<p>The fundamental knowledge on seismic anisotropy inferred from various data sets can enhance our understanding of its vertical resolution that is critical for a better interpretation of past and current dynamics and resultant crustal and mantle kinematics in the Hellenic Trench and its hinterland. To investigate the nature of deformation zones, we perform both local S-wave splitting (SWS) measurements and receiver functions (RFs) analysis. Our preliminary findings from the harmonic decomposition technique performed on radial and tangential RFs suggest relatively more substantial anisotropic signals in the lower crust and uppermost mantle with respect to upper and middle crustal structure in the region. Apparent anisotropic orientations obtained from RFs harmonic decomposition process show several consistencies with those discovered from local SWS measurements at selected stations. The actual anisotropic orientation for the structures, however, requires further modelling of the receiver functions obtained.</p>
<p>Upper mantle dynamics (e.g. subduction processes, slab roll-back, slab tearing and mantle upwelling) impact eastern Mediterranean region tectonics but a detailed understanding of the acting forces has remained elusive. Further progress requires more accurate measurements not just of the surface kinematics (from GPS) but also of indirect indicators of kinematics throughout the lithosphere and convecting upper mantle from seismology. A robust quantification of the magnitude, location and orientation of seismic anisotropy is a primary source of information to provide constraints on tectonic processes of the formation and evolution of the Anatolian Peninsula and the surrounding regions. Direct shear-wave splitting measurements in the Aegean to revealed mostly NNE-SSW oriented fast polarization directions, perpendicular to the trench and parallel to the mantle flow induced by the roll-back and large time delays (1.15-1.62 s) in the upper mantle. In southwestern Turkey the FPDs are more confusing and probably related to the tearing of the slab in the upper mantle underneath this region. With complex non-steady state 3D geodynamic modelling, the plate movement, mantle flow, anisotropy and SKS splitting parameters for the last 20-30 Ma in the regional subduction system of the eastern Mediterranean and Anatolia were calculated. The model shows that tearing underneath southwestern Turkey, a break-off in the collitional regime of eastern Anatolia as well as the retreat of the slab in the Aegean influence on the strength and direction of the mantle flow and anisotropy. At last a P-wave tomography study of the Eastern Mediterranean region, focusing on the upper mantle with a large data set was done. Since anisotropy is present in the region especially due to the active subduction system, travel times were corrected by including anisotropy as an aprori constraint, from the numerical model and SKS splitting parameters. In isotropic inversions as well as the ones corrected for anisotropy, tears in the northern Hellenic slab, underneath southwestern Turkey and in the Cyprian slab can be seen. Spatially large first order velocity perturbations are stable and similar in isotropic and anisotropy corrected models. But differences up to 2% and small geometrical discrepancies beween the models show the importance of including anisotropy to P-wave tomographies.</p>
The complex tectonic structure of eastern Anatolia results from the superposition of subduction and collisional structures along a long-lived convergent margin between the Gondwanan (Arabian) and Eurasian plates. The geodynamic processes shaping the tectonic setting and uplifting history of the region still remain enigmatic despite the fact that the number of geophysical, geological, and petrographic-based models/interpretations in recent years has increased notably. Further issues, i.e., how the spatiotemporal patterns of seismic activity are controlled by pre-existing deformational zones in the lithosphere and/or modern convergent stresses, and how magmatism is related to the lithospheric variability along the margin, are unclear. Models of seismological features of the Earth’s interiors provide insights on isotropic heterogeneity that are of great importance for constraining the current physical and chemical conditions, as they likely control the localization of structures. For this purpose, the present study aims to constrain lateral variations of crustal thickness, Moho topography, and average seismic velocities (Vp, Vp/Vs) by leveraging information from both teleseismic scattered (receiver function) and reflected (autocorrelation) waves (H-k-Vp stacking). Incorporating teleseismic autocorrelation waveforms from the P-wave coda, we can better constrain average crustal P-wave velocities (Vp) by highlighting the amplitude term of the Moho-reflected Pmp phase. Our dataset consists of digital waveforms extracted from 512 teleseismic events (within the epicentral distance range from 30° to100° and with Mw>6) observed at 33 permanent broadband seismic stations operated under the KOERI network between 2013 and 2022 and will result in a new map of crustal architecture and its physical properties (crustal thickness, Vp, and Vp/Vs) below eastern Anatolia. Preliminary results indicate a thickening crust from south to north reaching down to depths of ~50 km. High Vp/Vs ratios mark volcanic provinces as well as fault damage areas presumably characterized by highly fractured rocks with high amounts of water content. Lateral variations of P-wave velocities along two continental fault zones (EAFZ and NAFZ) of the region imply that the degree of shear deformation and resultant seismic activity is well-correlated with density/seismic wave speed variations. Moho depth variations across the NAFZ further suggest a much narrow and localized distribution of deformation in the lower crust and upper mantle compared to the EAFZ. Further analysis of these results will lead to a better understanding of the controlling mechanisms behind seismicity and magmatism in the Eastern Anatolian Plateau.
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