• Journal of the Korean earth science society
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• v.21 no.6
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• pp.675-682
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• 2000

25 seismic shot gathers were obtained to study the two dimensional subsurface shear wave velocities in a landfilled area near the Keum river estuary. Borehole(BH#1 and BH#2) tests at two sites were made in the same area. Standard Penetration Tests were also performed at the same time. The 2-D shear wave velocity structure resulted from the inversion of the seismic data shows that the subsurface of the studied area consists of the upper 1${\sim}$3 meter thick layer(200 m/sec${\sim}$700 m/sec), the middle 5${\sim}$8 m thick low velocity layer(100 m/sec${\sim}$400 m/sec), and the lower layer of 1000m/sec or higher shear wave velocities. The thickness of the low velocity layer decreases from the BH #1 site to the BH #2 site. The depth to the basement also decreases toward the BH #2 site. The examination of the S wave velocity structure, the description of the geologic contents, and the Standard Penetration Test values indicate that the middle layer of low shear wave velocity may be related to the clay content of the layer. On the other hand, the Standard Penetration test values increase with depth, showing no significant relationship with the geologic contents of the subsurface. This study shows that the inversion of surface waves can be effective in the study of the shear wave velocity, especially in the area where low velocity layers can be found. The method of inversion of surface waves also can be used as a viable technique to overcome the limit of the seismic refraction method.

• Economic and Environmental Geology
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• v.15 no.4
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• pp.177-188
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• 1982

The Chungju and Seosan Groups have been known usually as Precambrian formations in Korea. But their relative and absolute ages have been controvericial problem in relation with other geologic system such as so-called Ogcheon and Yeoncheon Systems in Korea. This study has mainly focused on the corelation of the Chungju Group with the Seosan Group in their stratigraphy, structure, metamorphism, and iron ore deposits. In the process of study, the auther surveyed and reclassified the Chungju and Seosan Groups and corelated with Gyeonggi and Ogch cheon metamorphic belts and got some new data. The Chungju iron-bearing formations showing transtitional relation with the Gyeonggi Gneiss Complex and the Jangamri Formation consisting mainly of pebble bearing calcarious phyllite, should be seperated from the Gyemyeongsan formation which is mainly composed of metavolcanic rocks. The Jangamri Formation and the coaly phyllite, which can be corelated respectively with the Hwaggangri Formation and Changri Formation in Ogcheon Group, are repeated in the Gyemyeonsan and Munjuri Formations with the overturned anticlinal folding(F1). So the Chungju Group which was defined as an indipendant geologic unit from the Ogcheon Group should be limited only on the Chungju iron Formation. The Seosan Group can be classified stratigraphically such as Seosan Formation consisting of iron-bearing quartzite and mica schist, Daesan Formation overlying unconformably on the Seosan Formation and Gyeonggi Gneiss Complex. Taean Formation overlying unconformably on the Daesan Formation should be seperated from Seosan Group. There are many similarity in the stratigrphy, structure, and metamorphic facies between Chungju and Seosan Groups exept the metavolcanic rocks in the Gyemyeongsan and Munjuri Formations and the pebble bearing calcareous phyllite in the Jangamri Formation. The two Groups were deformed with two kinds of differant stages, the first shows $N30^{\circ}-40^{\circ}E$ trend of fold axis, the second $N70^{\circ}-80^{\circ}W$ respectively. The Seosan Formation, which is the lowest formation in Seosan Group and bearing the iron formation, was metamorphosed at 2500 m. y. before. These age is similar with the metamorphic age of Gyeonggi metamorphic belt and with the age of Algoman and Kenoran Orogenies which devide the Precambrian into Archean and Proterozoic Era. So the Seosan Formation, which is included in some migmatitic rocks of Gyeonggi Gneiss Complex, is the oldest formation in Korea and can be corelated with the Anshan Group which bears the oldest iron formation in China. The metamorphic facies of the Precambrian metamorphism in Seosan area is simillar with that of Chungju area, showing high temperature-low pressure amphibolite facies which is corelated with the Gyeonggi metamorphic belt, the oldest metamorphic belt in Korea ($650^{\circ}-680^{\circ}C$, 3.2-4.4 Kb). The high temperature intermediate pressure amphibolite facies in Seosan area with the low temperature-intermediate presure greenschist facies of Taean formation is corelated with that of Ogcheon Group ($590^{\circ}-640^{\circ}$ C, 5.2-6.3 Kb). The Chungju and Seosan iron formations were deposited in Archean, showing geochemical composition of Precambrian iron formations. The Chungju iron formation was mainly formed by the chemical precipitation, on the other hand, the Seosan iron formation was formed by alternated action of chemical and detrital depositions.

