Comprehensive Test Ban Treaty Research Articles

Inferring the Focal Depths of Small Earthquakes in Southern California Using Physics-Based Waveform Features

ABSTRACT Determining the depths of small crustal earthquakes is challenging in many regions of the world, because most seismic networks are too sparse to resolve trade-offs between depth and origin time with conventional arrival-time methods. Precise and accurate depth estimation is important, because it can help seismologists discriminate between earthquakes and explosions, which is relevant to monitoring nuclear test ban treaties and producing earthquake catalogs that are uncontaminated by mining blasts. Here, we examine the depth sensitivity of several physics-based waveform features for ∼8000 earthquakes in southern California that have well-resolved depths from arrival-time inversion. We focus on small earthquakes (2<ML<4) recorded at local distances (<150 km), for which depth estimation is especially challenging. We find that differential magnitudes (Mw/ML–Mc) are positively correlated with focal depth, implying that coda wave excitation decreases with focal depth. We analyze a simple proxy for relative frequency content, Φ≡log10(M0)+3log10(fc), and find that source spectra are preferentially enriched in high frequencies, or “blue-shifted,” as focal depth increases. We also find that two spectral amplitude ratios Rg 0.5–2 Hz/Sg 0.5–8 Hz and Pg/Sg at 3–8 Hz decrease as focal depth increases. Using multilinear regression with these features as predictor variables, we develop models that can explain 11%–59% of the variance in depths within 10 subregions and 25% of the depth variance across southern California as a whole. We suggest that incorporating these features into a machine learning workflow could help resolve focal depths in regions that are poorly instrumented and lack large databases of well-located events. Some of the waveform features we evaluate in this study have previously been used as source discriminants, and our results imply that their effectiveness in discrimination is partially because explosions generally occur at shallower depths than earthquakes.

Stratospheric Gravity Waves Impact on Infrasound Transmission Losses Across the International Monitoring System

AbstractThe international monitoring system (IMS) has been put in place to monitor compliance with the comprehensive nuclear-test-ban treaty (CTBT). Its infrasound component, dedicated to the monitoring of atmospheric events, gives also room to civil applications (e.g. monitoring of volcanic eruptions, meteorites, severe weather). Infrasound detection capabilities are largely determined by the state of the middle atmosphere. This requires an accurate knowledge of the atmospheric processes at play. More particularly internal gravity waves (GW) pose a challenge to atmospheric modelling because of unresolved processes. Using high-resolution simulation outputs over winter 2020 (20 January–1 March) we present a method to assess the impact of GW on infrasound surface transmission losses across the IMS. We validate the method by comparing simulated GW perturbations to GW lidar observations at Observatoire de Haute-Provence in France, and satellite-based GW energy estimations globally. We perform propagation simulations using atmospheric specifications where GW are filtered out and kept in, respectively. We demonstrate that the largest impact of GW across the IMS is not where GW activity is the largest, but rather where GW activity combines with infrasound waveguides not firmly set in a given direction. In northern winter, the largest variations of transmission losses at 1 Hz due to GW occur in the southern (summer) hemisphere in the direction of the main guide (westward propagation), with average values ranging between 10 and 25 dB in the first shadow zone. It corresponds to an average signal amplification of at least a factor 5 to 15, while this amplification is around 2 to 5 for the main guide in the northern winter hemisphere (eastward propagation).

India’s Chequered Relationship with the Comprehensive Test Ban Treaty: Examining Cross-Linked Concerns over Nuclear Disarmament and National Security

In 1994, India enthusiastically supported the United Nations process for negotiating the Comprehensive Test Ban Treaty (CTBT). It expected the treaty would ban all types of nuclear testing and pave the way for nuclear disarmament. The final treaty negotiated in 1996 did not commit itself to this goal of disarmament and India ultimately rejected it. However, behind this rejection also lies the story of India’s deteriorating national security outlook and decision-makers’ keen desire to avoid their country being subjected to a discriminatory nonproliferation regime enacted by the nuclear weapon states. The key questions guiding the query on (CTBT) are: What were the reasons behind India’s initial support of the CTBT in 1993? And what transpired between 1994 and 1996 that led India to change its stand?

