The Comprehensive Nuclear Test Ban Treaty Technical Issues for the United States (2012) / Chapter Skim
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2 TECHNICAL MONITORING CAPABILITIES AND CHALLENGES
2 TECHNICAL MONITORING CAPABILITIES AND CHALLENGES
Pages 35-76
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From page 35... ...
OVERVIEW AND 2002 REPORT FINDINGS To monitor for compliance with the CTBT, it is essential to be able to put potential violators at risk of detection through vigilant monitoring for nuclear explosions. The possibility of nuclear-explosion testing must be considered in four environments -- underground, underwater, in the atmosphere, and in space.
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From page 36... ...
. Nuclear Detonation Phenomena FIGURE 2-1: Phenomenology of nuclear explosions, from the subsurface to outer space.
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From page 37... ...
observed at the ground from a space nuclear explosion has a very fast component (E1) produced by the gamma rays interacting with the atmosphere and a slow component (E3)
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From page 38... ...
and mine masking (concealing a nuclear explosion by conducting a nuclear test in a region that has frequent, large chemical explosions associated with mining operations)
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From page 39... ...
The auxiliary seismic network records continuously but currently its data are used only when deemed necessary to augment analysis of an event that has already been detected by the primary network 5 In assessing the capabilities of the IMS, it is important to understand that the treaty specifies that event identification, characterization, and the attribution of a nuclear explosion to a particular country are the responsibility of the member states, not the CTBTO. Thus the CTBTO provides data on all detected events, as well as subsets for which events characterized (with high confidence)
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From page 40... ...
SOURCE: Modified from CTBTO FIGURE 2-3: Location and status of 120 stations of the IMS Auxiliary Network, as of mid-2010. Auxiliary stations are supported by the hosting state and not the CTBTO.
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From page 41... ...
isotopes that are diagnostic of nuclear explosions. As of February 2011, 26 of these noble-gas stations were transmitting data to the IDC in Vienna.
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From page 42... ...
USAEDS and IMS share 22 seismic stations and 3 hydroacoustic stations. The raw data from the IMS is both protected and authenticated in multiple ways to decrease the likelihood that data collected and transmitted could be tampered with.
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From page 43... ...
MONITORING TECHNOLOGIES8 Seismic Seismology is the most effective technology for monitoring underground nuclearexplosion testing, the one environment that was not precluded from nuclear-explosion testing by the Limited Test Ban Treaty of 1963. Seismic monitoring for nuclear explosions is complicated by the great variety and number of earthquakes, chemical explosions, and other non-nuclear phenomena generating seismic signals every day.
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From page 44... ...
Note that yield and seismic magnitude scales are logarithmic; each unit of improvement is a factor of ten. Seismic sensitivity to nuclear explosions has improved significantly due to increased deployment of seismometers and improved data analysis.
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From page 45... ...
Teleseismic waves were the basis of most nuclear-explosion test monitoring prior to the 1990s. For sub-kiloton explosions, teleseismic monitoring can often still help with event detections but is likely to be inadequate for event identification and therefore monitoring benefits from regionaldistance signals.
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From page 46... ...
. The work of association is to identify the Formulas relating the body-wave sets of signals, from different stations, magnitude, mb, to the yield, Y, based on data which all originate from the same seismic from past underground nuclear explosions are of the form event such as an earthquake or an mb = A + B log(Y)
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From page 47... ...
As noted in Box 2-1 the strength of a seismic source as determined from the amplitude of its body waves is conventionally reported as the body wave magnitude, symbolized as mb.12 Correspondingly, the size of surface waves is reported as the surface wave magnitude, Ms. Shallow earthquakes have a larger relative surface-wave magnitude than do underground nuclear explosions having the same body-wave magnitude.
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From page 48... ...
Seismic Monitoring Sensitivity The relationship between explosive yield and event magnitudes depends on the geology in the region of the event and the strength of coupling to surrounding media. The mb-yield relations applicable to Semipalatinsk (a former Soviet test site in Kazakhstan)
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From page 49... ...
