Segments of subduction zones that are capable of generating tsunamigenic earthquakes appear to have characteristic structural configurations. These structures include heterogeneous plate interfaces, a small wedge of deformed sediment at the toe of the overriding plate (the frontal prism), and splay faults in the crust of the overriding plate that root within the plate boundary megathrust. Here we use seismic reflection imaging to show that these features also exist within a creeping segment of the Alaska subduction zone, the Shumagin Gap. We identify an active crustal-scale normal fault system that dips landward and resembles that involved in the 2011 Tohoku-oki earthquake in Japan. We also find that the Shumagin Gap has a small frontal prism, a deep-water splay fault, and that the plate interface here is rough and thinly sedimented. We propose that lateral propagation of rupture from a neighbouring segment into the Shumagin Gap may explain a tsunamigenic earthquake that occurred there in 1788 and that tsunamigenic potential should be considered in hazard assessments for the region. Our results demonstrate that structural configurations similar to those in Tohoku may exist in other subduction zones, including within creeping segments or segments with no record of historical megathrust earthquakes, but are under-recognized. Identifying similar configurations globally may improve our ability to anticipate regions capable of generating large tsunamis.

中文翻译：

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阿拉斯加俯冲带蠕变区的海啸构造

能够产生海啸地震的俯冲带段似乎具有特征性的结构构造。这些结构包括非均质的板界面，上覆板（前棱柱）趾部的变形沉积物的小楔形，以及上覆板的地壳中的张开断层，这些断层根植于板边界超大推力之内。在这里，我们使用地震反射成像来显示这些特征也存在于阿拉斯加俯冲带舒马金峡的蠕动段中。我们确定了一个活跃的地壳尺度正断层系统，该系统向陆地倾斜并类似于2011年日本东北冲地震中所涉及的那样。我们还发现Shumagin峡有一个小的前棱柱，一个深水八字形断层，而且这里的板块界面很粗糙，而且沉积物很薄。我们认为，破裂的横向传播是从相邻段进入舒马金峡的，这也许可以解释1788年发生的海啸地震，并且在该地区的危害评估中应考虑海啸发生的可能性。我们的结果表明，与东北地区相似的构造构造可能存在于其他俯冲带中，包括在蠕变段内或没有历史大推力地震记录的段内，但未被充分认识。在全球范围内识别相似的配置可能会提高我们预测可能产生大海啸的区域的能力。