• The Journal of the Petrological Society of Korea
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• v.24 no.4
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• pp.307-321
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• 2015

The study area, Bophi Vum, Myanmar, is composed of the harzburgite, serpentinite and dunite, those are covered by Quaternary alluvium. The chromite ore bodies are developed within dunite and harzburgite bodies, mainly within dunite bodies. To identify the extension of the chromite ore bodies, we carried out trench surveys in the 5 different sites. The chromite ore bodies have 0.3-1.5 m wide, and several meters of extension, and deformed strongly as a sigmoid and a boudin shapes with dunite and harzburgite bodies by ductile deformation. The ductile deformation have a top-to-the-west shear sense, indicating the existence of a westward thrusting. The NW-SE trending distribution of ore bodies is related to the dextral ductile shearing and/or to the block rotation as a book-shelf structure by dextral strike-slip movement.

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.13-23
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• 1998

An intensity of the 1997 Kyungju earthquake(M=4.3) was estimated at three hundred locations based on the field survey and questionaires from 2200 residents. The isoseismal shows almost circular pattern which doesnot reflect some specific geological trends. However,most of the Kyeongsang basin except the southwestern part is included within the area of MM intensity V. There occurred strong shaking, numerous cracks on the wall of the houses, and movement of slate on the roofs, falling of the tiles from the monument. The isoseismal of the highest MM intensity VII, 1-3 km in width and 9 km in length, is elongated along the Yangsan fault, which is located about 1.5 km west from epicenter. The lineaments near the epicenter exhibit almost N-S and NNE directions. The lineament distribution, the pattern of damage area and the solution of fault plane suggest that the Kyongju earthquake occurred with strike-slip sense along the Yangsan fault. The calculated intensity attenuation(I) with distance(R) is as follows : $I{\;}={\;}I_o{\;}+{\;}0.3461{\;}-{\;}0.3274{\;}{\times}{\;}1nR{\;}-{\;}0.086{\;}{\times}{\;}R$.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.127-132
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• 2011

We acquired and interpreted more than 650 km of high-resolution seismic reflection profiles in the Hupo Basin, offshore east coast of Korea at $37^{\circ}N$ in the East Sea (Japan Sea) to image shallow and basement deformation. The seismic profiles reveal that the main depocenter of the Hupo Basin in the study area is bounded by the large offset Hupo Fault on the east and an antithetic fault on the west; however, the antithetic fault is much smaller both in horizontal extension and in vertical displacement than the Hupo Fault. Sediment infill in the Hupo Basin consists of syn-rift (late Oligocene. early Miocene) and post-rift (middle Miocene.Holocene) units. The Hupo Fault and other faults newly defined in the Hupo Basin strike dominantly north and show a sense of normal displacement. Considering that the East Sea has been subjected to compression since the middle Miocene, we interpret that these normal faults were created during continental rifting in late Oligocene to early Miocene times. We suggest that the current ENE direction of maximum principal compressive stress observed in and around the Korean peninsula associated with the motion of the Amurian Plate induces the faults in the Hupo Basin to have reverse and right-lateral, strike-slip motion, when reactivated. A recent earthquake positioned on the Hupo Fault indicates that in the study area and possibly further in the eastern Korean margin, earthquakes would occur on the faults created during continental rifting in the Tertiary.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.244-244
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• 1997

The Janggunbong area(this study area) at the central-south part in the North Sobaegsan Massif, Korea, consists mainly of Precambrian(Wonnam and Yulri Formations)-Paleozoic [Joseon Supergroup(Jangsan Quarzite, Dueumri Formation and Janggum Limestone) and Pyeongan Group(Jaesan and Dongsugok Formations)] metasedimentary rocks and Mesozoic granitoid(Chunyang granite.) This study is to interpret geological structure of the North Sobaegsan Massif in the Jang-gunbong area by analysing rock-structure and microstructure of the constituent rocks. It indicates that its geological structure was formed at least by four phases of deformation after the formation of gneissosity(S0) in the Wonnam Formation and bedding plane(S0) in the Paleozoic metasedimentary rocks. The first phase deformation(D1) formed tight isoclinal fold(F1). Its axial plane(S1) strikes east-west and steeply dips north. Its axis (L1) subhorizontally plunges east-west. The second phase deformation(D2), which was related to ductile shear deformation, formed stretching lineation(L2) and shear foliation(S2). The sense of the shear movement indicates dextral strike-slip shearing(top-to-the east shearing). The third phase deformation(D3) formed open inclined fold(F3). Its axial plane(S3) strikes east-west and moderately or gently dips north. Its axis(L3) subhorizontally plunges east-west. The F3 fold reoriented the original north-dipping S1 foliation and D2 shear sense into south-dipping S1 foliation(top-to-the west shear sense on this foliation) at its a limb. The four phase of deformation(D4) formed asymmetric-type open inclined fold(F4) of NE-vergence with NW striking axial plane(S4) and NW-NNW plunging axis(L4). The F4 fold partly reoriented pre-D4 structural elements with east-west trend into those with north-south trend. Such reorientation is recognized mainly in the Paleozoic metasedimentary rocks.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.224-259
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• 1997

