A phase decomposition method of vertical array seismic data

We propose a phase decomposition technique of vertical array seismic data into P-, S-, Love and Rayleigh waves and applied to real data. Two important features of this technique are: (1) it has the ability to resolve mixture of phases, (2) it provides the waveforms which are decomposed from an array data into the phases. We assume a linear model for ground motions at a vertical seismic array. Ground motions are assumed to consists of vertical incident plane P- and S-waves, and laterally incident Love and Rayleigh waves. We assume that ground motions of a phase between a depth and surface are described by a transfer function. The decomposition is done by least-squares method in the frequency domain. Numerical tests show the ability of the decomposition of Love wave and Rayleigh wave and the limitation of the decomposition in low frequency. We analysed the data obtained by a vertical array of 5 accelerometers at CTS located on the Ashigara valley, a middle-sized sedimentary valley. Result of the analysis shows that the later waves mainly consist of surface waves. It seems that the surface waves are the basin-induced surface waves generated at the edge of the valley. Particle motions and the apparent velocity obtained with a horizontal array suppose this suggestion.