The Special Bureau for Mantle of IERS's
is established to provide services for information and data exchange to
facilitate research in the geodynamic effects due to motions in the mantle.
Accounting for 68% of the mass and 89% of the moment of inertia of the
entire Earth, the solid, but non-rigid, mantle is perpetually in motion.
There are motions caused by external forces, including tidal deformation,
atmospheric and oceanic loading, and occasional meteorite impacts. For
internal processes, volcanic eruptions and pre-seismic, coseismic and post-seismic
dislocations associated with an earthquake act on short timescales. On
longer timescales, present-day post-glacial rebound, surface processes
of soil erosion and deposition, and tectonic activity such as plate motion,
orogeny, and internal mantle convection, all transport large masses over
long distances. Finally, the entire solid Earth undergoes an equilibrium
adjustment in response to the secular slowing down of the Earth's spin
due to tidal friction.
As with any geophysical processes that involve mass transports, these large-scale motions produce variations in Earth's rotation, gravity field, and geocenter. Among them, however, currently only two topics have been extensively investigated:
Co-seismic Excitation of Earth Rotational and Gravitational Changes (B. F. Chao and R. S. Gross)