Bollettino di Geofisica Teorica ed Applicata Vol. 57, n. 4, pp. 329-342; December 2016

DOI 10.4430/bgta0182

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Interpretation of magnetic data in the Chenar-e Olya area of Asadabad, Hamedan, Iran, using analytic signal, Euler deconvolution, horizontal gradient and tilt derivative methods

Z. Golshadi1, a. Karbalaei rameZanali2 and K. Kafaei3 1 Institute of Geophysics, University of Tehran, Iran 2 Young Researchers and Elite Club, South Tehran Branch, Islamic Azad University, Tehran, Iran3 South Tehran Branch, Islamic Azad University, Tehran, Iran

(Received: August 13, 2015; accepted: October 20, 2016)

ABSTRACT The main goal of the present work is delineating and estimating the depth of amagneticanomalyintheChenar-eOlyaareaofAsadabad,Hamedan,Iran.Groundmagneticdatawereacquirednorthoftheregion,every15malonglinesthatwerespaced10mapart.Then,methodswereusedtoestimatethedepthandshapeofthebodycausingtheanomalies.Ourpatternrecognitioncriteriawerebasedonanalyticsignal, Euler deconvolution, horizontal gradient, and tilt derivative obtained frommagnetic data. Various steps were taken to decide, among the four methods, onthe depth estimation and contact location of the magnetite body.The best contactlocationwasfoundwherethehorizontalgradientcontactswereisolated.Comparingparallel contacts of horizontal gradient with analytic signal methods, the analyticsignalcontactsweredeemedmoreaccurate,anddiscontinuityofthecontactlocationwassupplementedwith tiltderivativeandEulerdeconvolutioncontacts.Fordepthestimation, in addition to the Euler deconvolution on the surface and tilt-depthestimation,upwardcontinuationwasapplied,witha reduction topoleapproachatheightsof10,20,30,and40metres,andthentheEulerdeconvolutionmethodwasperformedonthem.Ultimately,theresultswerecomparedwithboreholedata.Therearesixdrilledboreholesinthisareatovalidatethemagneticsurveyresultsfordepthestimationandcontactlocation.Aftercalculatingthecontactlocationanddepthofthemagnetitebody,theresultsshowgoodagreementwiththeboreholedataobtainedwithinthecalculatedcontactlocation.

Key words: magneticdata,Chenar-eOlya,Iran.

© 2016 – OGS

1. Introduction

A quick look at magnetic field maps tells much about the location and shape of buriedcomplicated features. However, a careful study of a map can provide extra details about thedepthandedgesofmagneticmaterialsthatareunderground.

In magnetic surveying, by delineating lateral changes in magnetic susceptibilities,information about structural trends and lithological changes are provided. To distinguishbetween different sizes and different depths of the geological structures, edge detection

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techniquesareused.Todelineatestructuralfeaturesfrommagneticdata,manytechniqueshavebeendeveloped.Also,estimationofthedepthofmagneticsourcesusingdifferentmethodscanbeappliedtogriddedmagneticdatasets.

Nabighian (1972) used the concept of the analytic signal for magnetic interpretation, andshowed that theanalyticsignalamplitudeyieldsaGaussian-shapedfunctionovereachcornerofa2Dbodywithpolygonalcrosssection.Roestet al.(1992)usedthetotalmagneticintensity,which required the 3D analytic signal to approximately estimate the positions of magneticcontactcornersandobtaindepthestimatesfromgriddeddata.Reidet al.(1990)usheredintheEulerdeconvolutionasaninterpretivetoolinthemagneticpotentialfieldforlocatingmagneticanomalies and thedeterminationof their depths bydeconvolutionusingEuler’s homogeneityrelation. Cordell and Grauch (1985) proposed a method for locating the horizontal extentsof the anomalous sources from the maxima of the horizontal gradient of the pseudogravitycomputedfromthegriddedmagneticdata.Verduzcoet al.(2004)developedtiltderivativefromthepotentialmagneticfieldanomalymapandusedthehorizontalgradientofthetiltderivativeasanedgedetectorformagneticanomaly.Salemet al.(2007)haveappliedanewmethodforinterpretationofgriddedmagneticdatabasedonthetiltderivative.Thetiltderivativemethod,by providing a means for estimating the depth to the basement, is a useful technique forinterpretingmagneticdata.

