Comparison of recent crustal movements with quaternary movements in japan and its plate-tectonic implication

Abstract

Recent crustal movements may be classified into two categories: one being associated with major earthquakes and the other being creep deformations without a direct association with any major earthquake. The spatial distribution of the rate of creep deformation during the last 70 years as detected by the precise re-leveling, shows a similar configuration on a map to the distribution of amount of Quaternary vertical movements, throughout the Japanese Islands with the exception of Hokkaido. Comparison of the rate of recent movement with the total amount of Quaternary movement suggests the following two interpretations, which have the advantage of simplicity compared with other possibilities: 1. (1) The rate of the recent movements is four times larger than the average rate for the Quaternary. 2. (2) If the rate of crustal movements is almost uniform as most of creep deformations can be shown to be, then the Quaternary movements must have started about 0.5 million years ago. Nevertheless, the author suggested in 1967, that the active period of Quaternary tectonic movements might have begun about one million years ago. This suggestion was based upon the measurement of the total amount of movement compared with the rate of movement as detected from the deformation of late Quaternary terraces. These tectonic movements, naturally include the crustal movements associated with major earthquakes. It is highly probable that the movements associated with major earthquakes and the creep deformations not directly associated with major earthquakes became active at the same time. If so, a third interpretation could be advanced: 3. (3) The rate of the recent creep deformations is about twice the average, and the crustal movements in the Japanese Islands commenced their active period about one million years ago. On the basis of a bend in the hot-spot trace along the Hawaiian volcanic chain, the Pacific plate seems to have changed the position of its rotation axis and its angular velocity about one million years ago. The agreement of both of these dates with the increasing rates of activity suggests that the Quaternary tectonic movement in Japan was activated by the change in the pole of rotation of the Pacific plate which took place at about one million years ago and in doing so caused the bend in the eastern end of the Hawaiian island chain.