REVISITING THE PHASOR-WALKOUT METHOD FOR DETAILED INVESTIGATION OF HARMONIC SIGNALS IN TIME-SERIES

A well-known but rarely used powerful method to investigate the presen ce of harmonic signals in time series is the Phasor Walkout method (ot her names are: Graphical Fourier Transform, Summation Dial, Complex De modulation). At a given test frequency the complex contributions (phas ors) to the Fourier Transform of each sample in an equidistantly sampl ed series are added vectorially in the complex plane. The resulting pa ttern, the walkout, reveals information about the properties of the si gnal which is not easy to obtain by other methods. Synthetic examples are used to demonstrate the resolving power of the method. The followi ng geophysical examples for the application of this method are shown: determination of the frequency of the breathing mode 0S0 of the earth after a large earthquake; the study of superconducting gravimeter reco rds after a large deep earthquake used in the 'core mode' interpretati on of a spectral peak, the study of the residual S3 (8 h period) signa l in a tidal record and the bichromatic Rayleigh-waves from Mount Pina tubo on June 15, 1991.