• Economic and Environmental Geology
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• v.19 no.3
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• pp.225-230
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• 1986

Various interpretations on the boundary between the $Okch{\check{o}}n$ system and the Great Limestone series of the $Chos{\check{o}}n$ system, and on the geologic structure and stratigraphy of the $Okch{\check{o}}n$ system have been yielded by the previous studies, and they are still in hot debate. The present work has mainly studied on the boundary between the $Okch{\check{o}}n$ and $Chos{\check{o}}n$ systems in the south of $Jech{\check{o}}n$, and the geology in its vicinity to clarify the previous misinterpretations if any on the geologic structure and in trun stratigraphy of the area concerned. The boundary between the $Okch{\check{o}}n$ system and the Great Limestone series of the $Chos{\check{o}}n$ system has been thought to be (1) gradational relation which means two systems are the same formation, (2) unconformable relation in which the $Okch{\check{o}}n$ system overlies the $Chos{\check{o}}n$ system, (3) unconformable relation in which the $Chos{\check{o}}n$ system overlies the Okchon system indicating that the age of the $Okch{\check{o}}n$ system is Precambrian, and (4) fault contact in which the $Okch{\check{o}}n$ system of Precambrian age comes in contact with the $Chos{\check{o}}n$ system of Cambro-Ordovician age. The present study clearly found that the relationship between the two systems is a fault zone contact. Shear zone of a width of 300 to 400m is developed, and andesitic volcanics and basic dikes are intruded along the fault zone. This fault contact is exactly the north extension of the Bonghwajae fault, which was denominated long time ago by two of the present authors. The eastern side of the fault has been uplifted so that the $S{\check{o}}changri$ formation of the $Okch{\check{o}}n$ system cropped out in the zone of the Great Limestone series. All the previous workers thought that the $S{\check{o}}changri$ formation rests on the Great Limestone series, but the present study found an overthrust having a strike of $N8^{\circ}E$ and dip of $30^{\circ}NW$ between them, and the $S{\check{o}}changri$ formation has thrusted over the Great Limestone series at the central part of the study area. In the southern and northern parts of this uplifted $S{\check{o}}changri$ formation, the Great Limestone series rests unconformably on it. In the eastern part of the study area where the Mt. Dangdu is located and the previous workers thought that the $S{\check{o}}changri$ formation rests on the Great Limestone series, Precambrian basement rock whose age is older than 1720+50 m.y. crops out in the northern part of the east-west trending high angle fault, and the Great Limestone series rests unconformably on the basement.

• Geophysics and Geophysical Exploration
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• v.22 no.2
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• pp.62-71
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• 2019

We conducted DC resistivity and MT survey to obtain the resistivity structure of the central Myanmar basin. We tried to analyze the underground structure through the resistivity variation of Myanmar by performing representative geophysical survey methods because researches on the electrical resistivity structure are insufficient in Myanmar. The electrical resistivity is expected to be low considering the marine sedimentary rocks composed of shale and sandstone in this area. The DC resistivity and MT survey were carried out using SmartRho of Geolux Co., Ltd. and MTU-5A of Phoenix geophysics Ltd., respectively, to visualize the electrical resistivity structure of study area. DC resistivity and MT survey showed an electrical resistivity less than dozens of ohm-m within the depth of 100 m. In particular, MT survey data were almost similar to TM and TE modes in the frequency range above 1 Hz. The two-dimensional inversion of MT data showed a subsurface structure with low resistivity below 150 ohm-m divided into east-west direction. We confirmed that the inversions of DC resisitivity and MT data along an overlapped survey line represented similar results. In the future, considering the high electrical conductivity, it would be effective to perform DC resistivity and MT survey simultaneously to study the electrical resistivity structure of the central Myanmar basin.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11b
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• pp.3-17
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• 2002

Tertiary Pohang basin distributed in south weatern part of the korean peninsula, is composed of Chunbuk formation as the basal conglomerate, Hakjon formation, Duho formation and intrusive basalt which is 15 Ma by absolute age data. The basement of the basin is represented by Cretaceous sedimentary rocks, Hakjon welded tuff and Chilpo welded tuff and rhyolite. The fault systems at the basement of the Pohang basin are consist of NNE direction fault, WNW to EW trend fault. NNE fault is not only strike-slip fault but also normal fault. n fault has sinistral strike-slip sene and the EW fault is strike-slip and normal fault. In the Tertiary basin, the fault system is represented by nm strike-slip fault, EW normal fault and NNE thrust fault. By these fault relationships and geometries, it is interpreted that NNE sinistral strike-slip fault and nomal fault have acted at Creceous times. At Tertiary tines, NNE dextralstrike-slip fault and EW normal fault has created. Progressively Tertiary Pohang basin was influenced by the trenspression to make thrust fault and fold, namely as inversion tectonics.

