Quantitative Classification of Near-Fault Ground Motions Using Wavelet Analysis

TLDR

The method quantitatively identifies ground motions with strong velocity pulses, such as those caused by near‑fault directivity. It uses wavelet analysis to extract the largest velocity pulse, compares its size to the original motion to classify it as pulselike, and applies additional criteria of early arrival and large amplitude, calibrated with a training set. The procedure determines pulse period, identified 91 large pulses in the NGA library—many likely from near‑fault directivity—and is useful for probabilistic seismic hazard analysis, attenuation modeling, and nonlinear dynamic analysis of structures.

Abstract

A method is described for quantitatively identifying ground motions containing strong velocity pulses, such as those caused by near-fault directivity. The approach uses wavelet analysis to extract the largest velocity pulse from a given ground motion. The size of the extracted pulse relative to the original ground motion is used to develop a quantitative criterion for classifying a ground motion as “pulselike.” The criterion is calibrated by using a training data set of manually classified ground motions. To identify the subset of these pulselike records of greatest engineering interest, two additional criteria are applied: the pulse arrives early in the ground motion and the absolute amplitude of the velocity pulse is large. The period of the velocity pulse (a quantity of interest to engineers) is easily determined as part of the procedure, using the pseudoperiods of the basis wavelets. This classification approach is useful for a variety of seismology and engineering topics where pulselike ground motions are of interest, such as probabilistic seismic hazard analysis, ground- motion prediction (“attenuation”) models, and nonlinear dynamic analysis of structures. The Next Generation Attenuation (nga) project ground motion library was processed using this approach, and 91 large-velocity pulses were found in the fault- normal components of the approximately 3500 strong ground motion recordings considered. It is believed that many of the identified pulses are caused by near-fault directivity effects. The procedure can be used as a stand-alone classification criterion or as a filter to identify ground motions deserving more careful study.