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分辨多数余震和后续主震是由静态应力触发(Stein,1999;Todaetal,2005;Parsons,2002)还是动态应力触发(Hilletal,1993;kilb,2003;Brodsky and Prejean,2005;Gomberg and Johnson,2005;Hill and Prejean,2007),对理解地震内在作用和预测地震危险性是有必要的(Freed,2005)。Felzer和Brodsky(2006)分析了2≤M<3和3≤M<4级主震后5min内余震的空间分布情况,发现距主震50km范围内M≥2余震具有特定的幂律衰减关系,且衰减曲线的斜率为-1.35。据此,他们认为余震随距离的衰减只能用动态触发来解释。基于上述假设我们进行了一系列的检验,但没有一个可通过检验,进而,本文中对这种衰减关系提出了另外一种解释。在距离2≤M<3主震300m以外的地方,主震前5min内的地震活动性衰减与主震后5min内的衰减没有显著的区别,表明主震对它静态触发区域以外的地方没有影响。表征余震基本特性的大森随时间衰减关系在距离主震10km以外的地方是不存在的。最后,发现在主震波前未到达之前的余震中发现了这种距离上的衰减,而这违背了因果关系。我们认为,Felzer和Brodsky(2006)隐含地假定两个独立余震中的第一个沿着断层破裂触发第二个,而且两个余震中的第一个是以蠕动或入侵方式触发了第二个,事实可能并非如此。
The resolution of most aftershocks and subsequent mainshocks is triggered by static stress (Stein, 1999; Todaetal, 2005; Parsons, 2002) or by dynamic stress triggers (Hilletal, 1993; Kilb, 2003; Brodsky and Prejean, 2005; Gomberg and Johnson, Hill and Prejean, 2007) is necessary to understand the intrinsic role of earthquakes and to predict seismic hazards (Freed, 2005). Felzer and Brodsky (2006) analyzed the spatial distribution of aftershocks within 5 min after 2≤M <3 and 3≤M <4 main shocks and found that there was a specific power law attenuation relationship with M≥2 aftershocks within 50 km of the main shock. And the slope of the decay curve is -1.35. Accordingly, they believe that the aftershock attenuation can only be explained by dynamic triggering. Based on the above assumptions, we conducted a series of tests, but none of them passed the test. Furthermore, another explanation of this attenuation relationship is proposed in this paper. At a distance of 300 km from 2≤M <3 main shock, there is no significant difference between the attenuation of seismicity within 5 minutes before the main shock and the attenuation within 5 minutes after the main shock, indicating that the main shock has no effect on the area outside its static triggering area . The decay relationship of the Omori, which characterizes the basic characteristics of aftershocks, does not exist at a distance of 10 km from the main shock. Finally, it was found that this attenuation of distance was found in the aftershock before the arrival of the main shock wavefront, which violated the causal relationship. We consider that Felzer and Brodsky (2006) implicitly assume that the first of two independent aftershocks triggers the second along the fault and that the first of the two aftershocks triggers the second This may not be the case.