本文基于自然正交函数展开方法,以地震应变为变量,计算1980年以来中国大陆7级以上大震前的地震应变,提取出大震前区域地震活动应变场的时空异常.结果表明大震前时间因子在平稳背景上会出现突跳上升或突跳下降异常变化.一般情况下,前4个应变场中至少有3个出现异常变化,异常分布具有多分量特点,出现的最早时间大约在震前3年,少数出现在震前1～6个月.对比应变场时间因子异常与研究区域每个网格单元(0.5°×0.5°)内的地震能量时间因子异常形态的相似性、时间的一致性,找出地震应变场空间异常位置.结果表明,多数大震前的空间异常分布在主震震中周围;少数大震的空间异常远离主震震中.产生这种现象的原因是大震前与主震不同距离的单元网格内发生中短期或者临震的震群、显著地震等地震活动性异常.%Based on natural orthogonal function expansion method and taking seismic strain as variable, we studied the seismic strain before the earthquakes above magnitude 7 in China since 1980, and extracted temporal and spatial anomalies of strain field before the earthquakes. The results show that the time factor before earthquakes above magnitude 7 show jump-up or jump-down changes, and under normal circumstances, at least 3 of the the first 4 strain fields show abnormal changes with multi component distribution characteristics, and the earliest time of abnormality is about 3 years before the earthquake, a few occurred 1～6 months ago. Contrasting the time factor of strain field with seismic energy within the time factor, abnormal shape similarity, the consistency of time in each grid cell (0.5°×0.5°), we can find the exact location of the anomalous seismic strain space. The spatial anomalies before most major earthquakes are distributed around the main earthquake. The spatial anomaly of a few large earthquakes is far away from the main earthquake epicenter. The reason for this phenomenon is that the short and short term or impending earthquake groups and significant earthquakes occur in the cell grid with different distances from the main earthquake before the major earthquake. Finally, the reasonableness of calculating the space-time anomaly of strain field to delete the aftershock is discussed.
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