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Scale dependence of rock friction at high work rate

机译：高工作速率下岩石摩擦的尺度依赖性

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Determination of the frictional properties of rocks is crucial for an understanding of earthquake mechanics, because most earthquakes are caused by frictional sliding along faults. Prior studies using rotary shear apparatus(1-13) revealed a marked decrease in frictional strength, which can cause a large stress drop and strong shaking, with increasing slip rate and increasing work rate. (The mechanical work rate per unit area equals the product of the shear stress and the slip rate.) However, those important findings were obtained in experiments using rock specimens with dimensions of only several centimetres, which are much smaller than the dimensions of a natural fault (of the order of 1,000 metres). Here we use a large-scale biaxial friction apparatus with metre-sized rock specimens to investigate scale-dependent rock friction. The experiments show that rock friction in metre-sized rock specimens starts to decrease at a work rate that is one order of magnitude smaller than that in centimetre-sized rock specimens. Mechanical, visual and material observations suggest that slip-evolved stress heterogeneity on the fault accounts for the difference. On the basis of these observations, we propose that stress-concentrated areas exist in which frictional slip produces more wear materials (gouge) than in areas outside, resulting in further stress concentrations at these areas. Shear stress on the fault is primarily sustained by stress-concentrated areas that undergo a high work rate, so those areas should weaken rapidly and cause the macroscopic frictional strength to decrease abruptly. To verify this idea, we conducted numerical simulations assuming that local friction follows the frictional properties observed on centimetre-sized rock specimens. The simulations reproduced the macroscopic frictional properties observed on the metre-sized rock specimens. Given that localized stress concentrations commonly occur naturally, our results suggest that a natural fault may lose its strength faster than would be expected from the properties estimated from centimetre-sized rock samples.
机译：确定岩石的摩擦特性对于理解地震力学至关重要，因为大多数地震是由沿断层的摩擦滑动引起的。先前使用旋转剪切仪（1-13）进行的研究表明，摩擦强度显着下降，这可能导致较大的应力下降和强烈的晃动，同时增加了滑移率和工作率。 （每单位面积的机械功率等于剪切应力和滑移率的乘积。）但是，这些重要发现是在使用尺寸仅为几厘米的岩石样本进行的实验中获得的，该样本比自然样本的尺寸小得多。故障（大约1,000米）。在这里，我们使用具有米级岩石标本的大型双轴摩擦装置来研究与尺度有关的岩石摩擦力。实验表明，米制岩石标本中的岩石摩擦力以比厘米尺寸岩石标本小一个数量级的工作速率开始减小。机械，视觉和材料的观察表明，断层上滑动演化的应力异质性是造成这种差异的原因。根据这些观察结果，我们建议存在一个应力集中区域，在该区域中，摩擦滑移比外部区域产生更多的磨损材料（标距），从而导致这些区域的应力进一步集中。断层上的剪切应力主要由应力集中的区域承受，该区域承受较高的工作效率，因此这些区域应迅速减弱并导致宏观摩擦强度突然降低。为了验证这个想法，我们进行了数值模拟，假设局部摩擦遵循在厘米大小的岩石样本上观察到的摩擦特性。模拟重现了在米级岩石标本上观察到的宏观摩擦特性。考虑到局部应力集中通常是自然发生的，我们的结果表明，天然断层的强度损失可能比厘米级岩石样品估计的特性所预期的更快。

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  • 来源
    《Nature》 |2015年第7581期|254-257|共4页
  • 作者

    Yamashita Futoshi; Fukuyama Eiichi; Mizoguchi Kazuo; Takizawa Shigeru; Xu Shiqing; Kawakata Hironori;

  • 作者单位

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan;

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan;

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan|Cent Res Inst Elect Power Ind, Abiko, Chiba 2701194, Japan;

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan;

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan;

    Natl Res Inst Earth Sci & Disaster Prevent NIED, Tsukuba, Ibaraki 3050006, Japan|Ritsumeikan Univ, Coll Sci & Engn, Kusatsu 5258577, Japan;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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