Table Of ContentP1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
Field Geophysics
Field Geophysics, Fourth Edition John Milsom and Asger Eriksen
© 2011 John Wiley & Sons, Ltd. ISBN: 978-0-470-74984-5
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
TheGeological FieldGuideSeries
Barnes,J.W.andLisle,R.J.(2004)BasicGeologicalMapping,4thedn.ISBN:
978-0-470-84986-6,5thednpublishing(2011).ISBN:978-0-470-68634-8
Fry,N.(1991)TheFieldDescriptionofMetamorphicRocks.
ISBN:978-0-471-93221-5
McClay,K.R.(1991)TheMappingofGeologicalStructures.
ISBN:978-0-471-93243-7
Milsom,J.andEriksen,A.(2011)FieldGeophysics,4thedn.
ISBN:978-0-470-74984-5
Tucker,M.E.(2011)SedimentaryRocksintheField,4thedn.
ISBN:978-0-470-68916-5
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
Field Geophysics
FOURTHEDITION
John Milsom
GladestryAssociates
Asger Eriksen
ZeticaLtd
A John Wiley and Sons, Ltd., Publication
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
Thiseditionfirstpublished2011,(cid:1)c 2011byJohnWiley&SonsLtd
Wiley-BlackwellisanimprintofJohnWiley&Sons,formedbythemergerofWiley’sglobal
Scientific,TechnicalandMedicalbusinesswithBlackwellPublishing.
Registeredoffice:JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester,West
Sussex,PO198SQ,UK
OtherEditorialOffices:
9600GarsingtonRoad,Oxford,OX42DQ,UK
111RiverStreet,Hoboken,NJ07030-5774,USA
Fordetailsofourglobaleditorialoffices,forcustomerservicesandforinformationabouthow
toapplyforpermissiontoreusethecopyrightmaterialinthisbookpleaseseeourwebsiteat
www.wiley.com/wiley-blackwell
Therightoftheauthortobeidentifiedastheauthorofthisworkhasbeenassertedin
accordancewiththeCopyright,DesignsandPatentsAct1988.
Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,
ortransmitted,inanyformorbyanymeans,electronic,mechanical,photocopying,recording
orotherwise,exceptaspermittedbytheUKCopyright,DesignsandPatentsAct1988,without
thepriorpermissionofthepublisher.
Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappearsin
printmaynotbeavailableinelectronicbooks.
Designationsusedbycompaniestodistinguishtheirproductsareoftenclaimedastrademarks.
Allbrandnamesandproductnamesusedinthisbookaretradenames,servicemarks,
trademarksorregisteredtrademarksoftheirrespectiveowners.Thepublisherisnotassociated
withanyproductorvendormentionedinthisbook.Thispublicationisdesignedtoprovide
accurateandauthoritativeinformationinregardtothesubjectmattercovered.Itissoldonthe
understandingthatthepublisherisnotengagedinrenderingprofessionalservices.If
professionaladviceorotherexpertassistanceisrequired,theservicesofacompetent
professionalshouldbesought.
LibraryofCongressCataloging-in-PublicationData
Milsom,John,1939-
Fieldgeophysics.–4thed./JohnMilsom,AsgerEriksen.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-0-470-74984-5(pbk.)
1.Prospecting–Geophysicalmethods. I.Eriksen,Asger. II.Title.
TN269.M532011
622(cid:1).15–dc22
2010033328
AcataloguerecordforthisbookisavailablefromtheBritishLibrary.
