Deprem Konumu ve Deprem Büyüklüğünün Hesaplanmasında Özel Durumlar
Özet
Bu çalışma, tarihsel süreçten günümüze sismolojinin gelişimini ve deprem büyüklüğü ile konumunun hesaplanmasında karşılaşılan özel durumları detaylıca incelemektedir. Sismometri tarihi, M.S. 132'de Chang Heng'in geliştirdiği ilk sismoskoptan Cecchi, Milne, Wiechert ve Galitzin'in modern sismograf tasarımlarına ve 1970'li yıllardaki dijital ağlara kadar uzanmaktadır. Türkiye'de 1894 İstanbul depremi sonrasında ivme kazanan sismolojik çalışmalar, günümüzde Kandilli Rasathanesi (KRDAE), AFAD ve üniversitelerin bünyesindeki araştırma merkezleri tarafından işletilen geniş sismik ağlarla yürütülmektedir. Deprem büyüklüğünün hesaplanmasında ML, MS, Mb, Md ve özellikle büyük depremlerde doygunluğa uğramayan Mw gibi farklı magnitüd türleri tercih edilmektedir. Deprem konumunun belirlenmesi ise enlem, boylam, derinlik ve oluş zamanından oluşan dört bilinmeyenli denklem takımının çözümüne dayanır. İstasyon dağılımı, veri kalitesi, kullanılan lokasyon yazılımları (Hypo71, Hypoinverse, Hypocenter vb.) ve bir boyutlu (1-B) sismik hız yapısı, deprem parametrelerini ve özellikle hesaplanması en belirsiz değer olan deprem derinliğini doğrudan etkilemektedir. Farklı kurumların farklı parametreler kullanması, raporlanan verilerde uyumsuzluklara ve toplumda kafa karışıklıklarına neden olabilmektedir. 25-28 Şubat 2022 Erzurum Tekman Turnagöl deprem etkinliği verileriyle yapılan analizler, farklı hız modellerinin ve lokasyon programlarının dış merkez ve derinlik çözümlerinde belirgin farklılıklar ürettiğini göstermiştir. Bu doğrultuda, deprem kataloglarının bölgeye özel 1-B sismik hız modelleri ve uygun yazılımlarla yeniden çözümlenerek güncellenmesi tavsiye edilmektedir.
This study examines in detail the historical development of seismology to the present day and the special cases encountered in calculating earthquake magnitude and location. The history of seismometry extends from the first seismoscope developed by Chang Heng in 132 AD to the modern seismograph designs of Cecchi, Milne, Wiechert, and Galitzin, as well as the digital networks of the 1970s. Seismological studies in Turkey, which gained momentum after the 1894 Istanbul earthquake, are currently conducted through extensive seismic networks operated by Kandilli Observatory (KOERI), AFAD, and university research centers. Different magnitude scales such as ML, MS, Mb, Md, and particularly Mw—which does not suffer from saturation during large earthquakes—are preferred for calculating earthquake magnitude. Determining the earthquake location relies on solving a system of equations with four unknowns: latitude, longitude, depth, and origin time. Station distribution, data quality, location software used (Hypo71, Hypoinverse, Hypocenter, etc.), and one-dimensional (1-D) seismic velocity structure directly affect earthquake parameters, especially earthquake depth, which is the most uncertain value to calculate. The use of different parameters by different institutions can lead to discrepancies in reported data and cause public confusion. Analyses conducted using data from the February 25–28, 2022 Erzurum Tekman Turnagöl earthquake activity showed that different velocity models and location software produce significant differences in epicenter and focal depth solutions. Accordingly, it is recommended to relocate and update earthquake catalogs using region-specific 1-D seismic velocity models and appropriate software.
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