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1969年7月18日渤海海域(北纬38°20′,东经119°27′)发生7.4级地震,属主震-余震型。 区域地震活动分析表明,主震前出现小震条带、b值低等异常现象。研究重新校订的余震目录资料,发现余震空间分布具有随时间由横向集中、垂向扩散到横向扩散、垂向集中的过程,及b值高、P值大等特点。另外,对于渤海地震与1975年海城7.3级地震的同异点等问题进行了讨论。
On July 18, 1969, the 7.4 magnitude earthquake occurred in the Bohai Sea (latitude 38o 20 ’north, longitude 119o 27’ east) and belongs to the main shock-aftershock type. The analysis of regional seismicity shows that the small seismic band appears before the main shock and the b value is abnormal. The aftershock catalog data of the re-calibration study shows that the aftershock spatial distribution has the characteristics of horizontal concentration, vertical diffusion to horizontal diffusion and vertical concentration over time, and high b value and large P value. In addition, the issues such as the similarities and differences between the Bohai Sea earthquake and the 1975 Haicheng earthquake of magnitude 7.3 are discussed.