Crustal deformations in the Mediterranean area computed from SLR and GPS observations

Space geodesy provides an efficient technique to determine contemporary crustal deformations. This paper discusses the computation of tectonic motions in the Mediterranean area from observations acquired by Satellite Laser Ranging (SLR) and Global Positioning System (GPS) instruments. The SLR contribution is based on measurements on LAGEOS-1, taken in the period September 1983 to December 1992. For this analysis, the period was divided into 38 consecutive intervals. An independent station coordinates solution was computed for each subinterval. During this 9.3 year interval, the WEGENER project organized four mobile SLR observation campaigns in the Mediterranean region, resulting in three or four independent position solutions for the majority of the sites in this area. The GPS contribution is based on observations taken during the Euref'89 campaign, which took place from May 16 to 28, 1989, and during the WEGENER/GPS-92 campaign, which took place from July 29 to August 3, 1992, as a sub-campaign for the IGS Epoch'92 campaign. Most of the space-geodetic reference points in the Mediterranean area were occupied with GPS receivers during both campaigns, providing two valuable additional position solutions. The time-series of position solutions for each station are converted into individual station motion vectors. The horizontal components of the latter reveal a clear and consistent picture of the deformations taking place in the area: the northward motion of Arabia, the lateral escape to the west of Anatolia, the NE-SW expansion in the Aegean Basin and the northward motion of Africa being transduced into the central part of the Mediterranean. The results are in agreement with the qualitative kinematical models for this region, derived from geophysical evidence. The vertical station motion solutions are generally very small and insignificant from a statistical point of view. The internal and mutual consistency of the independent SLR and GPS network solutions is also investigated. The agreement is shown to be at the level of 5-20 mm.