In the last 30 days

• Open/close Relationships between permeability, porosity and pore throat size in carbonate rocks using regression analysis and neural networks

  M R Rezaee et al  2006 J. Geophys. Eng. 3 370 Tag this article

  Article References Full text PDF (207 KB)

  Accurate estimation of permeability from other data has been a challenge for many years. The aim of this study was to establish relationships between permeability, porosity and pore throat size, and apply these relationships in a predictive sense. Regression analysis was utilized to achieve a set of relationships between permeability, porosity and pore throat size for 144 carbonate samples. These relationships can be used to estimate permeability from porosity and pore throat radii. Also in this study, a fully-connected multi-layer perceptron network was used to predict permeability from porosity and pore throat radii. An artificial neural network, a biologically inspired computing method which has an ability to learn, self-adjust, and be trained, provides a powerful tool in solving complex problems. These characteristics have enabled artificial neural networks to be more successful in predicting permeability when compared to regression analysis.

  This study also indicates that pore throat radii corresponding to a mercury saturation of 50% (r ₅₀) is the best permeability predictor for carbonates with complex pore networks.

• Open/close Comparison of Wenner and dipole–dipole arrays in the study of an underground three-dimensional cavity

  Ahmad Neyamadpour et al  2010 J. Geophys. Eng. 7 30 Tag this article

  Article References Full text PDF (4.26 MB)

  The objective of this paper was to compare Wenner and dipole–dipole configurations in delineating an underground cavity at a site near the University of Malaya, Malaysia. A three-dimensional electrical resistivity imaging survey was carried out along seven parallel lines using Wenner and dipole–dipole arrays. A three-dimensional least-squares algorithm, based on the robust inversion method, was used in the inversion of the apparent resistivity data. In the inverted model, both the horizontal and vertical extents of the anomalous zones were displayed. Results indicate the superiority of the Wenner array over the dipole–dipole array for determining the vertical distribution of the subsurface resistivity, although the dipole–dipole array produced a better lateral extent of the subsurface features. The results show that the three-dimensional electrical resistivity imaging survey using both the Wenner and dipole–dipole arrays, in combination with an appropriate three-dimensional inversion method and synthetic model analysis, can be highly useful for engineering and environmental applications, especially for underground three-dimensional cavity detection.

• Open/close Reply to comment on 'Statistical correlations of shear wave velocity and penetration resistance for soils'

  Ünal Dikmen  2010 J. Geophys. Eng. 7 803 Tag this article

  Article References Full text PDF (56 KB)

• Open/close Statistical correlations of shear wave velocity and penetration resistance for soils

  Ünal Dikmen  2009 J. Geophys. Eng. 6 61 Tag this article

  Article References Full text PDF (3.69 MB)

  In this paper, the correlation between shear wave velocity and standard penetration test blow counts (SPT- N) is investigated. The study focused primarily on the correlation of SPT- N and shear wave velocity ( V _s) for several soil categories: all soils, sand, silt and clay-type soils. New empirical formulae are suggested to correlate SPT- N and V _s, based on a dataset collected in a part of Eskişehir settlement in the western central Anatolia region of Turkey. The formulae are based on geotechnical soundings and active and passive seismic experiments. The new and previously suggested formulae showing correlations between uncorrected SPT- N and V _s have been compared and evaluated by using the same dataset. The results suggest that better correlations in estimation of V _s are acquired when the uncorrected blow counts are used. The blow count is a major parameter and the soil type has no significant influence on the results. In cohesive soils, the plasticity contents and, in non-cohesive soils except for gravels, the graded contents have no significant effect on the estimation of V _s. The results support most of the conclusions of earlier studies. These practical relationships developed between SPT- N and V _s should be used with caution in geotechnical engineering and should be checked against measured V _s.

• Open/close Noise suppression based on a fast discrete curvelet transform

  Zhi-yu Zhang et al  2010 J. Geophys. Eng. 7 105 Tag this article

  Article References Full text PDF (1.92 MB)

  A curvelet transform (CT) is a new kind of multi-scale analysis algorithm which is more suitable for image processing; as compared with a wavelet transform (WT), it can better analyse the line and curve edge characteristics, and it has better approximation precision and sparsity description and also has good directivity. This paper introduces ground roll suppression of a seismic signal based on a fast discrete curvelet transform (FDCT) and the direct wave removal in ground penetrating radar (GPR) based on a CT. A ground roll is an interferential wave existing widely in seismic data, and it is an important step in seismic data processing to suppress ground roll. The method can separate the different waves at the same time because of CT characteristics of frequency and direction. In the ground penetrating radar signal, the direct wave is a strong noise which has line singularity. In the time-space domain, the useful information in the GPR signal is badly polluted by a strong direct wave so that the underground objects cannot be recognized correctly. The FDCT is employed to remove the background noise and separate the direct wave. The experimental results show that a CT has better effects in ground-roll suppression and direct wave removal.

