Numerical simulation of 3-D mantle flow evolution in subduction zone environments in relation to seismic anisotropy beneath the eastern Mediterranean region

Abstract

Abstract Seismic anisotropy is a key parameter in understanding subduction zone dynamics in relation to the recent deformation history. It is usually controlled by the mantle flow patterns resulting from the dynamic interactions between a relatively dense subducting oceanic plate and the surrounding mantle. A proper modelling of mantle flow in subduction systems helps our understanding of the seismic anisotropy source, strength and evolution in time. This study further examines shear wave splitting parameters, one of the most well established measuring methods of seismic anisotropy, and their anisotropy source, based on 3-D geodynamic modelling, applied to the eastern Mediterranean Sea and Anatolia. Our model setting is chosen to be a first order representation of the present-day tectonic setting as it consists of a deforming Anatolian micro-plate, that is indented by slow moving African and Arabian plates, and an oceanic plate in between. The retreat of the slab in the Aegean region, the alleged tear in the subducting slab close to the Cyprus trench and the break-off in the slab in eastern Anatolia are considered in our modelling study in order to further explore their influence on mantle flow and splitting parameters. The synthetically calculated fast polarization directions (FPDs) mostly showed a reasonable matching with those inferred from previous seismological observations that are mainly SKS splitting measurements. Regions of FPD similarities between synthetic and observed shear waves mostly indicate N–S to NE–SW orientations of fast shear waves, which are parallel to the extension in the back-arc region and in general perpendicular to the trench. The pattern of FPDs seems to be more complex nearby the trench. Our modelling results suggest that the development of a tear in the African slab and the detachment occurring within the Arabian plate (break-off) appear to have a significant influence on the FPDs due to stronger mantle flow through the slab windows. The mantle flow through the tear close to Cyprus and the break-off in the East can be identified clearly, despite their recent appearances. A circular pattern around the edges of the slab can be observed as well as disruptions of the overall general fast polarization direction due to the flow through the tear.