Yüzey Topoğrafyasının Zemin Büyütmesine Etkisi

Abstract

Zemin büyütmesi, sismik dalgaların zemin tabakalarından geçerken genliklerindeki artış olarak bilinmektedir. Zemin büyütmesi, sismik ana kaya derinliği ve eğimi, fiziksel ve litolojik özellikleri, yanal ve düşey süreksizlikler, tabakalarının kalınlığı ve topoğrafya gibi bir çok etkene bağlıdır. Bu çalışmada yüzey topoğrafyasının yerel zemin büyütmesine etkisi araştırılmıştır. Zemin tepkisinin üç boyutlu (3-B) sonlu eleman yöntemiyle inceleyebilmek için SiteEffect3D isminde bir yazılım geliştirilmiştir. Bu yazılım ile yüzey topoğrafyasının yerel zemin büyütmesine etkisi çeşitli 3-B modeller kullanılarak incelenmiştir. Bu modeller 17 Ağustos 1999 depremi ivme kaydı ve sentetik ivme kayıtlarına maruz bırakılmış, dinamik analiz sonucunda en yüksek yer ivmesi (PGA) sonuçlarından grafikler elde edilmiştir. Dinamik analiz sonuçları, yüzey topoğrafyası kullanıldığında PGA değerlerinin önemli ölçüde değiştiğini göstermektedir. Düz alanların az olduğu tepeliklerde PGA değerleri yüksek çıkmakta, tepenin eğimi de sonucu etkilemektedir. Düz alanların daha geniş olduğu bölgelerde bulunan tepeliklerde de PGA sonuçlarında dikkate değer değişiklikler olmaktadır. Ancak geniş düzlükler içerisinde bulunan tepelerde eğim değişiminin etkisi görece daha azdır.

Keywords

• Zemin büyütmesi
• Yüzey topoğrafyası
• Deprem
• Jeofizik

Effect of Surface Topography on Soil Amplification

Abstract

Soil amplification is known as the increase in amplitudes of seismic waves as they pass through the soil layers. It depends on many factors such as seismic bedrock depth and slope, the thickness of its layers, physical and lithological properties, discontinuities, and topography. This study, the effect of surface topography on local soil amplification was investigated. A software called SiteEffect3D has been developed to examine soil behavior with the three-dimensional (3-D) finite element method. With this software, the effect of surface topography on local soil amplification was investigated using various 3D models. These models were exposed to the 17 August 1999 earthquake acceleration record and synthetic acceleration records, and the peak ground acceleration (PGA) graphs were obtained as a result of the dynamic analysis. Dynamic analysis results show that PGA values change significantly when surface topography is used. PGA values are high on hills with few flat areas, and the slope of the hill also affects the result. There are also remarkable changes in the PGA results on the hills located in the regions where the flat areas are wider. However, the effect of the slope is relatively less on the hills in the wide plains.

Keywords

• Soil amplification
• Surface topography
• Earthquake
• Geophysics

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