• Economic and Environmental Geology
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• v.9 no.3
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• pp.143-156
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• 1976

The Cretaceous metal ore deposits in the Gyeongsang basin of Gyeongsangbuk-do are characterized by the formation of metallogenic provinces which show zonal distribution pattern around Yeonil province where pneumatolytic type is dominated and hydrothermal type are distributed in the order of decreasing temperature type outward. Some Cretaceous granitic rocks include zoned alkali feldspars which reflect rapid variation of $H_2O$ during emplacement and crystallization of the water-saturated granitic magma. The ore deposits are considered to be originated from upward transportation of ore solution from the excess of water exhausted from uprising magma, which seems to be intimately related to the fact that the majority of the ore deposits in Daegu area are cummulated around the granites including zoned alkali feldspars. In order to collect geochemical data necessary for geochemical exploration in the study area, certain trace elements were chosen as pathfinders from monzonite and soil in the vicinity of Dalsung Tungsten Mine by studying the dispersion patterns of trace elements: Ba and Sr show trends to decrease toward ore deposit while Cu, Pb, and Mo increase. Around mining area there are distributed apparently Equisetum arvense Linne and Mentha sachinensis Kudo which may be used as index plants. In the viewpoint of geologic structure, the trends of the ore veins in contact aureole around the Palgongsan granite body correspond with the pre- and syn- plutonism joint pattern in hornfels in the area.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.215-219
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• 1990

Geological and electrical resistivity surveys along the survey line of about 3 km between Kyungsangbukdo Youngilgun Hodong and Gwangmyungdong using by dipole-dipole electrode array method were carried out to examine the boundary and structural relationship between Tertiary Pohang and Janggi basins. Electrical resistivity data were interpreted qualitatively and quantitatively by means of pseudosection of apparent electrical resitivity distribution and finite difference method for two dimensional geologic structure model. The nearly vertical fault zone with low electrical resistivity value of 1-5 Ohm-m and widths of about 200m at the surface and 400 m at depth exists around 1.2 km west of national road between Ocheoneup and Yangbukmyun. Mudrocks, sandstones and tuffaceous rocks are widely distributed with electrical resistivity values of 6-77 Ohm-m. Especially, tuffaceous rocks with relatively high electrical resistivity value are predominant at eastern side of fault zone. Consequently, it is known that Pohang and Janggi basins are in fault contact.

• Economic and Environmental Geology
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• v.28 no.1
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• pp.69-77
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• 1995

Tertiary Pohang basin distributed in south western part of the Korean peninsula, is composed of Chunbuk formation as the basal conglomerate, Hakjon formation, Duho formation and intrusive basalt having 15 Ma by absolute age data. The basement of the basin is represented to Cretaceous sedimentary rocks, Hakjon welded tuff and Chilpo welded tuff and rhyolite. The fault systems in the basement of Tertiary Pohang basin are consist of $N20^{\circ}E$ fault, $N60^{\circ}W$ and E-W trend. NNE fault is not only strike-slip but also normal dip-slip. WNW fault has sinistral strike-slip sense and the geometry of E-W fault is strike-slip and normal faults. In the basin, the fault system is represented to $N20^{\circ}E$ strike-slip, E-W normal and NNE thrust faults. By these fault relationship and geometry, it is interpreted that NNE sinistral strike-slip fault and N-S normal faults have acted at the Cretaceous basement. After Miocene NNE dextral strike-slip fault has acted and created E-W normal fault. Progressively Tertiary basin was influenced by the transpression to make thrust and fold, namely inversion tectonics.

• Tunnel and Underground Space
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• v.3 no.1
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• pp.63-79
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• 1993

The design of tunnels in rock masses often demands more informations on geologic features and rock mass properties than acquired by usual field survey and laboratory testings. In practice, the situation that a perfect set of geological and mechanical input data is given to geomechanics design engineer is rare, while the engineers are asked to achieve a high level of reliability in their design products. This study presents an artificial neural network which is developed to resolve the difficulties encountered in conventional design techniques, particulary the problem of deteriorating the confidence of existing numerical techniques such as the finite element, boundary element and distinct element methods due to the incomplete adn vague input data. The neural network has inferring capabilities to identify the possible failure modes, support requirements and its timing for underground openings, from previous case histories. Use of the neural network has resulted in a better estimate of the correlation between systems of rock mass classifications such as the RMR and Q systems. A back propagation learning algorithm together with a multi-layer network structure is adopted to enhance the inferential accuracy and efficiency of the neural network. A series of experiments comparing the results of the neural network with the actual field observations are performed to demonstrate the abilities of the artificial neural network as a new tunnel design assistance system.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.21-26
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• 2003

The visualization of three dimensional geophysical data is forcing a revolution in the way of working, and allowing the discovery and production of hydrocarbons at much lower costs than previously thought possible. There are many aspects of this revolution that are behind the scenes, such as the database structure, the storage and retrieval of data, and the exchange of data among programs. Also the user had changes where the interpreter (or manager, or processor) actually looks at and somehow interacts with the data. The use of opacity in volume rendering, and how its judicious application can assist in imaging geologic features in three dimensional seismic data. This revolutionary development of new technology is based on the philosophy of synergy of inter-disciplines of the oil industry. Group interaction fostered by large room visualization environments enables the integration of disciplines we strive for, by putting the petrophysicist, geologist, geophysicist, and reservoir engineer in one place, looking at one image together, without jargon or geography separating them. All these tools developed in the oil industry can be applied into the civil engineering industry also such as the prior geological and geophysical survey of the constructions. Many examples will show how three dimensional geophysical technology might make a revolution in the oil business industry now and in future. This change can be considered as a fusion process at data, information, and knowledge levels.