Thisbookispublishedinthefollowingelectronicformats:ePDF9780470972328;Wiley
OnlineLibrary9780470972311
Typesetin9/10.5ptTimesbyAptaraInc.,NewDelhi,India
FirstImpression2011
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
CONTENTS
PrefacetotheFirstEdition ix
PrefacetotheSecondEdition x
PrefacetotheThirdEdition xii
PrefacetotheFourthEdition xiv
1 Introduction 1
1.1 WhatGeophysicsMeasures 1
1.2 Fields 1
1.3 GeophysicalSurveyDesign 9
1.4 GeophysicalFieldwork 14
1.5 GeophysicalData 19
1.6 BasesandBaseNetworks 29
1.7 Real-TimeProfiling 32
2 GravityMethod 39
2.1 PhysicalBasisoftheGravityMethod 39
2.2 GravityMeters 41
2.3 GravityReductions 49
2.4 GravitySurveys 52
2.5 FieldInterpretation 61
3 MagneticMethod 65
3.1 MagneticProperties 65
3.2 TheMagneticFieldoftheEarth 67
3.3 MagneticInstruments 72
3.4 MagneticSurveys 75
3.5 SimpleMagneticInterpretation 81
4 RadiometricSurveys 85
4.1 NaturalRadiation 85
4.2 RadiationDetectors 90
4.3 RadiometricSurveys 92
5 ElectricCurrentMethods:GeneralConsiderations 97
5.1 ResistivityandConductivity 97
5.2 VaryingCurrents 102
v
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
CONTENTS
6 ResistivityMethods 109
6.1 DCSurveyFundamentals 109
6.2 DCPracticalities 117
6.3 ResistivityProfiling 122
6.4 ResistivityDepth-Sounding 125
6.5 ElectricalResistivityImaging(ERI) 128
6.6 CapacitiveCoupling 133
7 SPandIP 137
7.1 SPSurveys 137
7.2 PolarisationFundamentals 140
7.3 Time-DomainIPSurveys 143
7.4 Frequency-DomainSurveys 144
7.5 IPData 146
8 ElectromagneticMethods 149
8.1 Two-CoilCWSystems 149
8.2 CWEMConductivityMapping 158
8.3 Fixed-SourceMethods 161
8.4 TransientElectromagnetics 165
9 Remote-SourceElectromagnetics 171
9.1 NaturalElectromagneticRadiation 171
9.2 Controlled-SourceAudio-Magnetotellurics
(CSAMT) 180
10 GroundPenetratingRadar 185
10.1 RadarFundamentals 185
10.2 GPRSurveys 199
10.3 DataProcessing 205
11 SiesmicMethods:GeneralConsiderations 211
11.1 SeismicWaves 211
11.2 SeismicSources 216
11.3 DetectionofSeismicWaves 222
11.4 RecordingSeismicSignals 226
12 SeismicReflection 229
12.1 ReflectionTheory 229
12.2 ReflectionSurveys 233
13 SeismicRefraction 241
13.1 RefractionSurveys 241
13.2 Interpretation 247
13.3 LimitationsoftheRefractionMethod 257
vi
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
CONTENTS
14 SeismicSurfaceWaveMethods 261
14.1 SurfaceWaveSurveys 261
14.2 DataProcessing 266
14.3 LimitationsoftheMethod 270
15 Maps,MappingandGPS 273
15.1 MapsandMapping 273
15.2 SatelliteNavigation 276
Appendix:TerrainCorrectionsforHammerZonesBtoM 281
Index 283
vii
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
PREFACE TO THE FIRST EDITION
Thepurposeofthisbookistohelpanyoneinvolvedinsmall-scalegeophys-
icalsurveys.Itisnotatextbookinthetraditionalsense,inthatitisdesigned
foruseinthefieldandconcernsitselfwithpracticalmatters–withtheory
taking second place. Where theory determines field practice, it is stated,
notdevelopedorjustified.Forexample,noattemptismadetoexplainwhy
four-electroderesistivityworkswheretwo-electrodesurveysdonot.
Thebookdoesnotdealwithmarine,airborneordownholegeophysics,
norwithdeepseismicreflectionwork.Inpartthisisdictatedbythespace
available,butalsobythefactthatsuchsurveysareusuallycarriedoutby
quitelargefieldcrews,atleastsomeofwhom,itistobehoped,areboth
experiencedandwillingtospreadthebenefitofthatexperiencemorewidely.
Where appropriate, some attention is given to jargon. A field observer
needsnotonlytoknowwhattodobutalsotherightwordstouse,andright
inthiscontextmeansthewordswhichwillbeunderstoodbyothersinthe
samelineofbusiness,ifnotbythecompilersofstandarddictionaries.
Awordofapologyisnecessary.Thefieldobserverissometimesreferred
toas‘he’.Thisisunfortunatelyrealistic,as‘she’isstillalltoorare,butis
notintendedtoindicatethat‘she’iseitherunknownorunwelcomeinthe
geophysicalworld.Itishopedthatallgeophysicalfieldworkers,whether
maleorfemaleandwhethergeophysicists,geologistsorunspecializedfield
hands,willfindsomethingusefulinthisbook.
