ANALYSIS OF CORRELATION COEFFICIENTS BETWEEN TWO ORTHOGONAL COMPONENTS OF STRONG-MOTION RECORDS

With regard to horizontal components in seismic design of nuclear facilities in Japan when input ground motions are generated based on response spectrum, simulated ground motions composed of two mutually orthogonal components are generated for one target response spectrum. In such a case, the characteristics of the two ground motions are distinguished by the randomness of the phase angle given by the uniformly distributed random numbers and/or the difference in the phase characteristics of the two different components of the observation records. On the other hand, US Nuclear Regulatory Commission standards state that, when performing seismic response analysis for nuclear facilities using the method of simultaneous input of three earthquake ground motion components, the three components should be shown to be statistically independent of each other, and an absolute value for correlation coefficient as proposed by Chen (1975) is introduced as a criterion. In this paper, focusing on the correlation coefficient by Chen (1975), we found the correlation coefficients between two orthogonal components in records of observed strong motions in Japan after 2000, and performed statistical analyses of these correlation coefficients, then analyzed the impact of various earthquake-related parameters upon them. In addition, we actually generated simulated ground motions via a common practice based on the response spectrum and analyzed their correlation coefficients.