苍山5.2级地震前的R(t)图异常特征及其时间变化

R(T)ANOMALY CHARACTERISTICS AND TEMPORARY VARIATIONS BEFORE CANGSHAN 5 2 EARTHQUAKE

研究了１９９５ 年苍山５２ 级地震前地震时空分布参数Ｒ （ｔ） 图的异常变化， 由Ｒ （ｔ）图清楚的反映出苍山５２ 级地震前地震活动的三个阶段性发展特征。即早期地震活动增强，形成大的孕震空区； 中期在上述背景上地震活动再次向外围扩散并收缩， 地震活动逐渐减弱， 孕震空区缩小； 晚期地震活动出现短平静（１８ 个月无ＭＬ≥２５ 级地震） ； 临震前１８ 天孕震空区内出现３ 个特征前震，

This paper has studied the R(t)anomalous variations before Cangshan earthquake of M 5 2 in 1995.From the R(t),it is clearly demonstrated that there exist three developing features before the event.That is early period when seismicity increases and forming a big seismogenic gap;middle period when seismicity once again spreads outside and more concentrated,seismicity gradually drops down,and seismogenic area becomes smaller,late period when seismicity shows short quiescence(without ML≥2 5 in 18 months).18 days before the impending earthquake,there appear 3 characteristic foreshocks in the seismogenic area,forming a impending line.