• Proceedings of the KSEG Conference
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• 2002.04a
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• pp.173-182
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• 2002

단층이동자료를 이용하여 지구조 사건을 분별하고 단층의 운동시기 및 한반도 주변지구조체계와 비교하여 양산단층의 진화과정을 해석하였다. 양산단층은 팔레오세 때 단층형성이 시작되었고 그 후 NW-SE 신장 사건에 의해 우수주향이동을 했다. 우수주향이동은 장구한 시간동안 진행되어 마이오세 초에 확장축이 바뀜에 따라 약간의 변화가 있지만 우수운동은 지속되었다. 마이오세 말에 양산단층은 좌수이동으로 변하여 운동하게 되며, 마이오세 말 혹은 플라이스토세 초에 와서 양산단층은 N-S 방향의 최대 수평압축응력을 받게 된다. 이후 플라이스토세를 전후해서 E-W 방향의 최대수평압축응력에 의해 양산단층은 다시 우수이동을 한다. 이와 같이 양산단층은 한번의 운동으로 발달된 단층이 아니라 서로 다른 응력체계 하에서 다중변형을 받아 현재의 모습으로 진화되었다고 판단된다.

• Proceedings of the KSEG Conference
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• 2002.04a
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• pp.163-171
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• 2002

지금까지 양산단층에 대한 운동학적 해석은 단지 지질분포 특성의 차이를 근거로 단순 우수주향이동으로 해석해왔다. 그러나 일반적으로 대규모 단층들은 단계적으로 서로 다른 운동체계에서 복합적인 발달과정을 거치면서 현재의 모습으로 보인다. 따라서 양산단층의 주변 지질구조와 운동학적 관계를 알아보기 위하여 양산단층 주변의 지질분포, 지질구조, 단층주변의 소단층들에 대한 특성을 분석하였다. 양산단층 주변 퇴적암의 층리면 자세는 양산단 층이 동일한 사건의 주향이동으로 형성된 단층예인의 특성이 아니라 서로 다른 응력축의 지배를 받았거나 서로 다른 크기의 운동을 받았음을 암시하고 있다. 또한 단층의 주향을 따라 단층대 폭의 변화를 살펴본 결과 크게 5개의 주기를 가지면서 변화되고 각각의 주기는 약 25-30 km 로 규칙적으로 나타난다. 또한 단층조선이 발달된 소단층의 분석결과들은 양산단층이 한번의 운동으로 발달한 것이 아니라 매우 복잡하고 다양한 사건들을 겪은 다중 변형의 산물임을 지시하고 있다.

• The Journal of Engineering Geology
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• v.29 no.1
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• pp.1-12
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• 2019

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.349-359
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• 2020

The Ulsan Fault Zone (UFZ) of NNW trend is developed in the Gyeongsang Basin, the southeastern part of the Korean Peninsula, and the Quaternary faults have been found around the UFZ. The faults generally thrust the Bulguksa igneous rocks of Late Cretaceous-Early Tertiary upon the Quaternary deposits or are developed within the Quaternary deposits. They mainly show the reverse-slip sense of top-to-the west movement. The lines connecting the their outcrop sites show a zigzag-form which is similar to the orientation of their fault surfaces which show the various trends, like (W)NW, N-S, (E)NE, ENE trends. The E-W trending dextral strike(-slip) fault is found in the Quaternary deposits of the Singye-ri valley. It cuts the N-S trending reverse fault and are cut by the N-S trending thrust fault again. Two types of at least two times of Quaternary tectonic movements related to the formation of neotectonic fault zone in the Singye-ri valley are considered from such the geometric and kinematic characteristics of Quaternary faults. One is the reverse faulting of N-S trend by the E-W directed 1st compression and associated the strike-slip tear faulting of E-W trend, and then the thrust faulting of N-S trend by the E-W directed 2nd compression. The other is the reverse faulting of N-S trend, and then the dextral strike-slip faulting of E-W trend by the NW-SE directed compression, and then the thrust faulting of N-S trend. In this paper is suggested the development history of Singye-ri neotectonic fault zone on the basis of the various orientations of Quaternary fault surfaces around the UFZ, and the zigzag-form connecting line of their outcrop sites, and the compressive arc-shaped lineaments which convex to the west reported recently in the Yangsan Fault Zone.

