Introduction to geophysical methods: Techniques and targets

1 1 Applied geophysics IntroductionTechniques and targetsIntroduction to geophysical methods :Reference:Sharma p1-10 Reynolds p1-27 Applied geophysics IntroductionWhat do we mean by applied geophysics?2 Applied geophysics IntroductionRemote sensingConstraining the Earth s sub-surface with observations at the surfaceGeophysical Techniques measure physical phenomena: Gravity Magnetism Elastic waves Electricity Electromagnetic wavesWhich are sensitive to sub-surface physical properties: Density Magnetic susceptibility Seismic wave velocity and density Resistivity Conductance/inductance/permitivityOh, and it s relatively cheapApplied geophysics IntroductionActive and passiveActiveTransmit a signal into the subsurface and record what comes back Seismic arrival explosions Electrical current Electromagnetic wavesPassiveMeasure naturally occurring phenomena Gravity field Magnetic field Seismic arrivals - earthquakesthink scale3 Applied geophysics IntroductionOur to kilometersThe Techniques we ll talk about are used in the fields of Environmental geophysics Engineering geophysics Exploration geophysicsApplied geophysics IntroductionPlanning a survey4 Applied geophysics IntroductionTarget identificationApplied geophysics IntroductionMagneticsExamplesMain use.

2 Locating steel drums and pipes5 Applied geophysics IntroductionExamplesSeismic reflectionApplied geophysics IntroductionSeismic reflectionExamples6 Applied geophysics IntroductionGround penetrating radarExamplesApplied geophysics IntroductionGround penetrating radarExamples7 Applied geophysics IntroductionTechniques and targetsmmPPsResistivityMagneto-telluricP PPsPPPmPermitivity, conductivityEM Ground penetrating radarmmsssmPmmConductance, inductanceEM - VLFmPPPPPPPPsConductance, inductanceElectromagnetic (EM)mmmmmsmPmmResistivity, capacitanceInduced polarizationmmmPmPPotential differencesSpontaneous potentialmPsPPPPPmmResistivityResistivit ymssmPPElastic moduli, densitySeismic reflectionssPmPPElastic moduli, densitySeismic refractionPPmsPPPS usceptibilityMagneticsssssPPDensityGravi tyDependent physical propertyGeophysical MethodHydrocarbon exploration (coal, oil, gas)Regional geologic study(>100s km2)Exploration/development of mineral depositsEngineering site investigationsHydrogeologicalinvestigati onsDetection of subsurface cavitiesMapping leachate and contamination plumesLocation of buried metallic objectsArchaeogeophysicsForensic geophysicsP primary method; s secondary; m maybe sometimesApplied geophysics IntroductionProfiling vs.

3 MappingWhat is the nature of the target? 2D or 3D? Preliminary site evaluation necessary?8 Applied geophysics IntroductionStation spacingMust ensure that spacing is sufficient to sample anticipated signalApplied geophysics IntroductionLimitations methods require contrast in physical properties NonuniquenessDirect modeling: calculate the result of a specific structureInverse modeling: determine the causative structure from observations usually small shallow body vs. large deep body Resolution is determined by the wavelength of the signalsesimic: km, radar: cm Noise prevents recovery of low amplitude wind, traffic, water pumps, power lines9 Applied geophysics IntroductionMultiple improve uniqueness and cross-check interpretationsApplied geophysics IntroductionIntroductionsInstructors:Ric hard AllenRm 106 Weeks Hall; Tel: 262-7513; FrattaRm 2258 Engineering Hall; Tel: 265-5644; Assistant:Mei XueRm 111 Weeks Hall; 262 9784.

4 Hours:by appointment10 Applied geophysics IntroductionSourcesCourse webpage: - lecture notes, homeworks etcRequired text Environmental and Engineering Geophysics, 1sted, Sharma, 1997 Other reference textsAn Introduction to Applied and Environmental Geophysics, Reynolds, Geophysics, 2nded, Telford, Geldart, Sheriff, 1990 Exploration geophysics of the shallow subsurface, Burger, Earth Geophysics, Lillie, Introduction to geophysical exploration, Keary, Brooks and Hill, 2002 Applied geophysics IntroductionGrading50% - Homework: Bi-weekly problem sets10% - Quiz 1 October 7th15% - Quiz 2 November 23rd25% - FinalDecember 17th12:25pmAnnouncements of any changes will be made at the lectures and on the geophysics IntroductionTopic scheduleWeeks 1-2: Gravity MethodsWeeks 3-4: Magnetic MethodsWeeks 5-6: Resistivity MethodsWeeks 7-11: Seismic Reflection and Refraction MethodsWeeks 11-13: Electromagnetic MethodsWeek 14: Ground Penetrating Radar MethodsWeek 15: Borehole MethodsApplied geophysics IntroductionAdditional materialSummaries and examples of other methods12 Applied geophysics IntroductionGravityExamplesApplied geophysics IntroductionSeismic refractionExamples13 Applied geophysics IntroductionElectrical resistivityExamplesApplied geophysics IntroductionElectrical resistivityExamplespolluted sandclean sandpolluted sand14 Applied geophysics IntroductionElectromagnetic surveyingExamplesApplied geophysics IntroductionElectromagnetic surveyingExamples