경주시 양북면 단층암의 원소거동과 광물조성 특성

송수정(Su Jeong Song),추창오(Chang Oh Choo),장천중(Chun-Joong Chang),장윤득(Yun Deuk Jang) 한국암석학회 2013 암석학회지 Vol.22 No.2

단층활동 과정에서 암석 내 화학조성과 광물 조성 간의 연관성을 이해하기 위한 목적으로 경주시 양북면 용당리에 발달하는 단층암에 대하여 XRF, ICP, XRD, EPMA/BSE 분석을 시행하여 단층암 내의 광물조성 및 원소의 거동 경향성을 파악하였다. 단층암의 대표적인 주성분으로서 SiO₂는 61.6~71.0%의 범위로 가장 높은 함량을 나타내며, Al₂O₃는 10.8~15.8%이다. Na₂O는 0.22~4.63%, K₂O는 2.02~4.89%이고, Fe₂O₃는 3.80~12.5% 범위로 나타나 단층암 내에서 특히 이들 원소의 편차가 크다. 각력대에서 비지대로 갈수록 감소하는 경향을 나타내는 원소에는 Na₂O, Al₂O₃, K₂O, SiO₂, CaO, Ba, Sr 등이 있고, 증가하는 경향을 나타내는 원소에는 Fe₂O₃, MgO, MnO, Zr, Hf, Rb 등이 있다. 이러한 화학적 거동은 각력대가 대부분 석영, 장석류와 같은 주요 조암광물로 구성되는 반면, 비지대는 일라이트와 같은 점토광물이 다량 함유되는 것과 밀접한 관련성이 있다. 본 단층대에서는 기존 광물의 변질과 동시에 점토광물이 생성되는 데 있어 단층 활동에 수반된 유체활동이 큰 영향을 끼쳤다. 단층활동 초기에는 파쇄대가 열수의 통로로 작용하는 과정에서, 주원소 및 미량원소, 희토류원소는 기존 광물로부터 용탈되어 높은 원소 유동성을 나타내었으나, 파쇄대 중심부가 비지대로 점차 변화하는 과정에서는 이차적으로 형성된 점토광물로 인해 단층대의 투수성이 감소하고, 점토광물이 풍부해진 비지대 내에 농집되므로 낮은 원소 유동성을 가진 것으로 해석된다. This study is focused on element behaviors and mineral compositions of the fault rock developed in Yongdang-ri, Yangbuk-myeon, Gyeongju City, Korea, using XRF, ICP, XRD, and EPMA/BSE in order to better understand the chemical variations in fault rocks during the fault activity, with emphasis on dependence of chemical mobility on mineralogy across the fault zone. As one of the main components of the fault rocks, SiO₂ shows the highest content which ranges from 61.6 to 71.0%, and Al₂O₃ is also high as having the 10.8~15.8% range. Alkali elements such as Na₂O and K₂O are in the range of 0.22~4.63% and 2.02~4.89%, respectively, and Fe₂O₃ is 3.80~12.5%, indicating that there are significant variations within the fault rock. Based on the chemical characteristics in the fault rocks, it is evident that the fault gouge zone is depleted in Na₂O, Al₂O₃, K₂O, SiO₂, CaO, Ba and Sr, whereas enriched in Fe₂O₃, MgO, MnO, Zr, Hf and Rb relative to the fault breccia zone. Such chemical behaviors are closely related to the difference in the mineral compositions between breccia and gouge zones because the breccia zone consists of the rock-forming minerals including quartz and feldspar, whereas the gouge zone consists of abundant clay minerals such as illite and chlorite. The alteration of the primary minerals leading to the formation of the clay minerals in the fault zone was affected by the hydrothermal fluids involved in fault activity. Taking into account the fact that major, trace and rare earth elements were leached out from the precursor minerals, it is assumed that the element mobility was high during the first stage of the fault activity because the fracture zone is interpreted to have acted as a path of hydrothermal fluids. Moving toward the later stage of fault activity, the center of the fracture zone was transformed into the gouge zone during which the permeability in the fault zone gradually decreased with the formation of clay minerals. Consequently, elements were effectively constrained in the gouge zone mostly filled with authigenic minerals including clay minerals, characterized by the low element mobility.

