Gravity and Magnetic Exploration: Principles, Practices, and Applications

525 Pages·2013·23.61 MB·English

by  Hinze P.W.J.

GravityandMagneticExploration
Principles,Practices,andApplications
Thiscombinedstudyandreferencetextprovidesa fields.Hehasauthoredorco-authoredmorethan130journal
comprehensiveaccountoftheprinciples,practices,and publications,andfourbooks,andhasservedasAssociateEditor
applicationofgravityandmagneticmethodsforexploringthe ofGeophysicsandSeniorEditorofTheJournalofGeophysical
subsurfaceusingsurface,subsurface,marine,airborne,and Research–SolidEarth.ProfessorHinzehasbeenamemberof
satellitemeasurements.Keycurrenttopicsandtechniquesare numerousgovernmentandscientificpanelsdealingwithkey
described,includinghigh-resolutionmagneticinvestigations, issuesfromthegeophysicsandgeologyofcontinentstonuclear
time-variationgravityanalysisfromsurfaceandsatellitegravity wastedisposalandgeophysicaldata.Heisamemberofthe
measurements,absoluteandgradientgravimetry,andtheroleof SocietyofExplorationGeophysicists,theAmerican
GPSinmappinggravityandmagneticfields.Thebookalso GeophysicalUnion,andtheGeologicalSocietyofAmerica.
describesthephysicalpropertiesofrocksandotherEarth
RALPH R. B. VON FRESEisProfessorofEarthSciencesat
materialsthatarecriticaltotheeffectivedesign,implementation,
TheOhioStateUniversity,wherehehastaughtundergraduate
andinterpretationofsurveys,andpresentsanoverviewofdigital
andgraduatecoursesacrossgeophysicsandEarthsystemssince
dataanalysismethodsusedtoprocessandinterpretanomalies
1982.Hisresearchhasfocusedmostlyonarchaeologicaland
forsubsurfaceinformation.
planetaryapplicationsofgravityandmagneticfields,andhehas
Eachchapterstartswithageneraloverviewandconcludes
authoredorco-authoredmorethan100journalpublicationsand
withalistofkeyconceptsthathelpreadersreviewwhatthey
servedonseveralgovernmentandscientificpanels.Professor
havelearned.Anappendixprovidesagroundingonbasicdata
vonFreseisthefoundingco-chairoftheAntarcticDigital
analysisusingsimpleandaccessiblemathematicalnotation.
MagneticAnomalyProject(ADMAP),aninternational
Studyquestionsandproblemsetsonanaccompanyingwebsite,
collaborationoftheScientificCommitteeforAntarcticResearch
togetherwithcomputer-basedexercisesavailableonline,give
(SCAR)andtheInternationalAssociationofGeomagnetismand
readershands-onexperienceofprocessing,modeling,and
Aeronomy(IAGA).HeisamemberoftheSocietyof
interpretinggravityandmagneticanomalydata.A
ExplorationGeophysicists,theAmericanGeophysicalUnion,
comprehensivesuiteoffull-colorcasehistoriesonthebook’s
andtheGeologicalSocietyofAmerica.
