Assessment of the design spectrum with aggravation factors by 2D nonlinear numerical analyses: a case study in the Gemlik Basin, Turkey

The response spectra of multidimensional analyses are compared with one-dimensional (1D) local models to couple the irregular soil stratification effect at a site. In recent studies, the surface motion 2D/1D or 3D/1D spectra ratios are defined as the spectral aggravation factors for each region of a...

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Bibliographic Details
Published in:Bulletin of earthquake engineering 2022-02, Vol.20 (3), p.1371-1395
Main Authors: Ozaslan, B., Iyisan, R., Hasal, M. E., Khanbabazadeh, H., Yamanaka, H.
Format: Article
Language:English
Subjects:
Alluvial basins
Basin geometry
Basins
Borings
Building codes
Case studies
Civil Engineering
Earth and Environmental Science
Earth Sciences
Earthquakes
Elastoplasticity
Environmental Engineering/Biotechnology
Finite difference method
Geologic depressions
Geophysics/Geodesy
Geotechnical Engineering & Applied Earth Sciences
Ground motion
Hydrogeology
Mathematical analysis
Mathematical models
Nonlinear response
Numerical analysis
Numerical models
Original Article
Outcrops
P-waves
Propagation
Response spectra
Rocks
Sediments
Seismic waves
SH waves
Soil
Soils
Spectra
Stratification
Structural Geology
Surface motion
Three dimensional motion
Two dimensional analysis
Wave propagation
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Summary:The response spectra of multidimensional analyses are compared with one-dimensional (1D) local models to couple the irregular soil stratification effect at a site. In recent studies, the surface motion 2D/1D or 3D/1D spectra ratios are defined as the spectral aggravation factors for each region of a site. Particularly in alluvial basins, where the soil media is typically formed by fault ruptures or topographic depressions filled with sediments, the inclination of the rock outcrop at the edge of the basin has a considerable effect on the site response, and such an effect has not yet been taken into consideration in recent seismic building codes and general engineering applications. In this study, the natural alluvial basin near the North Anatolian Fault in Gemlik, Marmara region, Turkey, was investigated by 40 seismic site tests and 4 validation borings. The 2D and 1D nonlinear response history analyses in the north–south and east–west directions in the Gemlik basin were performed by numerical models on a finite difference scheme considering nonlinear elastoplastic material behaviors and geometric discontinuities. Twenty-two strong ground motions recorded at the rock site were excited vertically as SH waves. The numerical results showed that narrow basin effects were derived not only by reflection, refraction, and shifting behavior but also by the focusing and superposition of the seismic waves propagating from opposite basin edges. As a result, the site-specific spectral aggravation factors SAF 2D/1D defined by the ratio between the 2D and 1D acceleration response spectra for each period and any location on the site were proposed for the Gemlik basin. The variations in the aggravation factors were observed as values increasing to 1.2–2.2 near the edge and at the basin center.
ISSN:1570-761X
1573-1456
DOI:10.1007/s10518-021-01296-6