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

Abstract

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.

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

“…We therefore interpret our observations, in conjunction with the findings of previous studies, to indicate that the SNAF represents a weak zone within the Sakarya crust that most likely localises deformation caused by local rotation of the Armutlu and/or Almacik Blocks as central Anatolia extrudes (e.g. England et al [2016]). c ⃝2018 American Geophysical Union.…”

“…In western Anatolia the pull exerted by subduction along the Hellenic arc is the predominant tectonic force in the region, exerting control over the extrusion velocity of the Anatolian peninsula (Flerit et al [2004]) and, as indicated by the GPS vector field (Reilinger et al [2006]), causing the rotation of the extruding plate. While the NNAF propagates in the Sea of Marmara as a single throughgoing dexteral strike-slip fault (Le Pichon et al [2001]), the propagation of the SNAF is less clear, suggesting that this branch of the fault might have been formed to accommodate the rotation of the Almacik and Armutlu blocks within the Anatolian plate (England et al [2016]). …”

“…However, the importance of these two tectonic events and the mechanisms that drive them in present day motion of the Anatolian peninsula are debated (e.g. Reilinger et al [2006]; Özeren and Holt [2010]; England et al [2016]). Geological evidence (Şengör et al [2005]) supports the notion that the NAFZ, after inception in eastern Turkey, progressed westward and only reached the Marmara Sea approximately 4…”

Constraints on North Anatolian Fault Zone Width in the Crust and Upper Mantle From S Wave Teleseismic Tomography

“…The inception of the North Anatolian Fault occurred between 13 and 11 Ma (Şengör et al, ) and came about due to the confluence of two factors: the push of the Arabian plate toward the Eurasian plate in the southeast and subduction along the Aegean arc in the west. However, the importance of these two tectonic events and the mechanisms that drive them in present‐day motion of the Anatolian peninsula is debated (e.g., England et al, ; Özeren & Holt, ; Reilinger et al, ). Geological evidence (Şengör et al, ) supports the notion that the NAFZ, after inception in eastern Turkey, progressed westward and only reached the Marmara Sea approximately 4 Ma ago (Le Pichon et al, ).…”

Constraints from GPS measurements on the dynamics of the zone of convergence between Arabia and Eurasia

“…For example, the observed velocities near the southwest Caspian coast (segment SWC, Figure ) have a larger northerly component than do the calculated velocities; these misfits would be reduced by a corresponding increase in the northerly component of velocity on this section of the boundary. England et al [] demonstrated the viability of reducing residuals by local adjustments to the boundary conditions, and the insensitivity of the overall solution to such adjustments, but we do not repeat that exercise here.…”