Abstract The mechanical properties of sediment inputs to subduction zones are important for understanding rupture propagation through the accretionary prism during megathrust earthquakes. Clay minerals strongly influence the frictional behavior of fault gouges, and the clay content of subduction input materials varies through a stratigraphic section as well as for subduction margins globally. To establish the frictional properties of the shallow Cascadia subduction zone and place the results in a global context, we conducted high velocity rotary shear experiments on ODP core samples retrieved from Cascadia input sediments (35-45% clay) and a suite of individual clay species. We compared our results to a compilation of published high velocity experiments conducted on samples of wet gouge, dry gouge, and intact rock. For each sample type, three trends were identified with increasing normal stress: 1) the stress drop ( τ p − τ s s ) increases linearly, 2) the characteristic thermal weakening distance ( D t h ) decreases as a power law function except for wet clay-rich gouges, and 3) the fracture energy ( W b ) shows no dependence. However, fracture energy does vary with sample type. Clay-rich gouges under wet conditions have the lowest fracture energy, and fracture energy for both dry and wet gouges is at least an order of magnitude lower than estimates from intact rocks. Therefore when clay-rich lithologies are present, they may minimize spatial variations in frictional behavior, allowing earthquakes to propagate to the trench. For Cascadia input sediments, there is little variation in the fracture energy between lithologies, but the fracture energy of Cascadia sediments is around an order of magnitude higher than input sediments from other subduction margins. The high fracture energy of Cascadia sediments relative to other subduction margins may inhibit large amounts of shallow earthquake slip and dynamic overshoot.

中文翻译：

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沟渠破裂？Cascadia俯冲带传入沉积物的摩擦特性和断裂能

摘要 俯冲带沉积物输入的力学特性对于理解大逆冲地震期间通过增生棱柱的破裂传播非常重要。粘土矿物强烈影响断层泥的摩擦行为，俯冲输入材料的粘土含量随地层剖面以及全球俯冲边缘而变化。为了确定浅层卡斯卡迪亚俯冲带的摩擦特性并将结果放在全球范围内，我们对从卡斯卡迪亚输入沉积物（35-45% 粘土）和一组单个粘土物种中提取的 ODP 岩心样品进行了高速旋转剪切实验. 我们将我们的结果与已发表的对湿凿、干凿和完整岩石样本进行的高速实验的汇编进行了比较。对于每个样本类型，随着法向应力的增加，确定了三种趋势：1) 应力降 ( τ p − τ ss ) 线性增加， 2) 特征热减弱距离 ( D th ) 作为幂律函数减小，除了湿富含粘土的凿岩，以及3) 断裂能 (W b ) 没有相关性。然而，断裂能确实因样品类型而异。潮湿条件下富含粘土的凿岩具有最低的断裂能，干凿和湿凿的断裂能至少比完整岩石的估计值低一个数量级。因此，当存在富含粘土的岩性时，它们可以最大限度地减少摩擦行为的空间变化，使地震能够传播到海沟。对于 Cascadia 输入沉积物，岩性之间的断裂能变化很小，但卡斯卡迪亚沉积物的断裂能比来自其他俯冲边缘的输入沉积物高大约一个数量级。卡斯卡迪亚沉积物相对于其他俯冲边缘的高断裂能可能会抑制大量浅层地震滑动和动力超冲。