Single-pulse-like and double-pulse-like characteristics of near-fault ground motions

An approach is proposed for quantitatively identifying the number of one-cycle pulses of ground motions. The one-cycle pulse signals are derived from the original velocity time series using the low-pass acausal fourth-order Butterworth filter and the zero-point method, and the adaptive cut-off frequency of the filter is determined by the number of extreme points in the extracted pulse signals. Then, according to the relative energy and the comprehensive evaluation index of the extracted pulse signals, ground motions are classified into four classes: nonpulse-like, single-pulse-like, double-pulse-like, and ambiguous. The statistical relationships between pulse characteristics and source parameters, including moment magnitudes, site conditions, and rupture distances, are discussed. In addition, the relationship between the first-arriving-pulse signal and the last-arriving-pulse signal in double-pulse-like ground motion is investigated. Finally, this approach analyzes the distribution of double-pulse-like and single-pulse-like ground motions recorded during the 1999 Chi-Chi earthquake.