Evaluating Seismic Site Response in a Deep Alluvial Basin: The Case of the Bornova Basin (Izmir)

Öz

This research investigates the effects of deep alluvial basins in the Bornova region of Izmir on earthquake ground motion by combining field characterization with 1D and 2D equivalent linear soil response analyzes. In the study, soil-bedrock interfaces were modeled using two idealized two-dimensional geological sections representing the Bornova Basin. The study area has a geological environment characterized by east-west trending normal faults along the Inner Izmir Bay and covered by sedimentary units. Borehole data indicate the presence of heterogeneous geological units consisting of clay, silt, sand, and gravel in some areas. The Spatial Autocorrelation (SPAC) method indicates that, in the west, the alluvial units with low shear-wave velocities become thicker with depth, whereas in the east, shear-wave velocities increase from the surface downward. In the analysis, the shear modulus reduction and damping-ratio curves obtained from laboratory experiments were compared with widely used reference curves in the literature, and the most suitable curves were used in the analysis. The analysis used three different recordings: the 1999 Duzce earthquake record, the 30 October 2020 Samos earthquake record, and a superposition of Gabor pulse compatible with the target spectrum. The 2D analysis shows higher spectral acceleration values compared to the 1D analyses, and hip enlargement is concentrated in the ~0.3, 1.0, and 1.6 s period range. This situation aligns with the damage distribution observed during the 2020 Samos earthquake (Mw 6.6), indicating that basin effects in Bornova were decisive during the earthquake.

Anahtar Kelimeler

• Bornova Basin
• Site Response
• Basin Effects
• Dynamic Analysis

Derin Alüvyon Bir Basende Sismik Zemin Tepkisinin Tepkisi: Bornova Baseni (İzmir) Örneği

Öz

Bu araştırma, İzmir Bornova bölgesindeki derin alüvyon basenlerinin deprem yer hareketi üzerindeki etkilerini, saha karakterizasyonu ile 1B ve 2B eşdeğer lineer zemin tepki analizlerini birleştirilerek araştırmaktadır. Çalışmada, Bornova Basenini temsil eden iki adet idealize edilmiş iki boyutlu jeolojik kesit kullanılarak zemin–kaya ara yüzeyleri modellenmiştir. Çalışma alanı, İç İzmir Körfezi boyunca uzanan doğu-batı yönlü normal faylarla sınırlanan ve sedimanter birimlerle kaplı bir jeolojik yapıya sahiptir. Sondaj verileri, bazı bölgelerde kil, silt, kum ve yer yer çakılların olduğu heterojen jeolojik birimlerin olduğunu göstermektedir. Uzaysal Otokorelasyon (SPAC) yöntemi ise batıda düşük kayma dalgası hızına sahip alüvyon birimlerin derinleştiğini, doğuda ise kayma dalgası hızlarının yüzeyden derine doğru arttığını göstermektedir. Analizlerde, laboratuvar deneylerinden elde edilen kayma modülü azalım ve sönüm oranı eğrileri literatürde yaygın olarak kullanılan referans eğrilerle karşılaştırılarak en uygun eğriler analizlerde kullanılmıştır. Analizlerde, 1999 Düzce depremi kaydı, 30 Ekim 2020 Samos depremi kaydı ve hedef spektruma uyumlu Gabor dalgacıklarının süperpozisyonu ile oluşturulmuş üç farklı kayıt kullanılmıştır2B analizler, 1B analizlere kıyasla daha yüksek spektral ivme değerleri göstermiş; büyütme ise yaklaşık 0.3, 1.0 ve 1.6 s periyot aralıklarında yoğunlaşmıştır. Bu durum, 2020 Samos depremindeki (Mw 6.6) hasar dağılımıyla örtüşmekte ve Bornova’daki basen etkilerinin deprem sırasında belirleyici olduğunu göstermektedir.

Anahtar Kelimeler

• Bornova Baseni
• Saha Tepkisi
• Basen Etkileri
• Dinamik Analiz

Kaynakça

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