Study on Elastic Strain of the Ground in Earth Tides

Abstract

We have observed the tidal strain in six individual directions at Osakayama Observatory, 65 km distant from the nearest sea, and in three horizontal-components at Kishu mine, 15 km distant from the Kumano Sea, and in three horizontal-components at Suhara Observatory on the sea-shore. From these observations, M2-terms of the components of tidal strain at these three observation stations were analysed. And a comparison between the relative tidal strains obtained by the differences of observed values at pairs of these stations, and those obtained by means of elastic theory was made. The results obtained by the observations were in a fairly good agreement with the results of theoretical calculations at the pair of Osakayama-Kishu. The values of vertical strain, horizontal areal strain and cubical dilatation in the primary earth tidal effect were obtained directly from observations. [Figure omitted] [Figure omitted] From these materials the values of l, F(a), G(a), [Table omitted] and [Table omitted] at the earth's surface were ealculated. These values are in a good agreement with the theoretical values obtained by H. Takeuchi. As we have seen, both observational and theoretical values showed good agremeent in the first approximation, but if we look into minute points, the observational results obtained at Suhara, for instance, showed a considerably large anomalous character compared with those obtained at other two stations, and this local character is supposed to be explained by the complex geological structure near Suhara. The detailed study on the peculiar nature of tidal strain at Suhara will be postponed to near future. Acknowledgement: The author wishes to express his sincere thanks to Prof. Kenzo Sassa and Prof. Eiichi Nishimura of Kyoto University for their invaluable instructions throughout this study. Many thanks are also extended to Prof. Shoitiro Hayami of Kyoto University who read the whole in manuscript and offered many helpful suggestions.