We investigated spatiotemporal patterns of seismicity in the Shin-etsu region and Tokai region, central Japan, by separating the seismicity into clustered and non-clustered activity. We found that clustered activity occurred at various sites during short periods in each investigated region and that an alternation of active and quiet periods was clear for the clustered activity. In contrast, non-clustered earthquakes occur at an almost constant rate, and active or quiet periods cannot be distinguished in the non-clustered activity. Some evidence suggests that an increase of clustered activity indicates a buildup of the regional stress field. ¿ American Geophysical Union 1994