• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.269-282
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• 2006

We numerically studied tsunami propagation characteristics through Korean Straits based on nonlinear shallow water equation, a robust wave driver of the near field tsunamis. Tsunamis are presumed to be generated by the earthquake in Tsuhima-Koto fault line. The magnitude of earthquake is chosen to be 7.5 on Richter scale, which corresponds to most plausible one around Korean peninsula. It turns out that it takes only 60 minutes for leading waves to cross Korean straits, which supports recently raised concerns at warning system might be malfunctioned due to the lack of evacuation time. We also numerically obtained the probability of tsunami inundation of various levels, usually referred as tsunami hazard, along southern coastal area of Korean Peninsula based on simple seismological and Kajiura (1963)'s hydrodynamic model due to tsunami-generative earthquake in Tsuhima-Koto fault line. Using observed data at Akita and Fukaura during Okushiri tsunami in 1993, we verified probabilistic model of tsunami height proposed in this study. We believe this inundation probability of various levels to give valuable information for the amendment of current building code of coastal disaster prevention system to tame tsunami attack.

• Economic and Environmental Geology
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• v.53 no.5
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• pp.505-515
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• 2020

The Yellow Sea and northern East China Sea contain a transgressive sand layer. Numerous sedimentary studies have been carried out in these sand deposits using seismic exploration and core sediment techniques, but few mineralogical studies have been reported. The major purposes of this study are to describe the distributions of heavy minerals throughout the Yellow sea and northern East China Sea and to identify the provenance of coarse sediments using the mineral chemistry. Eight heavy mineral species were identified in the study area (epidote, amphibole, garnet, zircon, sphene, rutile, apatite, and monazite). The study region was divided into six areas (areas A to F) based on heavy mineral distributions and sampling locations. In mineral chemistry, the amphiboles present are classified as edenite and hornblende in the calcic amphibole group, and the garnets are identified primarily as almandine in the pyralspite group. A combined data set of heavy mineral distributions and mineral chemistry showed clear differentiation of the characteristics of the six classified areas, enabling determination of provenance and sedimentary environment. Area A and B in the eastern Yellow Sea were originated from the Korean peninsula, and these regions showed different heavy mineral characteristics by tidal current and coastal current. In addition, monazite was only found in the area B and could be used as an indicator from the southwestern Korean peninsula. Area D and E in the western Yellow Sea showed the characteristics of sediments originating from the Huanghe, and sediment in the area E was derived from the Changjiang. Area C in the northern East China Sea appeared to have Changjiang-origin sediment, and abundant apatite indicated that area C was formed close to the Last Glacial Maximum.

• Journal of the Korean Institute of Gas
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• v.9 no.4 s.29
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• pp.57-61
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• 2005

The objective of paper is to carry out a comparative Quantitative Risk Assessment (QRA) of two KOGAS tank designs using a fault tree methodology, a standard 'Full Containment' tank and a 'Membrane' tank. For the membrane tank, both the initial KOGAS design and 4 modified KOGAS designs have been assessed, giving six separate cases. In this paper, the frequencies of releases are quantified using a fault tree approach. For clarity in the analysis, and to ensure consistency, all cases have been quantified using the same fault tree. Logic within the fault tree is used to select each of the cases. Full quantification of risks is often difficult, owing to a lack of relevant failure data, but the aim of this study has been to be as quantitative as possible, with full transparency of failure information. The most significant general cause of external LNG leaks is predicted to be a seismic event, which has been quantified nominally. 4modified KOGAS desiens to Prevent damage of bottom membrane panels that was shown in preparatory estimation could quantitively confirm safety improvement. According to result, the predicted frequencies of an external LNG leak for the full containment and modified membrane tanks are very similar, failures due to dropped pumps are predicted to be significantly greater for the membrane tank with thickened plate than for the full containment tank.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.12-17
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• 2017

