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Depremler sırasında zemin tabakalarında oluşan deformasyon seviyeleri, yapı-zemin etkileşiminde önemli rol oynamaktadır. Kuvvetli yer hareketi kayıtları kullanılarak yapılan bir boyutlu (1D) dinamik analizlerle yüzeye yakın zemin tabakaları için hesaplanan kayma şekil değiştirmeleri; küçük genlikli titreşimler-mikrotremor verisi analiz sonuçlarının, tasarım yer hareketine ait en büyük yatay ivme değeriyle birlikte değerlendirilmesiyle de tahmin edilebilmektedir. Bu çalışmada, Kuzey Anadolu Fay Hattına yakın bir bölgede zemin tabakalarının deprem hareketi karşısındaki davranışı; hem 14 farklı anakaya ivme kaydı kullanılarak yapılan 1D eşdeğer lineer dinamik analizlerle hem de mikrotremor ölçümlerinin analizi yardımıyla elde edilmiştir. Verilerin değerlendirilmesi sonucunda, kuvvetli yer hareketi sırasında yüzeye yakın zemin tabakalarında oluşacak kayma birim şekil değiştirmesinin belirlenebilmesi amacıyla; elastik ve elasto-plastik deformasyon seviyelerini kapsayan bir bağıntı önerilmiştir.

Abstract:Local site conditions such as seismic bedrock depth, bedrock slope of the edge, geometry and characteristics of soil layers, topographical irregularities, etc. are the most important factors affecting earthquake ground motion in a specific site. The amplitude and frequency content of bedrock motion can be changed by local site effects, and this variation is denoted as an amplification or de-amplification. Among the several factors, basin edge effect plays an important role in the transformation of earthquake waves and increase of the surface motion duration and amplitude. The limited width of the soil layers or the edge geometry at the deep formations cause earthquake wave transformations, thus the amplitude of the surface ground motion may vary depending on its location. For this reason the frequency content of surface ground motion may differ from the calculated surface ground motion by one dimensional dynamic analysis. In this case two dimensional analysis is required. In this study, in order to compare the soil response under different strong ground motion, one and two dimensional dynamic analyses were performed by using the Dinar Basin model in Turkey. The acceleration time histories and absolute acceleration spectra were obtained for pre-selected points on the ground surface. The 2D/1D spectral acceleration ratios were calculated by dividing the absolute acceleration spectra obtained from two dimensional (2D) and one dimensional (1D) dynamic analysis. The variations of the spectral acceleration ratios (2D/1D) with distance from basin edge were evaluated for different period values. The calculated 2D/1D spectral acceleration ratios reached their maximum values at a certain zone (X/D<3) near basin edge for every interested period value. While approaching to center of basin models, especially at the zones after X/D=3 point it can be noticed that 2D/1D spectral acceleration ratios generally converged to 1 regardless of the edge bedrock slope values. The highest average spectral acceleration ratios were calculated when the relevant period values were between T=0.2~0.5 s. They took values varying between 2 and 3 for this period interval. A relationship between the results of 1D and 2D dynamic analyses was established. In addition, the approximate validity range of 1D and 2D dynamic analysis at the basin edges was investigated for the model.