Kabuk Anizotropi Araştırmalarında Deprem Kümelerinin İstatistiksel Analizi

Simav bölgesinin sismik aktivitesi çok yüksektir, bu nedenle genellikle bu bölgede küme depremleri meydana gelir. Bu tür kümeler, kayma dalgası ayırma yöntemi kullanılarak kabuksal anizotropinin ölçülmesi için uygundur. Bu yüzden, bu deprem kümeleri, bu bölgenin altındaki kabuksal anizotropinin ölçülmesini mümkün kılmıştır. Ayrıca, sismik anizotropi ile sismik b değeri arasındaki olası bir ilişkinin olup olmadığını bulmak için depremlerin frekans-büyüklük ilişkisi mekânın bir fonksiyonu olarak kullanılarak sismik b değeri ve stres değerleri hesaplanmıştır. Sismik b-değeri için, 1 Ocak 2010 – 28 Şubat 2019 arasında 1,0’den büyük olan KOERI (Boğaziçi Üniversitesi, Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü, Bölgesel Deprem-Tsunami İzleme Merkezi) tarafından hazırlanan bir deprem kataloğu kullanılmıştır. Bu nedenle, analizlerden elde edilen bulguların güvenilirliği artırılmıştır çünkü bu bölge için 2010 öncesi depremlerin yer parametrelerinin doğru olarak belirlenmesi, sismik istasyon kapsamı eksikliği nedeniyle güvenilir değildir. Ayrımlanma analizi için bu bölgede 2016'dan 2017'ye kadar meydana gelen mikro depremler ilk olarak seçilmiştir. Kayma dalgası bölme analizinden elde edilen sonuçlar ayrımlanma parametrelerinde güçlü saçılma olduğunu göstermiştir. Bu gözlem deprem sürülerinin neden olduğu stres birikimi ile tutarlı görünmektedir. Ayrıca, stresteki farklılıklar nedeniyle, her istasyon için ortalama zaman gecikmesinde değişiklikler gözlenmiştir. Çalışmanın bir diğer önemli gözlemi, kayma dalgası polarizasyonlarının 90 °’lik saçılımdır. Sismik olarak aktif fay düzlemlerinde dalgalı yüksek gözenekli sıvı basınçları, kayma dalgası bölme parametrelerinde saçılma modelinin en muhtemel nedenidir.

Statistical Analysis of the Earthquake Swarms in Crustal Anisotropic Investigations

The seismic activity of the Simav region is very high so that swarm earthquakes usually occur in this region. Such swarms were usually convenient to measure crustal anisotropy by using shear wave splitting method. Therefore, the swarms make possible to detect crustal anisotropy beneath the study area. In addition, seismic b-value and stress were investigated by using the frequency–magnitude relationship of earthquakes as a function of space in order to find out whether a possible relationship between seismic anisotropy and seismic bvalue is or not. For seismic b-value, an earthquake catalog prepared by the KOERI (BogaziciUniversity, Kandilli Observatory and Earthquake Research Institute, Regional EarthquakeTsunami Monitoring Center) with magnitude greater than 1.0 from 1 January 2010 to 28 February 2019 was used. Hence, the reliability of findings obtained from the analysis was improved because correctly determining location parameters of earthquakes before 2010 for this region is not reliable due to a lack of seismic station coverage. For splitting analysis, micro-earthquakes from 2016 to 2017 occurred in this region were initially selected. Results from shear wave splitting analysis indicated strong scattering in splitting parameters. This observation seems to be consistent with stress accumulation caused by the earthquake swarms. Additionally, due to variations in stress, changes in the average time-delay for eachstation were observed. Another important observation of the study is that 90°-flips in shearwave polarizations observed. Fluctuating high pore-fluid pressures on seismically active fault planes are the most likely cause of the scattering pattern in shear wave splitting parameters.

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