Measurements of tidal gravity and load deformations on Unst (Shetlands)

Summary The tidal gravimetric factor due to the elastic yielding of the Earth has been determined by gravimetric measurements on Unst (Shetland Islands), extending over the time of one month. Its corrected value isG=1.205±0.03. The influence of applying different methods of harmonic analysis, and the effects of ambient temperature and pressures and of the sea tides on the gravimetric results are discussed. No significant difference inG for semi-diurnal and diurnal tides remains after the necessary corrections have been made. The amplitude of the semidiurnal load depression is about 2 cm and it is shown that the more distant North Atlantic tides have a greater effect than the regional tides near the Shetlands. An approximate calculation gives 4.3×10¹¹ CGS-units as the mean rigidity of the part of the Earth's crust yielding to the maritime loading differences in this region.