26 Eylül 2019 (M5.8) ve 23 Nisan 2025 (M6.2) depremleri sonrasında Ana Marmara Fayı’nın sismik tehlikesinin yeniden değerlendirilmesi

Öz

Orta Marmara’da gerçekleşen iki orta büyüklükteki deprem (26 Eylül 2019 M5.8 ve 23 Nisan 2025 M6.2), dünyanın en önemli sismik boşluklarından biri olarak bilinen Marmara’da sismik tehlikenin yeniden tartışılmasına neden olmuştur. Bu çalışmada 2025 depremi sonrası bilim insanları arasında çokça gündeme gelen 5 tartışma maddesi üzerinden bir beyin fırtınası çalışması yapılmış ve elde edilen görüşler değerlendirilmiştir. Her iki depremin de Marmara’daki genel deprem tehlikesini değiştirecek ölçüde olmadığı düşünülmekle birlikte, gelecekte kırılması beklenen komşu fay segmentleri üzerinde oluşturdukları gerilme değişimlerinin göz ardı edilmemesi gerektiği vurgulanmıştır. Ana Marmara Fayı gerilme birikimi, depremsellik örüntüleri, gerilme eksen yönelimleri, odak mekanizmasındaki değişimler, fay geometrisi, kabuksal sismik hız yapısı gibi çeşitli faktörlerden etkilenen parçalı bir yapı sergilemekteyken, tarihsel büyük depremler yeterli gerilme birikimine sahip parçalı fay sistemlerinin M7 ve üzeri büyüklükte deprem üretebilme potansiyeline sahip olabileceğini göstermektedir. Artan sayılardaki kara ve deniz tabanı gözlem istasyonları, üç boyutlu kabuk hız yapısı araştırmaları ve makine öğrenmesine dayalı deprem algılama eşik değerlerinin düşürülmesi, Marmara’daki veri katkısı açısından oldukça kıymetli olduğu değerlendirilmiştir. Depremselliğin izlenmesi, depremler arası gerilme etkileşimlerinin anlaşılması ve açığa çıkan sismik enerjinin nicel olarak takibi, güncel deprem tehlikesinin değerlendirilmesi açısından son derece kritik öneme sahiptir.

Anahtar Kelimeler

• Marmara
• İstanbul
• Sismik tehlike
• Sismik boşluk
• Depremsellik

Reassessment of the seismic hazard of the Main Marmara Fault following the 26 September 2019 (M5.8) and 23 April 2025 (M6.2) earthquakes

Öz

Two moderate-sized earthquakes that occurred in the Central Marmara (M5.8 on September 26, 2019, and M6.2 on April 23, 2025) have reignited discussions regarding earthquake hazard in the Marmara, which is known as one of the most significant seismic gaps in the world. In this study, a brainstorming analysis based on five key discussion points that have been widely discussed among the earthquake scientists following the 2025 earthquake has been performed and obtained insights have been evaluated. Although the both earthquakes are not considered significant enough to alter the overall earthquake hazard in the Marmara, it has been emphasized that the stress changes imparted by them on adjacent fault segments that are expected to rupture in the future should not be overlooked. While the Main Marmara Fault (MMF) exhibits a segmented structure influenced by various factors including stress accumulation, seismicity patterns, orientations of stress axes, changes in focal mechanisms, fault geometry, and the crustal seismic velocity structures, the historical large earthquakes suggest that sufficiently stressed segmented fault system may have potential to generate M7+ earthquakes. The increasing number of on- and off-shore observation stations and 3D-crustal velocity structure studies and lowering of earthquake detection threshold values based on machine learning applications are considered highly valuable for data contribution in the Marmara. Monitoring of the seismicity, understanding of earthquake stress interactions and quantifying of the released seismic energy are all crucial for the up-to-date assessment of the earthquake hazard.

Anahtar Kelimeler

• Marmara
• Istanbul
• Seismic hazard
• Seismic gap
• Seismicity

Kaynakça

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