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1 자원환경지질, 제 51 권, 제 2 호, , 2018 Econ. Environ. Geol., 51(2), , pissn eissn 원자력시설물부지의장기적안전성확보를위한지질구조평가 진광민 1 김영석 2 * 1 한국지질자원연구원전략기술연구본부, 2 부경대학교환경해양대학지구환경과학과 Evaluation on Geological Structures to Secure Long-term Safety of Nuclear Facility Sites Kwangmin Jin 1 and Young-Seog Kim 2 * 1 Climate Change Mitigation and Sustainability Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea 2 Department of Earth & Environmental Sciences, Environmental and Marine Sciences and Technology, Pukyong National University, Busan 48513, Korea (Received: 12 March 2018 / Revised: 5 April 2018 / Accepted: 6 April 2018) Many large earthquakes have continuously been reported and resulted in significant human casualties and extensive damages to properties globally. The accident of Fukushima nuclear power plant in Japan was caused by a mega-tsunami, which is a secondary effect associated with the Tohoku large earthquake (M=9.0, ). Most earthquakes occur by reactivation of pre-existing active faults. Therefore, the importance of paleoseismological study have greatly been increased. The Korean peninsula has generally been considered to be a tectonically stable region compared with neighboring countries such as Japan and Taiwan, because it is located on the margin of the Eurasian intra-continental region. However, the recent earthquakes in Gyeongju and Pohang have brought considerable insecurity on earthquake hazard. In particular, this region should be secure against earthquake, because many nuclear facilties and large industrial facilities are located in this area. However, some large earthquakes have been reported in historic documents and also several active faults have been reported in southeast Korea. This study explains the evaluation methods of geological structures on active fault, fault damage zone, the relationship between earthquake and active fault, and respect distance. This study can contribute to selection of safe locations for nuclear facilities and to earthquake hazards and disaster prevention. Key words : nuclear facilities, site selection, earthquake hazard, active fault, fault damage zone, resepct distance 전세계적으로대규모지진의발생과이로인한인명피해와재산피해는끊임없이발생하고있다. 특히일본의동일본대지진 (M=9.0; ) 은이로인한쓰나미의발생으로상당한인명피해와경제적손실을가져왔고, 후쿠시마원전사고를유발하였다. 대부분의지진은기존활성단층들의재활성에의해발생한다. 따라서활성단층에의한지진의재발특성을이해하기위한고지진학적연구가활발히수행되고있다. 우리나라는유라시아판내부에위치하여이웃한일본이나대만과같은나라들에비해지진으로부터안전지대로여겨져왔다. 그러나최근경주지진 (M=5.8; ) 과포항지진 (M=5.4; 2017, ) 으로인해우리나라에서도지진재해에대한불안감이증가하고있다. 특히이지역은많은원자력관련시설물들과대규모산업단지가밀집되어있는지역들로지진재해로부터극도의안전성이확보되어야한다. 그러나한반도남동부의경우대규모지진들이제 4 기뿐만아니라역사시대에도자주발생한것으로보고되고있다. 따라서지진에의한피해를줄이기위해서는활성단층을추적하고, 활성단층을따른지표파열 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited. *Corresponding author: ysk7909@pknu.ac.kr 149

2 150 진광민 김영석 의특성을파악하여해당지역에서의지진과단층의거동특성을이해하는것이중요하다. 이연구에서는극도의안전성확보가필요한원자력관련시설물들의부지선정을위한활성단층, 단층손상대, 지진과활성단층의상관성, 그리고이격거리등의구조지질학적평가방법을설명하고, 이를통해안전한원자력관련시설물의부지선정뿐만아니라지진재해와방재에유용한정보를제공하고자한다. 주요어 : 원자력관련시설물, 부지선정, 지진재해, 활성단층, 단층손상대, 이격거리 1. 서론전세계적으로대규모지진에의해많은인명과재산피해가발생하고있다. 최근 2011년 3월 11일에는일본동일본지진 ( 규모 9.0; 2011년 3월 11일 ) 이발생하고이로인해지진해일이발생하여많은인명피해와경제적피해를가져왔고, 후쿠시마원자력발전소사고를유발하였다 (e.g., Yagi et al., 2011). 또한국내에서도 2016년 9월 12일경주지진 ( 규모 5.8) 과 2017년 11 월 15일포항지진 ( 규모 5.4) 이발생하여많은경제적피해가발생하였다. 특히이지역들은원자력발전소와방폐장이인접한지역으로국민들의많은불안감을초래하였다. 인구가밀집된지역이나위험한산업시설들이밀집한지역에서는인명과재산뿐만아니라 2차적인피해를더많이유발할수있기때문에철저한연구를바탕으로대비가필요하다. 우리나라에서는 1978년고리 1호기를시작으로원자력발전을한이래현재는 4개원전부지 ( 고리, 월성, 한빛, 한울 ) 에서총 24기의원전을가동중이며, 신한울 1, 2 호기를포함하여 4개원전을건설하고있고고리1호기는폐쇄후해체할예정이며, 하나의중저준위방사성폐기물처분장을운영중이다 (Ministry of Trade, Industry and Energy, 2015). 초기원자력발전을위한원전건설은대부분외국의기술에의존했으며, 일부국내지질학자들이조사에참여하는수준이었다. 그러나 1990년대이후의방사성폐기물처분장부지선정및평가, 2000년대의신규원자력발전소건설을위한지질조사와지반조사는국내학자들이주도하여조사를수행하였다. 특히 1995년에굴업도를방사성폐기물처분장으로선정하여한국지질자원연구원이부지정밀조사를수행하는과정에서해저활성단층이보고되었고이로인하여처분부지로서부적합하여사업이백지화되었다 (Kim et al., 2011). 이는매우어려운결정이었지만국민들에게조사의신뢰성과활성단층의중요성을인식시키는중요한전환점이되었다. 또한이를계기로 2000년대에들어서는전력수요의급증에따라신규원자력발전소의필요성이대두되었지만국민들의반 대로정부는원자력부지의선정에대한부담이적은기존의원전부지를확장하는방향으로원전건설을시작하였다. 이에국내학자들이주도하여신고리, 신월성, 신한울등의지질과지반안정성에대한조사를수행하였다. 특히신규부지의조사에서는이전조사경험의축적과국내지질환경에대한정보와국내조사기술의향상으로독립적인조사가이루어질수있었다 (e.g., KOPEC, 2002). 현재정부는탈원전을기조로하여고리1호기를폐로하기로결정하였으며, 공론화위원회의결정을바탕으로이미건설중인신고리 5, 6 호기원전은계속하여진행하기로하였으나앞으로신규원전은당분간건설하기어려울것으로예상된다. 그러나우리나라에서는고준위방사성폐기물처분장을위한고준위방사성폐기물관리기본계획의재공론화가추진중인상황이며, 현재원자력발전소내의사용후핵연료임시저장고는곧포화상태에이른다. 따라서고준위방사성폐기물처분장의건설이절실히요구되는상황이다. 고준위방사성폐기물처분장의경우처분시설의설계수명을약 10만년이상으로설정하고있으며, 전세계적으로심부지층처분을추천하고있다 (Munier and Hökmark, 2004). 따라서고준위방사성폐기물처분장의안전성확보를위해서는장기적인지질과지진안전성을확보하는것이무엇보다중요하다. 이논문에서는원자력관련시설물의장기적지질과지진안전성확보를위한구조지질에대한연구와평가방법을간략하게정리하고자하였다. 특히활성단층연구의중요성, 지질과지진의안전성확보를위한단층손상대의특성, 장기적안전성확보를위한단층과단열로부터의이격거리에대한중요성등을소개하고자한다. 이를통해극도의안전성확보가필요한원자력관련시설물의장기적지질과지진안전성확보를위한정보를제공하고자한다. 2. 활성단층의중요성 활성단층의정의는이를정의하는목적이나규정, 명

