Abstract
It is well known by experiments made on some rocks that they can not be regarded as perfect elastic bodies but as considerably viscous.
The mathematical expression for their stress-strain relation has been given as a form of in the 1st approximation. A property expressed by the former formula is called fermoviscosity and that expressed by the latter is called elasticoviscosity or plastisity. The author has treated mathematically the viscoelastic waves for the two media above mentioned in the same manner, and then tried to explain the peculiar form of ScS wave observed in seismograms assuming that the core of the earth has a plastic property.
