Principal earthquakes: Theory and observations from the 2008 West Bohemia swarm
Principal earthquakes: Theory and observations from the 2008 West Bohemia swarm
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主要地震：2008 年西波西米亚群地震的理论和观测
DOI：
10.1016/j.epsl.2011.03.002
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发表时间：
2011
影响因子：
5.3
通讯作者：
V. Vavryčuk
中科院分区：
文献类型：
--
作者：
V. Vavryčuk
发生在相对于构造应力状态的最佳定向断层面上的地震显示出两种不同的震源机制，并且是每个地震活跃区的基本特征。这些地震，我们称之为“主要的”，不需要与最强的地震重合，也不需要沿着该地区的主要活动断层发生。在一定应力下对不稳定断层面的稳定性分析表明，与不稳定断层面有关的震源机制与主震的震源机制不应有很大区别。P/T轴形成具有典型双翼或“蝴蝶”图案的簇。这种模式是特别明显的破坏曲线定义为投影的莫尔图中的莫尔-库仑破坏准则的焦球。的位置，形状和大小的故障曲线取决于应力方向，形状比，摩擦和Mohr's diagraph.理论分析的不稳定区域的大小进行了测试，使用准确确定的震源机制99微地震发生在2008年在西波希米亚/Vogtland地区的地震群。P/T轴的分布揭示了在数值模拟中预测的蝴蝶翅膀图案。断裂面主要集中在Mohr-Coulomb破坏准则有效的区域。断层的平均摩擦力为0.5，相当于主断层与σ 1轴的偏差为32°。左旋走滑主断裂是震群活动最活跃的断裂。它在地表上几乎没有地质表现，但在深度上被一组线性震源清楚地界定。右旋走滑主断层活动性较弱，但在地质上在地球表面表现良好。
Earthquakes that occur on optimally oriented fault planes with respect to the tectonic stress regime display two distinct focal mechanisms and are fundamental characteristics of each seismically active region. These earthquakes, which we term ‘principal’, need not coincide with the strongest earthquakes or need not occur along the major active faults in the region. Stability analysis of diversely oriented fault planes under a given stress reveals that the focal mechanisms connected with unstable fault planes should not be very distinct from those of the principal earthquakes. The P/T axes form clusters with a typical two-wing or ‘butterfly’ pattern. This pattern is particularly visible when constructing the failure curves defined as a projection of the Mohr–Coulomb failure criterion in the Mohr's diagram onto the focal sphere. The position, shape and size of the failure curves depend on the stress orientation, shape ratio, friction and on the size of the instability area in the Mohr's diagram.The theoretical analysis is tested using accurately determined focal mechanisms of 99 micro-earthquakes that occurred during the 2008 earthquake swarm in the West Bohemia/Vogtland region. The distribution of P/T axes reveals the butterfly wing pattern predicted in numerical modelling. The activated fault planes concentrate in the area of validity of the Mohr–Coulomb failure criterion. The average friction of faults is 0.5 and corresponds to a deviation of 32° of the principal faults from theσ1axis. The left-lateral strike-slip principal fault was the most active fault during the swarm. It shows little geological expression at the surface but it is clearly defined by a linear cluster of hypocentres at depth. The right-lateral strike-slip principal fault was less active but it is geologically well manifested on the Earth's surface.