Toestimatethepositionsofstructurallineamentsandmagneticanomalydepthinthestudyarea from total field data, analytic signal, Euler deconvolution, horizontal gradient, and tiltderivativemethodswereapplied.

2. Geological setting Thestudyareaislocatedapproximately3kmSEofChenar-eOlyavillageintheChaharduli

RuralDistrict,intheCentralDistrictofAsadabadCounty,HamadanProvince,Iran.Thestudy

Fig.1-GeologicalmapofChenar-e-Olyaareaaccomplishedwithironlensesandboreholes.

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area liesbetween latitude48°04’58”Nand48°05’19”Nand longitude34°52’04”Eand34°51’10”E.

The study area is underlain by metamorphosed rock covered with meta-limestone,marmorized dolomitic limestone, schist, calc-schist, and amphibole schist (Eghlimi, 2000).TherearesomesmallandlargeironlensesthathaveoutcropsinthisareaandhaveorientationfromSWtoNE(Fig.1).Thesedepositsofirondonothavesignificantlayeringandlieonthenorth-western end of the Sanandaj-Sirjan structural zone. In the Zagros Orogenic Belt, theSanandaj-SirjanZone(Stöcklin,1968)representsoneofthemainbasementtectonicblocksandislocatedbetweentheNW-IranBlock(Allenet al.,2011)andtheArabianPlate.ThemainoreinthisareaisMagnetite(Fe3O4)andismodifiedtoHematiteinsomeregions(Jafarzadeet al.,1995).Theorigin of this deposit isSkarn.TheMesozoic andCenozoic sedimentary rocks inthisSkarnareacontaininglimestones,marls,sandstones,conglomerates,andCenozoicvolcanicrocks,areinthecentralpartofthestudyarea(NadimiandKonon,2012).

3. Materials and methods

3.1. Analysis of magnetic dataGround magnetic data were acquired in the region every 15 m along lines in the north,

spaced10mapart.An interpretationdifficultywith totalmagnetic intensity anomalies is thattheyaredipolar(anomalieshavepositiveandnegativecomponents),suchthattheshapeoftheanomalydependstosomeextentonthepresenceofanyresidualmagnetizationandthemagneticinclination. Because the magnetic anomaly depends on the inclination and declination of the

Fig.2-Totalmagneticintensitymapwithsurveypointsandstudyarea.

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bodymagnetization,theinclinationanddeclinationofthelocalEarth’smagneticfield(Baranov,1957)andtotalfieldarecalculated.

BaranovandNaudy(1964)proposedamathematicalapproachcalled“reductiontopole”forsimplifyinganomalyshapeestimates.Thereductiontopoletechniquetransformstotalmagneticintensityanomaliesintoanomaliesthatwouldbemeasuredif thefieldwerevertical(meaningthere isonlyan inducing field).This reduction topole transformationmakes theshapeof themagneticanomaliesmorecloselyrelatedtothetruelocationofthesourcestructureandallowseasier interpretationof themagneticanomaly, as the locationof theanomalymaximawillbecentered over the body (assuming there is no residual magnetization).Thus, the reduction topole reduces the effect of the Earth’s ambient magnetic field and provides a more accurateinterpretationforthepositionandshapeofanomaloussources.

Totalmagneticfieldstrength(Fig.2),aswellasgeomagneticinclinationanddeclinationofthestudyarea(Table1),whichareprerequisiteparametersincomputingtheapparentmagneticsusceptibility,wasderivedforthestudyarea(NOAA,2013).Beforeapplyingthemethods,thetotal field anomaly data were reduced to pole using a magnetic inclination of 53.149° and adeclinationof4.497°(Fig.3).

Table 1 - Result of the calculated Earth’s magnetic field for Chenar-e Olya area using Geomagix Model.

Input Parameters

Location Latitude Longitude Elevation Date

Iran 34°51’01.787” 48°05’09.207” 2036 m September 2013

Calculated Parameters

Total field Inclination Declination

47342 nT 53.149° 4.497°

Fig.3-ReductiontopolemapofChenar-eOlyaarea.

