2013、2016年两次朝鲜核试验P波和面波信号幅值比差异的观测与分析

Observations and analyses of the amplitude-ratio differences among the P waves and surface waves between 2013 and 2016 nuclear tests of North Korea

2016年1月6日,朝鲜再次进行了地下核试验.和上次2013核试验相比,此次试验震中位置接近,不同震相的平均幅值比却表现出明显的差异:在短周期P波幅值减小的情况下,长周期Rayleigh面波幅值增强,Love面波幅值减小.这给判断两次试验当量的相对大小带来了困难.本文在给出两次试验短周期P波和长周期面波幅值比测量结果的基础上,从地下核爆炸震源机制的角度对观测现象进行分析解释.研究结果表明,虽然各种形式的构造应力源都可以很好地拟合单次试验的长周期面波资料,但只有逆断层形式的构造应力释放能够解释两次试验不同震相幅值比差异现象.这是关于朝鲜核试验震源机制的一个新的发现,对于认识其震源性质具有重要意义.

On 6 January 2016,North Korea carried out an underground nuclear explosion （UNE） again. In comparison with the last test in 2013, the mean amplitude ratios of different phases vary obviously though at a nearly same epicenter location. The latter generated stronger long-period Rayleigh waves with weaker short-period P waves and long-period Love waves. This phenomenon makes it difficult to judge the relative yields of the two tests. In this paper, the anomalous observations are presented first, then the explanations are given from the theory of UNEs＇ source mechanism. With any form of tectonic stress source, the long-period surface waves are all modeled well for a single test. It is important to note that only the form of a thrust fault is able to explain the amplitude-ratio differences between the two tests. This is a new discovery about the source mechanism of the North Korea nuclear tests and has a great meaning to recognize the source characters.