• Ocean and Polar Research
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• v.24 no.3
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• pp.179-187
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• 2002

The Ayu Trough, located in the southern end of the Philippine Sea, represents a divergent boundary between the Philippine Sea and the Caroline Plates. A detailed geophysical survey was carried out in the Ayu Trough by R/V Onnuri. Topographically, the Ayu Trough resembles an slow spreading ridge. The trough can be divided into three sections: the south $(0^{\circ}-1^{\circ}30'N),\;middle\;(1^{\circ}30'-4^{\circ}N)$, and north $(4^{\circ}-6^{\circ}30'N)$. The seafloor in the middle section is characterized by features asymmetric with respect to the axis. These features were probably produced by NW-SE and NNW-SSE extensions and seem to support the argument that the opening of the Ayu Trough occurred in an oblique fashion. Farther south, a long transform fault but with a short offset defines the boundary between middle and southern sections. The axial depth increases a stepwise to the south of $1^{\circ}30'N$. A clear difference can be seen between the southern and middle sections with the latter exhibiting much higher mantle Bouguer anomaly values in the axial region. The anomaly indicates that the axial crust perhaps experienced a much higher degree of extension in the middle than in the southern section. The analyses of magnetic field data reveal that the region beyond 100km exhibits considerable variations, whereas the magnetic anomalies within 100km from the trough axis are very much subdued. This observation suggests that the opening of the Ayu Trough involved an initial stage of rifting of existing volcanic arcs, followed by production of new seafloor.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.87-91
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• 1998

Geophysical survey techniques, such as electromagnetic(EM), GPR, and electrical method, have been tested in the landfill area to evaluate the applicability of these methods to soil contamination measurement. The EM method has proven to be excellent on mapping the areal distribution of contaminants and the migration path for leachate. Since the field operation of EM technique is simple as well as fast, we think the EM method must be the first choice for these purposes. Electrical survey techniques have proven to be very effective on mapping sectional distribution of contaminants. Generally, the GPR method is very good on high resolution survey of shallow depth, and field data acquisition is simple, too. But the resistivity method gives better information on deep area, for example, deeper than the depth of 20 m.

• Geophysics and Geophysical Exploration
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• v.13 no.2
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• pp.175-180
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• 2010

The small loop electromagnetic (EM) method is a fast and convenient geophysical tool which can provide resistivity distribution of shallow subsurface. Especially, it can be a useful alternative of resistivity method in a very conductive environment such as a reclaimed saline land. We applied the multi-frequency small loop EM method for the site investigation of reclaimed saline land. We inverted the measured EM data using one dimensional (1D) inversion program and merged to obtain three dimensional (3D) resistivity distribution over the survey area. Finally, comparing he EM results with the drill log and measured soil resistivity sampled at 16 drill holes, we can define the site character such as thickness of landfill, salinity distribution, and etc.

• Economic and Environmental Geology
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• v.45 no.6
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• pp.685-695
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• 2012

We studied the detailed bathymetry and the geophysical characteristics of the summit of the Dokdo volcano using mutibeam echosounding and geophysical survey data. The bathymetry around the main east and west islets of the Dokdo volcano shows very shallow within about 10 m water depth. From near islets to about 30 m b.s.l., the shallow water area has very steep slope and many irregular sunken rocks. The area from about 30 m to about 80 m b.s.l. shows gentle rises and falls, and less steep slope. The area from 80 m b.s.l. has gradually flat undulation and smooth slope seabaed and is extended to offshore. The main islets of the Dokdo volcano and the rocky sea bottom elongated from the islets might be the residual part of the eroded and collapsed main crater of the Dokdo volcano. The bathymetry and the seafloor image(from backscattering) data show small craters, assumed to be formed by the eruption of later volcanism. The seafloor images propose that, except some areas with shallow sand sedimentary deposits, there are typical rocky bottom such as rocky protrusions and lack of sediments in the main morphology of the survey area. The stepped slopes of the seabed are deduced to be submarine terraces. The several prominent submarine terraces are found at the summit of the Dokdo volcano, suggesting repetition of sea level changes(transgressions and regressions) in the Quaternary. The results of the magnetic anomaly and the analytic signal have a good coherence with other geophysical consequences regarding to the location of the residual crater.

