8/8/2019 WDMAM 1.02 2007 Edition Low Resolution Reduced1

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Code Areacovered Resolution Reference

13.0 MF5 5 km Maus et al. (2007a)

101.41 Marinetrack-linevariable NGDC,http://www.ngdc.noaa.gov/mgg/geodas/trackline.html

101.45 Interpolated(101.41)Non-interpolated(101.45)

1 21 . 43 Ar ct i c 5 k m G e os c ie n ce Ca na d a, h t t p: / /g s c. n rc a n. g c. c a/ in d ex _e . ph p131.45 ProjectMagnet variable NGDC,http://www.ngdc.noaa.gov/seg/geomag/proj_mag.shtml

171 .44 Oceanicmodel 10km NASA candidatemodel ,accompanyingDVD

2 01 . 2 Af ri c a 1 5 m in G E TE CH, h t t p :/ / www.g e te c h. c om

201.2 South America 15 min GETECH,http://www.getech.com

2 22 . 3 S o ut h Af ri c a 5 k m S ADC, h t tp : // www. sa d c. i nt

2 31 .3 2 B o ts wa na 5 k m h tt p: // ww w. go v. bw /  

3 02 . 43 An ta r ct i c 5 k m ADMAP , ht t p :/ / ea r th s ci e nc e s. o su . ed u /a d ma p

4 01 . 3 E u ra s ia 2 k m G e os c ie n ce Ca na d a, h t t p: / /g s c. n rc a n. g c. c a/ i nd e x_ e .p h p

4 11 . 43 E a st As ia 2 k m CCOP , h t tp : // www. cc o p. o r. t h

421 .43 MiddleEast 1km AAIME,http:/ /home.casema.nl/errenwijlens/ itc/aaime

4 41 .3 I nd ia 5 k m G SI , ht tp :/ /w ww .g si .g ov .i n

4 42 . 2 I n di a 5 0 k m Q u re s hy , M .N. , 1 98 2, P h ot o gr a mm e tr i a, Vo l. 3 7 , 16 1- 1 84

4 51 .3 2 J a pa n 1 k m h tt p: // ww w. ai st . go .j p/ GS J/  

5 04 . 43 Au st r al i a 1 k m G e os c ie n ce Au st r al i a, h t t p: / /www. g a. g ov . au

6 01 . 43 E u ro p e 5 k m W on i k, T . e t a l. , 2 00 1, T e rr a Nov a, Vo l 13 , 2 03 - 21 3

6 11 . 3 F e nn o sc a nd i a 5 k m G T K, h t t p: / /www. g tk . fi

621 .321 Austria 5km http://www.geolog ie.ac.at/  

622 .2 CanaryIslands 5km Publ .Tec.,No.35 ,Insti tutoGeograficoNacional ,Madrid,1996

6 24 . 22 F i nl a nd 1 k m h t tp : // p ro j ec t s. g tk . fi / WDM AM /  

6 25 . 2 F r an c e 1 0 k m I P GP , h t tp : // www. ip g p. j us s ie u .f r

6 26 . 2 I t al y 5 k m Ch ia p pi n i, M . e t a l. , 2 00 0, An n al i d i Ge op h ys i ca , Vol 4 3 , No . 5

6 27 . 43 S p ai n 1 . 5 mi n S o ci a s I. , e t a l. , 1 99 1 , Ea r th P l an e t. S c i. L e tt . , 1 05 , 5 5- 6 4

628.3 Russia 5 km VSEGEI, http://www.vsegei.ru/WAY/247038/locale/EN

701.43 NorthAmerica 1km NAMAG,http:/ /pubs.usgs.gov/sm/mag_map

7 11 . 32 M e xi c o 5 k m h t tp : // www. co r em i sg m .g ob . mx /  

811 .45 Argentinainland 5km SEGEMAR,http:/ /www.segemar.gov.ar/db

812.3 Argentina margin 5 km Instituto Antártico Argentino, http://ggt.conae.gov.ar/iaa/pictr2002

MAGNETIC ANOMALYMAP OFTHE WORLD

CARTE DES ANOMALIES MAGNÉTIQUES DU MONDE

EXPLANATORYN OTES /   NOTICE EXPLICATIVE

OBJECTIVE OFTHE MAP/ OBJECTIFDE LACARTEThis map is the firstglobalcompilation ofthewealth of magneticanomaly information derived frommorethan 50 yearsofaeromagneticsurveys overland areas, research vesselmagnetometertraverses atsea, and observations fromearth-

