Megathrust earthquake behavior in subduction zones is controlled by a variety of factors including the hydration state of the subducting slab. Increased hydration reduces the occur-rence of great, damaging earthquakes by diminishing the strength of the material along the interface between tectonic plates. Understanding variations in hydration in subductions zones is necessary for properly assessing the overall hazard posed by each region. Fortunately, seismic anisotropy is strongly dependent upon hydration of the subducting crust and litho-sphere. I present shear-wave splitting measurements that illuminate changes in anisotropy, and therefore hydration, of the subducting Pacific plate beneath the Alaska subduction zone (northern Pacific Ocean). Variations in shear-wave splitting directly correlate to changes in the behavior of great, megathrust earthquakes. My measurements show that the Shumagin seismic gap is characterized by a hydrated subducting slab, explaining the long-term lack of great earthquakes. Observations in the immediately adjacent Semidi segment, which experiences great events regularly, indicate a far less hydrated slab. These results are driven by the preferential alignment of paleo-spreading fabrics of the Pacific plate. Where fabrics are more closely aligned with the orientation of the trench, outer-rise faulting and plate hydration is enhanced. These results highlight the importance of changes in preexisting slab structures and subsequent hydration in the production of great, damaging earthquakes.

中文翻译：

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阿拉斯加俯冲带各向异性揭示的水合作用变化

俯冲带中的大逆冲地震行为受多种因素控制，包括俯冲板片的水化状态。增加的水合作用减少了沿构造板块之间界面的材料强度，从而减少了破坏性大地震的发生。了解俯冲带中水合作用的变化对于正确评估每个区域造成的整体危害是必要的。幸运的是，地震各向异性强烈依赖于俯冲地壳和岩石圈的水合作用。我提出了剪切波分裂测量结果，阐明了阿拉斯加俯冲带（北太平洋）下方俯冲太平洋板块的各向异性变化以及水合作用。横波分裂的变化与巨大的行为变化直接相关，特大地震。我的测量表明，舒马金地震间隙的特征是水合俯冲板片，这解释了长期缺乏大地震的原因。在紧邻的 Semidi 段中，定期经历重大事件的观测表明，其水化程度要低得多。这些结果是由太平洋板块古扩张织物的优先排列驱动的。在织物与海沟方向更紧密地对齐的地方，外层断层和板块水化得到增强。这些结果强调了预先存在的板结构的变化和随后的水合作用在产生大的破坏性地震中的重要性。在紧邻的 Semidi 段中，定期经历重大事件的观测表明，其水化程度要低得多。这些结果是由太平洋板块古扩张结构的优先排列驱动的。在织物与海沟方向更紧密地对齐的地方，外层断层和板块水化得到增强。这些结果强调了预先存在的板结构的变化和随后的水合作用在产生大的破坏性地震中的重要性。在紧邻的 Semidi 段中，定期经历重大事件的观测表明，其水化程度要低得多。这些结果是由太平洋板块古扩张织物的优先排列驱动的。在织物与海沟方向更紧密地对齐的地方，外层断层和板块水化得到增强。这些结果强调了预先存在的板结构的变化和随后的水合作用在产生大的破坏性地震中的重要性。外层断裂和板块水化作用增强。这些结果强调了预先存在的板结构的变化和随后的水合作用在产生大的破坏性地震中的重要性。外层断层和板块水化作用增强。这些结果强调了预先存在的板结构的变化和随后的水合作用在产生大的破坏性地震中的重要性。