PDF file - Laboratoire de Géologie de l'Ecole normale supérieure - Ens

X - 6 SIMONS ET AL.: GPS MEASUREMENTS IN S.E. ASIA TO REFINE SUNDALAND MOTION
sub-networks, conform to Table 1. For the campaign style observations,
most position outliers were due to seismic events, especially
in the Sulawesi region. The residuals are well within the range of
absolute accuracy indication given in the previous section. All of
the sites use a fixed antenna-setup, with the exception of the BAKO
monuments in Sulawesi, which were observed using tripods. Many
of these sites have poorer visibility and are located in/near deformation
zones, and therefore the residuals at these sites are slightly
higher w.r.t. to the linear trend fitted.
For the IGS sites used in the mapping, the residuals will be almost
identical to the ones of Table 3 (they were projected onto
their ITRF-2000 positions at each epoch, and only the weighting is
slightly different in the velocity estimation step). It is interesting to
look at the IGS sites in and near S.E. Asia that were not included
in the mapping, shown in Table 5. This gives another indication
on the quality of the mapping. Indeed, the IGS stations in Table 5,
located in and around the S.E. Asia network show good linear fits
with few outliers, and their performance is similar to that of other
regional and global sites. Only PIMO performs less well, caused
by the receiver problems due to the increased solar activity around
2000.
To illustrate the velocity estimation process, the result for MASS
station KUAL is shown in Figure 3, and demonstrates the robustness
and accuracy of the GPS data analysis presented here. Station
Table 6. Differences Obtained/ITRF-2000 IGS Station Velocities.
Shown are the velocity differences after subtracting the
ITRF-2000 velocity values from the ones estimated in this paper.
The top part is for IGS stations used in the mapping process,
while the bottom part is for IGS sites that were projected onto the
ITRF-2000 along with the S.E. Asia sites. In the remark section,
important events in the analyzed time series are given, and also
if a position jump was estimated during the linear trend fitting.
IGS Velocity differences (mm/yr) Remarks
Station North East Up
Used
ALGO -0.1 -0.1 -0.5
COCO 0.8 -0.6 0.4 before seismic event
FAIR -0.6 -0.3 2.0 seismic event / jump
GOLD 0.9 1.9 -6.2 seismic event / jump
GUAM -0.1 0.4 1.5 unknown event / jump
IISC -0.1 -0.3 0.1
KERG 0.9 0.2 2.8
KIT3 0.3 0.2 -1.7
KOKB -0.1 0.8 -1.1 antenna event / jump
KOSG -0.6 -0.6 1.6 antenna event / jump
KWJ1 -0.2 0.8 0.6
LHAS -0.3 1.7 2.7 relative new / noise
MAC1 -0.9 0.1 -2.4
MAS1 0.5 0.3 1.3
ONSA -0.7 -0.3 2.1
PERT 0.4 -0.1 3.3
TIDB 0.8 0.9 -4.7
TSKB -1.0 -0.1 -0.3 antenna event / jump
VILL 0.3 -0.2 1.5
WUHN -0.6 -0.7 -0.9
YAR1 -0.2 -0.3 -4.4
YELL 0.5 -0.4 0.6
Average 0.0 0.2 -0.1
RMS 0.6 0.7 2.5
Not used
BAKO 2.2 0.8 -8.1 improved wrt ITRF-2000
NTUS 3.7 0.3 0.7 improved wrt ITRF-2000
PIMO 29.1 -17.3 3.9 wrong in ITRF-2000
MKEA -0.4 0.1 -0.1 validation site
KARR 0.9 -0.5 2.8 validation site
SHAO -0.5 -0.1 -4.5 validation site
KUNM -0.5 0.5 5.3 validation site
DARW 2.9 -1.3 10.0 improved wrt ITRF-2000
XIAN -2.1 0.1 -2.3 new and few data
KUAL initially was a GEODYSSEA site, which was equipped with
a permanent receiver by DSMM at the end of 1998. One outlier
can be clearly noticed, for the 1997 measurement, due to a different
antenna used and/or a misalignment of the antenna setup. The
error estimates are 1-values, as they come out of the GPS data
analysis. The time series for the complete network are given at
http://www.deos.tudelft.nl/˜wims/sunda.html
In order to get more grip on the accuracy of the station velocities,
the obtained velocities for the IGS sites can be compared with
their velocities in ITRF-2000. The results are shown in Table 6. It
should be pointed out that in the GPS data analysis, the IGS sites
were nowhere constrained to both their ITRF-2000 positions and velocities.
The included IGS sub-network was only projected onto its
predicted positions using the ITRF-2000 for each campaign/weekly
averaged solution. Table 6 confirms that the mapping strategy was
stable throughout the time period the data was analyzed for. The
Figure 4. S.E. Asia 1994-2003 Velocities in ITRF-2000. The
error elipses are 3-values, and also the sites considered to be
located on rigid Sundaland are shown (open black dots).
Figure 5. Velocity residuals Sundaland sites w.r.t pole. The velocity
residuals are shown for both the (28) sites that are located
on rigid Sundaland (black dots) and the sites (19) that are located
in deformation zones near the Sundaland boundaries (red
crosses). The circle is drawn with a 3 mm/yr radius, which was
the treshold value to accept sites on rigid Sundaland.