We construct 3D SV-wave velocity structure of the crust and the upper mantle beneath East Asia from Rayleighwave group-velocity measurements. For the construction of the SV-wave velocity model at 10 ~ 100 km depth, we used seismic data recorded at 321 broadband stations in Korea, Japan, and China. Rayleigh-wave group-velocity dispersion curves were obtained by using the multiple filtering technique in the period range from 3 to 150 s. High SV-velocity anomalies are imaged beneath the East Sea from 10 km depth to deeper depth, implying that the Moho beneath the East Sea is between at 10 ~ 20 km depth. We estimated the Moho beneath the Korean peninsula to be around 35 km based on the depth where a high-velocity anomaly is observed. The SV-wave velocity model shows prominent fast S-velocity anomalies near northeastern Japan, associated with the subducting Pacific plate. Low-velocity anomalies are found beneath the east coast of the Korean peninsula at 100 km depth, which may play a role in the formation of the Ulleungdo and the Ulleung basin. We observed low-velocity anomalies beneath the Yamato basin at 100 km depth as well, which may indicate the upwelling of fluid from the Pacific plate via dehydration at deeper depth.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.439-448
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• 2016

Extended end-plate connections(EEPC) are a type of connection applied in Pre-Engineered Building structures comprising beam-column connections of steel structures or tapered members. Extended end-plate connections(EEPC) show different behavioral characteristics owing to the influence of plate thickness, gauge distance of high strength bolt, diameter of high strength bolt frame, and the number of high strength bolts. In the USA and Europe, extended end-plate connections(EEPC) are applied in beam-column connections of steel structures in various forms; however, these are not widely applied in structures in Korea.This can be attributed to the fact that the proposal of design strength types for extended end-plate connections(EEPC), proposal of connection specifications, evaluation of seismic performance, and are not being performed appropriately. Therefore, the purpose of this study is to provide basic data for the domestic application of Unstiffened extended endplate connections. To realize this, nonlinear finite element analysis was conducted on a 12-mm thick Unstiffened extended endplate connections.

• Journal of the Korean earth science society
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• v.34 no.1
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• pp.59-68
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• 2013

Focal mechanism solutions in the southwestern region of the Korean Peninsula ($34^{\circ}N-36^{\circ}N$, $126^{\circ}E-128^{\circ}E$) were obtained from the analysis of the recent 22 earthquakes ($M{\geq}2.0$) occurred from January, 2005 to March, 2011. The spatial differences between the epicenters recalculated by this study and those by KMA (Korea Meteorological Administration) and KIGAM (Korea Institute of Geoscience and Mineral Resources) are less than $0.05^{\circ}$, indicating a small deviation. However, they become a little bit larger in the coastal area due to a biased arrangement of seismic stations. Redetermined depths of hypocenters show a difference less than 12.7 km by comparison with the depth data announced by KIGAM. Most epicenters in inland area are located closely to the lineaments. Fault plane solutions were obtained from the analysis of P and SH wave polarities, and SH/P amplitude ratios. They show strike-slip faulting or strike-slip faulting with reverse components dominantly. The P-axes trends are mainly ENE-WSW or E-W directions. The direction of fault plane and auxiliary plane with 'NNE-SSW and WNW-ESE' or 'NE-SW and NW-SE' are dominant and almost parallel to the general trends of lineaments in the study area.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.67-74
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• 2000

Subsurface structure of the Bomun basin was studied along three survey tracks of Line-1, Line-2, and Line-3 using geomagnetic, radioactive, and seismic refraction methods. Abrupt changes found at 2.55 km west and 1.6 km east in the profile of magnetic anomaly along Line-1 are correlated with geologic boundary of the basin. Profiles of radioactive intensity also represent abrupt changes at 2.55 km west of Line-1 and at 1.9 km of Line-2. Cretaceous basement rock has relatively high magnetic anomaly of $200\;{\sim}\;500\;nT$ while sedimentary rocks of the Bomun basin have relatively low magnetic anomaly of $-100\;{\sim}\;+100\;nT$. Radioactive intensity also represents charateristic differences between Cretaceous basement and sedimentary rocks of the Bomun basin. Rocks of Cretaceous basement have lower radioactive intensity than the rocks of the Bomun basin. Magnetic anomaly of of the Bomun basin represents lowest anomaly in western part and increases gradullay toward east. This phenomenon is interpreted as a half graben structure dipping westward. Black shale known by previous studies near the western boundary has high magnetic anomalies and low radioactive intensity. This phenomenon provide a possibility of volcanic rock rather than black shale near the western boundary of the basin along Line-1. Sedimentary layers having velocities of 455 m/s, 1904 m/s, and 2662 m/s are developed to have westward dipping of $2.3^{\circ}$ in the central area of the Bomun basin. The result is consistent with a half-graben model dipping westward which were derieved from magnetic anomaly data.

