四川及邻区强震前地震活动频度的变化特征

Variation Characteristics of Seismic Frequency before Strong Earthquakes in Sichuan and Its Neighbouring Region

对发生在四川及邻区的 17次 6级以上强震事件的震前中小地震活动进行了分析 ,发现在这些主震前均出现了区域性、中期或短期的中小地震活动增强或平静的过程。这种过程可用四川地区 3 5～ 5 9级地震的月频次变化来进行量化 ,并可作为预测四川及其邻区 6级以上强震的一项指标。经反复试验 ,本文提出判别地震月频次异常的标准 ,给出将异常用于强地震预报的规则 ,同时 ,对该项指标的预测效能进行了内符检验。结果表明

In this paper, the seismicity of the moderate-small earthquakes prior to 17 strong earthquakes with M≥6.0 occurred in Sichuan and its neighbouring region is analyzed. Then, a phenomenon is discovered that before the occurrence of the 17 mainshocks, there was always a process in which the activity of the moderate-small earthquakes would enhance or become quiescent in a regional, moderate-term or short-term way. The process can be described quantitatively by the variation of monthly frequency of occurrence of earthquakes with the magnitudes range from 3.5 to 5.9 in Sichuan Region. Further, the process can be taken as an indicator for predicting the strong earthquakes with M≥6.0 in Sichuan and its neighbouring region. After repeated trials, the criteria for identifying the anomaly of monthly frequency and the rule for application of anomaly to the prediction efficiency of the indicator is tested by way of interior-fitting. The result shows that the indicator of monthly frequency has an ideal efficiency for the mid-term earthquake prediction. And it has certain efficiency for the short-term prediction.