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首页> 外文期刊>Journal of geophysical research. Solid earth: JGR >The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms
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The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms

机译：静态应力变化，动态应力变化和背景应力对余震震源机制的影响

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摘要

The focal mechanisms of earthquakes in Southern California before and after four M6.7 main shocks provide insight into how fault systems respond to stress and changes in stress. The main shock static stress changes have two observed impacts on the seismicity: changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress. The aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of 0.02MPa, for up to similar to 20years following the main shock. The dynamic stress changes have similar, although smaller, effects on the local focal mechanisms and the spatial seismicity distribution. Dynamic stress effects are best observed at long periods (30-60s) and for metrics based on repeated stress cycling in the same direction. This implies that dynamic triggering operates, at least in part, through cyclic shear stress loading in the direction of fault slip. The background stress also strongly controls both the preshock and aftershock mechanisms. While most aftershock mechanisms are well oriented in the background stress field, 10% of aftershocks are identified as poorly oriented outliers, which may indicate limited heterogeneity in the postmain shock stress field. The fault plane orientations of the outliers are well oriented in the background stress, while their slip directions are not, implying that the background stress restricts the distribution of available fault planes.
机译：在四次M6.7主震之前和之后，南加州地震的震源机制使人们可以深入了解断层系统如何应对应力和应力变化。观察到的主要冲击静应力变化对地震活动有两个影响：更改给定位置的震源机制，以偏向与静应力变化一致的震源机制;改变地震活动的空间分布，以偏向于静应力变化与背景一致的震源。强调。余震的震源机制与静应力变化显着一致，绝对应力变化为0.02MPa，长达20年。动应力变化对局部震源机制和空间地震活动性分布具有相似但较小的影响。动态应力效果最好在长时间（30-60s）内以及基于基于相同方向上反复应力循环的度量中观察到。这意味着动态触发至少部分地通过沿断层滑动方向的周期性剪切应力加载来进行。背景应力还强烈控制震前和震后机制。尽管大多数余震机制在背景应力场中都很好地定向，但是10％的余震被确定为定向差的离群值，这可能表明主震后应力场中的异质性有限。离群点的断层平面取向在背景应力中取向良好，而其滑动方向却不正确，这意味着背景应力限制了可用断层平面的分布。

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