• The Journal of the Petrological Society of Korea
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• v.23 no.2
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• pp.75-103
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• 2014

The Quaternary faults are extensively observed along major inherited fault zones (i.e. Yangsan Fault System, Ulsan Fault, Yeonil Tectonic Line, Ocheon Fault System) in SE Korea. Their geometry and kinematics provide a very useful piece of information about the Quaternary crustal deformation and stress field in and around Korean Peninsula. Using magnetic fabrics (AMS), we attempted to determine the slip senses of Jinti, Mohwa, Suseongji2, and Wangsan faults and then interpreted the fabric development process of fault gouge and the characteristics of stress field during the Quaternary. All the magnetic fabrics of the faults, except the Wangsan Fault, consistently indicate a dominant reverse-slip sense with weak strike-slip component. Most of the oblate fabrics are nearly parallel to the fault surface and the anisotropy degrees generally increase in proportion to the oblatenesses. These results suggest that the fabrics of the fault gouges resulted from a progressive deformation due to continuous simple shear during the last reactivation stage as reverse faulting. It is also interpreted that the pre-existing fabrics were overwhelmed and obliterated by the re-activated faulting. Paleostress field calculated from the fault slip data indicates an ENE-WNW compressive stress, which is in accord with those determined from previous fault tectonic analysis, focal mechanism solution, and hydraulic fracturing test in and around Korean Peninsula.

• The Journal of Engineering Geology
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• v.17 no.2 s.52
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• pp.299-307
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• 2007

We collected data of hydraulic fracturing tests and overcoring tests conducted in 84 boreholes in the south-east Korea in order to analyze the contemporary state of stress in this region. The average direction of the maximum horizontal stress was determined to be $N66^{\circ}{\pm}31^{\circ}E$. The relative magnitudes of the three principal stresses was ${\sigma}_v$ (vertical stress) < ${\sigma}_h$ (minimum horizontal stress) < ${\sigma}_H$ (maximum horizontal stress), indicating thrust fault stress regime. The stress ratio K (horizontal stress/vertical stress) was relatively high (2.2

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.23-30
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• 1998

An estimation of seismic risk parameters by seismic zones of the Korea Peninsula in order to calculate the seismic hazard values using these was erformed. Seven seismic source zones were selected in consideration of seismicity and geology of Korean Peninsula. The seismicity parameters that should be estimated are maximum intensity, activity rate and b value in the Gutenberg - Richter relation. For computation of these parameters, least square method or maximum likelihood method is applied to the earthquake data in two ways; the one for the data without maximum intensity and the other with maximum intensity. Earthquake data since Choseon Dynasty is regarded as complete and estimation of parameters was made for these data using above two ways. And recently, a new method is published that estimate the seismicity parameters using mixed data containing large historical events and recent complete observations. Therefore, this method is applied to the whole earthquake data of the Korean Peninsula. It turns out that the b value computed considering maximum intensity is slightly lower than that computed considering without maximum intensity, and it becomes still lower when the incomplete data prior to Choseon Dynasty is used. In the case of the activity rates, the values obtained without maximum intensity and that with maximum intensity are similar, though they are lower when the incomplete data is used. The values of maximum intensities are usually lower when considering incomplete data. In the seismic source zone including the Yangsan Fault zone, however, the values are higher when considering the incomplete data.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.59-71
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• 1990

Magnetic anisotropy of a total of 213 independently oriented Tertiary rock samples from Pohang-Ulsan area has been studied. The sampled strata comprise basalts, tuffs and black shale, and range in age from Eocene to Miocene. The previous palaeomagnetic studies indicate that their magnetic carrier minerals are titanomagnetites. Among 23 sampled sites, 11 sites were found to preserve magnetic load foliation parallel to the bedding plane caused by the Iithostatic load of the overlying strata. Other 4 sites showed magnetic lineation indicating the flow direction of lava and tuffs. The remaining 8 sites revealed the magnetic tectonic foliation nearly vertical to the bedding plane. This magnetic foliation is interpreted to be generated by tectonic compression which acted nearly horizontally during the solidification stage of the strata. The compression directions deduced from the tectonic foliation of the 8 sites can be grouped into internally very consistent two group: a N-S trending one and the other WNW-ESE trending one. It is interpreted that the former N-S compression was associated with the N-S spreading of the East Sea(Sea of Japan) and the dextral strike-slip movement of the Yangsan-Ulsan fault system. The latter WNW-ESE compression is interpreted to represent the folding and reverse faulting activity in the Korean and Tsushima straits during middle/late Miocene times.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.431-446
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• 1998

