Constraints from GPS measurements on the dynamics of deformation in Anatolia and the Aegean

We estimate the strength of the lithosphere in Anatolia and the Aegean, and the boundary forces acting upon it, using a dynamical model that treats the lithosphere as a thin fluid sheet deforming in response to variations in gravitational potential energy. This model has one free material parameter, the power law exponent, n, of the vertically averaged rheology of the lithosphere, and two parameters that specify the forces per unit length applied to its edges. Solutions to this model that best fit the velocities of 346 reliable GPS sites require an effective viscosity of the lithosphere of 1022 to 1021 Pa s at strain rates of 10 to 100 nanostrain per year. The best-fitting force at the Arabia-Anatolia boundary is consistent with the lithostatic pressure due to the high topography there, and the force at the Nubia-Aegean boundary is consistent with the contrast in lithostatic pressure across that boundary. No additional force, from “slab rollback” or basal tractions due to convection in the mantle, is required to explain the observations. These results are supported by scaling relations derived from approximate analytical solutions. The inverse relationship between the viscosity of the lithosphere and deviatoric stress produces strong slowly deforming regions in the Southern Aegean and Central Anatolia whose motions resemble those of microplates. The distribution of geodetic strain rates within the region, and the partitioning between normal and strike-slip faulting, are explained by the interplay between boundary conditions, internal variations in gravitational potential energy, and the power law rheology of the lithosphere

Morphology, displacement and slip rates along the North Antolian Fault (Turkey)

Geological and geomorphological offsets at different scales are used to constrain the localization of deformation, total displacement, and slip rates over various timescales along the central and eastern North Anatolian Fault (NAF) in Turkey. The NAF total displacement is reevaluated using large rivers valleys (80 ± 15 km) and structural markers (Pontide Suture, 85 ± 25 km; Tosya-Vezirko ̈pru ̈ basins, 80 ± 10 km). These suggest a Neogene slip rate of 6.5 mm/yr over 13 Myr. The river network morphology shows offsets at a range of scales (20 m to 14 km) across the main fault trace and is also used to estimate the degree to which deformation is localized. At a smaller scale the morphology associated with small rivers is offset by 200 m along the NAF. The age of these features can be correlated with the Holocene deglaciation and a slip rate of 18 ± 3.5 mm/yr is determined. This is consistent with a rate of 18 ± 5 mm/yr deduced independently from the 14C dating of stream terrace offsets. Over the short term, GPS data gives a similar rate of 22 ± 3 mm/yr. All our results tend to show that most of the deformation between the Anatolian and Eurasian lithospheric plates has been accommodated along, or very close to, the active trace of the NAF. The difference between the Neogene and the Holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the NAF. INDEX TERMS: 8107 Tectonophysics: Continental neotectonics; 8158 Tectonophysics: Plate motions—present and recent (3040); 7230 Seismology: Seismicity and seismotectonics; KEYWORDS: North Anatolian Fault, slip rate, total offset, strain localizatio

Late Cenozoic reorganization of the Arabia-Eurasia collision and the comparison of short-term and long-term deformation rates

The Arabia-Eurasia collision deforms an area of ∼3,000,000 km2 of continental crust, making it one of the largest regions of convergent deformation on Earth. There are now estimates for the active slip rates, total convergence and timing of collision-related deformation of regions from western Turkey to eastern Iran. This paper shows that extrapolating the present day slip rates of many active fault systems for ∼3–7 million years accounts for their total displacement. This result means that the present kinematics of the Arabia-Eurasia collision are unlikely be the same as at its start, which was probably in the early Miocene (16–23 Ma) or earlier. In some, but not all, active fault systems, short-term (∼10 year) and long-term (∼5 million year) average deformation rates are consistent. There is little active thickening across the Turkish-Iranian plateau and, possibly, the interior of the Greater Caucasus. These are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening, and where there are structural and/or stratigraphic data for pre-late Miocene deformation. We suggest that once thick crust (up to 60 km) built up in the Turkish-Iranian plateau and the Greater Caucasus, convergence took place more easily by crustal shortening in less elevated regions, such as the Zagros Simple Folded Zone, the South Caspian region and foothills of the Greater Caucasus, or in other ways, such as westward transport of Turkey between the North and East Anatolian faults. The time and duration of this changeover are not known for certain and are likely be diachronous, although deformation started or intensified in many of the currently active fault systems at ∼5 ± 2 Ma