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前言 关于地震前兆的反应距离问题,多年来一直为地震学者所关注。一些地震的资料表明,地震前后在震源及附近直至数百公里处,都可能出现异常现象。一般认为,震源附近(近场)出现前兆异常是有着较明确的机理的,而对远距离处的异常(远场)人们则常持审慎的态度。然而已有不少资料说明大陆地震的远场异常是客观存在的。近几年来苏联学者亦提出了远场前兆问题,认为这一现象增加了地震预报的难度。对此问题,从观测事实、概念到物理解释都有待更深入的工作来加以阐明。本文试以华北地区的资料为例,对地震前后的远场异常问题进行讨论。
Foreword The response distance to earthquake precursors has been of concern to seismologists for many years. Some earthquakes show that anomalies can occur in the Earth’s vicinity and up to hundreds of kilometers before and after the earthquake. It is generally believed that there is a definite mechanism for the occurrence of precursor anomalies near the source (near field), and people are often cautious about abnormalities (far fields) at long distances. However, a great deal of information shows that the far-field anomaly of the mainland earthquake is an objective reality. In recent years, Soviet scholars have also proposed the issue of far-field precursors, believing that this phenomenon has increased the difficulty of earthquake prediction. This problem, from the observation of facts, concepts to the physical explanation needs further work to clarify. This paper, taking the data of North China as an example, discusses the far-field anomalies before and after the earthquake.