Seismic Discrimination Between Nuclear Explosions and Natural Earthquakes using Multi-Machine Learning Techniques

AbstractIn the field of seismic signal analysis, it is of utmost importance to accurately differentiate between earthquakes and underground nuclear explosions. As a contribution for the verification regime of the Comprehensive Nuclear Test Ban Treaty (CTBT), Various methods have been employed for this purpose, including Complexity, Spectral ratio, mb—Ms (body wave and surface wave magnitudes), and corner frequency of P and S waves. These discrimination techniques have been examined to manually identify natural seismic events from nuclear explosions across different regions worldwide, such as China, India, Pakistan, North Korea, and the United States. To gather the necessary data, a comprehensive dataset comprising nuclear explosions and earthquakes of the same magnitude range (4 ≤ mb ≤ 6.5) of 35 seismic events from 1945 to 2017 has been compiled from the International Research Institute for Seismology (IRIS) using broadband and long period seismic stations. The objective of this study is to employ a range of linear and nonlinear Machine Learning (ML) models with the aim of automatically distinguishing between underground nuclear explosions and large earthquakes to enhance the accuracy of manual feature extraction. For this purpose, time domain waveforms and different classifier techniques focused on feature extraction have been used. The ML models employed include logistic regression, K-nearest neighbours classifier, decision tree classifier, random forest classifier, voting classifier, and Naive Bayes. The outcomes of the ROC and AUC analyses were employed to validate the validity of our proposed discrimination algorithm. The results show that the Random Forest Classifier is the most effective model, obtaining 100% accuracy in the case of feature extraction, while the best model for the time domain waveform classifier that achieved 75.5% accuracy is the voting classifier.

Gamma-spectrometry measurements of filtration media from an Advanced Gas-cooled Reactor

Filtration media used to quantify particulate and gaseous releases have been collected from Hartlepool Power Station in the United Kingdom and measured using high-sensitivity gamma-spectrometry systems. Radionuclides that are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have been detected. Results are reported and compared to detections recorded on the International Monitoring System (IMS). Time series activity plots have been produced and results interpreted with respect to known plant activities. The reported results improve the understanding of trace-level radionuclide emissions from Advanced Gas-cooled Reactors (AGRs) and aid interpretation of IMS measurements. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, US) and the Swedish Defence Agency (FOI, Sweden).

Relocation of 3 April 2017 Moiyabana Earthquake in Botswana Using Seismological Data from Local Network of Autonomously Recording Seismographs and International Monitoring System Stations

AbstractOn the 3rd April 2017 a widely felt Moiyabana earthquake shook Botswana and the rest of southern Africa. Previous Moiyabana earthquake locations used mainly teleseismic or regional seismograms; and/or non-seismic methods which include Synthetic Aperture Radar (InSAR), and magnetotelluric (MT). These results did not agree, as evidenced by the depth of the earthquake that ranged from zero to 30 km (i.e. indicating either a man-made event or a natural event); thus motivating us to re-assess the location parameters. Unfiltered seismic waveform data from the recent project of the Network of Autonomously Recording Seismographs (NARS) in Botswana was complimented with stations from the International Monitoring System (IMS) to relocate the event. Relocated parameters are origin time, epicentre, focal depth, and magnitude. Geotool software from the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), and the Regional Seismic Travel Time model (RSTT) were used to process vertical components waveforms from 9 NARS and 32 IMS stations. Geotool results are: earthquake epicentre (22.645 °S: 25.220 °E); origin time of 17:40:16.9 (UTC); hypocentral depth range of 22 to 24 km; body magnitude (mb) and local magnitude (ml) of 6.3 ± 0.6 and 6.0 ± 0.8, respectively. RSTT results are: earthquake epicentre (22.667 °S: 25.257 °E); origin time of 17:40:16.95 (UTC); hypocentral depth of 25 km; and mb of 6.65 ± 0.03. The seismological location parameters from Geotool and RSTT, agree very well within experimental uncertainties with the non-seismic geophysical methods.

The logic for US ratification of the Comprehensive Nuclear Test Ban Treaty

ABSTRACT The United States has accepted increasingly stringent limits on nuclear testing, culminating in the 1996 Comprehensive Nuclear Test Ban Treaty. However, the US Senate in 1999 failed to consent to ratification, given concerns about verifying the treaty and maintaining safe and reliable US nuclear weapons without testing. Since then, the US Stockpile Stewardship Program has matured and allowed certification that US nuclear weapons remain safe and reliable without nuclear explosive testing. Likewise, advances in the US Nuclear Detonation Detection System and the International Monitoring System make virtually all tests detectable. Bringing the Comprehensive Nuclear Test Ban Treaty into force is in the US interest, as it would lock in an American advantage in nuclear knowledge and expertise and hinder other states from developing more sophisticated nuclear arms. Unfortunately, however, American domestic politics and the difficult international environment make it unlikely that the treaty will enter into force in the near term.

