Global Positioning System observations in the Alps have now sufficient
precision to reliably observe vertical surface movement rates at the orogen scale. The
geodynamic modeling of converging plate margins requires constraints on the origin
of orogenic uplift, of which the two end members are pure crustal uplift and crustal
thickening, respectively. Gravity change rates joint with uplift measurements allows
to distinguish the two mechanisms. We use vertical uplift rates over the Alpine range
and the southern foreland basin, to predict the gravity change for different
geodynamic hypotheses of pure uplift and mantle inflow, or crustal thickening and
isostatic Moho lowering. The sensitivity of gravity as a tool to distinguish the two
mechanisms is investigated. This model differs from the predicted isostatic
movements, based on the glacial history and the mantle viscosity, since the uplift is
measured and not predicted. The estimate of this tectonic signal is important, when
gravity change rates, as those obtained from GRACE, are interpreted exclusively in
terms of hydrologic changes tied to climatic variation. It has been already shown that
in some areas, as the Tibetan plateau and the Himalayas, the tectonic signal is not
negligible. Here we estimate the effect of the tectonic signal for the uplift of smaller
mountain ranges, as is the Alpine arc. Our results indicate that tectonic and
hydrological signals superpose and we cannot ignore the tectonic signal when using
GRACE to invert for the equivalent water height (EWH).
