Fróðskaparrit - 01.01.1975, Blaðsíða 34

42
Earth Tides
new informations on the limits of the plates constituting
the earth’s crust.
Stations have been occupied on the Philippine plate to
check if this is a reasonable possibility.
6. Physics of the Earth’s interior
To describe easily the global elastic behaviour of the Earth
one uses convenient fundamental parameters called Love’s
numbers.
The determination of these numbers is evidently a basic
goal in the earth’s tide study.
As indicated by Poincare and later on by Jeffreys, Jeffreys-
Vicente and Molodensky, a resonance due to dynamical
effects in the liquid core causes a perturbation in the Love’s
numbers values for waves having their frequency near the
resonance.
Therefore we carefully separate these waves from the other
ones by harmonic analysis. New invstigations are presently
under way at the International Earth Tide Center on six
very long series (3000 to 4000 days) obtained with quartz
horizontal pendulums to try to determine the fine structure
of the diurnal spectrum.
On the other hand, the measure of the eventual lag of the
tides with respect to the acting potential should give basic
informations on the viscosity of the Earth. The present
results show a clear regional distribution but the extension
of the world net will help to understand correctly this
effect.
B. Program of measurements
1. Results of 14 years observations (1960—1974)
A great part of these investigations have been conducted
under supervision or with support of the International