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The reduction to pole signature of the Chenar-e Olya is marked by a rugged relief withpositiveandnegativeanomaliesofvariouswavelengthsandamplitudes.Thereductiontopoleanomaly, in thecentralportionof thestudyarea,showsan importantgradientzoneelongatedapproximatelyinNE-SWdirection,specifiedbymuchlongerwavelength.

3.2. Borehole dataAnothermethodofinvestigatingsubsurfacegeologyis,ofcourse,drillingboreholes.Fora

moreaccurate conclusionconcerningcontact locationanddepthestimation, the resultsof themagneticsurveyarecomparedwithboreholedata.

Therearesixboreholesdrilledinthisareathatareusedforcomparingdepthestimationwithresultsobtainedfromboreholes.Thedrilledboreholes(Fig.1)analyzedprovideddataaboutthemagnetiteoreanditsthicknessineachoftheboreholes(Fig.4).

Fig. 4 - The lithologyof boreholes and theirthicknessinmetres.

3.3. Depth estimation and contact locationIn the study area, the magnetic signature has anomalies of different wavelengths and

amplitudes. To estimate the positions of structural lineaments in this region from total field data, severalmethodshavebeensuggested in the literature, including theamplitudeof theanalyticsignal(Nabighian,1972;Roestet al.,1992),Eulerdeconvolutionmethod(Reidet al.,1990),themagnitudeofthehorizontalgradient(CordellandGrauch,1985;BlakelyandSimpson,1986)andtiltderivativemethod(Salemet al.,2007).Ineachcase,wecanestimatethesourcedepthsatthecontactlocationsderivedfrompeakingoverthecontacts.

3.3.1. Analytic signal methodThe analytic signal method is a well-known technique for locating the edges of magnetic

anomalies.Nabighian(1972)developedthenotionof2-DASofmagneticanomalies.In2D,theamplitudeoftheanalyticsignalisindependentofthedirectionofmagnetization,andrepresents

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boththeverticalandhorizontalderivativesoverallpossibledirectionsoftheEarth’sfieldandsourcemagnetization.In3D,Roestet al.(1992)introducedthetotalgradientofmagneticdataasanextensionofthe2Dcase.Thefunctionusedintheanalyticsignalmethodistheanalyticsignalamplitude(absolutevalue)oftheobservedmagneticfieldatthelocation(x,y),definedbythreeorthogonalgradientsofthetotalmagneticfieldusingtheexpression:

(1)

whereA(x,y)istheamplitudeoftheanalyticsignalat(x,y),andMistheobservedmagneticfieldat(x,y).

The analytic signal amplitude peaks over isolated magnetic contacts. Fig. 5 shows theanalyticsignalmap,alongwithidentifiedcrestsoftheanalyticsignalamplitude.

Fig. 5 - Analytic signal map with identified crests of the analytic signal amplitude, which can be used for contact location.

3.3.2. Euler deconvolution methodThereasonforemployingtheEulerdeconvolutionmethodisthattheresultsarenotaffected

bythepresenceofremanentmagnetization(Ravat,1996).ByapplyingtheEulerdeconvolutionmethodequation,werelatethemagneticfieldanditsgradientcomponentstothelocationanddepthofthesource(Yaghoobianet al.,1992).The3DEulerequationiswrittenas(Reidet al.,1990):

(2)

wherex, y,andzarethecoordinatesofapointofobservation,x0,y0,andz0arethecoordinates

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ofthesourcelocation,andBisabaselevel.ThestructuralindexN(ordegreeofhomogeneity)isameasureofthedecayingrateofthefieldwithdistancefromthesource.Itprovidesawayto discriminate between different source shapes by defining the anomaly attenuation rate atthe observation point and depends on the geometry of the source (Thompson, 1982). For ahomogeneouspointsourceN=3,alinearsource(lineofdipolesorpoles,andforahomogeneouscylinder,rod,etc.)N=2,forextrusivebodies(thinlayer,dike,etc.)N=1,foracontact,vertexofablockandapyramidwithabigheightN=0.Thechoiceofaproperstructuralindexisafunctionofthegeometryofcausativebodies.EstimationofthecorrectstructuralindexiscrucialforthesuccessfulapplicationoftheEulerdeconvolutionmethod.Reid(1995)showedthattheoptimumstructural index usually yields the tightest clustering of the solutions. In order to preventrepetitionforfindingthebeststructuralindex,andtopreservethemostattractivefeatureoftheEulerdeconvolutionmethodandautomaticinterpretationoflargeamountsofdata,wechosetoimplementthealgorithmofStavrev(1997)usinganunprescribedstructuralindex,whichallowssimultaneousestimationofthecoordinatesandthestructuralindicesofthesingularpoints.Asiswellknown,twoimportantparametersoftheEulerdeconvolutionarethechoiceofwindowandN.TheNvaluemustbeassumedasa prioriinformation.Byapplyingthisprogram(GerovskaandArauzo-Bravo,2003),thevalueofaveragedstructuralindicesiscalculatedas0.9.

