Deformation of western Turkey from a combination of permanent and campaign GPS data: Limits to block-like behavior

摘要

We present a new geodetic velocity field covering western Turkey, south of the North Anatolian fault. Our velocity field is derived from a combination of continuously recording GPS stations operating since 2003, survey-type GPS measurements carried out in the period 1997-2005, and velocities from Reilinger et al. (2006). The velocity field indicates that western Turkey currently undergoes extension whose rate increases from the Anatolia plateau to the Aegean coast. The overall extension in westernmost Turkey is about 20 rnm/yr, making it one of the fastest areas of continental extension in the world. We test whether the observed deformation is better represented by the rotation of crustal blocks or by more distributed deformation. While no deformation is detected in the central Anatolian plateau, we observe a deformation field west of the plateau that cannot be explained by block models, unless the blocks are so small as to be essentially indistinguishable from a continuum. Although concentration of strain rates (up to 140 nstrain/yr) are found across the major grabens, strain rates above 50 nstrain/yr are found throughout western Turkey. The distributions of topography and crustal thickness in western Turkey agree with the distributions expected if the crust there had a constant thickness at 5 Ma, equal to that of the present central Anatolian plateau, and had subsequently been thinned at the present-day distribution of strain rates. Our results, therefore, suggest that extensional strain affects the whole continental lithosphere of western Turkey, rather than being restricted to a small number of block boundaries.