3 원자력시설물부지의장기적안전성확보를위한지질구조평가 151 칭에따라다른의미를포함하고있으며, 국가와기관에따라정의가다양하여하나로통일하기는어렵다 (Kim et al., 2011). 이는근본적으로 활성단층 이란 최근지질시대에활동을하였고, 미래에다시활동할가능성이있는단층 이라는개념적정의에서시작되었기때문이다. 즉다시활동할가능성이있는단층을평가하는것이학자마다지체구조적특성에따라다르기때문에숫자로정확히일관되게정의하기어렵다는것이다. 우리나라에서는활성단층과관련된용어사용에서여전히많은혼동이있지만구별이상대적으로쉬운제 4기지층을절단한단층인제4기단층 (Quaternary fault), 원자력관련분야에서사용하는활동성단층 (capable fault) 과홀로세에활동한활성단층 (active fault) 으로제시하는연구자들이많이있었다 (Kim et al., 2011). 이정의에따르면제4기단층은현재로부터약 258만년이전이내의제4기의지층을절단하고있는단층을의미하며, 활동성단층은 5만년이내에한번이상활동하거나 50만년이내에두번이상활동한단층을의미하며, 이는주로원전관련시설의부지선정과규제에사용되고있으며, 미국등에서는활성단층은제4기후기인홀로세 ( 지금으로부터 11,000년이내 ) 에활동한단층을의미하는용어로사용되어왔다. 그러나최근미국과일본등에서도기존의활성단층연대범위를벗어나는단층이재활성하는경우들이보고 되면서활성단층의범위를넓혀가는추세이다. 즉제4 기의지층을절단한단층인제4기단층을활성가능성이있는단층으로보고조사하는분위기이다. 우리나라에서도최근에는이러한세계적추세에맞추고, 지진의활동성이상대적으로낮은지역적특성과조사의편리성을고려하여이러한제4기단층을활성가능단층으로보고조사하고있다 (e.g., National Emergency Management Agency, 2012). 대규모지진의재발주기는지체구조적환경에따라수십년에서수십만년까지의다양한재발주기로발생할수있다. 그러나대부분의지진 (90 % 이상 ) 은기존의활성단층에서발생하기때문에지진의발생과분포특성을이해하기위해서는활성단층에대한연구가필요하다 (Kim et al., 2011; Fig. 1). 활성단층연구는지진에대비하기위한활성단층지도 (active fault map) 와이를기반으로제작되는지진재해지도 (seismic hazard map) 를생산하기위한가장기본적인수단이된다. 이들자료는사회기반시설, 산업시설, 원전관련시설등다양한분야의내진설계에사용된다. 지진의발생과관련한가장기본적인관심은지진이언제, 어디서, 어느정도의규모로발생할가능성이있는지를장기적으로예측하여이에대비하는것이다. 지진이발생할경우지진동의영향은광범위하게나타나지만일반적으로지진규모 6.0 이상에서는발생할 Fig. 1. Photographs of the surface ruptures associated with large earthquakes (from Kim et al., 2011). (a) San Andreas Fault associated with 1906 San Francisco earthquake (Mw=8.3) (from Prentice's presentation, 2010). (b) Bogd Fault associated with 1957 Gobi-Altay earthquake (Mw=8.1). (c) Nojima Fault associated with 1995 Kobe earthquake (Mw=7.2). (d) Chelungpu Fault associated with 1999 Chi-Chi earthquake (Mw=7.6) (from Hwang, 2000).

4 152 진광민 김영석 수있는지표파열은활성단층을따라국부적으로발생하지만그파괴력은강력하다. 지진동의경우내진설계로극복이가능하나지표파열의경우현재의기술로서는극복할수없으며정밀한활성단층연구를통한지표파열이예상되는지점과지역을피하는것이최선이다 (Kim et al., 2003, 2004b). 또한지진이발생하고지표파열이발생할경우연약지반의산사태, 액상화와해저의경사이동단층운동에수반되는쓰나미등다양한 2차피해를줄이는것이중요하며, 이는정밀한활성단층연구등을통해어느정도예측이가능하다. 우리나라의활성단층존재는 1990년대초한국자원연구소와일본교토대학교의오카다교수팀의양산통도사입구에서의트렌치조사를통하여최초로시작되 었다 (Okada et al., 1994). 이후원자력발전소의건설을위한부지선정등의조사에서한반도남동부지역에대한집중적인조사가수행되어오고있으며, 약 60여개의활성단층내지제4기단층노두 ( 지점 ) 들이보고되었다 (Okada et al., 1994, 1995; 1998; Kyung, 1997, 2003; Kyung and Lee., 2006; Kyung and Chang, 2001; Kee et al., 2009; Fig. 2). 특히한반도남동부에서가장큰지질구조인양산단층주변의항공사진분석, 야외지질조사와트렌치조사를통해보고된제4기단층은청하, 강동, 언양, 양산일대에서제한적으로분포한다 (Fig. 2). 이러한제4기단층의분포는다른지역에발달하지않는것이아니라, 제한적이고단속적인제4기퇴적층의분포로인하여제4기 Fig. 2. Distribution map of the Quaternary faults in SE Korea (from Kee et al., 2009).

