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对大地震发生后强余震的震源机制,基于主要地震断层上小余震的时空分布进行了详细研究.近期在中国境内发生的强烈板内地震,如1976年唐山、1975年海城、1976年盐源—宁蒗等地震曾被中国地震台网很好记录.主震刚发生后的小余震以及强余震前后的小余震的震源用 S—P 时间的收敛法进行测定.强余震的断层是依靠这些小余震的震中分布来描绘的.可以看出有三种情况.第一,在主震断层区内,一次强余震发生在较小余震的比较不密集的部位;第二,一次强余震沿断层发生并与主震断层是共轭的;第三,一次强余震在沿平行并离开主震断层的断层上发生.可以认为,地质条件控制着强余震的发生.作为强余震的可能前兆,则有唐山地震的一次强余震,震级为7.1.其发生前,出现一些前震以及在接近主震断层方向上的某些地震台所记录的初动方向有变化.可以设想,这里的应力场在强余震发生前是有所变化的.
The focal mechanism of the strong aftershocks after the major earthquakes has been studied in detail based on the temporal and spatial distribution of small aftershocks on the major seismic faults. Recent strong intraplate earthquakes in China such as Tangshan in 1976, Haicheng in 1975, salt in 1976 Source - Ninglang and other earthquakes have been well recorded by China Seismological Network.After the main shock just after the small aftershocks and aftershocks before and after the aftershocks of aftershocks were determined by the convergence method S-P time.The strong aftershocks of the fault is to rely on The distribution of these small aftershocks is described by the epicenter distribution of the small aftershocks. There are three situations: First, a strong aftershock occurs in the less densely-spaced aftershock within the main shock zone; secondly, a strong aftershock along the fault Occurs and is conjugate with the mainshock fault; and thirdly, a strong aftershock occurs on a fault parallel to and away from the fault of the mainshock. It is believed that the geological conditions control the occurrence of strong aftershocks. As a possible precursor to strong aftershocks, There was a strong aftershock of the Tangshan earthquake with a magnitude of 7.1. Prior to its occurrence, some foreshocks and some seismographs in the direction of the fault near the main shock had recorded changes in the direction of initial motion. It is assumed that the stress here Strong aftershock occurs before the change.