抄録
Akita, one of our oldest fortified towns was violently shaken in 830. The various damages, landslides, and the sudden change in the course of the river Omono caused by this earthquake are satisfactorily explained by assuming that both the Akita- and Takasimizu-tears were then active.
These faults run nearly W to t across the hill on which the ancient fort of Akita was situated. In both faufts the throw is about 20m and the horizontal displacement about 500m.
They cut through petroliferous Neogene Tertiary and the Terauti beds which are old Quaternary fresh-water deposits in this district. As recent deposits cover alwost, the whole of the faults, they are very imperfectly exposed. Their sites were determined by means of key-beds obtained from oil-well records as well as by the geological survey of Takasimizu hill.
