地震活动的分形特征及其对地震预测的意义

FRACTAL FEATURES OF EARTHQUAKES AND ITS SIGNIFICANCE IN EARTHQUAKE PREDICTION

岩石破裂是一个自相似过程,地震作为地壳岩石破裂的结果,它在时间和空间上的分布具有分形结构。基于系统科学和分形几何学的观点,本文采用标度变换法和嵌入空间法,分别研究了唐山7.8级、海城7.3级和松潘7.2级地震前后地震活动时、空分布的分维数,同时分析了宁夏灵武5.5级震群和澜沧5.0级前震序列的时间分维随时间的变化特征。初步结果表明:大震后余震的分维数明显增大,无标度区范围减小,展示了震后地震活动随机干扰背景增强！前兆性地震序列的时间分维数相对偏低,有序性增加。此外,文中还研究了单轴压缩下岩石破裂声发射序列的分形特征,结果表明,声发射序列亦具有自相似性,在岩石破坏过程中,声发射序列的分线数随时间的变化不是单调的。最后,籍助于“耗散结构理论”的基本概念,简要地探讨了地震时间、空间分维与地震活动熵的关系。提出了地震时、空分维作为表征地震孕育系统演化过程的序参量之一,应用于地震预测的可能途径及需要进一步研究的若干问题。

Rock fracture is a process of self-similarity, the pattern of earthquake distribution, as a result of fracture in earth crust, possesses fractal features both in time and space. From system theory and the fractal geometry point of view, the fractal structure of seismic activities before and after Tangshan, Haicheng and Songpan-Pingwu earthquakes, as well as Lingwu earthpuake swarm, Lancang earthquake sequence with maximum magnitude 5.0 occurred in August 1988 have been investigated by using Scale Transform method and Inserted space technique. The results show that the fractal dimensions of seismic activities prior to major earthquake (M≥7.0) occurrence are lower than that after the earthquake, the non-scale range of self-similarity in seismic pattern narrowed after the main shocks. It is also illustrated that the precursory earthquake sequences may be possessed of lower fractal dimension. In addition, the fractal characteristics of acoustic emission (AE) of rock samples under uniaxial pressure in laboratory has been studied. It is shown that the fractal dimensions of. AE sequences varied unmonotonously with time before fracture. Finally, Relationship between fractal dimension and entropy of earthquake distribution on the basic concepts of Dissipative Structure Theory are discussed briefly. Possible way in predicting earthquake by using variations of fractal dimension of seismic activities, and some problems needed further study arc outlined.