Correlations of earthquake focal mechanisms
Correlations of earthquake focal mechanisms
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地震震源机制的相关性
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发表时间：
1992
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通讯作者：
Y. Kagan
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作者：
Y. Kagan
我们对地震矩张量解的哈佛目录进行了统计分析。我们研究了震源在地震震源球上的分布。震源沿着断层面集中分布，不同深度范围的地震震源分布无明显差异。为了研究震源机制的旋转，我们解决了一个双力偶震源三维旋转的反问题，即，对于每一对焦点机构，我们找到将一个机构旋转到另一个机构的所有四个3-D旋转。的随机失向的焦点机制是很好的近似旋转柯西分布，这是以前已经确定通过理论论证和模拟的结果，在介质中的随机缺陷引起的应力扰动。柯西分布由一个参数K表征; K = 0表示没有旋转，K > 0.5对应于近似随机旋转。对于地震震源机制，断层带中的K值在0.05和0.1之间，并且它随事件对之间的距离而增加。在断层面以外的方向上，K值达到0.5;柯西分布接近于完全随机旋转。虽然K随深度缓慢增加，但一般而言，不同深度范围内震源机制解的定向误差具有相同的相关性。因此，我们可以得出结论，深源地震与浅源地震一样，受相同的应力相互作用机制控制。这些测量的结果使我们对震源理论中常用的一些术语和模型的适用性提出了质疑。例如，我们认为，构造地震使具有大规模缺陷（或断层）的岩石材料破裂，其大小与它们起源的构造块体相当。岩石的性质应该与常规材料的性质显著不同，常规材料的缺陷尺寸通常远小于感兴趣的尺度。这些性质应强烈依赖于主要缺陷的几何形状（位置和方向）。
SUMMARY We performed a statistical analysis of the Harvard catalogue of seismic moment tensor solutions. We investigated the distribution of hypocentres on focal spheres of earthquakes. The hypocentres are concentrated along fault planes; the hypocentre distribution does not significantly differ for earthquakes in different depth ranges. To study the rotation of focal mechanisms, we have solved an inverse problem of a 3-D rotation of double-couple earthquake sources, i.e., for each pair of focal mechanisms we find all four 3-D rotations which rotate one mechanism into another. The stochastic disorientation of focal mechanisms is well approximated by the rotational Cauchy distribution which has previously been identified through theoretical arguments and simulations as the result of stress perturbations caused by random defects in the medium. The Cauchy distribution is characterized by one parameter, K; K = 0 means no rotations, and K > 0.5 corresponds to approximately random rotation. For earthquake focal mechanisms the value of K is between 0.05 and 0.1 in a fault zone, and it increases with distance between pairs of events. In directions other than a fault plane, K reaches the value 0.5; the Cauchy distribution is then close to completely random rotations. Although K increases slowly with depth, in general, disorientations of focal mechanisms in various depth ranges display the same dependence. Therefore, we can conclude that deep earthquakes are controlled by the same stress interaction regime as shallow events. The results of these measurements made us question the suitability of some terms and models that are commonly used in the theory of an earthquake source. For example, we argued that tectonic earthquakes rupture rock material which has large-scale defects (or faults), comparable in size with tectonic blocks in which they originate. Properties of the rocks should be significantly different from those of regular materials where the size of defects is typically much smaller than the scale of interest. These properties should strongly depend on the geometry (location and orientation) of major defects.