New confidence-building measures can reduce tensions around subcritical tests

ABSTRACT With rising tensions between the United States on one side, and China and Russia on the other, the three countries have grown mutually accusatory about some testing activities they conduct to maintain and modernize their nuclear arsenals, with allegations made by the United States focusing on very low-yield fission experiments. In a world where trust in the nonproliferation regime is weakening and most bilateral arms control measures have been suspended, many experts fear that recriminations over very low-yield tests could spark a new escalation spiral to full-scale nuclear tests. Transparency measures could diffuse the suspicions around these tests and strengthen the Comprehensive Nuclear Test Ban Treaty, which is largely being complied with but still not legally in force.

Preserving the nuclear test ban after Russia revoked its CTBT ratification

ABSTRACT Russia’s withdrawal of its ratification of the Comprehensive Nuclear Test Ban Treaty in 2023 raised concerns about the possible end of the existing moratorium on nuclear explosions. But the moratorium continues to hold, largely thanks to the de facto norm against full-scale nuclear tests and the strength of institutional structures created by the treaty. Transparency of nuclear experiments demonstrated by the United States will be an important factor in upholding the moratorium, and Russia and China should be encouraged to be more transparent about their activities as well. Any disputes about the exact nature of their experiments and their adherence to the strict definition of a zero-yield nuclear explosion should not become reasons to question the value of the moratorium—or the ability of parties to verify and enforce the test ban once the treaty comes into force.

Development and Operation of a Global‐Scale Seismographic Network: The IRIS/USGS GSN

AbstractFrom inception in the late 1980s up to the present, the Global Seismographic Network has produced high quality seismic data that has advanced research into the structure of the Earth's deep interior particularly the large‐scale heterogeneous elastic/anelastic structure of the mantle and core. The network's breadth of coverage enables images of great earthquakes impossible to obtain from regional networks or array data alone. Analysis of the data has provided new insights into non‐traditional seismic sources such as slow earthquakes, glaciers and landslides. Ancillary meteorological and infrasound sensors collocated at the sites support unique studies of volcanic events such as the recent eruption of the Hunga Tonga–Hunga Ha'apai volcano. Near real‐time transmission of the data to hazard warning centers has expanded the network's usefulness as a tool for rapid response to earthquakes, for warning communities effected by tsunamis, and for monitoring compliance with nuclear test ban treaties. The successful construction and operation of the network would not be possible without the outstanding international cooperation of many governmental, academic and private groups who have hosted components of the network.

Q&A Aftab Khan, a career in geophysics

Abstract Sue Bowler talks to Aftab Khan, who recently celebrated his 90th birthday, about his career in geophysics, from the origins of the modern subject, through the exploration of the African Rift Valley and the steps to a nuclear test ban treaty

Beyond The Nuclear Explosion Verification Monitoring, the Comprehensive Nuclear-Test-Ban Treaty Offers A Strong Capacity Building System Support

Purpose: The United Nations (UN) General Assembly, as part of nuclear non-proliferation and disarmament measures to prohibit nuclear test explosions and any other nuclear explosions in all environments (in the atmosphere, oceans, and underground) adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Thus, it ultimately enhances international peace and security. It is an essential step aimed at making the world a safer place. States that agree to sign on to this Treaty will be contributing to the protection of human health and the environment against nuclear test explosions and their severe impacts. This paper seeks to demonstrate that the CTBT beyond its global prohibition measure against all nuclear explosions, is offering a strong Capacity Building System support to State Signatories such as the Republic of Ghana. The CTBT global verification regime is built to monitor States Signatories compliance with the Treaty. CTBT Organization (O) through the International Data Centre (IDC) provides States Signatories with technical assistance to support their verification responsibilities to ensure effective global monitoring.
 Methodology: The Republic of Ghana through the Capacity Building project under the IDC technical assistance to States Signatories is a beneficiary of equipment support commissioned in July 2021. Under this project the GCI-III/VSAT equipment set was received from the IDC, establishing a new communication link for forwarding IMS waveform data from some selected stations in Africa in near-real-time to the National Data Centre – Ghana (NDC – GH). The IMS seismic data also contributes to prompt access to information on seismic events within our respective geographic territories globally, thus playing a complementary role.
 Findings: The monitoring data generated provides essential civil and scientific applications to greatly support to mitigate the effects of natural or man-made disasters. This is an example of what the CTBT is providing to Member States beyond the Treaty’s main purpose.
 Unique contributor to theory, policy and practice: It is therefore important for the international community to fashion out other multilateral agreements considering the possibility of incorporating the potential additional benefits States can derived from such agreements.

