Fault lubrication and earthquake propagation in thermally unstable rocks
Fault lubrication and earthquake propagation in thermally unstable rocks
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DOI：
10.1130/g31398.1
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发表时间：
2009-12
期刊：
影响因子：
5.8
通讯作者：
N. Paola;T. Hirose;T. Mitchell;G. Toro;C. Viti;T. Shimamoto
中科院分区：
文献类型：
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作者：
N. Paola;T. Hirose;T. Mitchell;G. Toro;C. Viti;T. Shimamoto
在白云石或镁方解石凿岩上以地震滑移速率 (v > 1 m/s) 和位移 (d > 1 m) 进行的实验表明，摩擦系数 μ 从峰值（Byerlee9s 范围内的 m p ≈ 0.8）呈指数衰减到在弱化距离 D w 上达到的极低稳态值（μ ss ≈ 0.1）。微观结构观察表明，在瞬态阶段（dw），滑移区产生了不连续的白云石纳米颗粒及其分解产物（方镁石和石灰或硅酸钙石）。这些观察结果与实验期间记录的 CO 2 排放数据相结合，表明滑移区中的颗粒相互作用产生的闪蒸温度足以激活化学和物理过程，例如脱碳反应 (T = 550 °C)。在稳态（d ≥ D w ）期间，剪切强度非常低并且不依赖于法向应力，这表明加压流体（CO 2 ）可能暂时被困在滑移区内。在此阶段，滑移区会形成连续的纳米颗粒层。对于 d >> D w ，观察到剪切强度略有但突然增加，并将其解释为由于流体逃离滑移区。在这个阶段，动态弱化似乎是由滑移区中产生的纳米粒子的速度相关特性控制的。实验得出的震源参数 Wb（即破裂功，控制传播裂缝动力学的能量）（1）与从公元 1997 年 M6 Colfiorito（意大利）地震的地震数据中获得的 Wb 值相匹配，该地震在本研究中测试的同一类型岩石中成核，并且（2）表明了类似的地震尺度关系，如从现有地震数据集推断的那样。我们得出的结论是，实验断层的动态弱化是由多种滑移弱化机制控制的，这些机制是由滑移带中的物理化学反应激活或抑制的。
Experiments performed on dolomite or Mg-calcite gouges at seismic slip rates ( v > 1 m/s) and displacements (d > 1 m) show that the frictional coefficient μ decays exponentially from peak values (m p ≈ 0.8, in the Byerlee9s range), to extremely low steady-state values (μ ss ≈ 0.1), attained over a weakening distance D w . Microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products (periclase and lime or portlandite) were produced in the slip zone during the transient stage (d w ). These observations, integrated with CO 2 emissions data recorded during the experiments, suggest that particle interaction in the slip zone produces flash temperatures that are large enough to activate chemical and physical processes, e.g., decarbonation reactions ( T = 550 °C). During steady state (d ≥ D w ), shear strength is very low and not dependent upon normal stresses, suggesting that pressurized fluids (CO 2 ) may have been temporarily trapped within the slip zone. At this stage a continuous layer of nanoparticles is developed in the slip zone. For d >> D w , a slight but abrupt increase in shear strength is observed and interpreted as due to fluids escaping the slip zone. At this stage, dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone. Experimentally derived seismic source parameter W b (i.e., breakdown work, the energy that controls the dynamics of a propagating fracture) (1) matches W b values obtained from seismological data of the A.D. 1997 M6 Colfiorito (Italy) earthquakes, which nucleated in the same type of rocks tested in this study, and (2) suggests similar earthquake-scaling relationships, as inferred from existing seismological data sets. We conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms, which are activated or inhibited by physicochemical reactions in the slip zone.