Fróðskaparrit - 01.01.1975, Page 33

Earth Tides
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and at difterent epochs also depends upon the precision
with which the tidal correction can be given. Special high
precision gravity profiles presently developed (Scandi-
navia) request a comparable precision. Here again a simple
analytical model is not sufficient.
In equatorial regions, the tidal variations of gravity
amount to 0.4 milligal. If the local elastic factors and local
phase lags are not measured in a reasonable number of
stations, systematic errors of 10 % can be expected.
In the same way, when high precision gravity base lines are
developel (a recent example is the new line Port Moresby
— Hobart), the tidal parameters (amplitude and phase)
must be measured at these stations to insure that no syste-
matic errors, even little, can be introduced in the base line
through some erroneous tidal corrections.
4. Oceanography
Ocean-continent interaction are carefully investigated in
Marine Geodesy. Transcontinental tidal profiles are now
under way in the United States, in Europe and in Asia in
order to determine with precision the loading effects pro-
duced by the oceanic tides on the upper crust.
The Asiatic profile just undertaken already, gives quite
different results than the European profile because the
distribution of oceanic tides in the Atlantic Ocean is mostly
of semi-diurnal type while it is of diurnal type in the
China Sea.
There is a serious hope that one will be able to solve the
inverse problem, that is to improve the cotidal and corange
charts on the basis of the amplitudes and phases observed
on the mainland for the solid earth tide (J. T. Kuo’s
programme).
5. Tectonics
Harmonic constants (amplitude and phase) of the main
tidal waves determined at many places could perhaps give
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