Note the Euler deconvolution that yielded the best results to resolve source depths andindicated the source edges, as shown in Fig. 6.The depth of edges is clarified with coloredpoints.Euler deconvolution calculates location anddepthbelow surveypoints.ThebasementdepthsestimatedthroughtheEulerdeconvolutiontechniquevaryfrom3.2kmto32m.

Fig. 6 - Applied Euler deconvolution method to resolve source depths and edges. The depth of edges is clarified with coloredpoints.TheEulerdepthsolutionmapshowstheclusterofsourcedepthlocationspositionedattheboundaries.

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3.3.3. Horizontal gradient methodUsing the horizontal gradient of pseudogravity for locating the edgesof magnetic sources

wasdevelopedbyCordellandGrauch(1985).Thesteepestgradientsofpseudogravityanomalyarelocatedjustbeyondtheedgesofthebody.Thus,crestsofthehorizontalgradientmagnitudeofthepseudogravityfieldareusedasatoolforlocatingtheedgesofmagneticbodies.

We can use this technique for edge detection in a window moving across the grid ofreductiontopole,whenevera linear trend(forexampleacontactorfault) isfoundwithinthewindow.Usingpseudogravitydata,themethodgivesresultsassumingedgesofthinhorizontalsheets(Phillips,2000).Fromempiricalobservationsmadeduringotherstudies,thismethodarenotreliableforsourcesdeeperthanabout150m(GrauchandBankey,2003).

Themethodrequirescalculationofthetwofirst-orderhorizontalderivativesofthemagneticfield.IfM(x,y)isthepseudogravityfield,thenthehorizontalgradientmagnitudeisgivenby:

(3)

Edges in the horizontal gradient magnitude can be searched for maxima by passing a small5-by-5 windows grid that contains grid values over the horizontal gradient grid (Blakely andSimpson,1986).Onlydepthestimateswithstandarderrorsof15%orbetterremaininthefinalinterpretation.

Fig.7showsthehorizontalgradientmapwithcolor-codedhorizontalgradientedgeestimatesinpink.

Fig.7-Horizontalgradientmapwithcolor-codedhorizontalgradientdepthestimates.Dotsindicatecrestsofhorizontalgradientachievedbypassingasmall5-by-5windowsgridoverthehorizontalgradientgrid.

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3.3.4. Tilt derivative methodSalemet al.(2007)developedthetiltderivativemethod,whichprovidesasimpleandrapid

techniquetoestimatethedepthofthemagneticbasementforlargeareas.Thetiltangleisatoolforlocatingmagneticsourcesofdataanddefinedas:

(4)

where

(5)

where are first-order derivatives of the magnetic field M in the x, y, and zdirections.The tilt angle has many interesting properties. For example, due to the nature ofthearctantrigonometricfunction,alltiltamplitudesarerestrictedtovaluesbetween–90°and+90°, regardlessof theamplitudeof theverticalor theabsolutevalueof the totalhorizontalgradient. Since the tilt angle consists of the ratio of the vertical and horizontal derivatives,the resulting tilt function, does not contain information about induced magnetization of thecausativebodies.