The Janggunbong area(this study area) at the central-south part in the North Sobaegsan Massif, Korea, consists mainly of Precambrian(Wonnam and Yulri Formations)-Paleozoic [Joseon Supergroupuangsan Quarzite, Dueumri Formation and Janggun Limestone) and Pyeongan Group (Jaesan and Dongsugok Formations)l metasedimentary rocks and Mesozoic granitoid(Chunyang granite). This study is to interpret geological structure of the North Sobaegsan Massif in the Janggunbong area by analysing rock-structure and microstructure of the constituent rocks. It indicates that its geological structure was formed at least by four phases of deformation after the formation of gneissosity(S0) in the Wonnam Formation and bedding plane(S0) in the Paleozoic metasedimentary rocks. The first phase deformation(D1) formed tight isoclinal fold(F1). Its axial plane(S1) strikes east-west and steeply dips north. Its axis(L1) subhorizontally plunges east-west. The second phase deformation(D2), which was related to ductile shear deformation, formed stretching lineation(L2) and shear foliation(S2). The sense of the shear movement indicates dextral strike-slip shearing(topto-the east shearing). The third phase deformation(D3) formed open inclined fold(F3). Its axial plane(S3) strikes east-west and moderately or gently dips north. Its axis(L3) subhorizontally plunges east-west. The F3 fold reoriented the original north-dipping S1 foliation and D2 shear sense into south-dipping S1 foliation(top-to-the west shear sense on this foliation) at its a limb. The four phase of deformation(D4) formed asymmetric-type open inclined fold(F4) of NE-vergence with NW striking axial plane(%) and NW-NNW plunging axis(L4). The F4 fold partly reoriented pre-D4 structural elements with east-west trend into those with north-south trend. Such reorientaion is recognized mainly in the Paleozoic metasedimentary rocks.

• The Journal of the Petrological Society of Korea
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• v.4 no.2
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• pp.144-152
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• 1995

The Jangsan Quartzite of the Joseon Supergroup and the foliated granite (so-called granitlc gneiss of presumed Precambrian age) of the Yeongnam massif are in direct contact at Cheondong-ri area, 6 km @SE of Danyang. sllthough it has been thought traditionally that the Jangsan Quartzite overlies unconformably the f&ted granite, it is difficult to interpret the contact as an unconformity smce the basal conglomerate in- the lower part of the Jangsan Quartzite does not have any clast of the foliated granite, Rather, recent structural studies of this area indlcate that the contact is a ductile shear zone. However, the sense and age of the shear movement are still problematic. Our mesoscopic and microscopic studies of &tre Cheondong-11 semi-brittle shear zone involving foliated cataclasite and phyllonite, which is a pa& of the Ogdong fault, indlcate a top-to-the northeast shearing, i.e., dextral strike slip. We also performed Pb-Pb dating for the age-unknown foliated granite, since the age of deformed granite ccarr emtrain the maximum age of deformation. The whole rock and feldspar Pb isotape data for the foliated granite and a micaceous xenolith define an isoc chron age of $2.16{\pm}0.15$ Ga ($2{\sigma}$;MSWD=4.4) which is interpreted as the emplacement age of the granite. This early Proterozoic age agrees with those of Precambrian igneous activity In the Yeongnam massif reported previously. The obtaiPrfid gge confirms the traditional idea about the age of the foliated granite and indicates that other methd(s) should be employed to constrain the age of the shear movement.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.299-308
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• 2009

A magentotelluric (MT) survey at the Uiseong area has been performed for the site investigation of pilot scale $CO_2$ sequestration. The purpose of the MT survey is to delineate deeply extended fracture systems that can act as a leakage path of injected $CO_2$ Plume. Since the target area is extremely noisy in electromagentic sense, low frequency data below 1 Hz cannot be used for inversion. Two- and three-dimensional interpretation of the MT data showed a very clear conductive anomaly, which has the direction of $N55\sim65^{\circ}W$ and is extended roughly down to 1.6 km. It have the same direction with the strike-slip faults, the Gaeum and Geumcheon Faults. On the contrary, the eastern part of the survey area shows relatively homogeneous to the depth of 2 km though some small fractures at shallow depths can be found. Test drilling and high-definition borehole surveys should be followed at the eastern part of the survey area and hydraulic fracturing is required for injection of $CO_2$, because mean porosity of the sedimetary rock in the area is only 1.47%.