• Journal of the Korean Geophysical Society
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• v.5 no.2
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• pp.111-129
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• 2002

Generally, investigation methods of cut slope are conucted only geological surface survey to gain engineering geological data of cut slopes. These methods have many problems such as limitations of investigation for a special area. So geophysical investigations such as geotomography, seismic and electrical resistivity methods have been used to search for failure surface in potential failure slopes or failed slopes. But investigation method using the borehole camera is recently a used method and it is thought that this method is more reliable method than other investigation methods because of being able to see by the eyes. Therefore, this paper was conducted investigations of borings and BIPS(Borehole Image Processing System) to search for potential sliding surfaces and was applied to obtain information of discontinuity on failed and potential failure slope in highway. As the results of BIPS, we could decide potential sliding surface in the slope, conducted to check slope stability and decided slope stability measures.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.41-51
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• 2008

To construct in situ velocity-porosity relationships for oceanic basalt, considering crack features, P- and S-wave velocity measurements on basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge were carried out under confining pressures up to 40 MPa. Assuming that the changes in velocities with confining pressures are originated by micro-crack closure, we estimated micro-crack aspect ratio spectra using the Kuster-$Toks{\ddot{o}}z$ theory. The result demonstrates that the normalised aspect ratio spectra of the different samples have similar characteristics. From the normalised aspect ratio spectrum, we then constructed theoretical velocity-porosity relationships by calculating an aspect ratio spectrum for each porosity. In addition, by considering micro-crack closure due to confining pressure, a velocity-porosity relationship as a function of confining pressure could be obtained. The theoretical relationships that take into account the aspect ratio spectra are consistent with the observed relationships for over 100 discrete samples measured at atmospheric pressure, and the commonly observed pressure dependent relationships for a wide porosity range. The agreement between the laboratory-derived data and theoretically estimated values demonstrates that the velocity-porosity relationships of the basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge, and their pressure dependence, can be described by the crack features (i.e. normalised aspect ratio spectra) and crack closure.

• Economic and Environmental Geology
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• v.30 no.1
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• pp.67-77
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• 1997

Seismic data from Lake Tanganyika indicate a complex tectonic, structural, and stratigraphic history. The Lake Tanganyika rift consists of half grabens which tend to alternate dip-direction along the strike of the rift. Adjacent half-grabens are separated by distinct accommodation zones of strike-slip motion. These are areas of relatively high basement, and are classified into two distinct forms which depend on the map-view geometry of the border faults on either side of the accommodation zone. One type is the high-relief accommodation zone which is a fault bounded area of high basement with little subsidence or sediment accumulation. These high-relief areas probably formed very early in the rifting process. The second type is the low-relief accommodation zone which is a large, faulted anticlinal warp with considerable rift sediment accumulated over its axis. These low-relief features continue to develop as rifting processes. This structural configuration profoundly influences depositional processes in Lake Tanganyika. Not only does structures dictate where discrete basins and depocenters can exist, it also controls the distribution of sedimentary facies within basins, both in space and time. This is because rift shoulder topography controls regional drainage patterns and sediment access into the lake. Large fluvial and deltaic systems tend to enter the rift from the up-dip side of half-grabens or along the rift axis, while fans tend to enter from the border fault side.