Salemet al.(2007)showedthatEq.4canbewrittenas:

(6)

where h is the horizontal distance from the horizontal location of the contact, and z is thedepthtothetopofthecontact.Eq.6indicatesthevalueofthetiltangleabovetheedgesofthecontact that isequal to0°(h=0).Thisvalueisequal to45°whenh=zand–45°whenh=–z.Thisclarifiesthatthecontoursofthemagnetictiltanglecanidentifyboththelocation(θ=0°)and depth (half the physical distance between ±45° contour lines) of contact-like structures(Salemetal.,2007).Thenegativecontourssuggesttheoutsideoftheregionsurroundingthesource of the magnetic body.The positive contour values are above the source bodies, andedges are marked by zero contour value.This method uses the reduction to pole field andassumesasimplevertical2Dcontact.Inthissection,wedemonstratethetiltderivativemethodon magnetic data over the metamorphosed rocks of the south-eastern Chenar-e-Olya area.Beforeapplyingthetiltderivativemethod,forabetterdemonstrationof thecontact location,data are upward continued to a height of 50 m.After that, by applying the tilt derivativemethodonthemagnetictiltanglemap,thecontoursof-0.78,0,and+0.78radianaredisplayed.Theblackcontourlinedemonstratestheedgeofthecontactandlocalizesthecontactlocation.Halfofthephysicaldistancebetweentwowhitecontourlinesisequaltothedepthofthebodycausingtheanomalies(Fig.7).

and

θ

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4. Results

4.1. Contact locations In order to better interpret the results related to the contact locations, we compare the

resultsobtainedfromtheanalyticsignalwithEulerdeconvolution,horizontalgradient,andtiltderivative images.The four sets of contact locations resulting from the four methods can becombinedandrankedasacompositeimagetoaidinthefinalinterpretationofcontactlocations.

To choose the best contact location, the following criteria were used. 1)The horizontalgradient method provides contacts that are continuous and parallel to the contours of thereductiontopolemagneticfield.Therefore,wherethehorizontalgradientcontactsareisolated,theyrepresent thebestcontact location.2)Where thehorizontalgradientcontactsareparalleltotheanalyticsignalcontactswithaslightoffset,theanalyticsignalcontactrepresentsthetruecontact locationand thehorizontalgradientcontact indicates thedowndipdirection(Phillips,2002).3)Where theanalytic signal contactsarediscontinuousdue tonoiseeffects, theymaybe supplemented with tilt derivative and Euler deconvolution contacts.The best results ofthesestepsaredisplayedinFig.9.ThefinalcontactlocationsareshowninFig.10.TheresultssuggestthatthestructuraltrendsareelongatedintheNE-SWdirection.

Fig.8 -Resultsof the tilt derivativemethodwith symbols for calculatingdepthestimates.Theblackcontour linedemonstratestheedgeofthecontactandlocalizesthecontactlocation.Thewhitecontourlinesareequalto±45°andcanbeusedforcalculatingdepthonedges.Forthebestinterpretationofdepthestimationbythetiltderivativemethod,points(AtoG)areselected.

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Fig.9-ThesuperimposedbestcontactsobtainedbyEulerdeconvolution,tiltderivative,analyticsignalandhorizontalgradient methods. The best contact location is represented where horizontal gradient contacts are isolated. Wherehorizontal gradient contacts are parallel to analytic signal contacts with slight offset, the analytic signal contactrepresentsthetruecontactlocationandthehorizontalgradientcontactindicatesthedowndipdirectionoftheedgeofthemagneticbody.Elsewhere,theymaybesupplementedwithtiltderivativeandEulerdeconvolutioncontacts.

Fig. 10 - The final contact location of magnetite body obtained by Euler deconvolution, tilt derivative, analytic signal, andhorizontalgradientmethods.TheresultssuggestthatthestructuraltrendsareelongatedintheNE-SWdirection.

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4.2. Depth estimatesFor thehorizontalgradientandanalyticsignalmethods,assuming thicksources,minimum

depthstomagneticsourceswereobtained.Depth estimates were calculated along contact location obtained from the tilt derivative

methodandthencomparedwiththeEulerdeconvolutiondepths(Table2).Inmagneticsurveys,upward continuation is particularly useful in tying together aeromagnetic surveys made fromdifferentflyingaltitudes(AllabyandAllaby,1999).ForcalculatingotherdepthsapartfromtheedgesofmagneticbodytobasementwithEulerdeconvolutiontechnique,upwardcontinuationwasappliedon reduction topole fieldatheightsof10,20,30,and40m,and then theEulerdeconvolutionmethodwithN=0.9wasperformedonthem.Comparisonsofthedepthestimatesfrom the Euler deconvolution and tilt derivative methods are represented in Table 2. ThelocationsofthetiltderivativepointsthatwereselectedfordepthestimationwerecomparedwiththenearestpointsobtainedfromEulerdeconvolutionmapsofupwardcontinuationatheightsof10,20,30,and40m,andalsothesurface.Thebestapproximationsfordepthofcontactlocationarederived.Eulerdeconvolutionis thebasisforestimatingdepthtobasement,andthenthosedepthsarecorrectedwithtiltderivativedepthestimations.Finally,a3DmapforthebodythatisshowninFig.11wasderivedforthearea.

