Slip-Weakening Distance of Faults during Frictional Melting as Inferred from Experimental and Natural Pseudotachylytes
Slip-Weakening Distance of Faults during Frictional Melting as Inferred from Experimental and Natural Pseudotachylytes
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DOI：
10.1785/0120040131
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发表时间：
2005-10
影响因子：
3
通讯作者：
T. Hirose;T. Shimamoto
中科院分区：
文献类型：
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作者：
T. Hirose;T. Shimamoto
在发震断层运动过程中，断层的滑动弱化距离dc是控制断层不稳定性的重要参数之一。在过去十年中，一个矛盾的现象是，实验室测量的常规摩擦实验（10−5 -10−3 m）的dc值与地震测定的自然地震（10−1 -10 0 m）的dc值之间存在巨大差异。对于天然断层来说，dc是一个难以估计的量，但本研究试图通过对实验和天然假achylytes的比较来确定含有假achylytes的天然断层的dc值的顺序。在恒定滑动速度为0.85 m/sec、法向应力为1.4 MPa的辉长岩上进行的实验表明，熔融层的逐渐增长导致明显的滑动减弱。滑移减弱（摩擦强度随位移而降低）和熔层增长（熔层厚度随位移而增加）都以指数变化为特征，特征距离几乎相同。对比表明，可以根据断层生成断层的假岩厚度与断层位移的关系来估计断层发育的顺序。Sibson（1975）在外赫布里底群岛的数据显示出类似的伪断层厚度与断层位移曲线，特征距离为0.38 m。这与地震推断的dc值是相同的数量级。摩擦熔化效应是D - c悖论的一种可能解决方案，尽管它不是唯一可能的解决方案，因为沿大断层的摩擦熔化相当罕见。
The slip-weakening distance, D c , over which a fault weakens during seismogenic fault motion, is one of most important parameters controlling fault instability. A paradox over the last decade has been the source of the large difference between laboratory-measured values of D c using conventional friction experiments (10 −5 –10 −3 m) and seismically determined D c values for natural earthquakes (10 −1 –10 0 m). D c is a difficult quantity to estimate for natural faults, but this study attempts to determine the order of D c values for natural faults containing pseudotachylytes based on a comparison between experimental and natural pseudotachylytes. Experiments at a constant slip velocity of 0.85 m/sec and a normal stress of 1.4 MPa on gabbro have revealed that the progressive growth of a molten layer causes marked slip weakening. Slip weakening (a reduction in frictional strength with displacement) and the growth of the molten layer (an increase in the thickness of the molten layer with displacement) are both characterized by exponential changes with nearly the same characteristic distances. The comparison suggests that the order of D c can be estimated from the relationship between pseudotachylyte thickness along its generation fault and fault displacement. Sibson’s (1975) data from the Outer Hebrides exhibit a similar pseudotachylyte-thickness-versus-fault-displacement curve with a characteristic distance of 0.38 m. This is the same order of magnitude as seismically inferred values of D c . The effect of frictional melting is a possible solution for the D c paradox, although it is not the only possible solution, since frictional melting along large faults is rather uncommon.