Seismic anisotropy of S-wave, trench-parallel or trench-normal polarization direction of fast S-wave, has been observed in the fore-arc and back-arc regions of subduction zones. Lattice preferred orientation (LPO) of elastically anisotropic chlorite has been suggested as one of the major causes of seismic anisotropy in subduction zones. However, there are two different LPOs of chlorite reported based on the previous studies of natural chlorite peridotites, which can produce different expression of seismic anisotropy. The mechanism for causing the two different LPOs of chlorite is not known. Therefore, we conducted deformation experiments of chlorite peridotite under high pressure–temperature conditions (P = 0.5–2.5 GPa, T = 540–720 °C). We found that two different chlorite LPOs were developed depending on the magnitude of shear strain. The type-1 chlorite LPO is characterized by the [001] axes aligned subnormal to the shear plane, and the type-2 chlorite LPO is characterized by a girdle distribution of the [001] axes subnormal to the shear direction. The type-1 chlorite LPO developed under low shear strain (γ ≤ 3.1 ± 0.3), producing trench-parallel seismic anisotropy. The type-2 chlorite LPO developed under high shear strain (γ ≥ 5.1 ± 1.5), producing trench-normal seismic anisotropy. The anisotropy of S-wave velocity (AVs) of chlorite was very strong up to AVs = 48.7% so that anomalous seismic anisotropy in subduction zones can be influenced by the chlorite LPOs.

中文翻译：

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俯冲带中亚氯酸盐的应变诱导织物转变及其对地震各向异性的影响

在俯冲带的前弧区和后弧区，已经观察到了Ｓ波的地震各向异性，快Ｓ波的平行或垂直极化方向。弹性各向异性亚氯酸盐的晶格优先取向（LPO）被认为是俯冲带地震各向异性的主要原因之一。但是，根据先前对天然亚氯酸盐橄榄岩的研究，报告了两种不同的亚氯酸盐LPO，它们可以产生不同的地震各向异性。导致亚氯酸盐的两个不同LPO的机理尚不清楚。因此，我们在高压-高温条件下（P = 0.5-2.5 GPa，T = 540-720°C）进行了绿泥石橄榄岩变形实验。我们发现，根据剪切应变的大小，开发了两种不同的亚氯酸盐LPO。1型亚氯酸盐LPO的特征是[001]轴垂直于剪切平面，而2型亚氯酸盐LPO的特征是[001]轴的腰带分布垂直于剪切方向。1型亚氯酸盐LPO在低剪切应变（γ≤3.1±0.3）下发展，产生了与沟槽平行的地震各向异性。2型绿泥石LPO在高剪切应变（γ≥5.1±1.5）下发展，产生了沟槽法向地震各向异性。高达AVs = 48.7％时，亚氯酸盐的S波速度（AVs）各向异性非常强，因此亚氯酸盐LPO可以影响俯冲带异常的地震各向异性。1型亚氯酸盐LPO在低剪切应变（γ≤3.1±0.3）下发展，产生了与沟槽平行的地震各向异性。2型亚氯酸盐LPO在高剪切应变（γ≥5.1±1.5）下发展，产生了沟槽法向地震各向异性。高达AVs = 48.7％时，亚氯酸盐的S波速度（AVs）的各向异性非常强，因此亚氯酸盐LPO可以影响俯冲带异常的地震各向异性。1型亚氯酸盐LPO在低剪切应变（γ≤3.1±0.3）下发展，产生了与沟槽平行的地震各向异性。2型亚氯酸盐LPO在高剪切应变（γ≥5.1±1.5）下发展，产生了沟槽法向地震各向异性。高达AVs = 48.7％时，亚氯酸盐的S波速度（AVs）的各向异性非常强，因此亚氯酸盐LPO可以影响俯冲带异常的地震各向异性。