抄録
Three problems in the field of engineering seismology; spatial variation of seismic motions, two-dimensional modelling in seismic simulation, and local generation of surface waves, are investigated through spectral ratios, correlation coefficients, propagation directions, and phase velocities which are estimated from array data of four moderate-sized earthquakes. As for the first problem, spectral ratios manifest that spatial variation at frequencies above 2 Hz is primarily influenced by the inhomogenity near ground surface. Correlation coefficients show they decrease with distance and frequency and, in particular, seismic motions separated over 70 m are uncorrelated at frequencies above 6 Hz and those over 150 m are uncorrelated at 3 Hz. As for the second problem, large variation of propagation direction means that seismic simulation based on two-dimensonal modelling does not reproduce recorded seismograms satisfactorily in amplitude and duration. Finally, as for the third problem, phase velocities show that just one of four events contains locally generated surface waves in large quantities, which suggests local generation of surface waves occurs on some limited conditions.
