In October 2023, a sequence of shallow seismo-acoustic events occurred in Izu Islands archipelago, south of Honshu, Japan’s main island. The sequence started on October 1, and within a span of 8 days, approximately 70 events with magnitudes of 4.0 (International Data Centre mb) or higher were reported in the Reviewed Events Bulletin (REB) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). An unusual tsunami of up to 60 cm was reported on October 09 by the Japan Meteorological Agency. The authorities suggested that it was triggered by a relatively small magnitude earthquake, however, other related phenomena were also considered. An underwater volcano eruption or quake-triggered seabed landslide could have caused the tsunami. In this work, we show features of signals recorded at the hydrophone stations of the International Monitoring System (IMS), which indicate that the tsunami might have originated from volcanic activity. In addition, hydroacoustic signals were also observed at island seismic stations. This presentation demonstrates how IMS data may contribute to the identification of underwater events, such as volcanic activity, which may result in catastrophic phenomena. Even though the IMS was built to detect nuclear explosion tests, the data are available for civil applications and are distributed to tsunami warning centres.

How to cite: Bittner, P., Ali, S. M., Qorbani, E., Kasmi, A., Villarroel, M., and Rambolamana, G.: Detection of underwater volcanic activity at stations belonging to the International Monitoring System - case of Izu Islands sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12634, https://doi.org/10.5194/egusphere-egu24-12634, 2024.

This study analyzes signals recorded by the CTBT-IMS hydroacoustic network from well-defined underwater explosions in the Atlantic Ocean, and looks at the relationships between yield, location, and detectability. The events analyzed are detonations of TNT charges and are used here to assess the ability of the CTBT-IMS hydroacoustic network to detect H-phases, which are signals from in-water explosions. The locations of the explosions ranged between the continental shelf, shelf break, and deep waters, and their yields were between 0.8 and 18,000 kg TNT. For high-yield explosions, T-stations (coastal seismometers) and Hydrophone stations effectively detected the explosions. For distant low-yield events, the ability of the network to detect the explosions depends heavily on the location of the source. Distant shallow events on the continental shelf can be more detectable than closer deep-water events. This is because the sound from the former events propagates off the shelf and skips off the shelf edge into the SOFAR channel, while events in deep water, depending on their depth, can have more difficulty coupling into the SOFAR channel. Similarly, explosions near the shelf break can have a favourable SOFAR channel coupling mechanism due to reflections from the shelf into the channel.

How to cite: Oliveira, T., Prior, M., Lin, Y.-T., and Dall’Osto, D.: Underwater explosions recorded at IMS hydroacoustic stations from well-defined experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7649, https://doi.org/10.5194/egusphere-egu24-7649, 2024.

Seismic, hydroacoustic, infrasound, and radionuclide are the four complementary monitoring technologies of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The International Monitoring System (IMS) of the CTBTO consists of, when complete, 50 primary and 120 auxiliary seismic stations, 11 hydroacoustic stations, 60 infrasound stations, 80 radionuclide stations and 16 radionuclide laboratories. Hydroacoustic and Infrasound stations of IMS are designed to detect events of any kind in and underwater, and in the atmosphere respectively. Hydroacoustic stations have been in operation since 1999; 11 stations, of which 6 hydrophones and 5 T-phase, have been sending data since the completion of the network in 2016. Infrasound data was introduced to routine data analysis in 2010 after improvements in automatic processing to reduce the number of false detections. Currently, 54 (out of 60) infrasound stations are being processed.

Both hydroacoustic and infrasound technologies have had significant contributions to detecting and to improving event location at the International Data Centre (IDC). This presentation assesses the data quality and performance of the hydroacoustic and infrasound stations in the data analysis aspect. We focus on signal and event detection rate and in turn the contribution of the data from hydroacoustic and infrasound stations to the data analysis. We show how the station performance changes temporally and discuss the results.

