The eastern Mediterranean hosts, within the span of a few hundred kilometers, extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Slab roll-back, toroidal flow, and lithospheric dripping/delamination processes are also believed to be operating. Associated asthenospheric flow and lithospheric deformation are expected to manifest as seismic anisotropy, measurable via study of SKS shear wave splitting. Surprisingly, previous SKS splitting investigations have resolved only long wavelength patterns of anisotropy in the region, interpreting them as large-scale asthenospheric flow; moreover, no anisotropic signature has been associated with the North Anatolian Fault (NAF), unlike other major strike-slip plate boundaries worldwide. We present a 29-year record of SKS splitting observations, revealing hitherto-unrecognized short-length-scale variations in anisotropy, and backazimuthal variations of splitting parameters that attest to multi-layered anisotropy. Lithospheric anisotropy beneath the NAF exhibits fast directions either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone. Elsewhere, anisotropy is consistent with asthenospheric flow through tomographically imaged slab gaps, and driven by Hellenic trench retreat. Evidence for westward flow of asthenosphere driving Anatolian plate motion is lacking. Shorter splitting delay times and nulls in central Anatolia suggest weaker azimuthal anisotropy in the asthenosphere, supporting models that invoke vertical mantle flow patterns (lithospheric dripping/asthenospheric upwelling). Thus, we conclude that the signal of mantle anisotropy more closely reflects the lithospheric deformation, complex slab architecture and geodynamic diversity of the region than previously recognized.

中文翻译：

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北安纳托利亚断层和碎裂板结构对东地中海上地幔地震各向异性的影响

东地中海在数百公里的跨度内，在一组破碎的俯冲板块上方具有伸展、走滑和碰撞构造。板坯回滚、环形流和岩石圈滴落/分层过程也被认为正在运行。预计相关的软流圈流动和岩石圈变形将表现为地震各向异性，可通过SKS剪切波分裂的研究。令人惊讶的是，之前的 SKS 分裂研究仅解决了该地区各向异性的长波长模式，将它们解释为大规模软流圈流动；此外，与全球其他主要走滑板块边界不同，北安纳托利亚断层 (NAF) 没有任何各向异性特征。我们展示了 29 年的 SKS 分裂观测记录，揭示了迄今为止尚未认识到的各向异性短尺度变化，以及证明多层各向异性的分裂参数的反向方位变化。NAF 下方的岩石圈各向异性表现出与断层平行或介于主拉伸应变率轴和断层走向之间的快速方向，诊断出相对低应变的横流地幔剪切带。别处，各向异性与通过断层成像板间隙的软流圈流动一致，并由希腊海沟后退驱动。缺乏软流圈向西流动驱动安纳托利亚板块运动的证据。安纳托利亚中部较短的分裂延迟时间和零点表明软流圈中的方位各向异性较弱，支持调用垂直地幔流动模式（岩石圈滴落/软流圈上升流）的模型。因此，我们得出结论，地幔各向异性信号比以前认识的更能反映该地区的岩石圈变形、复杂的板块结构和地球动力学多样性。安纳托利亚中部较短的分裂延迟时间和零点表明软流圈中的方位各向异性较弱，支持调用垂直地幔流动模式（岩石圈滴落/软流圈上升流）的模型。因此，我们得出结论，地幔各向异性信号比以前认识的更能反映该地区的岩石圈变形、复杂的板块结构和地球动力学多样性。安纳托利亚中部较短的分裂延迟时间和零点表明软流圈中的方位各向异性较弱，支持调用垂直地幔流动模式（岩石圈滴落/软流圈上升流）的模型。因此，我们得出结论，地幔各向异性信号比以前认识的更能反映该地区的岩石圈变形、复杂的板块结构和地球动力学多样性。