The calcretes from the Cretaceous Gyeongsang Supergroup in the vicinity of Ulsan city have been examined at five sites (Daedong, Seodong, Ansachon, Deogha, and Mangyangri). In these calcretes, evidences indicating pedogenic origin are recognized. Included are calcite aureoles around detrital grains, pedotubular pores, microstromatactis, circumgranular cracks, fitted structure of adjacent peloids, calcrete ooids, rhizocretions, and calcrete intraclasts. On the basis of calcrete development together with lithofacies, the depositional environments of those deposits are interpreted as lake margin (Daedong deposits), braided to low-sinuosity river (Seodong deposits), braid plain (Ansachon deposits), and meandering river (Deogha and Mangyangri). Stratigraphically, the fluvial deposits of study area show paleoenvironmental change from braided to low-sinuosity river plain under arid climatic condition to meandering river plain under seasonally wet an dry climatic condition. The stratigraphic successions of the Gyeongsang Supergroup of the study area Qacustrine-fluvial-Iacustrine) together with paleoenvironmental change of fluvial deposits suggest that those deposits can be correlated with the Banyaweol-Songnaedong-Geoncheonri formations of the Gyeongsang Supergroup in the western part of the Yangsan Fault.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.109-120
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• 2018

The distributional characteristics of fault segments in Cretaceous and Tertiary rocks from southeastern Gyeongsang Basin were derived. The 267 sets of fault segments showing linear type were extracted from the curved fault lines delineated on the regional geological map. First, the directional angle(${\theta}$)-length(L) chart for the whole fault segments was made. From the related chart, the general d istribution pattern of fault segments was derived. The distribution curve in the chart was divided into four sections according to its overall shape. NNE, NNW and WNW directions, corresponding to the peaks of the above sections, indicate those of the Yangsan, Ulsan and Gaeum fault systems. The fault segment population show near symmetrical distribution with respect to $N19^{\circ}E$ direction corresponding to the maximum peak. Second, the directional angle-frequency(N), mean length(Lm), total length(Lt) and density(${\rho}$) chart was made. From the related chart, whole domain of the above chart was divided into 19 domains in terms of the phases of the distribution curve. The directions corresponding to the peaks of the above domains suggest the directions of representative stresses acted on rock body. Third, the length-cumulative frequency graphs for the 18 sub-populations were made. From the related chart, the value of exponent(${\lambda}$) increase in the clockwise direction($N10{\sim}20^{\circ}E{\rightarrow}N50{\sim}60^{\circ}E$) and counterclockwise direction ($N10{\sim}20^{\circ}W{\rightarrow}N50{\sim}60^{\circ}W$). On the other hand, the width of distribution of lengths and mean length decrease. The chart for the above sub-populations having mutually different evolution characteristics, reveals a cross section of evolutionary process. Fourth, the general distribution chart for the 18 graphs was made. From the related chart, the above graphs were classified into five groups(A~E) according to the distribution area. The lengths of fault segments increase in order of group E ($N80{\sim}90^{\circ}E{\cdot}N70{\sim}80^{\circ}E{\cdot}N80{\sim}90^{\circ}W{\cdot}N50{\sim}60^{\circ}W{\cdot}N30{\sim}40^{\circ}W{\cdot}N40{\sim}50^{\circ}W$) < D ($N70{\sim}80^{\circ}W{\cdot}N60{\sim}70^{\circ}W{\cdot}N60{\sim}70^{\circ}E{\cdot}N50{\sim}60^{\circ}E{\cdot}N40{\sim}50^{\circ}E{\cdot}N0{\sim}10^{\circ}W$) < C ($N20{\sim}30^{\circ}W{\cdot}N10{\sim}20^{\circ}W$) < B ($N0{\sim}10^{\circ}E{\cdot}N30{\sim}40^{\circ}E$) < A ($N20{\sim}30^{\circ}E{\cdot}N10{\sim}20^{\circ}E$). Especially the forms of graph gradually transition from a uniform distribution to an exponential one. Lastly, the values of the six parameters for fault-segment length were divided into five groups. Among the six parameters, mean length and length of the longest fault segment decrease in the order of group III ($N10^{\circ}W{\sim}N20^{\circ}E$) > IV ($N20{\sim}60^{\circ}E$) > II ($N10{\sim}60^{\circ}W$) > I ($N60{\sim}90^{\circ}W$) > V ($N60{\sim}90^{\circ}E$). Frequency, longest length, total length, mean length and density of fault segments, belonging to group V, show the lowest values. The above order of arrangement among five groups suggests the interrelationship with the relative formation ages of fault segments.