Seismological studies of large‐scale processes at convergent plate boundaries typically probe lower crustal structures with wavelengths of several kilometers, whereas field‐based studies typically sample the resulting structures at a much smaller scale. To bridge this gap between scales, we derive effective petrophysical properties on the 20‐m, 100‐m, and kilometer scales based on numerical modeling with the finite element method. Geometries representative of eclogitization of crustal material are extracted from the partially eclogitized exposures on Holsnøy (Norway). We find that the P wave velocity is controlled by the properties of the lithologies rather than their geometric arrangement. P wave anisotropy, however, is dependent on the fabric orientation of the associated rocks, as fabric variations cause changes in the orientation of the initial anisotropy. As a result, different structural associations can result in effective anisotropies ranging from ~0–4% for eclogites not associated with ductile deformation to up to 8% for those formed during ductile deformation. For the kilometer‐scale structures, a scale that in principle can be resolved by seismological studies, we obtained P wave velocities between 7.7 and 8.0 km s⁻¹. The effective P wave anisotropy on the kilometer scale is ~3–4% and thus may explain the backazimuthal dependence of seismological images of, for example, the Indian lower crust currently underthrusting beneath the Himalaya. These results imply that seismic anisotropy could be the key to visualize structures in active subduction and collision zones that are currently invisible to geophysical methods and thus can be used to unravel the underlying processes active at depth.

中文翻译：

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有效岩石物理性质建模显示的下降地壳部分凝结引起的P波各向异性

在会聚板块边界进行的大规模过程的地震学研究通常会探测波长为几公里的下部地壳结构，而基于现场的研究通常会以较小的规模对所产生的结构进行采样。为了弥合尺度之间的差距，我们基于有限元方法的数值建模，得出了在20m，100m和千米尺度上的有效岩石物性。从Holsnøy（挪威）的部分地层化暴晒中提取出代表地壳材料地层化的几何形状。我们发现，P波速度受岩性的控制，而不是受其几何排列的控制。P然而，波浪各向异性取决于相关岩石的织物取向，因为织物变化会引起初始各向异性取向的变化。结果，不同的结构缔合可以导致有效的各向异性，范围从不与延性变形相关的榴辉岩的〜0–4％到在延性变形期间形成的榴辉岩的最大8％。对于千米尺度的结构，原则上可以通过地震学研究解决的尺度，我们获得了7.7至8.0 km s ^-1之间的P波速度。有效P千米尺度上的波浪各向异性约为3-4％，因此可以解释地震图像的反向方位角依赖性，例如，目前在喜马拉雅山下方未得到充分推力的印度下地壳。这些结果表明，地震各向异性可能是可视化地球物理方法目前看不见的活动俯冲带和碰撞带中结构的关键，因此可以用来揭示深层活动的潜在过程。