On Earth tides

Abstract

This paper is divided into six main sections, the abstracts for which are as follows:(1) This deals with the rigidity of the upper mantle of the Earth. A value is obtained for the effective modulus of rigidity of the Earth's upper mantle by using vector differences between tiltmetric observations at two suitably selected stations. By this method, the direct effects of Earth tides are almost entirely eliminated and the oceanic effects are accurately evaluated. (2) This deals with the particular motion of the Earth's surface near an active fault. Anomalous tilting diagrams obtained at six closely spaced stations near the sea are discussed in relation to the geologic structure of the surface ground. (3) Rigidity of the Earth as a whole is analyzed. A value of 1 + k − h is obtained from tiltmetric observations at a stable station far remote from the oceans, and values of the effective rigidity for the whole mantle and for the whole Earth are determined.(4) This is a study of tidal variation of latitude. From data over long periods at six International Latitude Observatories, tidal latitude variations are analyzed and used to determine values of 1 + k − ℓ. Unexplainable effects peculiar to the observing stations and to the epoch adopted in analysis are noted. From data resulting from 300,000 pairs of star observations, the mean value of L was estimated as 1.20. (5) This analyzed the time variation of the elasticity of the Earth's crust. An unusually large variation with time in the Earth tidal amplitude observed at Makimine is discussed and is considered to be intimately related to the bending of the Earth's crust caused by the load of sea water in the nearby Hyuganada, an active center of large‐scale sea earthquakes. (6) This is a study of the elastic anisotropy of the Earth's upper mantle. From an analysis of tiltmetric data obtained at several stations in Japan, it is suggested that the elasticity of the Earth's upper mantle in the N‐S direction is 20 to 30 per cent smaller than that in the E‐W direction. The study of longer series of observations and independent attacks on the problem are recommended.