Table2-ResultsofthecalculateddepthusingtiltderivativeandEulerdeconvolutionmethods.

Label X Y Tilt derivative Euler deconvolution depth (m) depth (m)

A 233719.9 3860290 30 24

B 233428.9 3860380 21 15.5

C 233476.5 3860253 27 29.5

D 233607.2 3860466 36 36

E 233547.9 3860347 18 16

F 233582.3 3860147 35 20

G 233401.9 3860297 15 16

Fig. 11 - The 3D map of themagnetite anomaly, showingthe depth and volume of themagnetic source. To producethis figure, all of the depths from Euler deconvolutionand tilt derivative methodsand final contact location fromEulerdeconvolution,tiltderivative,analyticsignalandhorizontal gradient methodswereused.

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5. Conclusion

In this study, analytic signal, Euler deconvolution, horizontal gradient, and tilt derivativemethodswereappliedtomagneticdata,obtainedfromfieldsurveys,toestimatethedepthandcontact locationof amagnetitebody in theChenar-eOlyaareaofAsadabad,Hamedan, Iran.To apply thesemethods, theGeosoft softwarewasused.To achieve thebest contact locationanddepthestimation,theresultsofallofthemethodswererankedandcombinedusingArcGISsoftware.

Foramorereliablereportaboutthemagnetitedepositinthisarea,theresultsobtainedinthisstudywerecomparedwiththesixgeologicalboreholesdrilledinthestudyregion.Thisprovidesthebestapproximationfordepthestimationatshallowdepths.Boreholes1,5,and6areinsidetheresultedcontact location,andwerecomparedwiththefinaldepthestimates.Borehole4isnear the contact location and can be compared with Euler deconvolution depth estimates onthesurface.Boreholes2and3areoutoftheestimatedbody,butevidencemagnetiteanomalyatshallowdepthsofabout8m.Boreholes1,4,5,and6showgoodagreementwiththeresultsofthisstudy.TheuncertaintiesoftheboreholeresultsareshownaspercentagesinTable3.Inconclusion,theshapeanddepthofthemagnetitebodyforexcavationwerereported.

Table 3 - Uncertainty obtained from the comparison of borehole data and final depth estimates and contact location derivedfromEulerdeconvolution,tiltderivative,analyticsignal,andhorizontalgradientmethods.

Borehole number Uncertainty (%)

1 4

4 4

5 4.5

6 7

Acknowledgements. TheauthorsareveryindebtedtotheResearchCommitteeoftheYoungResearcherClub (IslamicAzad University, South Tehran Branch), who provided magnetic and geological data ofboreholesintheChenar-eOlyaareaofAsadabad.TheauthorsalsoacknowledgevaluablediscussionswithSoheil Eyvazkhani and Mahyar Soltani from Rahpouyan Co., as well as their financial support and helpful suggestions.

REFERENCES

AllabyA.andAllabyM.;1999:Dictionary of Earth sciences.OxfordUniversityPress,Oxford,England,619pp.AllenM.B.,KheirkhahM.,EmamiM.H.andJonesS.J.;2011:Right-lateral shear across Iran and kinematic change

in the Arabia-Eurasia collision zone.Geophys.J.Int.,184,555-574.BaranovV.;1957:A new method for interpretation of aeromagnetic maps: pseudo-gravimetric anomalies.Geophys.,

22,359-382.BaranovV.andNaudyH.;1964:Numerical calculation of the formula of reduction to the magnetic pole.Geophys.,

29,67-79.BlakelyR.J.andSimpsonR.W.;1986:Approximating edges of source bodies from magnetic or gravity anomalies.

