The loading effect of earthquakes to structures is evaluated in terms of energy spectra. The energy spectra of seismic motions in the deep rock is assumed to be of the simplest form. The seismic motions in the deep rock are amplified due to the process of wave propagation through base rocks and sedimentary soils upon the rock. The well-established wave propagation theory is applied to the seismic motions in the deep rock and the energy spectra for the surface seismic motions are estimated for the practical design purposes.
