Identification of Near-Fault Velocity Pulses and Prediction of Resulting Response Spectra

Pulse-like near-fault ground motions resulting from directivity effects are a special class of ground motions that are challenging to characterize for seismic performance assessment. These motions contain a pulse in the velocity time history of the motion, often occurring in the direction perpendicular to the fault rupture at locations near the fault where the earthquake rupture has propagated towards the site. A recently proposed wavelet-based signal processing approach is used on a large ground motion library to empirically identify these pulses in ground motions. Example results are presented to demonstrate that the identified motions are often observed at sites where directivity effects are expected (although no claim is made that all observed pulses are due to directivity). The response spectra of these records are then studied using this approach, and it is seen that their spectra can be described using an existing ground motion prediction (attenuation) model coupled with a narrow-band amplification function in the region of the pulse period. The modified prediction can be incorporated in probabilistic seismic hazard analysis, providing a direct and transparent method of accounting for directivity effects.