岩爆的分形特征和机理

FRACTAL CHARACTER AND MECHANISM OF ROCK BURSTS

本文应用分形几何和损伤力学研究了岩爆诱发的微地震。使用分形的数目—半径关系考察了已报导的微地震事件的位置分布,发现它具有集聚(cluster)分形结构。当接近一个主岩爆时,微地震事件的集聚程度明显增加,并相应地出现分形维数值的减小。最低的分形维数值通常出现在一个主岩爆临近产生之时。这样,分形维数的变化就有可能用来进行岩爆的预测预报。这种变化与地震学中强震发生前的降维现象(b值减小)是完全一致的,我们使用损伤力学和分形概念从理论上分析了岩爆的分形和物理机理。研究表明:一个强的破坏(岩爆或地震)实际上等效于岩体内破裂的一个分形集聚。这个破裂的分形集聚所需能量耗散E随分形维数D的减小而按指数律增加:D=C_1exp[—C_2E]这样,岩爆和地震的分形自然在理论上得到很好的解释,并由此人们能更好地去理解岩爆和地震的发生和发展。

In this paper, the microseismicity associated with rock bursts is studied by using fractal geometry and damage mechanics. Based on the number-radius relationship of ffactals, the distributions of previously reported microseismic event locations are examined and are found to have a fractal clustering structure. The degree of clustering of microseismic events increases with the impending of a main rock burst and corresponds to a decreasing fractal dimension. The fractal demension generally attains a minimum near the occurrence of a rock burst. Thus, the fractal dimension has a potential use as a rock burst predictor. This fractal nature of rock bursts is consistent with the conclusion in seismology which says that a lower fractal dimension (or b-value) is associated with the occurrence of a main earthquake. The fractal and physical mechanisms of rock bursts are analyzed theoretically by using damage mechanics and the fractal concept. A violent failure (a rock burst or an earthquake) is regarded as being equivalent to a fractal cluster of fracturing within the rock mass. The energy release E of a fractal cluster of fracturing events within the rock mass increases exponentially with a decrease of the fractal dimension D in the form of D=C_1exp〔-C_2E〕. Thus,the fractal nature of rock bursts and earthquakes is well explained in theory, and a better understanding of rock bursts is obtained.