Seismic waveforms observed in the near-field during major earthquakes depend primarily on the dynamical rupture process on the fault, as well as on heterogeneous earth structures around the source, propagating path and recording sites. In order to investigate the faulting process of an earthquake, the expected ground motions are synthesized from record of several minor events such as foreshocks and aftershocks that occurred on the main shock fault, regarding these records as empirical Green functions which include the earth response. The technique used here is to convolve each of the phase delayed records with a specific time function correcting for the difference in the source function between the main shock and the smaller events, and to make summation over the entire fault surface.The method described above has been applied to the case of the 1969 central Gifu earthquake (M=6.6), by using four aftershocks with magnitudes 4.3-4.8 which are distributed along the main fault. The results indicate that the synthesized waveforms provide a satisfactory agreement to long-period components (T>5 sec) of the JMA strong motion records at the Gifu station (Δ=51km), but that shorter-period waves (T=1-2sec) cannot be accounted for by this synthesis.To provide a possible explanation to these short-period seismic waves, a stochastic fault model is tentatively introduced here with non-uniform displacements, slip angles and rupture velocities distributed over the fault. It is found that the most effective fault parameter to generate the short-period waves is the variation of the rupture velocities, and that this effect is enhanced with preserving long-period components if the rupture propagates with different velocities in large-scale fault segments. The synthesized waveforms, which have been obtained from the four aftershock records incorporating this type of incoherent rupture propagation, could better explain the general features of the strong-motion records including both of long- and short-period waves.Since the above model with the complicated rupture process is only tentative, it seems necessary as a next step to examine the effects of earth structure on the recorded waveforms more closely, by synthesizing theoretical waveforms from the present model.