The Influence of the North Anatolian Fault and a Fragmenting Slab Architecture on Upper Mantle Seismic Anisotropy in the Eastern Mediterranean
The Influence of the North Anatolian Fault and a Fragmenting Slab Architecture on Upper Mantle Seismic Anisotropy in the Eastern Mediterranean
复制标题
DOI：
10.1029/2021gc009896
复制
发表时间：
2021-08
期刊：
影响因子：
3.7
通讯作者：
Thomas A. J. Merry;I. Bastow;R. Kounoudis;C. Ogden;R. Bell;L. Jones
中科院分区：
文献类型：
--
作者：
Thomas A. J. Merry;I. Bastow;R. Kounoudis;C. Ogden;R. Bell;L. Jones
东地中海在几百公里的跨度内，在一组破碎的俯冲板块之上，存在着伸展、走滑和碰撞构造。板块回滚、环形流和岩石圈滴落/分层过程也被认为是在运行。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剪切波分裂的研究进行测量。令人惊讶的是，以前的SKS分裂调查只解决了该地区各向异性的长波长模式，将其解释为大规模的软流圈流动;此外，与世界各地其他主要走滑板块边界不同，没有与北安纳托利亚断层（NAF）相关的各向异性特征。我们提出了一个29年的SKS分裂观测记录，揭示了迄今未被认识到的各向异性的短尺度变化，以及证明多层各向异性的分裂参数的后方位角变化。NAF下方的岩石圈各向异性表现出快速方向，要么是断层平行，要么是主拉伸应变率轴和断层走向之间的中间方向，这是一个相对低应变的穿流地幔剪切带的特征。在其他地方，各向异性是一致的软流圈流通过断层成像板的差距，并驱动希腊海沟撤退。目前还缺乏软流层向西流动驱动安纳托利亚板块运动的证据。在安纳托利亚中部较短的分裂延迟时间和零表明较弱的软流圈方位各向异性，支持模型，调用垂直地幔流动模式（岩石圈滴/软流圈上涌）。因此，我们得出结论，地幔各向异性的信号更密切地反映了岩石圈变形，复杂的板片结构和地球动力学的多样性比以前认识到的。
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.