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1978年5月18日海城地震(M_s=6.0)发生在1975年2月4日海城破坏性地震(M_s=7.3)余震区的“空区”内.1975年2月4日海城7.3级强震发生之后,其余震(M_s≥2.0)的月频度衰减异常缓慢(P=0.73),而6级地震发生之后 P 值明显增大,即6级地震发生在月频度衰减曲线的“拐点”上.这次6级地震之前不同于7.3级强震前,在震源区没有丰富的前震活动.6级地震是7.3级强震的最大余震,作者认为它是区域应力在未曾充分破裂的“空区”内再次集中积累而发生的余震.
On May 18, 1978, the Haicheng earthquake (M_s = 6.0) occurred in the “empty area” of the aftershock area of Haicheng destructive earthquake (M_s = 7.3) on February 4, 1975. Haicheng 7.3 After the strong earthquakes occurred, the monthly frequency attenuation of the remaining earthquakes (M_s≥2.0) was very slow (P = 0.73), while the P value increased obviously after the M6 earthquakes occurred, ie, the M = 6 earthquakes occurred on the monthly frequency attenuation curve “Inflection point.” Prior to the M6.3 earthquake, there was no rich foreshock activity in the source area before the M6.6 earthquake, and the M6 is the largest aftershock of the 7.3-magnitude earthquake that the authors believe is the area that has not been fully fractured Of the “empty area” once again focus on the accumulation of aftershocks.