자원탐사와환경공학응용 In the broadest sense: The science of Geophysics is the application of physics to investigations of the Earth, Moon and Planets. In the normal sense: Geophysics is used in a more restricted way, being applied solely to the Earth It includes meteorology, hydrology, oceanography, seismology, volcanology, geomagnetism, geodesy, tectonophysics, geothermometry, etc. 1
use physics to study the interior of the Earth, from land surface to the inner core Global Geophysics or Pure Geophysics The study of the whole or substantial parts of the planets Applied Geophysics Is concerned with investigating the Earth s crust and near-surface Covers everything from experiments to determine the thickness of the crust to studies of shallow structures for engineering site investigations, exploring for ground water and for minerals and other economic resources, to locate narrow mine shafts or other forms of buried to locate narrow mine shafts or other forms of buried cavities, or the mapping of archaeological remains, or locating buried pipes and cables 2
Classification - Petroleum Geophysics ( 석유및천연가스 ) - Mining Geophysics ( 유용광물자원 ) - Engineering / Environmental Geophysics ( 토목지반조사및환경 Definition Based on the principles of physics and geology, one investigates subsurface geological structures that are bearing mineral resources such as oil, gas, methane gas hydrate, and that are important in environment and engineering. 3
Passive methods Active methods Source is natural generate t signals fields artificially detect variations exploration within the natural seismology fields associated with Electromagnetic the Earth, such as method gravitational and Electric resistivity magnetic fields method 중력탐사 (Gravity method) 자력탐사 (Magnetic method) 탄성파탐사 (Seismic method) - 굴절법 (refraction), 반사법 (reflection), 표면파법 (SASW) 전기탐사 (Electric method) - 전기비저항탐사 (DC resistivity method), 자연전위탐사 (Spontaneous potential), 유도분극탐사 (Induced Polarization) 전자탐사 (Electromagnetic method) - Electromagnetic (EM), VLF, Ground penetrating radar, Magneto-telluric) 4
Geophysical methods Physical Properties Measurement Applications 중력탐사밀도중력가속도의변화지질구조, 자원탐사 자력탐사대자율정적자기장의변화자원탐사, 문화재 탄성파탐사 전기비저항탐사 자연전위탐사 유도분극탐사 탄성계수, 밀도, 속도 전기전도도 산화전위, 이온농도및유동 암석구성입자의전기화학적특성 탄성파도달시간과진폭 겉보기전기비저항의변화 전기화학적, 전기역학적전위변화 석유 / 가스, 지반조사 광물자원, 지하수, 지반조사, 매립지 지하수, 광물자원 분극전위의변화환경오염, 광물자원 Geophysical methods 레이다탐사 전자탐사 방사능탐사 Physical Properties 유전율, 전기전도도 전기전도도, 투자율 방사능원소의함량 Measurement 레이다파의도달시간, 진폭 2 차자기장의강도및위상변화 방사선세기 Applications 환경오염, 지반조사, 문화재광물자원, 환경오염우라늄광, 환경오염 5
지표물리탐사 (Surface Geophysics) 항공물리탐사 (Airborne Geophysics) 시추공이용물리탐사 (Borehole Geophysics, Well Logging) 해상물리탐사 (Marine Geophysics) 지역선정 : 지질학적조사 측선및측점설정 : 측선의방향및측점간격등설정 탐사수행 자료처리 : 물성에의한효과이외의다른영향제거 자료해석 : 수치해석기법이용 : 모델링및역산 6
유일한해 (unique solution) 를얻기어려움 해결책 : 여러탐사를복합적으로적용하고, 지질학적정보와연관시켜해석함 적은비용으로지하심부구조를비교적정확히알아낼수있는유일한방법임 7
