Complex polarization analysis of particle motion

Abstract

Knowledge of particle motion polarization aids in identifying phases on three-component seismograms. The scheme of Montalbetti and Kanasewich (1970) is extended to analytic three-component seismograms, where the imaginary part of the signal is the Hilbert transform of the real part. This scheme has only one free parameter, the length of the time window over which the polarization parameters are estimated, so it can be applied in a routine way to three-component data. The azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained. Polarization analysis of strong motion data from the 1971 San Fernando earthquake aids in the discrimination between wave types, which is important for the understanding of the complicated earthquake-induced shaking observed in basins. Most arrivals are incident on the receivers in the direction of the back-azimuth to the epicenter, which suggests that despite the complicated motions, two-dimensional finite difference methods are sufficient to understand the effect on seismic waves of the Los Angeles and San Fernando basins (Vidale and Helmberger, 1986b).