5 원자력시설물부지의장기적안전성확보를위한지질구조평가 153 단층들을인지하기어렵기때문인것으로사료된다. 울산단층대는경주시동쪽에서울산광역시에걸쳐북북서 -남남동방향으로약 50 km에걸쳐발달하는단층대로서단층대의동쪽블록의융기와연관되어역단층성운동이우세한양상을보인다 (Kim et al., 2011). 울산단층대는일반적으로단층면을중심으로동쪽은단층애로인한급사면과산악지역을보여주는반면, 서쪽으로갈수로완만해지는지형을보인다. 일광단층대의제4기단층은트렌치조사를통해좌동과도야지점에서확인되었다 (Fig. 2). 또한동해안을따라분포하는제4기단층은구산단층, 구만단층, 하정단층, 오어사단층, 장항단층, 읍천단층, 수렴단층, 술마단층등총 10개의지점이보고되었다 (Kee et al., 2009; Fig. 2). 그리고최근 2016년경주지진과 2017년포항지진으로인해지진활동에대한관심의증가와이에따른후속조치로국가활성단층조사계획이수립되었고체계적인조사가시작되었다. 특히양산단층대와울산단층대주변에대한활성단층조사가활발하게진행되고있어, 이를통한한반도남동부에서의주요단층대에대한진화사및활성단층특성을규명하는연구결과가기대된다. 3. 단층손상대의중요성단층대에대한정밀한연구는단층활동으로인한지진발생특성을파악하고지진재해를평가하고예방하 는데많은기여를하고있다 (e.g., Wesnousky, 2008; Jin and Kim, 2010). 중규모이상의단층들은단층의중심부에위치하는단층핵과이들주변에발달하는변형되거나파괴된모암인단층손상대로구성된다 (Chester et al., 1993; Scholz, 2002). 최근단층을따른말단의모드 (tip mode), 단층에서의상대적위치 (location) 와단층의진화정도 (evolution stage) 등에따라단층대주변에서의단층손상대의형태와규모가달라지는것으로보고되었다 (Kim et al., 2003; 2004b). 단층손상대는단층면에대한발달위치와관찰위치에따라크게 3종류로분류 (i.e., along-fault, around-tip, and cross-fault damage zones) 될수있다 (Kim et al., 2004b;Choi et al., 2016; Fig. 3). 일반적으로단층대는단층핵, 혼합손상대 (mixed zone), 단층손상대로구성된다 (Choi et al., 2009; Fig. 4). 단층핵은모암의특성을거의읿어버린얇은단층비지대나단층각력암등으로구성되는반면단층손상대는모암의특성을갖고있지만모암에비해더심하게파쇄되고, 단층핵에비해상대적으로넓게발달한다. 단층손상대의경우여러번의지진에의한단층활동으로암석과기존의구조들이변형되어형성되며, 이는새로운지진이발생할때변형의집중과분산을야기시킨다 (e.g., Sibson, 2003; Thomas et al., 2014). 특히지표파열을유발할수있는지진이발생할경우단층분절의연결부또는말단부에는변형이나여진이집중되고이를통해응력을해소시키는기작이보고되었다 (Sibson, 1989; Kim Fig. 3. Schematic representation of fault damage zones around a segmented left-lateral strike-slip fault (from Choi et al., 2016). Fault damage zones can be divided into along-, around-tip, and cross-fault damage zones based on exposure, concerns, and descriptive concepts.

6 154 진광민 김영석 Fig. 4. A simplified Yangsan fault zone model is suggested based on the structures observed across the Yangsan fault zone (from Choi et al., 2009). This fault zone can be classified into fault core, mixed zone, and fault damage zone. and Saderson, 2008). 이러한연구를통해지진의발생뿐만아니라단층손상대의발달기작과진화특성을이해하는데많은도움을줄수있다. 단층의연결손상대 (linking damage zone) 는두개이상의단층들이인접하거나연결되는부분에서각응력들의변화에따른변위의변화를일으킨다. 특히이는단층의진화와구조적성숙도에따라연결성이변하는것으로이웃한단층의진화정도에따라지진파열의전파와확장에영향을미칠수있다 (Kim and Sanderson, 2005; Manighetti et al., 2005; Soliva et al., 2008; Jin and Kim, 2010). 두단층의진화와구조적성숙도가낮으면단층들의경계부에서는 2차적인지표변형이발달하는분산변형 (distributed deformation) 이형성되지만진화와구조적성숙도가높아질수록두단층의연결성이좋아짐으로서단순한형태의집중변형 (localized deformation) 형태로발달한다 (Choi et al., 2017). 또한이러한연결성의발달에따라지진과지표파열의형태뿐만아니라단층의변위특성도달라지게된다 (Kim and Sanderson, 2008). 따라서역으로이러한단층을따른변위의변화를잘분석하고이해한다면관련된단층시스템의진화정도와지표파열과지진의전파특성을이해하는데도움이될수있다. 단층의 3차원말단손상대 (around-tip damage zone) 의경우지진에의한지표파열의종료와관련된응력과변위가해소되는부분이다. 일반적으로진원은지표파열의최대변위지점과일치하지않으며, 많은지진변위자료는진원으로부터비대칭적인형태로발달하는것을보여준다. 또한단층의말단부로갈수록급격한변위의감소가발생하며, 이는주향이동단층이끝 나는양쪽말단부에서는인장력이작용하게하여단층의양측지괴에서비대칭적인구조가발달하게하는원인이된다 (Kim and Sanderson, 2008). 또한일부연구들 (Sibson, 1989; King et al., 1994; Das and Henry, 2003) 에의하면여진의분포가단층의말단손상대에집중이되며, 이부분에서지진에의해전파되는응력을해소하며주단층에비해상대적으로작은규모의많은단층들이형성되고변형이집중된다. 그리고큰단층의경우여러개의분절로이루어져있으며, 지진이발생할경우지진과지표파열이어떠한방향성을갖고전파되는현상이보고되었으며 (Stein et al., 1997) 일부분절의경우지진공백 (seismic gap) 을보일수도있다. 이는이미활동한다른분절들에비해응력이많이누적되어있다는것을의미하기때문에미래에지진이발생할수있는가능성이높다는것을의미한다 (Smith-Konter et al., 2011). 단층을가로지르는단층손상대 (cross-fault damage zone) 에서는경사이동단층에서단층손상대의범위가단층의상하반에서상대적으로많은차이를보인다 (Fig. 4). 경사이동단층에서의상반과하반의발달특성과손상대의차이로인해매우다른지진재해가보고되며, 특히단층의상반에서의지진재해와손상대특성이하반에서의그것보다훨씬심한것으로보고되고있다 (e.g., Abrahamson and Somerville, 1996; Yu and Gao, 2001; Berg and Skar, 2005; Ota et al., 2005; Fig. 5). 예를들면, 1999년규모 7.6의 Chi-Chi 지진에의해지표파열이발생하였으며, 특히충상단층인 Chelungpu 단층이활성화되면서상반과하반의피해차이는매우큰것으로나타났다 (Fig. 5). Fig. 5에서와

