Fatih UZUNCA, S.Bülent TANK, Tülay KAYA, LEVENT GÜLEN

Manyetotellürik Veri Üzerindeki Deniz Etkisinin İncelenmesi: Düzce Bölgesi Örneği

Bu çalışmada manyetotellürik (MT) veriler üzerindeki deniz etkisinin miktarının belirlenmesi amacıyla Kuzey Anadolu Fayı'nın batı kısmında Düzce bölgesine karşılık gelen alan temel alınarak düz çözüm çalışması yapılmıştır. Bölgenin tektonik yapısı dikkate alınarak oluşturulan modellerde, deniz için 0.3 ?-m ve kara için çeşitli modellerde 100 ?-m, 500 ?-m ve 1000 ?-m gibi sabit özdirenç değerleri atanmıştır. Deniz derinliğinin değişimi, fay, sediman ve Karadeniz kıyı şeridinin basit biçimde eklenmesi gibi parametreler de kullanılmıştır. Modellere ait MT tepkileri üç-boyutlu (3B) düz çözüm programı ile elde edilmiştir. Yapılan çalışma kuramsal bir çalışma olup, kuramsal veriler kullanılmıştır. Düz çözümden elde edilen özdirenç eğrileri, endüksiyon (irgitim, tesir) okları ve faz eğrileri karşılaştırılarak deniz etkisinin miktarı tartışılmıştır. Deniz derinliği ve deniz-kara sınırındaki özdirenç farklılığının artması ile MT tepkilerinin bozulmalara uğradığı sonucuna ulaşılmıştır. Deniz etkisinden dolayı E-kutuplaşması (transverse electric, TE mode) özdirenç eğrileri B-kutuplaşması (transverse magnetic, TM mode) özdirenç eğrilerine göre asıl olması gereken değerden büyük oranda farklı görülmektedir. Gerçek endüksiyon okları ise özdirenç eğrilerinin denizden etkilenmeye başladığı periyotlarda yön değiştirme eğilimi göstermiştir. Denize yakın yerlerde yapılan MT çalışmalarında deniz etkisinin MT tepkisinden giderilmesi gerekmektedir. Bu çalışma, denize yakın noktalarda yapılabilecek MT ölçümlerine dayanacak modeller geliştirildiğinde, doğru sonuca ulaşılabilmesi bakımından önemlidir.

Bulletin of the Earth Sciences Application and Research Centre of Hacettepe University

In this study, it was applied forward modeling to investigate the sea effect on the magnetotelluric (MT) measurements originating from a geometry that is similar to the Düzce area near Black Sea. It was used constant resistivity value for the sea 0.3 ?-m and for the land 100 ?-m, 500 ?-m and 1000 ?-m in the models while considering also the tectonic features in the area. Additionally, it was used parameters such as; depth, fault, sediments and coast line of the Black Sea. The three-dimensional MT responses were calculated for a number of models. This is a theoretical study based on synthetic data. The resistivity curves, induction arrows and phase curves obtained from models, were compared with each other using templates and the sea effect was discussed. Consequently, when the resistivity contrast between sea-land and the depth of sea are high, MT responses are effected significantly. When compared with E-polarization (transverse electric, TE mode) resistivity curves and B-polarization (transverse magnetic, TM mode) resistivity curves, E-polarization one has more distortion compared to the latter. Real induction arrows change direction beginning from the period when the sea effects on the MT measurements. Therefore, sea effect must be removed from the MT responses, if the study area is near the sea. This study is important in terms of obtaining accurate results when developing models based on MT measurements in coastal areas.

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