3A. A gravimetric method to determine stress related glacial isostatic adjustment in Fennoscandia

The Earth’s gravity field is a basic geophysical parameter that reflects the
Earth’s mass distribution and its changes with time. As the Earth is not a rigid
body but is constantly changing under the influence of external and internal
forces, the gravity field and its changes with time are of great significance for
studying various geodynamic and geophysical processes. The Earth’s temporal
deformations can be divided into secular, periodic and episodic (suddenly
accelerating or decelerating) phenomena. Our knowledge about the causes
and effects of these deformations vary, and, as one example, frequently a
longperiodic deformation is interpreted as a secular one. Some phenomena
such as Earth tide and Glacial isostatic Adjustment (GIA) have been observed
systematically for long time and are relatively well understood. Mass changes
in the Earth causes the Earth’s crust not only to move vertically, but also
horizontally and to tilt, and a major stress in the lithosphere is a likely precursor
of earthquakes. Here we use a gravimetric approach to model stress in the
Earth’s mantle and its temporal changes caused by GIA in Fennoscandia.
The result is useful in studying how changes of stress influence the stability
of faults and also in investigating whether postglacial rebound is the origin of
earthquakes. The outcome of this study is an alternative approach to studying
stresses and displacements as the responses to assumed ice load and Earth
modells. We show that the determined horizontal stress is correlated with
a land uplift model, and the secular rate of change of the horizontal stress
determined by GPS, is larger outside of the uplift dome than inside, of about
60 KPa/year.