websiteillustratesthepracticalutilityofmoderngravityand
magneticsurveysinenergy,mineral,environmental, AFIF H. SAADisaGeophysicalConsultanttotheoilandgas
archaeological,andengineeringexplorationandlithospheric explorationindustry,specializinginintegratedinterpretation,
studies,aswellastheirpotentiallimitations. modeling,magneticdepthestimation,softwaredevelopment,
Thisbookisanidealtextforadvancedundergraduateand andtraining.Hehasover40yearsofbroadexperienceinthe
graduatecoursesbutalsoservesasareferenceforresearch theoryandpracticeofgravityandmagneticmethodsin
academics,professionalgeophysicists,andmanagersof exploration,including25yearsintheoilindustry,andhas
explorationprogramsthatusegravityandmagneticmethods.It providedtrainingatseveralschoolsandworkshopsinbasic,
isavaluableresourceforallthoseinterestedinpetroleum, intermediate,andadvancedgravityandmagneticsintheUnited
engineering,mineral,environmental,geological,and Statesandoverseas.DrSaadhasauthoredorco-authoredseveral
archaeologicalexplorationofthelithosphere. publications,haspeer-reviewednumerouspapersandtextbooks
ingravityandmagneticsforGeophysicsandtheGeophysical
WILLIAM J. HINZEisEmeritusProfessorofGeophysicsat JournalInternational,andhasservedasAssociateEditorfor
PurdueUniversity,andhastaughtexplorationgeophysicsfor MagneticExplorationMethodsforGeophysics.Heisamember
40years.Hisextensiveteachingandresearchexperienceis oftheSocietyofExplorationGeophysicists(SEG),theSEG
complementedbyindustrialconsultingexperienceinthe GravityandMagneticsCommittee,theSEGGlobalAffairs
geologicalandengineeringapplicationsofgravityandmagnetic Committee,andtheGeophysicalSocietyofHouston.
“Writtenbythreeleadingresearchers,thisisacomprehensivetextbookthattakesitsread-
ersfromthefundamentalsofpotentialfieldsthroughmoderndataacquisition,processing,
modelingandinversiontopracticalinterpretation.Thetheoryandmathematicalderivations
are suitable for both beginners and experienced geophysicists. Well-organized and nicely
illustrated,itisbothinformativeandclearlywritten.”
–ProfessorDrAlanGreen
InstituteofGeophysics,ETH-SwissFederalInstituteofTechnology
“This extensive work is much more than just a textbook: it includes detailed discussions,
suchasthephilosophyofmodelingandthenatureoferrors,whicharecriticaltoproperly
interpretinggravityandmagneticdata,butareoftenglossedover.Averyusefuladditionto
practitioners’referenceshelvesandanexcellenttextbookforadvancedstudents.”
–RogerC.Searle,ProfessorEmeritus
DepartmentofEarthSciences,DurhamUniversity
“Thegeophysicalapplicationsofgravityandmagnetictechniqueshaveadvancedagreatdeal
in the twenty-first century. Thus, this rigorous book covering the physical basis, analysis,
interpretation,andapplicationsofthesetechniquesisatimelyandimportantcontribution.
It is designed to serve both the student and practitioner and is enhanced by an innovative
website.”
–ProfessorG.RandyKeller
GeologyandGeophysics,UniversityofOklahoma;
DirectorofOklahomaGeologicalSurvey
Gravity and
Magnetic
Exploration
Principles, Practices, and Applications
William J. Hinze
Purdue University
Ralph R. B. von Frese
The Ohio State University
Afif H. Saad
Saad GeoConsulting
cambridgeuniversitypress
Cambridge,NewYork,Melbourne,Madrid,CapeTown,
Singapore,Sa˜oPaulo,Delhi,MexicoCity
CambridgeUniversityPress
TheEdinburghBuilding,CambridgeCB28RU,UK
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Informationonthistitle:www.cambridge.org/9780521871013
(cid:2)C WilliamJ.Hinze,RalphR.B.vonFreseandAfifH.Saad2013
Thispublicationisincopyright.Subjecttostatutoryexception
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noreproductionofanypartmaytakeplacewithoutthewritten
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Firstpublished2013
PrintedandboundintheUnitedKingdombytheMPGBooksGroup
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ISBN 978-0-521-87101-3Hardback
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Contents
Preface pageix
Objectivesofthisbook ix
Relatedbooks x
Organizationofthisbook x
Studyquestionsandexercises xi
Units xi
Acknowledgements xii
1 Introduction 1
1.1 Overview 1
1.2 TheEarthanditsplanetaryforcefields 2