7 원자력시설물부지의장기적안전성확보를위한지질구조평가 155 Fig. 6. Number of fractures between hanging wall and footwall (Riley et al., 2010). Fractures are developed more widely in the hanging wall than footwall based on Pajarito Fault, New Mexico, U.S. Fig. 5. Contrasting damages on the hangingwall and footwall associated with 1999 Chi-Chi Earthquake in Taiwan (from Ota et al., 2005). Almost no damage occurred on the footwall although the buildings are located very close to the surface rupture. 같이상반에위치하는건물들은모두전파되었으나하반에위치하는건물들의경우단층과매우가까움에도 불구하고거의피해가발생하지않았다. 이단층의경우상반피해지역의폭이약 50 m이며, 이를벗어난지역에서는피해가거의발생하지않았다 (Ota et al., 2005). 또한경사이동단층에서상반과하반의변형차이는단열들의발달빈도에서도확연히나타난다 (Fig. 6). 이는특히지진파의전파가상반으로더잘전달될수있는지진학적특성뿐만아니라자유면을가지는상반을통해축적된응력이주로해소되는것으로생각된다. 따라서경사이동단층주변의원자력관련시설물의부지를선정하는데있어서는상반보다하반에위치를선정하는것이훨씬안정적일것이다. 단층을따라지진이발생할경우단층주변의암석은응력의변화가발생하며, 이는여진의분포와밀접 Fig. 7. Main shock, aftershock clusters and related damage zones around several large-scale strike-slip earthquake rupture (from Kim and Sanderson, 2008). Most aftershocks were localized in the fault damage zones.

8 156 진광민 김영석 하게연관된다 (e.g., Harris, 1998). 많은연구에서여진의분포가단층손상대에집중되는것이보고되었다 (e.g., Johnson and Hutton, 1982; Sibson, 1989; Reilinger et al., 2000; Perfettini and Avouac, 2007; Fig. 7). 단층손상대에여진이집중되는것은주단층면이아닌상대적으로약한부수적인단층이며, 응력의집중을의미하기때문에미래에지진이발생할수있는가능성도지시한다 (Kim and Sanderson, 2008). 따라서단층손상대의발달특성을잘이해한다면어떤단층에서발생할수있는지진의특성을예측하는데에 도도움을받을수있다. 단층손상대와관련되는유체유동에대한다양한연구가수행되었다 (e.g., Micklethwaite and Cox, 2004, 2006; Leckenby et al., 2005; Brogi, 2008; Zhang et al., 2008; Kim and Sanderson, 2010). 단층손상 대를따른유체유동은광상의배태, 지하수저류지의발달, 석유저류지의발달등을유도할수도있지만, 방사성폐기물지층처분장주변에서는핵종의이동통로와저류장의역할을할수있어이들의발달특성을이해하는것이매우중요하다 (Fig. 8). 전세계적으로고준위방사성폐기물지층처분의경우지하약 500 m 내외의깊이에건설하는것을추천하고있다. 그러나상대적으로깊은심도에서처분장을건설할경우건설시모암의파괴등으로대상암종들의변형을가져올수있으며, 기존에발달하고있는단층들이나단열들의지속적이거나갑작스런변형을초래할수있다 (USNRC, 2011). 또한이러한지질구조의갑작스런변형은지하수흐름의영향, 방사성폐기물에서방출되는고열, 이들의화학적반응등건설초기에예상되는복합적인반응보다더많은변수를가지는반응과 Fig. 8. Stages in the interpretation of ancient flow systems in reservoirs associated with faults and damages (from Kim and Sanderson, 2010). (a) Geometrical analysis of faults and damage zones; (b) Establishing deformation history; (c) Kinematic analysis of fractures; d) Evaluation of conductivity of fractures (from Sanderson and Zhang, 1999).

9 원자력시설물부지의장기적안전성확보를위한지질구조평가 157 변형을초래할수있다. 따라서처분장의위치를선정하는데있어기존단층과단열의발달특성을이해하는것이무엇보다중요하며, 건설중의변화와건설후의변화등에대한지속적인모니터링이중요하다. 따라서기존에발달하고있는단층의기하와발달특성들이정밀하게연구되어야만단층손상대를따른유체유동의특성을이해할수있고만약에있을핵종등의유출을예상할수있다. 4. 단층의분절과연결대규모단층의경우하나의큰단층으로이루어지기보다는여러개의구간이나몇개의작은단층들이연속적으로이어지는데이를분절현상 (segmentation) 이라고하며, 이들각각을분절 (segment) 이라고한다. 이웃한분절들이진화를거듭할수록연결 (linkage) 될수 있으며, 이는단층의진화와성장을이해하는데중요하다 (Kim and Sanderson, 2005). 이들분절들의연결은크게세단계로이루어진다 (Kim and Sanderson, 2005). 첫단계는독립된분절들이서로를향하여전파하는것이다. 두번째단계는분절의끝부분이뚜렷한연결은보이지않으나서로겹치게된다. 그리고마지막단계에서는각분절이끝부분에서이차적인단열들이형성되면서연결되는것이다 (Fig. 9). 대규모단층을따라지진이발생할경우전체의단층이파열되는것은매우드물며보통대규모단층대를구성하고있는분절들중일부분이파열되는것으로알려져있다. 또한대규모단층대를구성하는분절들이지진의전파에중요한역할을할수있기때문에지표파열은단층대의구조적또는형태적분절에의해제한될수있다 (Kim and Sanderson, 2005; Fig. 9). 그러나지진이발생할경우발생되는지진의 Fig. 9. Fault segmentation and linkage (from Kim and Sanderson, 2005). Faults evolve from isolated faults to interacting faults through segment linkage.

