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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Seismic site effects ： ウィキペディア英語版 Seismic site effects ''Seismic site effects'' are related to the amplification of seismic waves in surficial geological layers.〔Semblat J.F., Pecker A. (2009) ''Waves and vibrations in soils: earthquakes, traffic, shocks, construction works'', IUSS Press, Pavia, Italy, 499p.〕 The surface ground motion may be strongly amplified if the geological conditions are unfavourable (e.g. sediments). The damages due to an earthquake may thus be aggravated as in the case of the 1985 Mexico City earthquake. For alluvial basins, we may shake a (bowl of jelly ) to model the phenomenon at a small scale. This article defines site effects first, presents the 1985 Mexico City earthquake, describes the theoretical analysis of the phenomenon (through mechanical waves) and details several research results on seismic site effects in Caracas. == Definition of the phenomenon == When propagating, the seismic waves are reflected and refracted at the interface between the various geological layers (Fig.1). The example of Figure 1 depicts the seismic wave amplification in horizontal geological layers. We consider a homogeneous elastic half-space (in green) over which an elastic alluvial layer of constant thickness $h$ is located (in gray). A shear wave ($SH$) of amplitude $A\_2$ reaches the interface between the half-space and the alluvial layer with an incidence $\backslash theta\_2$. It thus generates: * a reflected wave in the half-space with amplitude $A\_2^\text{'}$ and incidence $\backslash theta\_2$ * a refracted wave in the surficial layer with amplitude $A\_1$ and incidence $\backslash theta\_1$ The refracted wave originates a reflected wave when reaching the free surface libre; its amplitude and incidence are denoted $A\_1^\text{'}$ and $\backslash theta\_1$ respectively. This latter wave will be reflected and refracted several times at the base and the top of the surficial layer. If the layer is softer than the half-space, the surface motion amplitude can be larger than $A\_2$ thus leading to the ''amplification of seismic waves'' or ''seismic site effetcs''. When the geological interfaces are not horizontal, it also possible to study seismic site effetcs by considering the ''basin effects'' due to the complexe geometry of the alluvial filling〔Bard P.Y., Bouchon M. (1985). The two dimensional resonance of sediment filled valleys, ''Bulletin of the Seismological Society of America'', 75, pp.519-541.〕 In this article, we propose several examples of seismic site effects (observed or simulated during large earthquakes) as well as a theoretical analysis of the amplification phenomenon. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Seismic site effects」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.