东南沿海地震带20世纪活跃幕划分及活动周期分析

探讨了东南沿海地震带20世纪以来在时间分布方面存在的密集－平静相互交替的丛集现象。 对以往按地震能量释放的分布划分出的活跃—平静幕数目不等的多种结果; 对东南沿海地区54次M≥43/4地震的时间间隔序列, 在使用有序样品聚类分析中的“离差平方和”法及误差函数法, 从误差随分段数增加而减少的拐点值及误差函数比值认为四段活跃幕划分是合理的。 从 1943 年之后, 计算得出的东南沿海地区中强以上地震序列的时间变异系数δ值为1.2 , 明显处于丛集状态。 对东南沿海地震区20世纪以来四个地震活跃幕中, 其丛集非线性时间结构演化幂指数, 即各幕地震的累积频次与发震系统内部时间的关系基本符合为N=ct^d。 4个活跃幕的演化幂指数d变化范围分布在0.7~0.8。 东南沿海地震区20世纪以来M6.0以上的强震也基本符合该关系式。 只是其活跃幕演化幂指数d为 0.47 。

Division of active episodes in 20th century and analysis on active period along the Southeast Coastal Seismic Zone

There is a phenomenon along China Southeast Coastal Seismic Zone that the earthquakes swarming and seismic tranquility have been alternately occurred since 20th century. According to the distribution of seismic strain relief, there are several results of division between the active episodes and quiet episodes. Using the square-error method among ordered sample sequence clustering analysis on 54 earthquakes occurrence time interval series, and according to the changes of parameters of the error function e.g. the point of inflexion, F value etc., we consider that dividing result of 4 active seismic episodes is more reasonable. Considering another parameter of the earthquake occurrence time interval series-time variation coefficient δ, the calculated results for moderately strong earthquake series (M≥4) along southeast coastal seismic zone since 1943 indicate that earthquake clustering situation has been obvious from then. For each of the 4 active episodes, the accumulated number of earthquakes vs. the earthquake occurrence time basically accorded with the formula N=ct^d. The evolution power exponent d changed from about 0.7 to 0.8, the accumulated number of strong earthquakes (M≥6.0) accorded with the formula too, but its power exponent d is 0.47.