Examining the potential for detecting simultaneous noble gas and aerosol samples in the international monitoring system radionuclide network

The purpose of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is to establish a legally binding ban on nuclear weapon test explosions or any other nuclear explosions. The Preparatory Commission for the CTBT Organization (CTBTO PrepCom) is developing the International Monitoring System (IMS) that includes a global network of 80 stations to monitor for airborne radionuclides upon entry into force of the CTBT. All 80 radionuclide stations will monitor for particulate radionuclides and at least half of the stations will monitor for radioxenon. The airborne radionuclide monitoring is an important verification technology both for the detection of a radionuclide release and in the determination of whether the release event originates from a nuclear explosion as opposed to an industrial use of nuclear materials.Nuclear power plants and many medical isotope production facilities release radioxenon into the atmosphere. Low levels of a few particulate isotopes, such as iodine, may also be released. Detections of multiple isotopes are useful for screening the radionuclide samples for relevance to the Treaty. This paper examines the anticipated joint detections in the IMS of noble gas and particulate isotopes from underground nuclear explosions where breaches in the underground containment vents from low levels to up to 1% of the radionuclide inventory of the resulting fission products to the atmosphere. Detection probabilities are based on 844 simulated release events spaced out at 17 release locations and one year in time. Six different release (venting) scenarios, including two fractionated scenarios, were analyzed.When ranked by detection probability, 11 particulate isotopes and one noble gas isotope (133Xe) appear in the top 20 isotopes for all six release scenarios. Using the 11 particulate isotopes and the one noble gas isotope, the IMS has nearly the same detection probability as when 45 particulate and 4 noble gas isotopes are used. Thus, a limited list of relevant radionuclides may be sufficient for treaty verification purposes. The probability that at least one particulate and at least one radioxenon isotope would be detected in the IMS from the release events ranged from 0.15 to 0.86 depending on the release scenario.

Tidal modulation of very-low-frequency and ultra-low-frequency ambient noise levels.

Several years of continuous low-frequency underwater ambient noise data from 0.1 to 125 Hz have been made available for examination by the United Nations Comprehensive Nuclear Test Ban Treaty Organization. Narrow-band noise time records between 0.5 and 10 Hz were selected for study, chosen deliberately to address noise sources tied primarily to the environment. Power spectra of the variable narrow-band time records were found to display sharp spectral lines at fluctuation frequencies that match lunar and solar diurnal and semidiurnal ocean tides.

Algorithm development for low level radioxenon 2D spectra analysis: A first case of study using spectral unmixing for a β-γ detector

In the scope of the verification regime of the Comprehensive nuclear Test Ban Treaty, the CEA/DAM is developing new β-γ measurement systems. In order to improve the analysis methods at low statistics, a new multiplicative spectral unmixing algorithm for full-spectrum analysis was tested on a particular setup for different types of mixtures. The reconstructed activities for simulated spectra and the characteristic limits found with this algorithm are compared to the classic ROI analysis method.

Моделирование нисходящего переноса 210Pb на примере естественного торфяника Иласского болотного массива Европейской Субарктики России: модель IP-CRS

The paper presents the results of the modelling of the transport of 210Pb down the peat core for the Ilassky natural bog massif. The activities of radionuclides 210Pb and 137Cs were investigated in the core layer by layer. Due to the nonexponential decrease of 210Pb activity, significant errors are possible in determining the age and accumulation rates of peat when applying classical dating models. The article presents 210Pb dating data obtained using the IP-CRS model. Data analysis showed that the vertical distribution of 137Cs and 210Pb is related to peat parameters: ash content and bulk density. The 210Pb dating of the core showed an age of 1963 for a depth of 17—19 cm, which is consistent with the 137Cs data. The dating of this horizon is indirectly confirmed by the data of the ash content and bulk density of peat. The above mentioned confirms the correctness and adequacy of the chosen model of dating of the natural peat bog. The peak of anthropogenic radionuclide content in peat deposits corresponds to 1963, the date of signing the Partial Nuclear Test Ban Treaty, being a reference point for geochronological studies. The results of linear accumulation rate, peat deposit mass accumulation rate and the magnitude of the atmospheric flux of 210Pb presented in the study are in good agreement with the data on peatlands of Northern Europe and the European Subarctic of Russia.

