The origin of large or great thrust-type earthquakes along subducting plate boundaries
The origin of large or great thrust-type earthquakes along subducting plate boundaries
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沿俯冲板块边界发生大或特大逆冲型地震的起源
DOI：
10.1016/0040-1951(85)90032-0
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发表时间：
1985
期刊：
影响因子：
2.9
通讯作者：
T. Shimamoto
中科院分区：
文献类型：
--
作者：
T. Shimamoto
综述了俯冲板块边界的地震活动、变形、应力状态和流体丰度，并根据近期岩盐和蛇纹岩断层滑移行为的实验结果，讨论了大型或特大逆冲型地震的成因。深度20~25 km以上的浅层俯冲板块边界具有低地震活动、低构造应力、板间解耦、与变质片理形成相关的韧性变形的特征（除了在非常浅的深度），变质作用表明大规模的溶解过程，并且存在丰富的水。有人认为，这些独特的特征是由于压溶过程、高流体压力、潮湿环境下粘土沉积物的低强度和稳定行为，和/或非常浅深度的松软、松散沉积物的变形造成的。该带的低地震活动性与主要走滑断层形成鲜明对比，沿走滑断层发生大地震的深度小于15-20公里。需要强调的是，这些独特的特征仅适用于由于渐进变质作用而持续供应 H2O 或岩石中的流体被困住而无法逃逸到地表的有限区域。俯冲带中的大型或特大逆冲型地震始于浅解耦带以下 30-50 公里的深度。在这个震源深度范围内，渐进变质作用期间水的供应可能会向下减少，在地震间期的大部分时间里，上覆板块和俯冲板块相互耦合并相互粘附，并且抗滑移（或剪切应力）的阻力可能很高。有人认为这些地震开始发生在板块边界区变得相当干燥的深度。这些深度的变形似乎主要是延性的，因此地震不能简单地视为脆性现象。 （1）蠕变不稳定，即与塑性变形相关的不稳定，（2）脱水引起的不稳定是引发地震的最可能机制，并且两者都有一些实验支持。描述并讨论了石盐凿岩在主要通过晶内滑动进行延性变形时的粘滑现象，作为 (1) 的支持证据。在粘滑状态下，岩盐凿岩的抗剪力随着围压的增加而增加。因此，尽管变形织构无法与压力不敏感流形成的变形织构区分开来，但观察到的粘滑运动可能是关于剪切阻力的压力依赖性的半脆性现象。蛇纹石凿岩在干燥而不是潮湿的环境下分解时表现出剧烈的粘滑，支持了上述机制（2）。导致不稳定断层运动的确切机制目前还知之甚少，但只有当摩擦的滑移速率依赖性为负时，即在较快的滑移速率下摩擦力较低时，才能识别石盐和蛇纹石凿岩的粘滑现象，这与 Rice 和 Ruina (1983) 的理论预测一致。逆冲型地震有可能基本上可以在 Dieterich (1979) 和 Ruina (1983) 提出的断层本构定律框架内得到解释。
Seismicity, deformation, state of stress, and abundance of fluids along subducting plate boundaries are reviewed, and the origin of large or great thrust-type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges.Shallow subducting plate boundaries above 20–25 km in depth are characterized by low seismicity, low tectonic stress, inter-plate decoupling, ductile deformation associated with the formation of metamorphic schistosity (except at very shallow depths), metamorphism suggesting solution processes on massive scale, and presence of abundant H2O. It is argued that these unique features are due to pressure-solution processes, to high fluid pressure, to low strength and stable behavior of clayey sediments under wet environments, and/or to the deformation of soft, unconsolidated sediments at very shallow depths. The low seismicity in this zone is in marked contrast with major strike-slip faults along which large earthquakes occur at depths shallower than 15–20 km. It is emphasized that these unique features are expected only for restricted regions where there is constant supply of H2O due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface.Large or great thrust-type earthquakes in subduction zones initiate at depths of 30–50 km, below the shallow decoupled zone. In this focal depth range, the supply of H2O during progressive metamorphism perhaps diminishes downwards, the overriding and subducting plates are coupled and stick to each other during much of the inter-seismic period, and the resistance to slip (or shear stress) is presumably high. It is suggested that these earthquakes begin to occur at a depth where the plate-boundary zone becomes fairly dry. Deformation at these depths appears to be predominantly ductile, so that the earthquakes cannot be regarded simply as a brittle phenomenon. (1) Creep instability i.e., instability associated with plastic deformation, and (2) dehydration-induced instability are the most likely mechanisms for initiating the earthquakes, and both have some experimental support. Stick-slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for (1). Shear resistance of halite gouge increases with increasing confining pressure in stick-slip regimes. Hence the observed stick-slip may be a semi-brittle phenomenon with respect to the pressure dependence of the shear resistance, although the deformation texture cannot be distinguished from that formed by pressure-insensitive flow. Serpentine gouge exhibits violent stick-slip upon its decomposition under dry, not wet, environments, supporting the mechanism (2) above. Exact mechanisms which lead to the unstable fault motion are poorly understood as yet, but stick-slip of both halite and serpentine gouges is recognized only when the slip-rate dependence of friction is negative i.e., lower friction at faster slip rate, consistent with the theoretical prediction of Rice and Ruina (1983). There is a possibility that the thrust-type earthquakes can be explained essentially within the framework of fault constitutive laws developed by Dieterich (1979) and Ruina (1983).