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本文利用我国22个地磁台1971～1977年的垂直分量静日变幅值,通过年变、季变、纬变影响等改正后算取的季均值作为基本数据,分析了其震前特征。研究发现,华北、川滇地区的四次大震,均在震前一个季度,其日变幅值的空间分布出现以未来大震震中区为中心的一个大范围的正异常,日变时序曲线同样具有清晰的异常反映。用日变时序曲线与波速比异常相比后认为,日变异常主要是由于孕震区流体(水)运动产生电导率异常,使地磁内场变化的结果。因而,应用地磁日变时、空特征预测大震的可能位置及发震时间,具有一定的价值。
Based on the static daily variation of vertical component of 22 geomagnetic stations from 1971 to 1977 in our country, this paper analyzes the pre-earthquake features by taking the quarter-averaged values of the vertical component obtained from the correction of annual change, seasonal change and latitudinal change as basic data. It is found that the four major earthquakes in North China, Sichuan-Yunnan region all showed a large range of positive anomalies and diurnal variation curves centered around the epicenter of the future epicenter during the quarter before earthquakes The same has a clear exception. Compared with the anomaly of the wave velocity ratio, the diurnal variation curves show that the diurnal variation is mainly due to the abnormal conductivity caused by fluid (water) movement in the seismogenic zone and the change of the geomagnetic field. Therefore, when geomagnetic diurnal variation is used, it is of some value to predict the possible locations of major earthquakes and the time of occurrence of an earthquake with the space feature.