FINAL GEODETIC RESULTS OF THE GEODYSSEA PROJECT: THE COMBINATION SOLUTION
AMBROSIUS 1), B.A.C., D. ANGERMAN 2), M. BECKER 3), P. NEUMAIER 3), R. NOOMEN 1), E. REINHART 3), W.J.F. SIMONS 1), C. VIGNY 4), A. WALPERSDORF 4), P. WILSON 2)
The GPS measurements acquired in the framework of the GEODYSSEA project have
been processed by four different analysis groups, using various software
packages and applying different analysis strategies. The data were collected
during two 5-day campaigns in November/December 1994 and in April 1996. The main
network consists of 41 designated GEODYSSEA stations covering the region of the
triple junction of the Eurasian, Philippine and Indo-Australian tectonic plates.
In addition, data were used from 4 more stations on the Indo-Australian plate
and from 5 IGS stations around the area. The computations resulted in four
independent series of unconstrained daily station coordinate solutions for the
complete network. Day-to-day repeatability of the coordinates was found to be
of the order of 3 to 5 mm for the north and east components and 9 mm for the
vertical.
In the following step, these results were merged into separate combination
solutions for each of the two campaigns. This was done in a careful analysis and
weighting process, using special software. It provided a unique possibility to
cross-check the performance of the different software packages and to identify
anomalous results in the individual solutions. Allowing for systematic effects,
the various solutions were found to be quite consistent, the rms differences
being even less than the day-to-day repeatability, i.e. 2.5, 4 and 7 mm,
respectively.
Finally, a kinematic model for the motion of the stations was derived from the
differences in the station coordinates between the two combined solutions. The
observed displacements range from a few millimeters up to more than one meter.
Although the results are only based on two campaigns, the accuracy appears to be
remarkably good. An important indication for this is the strong coherence
between the recovered velocity vectors of individual stations located on the
same tectonic block. Also, for the more stable regions the observed horizontal
motions are in close agreement with the motions predicted by global plate
tectonic models. The overall uncertainty of the horizontal velocities is
estimated to be about 2 - 3 mm/yr. The results provide significant new
information on the precise location of the active plate boundaries, deformation
processes in the Sulawesi region and tectonic activities in the Philippine
archipelago. Also, several 'anomalies' in the results have been related to
earthquakes in the vicinity of some of the stations during the one-and-a-half
year interval between the observations.
The coordinate solutions and velocity fields described in this paper represent
the 'official' final geodetic results of the GEODYSSEA project.
1) Delft University of Technology (DUT), Delft, the Netherlands
2) GFZ, Potsdam, Germany
3) IfAG, Frankfurt, Germany
4) Ecole Normale Superieure, Paris, France
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