Empirical correlations between the effective number of cycles and other intensity measures of ground motions

The effective number of cycles is an important ground motion parameter for the assessment of liquefaction potential. In this paper, empirical correlations for two measures of the effective number of cycles with seven amplitude-, cumulative-, and duration-based intensity measures (IMs) are studied and compared, based on the NGA strong motion database and several ground motion prediction equations. The adopted definitions of the effective number of cycles include an absolute measure (N-A) and a relative measure (N-R). It is shown that NA is highly correlated with high-frequency IMs, such as spectral acceleration (SA) at short periods, Arias intensity, and negatively correlated with signification durations (Ds). On the other hand, NR shows generally negative correlations with both amplitude- and cumulative-based IMs. N-R also exhibits small-to-moderate positive correlations with Ds, which are commonly regarded as similar parameters to the effect number of cycles. Simple parametric functions are provided to describe the N-A-SA and N-R-SA correlations for various cases. The importance of considering multiple IMs rather than SA only in ground-motion selection is also briefly demonstrated.