How to cite: Qorbani Chegeni, E., Bittner, P., Applbaum, D., and Rambolamanana, G.: Performance variability of the Hydroacoustic and Infrasound IMS stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20403, https://doi.org/10.5194/egusphere-egu24-20403, 2024.

During the last 20 years, an increasing number of rocket launches for space missions per year was conducted from various space ports all around the world. These missions were mainly launched to place satellites in Earth’s orbit, but also for space station flights and the exploration of the Moon and other bodies in the solar system.  

Rocket launches can be detected at infrasound arrays in thousands of kilometers distance. We use infrasound data from stations 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 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 highlight 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.

How to cite: Pilger, C., Hupe, P., and Gaebler, P.: Identifying rocket launches for space missions using infrasound detections across the IMS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7502, https://doi.org/10.5194/egusphere-egu24-7502, 2024.

Within the International Monitoring System Infrasound Stations, Wind Noise reduction Systems (WNRS) help to improve the infrasound signal quality and analysis by eliminating local atmospheric noise. A standardized system has been designed for the monitoring of nuclear explosions, with a frequency range of interest of 0.1Hz to 10Hz.

This standardized system, a pipe-array rosette, has many options for adaptation with different pipe length, material, and geometry. The type of air inlet and the use or not of primary manifolds will change WNRS characteristics.  All these options of adaptation, give the possibilities to turn the WNRS into tailor-made flexible systems which can be further customized according to their use.

Other types of WNRS have been developed and tested. Enviroearth offers to compare and assess their particular performances : considering their different characteristics, those distinct WNRS model could be practical and optimal for specific applications. By modifying the geometry and characteristics of a WNRS, frequency at which maximum noise reduction is reached can be changed. Therefore, adapted WNRS can be used in measurement stations to monitor natural events (Seismic, Storm, hurricane …) which data can be used for early warning and/or climate change adaptation systems.

How to cite: Lucas, J. and Bednarowicz, C.: Wind Noise Reduction System models state of the art assessment and study of their respective optimal field of application, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17139, https://doi.org/10.5194/egusphere-egu24-17139, 2024.

How to cite: Saragiotis, C.: Calculation of slowness-azimuth station corrections for the IMS seismological networks , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12096, https://doi.org/10.5194/egusphere-egu24-12096, 2024.

NET-VISA stands for NETwork processing - Vertically Integrated Seismic Analysis. The package comprises a physics-based, probabilistic model and a heuristic inference algorithm to find the most probable set of seismic events to explain a series of arrivals detected by a global seismic network. It has been extended to find events in any of three mediums – rock, air, and water- and supports seismic, hydro-acoustic, and infrasound sensors.

Large seismic events often trigger a wave train of slow decaying energy known as the coda that can mislead signal detectors into forming coda detections that look like regular phase detections. These coda detections can confuse event formation algorithms into building false events known as coda events. Naive solutions to this problem by dropping any detection that looks like coda detection can have the negative consequence of missing real events. 

We propose to address this issue by extending an existing Bayesian Approach, designed to build event bulletins using a generative model of global-scale seismology. Our extensions significantly boost to the existing work by reducing the total number of false events and virtually eliminating coda events at the cost of a very small drop in the number of real events.

How to cite: Shashkin, A., Arora, N. S., Mohamed Ali, S., Khukhuudei, U., Miljanovic Tamarit, V., and Rambolamanana, G.: Suppressing Coda Events with a Bayesian Model of Global Scale Seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21035, https://doi.org/10.5194/egusphere-egu24-21035, 2024.