Geophys.,51,1494-1498.CordellL.andGrauchV.J.S.;1985:Mapping basement magnetization zones from aeromagnetic data in the San Juan

Basin, New Mexico.In: W.J.Hinze(ed),Theutilityofregionalgravityandmagneticmaps,SocietyofExplorationGeophysicists,Tulsa,OK,USA,pp.181-197,doi:10.1190/1.1826915.

EghlimiB.;2000:Geological map: geological survey and mineral exploration of Iran, scale 1:100000.

342

Boll. Geof. Teor. Appl., 57, 329-342 Golshadi et al.

GerovskaD.andArauzo-BravoM.J.;2003:Automatic interpretation of magnetic data based on Euler deconvolution with unprescribed structural index.Comput.Geosci.,29,949-960.

GrauchV.J.S.andBankeyV.;2003:Aeromagnetic interpretations for understanding the hydrogeologic framework of the southern Espanola Basin, New Mexico.U.S.GeologicalSurvey,USA,Openfilereport03-124.

JafarzadeA.,GhorbaniM.andPezashkhorM.;1995:Geology of Iran, iron deposite, Mesozoic iron ore.GeologicalSurveyofIran.

Nabighian M.N.; 1972: The analytic signal of two-dimensional magnetic bodies with polygonal cross-section; its properties and use for automated anomaly interpretation.Geophys.,37,507-517.

NadimiA.andKononA.;2012:Strike-slip faulting in the central part of the Sanandaj-Sirjan zone, Zagros orogen, Iran.J.Struct.Geol.,40,2-16.

NOAA;2013:Magnetic field calculators, Volume 2013.NationalGeophysicalDataCenter (NOAA),<http://www.ngdc.noaa.gov/geomag-web/#declination>.

PhillipsJ.D.;2000:Locating magnetic contacts: a comparison of the horizontal gradient, analytic signal and local wavenumber methods. In: Expanded abstracts, 70thAnnual Meeting, Soc. Explor. Geophys., Calgary,Alberta,Canada,vol.1,pp.402-405.

Phillips J.D.; 2002: Processing and interpretation of aeromagnetic data for the Santa Cruz Basin-Patagonia mountains area, south-central Arizona.U.S.GeologicalSurvey,USA,Openfilereport02-98.

Ravat D.; 1996: Analysis of the Euler method and its applicability in environmental magnetic investigations. J.Environ.Eng.Geophys.,1,217-219.

ReidA.B.; 1995: Euler deconvolution: past, present, and future: a review. In: Expanded abstracts, 65thAnnualMeeting,Soc.Explor.Geophys.,Tulsa,TX,USA,pp.272-273.

ReidA.B.,Allsop J.M., Granser H., MillettA.J. and Somerton I.W.; 1990: Magnetic interpretation in three dimensions using Euler deconvolution.Geophys.,55,80-91.

RoestW.R.,VerhoefJ.andPilkingtonM.;1992:Magnetic interpretation using the 3-D analytic signal.Geophys.,57,116-125.

SalemA.,WilliamsS.,Fairhead J.D.,RavatD. andSmithR.; 2007:Tilt-depth method: a simple depth estimation method using first-order magnetic derivatives.TheLeadingEdge,26,1502-1505.

Stavrev P.Y.; 1997: Euler deconvolution using differential similarity transformations of gravity or magnetic anomalies.Geophys.Prospect.,45,207-246.

StöcklinJ.;1968:Structural history and tectonics of Iran: a review.Am.Assoc.Pet.Geol.Bull.,52,1229-1258.ThompsonD.T.;1982:EULDPH: a new technique for making computer-assisted depth estimates from magnetic data.

Geophys.,47,31-37.Verduzco B., Fairhead J.D., Green C.M. and Mackenzie C.; 2004: New insights into magnetic derivatives for

structural mapping.TheLeadingEdge,23,116-119.YaghoobianA., Boustead G.A. and DobushT.M.; 1992: Object delineation using Euler’s homogeneity equation,

location and depth determination of buried ferro-metallic bodies.In:Proc.SAGEEP‘92,SanDiego,CA,USA,pp.613-632,

Corresponding author: Zeynab Golshadi Institute of Geophysics, University of Tehran No. 6, Sevom Sharghi alley, Saadatabad St., Tehran, Iran Phone: +98 919 2906527; fax: +98 216 6757705; e-mail:z.golshadi@ut.ac.ir