Topographic, geologic and cavity effects on the harmonic content of tidal strain

Summary. The combined effects of topography, geology and cavities upon the measurements of tidal strains are considered. A theoretical model is proposed in which the topography and geology are modelled with finite elements, and the cavity (assumed to be elliptical) modelled using the analytical theory. The three effects are then superimposed to form a total model. Previous experimental results obtained for the solid tidal strain in Eastern Australia (Blair & Sydenham) are compared with the present theoretical model and reasonable agreement is found assuming values of the Love numbers for the Gutenberg—Bullen A earth model in which h = 0.61 and l = 0.08 (Farrell). Further experimental results are presented for two strain meters, only one of which is not significantly influenced by the cavity. The relative difference, in harmonic content between the recordings of both strain meters is compared with that predicted by the theoretical model.