Research Article. ISSN (Print) *Corresponding author Askari, A

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1 Sholrs Journl of Engineering n Tehnology (SJET) Sh. J. Eng. Teh., 4; (6B): Sholrs Aemi n Sientifi Pulisher (An Interntionl Pulisher for Aemi n Sientifi Resoures) ISSN 3-435X (Online) ISSN (Print) Reserh Artile Ege etetion of grvity nomly soures vi the tilt ngle, totl horizontl erivtive, totl horizontl erivtive of the tilt ngle n new normlize totl horizontl erivtive Askr A Assistnt professor, Hkim Szevri University, Szevr, Irn *Corresponing uthor Askr A Emil: Astrt: In this pper the pplition of ege etetion tehniques to grvity t re esrie. Ege enhnement in potentil-fiel t helps geologi interprettion. There exist severl methos for enhning eges, suh s tilt ngle, n the erivtive of tilt ngle. Most of these methos re high-pss filters se on the horizontl or vertil erivtives of the fiel. To etermine the filters new normlize totl horizontl erivtive (N), normlize horizontl erivtive (), totl horizontl erivtive (TDX) n tilt ngle s n ege etetor (THDR), omputer oe in Mtl ws prepre. The filter hs een teste y omprison with relte high-pss filters with syntheti t n mesure t; it gives outstning results for the t sets employe for whih the N metho n mke lrge n smll mplitues of soure eges eqully visile, with more etil wherever the t re reltively smooth. N, new ege-etetion filter, is se on rtios of horizontl erivtive to the men of the nery horizontl erivtives. Compre with other filters, the N filter proues more etile results. The vntge of the N metho in the reognition of soure eges is ue to the ft tht it n mke the strong n wek mplitue eges visile simultneously, n n ring out more etils. The vntge of the N metho is most ovious in the regions where the t re reltively smooth. As the stnr evition of this metho (.784) is greter thn the metho (.7), this metho isplys the grvity nomlies more lerly thn the. Keywors: Grvity grient, Tilt ngle, Ege etetion, New normlize horizontl erivtive INTRODUCTION There exist severl types of high pss filters whih enhne sutle etil in potentil fiel t, suh s ownwr ontinution, horizontl n vertil erivtives. The horizontl lotion of the eges of ustive soures is ommonly requeste tsk in the interprettion of geophysil t; mny filters re ville to omplish this tsk. The vertil Derivtive hs een use for mny yers to elinete eges in grvity n mgneti fiel t[- 3The uthors hve ommente on the utility of the horizontl n vertil mgneti grients for elineting the ege of oy tht hs vertil sies. Gruh n Corell [4] hve investigte the effet of sloping sie on the lotion of the mximum horizontl grient. Telfor et l. [5] expline tht the lotion of the mximum horizontl grient my e use s n initor of the lotion of the eges of the soure. In generl, the first vertil erivtive is positive over the soure, zero over the ege n negtive outsie of vertil sie soure. The horizontl grient peks over the eges n is zero over the oy. Thus, either of these two mesures will lote the eges of n isolte nomly soure, similr to the nlytil signl of Roest et l. [6]. Other uthors hve vote use of seon vertil erivtive for loting the eges[7]. However, even with the seon erivtive, the zero vlue is not lote extly over the ege. It is noteworthy tht in ll of ove-mentione methos, if there exist more thn one soure of nomly, the resolution will lso vries. Shllower soures re well resolve, ut the eeper ones with shllower grients my not e s pprent euse the effetive mesure is the grient mplitue. There my e onsierle ynmi rnge in the size of the grients, implying tht profiles or mps nnot provie enough signl to e etete. The tilt ngle overomes this prolem y eling with the rtio of the vertil erivtive to the horizontl grient. As oth will e smller for eeper soures, the rtio will e lrge over the soure. It eomes zero over or ner the ege where the vertil erivtive is zero n the horizontl grient is mximum, while eomes negtive outsie the oy where the vertil erivtive is negtive. By expressing 84