1.3 Basisofthegravityandmagneticmethods 3
1.4 Foundationsofgeophysicalmethods 5
1.5 Geophysicalpractices 7
1.6 Natureofgeophysicaldata 11
1.7 Keyconcepts 14
PartI Gravityexploration 17
2 Thegravitymethod 19
2.1 Overview 19
2.2 Roleofthegravitymethod 20
2.3 TheEarth’sgravityfield 21
2.4 Historyofthegravitymethod 27
2.5 Implementingthegravitymethod 32
2.6 Keyconcepts 36
3 Gravitypotentialtheory 38
3.1 Overview 38
3.2 Introduction 38
3.3 Gravityeffectsofapointmass 39
3.4 Gravityeffectsofanextendedbody 41
3.5 Idealizedsourcegravitymodeling 48
3.6 Generalsourcegravitymodeling 53
3.7 Gauss’law 59
3.8 Gravityanomalyambiguity 60
3.9 Poisson’stheorem 61
3.10 Pseudoanomalies 61
3.11 Keyconcepts 62
v
vi Contents
4 DensityofEarthmaterials 64
4.1 Overview 64
4.2 Introduction 64
4.3 Typesofdensities 65
4.4 DensityoftheEarth’sinterior 66
4.5 Rockdensities 68
4.6 Densitymeasurements 75
4.7 Densitytabulations 85
4.8 Keyconcepts 86
5 Gravitydataacquisition 88
5.1 Overview 88
5.2 Introduction 89
5.3 Measuringgravity 89
5.4 Gravitysurveying 107
5.5 Gravitymeasurementsfromspace 113
5.6 Keyconcepts 120
6 Gravitydataprocessing 122
6.1 Overview 122
6.2 Introduction 122
6.3 Extraneousgravityvariations 123
6.4 Gravityanomalies 143
6.5 Anomalyisolationandenhancement 155
6.6 Keyconcepts 173
7 Gravityanomalyinterpretation 175
7.1 Overview 175
7.2 Introduction 175
7.3 Interpretationparameters 181
7.4 Simplifiedinterpretationtechniques 189
7.5 Modelinganomalysources 200
7.6 Keyconcepts 211
PartII Magneticexploration 213
8 Themagneticmethod 215
8.1 Overview 215
8.2 Roleofthemagneticmethod 215
8.3 TheEarth’smagneticfield 216
8.4 Historyofthemagneticmethodinexploration 229
8.5 Implementingthemagneticmethod 231
8.6 Keyconcepts 233
9 Magneticpotentialtheory 235
9.1 Overview 235
9.2 Introduction 235
9.3 Magneticpotentialofapointdipole 236
9.4 Magneticeffectsofapointdipole 236
9.5 Magneticeffectsofanextendedbody 238
9.6 Idealizedsourcemagneticmodeling 243
9.7 Generalsourcemagneticmodeling 244
9.8 Totalmagneticmoment 250
Contents vii
9.9 Magneticsourceambiguity 250
9.10 Combinedmagneticandgravitypotentials 250
9.11 Keyconcepts 251
10 MagnetizationofEarthmaterials 252
10.1 Overview 252
10.2 Introduction 252
10.3 MagnetismofEarthmaterials 253
10.4 Mineralmagnetism 257
10.5 Magneticsusceptibility 259
10.6 Magnetizationofrocksandsoils 261
10.7 Magneticpropertymeasurements 272
10.8 Magneticpropertytabulations 273
10.9 Keyconcepts 274
11 Magneticdataacquisition 276
11.1 Overview 276
11.2 Introduction 276
11.3 Instrumentation 277
11.4 Surveydesignandprocedures 284
11.5 Magneticmeasurementsfromspace 291
11.6 Keyconcepts 297
12 Magneticdataprocessing 300
12.1 Overview 300
12.2 Introduction 301
12.3 Extraneousmagneticvariations 302
12.4 Anomalyisolationandenhancement 314
12.5 Keyconcepts 336
13 Magneticanomalyinterpretation 338
13.1 Overview 338
13.2 Introduction 339
13.3 Interpretationconstraints 342
13.4 Interpretationtechniques 355
13.5 Modelinganomalysources 394
13.6 Keyconcepts 411
PartIII Applications 413
14 Applicationsofthegravityandmagneticmethods 415
14.1 Introduction 415
14.2 Generalviewofapplications 415
14.3 Near-surfacestudies 416
14.4 Energyresourceapplications 417
14.5 Mineralresourceexploration 418
14.6 Lithosphericinvestigations 420
AppendixA Datasystemsprocessing 422
A.1 Overview 422
A.2 Introduction 422
A.3 Databasesandstandards 423
A.4 Mathematicalmethods 424
viii Contents
A.5 Anomalyanalysis 444
A.6 Datagraphics 463
A.7 Keyconcepts 475
References 477
Index 502
Preface
Objectivesofthisbook ciples. Case histories in supplemental chapters, which
are available on an accompanying website, illustrate the
Investigations of terrestrial gravity and magnetic fields advantages and limitations of the methods in a variety
areamongtheoldestmethodsfordeterminingthenature of applications including near-surface engineering and
and processes of the Earth. Despite the development of archaeologicalstudies,mineralandenergyresourceinves-
anincreasingnumberofadditionalcomplementaryinves- tigations,andplanetarycrustalandsubcrustalstudies.A
tigative methods, some of which have better subsurface finalchapterofthisbooksummarizestheseapplications.