In 1961, AWE Blacknest became the home of Forensic Seismology in the UK, with the aim of developing and maintaining a capability to provide seismological advice to the UK government. During the 1960s the group set up a seismometer array in Scotland and worked with host countries to set up arrays in Canada, Australia (now both IMS stations), India and Brazil. AWE Blacknest has continuous data archives from these sites dating back to 1961 on a mix of paper helicorder records (seismic and infrasound traces), analogue FM-encoded tape and digital tape. From 2006-15 Blacknest developed and ran an extensive programme to overcome the ageing issues presented by vintage magnetic media condition and formats, and recovered and digitised the tapes, putting the continuous data on to modern computer storage systems. Since the 1990s data have been directly recorded to digital storage systems. Historically only events of interest, including data recorded from suspected nuclear explosions, were extracted, and Blacknest is running a programme of analysing these events and preparing the data and analysis in a form for public release. I will present on the work undertaken to develop the programme, data recovery and digitization methods from magnetic media, and the modern storage systems Blacknest use for serving seismic data. This will also include analysis work and the data inventories that Blacknest is making available.
UK Ministry of Defence © Crown Owned Copyright 2024/AWE

How to cite: Peacock, S. and Bartholomew, P. and the Forensic Seismology Team: Seismic Data Archive in the United Kingdom to support Nuclear Test Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15475, https://doi.org/10.5194/egusphere-egu24-15475, 2024.

As part of the EU-funded joint research project "Metrology for low-frequency sound and vibration - 19ENV03 Infra-AUV" laboratory calibration methods for seismometers in the low frequency range down to 0.01 Hz have been developed. The reliable knowledge of the full complex sensor response and its associated measurement uncertainty for both, magnitude and phase, improve data quality and reliability by correctly estimating estimating signal amplitude and phase information. Using newly developed on-site calibration approaches, full-frequency responses are estimated for, and the traceability can be transferred to station seismometers of the Comprehensive Nuclear-Test-Ban Treaty Organization’s (CTBTO) International Monitoring System (IMS) during operation without disturbing their regular measurements.

With the on-site methodologies in place for co-located sensors, we show how precisely determined full-frequency response information effects seismogram interpretation and the determination of key parameters such as amplitudes and subsequently magnitudes, as well as first motion polarity or event localisation. For that purpose, we use data from on-site calibration tests performed at IMS station PS19 in Germany with both short-period and broadband seismometers calibrated in the laboratories at PTB.

Furthermore, the possibility of an array-wide calibration of seismometers with a number of temporary and stationary reference sensors is assessed using suitable excitation signals and station-wide similarity measures. The primary focus is to estimate the required quantity, spacing, and distribution of reference sensors throughout the array.

How to cite: Schwardt, M., Bruns, T., and Pilger, C.: Why do field seismometers need to be calibrated? Benefits through traceably calibrated seismometers from the laboratory to the field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17018, https://doi.org/10.5194/egusphere-egu24-17018, 2024.

At least since 1998, we know that the main nuclear weapons states are using computer simulations aimed at having the capability of designing new nuclear weapons without conducting any nuclear test, among other relevant jobs in which computer simulations are used. Currently, three important developments have increased the power of computer simulations: a) the development of new supercomputers with a tremendous capacity for processing and realising complex jobs; b) the accumulation of billions of data useful for simulations considering the number of nuclear tests conducted in the past and the results of computer simulations, and c) the recent developments of powerful AI foundation models with billions of parameters that can be used in nuclear weapon design very successful. The dominant thesis, since 2002, is that experiments “using simulants to replace nuclear materials are permitted under the Comprehensive Test Ban Treaty (CTBT)”. What this means is that states can develop new nuclear weapons complying with the CTBT, but this, I consider, is contrary to the goal of the CTBT and CTBTO. Nuclear proliferation was expected during the first two decades of the 21st century.  However, in the current global geopolitical situation, where other forms of nuclear proliferation are observed, these computer simulations pose challenges to the CTBT and CTBTO.

How to cite: Vargas, C.: Computer Simulations and the Need for Nuclear Weapon Testing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7049, https://doi.org/10.5194/egusphere-egu24-7049, 2024.

