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ABSTRACT
Modern methods of nuclear-explosion monitoring are vastly more capable than they were when underground nuclear testing began in the late 1950s, in part because a cycle of improvements in explosion monitoring in the 1960–80 period led to improvements in monitoring for earthquakes and other phenomena, which then led to a general growth in monitoring assets that in turn has been applied back to explosion monitoring. Practical experiences in nuclear-explosion monitoring, acquired during the era of active testing prior to finalization of the CTBT text in 1996, laid the basis for monitoring in support of this arms-control initiative. This article elaborates on the future of nuclear-test-monitoring technology, which can build upon an additional and remarkable growth of general monitoring assets that began in the 1990s, largely unrelated to the specifics of nuclear-test monitoring. A new cycle of improvements in earthquake monitoring is likely to improve monitoring for explosions. While it is not easy to quantify the degree of monitoring improvement afforded by such new assets, an example from North Korea indicates the improvement can be substantial.
Acknowledgements
I appreciate support in recent years from the Consortium for Verification Technology, which is funded by the National Nuclear Security Administration, NA-22, and organized through the University of Michigan. Help from Won-Young Kim is greatly appreciated, in particular with Fig. 4. This is Lamont-Doherty Earth Observatory contribution number 8074.
Notes
1 Donald Kerr, “The purpose of nuclear test explosions,” in Jozef Goldblat and David Cox, eds., Nuclear Weapons Tests: Prohibition or Limitation? (SIPRI Monograph Series, 1988), p. 43.
2 See, for example, Xiaoping Yang, Robert North, Carl Romney, and Paul G. Richards., “Worldwide Nuclear Explosions,” in W.H.K. Lee, H. Kanamori, P. Jennings, and C. Kisslinger, eds., International Handbook of Earthquake and Engineering Seismology (Academic Press, 2002).
3 The IMS uses seismic, hydroacoustic, infrasound, and radionuclide technologies to monitor for nuclear explosions.
4 See, for example, the National Academy of Sciences (NAS), Technical Issues Related to the Comprehensive Nuclear-Test-Ban Treaty (Washington, DC: National Academy Press, 2002). An eight-page account of explosion monitoring with particular reference to seismology and the work of the IMS and IDC in Vienna is given by Paul G. Richards and Won-Young Kim, “Monitoring for Nuclear Explosions,” Scientific American 300 (March 2009), pp. 70–77. Kaegan McGrath, “Verifiability, Reliability, and National Security,” Nonproliferation Review 16 (November 2009), pp. 407–33, describes the international monitoring effort associated with the CTBTO as it was growing in the period 2000–09. The book by Ola Dahlman, Svein Mykkeltveit, and Hein Haak, Nuclear Test Ban: Connecting Political Visions to Reality (Heidelberg, Germany: Springer, 2009), p. 277, gives a historical overview of nuclear testing and CTBT negotiations, and it then reviews the treaty text and technical aspects of the international verification system.
5 NAS, The Comprehensive Nuclear Test Ban Treaty: Technical Issues for the United States (Washington, DC: National Academy Press, March 2012). Information on web-based and other resources for learning about explosion monitoring is given by Paul G. Richards, “Comprehensive Nuclear-Test-Ban Treaty Seismic Monitoring: 2012 USNAS Report and Recent Explosions, Earthquakes, and Other Seismic Sources,” in P. Corden, D. Hafemeister, and P. Zimmerman, eds., Nuclear Weapons Issues in the 21st Century (Melvill, NY: American Institute of Physics Conference Proceedings, 2014), which also reviews key conclusions of the 2012 NAS report.
6 For example, for the nuclear-test explosion of January 6, 2016, the IDC automatically made the initial detection using data from twenty-seven so-called primary stations of the IMS (meaning that they were part of an IMS network providing data to the IDC that the IDC is committed to analyzing continuously). See “Media Stakeout: Update on the Seismic Event Detected in North Korea,” January 7, 2016, CTBTO Preparatory Commission, <www.ctbto.org/the-treaty/developments-after-1996/2016-dprk-announced-nuclear-test/technical-findings/>.
