利用区域地震波形振幅包络约束朝鲜地下核试验的埋深和当量

Yield and burial depth of the North Korean underground nuclear tests constrained by amplitude envelopes of regional seismic waveforms

核爆当量和埋藏深度是地下核试验的两个重要参数.根据中国东北地区区域范围内地震台站观测记录,利用Pn,Pg,Sn和Lg波波形,计算水平分量的尾波振幅包络,调查2006年10月9日,2009年5月25日,2013年2月13日和2016年1月6日四次朝鲜地下核试验的爆炸当量和埋藏深度.以牡丹江(MDJ)台站记录为例,对两个水平分量波形进行带通滤波,计算平均波形的振幅包络.最终得到区域地震台站水平分量振幅包络,振幅稳定,包络振幅的变化清晰地显示区域震相的位置.区域震相的时间域振幅包络由震源谱函数、传播效应、台基响应和传递函数及尾波形状函数构成.通过网格搜索的方法,拟合水平分量记录的波形包络,可以获得核爆当量和埋藏深度的估计.结果表明,朝鲜四次地下核试验爆炸当量以时间为序从0.6±0.2kt到3.0±1.5kt,增加至10.0±2.0kt,再降到8.0±2.0kt.2006年核爆的埋藏深度较浅,为150±100m,2009年朝鲜核试验的埋藏深度为350±100m,2013年和2016年朝鲜核试验的深度非常一致,均为500±200m.这些结果与前人的调查结果一致性较高,说明使用单一地震台站时间域水平分量尾波振幅包络是可能同时约束地下核试验爆炸当量和埋藏深度的.

Both the yield and burial depth of a nuclear explosion are important parameters of an underground nuclear explosion test.According to the regional seismic stations in northeast China,we investigate these two parameters of the North Korean nuclear tests on 9October 2006,25 May 2009,13 February 2013and 6January 2016 by calculating the horizontal component waveforms of coda amplitude envelopes using Pn,Pg,Sn and Lg waves.As an example,we use the seismograms recorded at the Mudanjiang（MDJ）station to show the procedure of calculating amplitude envelopes by applying a bandpass filter to horizontal component waveforms.Thus,weobtain stable estimations of amplitude envelopes at regional seismic stations,from which the regional phases are apparently displayed.The time-domain amplitude envelopes of regional phases can be modeled by using source spectral function,geometric spreading,site response,transfer function and coda shape function.Based on the grid searching method,we simultaneously estimate the yields and burial depths of the North Korean nuclear tests.The results show that the yields increase from 0.6±0.2kt to 3.0±1.5kt and then 10.0±2.0kt,decrease to 8.0±2.0kt according to their origin time.The first test has a shallow burial depth of 150±100m,for the second one,the depth is estimated to be 350±100 m,while both the 2013 and 2016North Korean nuclear tests have very similar depths of 500±200m.Our results are consistent with the previous findings,which suggest that the yield and burial depth of the underground nuclear explosion tests can be simultaneously constrained by using the time-domain horizontal component of amplitude envelopes at a single station or a few stations.