2 Y(m) Askri A., Sh. J. Eng. Teh., 4; (6B): this s tilt ngle rther thn rtio, it will lwys e in the rnge of -9 < TILT< 9. The tilt ngle is reltively insensitive to the epth of the soure n shoul resolve shllow n eep soures eqully. Miller n Singh[8] introue the tilt ngle, n mplitue normlize vertil erivtive: T tn f z f f x y where f is the mgneti or grvity fiel. () As one n oserve from eqution (), the tilt ngle enhnes lrge n smll mplitues of nomlies well. This is ue to the ft tht, the tilt ngle is etermine se on the rtio of the totl horizontl erivtive to the vertil erivtive. It is to e note tht, the tilt ngle is positive over the soure of nomly n psses through zero when it ples over or ner the ege of nomly. It is effetive in lning the mplitue of strong n wek nomlies, ut it is not primrily n ege-etetion metho[9]. A ommonly use ege-etetion filter is the totl horizontl erivtive (TDX), TDX f f x y () Veruzo et l. [] suggest using the totl horizontl erivtive of the tilt ngle s n ege etetor (THDR): THDR T x T y (3) The THDR suessfully elinetes the eges of the lrgest mplitue nomly, ut its results for the eeper oies re less impressive. Beuse the THDR uses erivtives of erivtive-se filter, i.e., the tilt ngle, it n lso enhne noise in the t. In this pper, we present ege-etetion filter using the normlize totl horizontl erivtive () to elinete the eges of soures. M n Li [] introue the normlize horizontl erivtive (): (4) ( mx[ i m : i m, j n : j n] The normlize totl horizontl erivtive () is the rtio of the horizontl erivtive to the mxim of nery horizontl erivtives. The new normlize totl horizontl erivtive (N) is the rtio of the horizontl erivtive to the men of nery horizontl erivtives. This metho oes not require the omputtion of the vertil erivtive, mking the filter omputtionlly more stle. It n e expresse s: (5) N( men[ i m : i m, j n : j n] Where N ( represents the output vlue of ( i,, TDX represents the totl horizontl erivtives n m n n oth re the size of winow (i.e., the size of the smple). Horizontl erivtive, tilt ngle n the totl horizontl erivtive of the tilt ngle is wiely use metho. The totl horizontl erivtives n the totl horizontl erivtive of the tilt ngle n lso utomtilly reognize eges in potentil fiel t vi their mxim, while the tilt ngle n e use to verify the existene of wek nomlies. From expression (5), we n see tht the size of the winow influenes the results. In the proess of elineting eges in potentil fiel t, we n first test the effet of ifferent winows, n then selet the est results. SYNTHETIC GRAVITY ANOMALY In orer to test the fesiility of the N metho, we hoose four other similr methos to ompre results. They inlue the tilt ngle (eqution ), totl horizontl erivtive eqution ), totl horizontl erivtive of the tilt ngle eqution 3) n the normlize horizontl erivtive (NHD) (eqution 4). Figure shows the grvity nomly generte y two ientil prisms t entrl epths of 5 n m (Figure ). The totl horizontl erivtive of Figure is shown in Figure. The eges of soures hve een enhne, ut unfortuntely the eges of the eeper oy nnot e reognize lerly. The tilt ngle of Figure is shown in Figure. Although the tilt ngle is vli metho in lning the mplitues of ifferent nomlies, it is not minly n ege-etetion filter. The THDR of Figure is shown in Figure. The THDR n elinete the eges of the shllower soure suessfully, lthough the eges of the eeper oy re rther vgue. The results of Figure with ifferent winows re shown in Figs. 3-. The N results of Figure with ifferent winows re shown in Figs. 3-. The N metho isplys the eges of the shllow n eep soures more lerly n improves the resolution power of the oy s lterl lotion X(m) Fig-:Two ientil soures t ifferent epths. 843

3 Askri A., Sh. J. Eng. Teh., 4; (6B): GRAVITY ANOMALY 4 4 mgl TDX 4 mgl/m TILT ANGLE r THDR r/m Fig-: () Syntheti grvity nomly fiel generte y two ientil soures t ifferent epths. () Totl horizontl erivtive of the t in () ompute using Eq.. () Tilt ngle of the t in (), ompute using Eq.. () THDR of the t in (), ompute using Eq N 4 N Fig-3: () of the t in Figure, ompute using Eq. 4 with winow size of 5 x 5. () of the t in Figure, ompute using Eq. 4 with winow size of 3 x 3 () N of the t in Figure, ompute using Eq. 5 with winow size of 5 x 5. () N of the t in Figure, ompute using Eq. 5 with winow size of 3 x 3. APPLICATION OF REAL GRAVITY ANOMALIES The present investigtion onerns the grvity tset in orer to enhne eges struture from grvity t. Figure 4 shows grvity mp of southwest Irn n north of the Omn Se, isplying intense high grvity with the est-vest (EW) trens, orresponing to Prism seimentry Mkrn, while Figure 4- shows the TDX, tilt ngle n THDR of the t in Figure 4. Aoring to Figures 4- n 5-, the TDX, the tilt ngle n the THDR re oserve with high-mplitue nomlies. As grvity t often ontin nomlies with lrge rnge in mplitue, the proesse grvity imges suh s TDX, tilt ngle, THDR, n similrly ontin fetures with lrge flututions in mplitue. It is possile tht the smller mplitue nomlies might e of onsierle geologi interest, ut they n e hr to elinete mong those of lrger mplitue. In Figure 4- n Figure 5- the mximum vlues re lote over ustive oies. In other wors, there is no lne etween the outputs. Figure4 - n Figure5 - provies the est resolution of the grvity 844