The identification of a sample associated with a nuclear test is a challenging task for the CTBTO because of the presence of a noble gas background in the constant evolving atmosphere. This background is caused by nuclear power plants, nuclear research reactors, and medical isotope production facilities and contributes to samples collected by the noble gas systems of the International Monitoring Stations (IMS). Because of that background, standard linear inverse model applied to Xe-133 measurements is prone to substantial errors. To address this problem, we investigate possible methods for separation of the background signal and any signal from a nuclear explosion, which is further processed for estimation of the Xe-133 source term.

We assume that the observed unknown point release of Xe-133 can be modeled as a linear model y=Mx, where y is the vector of observations, M is source-receptor sensitivity (SRS) matrix, and x is the temporal profile of the unknown release from a nuclear explosion, i.e. its source term. Since the signal in the observation vector is most probably mixed with civilian emitters, we test methods for separation of the contributions from the unknown signal and the background. We compare various approaches, ranging from simple model calibration, to simulated background term and their combinations with anomaly detection.

The results are demonstrated on the data from the 1st Nuclear Explosion Signal Screening Open Inter-Comparison Exercise 2021 where advantages and disadvantages of studied methods are discussed and results are evaluated with the use of ground truth information on temporal and spatial location of the Xe-133 source.

Acknowledgment: This research has been supported by the Czech Science Foundation (grant no. GA24-10400S). The work was performed under the CTBTO awarded contract for ”Provision of Software Engineering Services for the Scientific Development of a Source Term Estimator Tool (STE)” under funding from the European Union Council Decision VIII.

How to cite: Tichý, O., Šmídl, V., Mácha, V., Kuśmierczyk-Michulec, J., Sommerer, W., and Tipka, A.: Estimation of unknown source term based on radioxenon observations with the presence of background signal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3075, https://doi.org/10.5194/egusphere-egu24-3075, 2024.

Part of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is  a network of highly sensitive radionuclide stations sniffing for tiny traces of fission and activation products in the atmosphere.  All IMS radionuclide stations have a high volume sampler for the detection of particulate radionuclides, some are equipped with noble gas systems for the measurement of radioxenon. The specific radioactive xenon isotopes are more likely to escape from underground nuclear explosions and have less complex features in atmospheric transport. There are also radioxenon background emissions from legitimate nuclear facilities. Isotopic ratio analysis allows to a certain extend for source characterization and timing. Atmospheric Transport Modelling (ATM) in backward and forward mode is applied to connect the measurements in space and time with potential releases.  

Noble gas systems at IMS radionuclide stations used to operate with 24 or 12 hours sampling time. The next generation noble gas systems utilize shorter sampling periods. At station RN33 on Mount Schauinsland, Germany, a SPALAX system with 24 hours sampling is operated by BfS. In the phase II testing a  “Xenon International” system with six hours sampling time and better sensitivity to Xe-135, Xe-133m and Xe-131m was installed in parallel from July 2021 to April 2022. The main contributing emitter to elevated xenon activity concentrations at RN33 is the medical isotope production facility at Fleurus, Belgium.

We investigated how the increase in time resolution in sampling and ATM changes the location capability of backward ATM. For that, the Lagrangian Particle Dispersion model HYSPLIT (NOAA-ARL) is applied driven by GFS meteorological data for all samples of the test phase. Calculation of expected Xe-133 contributions from Fleurus derived by ATM backward sensitivities and emission data show generally good agreement. As the Xenon International system also allows for additional detections particularly of Xe-135 and isomers Xe-133m and Xe-131m, the sensitivity to unknown additional sources is potentially improved and analysed. A coincidence analysis of repeating or in respect to isotopic composition remarkable detections which could not be well explained by emissions from Fleurus show several other potential source regions pointing to several  Nuclear Power Plants and research reactors.

How to cite: Ross, J. O. and Brander, S.: Source localization by backward atmospheric transport modelling for radioxenon detections at Mount Schauinsland with six hours sampling duration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19291, https://doi.org/10.5194/egusphere-egu24-19291, 2024.