Identiﬁcation of resonant earthquake ground motion
Resonant ground motion has been observed in earthquake records measured at several parts of the world. This class of ground motion is characterized by its energy being contained in a narrow frequency band. This paper develops measures to quantify the frequency content of the ground motion using the entropy principle and the dispersion index. These measures are based on the geometric properties of the power spectral density function of the ground acceleration. The application of these measures to quantify the frequency content of random earthquake models is demonstrated ﬁrst. Subsequently, these measures are used to quantify the frequency content of the ground acceleration for near-ﬁeld records measured at rock and soil sites, short-duration and long-duration earthquakes.