Application of Enhanced Local Wave Number Technique to the Total Field Magnetic Anomalies for Computing Model Parameters of Magnetized Geological Structures

Abstract

In this study, enhanced local wave number (ELWN) technique is presented to compute some model parameters of isolated and magnetized geological structures such as horizontal position (exact origin), depth and source geometry using the total field magnetic anomalies (TMAs). The technique uses analytical signal amplitude (ASA) and first- and second-degree horizontal and vertical derivatives of observed TMAs, and then simply computes the model parameters without requiring a priori knowledge about the nature of the causative magnetized body.

Additionally, inclination and declination angles of both magnetization and ambient field have no effects on the results. In the ELWN technique source geometry, viz., structural index (contact/fault, dyke, horizontal cylinder and sphere) is determined using the depth and exact origin computed previously. Hypothetic simulations performed using TMAs due to some simple shaped geological models have showed the ability of the technique. Moreover, an actual magnetic data taken over the Kesikköprü iron deposit (Central Turkey), one of the largest iron reserve in Turkey,has been also analysed. A depth of 21.39 m has been computed for the magnetized geological source which includes the mafic rocks rich in magnetic properties, and the iron ore body. The structural indices obtained have indicated a dike-like or an intermediate form between a dike and a horizontal cylinder body for the magnetized source. These findings are compatible with those of a recently published study.  Hence, the use of ELWN technique is proposed for rapid and reliable model parameter estimations from TMAs as an alternative or supportive experiment to the inverse modelling studies.

Keywords

• Directional derivatives,Enhanced local wave number,Magnetized geological structures,Model parameters,Total field magnetic anomalies

Manyetize Olmuş Jeolojik Yapıların Model Parametrelerinin Belirlenebilmesi için Gelişmiş Lokal Dalga Sayısı Tekniğinin Toplam Alan Manyetik Anomalilere Uygulanması

Abstract

Bu çalışmada, toplam alan manyetik anomaliler (TMA) kullanarak izole ve manyetize olmuş jeolojik yapıların ölçüm profili düzlemindeki yatay uzaklığı, derinliği ve yapı geometrisi gibi model parametrelerinin hesaplanabilmesi için gelişmiş lokal dalga sayısı (GLDS) tekniği sunulmuştur. Teknik, ölçülen TMA’lerin analitik sinyal genliğini (ASG) ve birinci- ve ikinci-dereceden yatay ve düşey türevlerini kullanmakta ve ardından manyetik anomaliye neden olan kaynağın doğası hakkında herhangi bir ön bir bilgiye ihtiyaç duymaksızın model parametrelerini kolay bir şekilde hesaplamaktadır. Ayrıca, mıknatıslanma ve ortam manyetik alan doğrultularının (eğim ve sapma açıları) sonuçlar üzerinde bir etkisi bulunmamaktadır. GLDS tekniğinde yapı geometrisi, yani yapısal indeksi (kontak/fay, dayk, yatay silindir ve küre) bir önceki hesaplamalardan elde edilen yapı derinliği ve yapının profil düzlemindeki yatay uzaklığı yardımıyla hesaplanmaktadır. Bazı basit şekilli jeolojik modellerden üretilen TMA’lerle gerçekleştirilen teorik uygulamalar tekniğin kullanışlılığını göstermiştir. Ayrıca, gerçek veri uygulaması olarak Türkiye’nin en büyük demir rezervlerinden biri olan Kesikköprü-Bala demir yatağında (Orta Türkiye) ölçülmüş TMA analiz edilmiştir.  Manyetik özellikçe zengin mafik kayaçları ve demir cevherini içeren manyetize olmuş kaynak yapı derinliği 21.39 m olarak hesaplanmıştır. Yapısal indeks değerleri ise dayk-benzeri veya dayk ve yatay silindir arası manyetize olmuş bir yapıyı işaret etmiştir. Bu bulgular yeni yayınlanmış bir çalışmanın sonuçlarıyla da uyumludur.  Bu nedenle, TMA’lerden hızlı ve güvenilir model parametreleri kestirimi yapabilmek için GLDS tekniğinin kullanımı ters çözüm çalışmalarına bir alternatif veya destekleyici çalışma olarak önerilmektedir.

Keywords

• Gelişmiş lokal dalga sayısı,Manyetize olmuş jeolojik yapılar,Model parametreleri,Toplam alan manyetik anomaliler,Yönsel türevler

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