The stabilizing effect of high pore-fluid pressure along subduction megathrust faults: Evidence from friction experiments on accretionary sediments from the Nankai Trough
The stabilizing effect of high pore-fluid pressure along subduction megathrust faults: Evidence from friction experiments on accretionary sediments from the Nankai Trough
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DOI：
10.1016/j.epsl.2021.117161
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发表时间：
2021-09-06
影响因子：
5.3
通讯作者：
Hirose, Takehiro
中科院分区：
文献类型：
--
作者：
Bedford, John D.;Faulkner, Daniel R.;Hirose, Takehiro
孔隙流体压力是控制断层力学的一个重要参数，因为它降低了有效正应力，允许断层在较低剪应力下滑动。它还被认为影响了断层滑动的性质，特别是在俯冲带，在那里，缓慢滑动的区域与孔隙流体压力升高的区域相联系。尽管孔隙流体压力在断层力学中很重要，但它在控制断层稳定性方面的作用(由摩擦率参数(a-b)决定)很少受到限制，特别是对来自俯冲带的断层物质。2018-19年冬季，覆盖在南开海槽俯冲带(日本西南部)之上的吸积复合体作为综合大洋钻探计划(IODP)考察358的一部分进行了钻探。在这里，我们通过对粉状样品(模拟断层泥)进行一系列的速度步进实验，同时系统地改变孔隙流体压力和有效正应力条件，来测试在考察中发现的增生沉积物的摩擦稳定性。南开断层泥尽管只含有25%的层状硅酸盐，但具有很强的速率强化作用，并且速率和状态参数b为负值。我们发现，在保持有效正应力不变、增加孔隙流体压力的实验中，南开断层泥变得更加速率强化，从而更加稳定(随着孔隙压力的增加，(a-b)的增加幅度接近6×10(-5)Mpa-1)。相反，当孔隙流体压力保持不变，而有效法向应力变化时，对断层泥的摩擦稳定性影响很小。在较高的孔隙流体压力下，泥的摩擦稳定性的增加是由于速率和状态参数b的变化引起的，该参数在较高的孔隙流体压力下变得更负。这些结果对理解俯冲带中滑动的性质具有重要意义，并表明孔隙流体压力的稳定作用可能会促进俯冲界面上可能发生地震破裂的地区的缓慢滑动或无震蠕变。(C)2021年爱思唯尔B.V.保留所有权利。
Pore-fluid pressure is an important parameter in controlling fault mechanics as it lowers the effective normal stress, allowing fault slip at lower shear stress. It is also thought to influence the nature of fault slip, particularly in subduction zones where areas of slow slip have been linked to regions of elevated pore-fluid pressure. Despite the importance of pore-fluid pressure on fault mechanics, its role on controlling fault stability, which is determined by the friction rate parameter (a - b), is poorly constrained, particularly for fault materials from subduction zones. In the winter of 2018-19 the accretionary complex overlying the Nankai Trough subduction zone (SW Japan) was drilled as part of Integrated Ocean Drilling Program (IODP) Expedition 358. Here we test the frictional stability of the accretionary sediments recovered during the expedition by performing a series of velocity-stepping experiments on powdered samples (to simulate fault gouge) while systematically varying the pore-fluid pressure and effective normal stress conditions. The Nankai gouges, despite only containing 25% phyllosilicates, are strongly rate-strengthening and exhibit negative values for the rate-and-state parameter b. We find that for experiments where the effective normal stress is held constant and the pore-fluid pressure is increased the Nankai gouges become more rate-strengthening, and thus more stable (an increase in (a - b) of similar to 6 x 10(-5) MPa-1 with increasing pore-pressure). In contrast, when the pore-fluid pressure is held constant and the effective normal stress is varied, there is minimal effect on the frictional stability of the gouge. The increase in frictional stability of the gouge at elevated pore-fluid pressure is caused by an evolution in the rate-and-state parameter b, which becomes more negative at high pore-fluid pressure. These results have important implications for understanding the nature of slip in subduction zones and suggest the stabilizing effect of pore-fluid pressure could promote slow slip or aseismic creep on areas of the subduction interface that might otherwise experience earthquake rupture. (c) 2021 Elsevier B.V. All rights reserved.