华东地区地震活动性参数的中短期异常动态变化特征

系统地研究了华东地区中强震前地震活动参数的演化特征 ,尤其是追踪研究了中短期阶段各参数的动态变化特征。结果表明 ,华东地区中强震孕育中短期阶段 ,有不少地震活动性参数图像出现明显的变化 ,如C值、D值、Mf 值和b值在中期阶段存在的大面积异常区开始出现明显的收缩甚至消失 ,这种变化是地震孕育过程进入中短期阶段的重要标志。未来主震往往发生在收缩区边缘或异常消失区 ,若当消失区再次出现小片异常 ,则该异常区是未来最为值得注意的危险区 ,而且时间上很可能进入短临。再如地震算法复杂性AC值由超出 1倍均方差的峰值下降、广义分维Dt由正常值下降并出现超过 1倍均方差的低值异常 ,也是地震孕育过程进入中短期阶段的判据。由于地震孕育是一个十分复杂的过程 ,在实际工作中需应用多种参数扫描结果进行综合判定 ,以便于缩小异常区 ,提高中短期预报的准确率。

Characteristics of the middle short- term dynamic variations in the anomalies of seismicity parameters in the East China region

The characteristics of the evolution of the seismicity parameters prior to moderate earthquakes in the East China region have been studied systematically,especially,the characteristics of the dynamic variations of the parameters in the middle short-term stage have been tracked The results have shown that obvious variations appear in the seismicity patterns for a number of seismicity parameters during the middle short-term stage of the preparation of moderate earthquakes in the East China region An important indicator for the entry of the earthquake preparation process into the middle short-term stage is that the large anomalous areas of the C -value,D-value, M f-value and b -value existing in the middle-term stage begin to contract obviously or even to disappear The impending mainshock occurs often in the marginal area of the contracted area or in the area of anomaly disappearance If small anomalous area appears again in the area of disappeared anomalies,this anomalous area will be a dangerous area worthy of most attention,and the phenomenon might probably mean the entry of the earthquake preparation process into the short-term/imminent stage Each of the following two phenomena can be taken as such criterion for the entry into the middle short-term stage too: 1 The AC -value(the algorithmic complexity)decreases from the peak exceeding its normal value by more than one standard deviations 2 The D t-value(the fractal in a broad sense)decreases from its normal value and low-value anomalies with an amplitude larger than one standard deviation appear Due to the complexity of the earthquake preparation process,a combined examination based on the scanning results from several parameters should be made in the practice to reduce the anomalous area and to enhance the accuracy of the middle short-term earthquake prediction