Abstract
Using the data obtained at the Urakawa Seismological Observatory (KMU), the seismicity in and near Hokkaido was investigated for the period from May 1964 through December 1972. An aftereffect of the 1968 Tokachioki earthquake of magnitude 7.9 has been recognized up to date, the end of 1972. Some features of aftershock and foreshock sequences detected at KMU are described. Aftershock activity differs considerably from place to place in the region concerned, but it shows no systematic trends. The phenomenon of secondary aftershocks is not rare. Considering the relation of the number of aftershocks to the magnitude of a triggering earthquake, the secondary aftershock activity is comparable to the primary aftershock activity in most cases.