Definition and classification of fault damage zones: A review and a new methodological approach

Choi, J.H.,Edwards, P.,Ko, K.,Kim, Y.S. Elsevier Pub. Co 2016 Earth-science reviews Vol.152 No.-

<P>Although the widths of fault damage zones commonly show a positive correlation with displacements, these relationships also show a somewhat scattered distribution. We believe that one of the fundamental reasons for this problem is strongly related to subjective definitions and inconsistent uses of the term 'damage zone'. Thus, firstly we classify damage zones into along-fault, around-tip and cross-fault damage zones based on descriptive views of an arbitrary fault exposure as well as their tridimensional locations around a segmented fault system. Secondly, we propose an advanced field technique and data acquisition method to more accurately define a damage zone using the distribution of cumulative fracture frequency. We tested this method on new field and borehole observations as well as previously published data to identify damage zone boundaries, and express them as a change in slope gradients of the cumulative distribution of deformation structures. The results show how this slope change can be a useful criterion in accurately defining the width of damage zones and some internal properties of fault zones. We argue that this damage zone classification and definition method should be adopted and used to prevent discrepancies in field data. This will help us to gain a better understanding of fault damage zone properties and their scaling with fault displacement. (C) 2015 Elsevier B.V. All rights reserved.</P>

Fault zone processes during caldera collapse: Jangsan Caldera, Korea

Kim, Chang-Min,Han, Raehee,Kim, Jong-Sun,Sohn, Young Kwan,Jeong, Jong Ok,Jeong, Gi Young,Yi, Keewook,Kim, Jeong Chan Elsevier 2019 Journal of structural geology Vol.124 No.-

<P><B>Abstract</B></P> <P>Caldera fault zones, identified in many modern and ancient volcanoes, have been the subject of geological and geophysical observations and of analog and numerical modeling. However, the physicochemical processes in fault zones during a caldera collapse are still poorly understood. Here, we present field observations from a caldera fault zone in the Cretaceous Jangsan Caldera, SE Korea. The fault zone is ∼30 m wide and juxtaposes an intracaldera rhyolitic volcanic complex against older dacitic rocks; it consists of a minor fault, a main fault, and a series of fault-related intrusions (rhyolite and tuffisite). The main fault dips 90°–88°NW (vertically to steeply inward) and strikes N30°–40°E. A layer of pseudotachylyte (less than ∼10 cm thick) with some injection veins occurs along the main fault. The pseudotachylyte contains rounded to sub-rounded clasts, commonly displaying fuzzy or embayed boundaries, as well as euhedral feldspar microlites (<10 μm) and flow structures similar to those typically observed in tectonic pseudotachylytes. The tuffisite not only intrudes sharply into the pseudotachylyte and dacitic wall rocks but also displays a mingling structure with the pseudotachylyte. The contact between the rhyolitic intrusion and the tuffisite is nonplanar and complex. Based on the observed field relationships, we conclude that frictional melting and magmatic intrusion were near-coeval and that intrusion outlasted frictional melting by a short period. Although volcano–tectonic pseudotachylytes have rarely been identified in calderas (e.g., in the Glencoe Caldera, Scotland), our results suggest that frictional melting may be an important fault zone process during caldera collapse.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pseudotachylyte, rhyolitic intrusions and tuffisite are identified in a caldera fault zone of the deeply eroded and ancient Jangsan Caldera, SE Korea. </LI> <LI> The intrusion of pyroclastic and magmatic materials occurred shortly after frictional melting and outlasted by a short period. </LI> <LI> Frictional melting may be an important fault zone process during caldera collapse. </LI> </UL> </P>

Development of the intracontinental, continuous, narrow transpressional zone along the Sinnyeong Fault in the Cretaceous Gyeongsang Basin, SE Korea

