Long-wavelength undulations of the seismic Moho beneath the strongly stretched Western Anatolia

Abstract

SUMMARY Western Turkey provides spectacular examples of the two end-member models of deformation of the continental lithosphere, with strain localization along the North Anatolian fault and distributed north–south extension along the Aegean coast. To provide constraints on the mechanisms of continental deformation, we present a new high-resolution image of lithospheric structurealonga ∼650kmtransectcrossingWesternAnatoliaat28 ◦ ElongitudefromtheBlack Sea to the Mediterranean. More than 2600 receiver functions are computed from records of teleseismic earthquakes at 40 broadband seismic stations with an average spacing of 15km. Lateral variations of crustal thickness and Vp/Vs ratio are inferred from both H-k and common conversion point stacks. We observe long-wavelength variations of Moho depth from ∼31km in the Thrace basin to ∼25km beneath the Marmara Sea, ∼32km beneath the Izmir–Ankara suture, ∼25km beneath the Menderes Massif and ∼20km on the coast of the Mediterranean. No mid- or lower-crustal interface is visible in the migrated depth section and seismic discontinuities are confined to the shallow crust. The small-amplitude and long-wavelength lateral variations of the Moho topography suggest that viscous flow in a hot lower crust has smoothed out the lateral variations of crustal thickness induced by Cenozoic continent–continent collision.Thecrust–mantleboundaryisflatbeneaththecentralandsouthernMenderesMassif.The rougher Moho topography and more heterogeneous crust of the Marmara region likely result from transtension in the North Anatolian Fault Zone superimposed onto Aegean extension. The Moho of the subducted African lithosphere is observed dipping northward between ∼40 and ∼60km depth at the southern end of the profile. The abrupt termination of the subducted slab only 50km to the north of the Mediterranean coast confirms the slab tear inferred from previous tomographic studies.