Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates
Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates
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慢滑移速率下模拟煤断层泥中的摩擦滑移减弱和剪切增强结晶度
DOI：
10.5194/se-11-1399-2020
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发表时间：
2020-07
期刊：
影响因子：
3.4
通讯作者：
Spiers Christopher J.
中科院分区：
文献类型：
--
作者：
Fan Caiyuan;Liu Jinfeng;Hunfeld Luuk B.;Spiers Christopher J.
以往的研究表明，富含有机质的断层斑块可能在促进不稳定断层滑动方面发挥重要作用。然而，具有接近100%有机物含量的岩石材料的摩擦性能，例如，煤，和控制微观机制仍不清楚。在这里，我们报告七个速度步进（VS）实验和一个滑动-保持-滑动（SHS）摩擦实验进行模拟断层泥从上西里西亚盆地收集的烟煤波兰。这些实验在25-45 MPa有效正应力和100 ℃下进行，采用0.1-100 µm砂的滑动速度，使用常规三轴仪加直接剪切组件。在剪切位移超过1 -2 mm时，无论有效正应力大小，无论是真空干燥还是在15 MPa孔隙流体压力下用蒸馏水浸泡，所有试样都表现出明显的滑移弱化行为，摩擦系数从峰值接近（接近）稳态值。通过显微结构观察、微区X射线衍射（XRD）和拉曼光谱对未剪切和剪切样品的分析表明，显著的滑移弱化行为可以归因于R-、B-和Y-剪切带的发展，以及内部剪切增强的煤结晶度的发展。进行的SHS实验表明，瞬时峰值愈合（再强化）的效果，增加与保持时间的对数在线性化率。我们还确定了所有VS样品的稳态摩擦的速率依赖性，使用全速率和状态摩擦的方法。这表明，在真空干燥条件下，煤样的滑动速度为μm时，速度从增强过渡到减弱，但在15 MPa孔隙压力下，煤样暴露于去离子水时，速度为μm时，速度从增强过渡到减弱。所观察到的行为可能是控制之间的竞争澄清剂颗粒流和压实增强水的存在。再加上我们以前对煤-页岩混合物摩擦特性的研究，我们的研究结果意味着，断层上以煤为主的薄弱斑块切割或涂抹煤层可能会促进不稳定的孕震滑动行为，尽管这在增强诱发或自然地震活动方面的重要性取决于当地条件。
Previous studies show that organic-rich fault patches may play an important role in promoting unstable fault slip. However, the frictional properties of rock materials with nearly 100 % organic content, e.g., coal, and the controlling microscale mechanisms remain unclear. Here, we report seven velocity stepping (VS) experiments and one slide–hold–slide (SHS) friction experiment performed on simulated fault gouges prepared from bituminous coal collected from the upper Silesian Basin of Poland. These experiments were performed at 25–45 MPa effective normal stress and 100C, employing sliding velocities of 0.1–100 µm sand using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip-weakening behavior at shear displacements beyond1–2 mm, from a peak friction coefficient approachingto (nearly) steady-state values of, regardless of effective normal stress or whether vacuum-dry or flooded with distilled (DI) water at 15 MPa pore fluid pressure. Analysis of both unsheared and sheared samples by means of microstructural observation, micro-area X-ray diffraction (XRD) and Raman spectroscopy suggests that the marked slip-weakening behavior can be attributed to the development of R-, B- and Y-shear bands, with internal shear-enhanced coal crystallinity development. The SHS experiment performed showed a transient peak healing (restrengthening) effect that increased with the logarithm of hold time at a linearized rate of. We also determined the rate dependence of steady-state friction for all VS samples using a full rate and state friction approach. This showed a transition from velocity strengthening to velocity weakening at slip velocitiesµm sin the coal sample under vacuum-dry conditions but atµm sin coal samples exposed to DI water at 15 MPa pore pressure. The observed behavior may be controlled by competition between dilatant granular flow and compaction enhanced by the presence of water. Together with our previous work on the frictional properties of coal–shale mixtures, our results imply that the presence of a weak, coal-dominated patch on faults that cut or smear out coal seams may promote unstable, seismogenic slip behavior, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.
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影响因子：
3.9
作者：
Aharonov, Einat;Scholz, Christopher H.
通讯作者：
Scholz, Christopher H.
影响因子：
18.3
作者：
Ikari, Matt J.;Marone, Chris;Kopf, Achim J.
通讯作者：
Kopf, Achim J.
DOI：
10.5860/choice.28-1579
发表时间：
2016
期刊：
--
影响因子：
--
作者：
Leon Bieber
通讯作者：
Leon Bieber
影响因子：
3.1
作者：
Wenyong Zhang;Shancheng Chen;Fenglin Han;D. Wu
通讯作者：
Wenyong Zhang;Shancheng Chen;Fenglin Han;D. Wu
影响因子：
3.1
作者：
E. Rutter;A. Hackston;E. Yeatman;K. Brodie;J. Mecklenburgh;S. E. May
通讯作者：
E. Rutter;A. Hackston;E. Yeatman;K. Brodie;J. Mecklenburgh;S. E. May