The horizontal components of tectonic motion that have been estimated from the GSFC analysis of SLR data are plotted as white vectors on this map. The blue vectors represent the motions for the sites as given by the NUVEL-1A geologically determined plate motion model. The frame within which these motions are placed is defined mathematically such that, in an integrated sense, there is no uniform net rotation remaining (called a "no net rotation" frame, or NNR frame). One should keep in mind that this is a mathematical idealization and that these motions only approximate the velocity relative to a fixed mantle.
Across Europe, most of the results from the SLR analysis exhibit northeastward motion on the order of 25 to 30 mm/yr (a little more than an inch per year). The uncertainties for the velocities range from better than ±2 mm/yr to ±20 mm/yr. Th ese are shown as pink error ellipses centered at the tip of each vector. The size of these error ellipses is chiefly determined by the number of observations and length of time that the observations were taken.
Note that the vectors in the Greek and Turkish regions are not very well aligned with those predicted by the NUVEL-1A model. This is due to rather dramatic deformational processes ocurring across this region. One can get a better understanding of the defo rmation in this region via a simple thought experiment. Imagine a vector connecting the tip of a site's blue vector with the tip of it's white vector. This imagined vector represents what the motion of the site would be relative to fixed Europe (this is n ot true for the three sites in the lower right hand corner of the map since the blue vectors for these sites represent motions of other plates). In other words, if one were to "nail-down" the main body of Europe, these imagined vectors would represent the deformational motion relative to Europe. These are shown for the Aegean region in the figure below.
The vectors plotted in this map of Greece are now relative to fixed northern Europe. This provides a sense of how the crust in the Aegean is literally streching from north to south. The block of crustal material along the arc of islands in the southern Ae gean is overriding the African Plate. This is reflected in the southwestward motions for the SLR sites across the region.
Responsible NASA Official: Ben Chao
Original Web Implementation: John W. Robbins