Crustal deformations at permanent GPS sites in Denmark

1
Crustal deformations at permanent GPS sites in
Denmark

• Shfaqat Abbas Khan and Per Knudsen, Geodetic
  Dept., Kort Matrikelstyrelsen, Rentemestervej
  8, Copenhagen NV, Denmark. E-mail sak_at_kms.dk
• Carl Christian Tscherning, University of
  Copenhagen, Department of Geophysics, Juliane
  Maries Vej 30, Copenhagen Ø, Denmark. E-mail
  cct_at_gfy.ku.dk

Abstract Permanent GPS sites in Denmark and the
surrounding countrys are used in order to study
crustal deformations. The Danish GPS sites have
been operating since early 1999 and more than 3
years of continuous GPS data is available. Using
the Bernese software, we have calculated daily
baseline solutions between the selected GPS
sites. The time series of the baseline solutions
are then used in order to calculate relative
three-dimensional crustal motions (vertical and
horizontal). The time series are analysed for
post glacial rebound. The observed relative
motions due to glacial updrift are consistent
with modelled adjustments of the glacial
isostatic of Fennoscandia. The glacial rebound
modelling is carried out by Milne et al., 2001.
Data Analysis The data was processed using the
Bernese 4.2 software Beutler et al, 2000. Phase
ambiguities were solved and kept fixed. Pole
tide, solid earth tide and ocean tide loading
corrections were applied. Precise IGS satellite
orbit solutions were used and troposphere
corrections were applied. The daily baseline
solutions were processed for all the baseline
combinations between the selected 5 GPS sites. In
addition, Onsala were kept as fixed station.
Hence, all the deformational rates displays here
are relative to Onsala. Figure 2 is an example of
baseline time series between Onsala and Buddinge.
Locations of the sites are shown in figure 1. The
figure also displays horizontal deformation rates
observed using GPS. Furthermore, figure 3
displays modelled postglacial rebound (Milne
model). The figure is adopted from the homepage
of Hans Georg Scherneck. http//www.oso.chalmers.s
e/hgs/ The vertical deformation rates for the
GPS solutions are listed in table 3. The observed
relative motions due to glacial updrift are
consistent with modelled adjustments of the
glacial isostatic of Fennoscandia. However, the
updrift rate for BUDP seems to be too low.
Moreover, the horizontal rates are consistent for
all stations.
Site Vertical Std. North std East Std
mm/yr mm/yr mm/yr mm/yr mm/yr mm/yr
ONSA -0.26 0.22 -0.23 0.05 -1.45 0.13
POTS -1.86 0.18 0.77 0.04 -0.63 0.13
BUDP -2.44 0.20 0.58 0.04 -0.49 0.12
SMID -1.23 0.20 0.15 0.04 -0.44 0.12
SULD -0.72 0.20 -0.03 0.04 -1.07 0.12
Figure 1 Observed postglacial rebound
(horizontal deformations) at danish GPS sites
Table 1 Relative deformational rates observed by
GPS for the selected sites.
Conclusion The study concerning crustal
deformation in Denmark is ongoing and will be
carried out in more details in the future. Here,
we have ignored non-glacial internal deformations
between the selected sites. However, these
effects will be taken into account in future
studies, when longer GPS time series are
available. Here, we have used Onsala as reference
station. Hence, all the results are dependent on
how well post glacial rebound is determined for
Onsala. However, in the future work more stations
will be considers and we will look for a more
regional network than the local one presented
here.
References Johansson, J. M., J. L. Davis, H.-G.
Scherneck, G. A. Milne, M. Vermeer, J. X.
Mitrovica, R. A. Bennett, B. Jonsson, G. Elgered,
P. Elósegui, H. Koivula, M. Poutanen, B. O.
Rönnäng, and, I. I. Shapiro, Continuous GPS
measurements of postglacial adjustment in
Fennoscandia 1. Geodetic results, Journal
Geophys. Research, vol. 107, B8, 10.1026,
2002. Milne, G.M.,  J. L. Davis, Jerry X.
Mitrovica, H.-G. Scherneck, J. M. Johansson, M.
Vermeer, H. Koivula, Space-Geodetic Constraints
on Glacial Isostatic Adjustment in Fennoscandia,
Science, Vol. 291, 2001.
Figure 3 Modelled postglacial rebound (Milne
model) The figure is adopted from the homepage of
Hans Georg Scherneck. http//www.oso.chalmers.se/
hgs/
Figure 2 Time series of daily GPS solutions for
the baseline from Onsala (ONSA) to Buddinge
(BUDP)