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对中国大陆具备相对完整资料的367次5级以上地震,分5个工作片区进行统一定性要求的地震空区图像扫描,得到194次震前的空区图像.其中震前有空区地震与研究地震的比例分别为:华北片区14∶36;华东南片区21∶24;川滇片区68∶124;青藏高原北部片区36∶82;新疆片区55∶101.震前出现空区图像比例最低的为华北地区,最高的为华东南地区,新疆与川滇地区基本相当.在此基础上着重讨论了空区形成后发生的主震与空区形成持续时间、空区空间分布尺度及围空地震震级等的统计关系.结果表明,空区的持续时间、空间尺度与主震震级间存在一定的相关关系,但其误差较大.而围空的起始震级在5级主震前为ML2.5左右,6级主震前为ML3.5左右,7级以上主震前为ML4.0左右.主震通常发生在空区的边缘及附近的外部地区.5级、6级和7级地震前出现空区图像的比例分别为45.8%、72.6%和100%,一定程度上表明了震前空区图像是强震前的重要异常判据.
367 earthquakes of magnitude 5 and above, with relatively complete information in mainland China, were scanned in five working areas for the qualitative and quantitative requirements of the seismogram, and 194 images of the vacant area before the earthquake were obtained. The proportions of the earthquakes were respectively 14:36 in the North China region, 21:24 in the southeast China region, 68:124 in the Sichuan-Yunnan region, 36:82 in the northern part of the Qinghai-Tibet Plateau and 55:101 in the Xinjiang region. In North China, the highest is in southeastern China and Xinjiang is basically the same as in Sichuan and Yunnan Provinces, and on this basis, the durations of formation of main and vacant areas, the spatial distribution of empty areas and the magnitude of the quake Etc. The results show that there is a certain correlation between the duration and spatial scale of the empty area and the magnitude of the main shock but the error is relatively large.The starting magnitude of the space before ML5 is ML2.5 , The magnitude before ML6 is about ML3.5, and the ML4.0 before ML7 above 3. The main shock usually occurs at the edge of the open area and nearby outer areas. Before the earthquakes of magnitude 5, 6 and 7 The proportions of empty images appear to be 45.8%, 72.6% and 100% respectively Show before the earthquake empty area of the image is an important criterion before the earthquake abnormal extent.