A Numerical Study on Comparison of 1D and 2D Seismic Responses of a Basin in Turkey

Abstract

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.

Does the One-Dimensional Assumption Hold for Site Response Analysis? A Study of Seismic Site Responses and Implication for Ground Motion Assessment Using KiK-Net Strong-Motion Data

“…A quantitative description of the limits of the 1-D assumption and corresponding predictions of the influence of 2-D and 3-D effects, however, remains a difficult task. While a large number of numerical studies have focused on simulations in idealized 2-D basins with well-known shapes of the sediment-bedrock interface and idealized topographies (e.g., Hisada and Yamamoto 1996, Makra et al 2012, Hasal and Iyisan 2014, Zhu and Thambiratnam 2016, Riga et al 2016, 2018, Zhu et al 2018), only a small number (e.g., Thompson et al 2012, Laurendeau et al 2018) have tried to evaluate the validity of the 1-D assumption and identify the different levels of complexity of site response that should be accounted for. Thompson et al (2012) analyzed 104 arrays in Japan that have recorded surface acceleration higher than 0.3 g and concluded that 16 of these sites resemble the 1-D site response.…”

SiSeRHMap v1.0: a simulator for mapped seismic response using a hybrid model

“…(iii) The maps generated by SiSeRHMap may suffer of substantial uncertainties when high complex subsoil features are present. The latter are summarized in the high slope degree of the interfaces (L/H < 8-10 in Hasal and Iyisan, 2014) and in general by sharp variation of the buried morphology. On these effects, it is noted that 1-D seismic response seems to be underperformed mainly at the edge of the valley (Gelagoti et al, 2010).…”