실체파 (Body waves): 지구내부를전파 P 파 : 종파, 음파, 소밀파, 압축파 S 파 (SH and SV waves): 횡파, 전단파 표면파 (Surface waves): 표면이나경계면을따라전파레일리파 (Rayleigh waves): P파와 SV파의 coupling 러브파 (Love waves): SH파의변형 음파파동방정식 (acoustic wave equation) P 파 탄성파동방정식 (Elastic wave equations) P 파 SV 파, 레일리파, 모드변환파등 SH wave equation 독립적임 8
다이너마이트 (Dynamite) 바이브로사이스 (Vibroseis) Weight drop-thumper Geophone vertical - 3-component -group 9
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V = 2000 m/s V= 4000 m/s Direct waves Reflection waves Head waves 12
2 km Vp = 2000 m/s Vs=1000 m/s 03km 0.3 0.7 km Vp=4000 m/s Vs=2500 m/s 13
Direct waves P -Reflection PS-Reflection Rayleigh SS-Reflection 14
석유, 가스등의탄화수소자원탐사 배사구조, AVO (Amplitude Variation with Offset) 현상 메탄가스하이드레이트탐사 ( 동해울릉분지 ) BSR (Bottom Simulated Reflectors) Coal seam탐사 지반조사및구조물의안정성평가 Engineering site 선정 ( 굴절법 ) 댐의안정성평가 (SH파반사법, 표면파탐사 ) Marmousi-2 model (Martin et al., 2002) North Quenguela Trough in Angola 15
3D 탐사, OBC 이용 역산 구조보정 16
P 파중합단면도 S 파중합단면도 P 파속도 S 파속도 Vs = μ ρ Vs = Vp 1 2σ 21 ( σ ) 포아송의비 17
물성 : 전기비저항 전기탐사 : 전위차측정 전기비저항탐사 : 땅속에전류를흘려보낸후전위차측정 자연전위탐사 : 자연적으로발생하는전위차측정 유도분극탐사 : 전류를흘려보내다가끊은후에전위차가서서히감소하는패턴을측정 전자탐사 (Electromagnetic method) 2차장측정 EM탐사 : 인위적인송신원을이용, 시간영역탐사, 주파수영역탐사 MT탐사 : 자연적으로존재하는전자기장이용. 지구자기장, 번개 18
Frequency (Hz) DC, IP, SP MT higher resolution CSMT, LOTEM CSEM deeper investigation HFEM Radar Homogeneous half space Case of Resistor 금속광상탐사, 지하수탐사, 매립지탐사 19
전기역학적전위 ( 물의이동 ), 전기화학적전위 ( 농도및온도 ), 광화전위 ( 광물 ) 황화광물, 흑연, 자철광, 흑연, 석탄층에서광화전위발생 ; 항상음의전위값 지열탐사, 댐의누수등에이용 주로 Secondary method 로이용임 흑연광체 금속광물의분극현상을측정 Disseminated sulfide ore; 좋은유도분극반응을보임 Disseminated sulfide ore; 좋은유도분극반응을보임 Clay minerals; 중요한유도분극반응나타남 20
Transmitter Receiver Ground surface Eddy current Conductive ore body Primary field Secondary field 이용되는주파수대역에따라다르지만비교적심부에대한정보제공 지열탐사및심부광상탐사에활용 해양 MT 의경우최근석유탐사에서 secondary method 로활용 고주파수대역활용 탄성파탐사와자료처리과정및해석과정이유사 철근구조물의위치파악등 21
금, 은광상 Input data : surface & hole-to-surface Established underground model Geology + Core logging + Well logging + Tomography images 22
Started in the year 2003 For district heating Selected target area based on Geothermal anomaly Lineament distribution Existing well development data Target depth: 2 km Expected temperature: 75 ⁰C 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 Elevation (m) For test well site selection - Gravity and magnetic survey - 2-D & 3-D MT survey -SP survey During test well drilling - Well logging g During pumping test - SP monitoring - Groundwater level monitoring Rotary Drill Rig: BH-2 Pumping test 23
중력탐사 중력장측정 지하매질의밀도변화에따른중력이상 지하매질의밀도분포를유추해냄 기반암의분포 전도성이상체의평가 ; low-density graphite or higher-density sulfide deposit 인공위성중력자료활용 지표및항공탐사 24
자력탐사 자기장측정 지하매질의대자율변화에따른자력이상 화성암의분포 금속광물자원탐사에활용 ( 철광등 ) 지표및항공탐사수행 25
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