Frequently, normal dispersed, long-period, wave trains for which surface particle motion is elliptical and progressive in the plane of propagation of SV wave apear near the arrival time of S or SS waves at middle epicentral distant earthquakes.
The analyses of these seismograms recorded at Abuyama and Matsushiro Observatory show a good agreement with the results of direct-PL waves obtained from other shocks occurred on the same path.
Thus, such long period waves can be explained as the result of coupling between the incident SV and dispersive PL waves in the wave-guid when the apparent surface velocity of SV equals the phase velocity of PL wave at the same period and Oliver's hypothesis for the coupling could be almost confirmed from present study based on arrival times of S and SS-PL waves.
Also, the comparison between the PL wave and Rayleigh wave for the observed group velocities was made by using the theoretical dispersion curves computed by YOSHII for leaking mode and YAMAGUCHI, KIZAWA for normal mode respectively.