• Economic and Environmental Geology
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• v.27 no.2
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• pp.201-207
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• 1994

This paper presents a technique to determine anisotropic elastic coefficients from traveltimes of seismic reflections or vertical seismic profiling (VSP) in tranversely isotropic layers whose thicknesses are known. The elastic coefficients are calculated from three different velocities (vertical, horizontal and skew velocities) which are determined from skew hyperbolic traveltimes by least-square fitting or semblance analysis. This interpretation technique is tested for synthetic traveltime data obtained for transversely isotropic models. The test shows that the anisotropic elastic constants of the models are determined accurately by this interpretation method.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.1-5
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• 2013

Stacking in seismic processing plays an important role in improving signal-to-noise ratio and imaging quality of seismic data. However, the conventional stacking method doesn't remove random noises with various distributions and outliers up to a satisfactory level. This paper introduces a robust and optimum weighted stack method which shows both robustness to outlier noises and optimum in removing random noises. This was achieved by combining the robust median stacking with the optimum weighted stacking using local correlation. Application of the method to synthetic data showed that the proposed method is very effective in suppressing random noises with various distributions including outliers.

• Earthquakes and Structures
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• v.13 no.1
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• pp.79-87
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• 2017

Seismic analysis of local site conditions is fundamental for a reliable site seismic hazard assessment. It plays a major role in mitigation of seismic damage potential through the prediction of surface ground motion in terms of amplitude, frequency content and duration. Such analysis requires the determination of the transfer function, which is a simple tool for characterizing a soil profile by estimating its vibration frequencies and its amplification potential. In this study, numerical simulations are carried out and are then combined with a statistical study to allow the characterization of design sites classified by the Algerian Building Seismic Code (RPA99, ver 2003), by average transfer functions. The mean transfer functions are thereafter used to compute RPA99 average site factors. In this regard, coming up seismic fields are simulated based on Power Spectral Density Functions (PSDF) defined at the rock basement. Results are also used to compute average site factor where, actual and synthetic time histories are introduced. In absence of measurement data, it is found that the proposed approach can be used for a better soil characterization.

• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.211-229
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• 2004

The main purpose of this paper is the numerical analysis of the non-linear seismic response of a RC building mock-up. The mock-up is subjected to different synthetic horizontal seismic excitations. The numerical approach is based on a 3D-model involving multilayered shell elements. These elements are composed of several single-layer membranes with various eccentricities. Bending effects are included through these eccentricities. Basic equations are first written for a single membrane element with its own eccentricity and then generalised to the multilayered shell element by superposition. The multilayered shell is considered as a classical shell element : all information about non-linear constitutive relations are investigated at the local scale of each layer, whereas balance and kinematics are checked afterwards at global scale. The non-linear dynamic response of the building is computed with Newmark algorithm. The numerical dynamic results (blind simulations) are considered in the linear and non linear cases and compared with experimental results from shaking table tests. Multilayered shell elements are found to be a promising tool for predictive computations of RC structures behaviour under 3D seismic loadings. This study was part of the CAMUS International Benchmark.

• Geophysics and Geophysical Exploration
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• v.6 no.4
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• pp.171-179
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• 2003

In land and marine seismic survey, we generally set receivers with equal interval suppose that sampling interval Is too narrow. But the cost of seismic data acquisition and that of data processing are much higher, therefore we should design proper receiver interval. Spatial aliasing can be occurred on seismic data when sampling interval is too coarse. If we Process spatial aliasing data, we can not obtain a good imaging result. Trace interpolation is used to improve the quality of multichannel seismic data processing. In this study, we applied the Spitz algorithm which is widely used in seismic data processing. This algorithm works well regardless of dip information of the complex underground structure. Using prediction filter and original traces with linear event we interpolated in f-x domain. We confirm our algorithm by examining for some synthetic data and marine data. After interpolation, we could find that receiver intervals get more narrow and the number of receiver is increased. We also could see that continuity of traces is more linear than before Applying this interpolation algorithm on seismic data with spatial aliasing, we may obtain a better migration imaging.

• Geophysics and Geophysical Exploration
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• v.21 no.1
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• pp.15-25
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• 2018

Seismic inversion is a high-resolution tool to delineate the subsurface structures which may contain oil or gas. On the other hand, marine controlled-source electromagnetic (mCSEM) inversion can be a direct tool to indicate hydrocarbon. Thus, the joint inversion using both EM and seismic data together not only reduces the uncertainties but also takes advantage of both data simultaneously. In this paper, we have developed a simultaneous joint inversion approach for the direct estimation of reservoir petrophysical parameters, by linking electromagnetic and seismic data through rock physics model. A cross-gradient constraint is used to enhance the resolution of the inversion image and the maximum likelihood principle is applied to the relative weighting factor which controls the balance between two disparate data. By applying the developed algorithm to the synthetic model simulating the simplified gas field, we could confirm that the high-resolution images of petrophysical parameters can be obtained. However, from the other test using the synthetic model simulating an anticline reservoir, we noticed that the joint inversion produced different images depending on the model constraint used. Therefore, we modified the algorithm which has different model weighting matrix depending on the type of model parameters. Smoothness constraint and Marquardt-Levenberg constraint were applied to the water-saturation and porosity, respectively. When the improved algorithm is applied to the anticline model again, reliable porosity and water-saturation of reservoir were obtained. The inversion results indicate that the developed joint inversion algorithm can be contributed to the calculation of the accurate oil and gas reserves directly.