10 158 진광민 김영석 규모와방출되는에너지의양이일정하지않기때문에때로는형태적으로나뉘어진분절들간에지진이나지표파열이전파되는경우도있지만멀리떨어진분절로의전파는매우제한적이기때문에단층대의형태적분절을이해하는것이매우중요하다. 지진에의한지표파열의특성을이해하는데있어가장중요한요인중에하나는단층의분절이다 (Choi et al., 2017). 특히대규모지진에의해발달할수있는지표파열의규모는활성단층에대한최대규모의단층분절을이해하는것이중요하다 (Klinger, 2010). 이는다양한규모에서발달하는단층의구조적분절 (structural segment) 로부터지진에의해지표파열의움직임에영향을줄수있는지진학적분절 (seismic segment) 을파악하는것이필요하다는것을의미한다. 특히지진원규모의분절경계부가개별적으로대규모지진에의한지표파열의시작, 전파, 확장, 종결등에많은영향을줄수있으며, 이러한영향이반복적인지진에의해지속되기때문이다 (Segall and Pollard, 1980; King and Nabelec, 1985; Klinger, 2010). 단층의분절시스템은 1) fault bend: 단층의주향변화와관련된단층굴곡, 2) fault jog & fault step: 서로평행한두단층분절의계단식배열과분절의분리내지연결에따른계단식분절, 3) branch point: 가 지단층의분기점, 4) intersection point: 다른단층과의교차점등의형태로구분될수있다 (Choi et al., 2017). 이러한단층분절의특성은경사이동단층보다는지진에의한지표파열의전파와확장이변위와평행하게진행됨으로서이웃한분절로의에너지전달이비교적용이한주향이동단층에서잘발달한다 (Choi et al., 2017). 이러한단층분절들의기하, 변위, 운동감각등은지진에의한지표파열의전파와종결에많은영향을미침으로서각단층에서의지진거동특성을결정하는데중요한요소중하나이다. 따라서단층의분절특성과분절경계부의발달특성을이해할경우지진재해에대한많은정보를제공할수있을것으로판단된다. 특히지표에위치하는원자력관련시설물의위치선정과지하깊은곳에위치할수있는방사성폐기물처분장의안전성확보를위해서는지표에서관찰되는단층들의발달특성에대한이해를바탕으로심부의지하구조를 3차원적으로이해하는것이매우중요하다. 5. 고고지진학적연구최근지진재해연구에있어지진학적, 지체구조적, 고지진학적연구들과함께고고지진학 (archaeoseismology) 을통한연구들이활발히진행되고있다 (Jin et al., Fig. 10. The fallen large Buddha statue was discovered resting on the steep slope of the Yeolam valley, Mt. Nam, Gyeongju. It may be fallen by episodic event such as earthquake (from Jin et al., 2011).

11 원자력시설물부지의장기적안전성확보를위한지질구조평가 , 2011; Fig. 10). 고고지진학적연구는단층주변의문화재파괴등을이용하여지진의특성을이해하는연구이다. 고고지진학은과거지진에의해피해를입은문화재나문화재지역을연구하는학문으로역사기록이나피해를입은문화재를지질학적으로접근하는분야이다. 이런연구는문화재가만들어진시기를알수있는경우이후에발생한지진에의한피해를통해지진재해의특성, 지진규모와시기를정확하게알수있기때문에지진재해예측을하는데있어매우유용한연구방법이다 (e.g., Ambraseys, 1973; Karcz et al., 1977). 우리나라의역사서인삼국사기에따르면 779년경주에서지진이발생하여약 100여명이사망하는인명피해가발생하였으며, 이지진의규모는약 6.7로추정되었다 (Lee et al., 1998). 또한 1643년울산에서추정규모 7.0의큰지진이발생하였으며, 비교적큰지진들이한반도남동부에서종종발생하고있는것으로보고되었다 (Lee et al., 1998). 그러나우리나라는 1905 년이후지진계가설치된이후의계기지진기록을가지고있으나상대적으로큰규모 5이상의지진들이발생하지않아지진의안전지대로인식되어대규모지진에대한관심과연구가부족한상황이다. 그러나최근규모 5.8의경주지진과규모 5.4의포항지진의발생으로역사지진기록에대한관심이높아졌다. 앞서언급한바와같이역사적으로도대규모지진에따른인명피해와재산피해가많은것은절대우리나라가지진으로부터안전한지대가아니라는것을의미하며, 한반도남동부에대규모지진이발생할가능성이높음을 시사한다. 따라서고고지진학연구는고지진학적자료와계기지진자료의시간범위사이의연구를통하여해결할수있을뿐만아니라역사시대의지진특성을통해미래의지진재해특성을이해할수있는중요한자료를제공할수있다 (Fig. 11). 6. 이격거리 (respect distance) 의중요성 원자력관련시설물의위치를선정하는데있어부지주변활성단층의발달여부는필수적으로고려되어야할사항이다. 앞서언급한바와같이지진동의경우내진설계와적절한시공을통하여대응이가능하지만, 활성단층의지표파열은현재기술로서는극복할수가없고단지정밀한연구를통해피하는것이최선의방법이다. 특히원전관련시설부지는지진을유발할수 있는단층에서어느정도의거리를두어지진에의한지표파열로부터안전성을확보하는것이중요하다. 최근고준위방사성폐기물처분장분야에서세계최고의기술을자랑하는스웨덴의경우처분장부지의안전성확보를위해여러후보지역을선정하고모든후보지역에대해약 15년동안의조사와연구를실시하여최종처분장의부지를선정하였다. 특히이들은지진이 발생할경우움직일수있는단층과단열들로부터방폐장과처분용기의피해를최소화하기위한방법으로 Respect distance 개념을적용하여다음과같이제안하고있다. The respect distance is the perpendicular distance from a deformation zone that defines the Fig. 11. Histogram of historic earthquake catalogue from 2 AD to 1810 AD for >M L =3.5 (from Jin et al., 2011). It shows three earthquake clusters from 1013 AD and various recurrence intervals in Gyeongju area.

