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# Three-Dimensional scattering of plane harmonic SH, SV, and P waves in multilayered alluvial valleys

ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING) 01/2010; 11:605-626.

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**ABSTRACT:**Instrumental observations of ground motion in Mexico City during the April 25, 1989, Guerrero earthquake were analyzed. Our aim was to understand various aspects of the seismic response of the valley that had not been completely resolved. Such understanding of the basic mechanisms that control the seismic behavior of the valley sediments is crucial in any modeling attempt. The study of vertical motion for this event, which was shown to be practically unaffected by site conditions, lead to the identification of a prominent long-period Rayleigh wave. This, together with the availability of absolute time for some stations, allowed the establishment of a common time reference for all recordings. Horizontal motion, in contrast, was significantly amplified, with large increases in duration, at lake bed sites.In order to interpret the observed complexity of ground motion we studied two simplified models of soft alluvial valleys. One of these is two-dimensional and it is excited by plane S waves with variable polarization and incidence angles. This model allows three-dimensional response. The other is a three-dimensional axi-symmetric flat valley with a rigid base. Computations were performed in the frequency domain by means of a boundary integral method for the two-dimensional model and using a collocation least-squares technique for the three-dimensional one. Seismograms were obtained through Fourier synthesis. It was found that the irregular soft layer response produces polarization patterns which are similar to the observations, suggesting that the latter are a consequence of three-dimensional effects.Tectonophysics. 01/1993; - [Show abstract] [Hide abstract]

**ABSTRACT:**An indirect boundary-method formulation to obtain the three-dimensional response of an infinitely long canyon of uniform but arbitrary cross-section cut in a layered viscoelastic half-space is presented. Seismic excitation in the form of plane elastic waves acting at an arbitrary angle with respect to the axis of the canyon is considered. Numerical results for SH-, SV- and P-wave excitation of a circular canyon and of a canyon with a topography similar to that in the vicinity of Pacoima Dam are discussed in some detail.Earthquake Engineering & Structural Dynamics 11/2006; 19(6):799 - 817. · 1.90 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Diffraction of plane harmonic waves by three-dimensional surface irregularities is investigated through the use of an indirect boundary integral equation method. The irregularity of an arbitrary shape is embedded in an elastic half-space and subjected to incident P, SV, SH, and Rayleigh waves. The material of the half-space is assumed to be linear, weakly anelastic, homogeneous and isotropic.The accuracy of the method is demonstrated through comparison of the results with existing axisymmetric solutions. Several numerical examples for non-axisymmetric canyons are presented. The resulting amplification patterns exhibit strong sensitivity on type and angle of the incident waves and on the location of the observation point. Systematic comparisons of three-dimensional and corresponding two-dimensional models demonstrate similarity of the amplification pattern. The amplification is larger in some three-dimensional models than in two-dimensional ones. Strong coupling between SH and P-SV modes is observed for off-azimuthal incident waves. This phenomenon is specially pronounced for incident SH waves and it is intrinsic to three-dimensional scattering.Wave Motion. 11/1989;

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