• Geomechanics and Engineering
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• v.4 no.1
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• pp.1-18
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• 2012

The spatial variation of ground motion in Kolkata Metropolitan District (KMD) has been estimated by generating synthetic ground motion considering the point source model coupled with site response analysis. The most vulnerable source was identified from regional seismotectonic map for an area of about 350 km radius around Kolkata. The rock level acceleration time histories at 121 borehole locations in Kolkata for the vulnerable source, Eocene Hinge Zone, due to maximum credible earthquake (MCE) moment magnitude 6.2 were generated by synthetic ground motion model. Soil investigation data of 121 boreholes were collected from the report of Soil Data Bank Project, Jadavpur University, Kolkata. Surface level ground motion parameters were determined using SHAKE2000 software. The results are presented in the form of peak ground acceleration (PGA) at rock level and ground surface, amplification factor, and the response spectra at the ground surface for frequency 1.5 Hz, 3 Hz, 5 Hz and 10 Hz and 5% damping ratio. Site response study shows higher PGA in comparison with rock level acceleration. Maximum amplification in some portion in KMD area is found to be as high as 3.0 times compared to rock level.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.25 no.1
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• pp.23-34
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• 1997

Seismic tomography using the graph theoretical method of ray tracing is performed in two synthetic data sets with laterally varying velocity structures. The straight-ray tomography shows so poor results in imaging the laterally varying velocity structure that the ray-traced tomographic techniques should be used. Conventional ray tracing methods have serious drawbacks, i.e. problems of convergence and local minima, when they are applied to seismic tomography. The graph theretical method finds good approximated raypaths in rapidly varying media even in shadow zones, where shooting methods meet with convergence problems. The graph theoretical method ensures the globally minimal traveltime raypath while bending methods often cause local minima problems. Especially, the graph theoretical method is efficient in case that many sources and receivers exist, since it can find the traveltimes and corresponding raypaths to all receivers from a specific source at one time. Moreover, the algorithm of graph theoretical method is easily applicable to the ray tracing in anisotropic media, and even to the three dimensional case. Among the row-active inversion techniques, the conjugate gradient (CG) method is used because of fast convergence and high efficiency. The iterative sequence of the ray tracing by the graph theoretical method and the inversion by the CG method is an efficient and robust algorithm for seismic tomography in laterally varying velocity structures.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.6-17
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• 2013

Multicomponent seismic data including both P- and PS-waves have advantages in discriminating the type of pore fluid, characterizing the lithologic attributes and producing the high resolution image. However, multicomponent seismic data recorded at the vertical and horizontal component receivers contain both P- and PS-waves which have different features, simultaneously. Therefore, the wavefield separation of P- and PS-waves as a preprocessing is inevitable in order to use the multicomponent seismic data successfully. In this study, we analyzed the previous study of the wavefield separation method suggested by Jeong and Byun in 2011, where the approximated reflection angle calculated only from one refernce depth is used in rotation transform, and showed its limitation for seismic data containing various reflected events from the multi-layered structure. In order to overcome its limitation, we suggested a new effective wavefield separation method of P- and PS-waves. In new method, we calculate the reflection angles with various reference depths and apply rotation transforms to the data with those reflection angles. Then we stack all results to obtain the final separated data. To verify our new method, we applied it to the synthetic data sets from a multi-layered model, a fault model, and the Marmousi-2 model. The results showed that the proposed method separated successfully P- and PS-reflection events from the multicomponent data from mild dipping layered model as long as the dip is not too steep.

• Journal of the Korean Geotechnical Society
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• v.25 no.1
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• pp.5-19
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• 2009

Most of earthquake-induced geotechnical hazards have been caused by the site effects relating to the amplification of ground motion, which is strongly influenced by the local geologic conditions such as soil thickness or bedrock depth and soil stiffness. In this study, an integrated GIS-based information system for geotechnical data, called geotechnical information system (GTIS), was constructed to establish a regional counterplan against earthquake-induced hazards at an urban area of Daejeon, which is represented as a hub of research and development in Korea. To build the GTIS for the area concerned, pre-existing geotechnical data collections were performed across the extended area including the study area and site visits were additionally carried out to acquire surface geo-knowledge data. For practical application of the GTIS used to estimate the site effects at the area concerned, seismic zoning map of the site period was created and presented as regional synthetic strategy for earthquake-induced hazards prediction. In addition, seismic zonation for site classification according to the spatial distribution of the site period was also performed to determine the site amplification coefficients for seismic design and seismic performance evaluation at any site in the study area. Based on this case study on seismic zonations in Daejeon, it was verified that the GIS-based GTIS was very useful for the regional prediction of seismic hazards and also the decision support for seismic hazard mitigation.