distributed deformation in Alborz and Zagros collision zones in Iran. We applied P receiver function method to image the variations geometry of the crust– mantle boundary in two major mountain belts of the Alborz and Zagros in Iranian plateau. We used data from 65 seismic stations, which consists of 50 seismic stations of Institute of Geophysics, University of Tehran (IGUT), and 15 broadband stations of International Institute of Earthquake Engineering and Seismology (IIEES). Our results indicate that the average crustal thickness beneath central Iran domain (CD) is about ~48 km. The crustal thickness in this region varies between ~34 km beneath CHK station and ~55 km beneath IL3 station. We have found the Moho depth of about 45 km beneath the Zagros fold and thrust belt (ZFTB). Toward SE in ZFTB, we observe an increase in the Moho depth where it reaches ~59 km beneath BNDS and BNB stations. Crustal thickening (~54 km) has been observed beneath the central Alborz. ...

Summary : Ground penetrating radar (GPR) method is a non-destructive geophysical method that is used to detect subsurface heterogeneities, and also, to recognize various shallow targets. In the present research, forward and inverse modeling of GPR data was carried out to detect subsurface buried pipes. In Shahrood University of Technology campus, GPR data along several survey lines were acquired using 250 MHz shielded antenna to detect hydrocarbon transfer pipes. To achieve the goal, the real radargram along the survey lines in the area was obtained after applying different processing operations including signal saturation correction, static correction and amplitude gain on the GPR data using ReflexW software. Then, the synthetic radargram corresponding to the real radargrams was simulated using finite-different time domain (FDTD) method. In this study, acquisition of field GPR data and synthetic models were carried out in TM mode. ...

Summary: The aim of this research is to develop methods to derive sharp images of subsurface, which show the geometry of the structures in the region of interest. Structural inversion of gravity data-deriving robust images of the subsurface by delineating litho-type boundaries using density anomalies-is an important goal in a range of exploration settings (e. g., ore bodies, salt flanks). In this paper, an L1-norm based inversion approach is investigated. The density distribution of the subsurface is modeled on a uniform grid of cells. The model parameters are the density of each cell that is inverted by minimizing the L1-norm objective function using linear programming (LP) while satisfying a priori density constraints. LP method for structural inversion has two advantages: 1. It offers a natural way to incorporate a priori information regarding the model parameters. 2. It gives a subsurface image with sharp boundaries (structure). The inversion quality depends on a good priori estimation of the minimum depth of the anomalous body. Introduction LP is used as a method for performing constrained optimization. The constraints consist of linear inequalities in the variables, and the objective function is also a linear function of variables. LP can also be used to perform an implicit structural inversion. As we know, a set of inequalities has no solution, one solution or more than one solution. However, there are usually many combinations of the variables that satisfy all the constraints. The set of all these combination is called feasible set. A LP problem can be solved using simplex method. Methodology and Approaches To apply linear programming to exploration geophysics, an objective function should be defined, and some constraints should be set. In the case of gravity anomalies, the model vector m contains the density contrasts of the prisms with respect to some background values. First, subsurface should be parameterized with prisms for which density contrasts are sought. The unknowns are the density contrast of each homogenous prism relative to the background. Next, we use a L1-norm objective function to be minimized. The first constraint, which should be assumed, is an upper limit for density contrast as a priori. Then, we introduce some new variables and add additional constraints. The LP problem can be solved using simplex method. This method is based on that if an optimal solution exists, then an optimal extreme point also exists. Extreme points are then characterized in terms of basic feasible solutions. The LP method is first applied on free-noise synthetic gravity data, then, we test the method further by perturbing the synthetic data with low levels of noise and performing the inversion of all perturbed data sets. At the end, we perform the algorithm on real gravity data acquired from Safo mine. All the results have been given and discussed in this paper. Results and Conclusions The inversion method, proposed in this paper, gives us a well shaped model even in the presence of substantial noise. This method can be used in exploration situation with sharp boundaries (density contrast) such as salt flank, ore bodies, dikes, etc. The need to know the top of the anomalous body, at first, appears to be a serious shortcoming of our approach, but here we use another method such as Euler method to extract the minimum depth of the anomalous body. However, our focus is on delineating the structure laterally (sides of dikes, flanks… ). Information regarding the tops of such structures may often be available from other geophysical techniques or from geologic considerations.

Summary: The visco-elasticity of the earth causes dissipation of the energy of seismic waves when traveling through a medium, a phenomenon referred to as seismic attenuation. The attenuation property of a medium is described by a quantity called quality factor, or Q, which describes the amount of energy loss. The quality factor is related to the frequency of the propagation wave. In seismic data processing, our knowledge about this quantity is used to enhance the quality of seismic data, as an increase in the temporal resolution of the data, via absorption compensation tools. An exact formulation of seismic attenuation and its effect on the recorded data are unknown but there are simple models for describing the attenuation behavior approximately. The constant Q model relates a single value for Q to all frequencies in a trace. An important step in dealing with absorption compensation is the estimation of Q value. ...