Modelling the compliance of crustal rock—II. Response to temporal changes before earthquakes
Modelling the compliance of crustal rock—II. Response to temporal changes before earthquakes
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DOI：
10.1111/j.1365-246x.1997.tb04489.x
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发表时间：
1997-06
影响因子：
2.8
通讯作者：
S. Crampin;S. Zatsepin
中科院分区：
文献类型：
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作者：
S. Crampin;S. Zatsepin
有几种说法认为地震剪切波对地震前的应力变化有反应。配套文件开发了一个应力敏感模型（APE）的行为低孔隙度低渗透率的结晶岩石中含有普遍分布的充满流体的粒间微裂纹，本文使用APE模拟地震前的行为。模拟与APE表明，这种充满流体的微裂纹的分布的微观几何形状和统计几乎立即响应应力的变化，并且可以通过分析地震剪切波分裂的行为进行监测。讨论了横波分裂与差应力耦合的物理原因。在本文中，我们扩展了模型，利用逾渗理论表明，大的裂纹密度是有限的，在颗粒尺度水平的逾渗阈值，相互作用的裂纹群导致显着增加岩石基质的渗透性。在最简单的公式中，建模是无量纲的，几乎完全受约束，没有自由参数。然而，APE模拟应力下流体饱和岩石的演化再现了所观察到的断裂临界性和地壳岩石中剪切波方位各向异性的窄范围。它还再现了1986年，M= 6，北棕榈泉地震，南加州，和其他几个较小的地震之前和之后观察到的剪切波分裂的时间变化的行为。APE建模与广泛的观测结果的一致性证实，流体饱和的结晶岩石是应力敏感的，并在微观水平上通过临界流体-岩石相互作用对应力变化作出反应。这意味着应力和其他参数变化的影响可以通过适当的地震剪切波观测进行数值模拟和监测。
SUMMARY There have been several claims that seismic shear waves respond to changes in stress before earthquakes. The companion paper develops a stress-sensitive model (APE) for the behaviour of low-porosity low-permeability crystalline rocks containing pervasive distributions of fluid-filled intergranular microcracks, and this paper uses APE to model the behaviour before earthquakes. Modelling with APE shows that the microgeometry and statistics of distributions of such fluid-filled microcracks respond almost immediately to changes in stress, and that the behaviour can be monitored by analysing seismic shear-wave splitting. The physical reasons for the coupling between shear-wave splitting and differential stress are discussed. In this paper, we extend the model by using percolation theory to show that large crack densities are limited at the grain-scale level by the percolation threshold at which interacting crack clusters lead to pronounced increases in rock-matrix permeability. In the simplest formulation, the modelling is dimensionless and almost entirely constrained without free parameters. Nevertheless, APE modelling of the evolution of fluid-saturated rocks under stress reproduces the observed fracture criticality and the narrow range of shear-wave azimuthal anisotropy in crustal rocks. It also reproduces the behaviour of temporal variations in shear-wave splitting observed before and after the 1986, M= 6, North Palm Springs earthquake, Southern California, and several other smaller earthquakes. The agreement of APE modelling with a wide range of observations confirms that fluid-saturated crystalline rocks are stress-sensitive and respond to changes in stress by critical fluid-rock interactions at the microscale level. This means that the effects of changes in stress and other parameters can be numerically modelled and monitored by appropriate observations of seismic shear waves.