천영범,조형성,송철우,손문 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.1

The WNW-ESE-striking Sinnyeong Fault, the most conspicuous fault of the Gaeum Fault System in the Cretaceous Gyeongsang Basin of Korea, provides an opportunity to understand the architectures and evolution of an intracontinental transpressional fault zone. We focus on the structural characteristics of the Sinnyeong Fault based on detailed field observations and magnetic fabric analysis. Its main movement is interpreted as sinistral slip with a small reverse component, although it could also have been active before the main movement. The deformation zone is asymmetric about the fault core. Sedimentary strata of the southern deformation zone are more extensively folded and deformed than those of the northern part, and the southern zone is much wider than the northern zone. NW-SE-trending en-echelon folds are limited to the southern periphery of the fault zone, where it is narrow, and underwent rotation toward the fault surface. These contractional deformations along the entire length of the fault are interpreted to have formed approximately coevally with the sinistral faulting. Newly observed WNW-ESE-striking mappable faults show a similar structural feature. Our results suggest that the damage asymmetry resulted from the eastward transport direction and relative uplift of south blocks of the faults under NE-SW compressive stress, which oriented at high angle (60–70°) to pre-existing strike of the faults. During progressive deformation, continuing slip accumulation along vertically tilted and fault-parallel sedimentary strata located directly south of the fault cores was responsible for the larger motions of the southern blocks of the faults rather than the relatively fixed northern blocks. We highlight that the sinistral reactivation of the Sinnyeong Fault formed a continuous, narrow transpressional zone during its long-term evolution.

Rebuild the Basement Tectonic Framework of the Western South China Sea

보안공학연구지원센터(IJSIA) 보안공학연구지원센터 2015 International Journal of Security and Its Applicat Vol.9 No.10

The west margin fault zone of the South China Sea is a tensional basement fault in the extended segment of the Indosinian Subplate toward the sea. It originally formed in the Mesozoic, and reactivated and developed further in the Cenozoic. It is not appropriate to regard this fault as a regional tectonic line between the Indosinian Subplate and the South China Sea Subplate because it does not exhibit the basic features of a regional boundary fault. A zone of gravity and magnetic anomalies in the southwest subbasin of the South China Sea extends westwards to the Zhongjian Island-Guangya Reef arcuate fault zone, and is the real regional tectonic line between the Indosinian Subplate and South China Sea Subplate. The formation of this basement tectonic framework might be closely associated with tectonic evolution of the ancient arc-trench system from the Proterozoic to the Mesozoic. The major faults are the south margin fault zone of the Qiongdongnan-Shenhu-Dongsha massif, the Red River fault zone, and the Zhongjian Island-Guangya Reef arcuate fault zone, which construct the basement tectonic framework of the South China Subplate, the Indosinian Subplate, and the South China Sea Subplate, and control the development and evolution of basement tectonics.

Fault reactivation with rapid slip along subsidiary faults in the Yangsan Fault zone, SE Korea

김창민,천영범,한래희,정기영,정종옥 한국지질과학협의회 2022 Geosciences Journal Vol.26 No.2

Earthquake fault slip accompanied by surface ruptures may occur not only along main fault cores but also along subsidiary faults in damage zones of major (or mature) faults. Nevertheless, most previous studies of fault and earthquake geology have focused on geological observations of main core zones rather than subsidiary faults. We conducted microstructural and mineralogical analyses of fault rock materials from two subsidiary faults (F1 and F2) of the NNE-SSW-striking Yangsan Fault, which is a major strikeslip fault in southeastern Korea (F1 at Pohang Bogyeongsa and F2 at Ulsan Eonyang–Bangok), to understand their possible slip zone processes and slip behaviors. The fault cores of the subsidiary faults are up to 20 cm thick and are composed of clay-rich gouge bands measuring a few millimeters in thickness and enclosed fractured lenses. Microscopic observations reveal that linear, and narrow microscale principal slip zones (micro-PSZs; < 20 μm thick), which are characterized by strong preferred orientation of clay minerals, occur not only at the boundaries between the gouge band and adjacent fault rocks but also in the central part of the gouge band. Along the micro-PSZs, microstructures such as clasts truncated by rapid slip localization and gouge injections by thermal pressurization of wet gouge materials during rapid slip are observed. Thus, the structures together may indicate the occurrence of seismic slip on the subsidiary faults. Mineralogical analyses reveal that the total clay fractions (consisting mainly of illite, chlorite, and kaolin) of the gouge materials of F1 and F2 are 60.1 and 59.7 wt%, respectively. The gouge band of F2 is enriched with kaolin (59.7 wt%), which is regarded as a gouge material that can trigger dynamic weakening by dehydration-induced thermal pressurization during seismic slip. Therefore, these results imply that the kaolin-rich gouge band in F2 may be dynamically weakened when seismic reactivation occurs along F2. This study shows that a comprehensive investigation of slip behaviors of subsidiary faults as well as main fault cores is necessary to improve our understanding of the seismic faulting mechanisms of major tectonic fault zones.