Long-range underwater acoustic detection of aircraft surface impacts—The influence of acoustic propagation conditions and impact parameters

The 2019 crash of an F35 fighter aircraft off the east coast of Japan was detected at a range of approximately 3000 km by a hydroacoustic station of the Comprehensive Nuclear Test Ban Treaty Organisation’s International Monitoring System. In this paper we compare the acoustic propagation conditions relating to that detection to those relating to the crash of Malaysian Airlines flight MH370 in the Indian Ocean in 2014 with a view to reassessing the likelihood that acoustic signals detected on a similar hydroacoustic station could have been related to the loss of MH370. Possible differences in source levels due to different assumptions about impact parameters are also considered. Despite several extensive searches, the location of the wreckage of MH370 remains unknown.

Evidence of oceanic and atmospheric tides in underwater ambient noise time records

Multiyear time records of low-frequency ocean ambient noise show clear evidence of a modulating influence by major semi-diurnal and diurnal gravitational tides. These are displayed by means of a variance spectral analysis of noise time records obtained from the United Nations Comprehensive Nuclear Test Ban Treaty Organization for hydrophone stations at Wake Island, Ascension Island and Diego Garcia. Narrow-band noise frequencies ranged from ½ to 10 Hz. There is also evidence in the noise records of a diurnal atmospheric tide related to solar radiation and atmospheric loading. This same tidal presence is seen in wind speed records as well. Part of the challenge in the analysis is to distinguish between expected diurnal behavior in wind speed, with its accompanying effect on ambient noise, and the presence of actual tidal lines. A brief history of earlier observations of diurnal variation in underwater acoustics is presented, along with some suggestions of causal mechanisms.

Worldwide detection of rocket launches for space missions using International Monitoring System infrasound arrays

The signals of rocket launches can be detected at infrasound arrays in thousands of kilometers distance. We use microbarometer arrays, which are part of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT), to identify and characterize rocket launches all over the world. We studied more than 1000 launch events for space missions and their infrasonic signatures. Even small-lift launch vehicles such as Electron rockets starting from New Zealand with payloads of only a few hundreds of kilograms, e.g., for small satellites, can regularly be detected by one or more remote infrasound stations. We present selected cases of interest, including the latest NASA Artemis 1 Space Launch System and SpaceX Starship launches as well as airborne rocket starts and small-lift launches by different companies. Furthermore, we present a systematic analysis of infrasound recorded from multiple and regularly launched vehicles like Ariane 5, Falcon 9, and various Soyuz and Long March rocket types. Our main focus is on the connection between the observed signatures and propagation-corrected acoustic amplitudes of rocket launches as well as rocket parameters like payload, size and thrust, rocket stage, and engine characteristics of different rocket types.

Basin scale propagation modeling of MLS signals from the Kauai Beacon source

Long distance underwater acoustic propagation is of interest for a variety of applications including underwater navigation, yet modeling such propagation is challenging due to the large degree of environmental uncertainty. In this presentation, the propagation of 75Hz center frequency maximum length sequence (MLS) signals emitted from a submerged source near Kauai and received at various sites throughout the Pacific Ocean Basin is modeled with the Bellhop ray tracing [1] and Monterey-Newport Parabolic Equation [2] models. Sites such as the Monterey Accelerated Research System (MARS) observatory and the Comprehensive Nuclear Test Ban Organization (CTBTO) hydroacoustic monitoring station near Wake Island are included in the discussion. The range-dependent environment is based on historical profiles from the World Ocean Atlas database and reanalysis data from the hybrid coordinate ocean model (HYCOM) [3]. Bathymetry profiles along the axis of propagation are interpolated from the General Bathymetric Chart of the Oceans (GEBCO) 2021 database [4]. Simulated broadband channel impulse responses transmission loss levels in the modeled environment are compared to selected receptions of the signal at the hydrophone sites. Additionally, fluctuations of the modeled transmission loss in the presence of an internal wave model [5] are discussed.