The Role of Oceanic Transform Faults in Seafloor Spreading: A Global Perspective From Seismic Anisotropy.
The Role of Oceanic Transform Faults in Seafloor Spreading: A Global Perspective From Seismic Anisotropy.
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DOI：
10.1002/2017jb015176
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发表时间：
2018-03
期刊：
影响因子：
--
通讯作者：
Harmon N
中科院分区：
文献类型：
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作者：
Eakin CM;Rychert CA;Harmon N
大洋中脊下方的地幔各向异性和海洋转变是我们理解海底扩张和不同板块边界的潜在动力学的关键。然而，鉴于海洋的偏远和地震仪器的困难，观测结果很少。为了克服这个问题，我们利用沿转换断层的地震活动的全球分布来测量在全球 56 个精心挑选的地震台记录的 550 多个直接 S 相的剪切波分裂。应用这种源侧分裂技术可以表征上地幔地震各向异性，从而表征地震活动转换断层正下方的地幔流模式。大多数结果 (60%) 返回空值（无分裂），而非空测量结果显示出明显的方位角依赖性。这可以通过具有接近垂直对称轴的各向异性来简单地解释，这与数值模型所表明的海洋变换下的地幔上涌一致。因此，海底扩张的长期稳定性可能与转变下方广泛的地幔上涌有关，产生了温暖而弱的断层，将应变局部化到了板块边界。通过全球源侧分裂分析揭示了海洋变换下的地震各向异性 结果以零值 (60%) 和方位角相关分裂为特征 发现的模式与数值模型表明的广泛地幔上升流一致
Mantle anisotropy beneath mid‐ocean ridges and oceanic transforms is key to our understanding of seafloor spreading and underlying dynamics of divergent plate boundaries. Observations are sparse, however, given the remoteness of the oceans and the difficulties of seismic instrumentation. To overcome this, we utilize the global distribution of seismicity along transform faults to measure shear wave splitting of over 550 direct S phases recorded at 56 carefully selected seismic stations worldwide. Applying this source‐side splitting technique allows for characterization of the upper mantle seismic anisotropy, and therefore the pattern of mantle flow, directly beneath seismically active transform faults. The majority of the results (60%) return nulls (no splitting), while the non‐null measurements display clear azimuthal dependency. This is best simply explained by anisotropy with a near vertical symmetry axis, consistent with mantle upwelling beneath oceanic transforms as suggested by numerical models. It appears therefore that the long‐term stability of seafloor spreading may be associated with widespread mantle upwelling beneath the transforms creating warm and weak faults that localize strain to the plate boundary. Seismic anisotropy beneath oceanic transforms is revealed by global source‐side splitting analysis Results are characterized by nulls (60%) and azimuthally dependent splitting The pattern found is consistent with widespread mantle upwelling as suggested by numerical models