地震活動に関係した地殻変動(1) ―東北日本外帯の地震活動と細倉で観測された地殻変動―

Abstract

The present paper is a general report on the long term observation of crustal move-ments at the Hosokura station in the T6hoku district, and further, the first of a series ofpapers in which the relation between the seismic activities and crustal movements in somerestricted areas will be presented.Observational results in the case of the outer zone of the T6hoku district are as fol-lows: as far as the E-W direction is concerned, the mean velocity of tilting motion ofthe ground at Hosokura changes coincidentally with the alternations of sequence ofshallow earthquakes occurred in the region of Sanrikuoki (Off the eastern coast of thedistrict), and elastic deformations as shown by the see-saw motion superpose on thesestepwise motion of secular ground tilt, decreasing its amplitude and shortening its periodwith time. Earthquake swarms occur near the peaks of the curve showing the see-sawmotion. These modes of crustal movements at Hosokura are essentially similar to thoseof the Makimine station related to the seismic activities in the sea area of Hyoganada.Besides, an attention is drawn to the plastic deformation caused by a series of veryshallow earthquakes originated near Hosokura.