Influence of Upper Mantle Anisotropy on Isotropic P‐Wave Tomography Images Obtained in the Eastern Mediterranean Region. Issue 8 (12th August 2020)

• Record Type: Journal Article
• Authors: Confal, Judith M.; Bezada, Maximiliano J.; Eken, Tuna; Faccenda, Manuele; Saygin, Erdinc; Taymaz, Tuncay
• Is Part Of: Journal of geophysical research. Volume 125:Issue 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-12
• Subjects: seismic anisotropy -- subduction tectonics -- seismic tomography -- Eastern Mediterranean -- upper mantle; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2019JB018559
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Seismic body‐wave tomography studies typically assume an isotropic upper mantle, possibly mapping anisotropy into artificial isotropic velocity anomalies in the resulting images. The Eastern Mediterranean with its oceanic, continental, and extinct subduction systems, as well as dense station coverage, provides an ideal setting to explore this issue. To examine the influence of seismic anisotropy, our study deals with both synthetic and real data inversions in which realistic seismic anisotropy models derived from 3D mantle convection simulations and shear wave splitting measurements are taken as a priori constraints. Spatial large‐scale velocity perturbations are mostly consistent between models derived with and without considering anisotropy. Small differences in the magnitude (up to 2%) and shape of velocity perturbations occur, and some structures are less diffuse when including anisotropy. Additionally, good backazimuthal coverage of teleseismic events and a larger data set improve the resolution of our model with respect to previous tomography studies and allow us to better interpret first‐order isotropic velocity anomalies. Key features, such as the half‐arc subducting oceanic plate in the southern Aegean and a wide and deep tear in the slab beneath southwestern Turkey, are clearly visible in all models. Our final tomography images also provide evidence for a shallow horizontal tear in the northern Hellenides and a vertical tear between two parts of the Cyprian slab. In eastern Anatolia, slab‐related high‐velocity anomalies are absent due to the continental collision and break‐off. Plain Language Summary: Understanding current and prior mantle flow in the upper mantle is fundamental for the reconstruction of plate tectonics. P ‐wave tomography is used as a method to monitor seismic velocity changes at great depths. These anomalies give clues about various geodynamic events, for example, downgoing plates and upwelling mantle material. However, whenever mantle flow is involved, intrinsically anisotropic minerals tend to align in certain directions, which makes the velocities directionally dependent and hence could lead to distortion of the results. Therefore, it may be important to include directional parameters in the calculations, to achieve a better resolution and a more accurate knowledge of the subsurface. Considering the effect of seismic anisotropy is particularly important in the very tectonically active region of the Eastern Mediterranean. We found that by including seismic anisotropy, the magnitude and geometry of some anomalies change but spatially large anomalies do not change significantly. We were able to recover the shape of the slab in detail and found evidence for break‐offs and tears in western Greece and Turkey, nearby Cyprus and eastern Turkey in all models. Key Points: Velocity perturbations show several tears and break‐off areas in the Hellenic and Cyprian slabs Main P‐ wave velocity perturbation features are similar in isotropic and anisotropy corrected models Discrepancies of up to ±2% between models highlight the importance of anisotropy to resolve small structures