12 160 진광민 김영석 Fig. 12. Schematic cartoon of respect distance (from Munier and Hökmark, 2004). volume within which deposition of canisters is prohibited, due to anticipated, future seismic effects on canister integrity (Munier and Hökmark, 2004; Fig. 12). 즉 Respect distance 는미래에예상되는지진의영향이처분용기와처분용기위치의무결성에영향을줄수있는변형대로부터의수직거리를의미한다. 이러한이격거리의연구는다음과같은의문점에서시작되었다 1) 만약에처분장예상부지가지진에의해활성화될수있는단층으로부터영향을받을수있는거리에위치한다면, 방폐장에영향을줄수있는단층과단열의최대크기는얼마인가? 2) 이런단층과단열로부터피해를받지않을수있는최소거리는얼마인가? 3) 지진에의해활성화될수있는단층과단열의최대변위는얼마인가? 이에연구자들은이격거리를추정하기위해여러가지분석과연구들을실시하였다 (earthquake magnitude, earthquake fault geometry, source mechanism, orientation of the target fracture, position of the target fracture, mechanical properties of the target fracture, size of the target fracture, mechanical properties of the host rock, host rock initial stresses, maximum allowable displacement that the canister-bentonite system can accommodate). 이와같은여러요인을분석하기위해서는다양한방법들을통하여접근하여야하며, 부지선정을위한규모별접근방법도고려되어야한다. 전국규모로발달하는대규모내지중규모이상의단층들에대한발달특성을이해하고이를통해단층으로부터의이격거리를설정해야만한다. 예를들면, 최근 Jin et al.(2018) 은한반도남동부양산단층과거의평행하게발달하는일광단층에대한변형대의두께를야외조사를통해보고한바있다. 이단층의경우육지에서선형구조로인지되는단층의길이는약 25 km이며, 변위는약 1.2 km이지만이단층이발달하는지역에서의암석이괴상의화산암일경우와퇴적암일경우변형대두께가다른것을보고하였다. 화산암에서는변형대의두께가약 200 m이나퇴적암에서는약 1km로 5배의차이가났

13 원자력시설물부지의장기적안전성확보를위한지질구조평가 161 다. 이는물론전문가의판단의기준이다를수는있지만일광단층으로부터의이격거리는암종에따라다르게적용되어야하며최소 200 m 이상의이격거리를두는것이안전한것을의미한다. 그러나후보부지군내지최종후보부지의경우중규모이하의단층대에대한정밀한분석이필요하다. 특히최종후보지역내에서는처분용기가위치할지점들에대해서는좀더구체적인이격거리설정이중요하다. 또한이를위해서는단층과단열들의발달특성을고려한모델링이필요할것으로예상된다. 즉, 단층의길이, 최대지진규모와최대지진변위등의값을추정할경우그로부터의이격거리를설정할수있다. 예를들면, 스웨덴의방폐장연구를위한모델링에서는지표에발달하는어떤단층의지표파열길이가 5km, 발생할수있는최대지진규모가 6, 발생할수있는최대변위는 0.1m 이하일경우로예측된다면그단층으로부터의이격거리는 0.1 m 이상설정할것을보고하였다 (Munier and Hökmark, 2004). 또한처분용기주변의작은단층이나단열이어떤규모의지진이발생하여변위가생긴다면, 그변위가전체처분용기내지처분용기를감싸고있는완충제까지도달하지않을거리를두는것이다. 이로인해발생할수있는지진과그에따른단층의변위를예상하여단층과단열로부터의거리를설정할경우처분장과처분용기의안전성을확보할수있다. 7. 활성단층지도와지진재해지도의중요성 대부분의선진국에서는지진재해에대비하기위한활성단층지도 (active fault map) 와지진재해지도 (seismic hazard map) 를제작하고있다. 활성단층도의경우각단층들의발달특성, 변위량, 운동횟수, 운동시기, 평균변위율등을종합하여최대지진규모와재발주기를추정하는연구를기반으로제작되며, 이를통해기재된각단층들의재발가능성과발생가능지진규모등을기재하는식으로제작되고있다 (e.g., usgs.gov/hazards/qfaults/map/#qfaults; gsj.jp/activefault/index_e_gmap.html). 지진재해지도의경우과거의지진기록으로부터미래에발생할수있는지진에의한지반운동의특성을예측하는것을목적으로활성단층에대한정보뿐만아니라과거지진의활동성, 빈도, 규모등을평가하여제작된다 (e.g., Hyndman and Hyndman, 2006; earthquake.usgs.gov/hazards/hazmaps/). 지진재해지도 는어떤지역에서지진이발생할경우유발되는최대지반가속도또는응답가속도와발생빈도를나타내는그지역의고유물리량이다. 지진재해지도는결정론적인재해도분석과확률론적분석으로구성되며, 확률론적인분석은시간적개념을포함한다. 또한이런지진재해지도의작성에있어활성단층지도와역사지진자료들은중요한입력요소로고려되고있다 (Kim et al., 2011). 그러나현재우리나라는활성단층지도가없기때문에현재사용되는지진재해지도는역사지진자료와계기지진자료에만의존하고있어재발주기가긴대규모지진에대한반영이제대로이루어지지못하여국가적인활성단층지도의필요성을요구하는목소리가어느때보다도높은상태이다. 이에정부에서는 2017 년부터행정안전부를중심으로국가활성단층지도제작에착수하였으며, 이외에도다양하고심도있는활성단층연구와지진재해와관련된연구들이진행되고있다. 이러한연구결과들은궁극적으로는더욱신뢰도가높은지진재해지도의작성뿐만아니라주요한구조물들의내진설계기준을마련하는데에도크게기여할수있을것으로기대한다. 8. 토론 : 활성단층연구의한계와가능성우리나라의활성단층에대한연구사는상대적으로짧다. 1980년대까지는지질학에서의주요관심은광물자원탐사를위한광산과그주변에대한조사가대부분이었다. 급진적인산업화와경제발전으로에너지의수요가급격하게증가하면서원자력발전소의건설을추진하게되었으며, 1978년고리 1호기건설을위한조사가시작되면서활성단층연구와신기지체구조들에대한연구가본격적으로수행되었다. 그러나초기원자력발전소건설에필요한신기지체구조연구와지반조사는이분야에대한우리나라전문가의부족으로대부분외국전문가들에의해수행되었다. 그러나 1990년대부터는국내전문가들의역량이향상되어원전관련부지조사는대부분국내의전문가들이주도적으로수행하였다. 특히대표적인활성단층에대한근대적인연구는 1998년에신월성 1, 2호기주변에서발견된읍천단층에대한연구로우리나라에서활성단층연구에서가장대규모트렌치작업이수행되었으며, 이를통하여변위량, 운동횟수, 운동시기등이체계적으로조사되고보고되었다 (Kim et al., 2004a; Kee et al., 2007; Kim et al., 2011). 이단층에대한연구는우리나라에서의활성단층에대한개념뿐만아니라활성단층연

