NATIONAL REPORT OF THE FEDERAL REPUBLIC OF ... - IAG Office

In Europe, there are detailed investigations on vertical
crustal movements covering the whole continent and concentrating
on specific regions, respectively. Long time
series of continuous GPS observations, principally within
the European Reference Frame (EUREF) provided by H.
HABRICH, BKG, were used to study atmospheric loading
effects and to derive local regression coefficients between
the atmospheric pressure and vertical displacements
(KANIUTH and HUBER, 2003, 2004; KANIUTH and VETTER,
2006). Ocean loading is a strong effect of vertical motions
at coastal sites, which can be estimated from GPS observation
data (KANIUTH and VETTER, 2005). RICHTER et al.
(2004) combined space geodetic results (GPS and VLBI)
with absolute gravimetric observations in Medicina, Italy,
and found high correlations but also interesting discrepancies.
Investigations on regional crustal movements outside
Europe concentrated primarily on South America. DREWES
et al. (2005) compared the results of two continental GPS
campaigns of the SIRGAS project 1995 and 2000 to derive
3D station displacements. These results entered into a
continental deformation model derived by a combination
of the finite-element method and a geodetic collocation
approach (DREWES and HEIDBACH, 2005). The number of
continuously observing GPS stations in South America has
strongly increased during the last years (SEEMÜLLER and
DREWES, 2004). Time series of weekly station coordinates
and velocities from multi-year solutions were provided by
SEEMÜLLER et al. (2004). Environmental effects and local
displacements were studied by KANIUTH and STUBER
(2005) in two GPS stations at the IGS site Bogotá,
Colombia.
Theoretical studies
The application of satellite gravity missions for monitoring
vertical crustal deformations due to hydrological mass
loading requires the detailed investigation on the complex
relations between the mass displacements and gravity
variations. KUSCHE and SCHRAMA (2005) studied inversion
by comparing time series of the GRACE gravity field with
those of the global GPS network. RAMILLIEN et al. (2005)
recovered the surface-water masses by the inversion of
GRACE geoid models. Other authors (e.g., SCHMIDT et al.
2006) used these models for the representation of mass
variations and subsequent vertical crustal movements by
suitable mathematical functions.
In a theoretical study concerning glacial-isostatic adjustment,
KLEMANN et al. (2003) deal with the appropriate
consideration of compressibility in viscoelastic earth
models. Deriving analytical solutions for the load-induced
perturbations of a homogeneous half space, they showed
that the solution to the problem involves several types of
singularities. In addition, Rayleigh-Taylor instabilities
resulting from internal buoyancy arise. These compressibility
effects correspond to those recently analysed by
Vermeersen and Hanyk for a homogeneous viscoelastic
sphere. In a further theoretical study, MARTINEC (2007)
derived the propagator matrix for the response of a multilayered
viscoelastic sphere to surface toroidal traction in
H. Drewes, D. Wolf: Crustal deformation and Geodynamics 81
analytical form. The solution is suitable for testing the
performance of numerical algorithms for computing GIA.
Statistical analyses of the components of the strain tensor
in southern and western Europe derived from space geodetic
observations were presented by CAI and GRAFAREND
(2007a). They applied the method to studies of the strain
in Fennoscandia. RIEDEL et al. (2007) developed an
approach for the analysis of landslides from differential
InSAR measurements.
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