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通常,修正的大森定律 n(t)∝t~(-p)能很好地描述余震的衰减速率,其中n(t)表示单位时间的余震数,t 是主震后的时间,p 为0.9～1.5之间并通常接近于1的常数。然而,也存在一些更复杂的余震序列,大森定律只能被用作其一级近似。1996年2月18日发生在东比利牛斯地震的余震序列就是这些复杂余震系列中的一个,correig 等(1997)对该地震进行过详细的描述。本文中,我们受动态纤维束模型的启发而提出了一种新的模型,用来解释余震速率突然增加的这类复杂的余震序列,而速率的增加与余震的震级无直接关系(如传染型余震序列)。这是一种简单、离散和随机破裂的模型,它的单元(凹凸体或障碍体)会由于局部荷载共享规律而引起的静态疲劳和应力转移而破裂并又重新生成。我们发现这种模型与东比利牛斯余震序列非常一致,除岩石强度随时间变化的部分之外,我们认为余震的主要机制是存在动态应力的变化,而这种变化往往又为序列中下一个余震重新设置了初始条件。
In general, the modified Omori’s law n (t) αt ~ (-p) is a good description of the aftershock decay rate, where n (t) represents the number of aftershocks per unit time, t the time after the mainshock, and p is 0.9 ~ 1.5 and usually close to a constant of 1. However, there are also some more complex aftershock sequences, and Omori’s law can only be used as a first-order approximation. The aftershock sequence that occurred on February 18, 1996 in the East Pyrenees is one of these complex series of aftershocks, which Correig et al. (1997) described in detail. In this paper, we propose a new model, inspired by the dynamic fiber bundle model, to explain such a complex aftershock sequence with a sudden increase in aftershock rate without any direct correlation with the magnitude of aftershocks Aftershock sequence). This is a simple, discrete and stochastic model. Its elements (asperities or obstacles) are ruptured and regenerated due to static fatigue and stress transfer caused by the law of local load sharing. We find that this model is in good agreement with the East Pyrenees aftershock sequence. Except for the part of rock strength that varies with time, we believe that the main mechanism of aftershock is the existence of dynamic stress changes, A aftershock reset the initial conditions.