14 162 진광민 김영석 구의중요성을인식시키는큰전환점을갖게하였다. 그러나우리나라의대규모단층연구와활성단층의연구에있어아직까지도제한적인상황이여러가지가있다. 한반도남동부에위치하는대규모지체구조선으로는양산단층과울산단층이존재하며, 이들단층주변으로거의평행한중규모이상의단층들 ( 밀양, 모량, 동래, 일광등 ) 이다수발달한다. 또한이들단층주변으로약 60여개의지점들에서소규모활성단층또는제 4기단층들이보고되었다. 특히 Lee and Na (1983) 는양산단층의활성가능성을처음으로제기하였다. 따라서이를규명하기위한다양한고지진학적연구가수행되었으나, 우리나라의지진발생빈도가낮고규모도상대적으로작아연구에대한지원과투자가부족하여양산단층의실체, 기하학적특성, 분절시스템, 운동시기, 운동횟수등은아직도명확하게규명되지않고있다. 또한북북서 -남남동방향의울산단층은주변에서많은활성단층이보고되고있으며, 양산단층과는 λ-단층시스템 (Du and Aydin, 1995) 으로해석되었다 (Han et al., 2009). Han et al. (2009) 은양산-울산단층시스템의쿨롬응력변화모델링을통하여현생지구조적응력장하에서양산단층의북부와울산단층의동측지괴에응력이주로집중되고있는것으로해석하였다. 이연구는또한활성단층의분포지역과고지진의발생이력그리고미소지진의분포가매우밀접하게연관되어있음을보여주었다. 따라서원전관련시설과대규모산업단지가위치하는한반도남동부의지진재해특성을이해하기위해서는이들대규모단층의발달특성을우선적으로밝혀야할것이다. 우리나라에서활성단층이집중적으로보고되는지역은한반도남동부이다. 이는우리나라의지진활동이상대적으로한반도의남동부에서더욱활발하다는것을지시하는것일수도있지만원자력발전소와중저준위방폐장건설에따른다양한조사가이지역을중심으로수행되었기때문일수도있다. 따라서우리나라전체에대한체계적인조사가이루어진다면다른지역에서도많은활성단층들이보고될가능성이있다. 그러나현재까지대부분의우리나라활성단층은점단위로만조사가되었으며, 단층선으로구획된활성단층은현재까지보고되지않았다. 그러나지진의발달특성을이해하기위해서는점단위가아닌단층선으로의연결이중요하며, 이들의연결에따라지진의규모, 발생빈도, 시기등이많이달라질수있다. 따라서현 재까지보고된활성단층들뿐만아니라앞으로발견되는활성단층들에대한단층선으로서의조사와분석을수행하여야한다. 고지진에수반된지질학적증거들을인지하는데에는많은어려움이있다. 규모가작거나심도가깊은곳에서발생한지진의경우지표파열을수반하지않을수있으며, 고지진에수반된지표파열일지라도빠른풍화와경작활동등에의해지질학적증거들이지워질수도있다 (McCalpin, 2009). 그러나활성단층여부를인지할수있는가장확실한증거는활성단층의상위에퇴적되는제4기층의변형또는절단여부이다. 하지만앞서언급한지하심부에서의변형, 빠른풍화, 삭박, 경작등에의해제4기층내의변형구조가발달하지못하거나지워진다면비록활성단층을발견하더라도그활동에대한증거를인지하기가매우어렵다. 특히현재까지우리나라의활성단층분포도 (Fig. 2) 에분포하는활성단층의경우대부분제4기층의변형이인지된지점들이다. 따라서제4기층의부재로인해이들의활동이인지되기어려운지역의경우조사에더많은어려움이있으며, 이를경우이들을활성단층으로인지하지못할가능성도많을것으로판단된다. 활성단층조사에는다양한연구방법들이적용되어종합적으로해석되어야한다. 원격영상, 항공사진분석, 야외조사, 트렌치조사, 연대측정등이단층의위치, 발달특성, 운동횟수, 시기등을규명하기위해적용된다. 그러나이방법들은각각의문제점내지한계점이있다. 연대측정의경우각연대측정방법들 (OSL, 14 C, ESR 등 ) 에따라적용대상과연대의범위가다르기때문에활성단층의운동시기를규명하는데일부제한이있다 (Kim et al., 2011). 트렌치조사의경우이조사를통해인지할수있는단층은지표까지도달한 지표지진단층 에만한정되고, 트렌치를굴착했을때트렌치단면의정보가그단층전체의활동이력을어느정도기록하고있는가는또다른한계로지적될수있다. 또한그단층을따라발생한지진의정밀한시간분해능을해석하기위해서는새로운퇴적층이지속적으로쌓인곳을선정하여트렌치를굴착해야하는데이러한위치를선정하는것이쉽지않다는것이다. 그리고무엇보다중요한것은트렌치조사시발달하는구조들의분석방법과해석의객관성을확보하는것이다. 따라서다양한기술의접목뿐만아니라이들한계점들을지속적으로해결할경우대상단층에대한정밀한자료를얻을수있을것이다.

15 원자력시설물부지의장기적안전성확보를위한지질구조평가 163 Fig. 13. Schematic diagram for safe locations of the nuclear facilities from active faults. It shows a relatively safe locations from faults based on fault characteristics. 9. 결론지진재해와방재에있어세계최고의기술을보유한일본은 2011년발생한도호쿠지진과이에수반된쓰나미로인해후쿠시마원전에서사고가일어나일본뿐만아니라전세계적으로큰충격을주었다. 최근우리나라의경우원자력발전소의사용후핵연료저장소가곧포화상태에이른다. 이에고준위방사성폐기물지층처분장의건설이시급한상황이다. 이처분장의경우최소 10만년이상의장기적인안전성이확보되어야하는시설물로지질학적과지진학적으로안전한지반에건설되어야한다. 따라서지질과지진학적으로안전성을확보하기위해서는구조지질학적연구와평가가중요하다. 원자력관련시설물들은극도의안전성을위해내진설계가가장엄격하게적용되고있어지진동에의한피해는내진설계로막을수있으나중규모이상의지진이발생할경우수반되는지표파열의경우내진설계로는막을수없다. 지표파열로부터피해를막는유일한방법은지표파열이예상되는단층을피하는것이현재로서는유일한방법이다. 이를위해서는단층의기하, 운동특성, 응력상태등다양한요인들을이해하는것이중요하다. 특히단층손상대의발달특성을정밀하게분석할경우지진과변위와의관계, 여진의분포, 유체유동특성 의예측등다양한정보를확보할수있다. 이러한연구를위해서는지진을유발할수있는단층, 즉활성단층에대한연구가무엇보다중요하다. 특히최근정밀한위성사진과 LiDAR를이용하여제4기의변형흔적을추적하고, 정밀한연대측정등최근의활성단층조사기법들을활용할경우정밀한정보를확보할수있을것이다. 또한활성단층의고지진학적연구뿐만아니라역사지진과고고지진학적연구를통하여고지진학적시간과계기지진사이의시간적틈을채울수있을것이다. 활성단층과지진재해에대한다양한정보가축적되면우리나라의활성단층도뿐만아니라더욱신뢰도가높은지진재해도를제작할수있으며, 이와같은일련의과정을통하여미래의큰지진에대해원전관련시설물뿐만아니라사회기반시설의안전성을확보하고국민의안전을확보할수있을것이다 (Fig. 13). 원전관련시설은안전이최우선으로고려되어야하기때문에부지선정에서최우선적으로정밀한지질조사를기반으로상대적으로안전한후보부지들을선정한후최종적으로정치적, 사회적합의를통하여최종부지를선정하는일련의과정이필요하다. 또한조사에대한투명한자료공개를통해조사기관뿐만아니라정부와국민사이의신뢰를높이는것이이러한부지선정의문제를해결하는아주중요한요소라고생각된다. 우리나라는유라시아판내부내지연변부에위치하여상대적으로지진으로부터안전지대라고여겨져왔

