Geoteknik deprem mühendisliğinde karşılaşılan en önemli problemlerden biri, zemin tabakalarının deprem sırasında gösterdiği davranışın belirlenmesidir. Bir sahada oluşan deprem hareketininözellikleri tektonik yapı, kırılma mekanizması, doğrultu etkisi, merkez üstü uzaklığı, jeolojik yapınınve yerel zemin koşullarının etkisi gibi birçok faktöre bağlıdır. Zemin tabakalarının dinamik analiziiçin geliştirilen hesap yöntemleri bir, iki ve üç boyutlu olarak tanımlanmaktadır. İki ve üç boyutluanalizlerde, zemin kesitindeki tabakaların iki veya üç boyutlu geometrisi gerektiği için, bir boyutluyaklaşımın kullanımı daha fazla tercih edilmektedir. Ancak zemin tabakalarının bir boyutlu dinamikanalizinde; yüzey topografyası, tabakaların eğimi ve tabakaların sınırlı enine genişliğinin etkisi ihmal edilmektedir. Zemin tabakalarının yatay yönde sınırlı genişliğe sahip olması, vadi kenarlarındadalga hareketi dönüşümlerine sebep olmakta, dolayısıyla yer hareketinin frekans içeriği ve yüzey deki etkisi vadilerin ortasından kenarlarına doğru değişebilmektedir. Bu çalışmada, seçilen trapezkesitli simetrik vadi modellerinde yerel zemin koşullarının zemin büyütmesine etkisi incelenmiştir.Bu amaçla, kenarlarda anakaya eğimi sabit olan, derinlik ve genişliği farklı vadi modelleri kullanı larak, farklı anakaya ivme kayıtları için bir ve iki boyutlu dinamik analizler yapılmış, elde edilensonuçlar karşılaştırılmıştır. Her modelde zemin kesitinde en üstte kil tabakasının yer aldığı kabuledilmiştir. Yapılan analizler sonucunda, vadi yüzeyindeki ivme spektrumları, Afet Bölgelerinde Ya pılacak Yapılar Hakkında Yönetmelik’te tanımlanan yerel zemin sınıfları için elde edilmiştir. Yü zeyde hesaplanan en büyük ivme değerleri, anakaya ivmelerine oranlanarak zaman ortamındaki zemin büyütmeleri elde edilmiş ve uzaklığa bağlı değişimleri incelenmiştir.

One of the most commonly encountered problems ingeotechnical earthquake engineering is the evalua tion of ground response. The characteristics ofground motion at a particular site depend on manyfactors such as tectonics of the region, epicentraldistance, geological formations, bedrock depth, geo technical site conditions, local surface and subsur face topography. The topographical characteristicsinclude the effects of surface formations, the two andthree dimensional geometry of the subsurface soillayers and bedrock to the local site ground response.The calculation methods developed for the dynamicanalysis of the soil layers are usually defined as twoand three dimensional according to the necessity ofthe problem met.The two and three dimensional geometry of the soillayers and bedrock is required to perform two andthree dimensional ground response analysis, so be cause of the application convenience one dimen sional dynamic analysis is mostly preferred. How ever in one dimensional ground response analysisthe surface topography, two or three dimensionalgeometry of the subsurface and the effects of the lim ited width of the soil layers are being neglected. Infact because of the limited lateral width of the soil layers wave transformations at the basin edges oc- cur, surface waves are being focused to the valleycenter, two dimensional resonance models may oc cur and consequently the amplitude and frequencycontent of the ground motion may change from thecenter of the valley to the edges.In this paper, in order to study the effects of localsite conditions, the depth and width of soil layers,the frequency content and amplitude of strongground motion to the site amplification and fre quency content of surface wave motion, one and twodimensional dynamic analyses were performed forfive different bedrock acceleration records by usingidealized trapezoidal symmetrical valley models.The results of the one and two dimensional analyseswere compared, and the variations of the amplifica tions with the distance from the valley edges wereinvestigated. These models have different depths andwidths. In the valley models, the soil layers were assumed to extend horizontally limited with valleyedges having a constant slope angle of 45°. The top soil layer was selected as high plasticity clay foreach model. The parameters such as the thicknessand initial shear wave velocities of the soil layersabove bedrock, which play the main role in the de termination of dynamic response, were selected inaccordance with the soil groups and soil classes de fined in Turkish Earthquake Design Code (1998).With this aim, the valley models were subjected to1D and 2D dynamic analyses by using five differentbedrock strong ground motion records and the re sults were compared .The results that will be ob tained from the 1D and 2D analyses were aimed toreflect the seismotectonical structure of the NorthAnatolian fault in Turkey. Therefore two bedrockacceleration time histories were selected among theTurkey earthquakes. The vertical and horizontalboundary conditions become important especially inthe dynamic analyses of 2D models. In this studyviscous dashpots, which are, calculated proportionalto the shear and pressure waves of the relevant lay ers were put at the vertical and horizontal layers.High amplification values were calculated at thesurface of rigid valley models having local site classof Z2. In the models having local site class of Z3 orZ4, the amplifications decreased at the high bedrockacceleration values. At the models with sudden ri gidity change in the soil profile, the amplificationsrelatively increased for the surface sections, whichare located at the beginning of valley edge (X/H=1).For the deeper valley models having a graded rigid ity decrement from bottom to upper layers, the am plifications decreased noticeably and the increase inthe peak bedrock acceleration values made thissituation more remarkable. The bedrock topographymust be carefully investigated to obtain the 2D dy namic behaviour of laterally limited soil layers un der earthquake excitation. So the geological andgeotechnical investigations should be done carefullyto satisfy this condition. When the data about thetopography of soil layers and bedrock is insufficient,it will be obligatory to prefer 1D dynamic analysisbased upon the assumption of horizontal soil layersextending to infinity. However 1D and 2D dynamicanalyses give similar results only for the sectionsnear the middle part of very wide valleys.