通过地震活动特征分析、研究地震活动基本规律,对于了解大地震的孕育过程及地震前兆有重要意义.采用"RTL(Region-Time-Length)"算法和"区域网格点密集值"算法对河北地区中强震前的地震活动特征进行分析研究.利用RTL算法对河北地区1970年以来的MS5.0以上地震在时间和空间上进行回顾性检验,以震例6年前地震目录为计算数据.时间扫描结果显示,4次地震震前地震活动平静,1次地震震前地震活动增强.空间扫描结果给出了震例震前三年以1年尺度滑动的扫描图像,与时间结果对应相吻合.区域网格点密集值算法所选资料与RTL算法相同,对研究震例中的三次较大地震(ML≥6.0)进行震前三年尺度滑动的空间扫描.结果显示,随着时间滑动,截至发震前,震中附近区域网格密集值逐渐减小,趋于平静.通过综合应用两种方法,发现地震活动平静的低值点和地震活动增强的高值点对地震的发生有一定的指示意义.%It is of great significance to understand the preparation process and precursor of large earthquake based on analyzing the characteristics of seismic activity and studying on the basic laws of seismic activity. In this paper, RTL (Region-Time-Length) algorithm and seismic density calculation algorithm are used to analyze the seismic activity characteristics of the medium and strong earthquake in Hebei. The RTL algorithm is used to temporally and spatially retrospectively examine the earthquakes above MW5.0 in the study area since 1970, and the seismic catalogues of 6 years ago are used. Time scanning result shows that the seismic activity is calm before the four earthquakes and the seismic activity is stronger before one earthquake. The spatial scanning results show the scanning image in one-year-scale for three years before the earthquake, and the result is consistent with temporal result. The selected data of seismic density algorithm is same as the RTL algorithm, the spatial scanning of three years scale slip before the earthquake is carried out for the three major earthquakes (ML≥6.0) in the earthquake cases. The results show that, with time sliding, the seismic density of the area near the epicenter gradually decreases and tends towards calm before the earthquake. The results of the two methods show that the low point of seismic activity and the high value point of seismic activity may have some reference value for the prediction of earthquake in this region.
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