2017

Marmara Bölgesi İçin Kapsamlı SKS Polarizasyon Analizleri ve Üst Manto Deformasyonu Hakkında Düşündürdükleri

Bu çalışmada, telesismik (uzak) depremlere ait dalga formu kayıtları üzerinde gözlenen SKS fazıkullanılarak Marmara Bölgesi’nin altında kalan manto yapısının deformasyonu ile ilişkili anizotropikbulgular incelenmiştir. Bu amaçla kullanılan 34 adet istasyonda, tek-tabakalı anizotropi modelivarsayılarak hesaplanan 572 adet iyi kalitede SKS ayrımlaşması parametresi, hızlı ve yavaş S dalgalarıarasındaki zaman gecikmelerinin 0.97 sn ile 2.17 sn aralığında değiştiğini göstermektedir. İstasyonortalamaları alınarak hesaplanan hızlanma polarizasyonu yönleri K10°D ile K63°D arasında değişerekbüyük çoğunlukla KD-GB yönlü bir dağılıma işaret etmektedir. Hesaplanan istasyon ortalaması alınmışzaman gecikmeleri ve hızlanma yönleri, Anadolu için elde edilen ortalama değerlerle benzer bir dağılımgösterir. Bu ise bize, Marmara Bölgesi altında gözlenen sismik anizotropinin, Helenik Yay’ı boyuncaAnadolu kıtası altına dalım yapan Afrika levhasının geriye çekme etkisi sonucu şekillenen mantokonveksiyon akımları ve buna bağlı gelişen kafes tipi tercihi yönelim (LPO) ile ilişkili olduğunugöstermektedir. Buna ek olarak, SKS ayrışma parametrelerinin yönsel değişimleri üzerine uygulanan iki-tabakalı anizotropik yapı modellemeleri bu sonucu destekler niteliktedir. Bu çalışmadan elde edilenbulgular, Marmara Bölgesi için önceki yıllarda lokal S dalgaları kullanılarak gözlemlenmiş üst-kabuk (8-10km) anizotropisi ile kıyaslandığında, deformasyonun düşey yönde kabuktan litosfer boyunca üstmantoya kadar sürekli bir şekilde iletilmediğini göstermektedir.

Comprehensive SKS Polarization Analyses in the Marmara Region and Implications for the Upper Mantle Deformation

In the present study, deformation pattern within the upper mantle part beneath the Marmara region was investigated using SKS phases observed on the waveform recordings of teleseismic events. 572 good-quality SKS splitting measurements observed at 34 seismic stations, assuming a single-layer anisotropy, resulted in splitting time delays (TD) between fast and slow S-waves ranging from 0.97 s to 2.17 s. Station-averaged fast polarization directions exhibits an overall NE-SW oriented distribution. They vary between N10°E and N63°E. Staion-averaged splitting measurements are in a good accordance with those obtained at various parts of Anatolia as this implies observed seismic anisotropy beneath the Marmara region is likely due to the mantle convection flow and associated lattice preferred orientation (LPO) that have been developed by the roll-back effect of subducting African plate beneath the Anatolia along the Hellenic Trench. Two-layer anisotropy modeling results inferred from directional dependency of apparent SKS splitting parameters tend to support this result. Comparison of the findings from present study with those from local S-wave splitting-derived upper crust (8-10 km) anisotropy results suggest that there is no a vertical coherency in transmitting the deformation from the crust to lithosphere and upper mantle in the study area.

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