Recommendation 2-3: To meet its national security needs, the United States should continue to enhance and sustain its NTM seismic monitoring capabilities. IMS Seismic Monitoring One of the major advances of the last 10 years is that 84 percent of the planned primary seismic stations are operating and certified for data quality (including calibration)
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From page 50... ...
for wellcoupled nuclear explosions is being significantly exceeded by existing IMS primary and auxiliary stations today. Globally, the IMS seismic network provides complete coverage at magnitude 3.8, with about 80 percent of stations operational.
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From page 51... ...
The capabilities shown in this table represent the minimum detectable seismic events likely to be included in IMS bulletins sent to national data centers. To conclusively confirm that a reportable event is the result of a nuclear explosion at such low yields would likely require additional evidence; for example, the collection of radioactive debris or possibly even an on-site inspection.
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From page 52... ...
• Continued development of improved models of the Earth's crust and upper mantle to provide 3-D velocity and attenuation models will improve event location and identification accuracy. • Continued development of seismic source models will allow prediction of potential explosion signals in untested emplacement geometries and geologies and would enhance monitoring capabilities.
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From page 53... ...
both radioactive xenon and Radionuclides are detected as particulate matter or as radioactive argon are targeted. noble gases, some of which, such as xenon and argon, are Long-term seepage exceeding important indicators of a nuclear explosion.
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From page 54... ...
Changes Since the 2002 Report The most significant improvement in radionuclide detection since 2002 has been the development of radioactive xenon noble-gas detection. The concept of this type of monitoring as part of the IMS was considered new during the drafting of the Treaty, and therefore only 40 of the 80 Treaty-defined monitoring stations were specified as noble gas stations.
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From page 55... ...
Radionuclide Event Location Accuracy The detection of radionuclides is normally not the first sign of a possible nuclear explosion. Although seismic or other signals may be detected first, a capable radionuclide monitoring network may provide the key measurements that will confirm a potential event was nuclear.
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From page 56... ...
These include the development of new techniques to collect and measure radioactive xenon, substantial improvements in gamma ray spectrometry capabilities, new abilities to discriminate xenon backgrounds from man-made sources, nuclear detection algorithm development, improved ATM, and other technologies. The NNSA Office of Nuclear Detonation Detection's Ground-Based Systems Nuclear Explosion Monitoring Research and Development (GNEMRD)
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From page 57... ...
Radionuclide Signal Detection Based on the current coverage of the radionuclide detection stations listed in the Treaty, there is very little chance that an atmospheric detonation of even a modest size would go undetected by the IMS, largely due to the high sensitivity of radionuclide samplers in the network. Figure 2-9 illustrates a calculation17 of the probability of detection of a 1-kiloton atmospheric nuclear detonation after 14 days by the IMS, based on a 79-station network and detection of a single species of isotope.
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From page 58... ...
Other Radionuclide Monitoring Capabilities There are a number of national efforts in other countries to detect airborne radionuclides that would indicate a nuclear-explosion test, but these efforts are essentially NTM, and the number of open sources is relatively low. However, some national programs make atmospheric measurements of radionuclides for health and safety purposes -- especially for remote monitoring for accidental releases from nuclear reactors -- that could have some application to the detection of nuclear explosions, especially atmospheric testing.
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From page 59... ...
ability to monitor underwater nuclear-explosion testing have occurred since the 2002 Report in two areas: • The near completion of the IMS hydroacoustic network has improved global underwater monitoring capabilities. This network also enhances underground monitoring in and around the ocean basins.
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From page 60... ...
For in-water events, when a hydroacoustic station has a clear SOFAR channel view to the source, the detection threshold is very low. If the SOFAR channel is blocked by land or does not exist due to low temperatures at high latitudes, detection capability is worse.19 Figure 2-11 gives a map showing the CTBT IMS detection threshold for in-water explosions around the world using both seismic and hydroacoustic data.
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From page 61... ...
However, hydroacoustic tracking of events on land or below the ocean floor yields degraded location accuracy. Hydroacoustic Event Classification There is no way using only hydroacoustic monitoring to distinguish between a large inwater chemical explosion and an in-water nuclear explosion.
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From page 62... ...
NTM network. IMS Hydroacoustic Monitoring The CTBT IMS hydroacoustic network consists of an 11-station network consisting of 6 hydroacoustic (H-phase)
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From page 63... ...
