Phase characteristics of earthquake motions

The earthquake motion used for the aseismatic design of nuclear power plants is adequately expressed by three elements; the maximum amplitude, the frequency characteristics and the duration time of earthquake and the time history of amplitude envelope. As the time history of amplitude envelope is not clarified sufficiently, the phase characteristics of earthquake motions, which have the close connection to the time history of amplitude envelope, were studied and evaluated. The flow chart of this analysis is presented. In this study, the phase spectrum was expressed by the incremental function, then this phase characteristics were analyzed for the frequency and phase. Concerning the analytical condition, the incremental function for phase spectrum and the polynominal regression analysis were utilized to judge if the reversion of phase angle is continuous to the phase heretofore or local fluctuation; from the developed curve of phase vs. frequency. As the examples of applying the analytical method mentioned above, the Golden Gate Park waves (maximum acceleration 102 gal, maximum velocity 4.6 cm/sec and maximum displacement 0.8 cm), the Hoshina waves (maximum acceleration 392 gal) and the Taft waves (maximum acceleration 176 gal) were analyzed by this method especially for the phase, taking the wave duration time from 10 sec to 30 sec and the cut up time from 0.01 sec to 0.1 sec. The relation between the acceleration and the time, and also between the continuous phase spectrum and the frequency were obtained for these three earthquake waves. (Nakai, Y.)