Body Wave Propagation and Site Effects
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Body Wave Propagation and Site Effects Angela Ricciardello
Received: 21 December 2011 / Accepted: 5 April 2012 / Published online: 30 May 2012 © Springer Science+Business Media B.V. 2012
Abstract The interaction between seismic radiation and near-surface geology plays a role of primary importance in the risk hazard mitigation especially due to the so called site effects. Such kind of phenomena depends on the geological conditions that may cause spatial variability of ground motion, such as producing an amplification of the seismic signal at defined frequencies. For this reason the analysis of site effects plays a key role in the seismic risk mitigation and the numerical simulation represents a powerful tool in this field. This work contemplates the simulation of seismic signals and analysis of their power spectra, varying the intensity of the impulse and its location in the domain, as well as the number of layers and/or their physical properties in order to guess a possible relation between the maximum of peak amplification and the geometrical and physical characteristics of the medium where seismic waves propagate. The seismic wave propagation is described by means of an Initial Boundary Value Problem on a three-dimensional domain with an arbitrary topography, whose numerical integration, obtained by implementing the Finite Element Method, provides the analyzed seismic signals. We present several cases and analyze the corresponding power spectra in order to recognize the maximum frequency involved in the soil shaking amplification. Keywords Seismic wave propagation · Elasticity · Finite element method · Power spectra · Site effects Mathematics Subject Classification 65M60 · 74B05 · 74J05 · 86A15
1 Introduction In the context of the seismic hazard mitigation, the modeling of seismic phenomena gained an increasing relevance in the scientific community, in particular during the last years. This A. Ricciardello () Department of Mathematics, University of Messina, Viale F. Stagno d’Alcontres, 31, 98166 Messina, Italy e-mail: [email protected]
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because it is almost impossible to make any estimate based on actual measurements of ground motion induced by earthquakes for cities where strong ground motion recordings are not available and/or cities with moderate seismicity. Therefore, in absence of experimental data, the development of techniques able to infer the spatial variability of ground motion during earthquakes is particularly important. The seismic waves generated during an earthquake follow unpredictable paths when they travel from the source to the surface. These paths depend on the topography and on the near geology characteristics, and may produce an amplification/mitigation of the seismic signal, causing very different damages at the surface. Indeed, local geologic conditions may cause differences in the shaking intensity at one site that can be 10 times stronger than that at another site, at the same distance from the fault. In particular, the soil shaking may be amplified by the
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