orbitingsatellites, supplemented byanomaly values derived fromoceaniccrustalages. Theobjectiveis to providean

interpretivedimension to surface observations of theEarth’s composition and geologicstructure. Metamorphism,

petrology, and redox stateallhaveimportant effects on themagnetismof crustalmaterials. Themagneticanomaliesrepresented on this map originateprimarily in igneous and metamorphicrocks, in the Earth’s crustand possibly,

uppermostmantle. Magneticanomalies representan estimateofthe short-wavelength (<2600 km)fields associated

with theseparts ofthe Earth, afterestimates offields fromothersources havebeen subtracted fromthemeasured field

magnitude. In mostplaces themagneticanomaly field is less than 1 percentof thetotal magneticfield. Thenaturalincreaseoftemperaturewith depth in the Earth means thatrocks below a certain depth, termed theCuriedepth, willbe

essentially non-magnetic. This depth is typically in excess of20 km in stablecontinentalregions, butmay be as shallow

as 2 km in young oceanic regions. Studies of crustal magnetism have contributed to geodynamic models of the

lithosphere, geologicmapping, and natural resourceexploration. Inferences fromcrustal magneticfield maps such asthese, interpreted in conjunction with otherinformation, can help delineategeologicprovinces, locateimpactstructures,

dikes, faults, and othergeologicentities thathavea magneticcontrastwith theirsurroundings. To this end, theMagnetic

Anomaly Map oftheWorld is availablein both digitaland map form. Theanomalyfield itselfis shown atan altitudeof 5kmabovethe WGS84 ellipsoid.

Themagneticfields shown on this map aredesigned to beinternally consistentoverthemeasurementdomain, extending

fromthesurface tosatellitealtitude. Upward continuation ofthe data shown on this map to satellitealtitudeyields themagneticanomaly field modelderived fromtheCHAMP satellite(MF5, Maus etal., 2007a). Long-wavelength features

appearing in themap arebased on downward continuation of theMF5 model. Short-wavelength anomalies arefrom

marineand aeromagneticcompilations computed at5 kmaltitude, orfroma model based on a digitalagemap ofthe

ocean combined with thegeomagneticpolarity timescale. Thenear-surfacecompilations aredistinguished fromthesatellite-based and oceanicmodeldata by way ofshading, and theirdistribution can be seen in theaccompanying index

map. Finally, theentire data setis displayed using thenaturalcolorscale(red = high, blue= low)with a shaded relief 

effectusing artificialillumination.

PREPARATION OFTHE MAP/  PRÉPARATION DE LACARTELeast-squares collocation (LSC), a technique commonly used in geodesy (Moritz, 1980)was the primary method used

forgridding and estimating theanomalies at3 minutes of arcspacing. Themodelcorrelation functions weretuned to the

observed correlations fromthedata overAustralia, Russia and North America. Thedetails oftheLSC modelfunctionsand theprocess itselfare described in Maus etal. (2007b). Othermethods ofinterpolation and gridding, embedded in

Geosoft®orGMT(Wesseland Smith, 1998), werealsoused.

Differentpre-existing data compilations weremerged by initiallyremovinglineartrends and then using the LSCtechniques, with weights proportionalto distancefrom themargins ofthe grids. Long-wavelengths (>400 km, or

sphericalharmonicdegrees <100) wereremoved fromthe individualcompilations, and replaced with theCHAMP

magneticanomaly field downward continued to 5 kmaltitude(Hemant etal., 2007). Themarinedata availablefromthe

NationalGeophysicalData Center(NGDC) was reduced using theComprehensiveModel(Sabaka etal., 2004). Themarinedata wereinterpolated wheneverthedata density was sufficientlyhigh (Hamoudiet al., 2007).

