Solid earth and oceanic tides recorded on the ocean floor off the coast of northern California

Abstract

For the first time the ocean and solid earth tide are simultaneously measured on the deep ocean floor. Two months of continuous data has been obtained from a long-period feedback seismometer and a long-period pressure transducer mounted in an instrumental package, Obs 3, located on the ocean bottom at a depth of 3903 meters off the coast of Northern California. Significant spectral components are found by (a) harmonic analysis, (b) least squares, and (c) convolution method for both tides corresponding to the O1, K1, N2, M2, and S2 constituents. Theoretical fluctuation of gravity and tidal residues were calculated for the same period. For the largest component of oceanic tide M2, the amplitudes and phases vary between 54.035 and 54.673 cm and 312.91° and 316.03°, respectively, depending on the method of analysis used. The amplitudes at Obs 3 are in closer agreement with those at San Francisco than their corresponding epochs. The differences between amplitudes are about 5 cm whereas the extreme differences in epochs are about 25°. The gravimetric factors for resolved components of solid earth tides are estimated after approximate removal of the effect of ocean tide from the observed fluctuations of gravity. The value for the most reliable M2 constituent is 1.126±0.056 and for the O1 constituent is 1.140±0.057. The phase differences between the theoretical and observed fluctuation of gravity after removal of the effect of oceanic tides from the observed values are 5.66° for the M2 constituent and 3.67° for the O1 constituent.