They are also produced by ground motion from underground explosions and provide a complementary source of data to detect and discriminate underground nuclear-explosion tests. The IMS uses its infrasound stations to detect and locate atmospheric nuclear-explosion tests.
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From page 64... ...
Finding 2-15: Infrasound detection is a valuable approach for monitoring atmospheric nuclear explosions. Although the IDC infrasound network is ostensibly for monitoring nuclear-explosion tests in the atmosphere, it has great potential to be used in parallel with seismic techniques to detect, locate, and identify underground or near-surface explosions.
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From page 65... ...
Different phenomena are detectable at various altitudes depending on where the nuclear explosion takes place. Based on this knowledge and experience starting with the Vela satellites in the early 1960s, the United States has produced and maintained an impressive satellite nuclear detonation detection capability for continuous coverage of Earth and space.
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From page 66... ...
DOE/NNSA has continued to fund the national labs to develop the technically complex satellite detonation detection systems, including data processing and display systems. AFTAC continues to operate the satellite nuclear detonation detection portion of the USAEDS, including the anticipation of upgrades and improvements in the detection capabilities.
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From page 67... ...
Decisions regarding whether and at what level to maintain the satellite nuclear detonation detection capability should be made as part of high-level national security policy and acquisition assessments. OPERATIONAL CAPABILITIES OF THE CTBTO The committee was asked to assess what commitments are required to sustain an adequate international verification regime, including on-site inspection.
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From page 68... ...
Sustaining the monitoring capabilities into the future will require further steps. For example, the CTBTO is subject to a number of political and funding restrictions outside its control.
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From page 69... ...
This would be straightforward to do technically, but because the Treaty states that auxiliary data is "upon request" and auxiliary stations are supported by the hosting state and not the CTBTO, making such a change is a political issue and does not seem to be under consideration at present.21 Finding 2-19: A technical exercise that tests the advantages of incorporating auxiliary seismic station data into the CTBTO's automated system would be useful to demonstrate the feasibility of this proposed improvement. Finding 2-20: Location accuracy of events identified with waveform signals (seismic, hydroacoustic or infrasound)
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From page 70... ...
. to clarify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out in violation of Article I and, to the extent possible, to gather any facts which might assist in identifying any possible violator" (CTBT Art.IV.D.35)
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From page 71... ...
In addition to radionuclide evidence, other evidence associated with nuclear-explosion testing, such as detection of a borehole casing or other nuclear-explosion test artifacts, evidence of containment measures, disturbed ground, and/or location of the explosion cavity or rubble zone, may be considered sufficient. Some of the radionuclides associated with a nuclear-explosion test are long-lived radioactive noble gases, which are known to seep slowly from a nuclear explosion site (Carrigan et al., 1996)
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From page 72... ...
FIGURE 2-14: Plot of the approximate surface concentrations of the noble gases expected after a 1-kt nuclear detonation. The horizontal lines represent the detection limits that are expected from instrumentation that will be used during an OSI.
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From page 73... ...
For example, China, Russia, the U.S., France and the UK all claim to sustain nuclear arsenals through stockpile stewardship programs involving no nuclear explosions, and there are many aspects of these programs that can be discussed openly and in a manner enhancing mutual confidence. Several areas that could be considered are: 1.
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From page 74... ...
Finding 2-23: There are many opportunities for confidence-building measures to support nuclear explosion monitoring, particularly through engaging scientists and engineers in cooperative efforts. Recommendation 2-10: The United States should pursue bilateral (and, to the extent justified and politically feasible, limited multilateral)
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From page 75... ...
These measurements showed that it is possible to conduct a series of null-measurements at a nuclearexplosion test site and give some level of confidence that the activities were not consistent with a nuclear-explosion test. NNSA concluded that, among other technologies, passive seismic, acoustic, radioactive xenon noble gases, and video would be effective for test site transparency applications.
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From page 76... ...
Observations: • The seismic signals from the two events clearly indicate that they were explosions and not earthquakes. The 2006 nuclear explosion was an excellent real world test of empirical seismic methods for a sub-kiloton explosion in a new region and the discrimination methods worked very well.
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