16 164 진광민 김영석 으나최근경주지진과포항지진으로우리나라는더이상지진으로부터의안전지대가아니라는인식이확산되고있다. 또한최근에보고되는활성단층들의존재, 역사적자료에기록된지진의기록등을볼때우리나라는이웃한일본, 대만, 중국에비해규모가상대적으로작거나재발주기가상대적으로길뿐이지절대지진으로부터의안전지대는아니다. 그러나중요한것은 우리나라가지진으로부터안전지대는아니지만활성단층과지진재해에대한정밀한조사와연구를바탕으로한자료의축적을통하여지진재해의위험도에대한구획이가능할수있을것으로판단된다. 사 사 이연구는한국지질자원연구원이정부출연사업으로수행중인 HLW 지층처분후보부지선정을위한전국규모지질환경정보도작성 ( ) 과제의일환으로수행되었으며, 한국수력원자력중앙연구원 월성부지인근단층조사및확률론적지진재해도평가 (A16IP55) 과제의지원을받아수행되었습니다. 그리고논문을꼼꼼히검토하여유익한조언을해주신익명의심사위원들에게도감사를드립니다. References Abrahamson, N.A. and Somerville, P.G. (1996) Effects of the hanging wall and footwall on ground motions recorded during the Northridge earthquake. Bulletin of the Seismological Society of America, v.86, p.s93- S99. Ambraseys, N.N. (2006) Earthquakes and archaeology. Journal of Archaeological Science, v.33, p Berg, S.S. and Skar, T. (2005) Controls on damage zone asymmetry of a normal fault zone: outcrop analyses of a segment of the Moab fault, SE Utah. Journal of Structural Geology, v.27, p Brogi, A. (2008) Fault zone architecture and permeability features in siliceous sedimentary rocks: Insights from the Rapolano geothermal area (Northern Apennines, Italy). Journal of Structural Geology, v.30, p Chang, T.W. (2001) Quaternary tectonic activity at the Eastern Block of the Ulsan Fault. Journal of the Geological Society of Korea, v.37, p (in Korean with English abstract). Chester, F.M., Evans, J.P. and Biegel, R.L. (1993) Internal structure and weakening mechanisms of the San Andreas Fault. Journal of Geophysical Research, v.98 (B1), p Choi, J.-H., Yang, S.-J. and Kim, Y.-S. (2009) Fault zone classification and structural characteristics of the southern Yangsan fault in the Sangcheon-ri area, SE Korea. Journal of the Geological Society of Korea, v.45(1), p.9-28 (in Korean with English abstract). Choi, J.-H., Edwards, P., Ko, K. and Kim, Y.-S. (2016) Definition and classification of fault damage zones: A review and a new methodological approach. Earth- Science Reviews, v.152, p Choi, J.-H., Kim, Y.-S. and Klinger, Y. (2017) Recent progress in studies on the characteristics of surface rupture associated with large earthquake. Journal of the Geological Society of Korea, v.53, p Das, S. and Henry, C. (2003) Spatial relation between main earthquake slip and its aftershock distribution. Reviews of Geophysics, v.41(3), p Du, Y. and Aydin, A. (1995) Shear fracture patterns and connectivity at geometric complexities along strikeslip faults. Journal of Geophysical Research, v.100, p Han, S.-R., Park, J.Y. and Kim, Y.-S. (2009) Evolution modeling of the Yangsan-Ulsan fault system with stress changes. Journal of the Geological Society of Korea, v.45, p (in Korean with English abstract). Harris, S.D., Vaszi, A.Z. and Knipe, R.J. (2007) Threedimensional upscaling of fault damage zones for reservoir simulation. Geological Society of London, Special Publications, v.292, p Hwang, H.Y. (2000) Taiwan Chi-Chi earthquake Bird s eye view of Cher-Lung-Pu fault. Flying Tiger Cultural Publ. Taipei, Taiwan, 435p. Hyndman, D. and Hyndman, D. (2006) Natural Hazard and Disaster. Thomson Learning, 533p. Jin, K., Lee, M. and Kim, Y.-S. (2009) Geological study on the collapse of a carved stone Buddha statue in Yeolam valley of Namsan, Gyeongju, Korea. Journal of the Geological Society of Korea, v.45, p (in Korean with English abstract). Jin, K. and Kim, Y.-S. (2010) Review and new interpretation for the propagation characteristics associated with the 1999 Chi-Chi earthquake faulting event. Island Arc, v.19, p Jin, K., Lee, M., Kim, Y.-S. and Choi, J.-H. (2011) Archaeoseismological studies on historical heritages sites in the Gyeongju area, SE Korea. Quaternary International, v.242, p Jin, K., Kim, Y.-S., Yang, S.-J., Choi, J.-H. and Kim, K.-O. (2018) Deformation history and characteristics of the Ilgwang Fault in Southeast Korea. Geosciences Journal, v.22, p Johnson, C.E. and Hutton, L.K. (1982) Aftershocks and pre-earthquake seismicity, the Imperial Valley, California, earthquake, October 15, USGS 1254, Karcz, I., Kafri, U. and Meshel, Z. (1977) Archaeological evidence for Subrecent seismic activity along the Dead Sea-Jordan Rift, Nature, v.269, p Kee, W.-S., Kim, B.C., Hwang, J.H., Song, K.-Y. and Khim, Y.-H. (2007) Structural characteristics of Quaternary reverse faulting of the Eupcheon Fault, SE Korea. Journal of the Geological Society of Korea, v.43, p Kee, W.-S., Kihm, Y.H., Lee, H., Cho, D.L., Kim, B.C., Song, K.-Y., Koh, H.J., Lee, S.R., Yeon, Y.-K., Hwang, S., Park, K,G. and Seong, N.-H. (2009) Evaluation and database construction of Quaternary faults in SE

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