Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow
Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow
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DOI：
10.1130/g37181.1
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发表时间：
2015-12
期刊：
影响因子：
5.8
通讯作者：
M. Bodmer;D. Toomey;E. Hooft;John Náb;lek;J. Braunmiller
中科院分区：
文献类型：
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作者：
M. Bodmer;D. Toomey;E. Hooft;John Náb;lek;J. Braunmiller
在这里，我们使用SKS剪切波分裂观测海底地震仪数据来推断胡安德富卡板块及其毗邻边界下的地幔变形模式。我们的研究结果表明，软流层下方的胡安德富卡板块在很大程度上响应绝对板块运动的各向异性层迅速发展的脊附近，并坚持到俯冲带。受地理限制偏离这种模式表明存在次级过程。在离散的板块边界，如布兰科转换断层，地震各向异性归因于狭窄区域（<50 km）内的相对板块运动。在变形的南部戈尔达板块区域之下，扩散的板块边界分裂观测同样表明，变形主要由刚性胡安·德富卡和太平洋板块之间的相对运动控制，但分布在一个广阔的区域（约200公里）。我们的研究结果是不一致的环形流周围的俯冲板的南部边缘由于回滚，建议由陆上研究。相反，重组与板块碎裂的上地幔流似乎占主导地位的各向异性签名南部卡斯卡迪亚。
Here we use SKS shear wave splitting observations from ocean-bottom seismometer data to infer patterns of mantle deformation beneath the Juan de Fuca plate and its adjoining boundaries. Our results indicate that the asthenosphere beneath the Juan de Fuca plate responds largely to absolute plate motion with an anisotropic layer developing rapidly near the ridge and persisting into the subduction zone. Geographically restricted deviations from this pattern indicate the presence of secondary processes. At discrete plate boundaries, such as the Blanco transform fault, seismic anisotropy is attributed to relative plate motion within a narrow zone (<50 km). Beneath the deforming southern Gorda plate region—a diffuse plate boundary—splitting observations similarly suggest deformation dominated by relative motion between the rigid Juan de Fuca and Pacific plates but distributed over a broad zone (∼200 km). Our results are inconsistent with toroidal flow around the southern edge of the subducting slab due to rollback, as suggested by onshore studies. Instead, reorganization of upper mantle flow associated with plate fragmentation seems to dominate the anisotropic signature of southern Cascadia.