7 Magnitude is an empirical attribute of a seismic event, used to characterize the strength of recorded signals and to provide a basis for estimating the size of the source, in particular the yield, for an underground explosion. A variety of different seismic waves can be made on the basis of a magnitude scale, and the degree to which the same event has different magnitudes on different scales provides a basis for useful methods of identifying an event as an earthquake or an explosion.
8 NORSAR gave the origin time as 2016/01/06 01:30:00 UTC and the location in North Korea as (41.28°N 129.07°E). “New nuclear test by North Korea,” NORSAR, n.d., <www.norsar.no/press/latest-press-release/archive/update-on-the-location-of-north-korea-s-latest-nuclear-test-article1291-984.html>.
9 “Special Event: 2016 North Korean nuclear test,” Incorporated Research Institutions for Seismology, last updated February 1, 2016, <http://ds.iris.edu/ds/nodes/dmc/specialevents/2016/01/05/2016-north-korean-nuclear-test/>.
10 Results were reported at Lianxing Wen’s Geogroup, “North Korea's Nuclear Test Location and Yield: Seismic Results from USTC,” University of Science and Technology of China, <http://seis.ustc.edu.cn/en/201601/t20160106_234881.html>. They were essentially the same as shown in and in terms of relative locations and explosion size.
11 This summary sentence should not be taken to imply that agencies with responsibility for monitoring had any difficulty with prompt reporting of the small nuclear test in October 2006. Furthermore, the New York Times on October 10, 2006, carried a detailed article on the location of the previous day's test and a comparison of its seismic signals with those of a small earthquake in the region (see William J. Broad and Mark Mazzetti, “Blast May Be Only a Partial Success, Experts Say,” New York Times, October 10, 2006, <www.nytimes.com/2006/10/10/world/asia/10detect.html>). The point of the summary sentence is that for the nuclear tests of January and September 2016, there were multiple sources of good information, including detailed analysis on the location of the explosion, coming directly from experts in China.
12 Lars-Erik De Geer, “Radionuclide Evidence for Low-Yield Nuclear Testing in North Korea in April/May 2010,” Science & Global Security 20 (March 2012), pp. 1–29.
13 D.P Schaff, W.Y. Kim, and P.G. Richards, “Seismological Constraints on Proposed Low-Yield Nuclear Testing in Particular Regions and Time Periods in the Past, with Comments on ‘Radionuclide Evidence for Low-Yield Nuclear Testing in North Korea in April/May 2010’ by Lars-Erik De Geer,” Science & Global Security 20 (2012), pp. 155–71.
14 Miao Zhang, and Lianxing Wen, “Seismological Evidence for a Low-Yield Nuclear Test on 12 May 2010 in North Korea,” Seismological Research Letters 86 (January/February 2015), pp. 1–8.
15 Won-Young Kim, Paul G. Richards, David P. Schaff, and Karl Koch, “Evaluation of a Seismic Event, 12 May 2010, in North Korea,” forthcoming, Bulletin of the Seismological Society of America.
16 See Figure 2–2 of the 2002 NAS report and the magnitude 3.25 capability; and Figures 2–8 and 4–8 of the 2012 NAS report for lower values.
17 For example, David Bowers and William R. Walter, “Discriminating between Large Mine Collapses and Explosions using Teleseismic P-waves,” Pure and Applied Geophysics 159 (2002), pp. 803–30.
18 Paul G. Richards and Won-Young Kim, “Testing the nuclear test-ban treaty,” Nature 389 (October 23, 1997), pp. 781–82; and David Bowers, “Was the 16 August 1997 Seismic Disturbance near Novaya Zemlya an Earthquake?” Bulletin of the Seismological Society of America 92 (August 2002), pp. 2400–09. Measurements of the comparative strength of seismic pressure-waves and shock waves now provide one of the best objective methods of distinguishing between earthquake and explosion signals. See, in this volume, Andreas Persbo, “Compliance science: The CTBT’s global verification system,” Nonproliferation Review 23 (June/July 2016), pp. 317–328.