Finally,awordofthanks.PaulHaystonofBPMineralsandTimLangdale-
SmithofTerronicsreadearlydraftsofthetextandmadenumerousinvaluable
suggestions.Tothem,toJanetBaker,whodrewmanyofthesketches,and
to the companies which provided data and illustrations, I am extremely
grateful.
ix
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
PREFACE TO THE SECOND EDITION
Sincethefirsteditionofthisbookwaspublishedin1989,therehavebeen
some changes in the world of field geophysics, not least in its frequent
appearance in television coverage of arthaeological ‘digs’. In this work,
andinsurveysofcontaminatedgroundandlandfillsites(thearchaeological
treasure houses of the future), very large numbers of readings are taken
atverysmallspacingsandwritingdowntheresultscouldabsorbamajor
part of the entire time in the field. Automatic data logging has therefore
become much more important and is being make ever easier as personal
computersbecomesmallerandmorepowerful.Newfieldtechniqueshave
been developed and image processing methods are now routinely usedto
handle the large volumes of data. Comments made in the first edition on
theneedtorecordinformationaboutthesurveyareaaswellasgeophysical
data have equal, and perhaps even more, force in these instances, but it
isobviouslyusuallynotpracticalorappropriatetomakeindividualnotes
relatingtoindividualreadings.
Theincreaseinthenumberofgeophysicalsurveysdirectedatthevery
shallowsubsurface(1–5m)hasalsoledtotheincreasinguseofnoncon-
tacting(electromagnetic)methodsofconductivitymapping.Moreover,the
increased computing power now at every geophysicist’s disposal has in-
troduced inversion methods into the interpretation of conventional direct
currentresistivitysoundingsandhasrequiredcorrespondingmodifications
tofieldoperations.Itishopedthatthesechangesareadequatelycoveredin
thisnewedition.afurtherdevelopmenthasbeenthemuchwideravailability
ofgroundpenetratingradarsystemsandarecentandfairlyrapidfallintheir
cost.Achapterhasbeenaddedtocoverthisrelativelynewmethod.
Muchelsehasremainedunchanged,andadvancesinairbornetechniques
have actually inhibited research into improving ground-based instrumen-
tationformineralexploration.Automaticandself-levellinggravitymeters
arebecomingmorewidelyavailable,butarestillfairlyuncommon.Magne-
tometersmoresensitivethantheconventionalprotonprecessionorfluxgate
instrumentsarewidelyadvertised,butinmostcircumstancesprovidemore
precision than can be readily used, except in the measurement of field
gradients.
VLF methods are enjoying something of a revival in exploration for
fracture aquifers in basement rocks, and the importance of ease of use is
being recognized by manufacturers. Instruments for induced polarization
x
P1:TIX/OTE/SPH P2:OTE
fm JWST016-Milsom December18,2010 8:9 PrinterName:YettoCome
PREFACETOTHESECONDEDITION
and time-domain electromagnetic surveys also continue to be improved,
but their basic principles remain unchanged. More use is being made of
reflectedseismicwaves,partlybecauseoftheformerlyundreamedofpro-
cessingpowernowavailableinportablefieldseismographs,butrefraction
stilldominatesseismicstudiesoftheshallowsubsurface.
Inevitably,notallthemethodscurrentlyinusecouldbecoveredinthe
spaceavailable.Seismo-electricalmethods,inwhichthesourcepulsesare
mechanicalandthesignalpulsesareelectrical,arebeginningtomaketheir
presence felt and may demand a place in textbooks in the future. Few
case histories have yet been published. Magnetotelluric methods have a
much longer history and continue to be developed, in conjunction with
developmentsintheuseofcontrolled(CSAMT)ratherthannaturalsources,
butmanygeneralpurposegeophysicistswillgothroughtheirentirecareers
withoutbeinginvolvedinonesuchsurvey.
Despite the considerable rewriting, and the slight increase in size (for
whichIamimmenselygratefultothenewpublishers),theaimofthebook
remainsthesame.Likeitspredecessoritisnotatextbookintheconventional
sense, but aims to provide practical information and assistance to anyone
engagedinsmall-scalesurveysontheground.Inhelpingmetowardsthis
objective,IamgratefulparticularlytoPaulHayston(RTZ)forintroducing
metomineralexplorationinanewandexcitingarea,toAsgeirEriksenof
GeophysicalServicesInternational(UK)forkeepingmeintouchwiththe
realitiesofengineeringandground-watergeophysics,andtomystudents
for reminding me every year of where the worst problems lie. I am also
gratefultoallthosewhohavegiventheirpermissionforillustrationstobe
reproduced(includingmydaughter,Kate,whoseviewoffieldgeophysics
isshowninFig.5.1),andmostespeciallytomywife,Pam,forretypingthe
originaltextandforputtingupwiththisalloveragain.
JohnMilsom
xi
