Specially designed arrays of strong motion accelerograms are required for engineeringstudies of the spatial variation of seismic motions. The LSST-Hualien array in Taiwan providesgood records for this type of study. Usual design considérations are based on the travelling waveassumption to estimates the torsional ground motion. This assumption, however, ignores the contributionof spatial incoherence of seismic motions. The purpose of the paper is the analysis of thetorsional component of seismic motion, induced by scattering of translational horizontal motion. Inthis study, the 01/05/1995 earthquake is considered, which is LSST-07, with a magnitude of 4,9and pic acceleration of 0,136g. In first time, free-field experimental rotation results are obtained bythe association of record stations in 28 couples of stations. In second time, a theoretical stochasticalmodel, which include both travelling wave and spatial incoherence phenomena, with correlationdistance, scattering and apparent velocity parameters, is proposed; it introduces a non dimensionalrotation which leads to a good agreement with experimental rotational results. Both correlationdistance, apparent velocity and scattering standard deviation are identify by the model.
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