Abstract
The spatial coherencies of ground motions are the key to establishing multi-support excitation for large-dimension structures. Most of the existing models were established based on ground motions recorded at dense observation arrays which barely show any detailed information on the focal mechanism. However, in the near field, ground motions are dominated by the source, and so are the spatial coherencies of ground motions. In this paper, a deterministic physics-based method was used to simulate ground motions in the near field for various focal mechanism scenarios. The coherencies of the simulated ground motions were calculated. The Loh coherency model was used to fit the variation in the calculated coherencies for each scenario. The results show that the focal mechanism has a significant effect on the spatial coherencies of simulated ground motions. Finally, the probability density distributions of the parameters, a and b, of the Loh coherency model were obtained, and a coherency model was proposed, based on the Loh coherency model, in which the parameters are taken to be dependent on the focal mechanism.
Highlights
Academic Editor: Claudia CasapullaThe ground motions measured at different locations within the dimensions of an engineered structure are typically different
It is generally believed that the spatial variations in ground motions are produced by: (1) The wavepassage effect, which describes the time differences in the seismic waves arriving at different locations; (2) The incoherency effect, which represents the differences in the ways of superposing waves from an extended source, with a consideration of the scattering by irregularities and inhomogeneities along the path and at the site; and (3) The local site effect, which accounts for the changes in the amplitude and frequency contents of the bedrock motions caused by the local soil conditions [6,7]
The coherencies of the seismograms simulated based on the uniform single medium show that the seismic waves along different propagation paths are different, which proves that the fault strike is an important factor affecting the spatial coherency of ground-motion fields [30]
Summary
The ground motions measured at different locations within the dimensions of an engineered structure are typically different This variation has an impact on large-dimension structures, which cannot be neglected, especially in the near field [1,2,3,4,5]. Records of dense array do not come with detailed information on the causative fault This makes it difficult to include a focal-mechanism-related item in the coherency model. The coherencies of the seismograms simulated based on the uniform single medium show that the seismic waves along different propagation paths are different, which proves that the fault strike is an important factor affecting the spatial coherency of ground-motion fields [30]. A deterministic physics-based method was used to simulate ground motions in the near field for various focal mechanism scenarios. The coherencies of simulated ground motions were calculated, and a coherency model with focal-mechanism-dependent parameters was developed based on the Loh coherency model
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