In marineareas whereno near-surfacedata exist, thedigitalage map oftheoceans (Mülleret al., 1997)was combinedwith themagnetictime scales ofGee and Kent(2007)and Kentand Gradstein (1986)in orderto estimatethenear-

surfacefields. Theassumptions utilized in estimating thesefields do notwork well overthe Cretaceous and Jurassic

quietzones, and hencethefields overthese features arenot shown in this map. Magneticfields calculated fromthe

digitalagemap ofthe oceans should only beused to indicatethegeneral characterofthe magneticfield pattern in aregion, and may proveunreliableindicators ofactualindividualmagneticfield amplitudes orpolarities.

Two versions (Aand B)of themap areavailablein digitalform on theaccompanying DVD. TheB version is shown in

theaccompanying map. TheAversion differs in its handling of areas withoutnear-surfacedata, which arefilled with thedownward-continued CHAMPmagneticfield model. In contrast, theB version contains both model data derived from

CHAMP, and marineages, with a priority given tothe marineagedata. Both versions, when upward-continued to

satellitealtitude, reproducethemagneticanomalyfield derived fromtheCHAMPsatellite.

Thethick whitelines shown on the map locateundifferentiated tectonicelements, and includeridges, fracturezones, and

trenches. Theblack lines locatecoastlines, and a few majorrivers. In thecaseofthe Antarctic, theAntarcticDigitalData

basehas been used forcoastlines.

BIBLIOGRAPHY/  BIBLIOGRAPHIEGee, J.S. and Kent, D.V., 2007. Sourceofoceanicmagneticanomalies and the geomagneticpolaritytimescale,Chapter

12,in Kono,M.,ed.,Volume5.Geomagnetism:Treatiseon Geophysics:Amsterdam, Elsevier , in press.Hamoudi, M., Thebault, E., Lesur, V., and Mandea, M., 2007. GeoForschungsZentrum Anomaly MagneticMap

(GAMMA):A candidatemodelfor theWorldDigital MagneticAnomalyMap, Geochem. Geophys. Geosyst., in press, doi:10.1029/2007GC001638 

Hemant, K., Thebault, E., Mandea, M., Ravat, D., and Maus, S., 2007.Magneticanomaly map ofthe world:merging

airborne, marineand ground-based magneticdata sets, Earth Planet. Sci. Lett., in pressKent,D.V.andGradstein,F.M.,1986. JurassictoRecentchronology,inP.R.VogtandB.E.Tucholke(editors), TheWestern

 North AtlanticRegion, GeologyofNorth America VolumeM  (GeologicalSocietyAmerica, Boulder), 45–50.

Maus, S., Lühr, H., Rother, M., Hemant, K., Balasis, G., Ritter, P., and Stolle, C., 2007a. Fifth generation lithosphericmagneticfield modelfromCHAMPsatellitemeasurements, Geochem. Geophys. Geosyst., in press.

Maus, S., Sazonova, T., Hemant, K., Fairhead, D. and Ravat, D., 2007b.TheNGDC candidatefor theWorld Digital

MagneticAnomaly Map, Geochem.Geophys. Geosyst., in press.Moritz, H., 1980. Advanced PhysicalGeodesy, HerbertWichmann Verlag, Karlsruhe.Müller, R. D., Roest, W.R., Royer, J.-Y., Gahagan, L.M., and Sclater, J.G., 1997. Digitalisochrons oftheworld’s ocean

floor, J. Geophys. Res, 102, 3211-3214.

Sabaka, T.J., Olsen, N., and Purucker, M.E., 2004. Extendingcomprehensivemodels oftheEarth's magneticfield with

Oersted and CHAMPdata, Geophys. J. Int., 159, 521-547, doi:10.1111/j.1365-246X.2004.02421.xWessel, P. and Smith, W., 1998. New, improved version ofGenericMapping Tools released, EOS transactions of the

American GeophysicalUnion, 79, 579.

MAJOR DATASETS, THEIR WDMAMCODES, SPATIALRESOLUTION, AND LINKS

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