抄録
It is very important to determine the initiation ages of active faulting in order to clarify the tectonic history of the Japanese Islands and to predict the evolution of the geological environment. In this study, we compiled existing information about the initiation ages of active faulting in the Japanese Islands; these ages were estimated by stratigraphic interpretation and calculation. We also included the initiation ages that we calculated from the total displacement and slip rate of active faults. The number of active faults, which started current style of activity, seems to have gradually increased from about 3 Ma. Since then, N-S trending reverse faulting has been observed in northeast and southwest Japan, and strike-slip faults in central Japan. The number of active faults increased drastically after 1.5 Ma, and peaked at around 0.5 Ma. Since 1.5 Ma, NE-SW trending reverse faulting occurred in the region extending from the southern part of northeast Japan to southwest Japan. Most of the active faulting in Kanto and Izu districts, which is attributed to reverse and strike-slip faults, started after 1 Ma. The trend of the initiation ages of active faulting almost correspond to the periods of the tectonic events that occurred near the Japanese Islands. After the peak of the initiation of active faulting around 0.5 Ma, the number of new active faults decreased. However, it is possible that the new active faults were undetectable because of their small displacements.
