Treaty International Monitoring System Research Articles

Shear wave effects in hydroacoustic recordings of the Comprehensive Nuclear-Test-Ban Treaty International Monitoring System

The hydroacoustic (HA) component of the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System (IMS) comprises six stations with triplets of moored hydrophones suspended in the SOFAR channel and five near-shore seismometer stations for T-phase detection. Understanding the conversion between compressional and elastic waves at the crust-ocean boundary or at large bodies of ice can contribute to better identification and association of arrivals. In this talk, examples recorded by the IMS HA network are presented with a view to stimulating discussion and further analysis: (i) T-phases from the September 2017 announced DPRK underground nuclear test recorded by the hydrophones of HA11 (Wake Island); (ii) a “precursor” southerly arrival at HA04 (Crozet Islands), associated with the hydroacoustic anomaly related to the loss of the Argentine submarine ARA San Juan, which is inter alia compatible with a Lamb wave propagating through the Antarctic ice-sheet; (iii) T-phases from earthquakes along the Nazca subduction zone scattered horizontally by the Juan Fernandez sea-mounts and recorded by HA03 (Chile); and (iv) conversion of signals from distant underwater explosions at the crust-ocean boundary near IMS T-stations. Benchmark studies to assess the accuracy of spectral element model setups previously used for scenarios (iv) would be particularly desirable.

Hydroacoustic Signals Originating from Marine Volcanic Activity at Kadovar Island, Papua New Guinea, Recorded by the Comprehensive Nuclear-Test-Ban Treaty International Monitoring System

Hydroacoustic signals originating from marine volcanic activity at Kadovar Island (Papua New Guinea), recorded by the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) hydroacoustic (HA) station HA11 Wake Island (USA), are examined herein. Episodes of high volcanic activity were identified on two occasions, separated by a period of 1 month. The events studied pertain to an initial eruption series during a period between January and February 2018. Based on local visual observations, the Kadovar volcano began to erupt at the summit and then created a new vent spot near the coast. This series of events also included the collapse of a lava dome. Direction-of-arrival estimates for the hydroacoustic signals detected at HA11 were computed using a cross-correlation technique, which allowed for the discrimination between hydroacoustic signals originating from the Kadovar volcanic activity and numerous other hydroacoustic signals attributed to seismic activity in the Pacific Ocean. The Kadovar-related seismic signals could not be identified by regional IMS seismic stations, suggesting a submarine origin of these events. On the other hand, hydroacoustic signals originating from the Kadovar volcanic activity were identified by the seismometer at Manus Island, which is located between Kadovar and HA11. The study suggests that a series of explosive bursts followed by an unusual rumble and a broadband signal plus rumble may constrain the time of the lava dome collapse event at Kadovar Island to 00:30 UTC, 00:33 UTC, and 00:46 UTC on 09 February 2018. Given the compatibility of this observation with the tsunami generation reported by eyewitnesses on the nearby island of Blup Blup, the authors interpret this particular hydroacoustic signal as being a remote observation of this tsunamigenic event. The objective of this study was to assess the potential added value of IMS hydroacoustic data for remote surveillance of geohazards in otherwise sparsely monitored areas.

T‐phase and tsunami pressure waveforms recorded by near‐source IMS water‐column hydrophone triplets during the 2015 Chile earthquake

AbstractUnderwater acoustic signal waveforms recorded during the 2015 Chile earthquake (Mw 8.3) by the hydrophones of hydroacoustic station HA03, located at the Juan Fernandez Islands, are analyzed. HA03 is part of the Comprehensive Nuclear‐Test‐Ban Treaty International Monitoring System. The interest in the particular data set stems from the fact that HA03 is located only approximately 700 km SW from the epicenter of the earthquake. This makes it possible to study aspects of the signal associated with the tsunamigenic earthquake, which would be more difficult to detect had the hydrophones been located far from the source. The analysis shows that the direction of arrival of the T phase can be estimated by means of a three‐step preprocessing technique which circumvents spatial aliasing caused by the hydrophone spacing, the latter being large compared to the wavelength. Following this preprocessing step, standard frequency‐wave number analysis (F‐K analysis) can accurately estimate back azimuth and slowness of T‐phase signals. The data analysis also shows that the dispersive tsunami signals can be identified by the water‐column hydrophones at the time when the tsunami surface gravity wave reaches the station.

Compliance science: the CTBT's global verification system

ABSTRACTThe Comprehensive Nuclear-Test-Ban Treaty's verification regime is arguably one of the most effective and efficient systems of arms-control and disarmament monitoring in operation today. The science and technology underpinning the system have been developed over several decades. This article goes through the treaty's international monitoring system and pays particular attention to its waveform-monitoring techniques. It then considers the concept of data fusion, before describing the agreement's on-site-inspection mechanism. It briefly discusses how alleged noncompliance is likely to be resolved. It concludes by arguing that the treaty's verification regime is expected to make cheating costly, which enhances the treaty's deterrent effect.

Ultra-low background measurements of decayed aerosol filters.

Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 μBq/m3 of air for 140Ba, which would imply ~106 fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including 131I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed.

Hello from the New Editor of SRL

When I returned to academia after a sojourn of seven years in Vienna, I applied for the Seismological Research Letters editor position as a way to reintegrate myself to the academic world and to perhaps serve as a liaison between the many “worlds” I have experienced during my professional career. In Vienna, I worked for the Comprehensive Nuclear-Test-Ban Treaty Organization to establish the Treaty's International Monitoring System. Now, as I write my self-introduction as the new SRL editor, I keep wondering: Why did I do it? Those of you who know me know that I am not usually short for words, but now that I am in the spotlight, I am speechless. At first I found it comforting to be following in the footsteps of Editors John Ebel and Susan Hough, but now I know that it is not going to be easy. Over the past 11 years they managed to establish this flexible scientific publication as a respected journal among earthquake scientists and engineers. SRL was conceived as a general forum for informal communication amongst its constituency. In the first SRL Opinion, John wrote, “I took the job as editor of the New SRL because I feel strongly that more communication …

Hydroacoustic observations of Indian earthquake provide new data on T‐waves

The magnitude 7.8 earthquake that devastated the Bhuj area of western India on 26 January 2001 was recorded not only by seismometers around the world, but also by a new hydroacoustic array in the Indian Ocean. This array, located 3290 km south of the epicentral area (see Figure 1a), consists of two tripartite hydrophone arrays surrounding the atoll of Diego Garcia at the southern end of the Chagos Plateau. Installed as part of the hydroacoustic monitoring network for the Comprehensive Nuclear Test Ban Treaty's International Monitoring System (IMS), the array has since been recording the acoustic T‐wave signals generated by many shallow earthquakes below the Indian Ocean since the summer of 2000.

Detection and analysis of xenon isotopes for the comprehensive nuclear-test-ban treaty international monitoring system

The use of the xenon isotopes for detection of nuclear explosions is of great interest for monitoring compliance with the comprehensive nuclear-test-ban treaty (CTBT). Recently, the automated radioxenon sampler-analyzer (ARSA) was tested at the Institute for Atmospheric Radioactivity (IAR) in Freiburg, Germany to ascertain its use for the CTBT by comparing its results to laboratory-based analyses, determining its detection sensitivity and analyzing its results in light of historical xenon isotope levels and known reactor operations in the area. Xe-133 was detected nearly every day throughout the test at activity concentrations ranging between approximately 0.1 mBq/m 3 to as high as 120 mBq/m 3. Xe-133m and 135Xe were also detected occasionally during the test at concentrations of less than 1 to a few mBq/m 3.