Bibliography ============= 1. Gibert R. -J. - Vibrations of structures, Collection of the Direction des Études et Recherches d'Électrice de France, No. 69, Eyrolles 1988. 2. Nigam, N.C., Jennings, P.C. - Calculation of Response Spectra from Motion Earthquake - Bull. of the Seismological Society of America, Vol.59 No. 2 pp 909 - 922 April 1969. 3. Preumont, A. - Frequency domain analysis of time integration operators, Earthq. Eng. Structure. Dyna. 10, pp. 691-697, 1982. 4. Seismic response by spectral method [:ref:`R4.05.03 `].