東北日本の地殼歪(II)

抄録

The Tohoku (North-East) Japan is divided into sixteen blocks, in which strain components are deduced from displacement vectors by the method of least squares adjustment developed in the first report. The principal strains, maximum shear strains, and dilatations as well as their yeary rates are deduced from strain components with variancecovariance matrices propagated from the ones in strain components. The results of numerical calculations are discussed with references to tectonics in the Tohohu district. The main conclusions are: (1) General pattern of distribution of principal axes in the blocks shows that the axis of minimum principal strain (compression axis) is directed to N60°-80°W. This direction almost coincide with the one of relative plate motion of the Pacific plate to the North American plate estimated by Minster and Jordan (1978). (2) Rates of maximum shear strain range from 0.03 to 0.22 microstrain/a. It is well recognized that strain rates inclease from the Pacific Ocean side to the Japan Sea side. (3) We found contemporary large strain rates in the source region of the 1896 Rikuu earthquake or in the Oga peninsula. (4) Comparison of geodetic strain rates with the ones in Quaternary estimated by Kaizuka and Imaizumi (1984) informes us that the former of the order of 10^-8/a-10^-7/a is ten times larger than the later.