• Open/close Regional gravity anomaly separation using wavelet transform and spectrum analysis

  Ya Xu et al  2009 J. Geophys. Eng. 6 279 Tag this article

  Article References Full text PDF (2.01 MB)

  In this paper, we propose the separation of the regional gravity anomaly using wavelet multi-scale analysis and choose rational decomposition results based on the spectrum analysis and their depth estimation results. The isotropic, symmetrical and low-pass wavelet filter, Halo wavelet, is used for wavelet transform and regional anomaly separation. The anomaly separation method is verified by the synthetic model of combined cuboids. It has also been used for regional gravity separation and deep structure study in the Dagang area, North China. The regional anomalies are obtained from large-scale wavelet decomposition results. The average depths estimated from the radial power spectrum and the stratum density are used to establish the relationship between the separation anomaly and buried geologic units. The results from seismic data and magnetotellurics inversion are used to assist the regional anomaly interpretation. From the wavelet analysis and spectrum comparisons, the regional anomalies caused by Moho and Cenozoic basement are given for further deep structure analysis.

• Open/close Comment on 'Statistical correlations of shear wave velocity and penetration resistance for soils'

  Ümit Gülerce  2010 J. Geophys. Eng. 7 801 Tag this article

  Article References Full text PDF (43 KB)

  A discussion is presented on a study that introduces statistical correlations between shear wave velocity (Vs) and Standard Penetration Test N (SPT-N) values. Selected key information on in situ methods that provide the best available options to obtain correlations between Vs and SPT-N is summarized with the limitations of other in situ methods. Effects of in situ tests used in the study and methodology for compilation and assessment of Vs/SPT-N data pairs are evaluated and possible uncertainties inherent in the presented correlation due to approximations and missing details are emphasized.

• Open/close Mapping water seepage from Lake Nasser, Egypt, using the VLF-EM method: a case study

  Mohamed A Khalil et al  2009 J. Geophys. Eng. 6 101 Tag this article

  Article References Full text PDF (1.40 MB)

  In order to map the spatial distribution of water seepage from the Nasser Lake to its adjacent shallow Nubian sandstone aquifer, a geophysical survey was carried out at a seismically active area called Khor El Ramlah-west that contains the Khor El Ramlah regional fault. The survey comprised nine, roughly E–W, very-low-frequency electromagnetics (VLF-EM) traverse profiles and three N–S longitudinal profiles. Qualitative interpretation of the VLF-EM data was carried out using Fraser and Karous–Hjelt filters. Quantitative interpretation of the data was done with a 2D code that performs the inversion of the tipper data. The resulted 2D inversion models revealed low resistivity zones that were interpreted as correlated (1) to sandstone formation saturated with water from seepage and (2) to a NW–SE fault that may represent a preferential path for the water flow from the lake to the onshore aquifer.

• Open/close Seismic first-arrival tomography with functional description of traveltimes

  G Göktürkler  2009 J. Geophys. Eng. 6 374 Tag this article

  Article References Full text PDF (3.09 MB)

  A two-dimensional smoothness-constrained least-squares inversion scheme was applied to seismic first-arrival time data. The inversion scheme was based on the functional description of traveltimes; thus, it did not require a step of ray tracing, and traveltimes were obtained by a finite-difference eikonal solver. The Laplacian difference of cell slownesses was used for the smoothness constraint. Model velocities were obtained by matrix inversion including the QR decomposition and iterative LSQR method. The Jacobian matrix of the partial derivatives was constructed by a finite-difference approximation based on the perturbation of the cell slowness. Since the construction of the Jacobian matrix was the most time-consuming step of the inversion scheme, Broyden's update was used for this matrix, and it was replaced by its numerical approximation obtained from Broyden's method after the third iteration and for all subsequent iterations to expedite the inversion process. This significantly improved the computational performance of the scheme by reducing the computer time for the calculation of the Jacobian matrix. The algorithm was tested by using a number of synthetic and field data sets. The test studies included both surface seismic refraction and crosshole seismic data acquisition configurations. Also image appraisal analyses were performed for the solutions obtained from both surface and crosshole field data sets by calculating model covariance and model resolution matrices. The presented algorithm yielded satisfactory results during the test studies. The stability and fast convergence rate were the main characteristics of the algorithm.

• Open/close Two-dimensional individual and joint inversion of three- and four-electrode array dc resistivity data

  M E Candansayar  2008 J. Geophys. Eng. 5 290 Tag this article

  Article References Full text PDF (1.76 MB)

  In this paper, I suggest the use of combined inversion for three- and four-electrode array data. Two-dimensional (2D) inversion results calculated using Wenner (W), Schlumberger (S), Dipol–Dipol (DD), left- and right-side pole–dipole (PD-L and PD-R), synthetic data and their combined inversion results were compared with respect to the resolution and accuracy of the inverted models. This comparison showed that the combined inversion of data from any two sets of arrays (e.g. W + S, W + DD, PD-L + DD) gave better resolution than the individual inversion of data from each array compared with the real model. However, inversion of the PD-L, PD-R and DD data sets jointly gave a better result than the single use of any electrode array and the combined inversion of any two electrode arrays. Furthermore, model resolution matrices obtained for all individual and combined data inversions showed that the combined data set inversion can recover the block resistivities at both the beginning and the end of the profile. Field data inversions also support the synthetic data inversion result.