Inferred fluid flow through fault damage zones based on the observation of stalactites in carbonate caves

Kim, Y.S.,Sanderson, D.J. Pergamon Press 2010 Journal of structural geology Vol.32 No.9

Faults and fractures are important factors that control fluid flow in rock masses in hydrothermal, groundwater, and hydrocarbon systems. In this paper we examine local variations in fluid flow as evidenced by the distribution patterns and sizes of stalactites in fractured limestone. We observe that the size and distribution of stalactites relate to fluid flow and is strongly controlled by the fracture apertures, intersection of fractures, and development of damage zones around a fault. Fault damage zones are the volumes of deformed wall rocks around a fault surface that result from the initiation, propagation, interaction, termination, and build-up of slip along the fault. They are divided into tip-, wall-, and linkage damage zones depending on their location along the fault. The pattern of deformation within a damage zone mainly depends on fault tip modes (mode II or III), the 3-D locations around a fault surface, and the evolutionary stage of the fault. The development of different structures within damage zones gives valuable information about fault initiation and termination, fault propagation and growth, and fluid flow. Stalactites indicate fluid flow variation within a fault in that fluid flow is high in dilational jogs, variable along the main fault traces, and low in contractional jogs. Variation in ore fluid flow within faults is also important in controlling the position of ore shoots in structurally-controlled hydrothermal mineral deposits. Thus, the characteristics of fluid flow in fractured carbonate rocks can be related to patterns of damage around faults. Hence, the mapping of damage zones can be applied to the study of fracture-controlled fluid flow in the fields of petroleum geology, hydrogeology, and ore deposits.

Parametric Study of Water Inrush in a Tunnel Crossing a Fault based on the “Three Zones” fault structure

Jing Wu,Xintong Wang,Li Wu,Ya-ni Lu,Yanhua Han 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.8

As tunnelling progresses into the complex geological environment such as fault zones, water inrush has become one of the main geological hazards during tunnel construction. Consequently, understanding the evolution of pore pressure and flow velocity when a tunnel is excavated in a fault zone is crucial to ensure safe working conditions and reduce construction risks. In this work, based on the concept of “Three Zones” fault structure, we simulate the nonlinear water inrush process by solving the Darcy-Brinkman flow equation for the host rock and the fault zone. We examine the impacts of 1) the angle between the tunnelling direction and the fault and 2) the relative position from the tunnel face to the fault on the evolution of pore pressure and flow velocity near the tunnel face. The results show that within 5 m to 20 m ahead of the working face, pore pressure, flow velocity, and water inrush rate are the smallest when the angle is 90°. As the angle decreases, both pore pressure and flow velocity ahead of the working face increase. The pore pressure is larger when the tunnel has not reached the fault zone than when the tunnel has crossed the fault zone. Flow velocity also exhibits similar behaviour as pore pressure. With different relative positions from the tunnel working face to the fault, the closer the tunnel face to the fault, the lower the pore pressure and the larger the flow velocity ahead of the tunnel face. The largest water inrush rate occurs when the tunnel face is excavated to the center of the fault core, and the water inrush rate declines as the distance away from the fault increases. The simulation results provided a new method for simulating water inrush when a tunnel crosses a fault and could provide valuable references for the prediction of water inrush for underground projects.

경주시 외동읍 신계리 계곡에 발달하는 신기 단층대 발달사

강지훈 ( Ji-hoon Kang ),손문 ( Moon Son ),류충렬 ( Chung-ryul Ryoo ) 한국암석학회·(사)한국광물학회 2020 광물과 암석 (J.Miner.Soc.Korea) Vol.33 No.4

