Deformations between African and Euroasian plates from the

Deformations between African and Euroasian
plates from the methods of space geodesy
Zeman A. (1), Kostelecký J. (1,2), Kostelecký J. (jr.) (2), Ryšavý V. (1)
(1) Czech Technical University in Prague, Faculty of Civil
Engineering, Thakurova 7, 166 29 Praha 6, Czech Republic
(2) Research Institute of Geodesy, Topography and Cartography,
Zdiby 98, Czech Republic
SUMMARY
On the basis of the results of GPS observations in the EPN network
and the results presented in the frame of the coordinate system
ITRS2000 and using the apparatus of the mechanics of continuum,
the regions of possible mutual interactions of the Euroasian and
African plates are detected.
1. INTRODUCTION
In (Zeman et al., 2005) the GPS data of 143 sites of the EUREF
(EUropean REference Frame) permanent network (EPN) realized in
time interval 1996-2002.8, i.e nearly 7 years interval, were analyzed.
Horizontal shifts were analyzed relatively to specially defined
coordinate system of 10 sites at stable part of central Europe, which
would have to represent zero motion with respect to the Euroasian
plate. The sites were chosen to fulfil certain criteria, which were
described at above mentioned paper. Analyzed horizontal shifts so
represent the relative values just to system defined like this.
In present contribution the zero motion is defined other way
according to criteria from paper (Kenyeres A., 2004). From these
criteria follow partly possibility of more universal comparison with
the results of other analytic centers, partly it is apparent that the
result of analyses of horizontal shifts are rather different from
previous paper (Zeman et al., 2005).
Not to be fixed to subjectively defined systems we used as in
previous paper so in present analyses the computations following
from the theory of continuum mechanics giving invariant values of
tensors of deformation, even if we kept in mind – see (Kostelecký J.
(jr.), 2000) that we commit the great geodynamic simplification
because Europe can not be as continent considered as a continuum
from the point of view of continuum mechanics. Tensors of
deformation were computed for 143 sites of the EPN in (Zeman et
al., 2005).
Figure 2
In previous paper (Zeman et al., 2005) we also applied continuum
mechanics theory to the sites of ITRF2000 (current reference
realization of the ITRS).
Realizations of the ITRS (International Terrestrial Reference
System) are produced by the IERS (International Earth Rotation
Service) ITRS Product Center (ITRS-PC) under the name
International Reference Frame (ITRF).
Results of this analysis which include new sites in Alpine region
were compared with older model ITRF97. Greater changes in this
region based on ITRF2000 were detected due to these new GPS
stations – see Fig. 4.
Figure 4
In present contribution there are the data of EPN sites, which can
be find at previous paper and new sites to the year 2006 were
analyzed. Analysis is concentrated on the region of Mediterranean
Sea with aim to obtain information on basic geodynamic activity of
the region of contact line between African and Euroasian plate
(horizontal shifts and tensors of deformation). Plate tectonics
borders between these elements are defined from the results of
geodynamic, geophysical and other observations as estimated
contact line – see following figures. Dynamic of this line given
from the results of analyses of geodetic methods is just the main
aim of this contribution.
2. NEW EUREF EPN
In the paper (Zeman et al., 2005) 143 sites were analyzed, in present
contribution there are 165 sites used, but it is necessary to know that
11 sites were eliminated and 33 added. The reason for elimination of
the sites is either problems with quality or removing of the GPS
antenna of the station. The stations added see Fig. 5.
BOGI
DARE
INVE
MORP
PRAT
SMID
VLNS
BUDP
GANP
JOZ2
MSEL
QAQ1
SPTO
WARN
BUTE
HERT
KATO
NEWL
REDU
SULD
ZOUF
CAGZ
HOER
KRAW NYPR
SASS
THU3
MIKL
SKEO
TUC2
COMO IENG
OBET
Figure 5
The coordinates of EUREF permanent network (EPN) sites were
analyzed to find the secular time changes. Analysis is based on
weekly combined solution of EPN using method of finding jumps,
trends and periodicities. The input data was read from weekly
combined SINEX solutions of the EUREF permanent network (EPN)
as quasi-observations. All network stations which were included
provided their time series at least half year long (26 weeks). During
the processing of combined SINEX solution by CATREF software
short period effects of ocean loading and daily change of atmospheric
pressure were averaged and removed.
Findings and conclusions in this contribution are based on discrete
values of interpolated annual horizontal shifts and interpolated
tensors of deformation. These two quantities depend on annual
horizontal shifts of each station in EPN, which are a partial results of
analyses and are distributed in N/E/Up system.
Every interpolated annual horizontal shift was computed by special
procedure from all annual horizontal shifts within the 20° radius.
Interpolated tensors of deformation were obtained by basic
relationship:
ε jk
1  ∂u j ∂uk
=
+