resolution,thegravityandmagneticmethodscontinueto This presentation of gravity and magnetic methods
have an important, often decisive role, in a wide vari- differs substantially from existing books. For example,
etyofterrestrialinvestigations.Incontrasttotheseveral it takes into account the rapidly accelerating availability
available texts on specific topics in gravity and magnet- of subsurface, terrestrial, marine, airborne, and satellite
ics,thisbookprovidesanoverall,modernresourceonthe measurements that the current information age is map-
principles,practices,andapplicationsofboththegravity pinginprodigiousvolumes.Further,itdevelopsstrategies
and magnetic methods to exploring the Earth. Although onthecombineduseoftheseanomalyfieldsforsolving
theseaspectsofthegravityandmagneticmethodsarewell subsurface problems. It also describes the newest stan-
grounded in widely described and accepted principles, dardsandmethodsforreducinggravityandmagneticdata
they are continually undergoing practical improvements to a usable form, as well as modern instrumentation for
and expanded understanding. The continued improve- observing both absolute and relative total field and vec-
mentsresultfromenhancedtechnologyforacquiring,pro- torialcomponents.Thebookemphasizespracticalproce-
cessing, and interpreting data made possible largely by dures and applications, and the physical properties and
increasingcomputationalpowerandnewtechniques.Spe- geologicalprinciplesthatconstrainsubsurfaceanalysesof
cialemphasisingravityandmagneticexplorationisbeing gravityandmagneticfields.Itdescribesallmajormodern
placed on high sensitivity mapping of anomalies at the topicsofgravityandmagneticmethodsthatarelikelyto
extremitiesoftheirspectra,bothshorterandlongerwave- be of general interest. More general descriptive material
lengths, increasing the vertical and horizontal resolution andproceduresarehighlighted,andreferenceismadeto
ofindividualanomalysources,andinvestigatingthetem- alternateproceduresorapproaches.However,necessarily
poralvariationsinthegravityandmagneticfieldsofthe numerous computational and interpretational procedures
EarthwhichpermitnewinsightsintoEarthprocesses.It describedinthegeophysicalliteraturewhichmayhavea
is hoped that this book which sets a benchmark in our morelimitedapplicationarenotincludedbecauseofspace
current knowledge of gravity and magnetic exploration limitations. Wherever possible, examples of these meth-
willencouragefurtherdevelopmentsinthesemethodsand ods are briefly described and pertinent literature is cited
applications. to guide the interested reader to additional information.
Boththetheoryandpracticeofgravityandmagnetic Derivationsofequationsarerestrictedtothoseofgeneral
methodsappliedtosubsurfaceinvestigationsaredescribed interestanddetailsofmanyproceduresarenotincludedin
in this book. The book considers the methods from the thedescriptions.Thereforethereaderofthistextwillneed
planning and organization of surveys through the analy- to make abundant use of the many references cited for
sis and interpretation of observations by digital compu- moredetailedandcomprehensivetreatmentofspecialized
tations incorporating both physical and geological prin- topics.
ix