The problem of the secular deceleration of the Earth has been intensively studied in astronomy and geophysics in the frame of the evolution of the Earth/Moon/Sun system. In general, these studies are devoted to the different processes like mantle anelasticity or oceanic dissipation that can account for the braking of the Earth rotation; an important effort has also been undertaken in the observations to obtain the most accurate determination of this braking rate. Our contribution will mainly concern the various geodynamic consequences due to the secular deceleration. First we will consider the response of the fluid core when the mantle slows down. Then we investigate the radial and zonal deformation and related geometric and dynamic effects caused by changes in the rotational potential. The possibilities of resonant amplification in the Earth and core wobbles caused by forcing mechanisms related to the orbital motion of the Earth around the Sun supposed to be stable over geologic times are pointed out. Finally, possible implications of the secular change in the spin rate on the magnetic scaling laws, and especially on the history of the Earth magnetic field, are given.

Global Consequences of the Tidal Secular Deceleration for the Solid Earth and its Fluid Core

The purpose of this investigation is to i) give a review of the present status and conceptual evolution of height networks in America and Europe, ii) redefine path independent heights on a deforming earth, iii) develop temporal corrections to be applied to present day networks, iv) investigate the potential of terrestrial geodetic techniques as a tool to detect vertical crustal movements, v) formulate a classification of mathematical models to extract and represent the vertical displacement field of the earth, vi) present a survey of the changes that the geoid may experience in scale and shape, and vii) perform an actual computational example of temporal corrections to a height network in eastern Canada with temporal inhomogeneities in its levelling observations and reference surface. Recommendations are made for the redefinition of height networks regarding i) a selection of a height system,

Heights on a deforming earth

Rotational deformation of the earth — comments

The change in the inertia tensor of the Earth, due to the mass shift following a seismic event, has been computed by several authors for non-rotating earth models. Rotation is taken into account in the present paper, and the additional change in the inertia tensor is computed for an equivalent earth model, in which the axis of geometrical symmetry becomes tilted instead of the axis of greatest inertia. Rotation is thus seen to produce an increase by a factor 1.4 in the amplitude variation of the Chandler wobble, with respect to the non-rotating case, which, when added to the 1.4 amplitude increase due to the precessional re-adjustment of the equatorial bulge, gives a factor of 2 increase of the Chandler wobble amplitude with respect to the case of a rigid earth model.

Po-Yu Shen

Papers

Rotational deformation of the earth