【摘要】 １９７４年永善７．１级地震前地震活动性在演变过程中表现出很强的异常特征：（１）围绕主震形成一个地震活动增强区，而主震处于增强区内的空区，从而形成环形分布；（２）在孕震过程中，增强区经历了一个走向由ＮＥ向变为ＮＷ向、区域由大变小的过程；（３）增强区内地震活动性呈现出很强的２０年的韵律性，而在主震前增强区形成阶段长周期（２０年）却消失，短周期（５年以内）突出。然后从连续介质力学角度，运用包体模型的力学场特征对此次地震前活动异常特征进行了解释。从而对本研究区的地震趋势进行了预测。更多还原

【Abstract】 During the evolution process of seismicity before Yongshan Earthquake of 7.1 in 1974,the anomalous characteristics has shown as followings:(1) Seismicity enhanced region had been formed around the epicenter of the major shock which was situated in the gap.So the ring distribution was abvious.(2)In the process of earthquake preparation,the strike of the seismicity enhanced region was changed from NE to NW,and its size was changed from big to small.(3)There was a seismicity rhythm about 20 years in the seismicity enhanced region,however,there was only short period less than 5 years instead of the long period of 20 years in the stage before the major shock.Then we discussed these anomalous characteristics by using the model of two-dimensional circular inclusion,and made a prediction of seismicity trend in the studying region in this paper.更多还原