4 Askri A., Sh. J. Eng. Teh., 4; (6B): mrkers in the Omn Se struture. Avntge of the N metho is most ovious in the regions where the t re reltively smooth. As the stnr evition of this metho (.784) is greter thn the metho (.7), grvity nomlies re oviously etter. This filter hs suessfully enhne the eges of the low-mplitue soures. Aoring to Figure 4- n Figure 5- the otine TDX, tilt ngle, THDR, n N metho linements re onsistent with eh other, lthough N hs higher resolution. Figure 4 - n Figure 5 -, inites the horizontl lotion of ll soures. They re similr to the mp of the seon vertil erivtives whih hve een tritionlly use to lote the eges on the soures. The N mp hs the vntge of eteting oth shllow n eep soures, wheres the TDX, tilt ngle, THDR, respons preferentilly to shllower n smller soures. GRAVITY ANOMALY 6 mgl 6 TDX mgl/km TILT ANGLE 5 r - Fig-4: () Mesure grvity t from the Omn Se in southestern Irn. () Totl horizontl erivtive of the t in () using Eq.. () Tilt ngle of the t in () using Eq.. () THDR of the t in () using Eq THDR 5 r/km N 3 6 N Fig-5: () of the t in Figure 4 using Eq. 4 with winow size of 5 x 5. () of the t in Figure4 using Eq. 4 with winow size of 3 x 3, () N of the t in Figure 4 using Eq. 5 with winow size of 5 x 5, () N of the t in Figure 4, using Eq. 5 with winow size of 3 x

5 Askri A., Sh. J. Eng. Teh., 4; (6B): CONCLUSIONS In spite of the lst grient methos whih were use in ition to the min interprettion methos, the nlysis y spe plots oul e use inepenently s the primry nlysis, while there is no imgintion from type of geologi strutures. The pprent ivision is useful for quik seletion of seprtion points; however this tehnique is not lwys reile wy to withrw the smller nomlies. Lol phse filters (N,, TDX, T n THDR) s nomly etetor eges re very strong. The N ege-etetion filter - is se on the totl horizontl erivtive of potentil fiel nomlies. This metho vois the omputtion of vertil erivtives whih mkes the filter omputtionlly more stle. To etermine the filters N,, TDX, T n THDR, omputer oe in MATLAB ws prepre. The filter hs een teste y omprison with relte high-pss filters with syntheti n mesure t. Results inite tht the N metho n rete lrge n smll mplitues of soure eges eqully visile, with more etil wherever the t re reltively smooth. N mp enles the interpreter to etermine the pproximte horizontl lotion n lterl extent of the soures for oth shllow n eep onition. It my lso e use with the pprent strike informtion to proue stereo plot, summrizing the orienttion of the potentil fiel t ll gri points on the mp. This use enles the interpreter to sort out the vrious soures on the sis of their orienttion sttistis similr to the wy geologist plots orienttion t to sertin struture lignments. REFERENCES. Evjen HM; The ple of the vertil grient in grvittionl interprettions, Geophysis, 936; : Hoo PJ, Teskey DJ; Airorne griometer progrm of the Geologil Survey of Cn, Geophysis, 989; 54:-. 3. Thurston JB, Smit RS; Automti onversion of mgneti t to epth, ip, n suseptiility ontrst using the SPITM metho, Geophysis, 997; 6: Gruh VJS, Corell L; Limittions of etermining ensity or mgneti ounries from the horizontl erivtive of grvity or pseuo grvity t, Geophysis, 987; 5: Telfor WM, Gelrt LP, Sheriff RE; Applie geophysis, Cmrige Univ. Press, Cmrige, n e., 99; Roest WR, Verhoef J, Pilkington M; Mgneti interprettion using the nlyti signl, Geophysis, 99; 57: Bhtthry BK; Two imensionl hrmoni nlysis s tool for mgneti interprettion (vertil erivtive polriztion vetor), Geophysis, 965; 3: Miller HG, Singh V; Potentil fiel tilt new onept for lotion of potentil fiel soures, Journl of Applie Geophysis, 994; 3: Cooper GRJ, Cown DR; Enhning potentil fiel t using filters se on the lol phse, Computers n Geosienes, 6; 3: Veruzo B, Firhe JD, Green CM; New insights into mgneti erivtives for struturl mpping. The Leing Ege, 4; 3():6-9.. M G, Li L; Ege etetion in potentil fiels with the normlize totl horizontl erivtive, Computers n Geosienes, ; 3(7):