Abstract
　With the wide frequency and dynamic range seismographs distributed in Shizuoka prefecture, the destructive earthquake(1980, E-off Izu peninsula, M=6.7) and its preshocks and aftershocks were observed at three observation stations near the source region.
　We developed, accordingly, a method to synthesize the time history of strong motions in a main shock from the seismogram of an aftershock as Green function. When the mothod was applied to the seismograms mentioned above, the synthesized waves were coincident welI with the main shock seismograms at the three stations.
　We can, therefore, expect that the strong motions at a certain site in the nearfield adjacent to a presumed large earthquake source region may be estimated when some adequate small earthquakes occurred in the same source region.

*岐阜大学教育学部
Faculty of Education, Gifu University
**京都大学防災研究所
Disaster Prevention Research Institute, Kyoto University