Multi-pulse characteristics of near-fault ground motions

Multi-pulse characteristics of near-fault ground motions, such as the number of inherent pulses, pulse periods, and amplitudes, have notable influences on the response of structures. To investigate these important parameters, an automatic detection procedure, which is conducted on the rough pulse signal that is extracted by the HHT method, is proposed in this work. This procedure can localize all inherent pulses in the time domain independently and discontinuously. Important parameters can be automatically obtained at the same time. Then, statistical relationships between these multi-pulse parameters and earthquake parameters, including moment magnitudes, site conditions (Vs30), rupture distances and types of faults, are investigated comprehensively. With an increasing number of pulses, the multi-pulse ground motions are more likely to be recorded in relatively limited areas. All pulse periods in a velocity record are similar to each other and can be represented by the period of the pulse with the largest energy (TPE). TP(E)s are almost identical to periods of the first pulse in the time domain (TP1). They are related not only to magnitudes but also to fault-types and site conditions. New empirical models are proposed in this work according to fault-types that can predict most TP(E)s across all magnitudes (from 5.7 to 7.6). For amplitudes, all PGVs of inherent pulses can be expressed by the PGV of the pulse with the largest energy (PGV(E)) in a linear attenuation relationship. PGV(E)s are related to rupture distances, site conditions, and fault-types. New empirical models are also developed in this work.