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1969年7月18日渤海7.4级地震是一个典型的主余震序列。发生在郯城-营口大断裂的西侧,震中区位于冀-渤断块、鲁西断块和胶辽断块的交界部位,是一系列北西向构造与郯-营大断裂的交汇部位。利用主震的纵波初至符号,求得两组节面解。Ⅰ组:走向20°,倾向南东,倾角80°;Ⅱ组:走向292°,倾向南西,倾角75°。究竟那个是主震震源的断层面,是个被关注的问题。在构造复杂的渤海地区,基本上依地球物理资料推断断裂的展布情况,可靠性较差;且据所获零星散布于海岸的震前地球物理、地壳形变等资料,分析震源断层面有很大局限性。因此,对于震源断层面的走向存在有北北东向或北西向两种不同的意见。此两种看法基本上属推测性质,未提出令人信服的根据。
July 18, 1969 Bohai 7.4 earthquake is a typical main aftershock sequence. Occurred on the west side of Gaocheng-Yingkou Great Fault. The epicenter area is located at the junction of Hebei-Bohai fault block, Luxi fault block and Jiaoliao fault block. It is a series of intersections of a series of NW structures and 郯-Yingda faults. Using the first arrival of the longitudinal wave of the mainshock, two groups of nodal solutions are obtained. Group Ⅰ: Toward 20 °, southeastern and dip at 80 °; Group Ⅱ: Toward 292 ° and southwest and dip at 75 °. After all, that is the fault plane of the mainshock, which is a matter of concern. In the complicated Bohai area, the distribution of faults is basically deduced from the geophysical data, and the reliability is poor. Based on the acquired data of the geophysics and crustal deformation scattered on the coast, the analysis of focal fault planes Great limitations. Therefore, there are two different opinions about the strike of the source fault in the north-north or north-west direction. These two views are basically speculative and no convincing basis has been put forward.