地震空间分布因子Z_K及其在中强地震前后的变化特征

SEISMIC SPATIAL DISTRIBUTION FACTOR Z_K AND VARIED FEATURES AROUND MODERATELY STRONG EARTHQUAKES

本文引入空间距离方法用于定量分析地震空间分布特征,所定义的地震空间分布因子Z_K可以较好地判断地震空间分布类型,当Z_K→1时表征地震空间分布具有丛集的特征,Z_K在0.5附近波动说明空间中地震是随机分布的;Z_K→0则可能对应于地震的网格分布图象。从更深层次上来看,ZK值的变化从地震空间分布的角度出发,在某种程度上反映了孕震系统有序复杂程度的动态变化。 以1970年以来华北地区10次M_s≥5.8地震为例,对Z_K值在中强地震前后的变化特征进行了探讨。结果表明中强地震前普遍地可检测到高Z_K异常值,具有实用意义的是可以统一地取Z_(αυ=0.642作为异常判断标准。两个7级以上强震前的高Z_K异常值一般持续时间较短、上升较快、幅度较大,强震发生于Z_K最大值附近。中强地震前的高Z_K异常则持续时间较长、变化平缓、异常幅度较小,地震多于异常结束后一年多的时间内发生。 最后本文就震级下限、区域范围对Z_K值的影响等其它一些问题进行了讨论。

This paper introduced the spatial distance method to analyze the seismic spatical distribution features quantitatively. The seismic spatial distribution factor Zk defined can distinguish the seismic spatial distribution type better. When ZK approached 1, the spatial distribution of characteristic earthquakes is of clustering feature; When ZK value fluctuated around 0.5, it shows that spatial distribution of earthquakes is stochastic; When Zk approached O, it possibly corresponds to the network distribution pattern of earthquakes. From the angle of the seismic spatial distribution, Zit-value changes reflected the dynamic variation of the ordered and complicated degrees of seismogenic system to some extent.Taking 10 Ms ≥ 5.8 earthquakes in North China since 1970 for an example, the paper discussed the variation features of Zx around moderately strong earthquakes. Results show that high anomaly Zk value can be detected commonly before moderately strong events- The Zk = 0.642 can be taken for distinguishing criterion of anomaly. High anomaly Zk value before 2 M>7.0 strong quakes generally lasfed for a shorter period with faster rising and larger amplitude, and strong earthquakes occurred in the vicinity of maximum ZK value. The high anomaly Zk value before moderately strong earthquakes lasted for a longer period with smooth variation and smaller anomalous amplitude. Earthquakes occurred in more than one year after the ending of the anomaly-Finally, some problems, such as influences of low limit of magnitude and regional extent on the Zk value were discussed in this paper.