Comparison of the Rate of Changes in the Earth's Rotation and Those of Crustai Movements in Japan

Abstract

Comparisons of spectral characteristics of rates of changes in the Earth's rotation, the rate of the Earth's rotational speed and polar motion, and those of crustal movements in Japan are made. For variations of about one year, the rate of changes of the Earth's rotation is comparable with that of the gravity changes. The rates of changes in strain and tilt, however, show a large value than that of the Earth's rotation. For the spectral band of 1/10-1/100 y, it needs to study spectral characteristics of the rates of changes of the Earth's rotation and those of gravity, strain and tilt in the future.1. Observations of the Earth's rotation, changes of the Earth's rotational speed and polar motion, with new techniques may be affected from crustal movements of the observing sites. Since Japan may be an active region of crustal move ments, it may be of use to study frequency spectra of both the Earth's rotation and crustal movements in Japan [1]. In study of the Earth rotation we often use an expression of the rate of relative changes. This expression, however, is not convenient for vertical crustal deformations, because the definition of the standard scale is not clear. We consider only gravity, strain and tilt in crustal movements. We shall express the rate of rela tive changes in units of radian/year. For a case of a periodic variation the rate of relative changes is expressed by (relative changes of the amplitude)/(period) and it is written as 2π×(the amplitude of a variation/length of a day)/(period) for the Earth's rotational speed especially.