Morishita播散指数在地震空间分布丛集分析中的应用

APPLICATION OF MORISHITA SPREAD INDEX TO THE CLUSTER ANALYSIS OF SEISMIC SPACE DISTRIBUTION

本文以汾渭地震带地震丛集分布研究为例探讨了Morishita播散指数在地震空间分布分析中的应用,并与地震空间集中度C值统计方法进行了比较。结果表明,这种方法无需对资料中特定分布作任何假定,能够直接表述地震的空间分布集中程度,且计算方法简单、可靠。震例分析表明,5级左右中强地震前几年,地震形成小的丛集团块,地震活动以小震群为主,前一年左右地震成团块结构,尺度约为几十公里,但并不伴随明显的震群活动,这种不同时期的地震图象反映了非均匀的应力场变化图象,具有一定前兆意义。

Taking the research of seismic cluster distribution along Fenwei seismic zone as an example, the application of Morishita spread index to the seismic space distribution analysis has been approached and comparison between the index and the seismic space distribution value C has been made. The results show that the index method dose not nees any hypothesis; it is able to describe directly the concentration degree of seismic space distribution and compute simply and reliablly. Analysis of earthquake cases demonstrates that the earthquakes formed a cluster mass of a small scate and the seismicty is dominated by small earthquake swarms. And the seismicity showed a mass structure with a circumference of several tens square kilometers but no obvious swarm activity accompanied before several years and one or two years, respectively. These phenomena reflect a heterogeneous stress variation during the different episodes and have a certain precursory meaning.