Yerdeğiştirme Tabanlı Deprem Erken Uyarı Sistemleri

Öz

Yerdeğiştirme tabanlı deprem gözlemleri giderek yaygınlaşmakta ve buna bağlı olarak kullanım alanları genişlemektedir. Deprem başladıktan kısa süre içerisinde meydana gelen depremin nihai büyüklüğünün belirlenmesi, hem Deprem Erken Uyarı Sistemleri (DEU) hem de depremden bittikten sonraki dönemde kayıpların kestirilmesi ve yardım faaliyetlerinin koordinasyonu için büyük önem taşımaktadır. 1999 Chi-Chi (Mw7.6), 1999 Hector Mine (Mw7.1) ve 2003 Tokachi-Oki (Mw8.3) gibi büyük depremler için yapılan testlerde kuvvetli yer hareketi ölçerlerden elde edilen yerdeğiştirmeye dayalı kestirimlerin daha duyarlı olmakla birlikte özellikle büyük depremleri olması gerekenden daha küçük olarak kestirdiği gözlenmektedir (Brown vd. 2011; Crowell vd. 2013). Büyük depremler sırasında kaynağa yakın hızölçerlerin satüre olması, kaynağa uzak olmaları durumunda ise erken uyarı için yeterli zaman kalmaması nedeniyle hızölçerlerin erken uyarı amaçlı kullanımında sorunlar bulunmaktadır. Jeodezik ölçüler ve ivme kayıtlarının birlikte kullanımı ile elde edilen sismojeodezik dalga formları ise satürasyon sorunu içermemeleri nedeniyle kaynağa çok yakın mesafeden veri sağlamakta, GNSS alıcılarının inersiyal olmayan bir sistemde ölçüm yapmaları sayesinde doğrudan kalıcı yerdeğiştirmeler ve buna bağlı deprem büyüklüğü hesaplanabilmesine olanak sağlamaktadırlar. Günümüzde A.B.D. ve Japonya gibi depreme maruz kalan gelişmiş ülkelerde sismojeodezik verilere dayalı erken uyarı sistemleri kurulmuş ve yaygınlaşmaya başlamıştır. Bu çalışmada, ülkemizde yakın dönemde meydana gelen bazı büyük depremler için sadece GNSS dalgaformlarına dayalı olarak deprem büyüklükleri hesaplanmıştır. Gökova, Gökçeada ve Van depremlerinin GNSS yerdeğiştirme dalga formları ile tekrar hesaplanması soncunda sırası ile 6.6, 6.9, 7.2 Mw olan deprem büyüklüğü 6.54, 7.21 ve 7.22 Mw olarak hesaplanmıştır. Bu sonuçlar, özellikle büyük depremler için GNSS dalgaformlarına dayalı olarak hesap edilen deprem büyüklüklerinin yüksek duyarlık sağladığını ve deprem erken uyarı amaçlı kullanımındaki potansiyelini göstermektedir.

Anahtar Kelimeler

• Deprem Büyüklüğü,GNSS,Hızölçer,İvmeölçer,Sismometre,Sismojeodezi

Displacement Based Earthquake Early Warning Systems

Öz

Displacement based earthquake observations are becoming more common and application fields are becoming larger. The determination of the earthquake magnitude in a short time after the earthquake plays an important role both for Earthquake Early Warning Systems (EEW) and the estimation of the losses and coordinating the rescue efforts. However, magnitude estimation from the displacement waveforms for the 1999 Chi-Chi (Mw7.6), 1999 Hector Mine (Mw7.1) and 2003 Tokachi-Oki (Mw8.3) earthquake shows that while they are more precise, the earthquake magnitudes were underestimated (Brown et al. 2011; Crowell et al. 2013). There are well known bottlenecks with the velocity measuring seismometers due to the fact that they get saturated nearby large earthquakes or they do not provide sufficient time for early warning when they are away from the earthquake source. Geodetic measurements and accelerometer records provide data from the close vicinity of the earthquake source and enable to determine to static offsets and the earthquake magnitude based on displacements since GNSS receivers operate in a non-inertial reference frame. Nowadays, earthquake early warning systems based on seismogeodetic observations are being established and becoming more common in countries subject to earthquake hazard such as USA and Japan. In this study, earthquake magnitudes were estimated for several recent earthquakes in Turkey only by using the GNSS displacement waveforms. GNSS_based Re-estimation of the earthquake magnitudes for Gökova, Gökçeada and Van earthquakes resulted in the magnitudes of 6.54, 7.21 ve and 7.22 Mw, respectively, corresponding to the original magnitudes of 6.6, 6.9, 7.2. These results show that earthquake magnitudes based on GNSS waveforms provide high precision and their potential for use in earthquake early warning.

Anahtar Kelimeler

• Earthquake Magnitude,GNSS,Accelerometer,Seismometer,Sismogeodesy

Kaynakça

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