Abstract
The latest results conceming the prediction of the June 17, 1973, Nemuro-oki earthquake (magnitude 7.4), off the Pacific coast of Hokkaido are discussed with special emphasis on the mode of strain release. This earthquake filled in the seismic gap that had been cited as a likely place for a future earthquake, but the preseismic land subsidence extending over the Eastern Hokkaido was not recovered. These facts suggest that the seismic slip at the plate boundary was deficent. Presently available evidence indicates that such a slip deficiency is unlikely to be taken up in the near future, by either aseismic faulting or occurrence of a great shock. More likely case proposed here is that much of the stored strain energy may remain unreleased during the interseismic quiescent period of seismic activity. In this case, it is suggested that the area of faulting and amount of slip differs greatly each time inter-plate earthquakes recur in at least a certain area, in view of the idea that plate motions at the subduction zone are not regular in size on a time scale of several hundreds of years or more.
