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本文用P波频谱的资料,研究了1975年2月4日海城7.3级主震及1978年5月18日6.0级强余震的破裂过程。对于海城主震,采用包括正交破裂方式等几种可能的震源破裂模式,通过复合型法进行反演。结果表明:不对称双侧破裂方式的最佳解理论谱极小点与观测谱吻合程度最好。这组最佳解的主破裂方向为北西西向,破裂长度28km,破裂速度1.0km/sec。朝南东东方向的破裂长度为12km,破裂速度为0.7km/sec。1978年5月18日6.0级强余震的破裂方式为单侧破裂方式,主破裂方向也为北西西,破裂长度15km,破裂速度 1.4km/sec。以上研究结果与相应的余震分布图象非常相象。 本文通过研究海城主震后不同阶段地震空间分布的图象,发现在海城主震长度约50km的主破裂带中,在主震震中北西西方向上存在长近20km的未完全破裂的地段,海城主震后的八个5级以上的强余震中,除了一个例外,其它强震,包括其中最大的6.0级强震及六个5级强震,均发生在这个地段上或其两端。可以认为这些强震的发生,使得这个长近20km的障碍体,逐步破碎,并使主破裂带基本贯通。
In this paper, we use P wave spectrum data to study the rupture process of Haicheng 7.3 magnitude main shock on February 4, 1975 and magnitude 6.0 strong aftershock on May 18, 1978. For Haicheng mainshock, several possible source rupture modes including orthogonal rupture mode are adopted, and inversion is performed by composite method. The results show that the minimum point of the best solution spectrum of asymmetric bilateral rupture is the best match with the observed spectrum. The main failure direction of this group of solutions is northwestern and westward with a rupture length of 28km and a rupture speed of 1.0km / sec. The rupture length in the east-south direction is 12km and the rupture speed is 0.7km / sec. On May 18, 1978, the class 6.0 aftershock rupture mode is unilateral rupture mode, and the main rupture direction is also north west and west with rupture length of 15km and rupture speed of 1.4km / sec. The above results are very similar to the corresponding aftershock distribution images. In this paper, the image of the spatial distribution of the earthquakes at different stages after the main Haicheng earthquake is studied. It is found that in the main rupture zone about 50km long in Haicheng, there is an incompletely broken area of nearly 20km in the northwest-west direction of the main shock epicenter. Among the eight strong aftershocks of magnitude 5 or above after the earthquake, with one exception, the other strong earthquakes, including the largest of the 6.0 and the 5 of the 5, were all occurred on this lot or both ends. It can be considered that the occurrence of these strong earthquakes made the obstacle with a length of nearly 20km gradually broken down and the main rupture zone basically penetrated.