  Gravimetric methods are expected to play a decisive role in geophysical
modeling of the regional crustal structure applied to geoneutrino studies. GIGJ
(GOCE Inversion for Geoneutrinos at JUNO) is a 3D numerical model constituted
by ~46 x 10$^{3}$ voxels of 50 x 50 x 0.1 km, built by inverting gravimetric
data over the 6{\deg} x 4{\deg} area centered at the Jiangmen Underground
Neutrino Observatory (JUNO) experiment, currently under construction in the
Guangdong Province (China). The a-priori modeling is based on the adoption of
deep seismic sounding profiles, receiver functions, teleseismic P-wave velocity
models and Moho depth maps, according to their own accuracy and spatial
resolution. The inversion method allowed for integrating GOCE data with the
a-priori information and regularization conditions through a Bayesian approach
and a stochastic optimization. GIGJ fits the homogeneously distributed GOCE
gravity data, characterized by high accuracy, with a ~1 mGal standard deviation
of the residuals, compatible with the observation accuracy. Conversely to
existing global models, GIGJ provides a site-specific subdivision of the
crustal layers masses which uncertainties include estimation errors, associated
to the gravimetric solution, and systematic uncertainties, related to the
adoption of a fixed sedimentary layer. A consequence of this local
rearrangement of the crustal layer thicknesses is a ~21% reduction and a ~24%
increase of the middle and lower crust expected geoneutrino signal,
respectively. Finally, the geophysical uncertainties of geoneutrino signals at
JUNO produced by unitary uranium and thorium abundances distributed in the
upper, middle and lower crust are reduced by 77%, 55% and 78%, respectively.
The numerical model is available at http://www.fe.infn.it/u/radioactivity/GIGJ
