The Effect of Ocean Tide Loading on Tides of the Solid Earth Observed with the Superconducting Gravimeter

Abstract

The superconducting gravimeter has been calibrated to an accuracy of 0·2 per cent and was used to measure the influence of the ocean tides on the tides of the solid earth at two locations in southern California. These measurements, which show a signal to noise ratio of 70 db in the 1 and 2 cycle per day band, and the accurate calibration of the gravimeter make possible a quantitative test of ocean load calculations for the O1 and M2 constituents and the ocean models upon which they are based. We have computed the ocean load effect by using Farrell's Green's functions and modifications of previously published ocean co-tidal charts. The agreement between observed and computed earth tides is within 0·2 per cent and corroborates the placement of an M2 amphidrome at 1500 km south-west of San Diego. If the amplitudes of the computed tides are correct it also sets an upper limit of 0·1° on the phase shifts of the solid earth tides. We have also observed the loading effect on the coast due to the non-linear M4 ocean tide.