JOURNAL OF RESEARCH ON APPLIED GEOPHYSICS
Year:2018 | Volume:3 | Issue:2 |Papers Count:8

Inversion of magnetic data is one of the important steps in the interpretation of practical magnetic data. The inversion result can be obtained by minimization of Tikhonov objective function. The determination of an optimal regularization parameter is highly important in magnetic data inversion. In this paper, an attempt has been made to use unbiased predictive risk estimator (UPRE) method in selecting the best regularization parameter for 3D constrained inversion of magnetic data using gradient projection reduced Newton (GPRN) algorithm. To achieve this goal, an algorithm has been developed to estimate this parameter. The validity of the proposed algorithm has been evaluated by magnetic data acquired from a synthetic model. The results have been compared with the results of generalized cross validation (GCV) method. The GCV method failed to estimate the regularization parameter, but the UPRE method could find the best regularization parameter. Then, the algorithm was used for inversion of real magnetic data obtained from Allah Abad iron deposit. The results of three-dimensional (3-D) inversion of magnetic data from this iron deposit show that the GPRN algorithm can provide an adequate estimate of magnetic susceptibility and geometry of subsurface structures of mineral deposits. A comparison of the inversion results with drilling data clearly indicate that the proposed algorithm can be used for 3-D inversion of magnetic data to estimate precisely the magnetic susceptibility and geometry of magnetized ore bodies.

Deconvolution is one of the significant steps in seismic signal processing for obtaining high resolution images of subsurface. In this paper, a new nonstationary deconvolution is developed to retrieve the impulse response of the earth and remove the earth attenuation effects from it via a simulated annealing (SA) optimization. The time location of each spike and the corresponding quality factor is estimated by the SA method and its amplitude is calculated using a least-squares method. All three parameters of the reflection coefficient, time lag, and the quality factor for each layer are estimated simultaneously. Available information from well-logs can also be incorporated as a priori information. Numerical examples from simulated and field seismic data show high performance of the proposed algorithm for estimating the reflectivity structure and the model of the quality factor. Numerical examples confirm promising applicability of the new method for processing and interpretation of seismic data. The goal of non-stationary deconvolution is to remove the effects of the source wavelet and the attenuation filter from the data to retrieve the earth impulse response with an enhanced temporal resolution.

To optimize the widespread use of fossil fuels in Iran, different resources of renewable energy can be considered as promising challenges. The everincreasing energy demands of the country can be satisfied by the very rich resources of renewable energy such as wind, solar, biomass, and geothermal energies. This paper presents the results of Curie point depth calculations from spectral analysis of aeromagnetic data for preliminary exploration of geothermal resources in central region of Kerman Province. The calculations were performed for an area of 22010 km2 located north of Jiroft city and east of Baft city. RTP correction and band pass filtering were first applied to the data. Then, the block dimension of 80×80 km with an overlap of 50% was selected for the spectral analysis. The spectral power was calculated for all the blocks and the Curie depth map was obtained for the study area. The results showed that the shallowest Curie depths are about 9 km observed in the southeastern part of the study area. Different information layers including geological and surface information layers were, then, onvestigated in the ArcMap software. Concentration of several hot springs and presence of faults, intrusive structures, and volcanic rocks prove a high probability of geothermal anomaly in the area of shallowest Curie depth.

Seismic imaging is highly dependent on the quality of seismic data. Structural and stratigraphic interpretation of seismic sections that contain the least amount of noise is much easier. Reflection seismic data are often associated with noise. Coherent noise is a major category of noise that accompanies seismic data, and has the same trend in different seismic traces of the data. Ground roll is one of the main coherent noises that has a low frequency, high amplitude and low velocity. Various methods, such as frequency filters and frequency-wavenumber filter, have been used for ground-roll attenuation. Different advantages and disadvantages are mentioned for each of the methods. In this paper, we have used time – frequency transform and variational mode decomposition to attenuate the ground-roll.

To determine the location of subsurface objects from the potential field maps, edge detection methods are used. This methods are mainly derivatives of potential field. For edge detection, several methods or filters such as analytic signal, tilt angle, total horizontal derivative of tilt angle and normalized total horizontal derivative are commenly used in geophysical interpretation. In this regard, the method of normalized anisotropy variance (NAV) for edge detection is investigated in this paper. This filter directly do not use high-order derivatives, and also, vertical derivative in calculations, thus, stability of noisy data is preserved in this method. One of the effective parameters in the calculation of this method is the optimal window number that is obtained by maximum of variation of normalized anisotropy variance and window number. In order to assess performance of the NAV-method in the edge detection of gravity anomalies, cubic models used with positive and negative density contrast and different depth, and the NAV-method and also the above-mentioned filters were applied to synthetic models and real gravity data of Safo Manganese mine. Consequently, acceptable results from applying the NAV method for edge detection of gravity anomalies were obtained.

Different methods are used for seismic velocity analysis, including spectral analysis based on semblance, which is a reliable way to estimate the stacking velocity. The proposed method in this research is superior over other seismic velocity analysis methods because in the proposed method, the wave due to the absorption of the earth makes a reduction of the frequency content of the source in time, and results in poor temporal resolution. In this paper, the velocity analysis performed in the wavelet domain using undecimated discrete wavelet transform (UDWT). Random noise is often placed in high-frequency sub-bands and their effect leads to a reduction in coherency than other sub-bands. In this way, data analyses to high-pass and low-pass sub-bands and velocity analysis at any scale are performed using discrete wavelet transform and scaling filters. A Comparison of the obtained results showed that the spectral analysis of the velocity in the wavelet domain increases the accuracy of the velocity analysis in each band of frequencies.

The Zagros fold and thrust belt (ZFTB) is resulted from the collision of the Arabian Plate with the continental crust of Central Iran and is considered as an example of a young continent– continent collision belt. In this study, we have used P receiver function technique to determine the crustal thickness and Vp/Vs ratio in northwest of Zagros. Our dataset includes teleseismic data (with magnitude Mb ≥ 5. 5, epicentral distance  from 30◦ to 95◦ ) that have been recorded at 11 three component short-period and broadband stations of Kermanshah and Khoramabad telemetry seismic networks from 2010 to 2015. First, the differential travel time between the incident P wave and S converted wave (delay time) is used for computation of crustal thickness. Then, we have used the arrival times of crustal multiples (PpPs, PpSs + PsPs) to determine crustal thickness (H) and Vp/Vs ratio using Zhu and Kanamori method. Applying this method, the average Moho depth is determined that is 44 km in northwest of Zagros and varies between 36 km and 55 km. In northern part of the region, the average thickness of the crust is about 38 km, and toward the center and south of the region is going to be thicker. The average Vp/Vs ratio in the crust of northwest of Zagros is about 1. 74 and varies from 1. 66 to 1. 86.

Stripping is a common distress occurring on asphalt pavements. The source of this stress comes from moisture, thus, stripping and moisture damage are often used interchangeably. A common way to identify these failures is drilling and coring from road surfaces, and doing destructive tests. The most commonly used tests are bulk density, comparing indirect tensile stress in saturated to dry condition (TSR), and finding air void percentage. These tests are destructive, and take time more than usual. In addition, we must repair and patch the asphalt pavements where drilled and cored. Ground penetrating radar (GPR) is a method, which is not only a non-destructive method but it also evaluates the roads continuously and provides us with results much quicker than the common destructive tests. In this study, parts of the road networks in Tehran are evaluated using GPR, then several points of the road surface are drilled and cored. Finally, the results of the GPR measurements and destructive tests are analyzed and compared with each other.