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最近几年,前兆性震群的研究取得了新的进展.美国Omar J.Perez等(1980年)注意到:1976年1至4月间,阿拉斯加州圣·爱利斯地区突然发生M_b>4.2级地震,到1979年2月28日就在当地发生了7(1/4)级地震.由此他们认为,突发性地震活动可能是大地震发生前的一种征兆.许绍燮等(1981年)的论文提出,1975年2月4日海城7.3级地震前的小震群系列具有震源位置集中、频次急速增长、震源机制稳定等特点.朱传镇等(1981年)认为,唐山地震前一年左右,华北地区震群活动的增强与大面积上形变速率增大是符合的.苏联Ю·М·捷依捷里乌巴姆等人得出,主震前一年半或更短时间内出现小震群这种标志是比较稳定的,约占77%.王培德等(1981年)认为,在小震活动频度不高的地区出现的震群可能是强震或中强震的前兆.上述工作使前兆性震群的研究前进了一步.但还需要解决一个重要问
In recent years, new progress has been made in the study of precursory swarm. The United States noted in Omar J. Perez et al. (1980) that M_b> 4.2 suddenly occurred in St. Aires, Alaska, between January and April 1976 Magnitude earthquake occurred on July 28, 1979, with 7 (1/4) earthquakes on the ground, and they think that sudden earthquakes may be a symptom before the earthquake. Xu Shaoxie et al. (1981 ) Paper suggests that the series of small swarms before the MS 7.3 Haicheng earthquake on February 4, 1975 have the characteristics of focal location, rapid frequency growth and stable source mechanism. Zhu Chuang-zhen et al. (1981) considered that before the Tangshan earthquake In a year or so, the enhancement of the swarm activity in North China coincided with the increase of the deformation rate over a large area, and the Soviet Union Ю · М · 捷 依 捷 里乌巴姆 and others concluded that a year and a half ago or less before the main shock Small earthquakes within the group of such signs is relatively stable, accounting for about 77% .Wang Peide et al (1981) that the frequency of minor earthquakes occur frequently in the area may be earthquake precursors of strong earthquakes or moderate earthquakes The above work has taken a step forward in the study of precursory swarm.But it still needs to solve one important question