Abstract
Earth tilts and strains due to oceanic tides at two stations, Akibasan and Oura, in Wakayama, Japan have been estimated. The effects produced by the neighbouring sea have been calculated according to the theory of deformation of a multi-layered halfspace by J. T. Kuo. For the effects of the distant sea, Green's function method by I, M. Longman for the Gutenberg earth model has been used. Tilts and strains observed at Akibasan can be explained successfully by summing the direct earth tides expected from the Gutenberg model and the indirect effects due to oceanic tides expected from a similar model (The Gutenberg crust is replaced by a structure determined by local seismological observations). The surface tilt on this multi-layered model can be roughly expressed by the Boussinesq solution multiplied by the factor 12.6/(3.0+r) introduced by E. Nishimura. Decreasing rates of the tilt and strain to distance r are approximately proportional to r-2.4, which is equal to the decrease of strain steps with distance from moderate earthquake sources found by S. Takemoto et al. It is also nearly equal to the decreasing rate of an anomalous ground strain observed before and after the Yoshino Earthquake in 1951 by M. Takada.