19 David Bowers, “The October 30, 1994 Seismic Disturbance in South Africa: Earthquake or Large Rockburst?” Journal of Geophysical Research 102 (1997), pp. 9843–57. Also Bowers and Walter, “Discriminating between Large Mine Collapses and Explosions using Teleseismic P-waves.”
20 Technical details are taken from Xu Zhao, Wei Feng, Yipei Tan, Juan Li, Shunping Pei, Yanru An, Wei Hua, Shaolin He, Yong Zhao, Jie Liu, and Zhenxing Yao, “Seismological investigations of two massive explosions in Tianjin, China,” Seismological Research Letters 87 (July/August 2016), pp. 826–36.
21 See Olga P. Popva et al., “Chelyabinsk Airburst, Damage Assessment, Meteorite Recovery, and Characterization,” Science 342 (November 29, 2013), <www.sciencemag.org/content/342/6162/1069> for discussion of this, the largest natural airburst since the 1908 Tunguska event.
22 Ragnar Slunga, Sigurdur Th. Rögnvaldsson, and Reynir Bodvarsson, “Absolute and relative locations of similar events with application to micro-earthquakes in southern Iceland,” Geophysical Journal International 123 (1995), pp. 409–19.
23 Felix Waldhauser and William L. Ellsworth, “A double-difference earthquake-location algorithm: Method and application to the northern Hayward fault,” Bulletin of the Seismological Society of America 90 (December 2000), pp. 1353–68.
24 Felix Waldhauser and David P. Schaff, “Large-scale relocation of two decades of Northern California seismicity using cross-correlation, and double-difference methods,” Journal of Geophysical Research 113 (August 2008), <www.ldeo.columbia.edu/∼felixw/papers/Waldhauser_Schaff_JGR2008.pdf>.
25 D.A. Dodge and W.R. Walter, “Initial global seismic cross-correlation results: implications for empirical signal detectors,” Bulletin of the Seismological Society of America 105 (February 2015), pp. 240–256.
26 David P. Schaff and Felix Waldhauser, “One magnitude unit reduction in detection threshold by cross correlation applied to Parkfield (California) and China seismicity,” Bulletin of the Seismological Society of America 100 (December 2010), pp. 3224–338.
27 Megan Slinkard, David P. Schaff, Natalya N. Mikhailova, Stephen Heck, Christopher Young, and Paul G. Richards, “Multistation Validation of Waveform Correlation Techniques as Applied to Broad Regional Monitoring,” Bulletin of the Seismological Society of America 104 (December 2014), pp. 2767–81.
28 Megan Slinkard, Stephen Heck, David P. Schaff, Nedra Bonal, David Daily, Christopher Young, and Paul G. Richards, “Detection of the Wenchuan Aftershock Sequence using Waveform Correlation with a Composite Regional Network,” Bulletin of the Seismological Society of America 106 (August 2016).
For more on slow slip, see Naoki Uchida, Takeshi Iinuma, Robert M. Nadeau, Roland Bürgmann, and Ryota Hino, “Periodic slow slip triggers megathrust zone earthquakes in northeastern Japan,” Science 351 (January 25, 2016), pp. 488–92. They identified more than 6,000 sets of repeating earthquakes in the fault zone prior to the main event, and used the changing time of occurrence of earthquakes in each set to quantify the way in which slip accumulated during the twenty-eight-year period prior to the sudden slip release of the March 2011 main event.
29 “Verifying the CTBT—An Unprecedented Technical Undertaking,” n.d., CTBTO, <www.ctbto.org/press-centre/highlights/2011/verifying-the-ctbt-an-unprecedented-technical-undertaking/>.
30 Göran Ekström, Meredith Nettles, and Victor C. Tsai, “Seasonality and Increasing Frequency of Greenland Glacial earthquakes,” SCIENCE 311 (March 24, 2006), pp. 1756–58.
31 In particular, two reports of the US National Academy of Sciences gave a consensus view of nuclear-test-explosion monitoring capability (see endnote 4). The first of these in 2002 described the capability expected for monitoring systems then being built. The second, in 2012 described capabilities achieved by systems nearing completion when the report was written.