Iranian Journal of Geophysics

Iranian Journal of Geophysics

A study of the effects of different layering characteristics on the response of two and three-layered semi-sine hills

Document Type : Research Article

Authors
Mohammad Hossein Nateqi 1
Masoud Amelsakhi 2
Morteza Nateqi 3
1 M.Sc. Student, Department of Civil Engineering, Qom University of Technology, Qom, Iran
2 Assistant Professor, Department of Civil Engineering, Qom University of Technology, Qom, Iran
3 M.Sc. Student, Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran
10.30499/ijg.2025.502301.1667
Abstract
Seismic waves generate resonance when they move from bedrock into soil layers, which typically leads to increased damage to surface structures. The similarity of the soil layers affects this resonance; when their characteristics are similar, resonance is reduced, but greater differences between layers result in more resonance. Consequently, soft soil over bedrock can amplify acceleration, raising the risk of structural damage. Additionally, topographic amplification occurs when seismic waves are intensified or altered by the site's landscape features, such as hills and valleys, which can significantly impact how structures respond to seismic activity, potentially leading to greater ground motion and damage during earthquakes. The examination of the phenomenon of topographic amplification and the seismic response of sites is an important subject that has previously attracted the attention of many researchersStudies and research conducted on the effects of topography and the phenomenon of earthquake wave amplification as they pass through surface layers have demonstrated that topography significantly influences the level of damage caused by earthquakes. Local topographic features amplify ground motion during an earthquake, ultimately resulting in substantial damage. This paper investigates the effects of a semi-sine hill, which is one of the most common forms of topography in nature, on the seismic response of the ground surface affected by vertically propagating shear waves (SV), utilizing the FLAC 2D software, a two-dimensional finite difference program. In the numerical modeling, linear elastic behavior has been employed. To analyze the effects of layering on the response of the sinusoidal hills, two-layer and three-layer hills with varying characteristics and thicknesses of layers have been considered as the basis for this study. This research examines the impact of soil properties, layer thickness, and the position of the soft layer. The results indicate that the characteristics and thickness of the layering, as well as the position of the soft layer, have significant effects on the overall amplification trends over the hills and the reduction of amplification near the toe of the hills in response to horizontal motion for the acceleration, velocity, and displacement components. The study revealed that in two-layer hills, amplification increases at the top as the upper soil layer loosens, while in three-layer hills, it decreases at the top when the middle layer loosens. The reduction in amplification is more significant near the base in both cases. For two-layer hills, the thinning of the upper loose layer primarily results in increased amplification in the upper section and decreased amplification near the base. In contrast, for three-layer hills, the middle layer's thinning mainly causes decreased amplification in the upper half and also affects the toe area.
 
Keywords
Site Effect, amplification, semi-sinusoidal hill, layering, ricker wavelet
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Iranian Journal of Geophysics
Volume 19, Issue 5
November and December 2025
Pages 101-120