• Geophysics and Geophysical Exploration
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• v.5 no.4
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• pp.280-290
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• 2002

Three-dimensional (3-D) electromagnetic (EM) modeling algorithm has been developed using finite element method (FEM) to acquire more efficient interpretation techniques of EM data. When FEM based on nodal elements is applied to EM problem, spurious solutions, so called 'vector parasite', are occurred due to the discontinuity of normal electric fields and may lead the completely erroneous results. Among the methods curing the spurious problem, this study adopts vector element of which basis function has the amplitude and direction. To reduce computational cost and required core memory, complex bi-conjugate gradient (CBCG) method is applied to solving complex symmetric matrix of FEM and point Jacobi method is used to accelerate convergence rate. To verify the developed 3-D EM modeling algorithm, its electric and magnetic field for a layered-earth model are compared with those of layered-earth solution. As we expected, the vector based FEM developed in this study does not cause ny vector parasite problem, while conventional nodal based FEM causes lots of errors due to the discontinuity of field variables. For testing the applicability to high frequencies 100 MHz is used as an operating frequency for the layer structure. Modeled fields calculated from developed code are also well matched with the layered-earth ones for a model with dielectric anomaly as well as conductive anomaly. In a vertical electric dipole source case, however, the discontinuity of field variables causes the conventional nodal based FEM to include a lot of errors due to the vector parasite. Even for the case, the vector based FEM gave almost the same results as the layered-earth solution. The magnetic fields induced by a dielectric anomaly at high frequencies show unique behaviors different from those by a conductive anomaly. Since our 3-D EM modeling code can reflect the effect from a dielectric anomaly as well as a conductive anomaly, it may be a groundwork not only to apply high frequency EM method to the field survey but also to analyze the fold data obtained by high frequency EM method.

• ETRI Journal
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• v.27 no.3
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• pp.294-303
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• 2005

In this paper, a supervised algorithm for the evaluation of geophysical sites using a multi-level cellular neural network (ML-CNN) is introduced, developed, and applied to real data. ML-CNN is a stochastic image processing technique based on template optimization using neighborhood relationships of the pixels. The separation/enhancement and border detection performance of the proposed method is evaluated by various interesting real applications. A genetic algorithm is used in the optimization of CNN templates. The first application is concerned with the separation of potential field data of the Dumluca chromite region, which is one of the rich reserves of Turkey; in this context, the classical approach to the gravity anomaly separation method is one of the main problems in geophysics. The other application is the border detection of archeological ruins of the Hittite Empire in Turkey. The Hittite civilization sites located at the Sivas-Altinyayla region of Turkey are among the most important archeological sites in history, one reason among others being that written documentation was first produced by this civilization.

• Journal of the Korean Geophysical Society
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• v.4 no.4
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• pp.239-249
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• 2001

NAT (Network Address Translation) is an IP address modification protocol that translates private IP addresses into authentic Internet addresses. The main features of NAT are to improve network security and to save IP addresses. Generally speaking, in order to perform its functionality. NAT uses the address informaiton in the packet header. Certain application protocols, however, use the information in the packet data as well as the imformation in the packet header to perform end-to-end communication. Therefor, to support these types of application protocols, NAT should be able to perform appropriate translation of protocol information in the packet data. In this thesis, we design and implement a method which translates virtual IP information in the packet data into real IP information by using port proxy server.

• Journal of the Korean Geophysical Society
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• v.1 no.1
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• pp.51-58
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• 1998

A numerical program has been developed to model 2-D resistivity responses for a pole-pole array configuration in cross-hole resistivity measurements. Apparent resistivity and secondary potential were computed using the program for a cylindrical inhomogeneity in an uniform host medium excited by a point source of current in a borehole. Surprisingly apparent resistivity in the receiver hole turns out to be lower than the one of surrounding medium regardless of the conductivity of cylindrical inhomogeneity. Using only cross-hole data, therefore, it is impossible to interpret the conductivity of inhomogeneity. To overcome this problem, 3-D measurement and interpretation are necessary. If 3-D data acquisition is impossible, inline data should be used to get the information about the conductivity of inhomogeneity.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.35-39
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• 2003

A software to visualize and analyse 3-D seismic data is developed using OpenGL, one of the most popular 3-D graphic library, under the PC and Windows platform. The software can visualize the data as volume and slices, whose color distribution is specified by a special dialog box that can pick a color in RGB or HSV format. The dialog box can also designate opacity values so that several 3-D objects can be displayed superimposed each other. Horizon picking is implemented very easily with this software thanks to the guided picking method. The picked points from a horizon will compose a set of points, mesh, and a surface, which can be viewed and analysed in three dimensions.

• Geotechnical Engineering
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• v.9 no.3
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• pp.61-66
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• 1993

In this paper, the incorporation of qualitative(or soft) data, such as outputs of geophysical tests or construction experience which has so far been cumulated, was discussed for rock classsification. Geostatistics wart used for this research since the parameters for the design of tunnels are spatially correlated. In particular, indicator kriging technique, which is one of non -parametric approaches, was used. As a selection criteria for an optimal classification, the cost of errors was adopted and the binary classes were only considered for rock classification. In future, incorporating an appreciable amount of available qualitative data will be necessary in tunnelling projects in which quantitative data are scarce. In this respect, this research is of great significance.