한반도 남동부 경상분지에는 북북서 방향의 울산단층대가 발달하고, 울산단층대의 주변부에서 많은 제4기 단층들이 발견된다. 이들 단층은 주로 백악기 말-제3기 초의 불국사 화성암류를 상반으로 하고 제4기 퇴적층을 하반으로 하고 있거나 제4기 퇴적층들 사이에 발달하고, 주로 상반이 서쪽으로 충상하는 역이동성의 운동감각을 보여준다. 이들 단층의 발견 지점을 연결해 보면 (서)북서, 남-북, (북)북동, 동북동 방향 등으로 지그재그형 구간별 방향성을 보이고, 이러한 구간별 방향성은 이들 단층의 주요 단층면들의 방향성과 유사하다. 경주시 외동읍 신계리 계곡에 분포하는 제4기 퇴적층, 염기성 암맥, 불국사 화강암 등에서는 남-북 방향의 역단층을 절단하고, 상부가 서쪽으로 이동하는 동-서 방향의 주향(이동) 단층들이 다수 관찰된다. 동측의 염기성 암맥 및 불국사 화강암에 의해 충상되어 있는 서측의 제4기 퇴적층에서는 남-북 방향의 역단층을 절단하고, 남-북 방향의 충상단층에 의해 절단되는 동-서 방향의 우수 주향이동 단층이 관찰된다. 제4기 단층들의 이러한 기하학적 ·운동학적 특성으로부터 신계리 신기 단층대의 형성과 관련된 다음과 같은 두 가지 적어도 2회 이상의 제4기 지구조운동이 고찰된다. 하나는 첫 번째 동-서 방향의 압축력에 의한 첫 번째 남-북 방향의 역단층운동과 이에 수반된 동-서 방향의 주향이동성 인열 단층운동, 이후 두 번째 동-서 방향의 압축력에 의한 두 번째 남-북 방향의 역단층운동이다. 다른 하나는 첫 번째 남-북 방향의 역단층운동, 이후 북서-남동 방향의 압축력에 의한 동-서 방향의 우수 주향이동 단층운동, 이후 두 번째 남-북 방향의 역단층운동이다. 본 논문에서는 울산단층대 주변부에서 발견된 제4기 단층들의 다양한 단층면의 방향성과 지그재그형 노두연결 구간별 방향성, 신계리 계곡 제4기 단층들의 기하학적 ·운동학적 특성, 그리고 최근 양산단층대 일대에서 보고된 서쪽으로 볼록한 압축성 호상의 선상구조 등으로부터 신계리 신기 단층대의 발달사를 제시한다. 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 2^nd 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.

지구물리탐사와 지질조사에 의한 양산단층대 남부구간의 기하학적 특성

이현재 ( Hyoun-jae Lee ),함세영 ( Se-yeong Hamm ),박삼규 ( Samgyu Park ),류충렬 ( Chung-ryul Ryoo ) 대한지질공학회 2017 지질공학 Vol.27 No.1

현재까지 양산단층대 노출 구간의 전기비저항탐사를 통하여 단층대와 전기비저항 값을 부분적으로 비교·분석하는 몇몇 연구들이 수행되었다. 그러나 양산단층대과 같은 대규모 단층 내에서 단층면을 직접 관찰하기 어려울 뿐만 아니라 단층핵부의 풍화작용으로 인해 단층운동 특성을 직접적으로 관찰하기가 쉽지 않다. 본 연구에서는 양산단층대 남부 언양지역의 전기비저항탐사 및 미소지형 측량과 지질조사 결과를 종합적으로 해석하여 양산단층의 위치, 발달양상과 단층핵 구간과 이를 중심으로 발달하는 단층 손상대의 지하 발달 특성을 파악하였다. 전기비저항탐사에 의하면 북북동 내지 북동 방향으로 발달하는 저비저항 이 상대가 확인되었으며, 전기비저항탐사, 미지형 측량 및 야외 지질조사 결과를 종합할 때, 양산단층대는 하나의 단층핵 또는 파쇄대가 아닌 최소 3~5매의 단층핵, 단층 손상대 또는 파쇄대가 복합적으로 발달하는 것으로 밝혀졌다. To date, several studies have been carried out to partially compare and analyze the resistivity values within the Yangsan fault zone through the electrical resistivity survey of the exposed fault zone. However, it is not easy to directly observe a large scaled fault like Yangsan fault that has been weathered, especially due to the weathering of the fault core. This study aimed to reveal the characteristics of location, geometry, the fault core zone as well as underground distribution of the associated fault damage zone, based on the results of electrical resistivity and micro-topographic surveys as well as field geology survey in the southern Yangsan fault zone (Eonyang area). The resistivity anomaly zones developed in the NNE to NE direction were confirmed by the electrical resistivity survey. According to the electrical resistivity, micro-topographic, and field geologic surveys, the Yangsan fault has been formed by three to five fault cores, fault damage zones and/or fractured zones.