2  ∂xk ∂x j

,


where
• ∂u j is partial derivative of interpolated annual horizontal shift
∂xk component u with respect to
xk ,
j
•
the range of the indices is 1,2.
Partial derivatives of interpolated annual horizontal shifts were
computed from field of discrete values numerically.
Because of the size of the area of interest, the curvature of
reference shape could not be neglected and tensors of deformation
had to be transformed to spherical coordinates.
2.1 EUREF EPN FOR THE WHOLE
EUROPE
Fig. 6 informs about basic tendency of global horizontal shifts of the
sites of EUREF EPN shared with Euroasian plate. Shifts are in
principle at NE direction and reach the values greater than 20 mm per
year on the average. It is interesting that only several sites in region of
contact between African and Euroasian plates (Turkey, Greece) show
different (predominantly) tendency of horizontal shifts.
Figure 6
After filtering of average value of horizontal shift of Euroasian
plate residual vectors of horizontal shifts witness still more
prominent about fundamental (regional) tendencies of the EPN sites
– see Fig. 7 . Surface information give interpolated values in Fig. 8.
Figure 7
Figure 8
Independent on subjectively defined average horizontal shift of the
Euroasian plate is derivation of tensor of deformation for EPN sites
(including new sites). Fig. 9 gives information which is not at
variance with the information on horizontal shifts. Significance
(accuracy of determination) of the analyzed values follows from the
fact that not even their testing with 10 sigma error ellipses bring
(except for the stations in western Europe) their elimination.
Figure 9
2.2 EAST MEDITERRANEAN PART
OF EUREF EPN
More detailed information on fundamental horizontal movements
tendencies in East Mediterranean at the contact regions of African,
Euroasian and still Arabic plates show Figs. 10, 11 and 12.
Figure 10
Figure 11
Figure 12
2.3 EAST MEDITERRANEAN PART OF
EUREF EPN WITHOUT TUC2 SITE
To emphasize significance of one station for correct interpretation
of movement tendencies, the analyses were performed without the
station TUC2 on Crete. This site is on the list of new stations and its
parameters of stability, observations and others are on high quality
level – see Figs. 13 and 14.
Figure 13
Figure 14
Moving tendencies of this site significantly complete information
about the rotating movements at the region of east Mediterranean
– see Figs. 15 and 16. As it is clear from these Figures, important
role would play stations on the northern regions of Africa if they
would be at disposal.
Figure 15
Figure 16
3 CONCLUSIONS
Significant are above all following findings:
• significant shifts of the sites with tendency of counterclockwise
rotation in the region of East Mediterranean represented by the
stations inland of Turkey, Crete, Israel,
• significant tendency to residual clockwise rotation in the region
of Apennines peninsula (Italy) and Adriatic sea,
• demonstrable is also moving tendencies of the sites in western
Africa, Spain and Azores toward to west and in northern
Atlantic towards to east,
• middle and north Europe is the region without significant
tendencies of horizontal shifts.
Comment:
Of course it is necessary to consider possible false residual
information following from the definition of the system, which fix
whole movement of Euroasian plate.
REFERENCES
• Zeman A., Kostelecký J., Kostelecký J. (jr.) (2005): Detection of
the Deformations on the Contact Line between African and
Euroasian Plates from the Methods of Space Geodesy. Presented on
EGU 2005 General Assembly, 24-29 April 2005, Vienna, Austria.
•Kenyeres A. (2004): Contribution of the Time Series SP to the
European Velocity Field Project. EUREF 2004 Symposium, 2-5
June 2004, Bratislava, Slovakia,
http://www.epncb.oma.be/_dataproducts/timeseries/index.html
REFERENCES
• Kostelecký J (jr.), Kostelecký J., Zeman A. (2000): Relative
Changes in Station Position on the Territory of Europe Derived
from the Results of Space Geodesy Techniques and an Attempt of
Geodynamic Interpretation. Reports on Geodesy, No. 6 (52), WUT
Warsaw, 111-117, 2000.
• Kostelecký J., Zeman A. (2004): Horizontal and Vertical
Displacements of the Stations within the Frame of the Individual
Plates Based on the ITRS2000 Reference System. Acta Geodyn.
Geomater. Vol. 1, No. 3(135), 133-143, 2004.