华北地区中强震前中小地震活动的动态演化特征研究

应用地震活动加速指数AI算法对华北地区1970年以来M_L≥6.0地震进行了回溯性研究。 利用该方法统计中强震前的中小地震活动频度, 分析结果显示在空间上能够反应出中小震活动频度的异常。 另外, 应用有关地震活动的频度面积S值方法, 对M_L6.0级以上强震前后的中小地震活动在时间分布上进行了研究, 此方法对AI算法的计算结果在时间上给予了支持。 结果表明: AI指数能够量化地给出中强震前中小地震活动的相对增强或减弱程度, 中强震的S值在震前表现为高值或低值异常, 震后下降或上升。 S值的异常点与AI扫描值的异常结果在时空分布上相辅相成。 在地震目录完整的情况下, 中强震震中区及其附近地区震前1 a的中小地震活动与之前3 a、 5 a的活动背景相比, 出现明显的“加速”或“减速”现象。 利用这两个参量的变化, 可为该地区中强震的预测分析提供一定的判定指标。

Dynamic Evolution Characteristics of Small-middle Earthquake Activity before Moderate-strong Earthquakes in North China

The Acceleration Index (AI) algorithm was applied in a statistical retrospective research for earthquakes with M_L≥6.0 since 1970 in northern China.We calculated the activity frequency of small-middle earthquakes before strong earthquakes with this method. The results show that AI vales can reflect abnormal frequency of mid-small earthquakes in space. Moreover, studying the seismicity of small-middle earthquakes before and after the moderately strong earthquakes (M_L≥6.0) with Frequency-Area Method (namely S-value method), this method gives support on the calculating results of AI algorithm in time. AI valuse can quantitatively indicate activity strengthening or weakening level of micro-earthquakes before the moderate-to-strong shocks. The S-value of moderate-strong earthquakes exhibits high anomalous values or low anomalous ones before strong earthquake occurs and it decreases or increases after the strong earthquake occurred. Abnormal point of S-values and abnormal result of AI scan values are complementary in space and time. In the case of integral earthquake catalog, small-middle earthquakes activity 1 year before the earthquake compared with the activity background of previous three years, five years in moderately strong earthquake epicenter and its adjacent area, it shows obviously “accelerated” or “slow down” phenomenon. The change of the two parameters can be used as indicators for moderate-strong earthquake prediction in north China.