朱传镇, 傅昌洪, 罗胜利. 1981: 震群与大地震关系的研究(华北地区). 地震学报, 3(2): 105-117.
引用本文: 朱传镇, 傅昌洪, 罗胜利. 1981: 震群与大地震关系的研究(华北地区). 地震学报, 3(2): 105-117.
ZHU CHUAN-ZHEN, FU CHANG-HONG, LUO SHENG-LIcom sh adv. 1981: STUDY OF EARTHQUAKE SWARMS IN RELATION TO LARGE EARTHQUAKES (NORTH CHINA AREA). Acta Seismologica Sinica, 3(2): 105-117.
Citation: ZHU CHUAN-ZHEN, FU CHANG-HONG, LUO SHENG-LIcom sh adv. 1981: STUDY OF EARTHQUAKE SWARMS IN RELATION TO LARGE EARTHQUAKES (NORTH CHINA AREA). Acta Seismologica Sinica, 3(2): 105-117.

震群与大地震关系的研究(华北地区)

STUDY OF EARTHQUAKE SWARMS IN RELATION TO LARGE EARTHQUAKES (NORTH CHINA AREA)

  • 摘要: 1956-1976二十年来,华北地区(106E 以东,33N 以北,42N 以南,黄海以西)共发生震群37次,其中1966年邢台地震后到1976年唐山地震前,震群次数比1956-1966增加三倍多,近十年来华北四次七级以上地震就是在震群活动水平不断增高的背景上出现的.从空间分布上来看,1967-1972年震群分布范围相对缩小,仅靠近大震震中;1974年后,震群活动区域明显扩大,唐山地震前不到半年的时间内,震群活动沿唐山地震震中的 NE-SW 和 NW-SE 方向上分别延伸达一千多公里.这种地震活动随时间由未来大震震中逐步向外扩散的现象,在几次历史大地震前也类似出现过,据此粗略估计平均扩散速度约为100公里/年.除上述特点外,还观测到大震发生前一、二年至数月,在距未来震中不太远处(百公里)常发生前兆震群.分析了前兆震群与一般震群在震源机制、震源动力学参数、b 值以及 P 和 S 波振幅比等方面可能存在的差异.初步结果表明:与一般震群相比,前兆震群具有较高的应力降.最后,简要地分析了易于发生前兆震群可能的物理和构造条件.

     

    Abstract: From 1956 to 1976, there occurred thirty-seven earthquake swarms in North China, (i.e. east of 106 E, north of 33N, south of 42 N and west of Yellow sea). Among these, the number of earthquake swarms occurred just after the 1966 Xingtai (邢台) Earthquake to the 1976 Tangshan (唐山) Earthquake is about three times more than the number of swarms occurred in the period of 1956-1966. During the last ten years, all of the large earthquakes (M>7.0) occurred on the background of a continuously increasing activities of earthquake swarms.In view of the spatial distribution, the scope of activity of earthquake swarms) is limited in smaller areas, close to the epicenters of future large earthquakes. However, since 1974, the swarm activity has been clearly enlarged in spatial distribution. Around the epicenter of the subsequent Tangshan Earthquake, both in the NE-SW and NW-SE directions it was lengthened by more than 1000 kms, in less than half a year before the earthquake.Such a phenomenon of seismic activity spreading out from the epicenter of the impending major earthquake with the lapse of time can also be noticed before several historical earthquakes, the average spreading rate may be roughly estimated as about 100 km/year.Besides, it is also observed that precursory earthquake swarms, appear several months to one or two years before the impending large earthquakes at a not too far distance (about 100 kms).The possible differences between the precursory earthquake swarms and the ordinary ones in focal mechanism, dynamic source parameters, b value as well as the amplitude ratios of P and S waves have-been analysed. Preliminary results show that the stress drops for precursory earthquake swarms are higher. Finally, the physical and tectonic conditions under which precursory swarms might be observed are briefly discussed.

     

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