Exploitation of the IMS and Other Data for a Comprehensive Advanced Analysis of the North Korean Nuclear Tests
Exploitation of the IMS and Other Data for a Comprehensive Advanced Analysis of the North Korean Nuclear Tests
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2010-02
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通讯作者：
J. Murphy;B. Kohl;J. Stevens;T. J. Bennett;H. Israelsson
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作者：
J. Murphy;B. Kohl;J. Stevens;T. J. Bennett;H. Israelsson
2009年5月25日，朝鲜在2006年首次核试验的同一地区进行了第二次地下核试验。初步分析表明，第二次试验的爆炸当量大约是第一次试验的5倍，分布在全球各地的各种地震网络都有很好的记录。我们仔细分析了现有的短周期地震数据，试图确定朝鲜这两次核试验的准确位置、深度和当量。为了确定这两个事件的准确相对位置，我们在35个台站进行了非常精确的到达时间测量，这些台站以良好的信噪比记录了这两次爆炸。2006年爆炸的位置固定在先前确定的首选位置，2009年爆炸的相对位置使用联合震源确定（JHD），双差（DD）和差分波形干涉（DWIF）定位算法进行估计。所有这些相对定位技术都产生了非常相似的结果，表明2009年的测试是在2006年测试西北偏西2.5公里处进行的。这些相对地震位置随后与当地地形数据和卫星图像相结合，以确定我们认为这两次爆炸的非常合理和准确的位置。利用现有的到达时间数据或观测到的窄带网络平均的地震P波频谱数据不能可靠地确定相应的震源深度。因此，我们实施了一种新的方法，使用宽带P波频谱比的两个爆炸在共同的区域站，以获得相应的宽带源频谱比的估计。然后将所得网络平均源谱比与基于Mueller/Murphy的理论源谱比进行比较，以估计最佳拟合源深度和相关产量。分析结果表明，这两次爆炸不可能是在100至800米的合理深度范围内的任何共同深度引爆的，事实上，2006年试验的震源深度约为200米，2009年试验的震源深度约为550米，与观测到的光谱比数据最吻合。2009年5月25日爆炸的相应当量估计为约4.6千吨。2006年和2009年测试的长周期表面波Ms量级相对于历史经验似乎过大，产生不合理的大Ms产额估计和有问题的Ms/mb识别特征。对现有数据的正式矩张量反演分析表明，爆炸释放的构造应变能可能对观测到的异常有一定的贡献。然而，目前对这种构造释放的可能强度的估计还不足以完全解释所观察到的异常。需要进行额外的研究，以确定未解决的CLVD次要来源是否可以解释这种差异。根据在区域台站测量的高频Pn/Lg比值，将2009年和2006年的事件确定为爆炸是明确的;然而，根据Ms与Mb的区分结果是不确定的（再次可能是由于Ms的次级污染源）。
On May 25, 2009, the North Koreans conducted a second underground nuclear test in the same area as their initial 2006 test. Preliminary analysis indicated that the explosive yield of the second test was roughly 5 times that of the first, and it was found to have been well-recorded by a variety of globally distributed seismic networks. We carefully analyzed the available short-period seismic data in an attempt to define accurate locations, depths and yields for these two North Korean nuclear tests. In order to determine accurate relative locations for the two events, we made very precise arrival time measurements at 35 stations that recorded both explosions with good signal to noise ratios. The location of the 2006 explosion was then held fixed at the previously determined preferred location and the relative location of the 2009 explosion was estimated using the Joint Hypocenter Determination (JHD), Double Difference (DD) and Differential Waveform Interferometry (DWIF) location algorithms. All of these relative location techniques yielded very similar results, indicating that the 2009 test was conducted about 2.5 km west-northwest of the 2006 test. These relative seismic locations were subsequently integrated with the local topographic data and satellite imagery to define what we believe to be very reasonable and accurate locations for these two explosions. The corresponding source depths can not be reliably determined using the currently available arrival time data or the observed, narrowband network-averaged teleseismic P wave spectral data. Consequently, we implemented a new approach using broadband P wave spectral ratios of the two explosions at common regional stations to obtain estimates of the corresponding broadband source spectral ratios. The resulting network-averaged source spectral ratio was then compared with theoretical Mueller/Murphy based source spectral ratios to estimate best-fitting source depths and associated yields. The results of this analysis indicated that the two explosions could not have been detonated at any common depth in the plausible 100 to 800 m depth range and, in fact, the observed spectral ratio data are best fit by source depths of about 200 m for the 2006 test and 550 m for the 2009 test. The corresponding yield estimate for the May 25, 2009, explosion was then found to be about 4.6 kt. The long-period surface wave Ms magnitudes for both the 2006 and 2009 tests appear to be anomalously large relative to historical experience, producing unreasonably large Ms yield estimates and problematic Ms/mb identification characteristics. A formal moment tensor inversion analysis of the available data indicated that release of tectonic strain energy by the explosion may have contributed somewhat to the observed anomaly. However, current estimates of the likely strength of this tectonic release are not large enough to fully explain the observed anomaly. Additional research will be required to determine whether unresolved CLVD secondary sources may account for the discrepancy. Identification of the 2009 and 2006 events as explosions based on high-frequency Pn/Lg ratios measured at regional stations are unambiguous; however, results for discrimination based on Ms-versus-mb are inconclusive (again probably due to secondary source contamination to Ms).