强震前大范围地震活动性参数的时空扫描

在大地震发生之前, 伴随着应力的集中加强及其在震源附近区域引起的非弹性变形, 区域地震活动性可能呈现某些异常特征.本文选择一些有明显物理意义并得到岩石破裂实验支持的地震活动性参数, 例如有震面积数 A、平均释放能量E、地震累加频度 N 和大小地震比例系数 b 值等, 采用扫描方法在大范围内搜索, 识别孕育强震的危险地区, 并对假想孕震区进一步做时间扫描计算, 寻找并判断大震前由中期异常过渡到中短期异常的阶段, 在对华北、西南及东北若干强震资料扫描计算的基础上, 着重剖析唐山地震前华北地区区域地震活动异常变化的一些特征.讨论了上述地震活动性参数在强震中期预报中的不同效能, 认为这种时空扫描方法, 特别是 b 值扫描应用于强震的中期预报是有一定意义的. 

TIME AND SPACE SCANNING OF PARAMETERS OF SEISMICITY OVER A BROAD REGION BEFORE STRONG EARTHQUAKES

Before strong earthquakes, certain anomalous features may show up in the seismicity of a broad region possibly caused by the concentration of stress and the ensuing anelastic deformation at the source region of the earthquakes. Certain parameters of seismicity with rather obvious physical meanings and supported by the results of rock fracture experiments, are selected for the study, namely the areal extent A of the seismic active area, seismic energy released E, accumulative numbers N of earthquakes and the value b of large and small earthquakes and so on. A method of scanning has been adopted to search at first for the dangerous location under which a strong earthquake is in the process of development and then by applying time scanning to show further the transition from medium to medium-short range of anomalous features of seismic activity before the occurrence of a large earthquake.On the basis of scanning on the observed seismicity data of North China, Southwest China and Northeast China before several large earthquakes, emphasis has been laid on the anomalous seismic feature of North China before the 1976 Tangshan Earthquake of magnitude 7.8. The paper also discusses the different roles played by the parameters of seismicity in mediumterm prediction of strong earthquakes. It is believed that such a method of time and) space scanning, particularly of the b value has certain significance in medium-term earthquake prediction.