Comprehensive Nuclear-Test-Ban Treaty Organization Research Articles

Climate change as observed through the IMS radionuclide station in Spitzbergen

The International Monitoring System (IMS), installed and maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) with the support of States Signatories, is a global system of monitoring stations based on four complementary technologies: seismic, hydroacoustic, infrasound and radionuclide. One of the IMS radionuclide stations is located in Spitzbergen, the largest island of the Norwegian Svalbard Archipelago, which borders the Barents Sea and the Northern Atlantic Ocean. It has been demonstrated that signs of climate change are particularly noticeable in that region. As many other radionuclides observed in environmental measurements, 212Pb is always observed at IMS stations, in varying quantities. This is also the case for the IMS station RN49, Spitzbergen, where it can be demonstrated that the average concentration of the measured lead 212Pb increases. This is observable specifically October through December. This paper demonstrates the asset of IMS data to study climate change effects. Our conclusions are supported by global temperature anomaly data from NOAA’s Global Surface Temperature Analysis, covering the period 1850 to 2023.

A study on surface air Beryllium-7 concentration at radionuclide station in Tanah Rata, Cameron Highlands (MYP42) during southwest monsoon seasons in Malaysia

A study on surface air Beryllium-7 concentration at radionuclide station in Tanah Rata, Cameron Highlands (MYP42) during southwest monsoon seasons in Malaysia

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.

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.

Evolving infrasound measurement and growing infrasound monitoring network

Infrasound carries information useful for detecting a strong natural phenomenon such as volcanic eruption and tsunami, which may cause catastrophic disaster. Therefore, infrasound measurement is gathering attention for potential applications in disaster prevention and life protection. However, the methodology of its measurement has not been well established except a few specific applications such as Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Some sensor devices employ Micro Electro Mechanical Systems (MEMS) sensors, which are, in general, small and available at a low price. This advantage enables us to increase the number of locations where infrasound can be monitored at multiple observation points. Another attempt is to assemble multiple sensors of different characters for widening dynamic range and frequency coverage of the sensor. These progress in infrasound measurement would make it possible to utilize infrasound in various purposes. In this respect, infrasound measurement needs to be standardized because one may want to analyze infrasound data together with those acquired using different devices by other organizations. At the same time, a platform for sharing infrasound data is becoming important to accelerate such usage. This paper overviews recent development of sensor devices for infrasound measurement and sensor deployment on going in Japan.

Seismic Ocean Thermometry Using CTBTO Hydrophones

AbstractDue to limited observational coverage, monitoring the warming of the global ocean, especially the deep ocean, remains a challenging sampling problem. Seismic ocean thermometry (SOT) complements existing point measurements by inferring large‐scale averaged ocean temperature changes using the sound waves generated by submarine earthquakes, called T waves. We demonstrate here that Comprehensive Nuclear‐Test‐Ban Treaty Organization (CTBTO) hydrophones can record T waves with a higher signal‐to‐noise ratio compared to a previously used land‐based T‐wave station. This allows us to use small earthquakes (magnitude <4.0), which occur much more frequently than large events, dramatically improving the resulting temporal resolution of SOT. We also find that the travel time changes of T waves at the land‐based T‐wave station and the CTBTO hydrophone show small but systematic differences, although the two stations are only about 20 km apart. We attribute this feature to their different acoustic mode components sampling different parts of the ocean. Applying SOT to two CTBTO hydrophones in the East Indian Ocean reveals signals from decadal warming, seasonal variations, and mesoscale eddies, some of which are missing or underestimated in previously available temperature reconstructions. This application demonstrates the great advantage of hydrophone stations for global SOT, especially in regions with a low seismicity level.

A Statistical Approach to Estimate Seismic Monitoring Stations’ Biases and Error Levels

ABSTRACT Magnitudes are common and important measures for the size of seismic events. The International Data Centre (IDC) of the Comprehensive Nuclear-Test Ban Treaty Organization estimates an event magnitude by averaging the magnitudes calculated by individual stations that detected the event, excluding outliers. This approach assumes that all station magnitudes have the same error level and are unbiased, namely, they have no systematic errors. We show that the body-wave and surface-wave magnitudes published in the Reviewed Event Bulletin (REB) of the IDC are inconsistent with these assumptions. We thus consider a model where each station has an unknown bias and error level. Given a large collection of reported event magnitudes by a network of monitoring stations, we propose a novel approach to estimate each individual station’s bias and error level. From a statistical perspective, this is a challenging problem involving a huge number of variables, because in addition to the stations’ biases and error levels, the event magnitudes are also unknown. Our approach is based on analyzing differences between reported magnitude values at pairs of stations, which cancels out the unknown event magnitudes and allows us to derive a simple and computationally efficient algorithm. We use the estimated station biases as station correction terms and the estimated error levels to compute weights for event magnitude estimation. Using a large data set from the REB with millions of reported station magnitudes, we show that our approach yields more consistent station and event magnitudes.

Monitoring of Indonesian volcanoes with the IS06 infrasound array

Detecting and notifying ongoing volcanic explosive eruptions is crucial in supporting the Volcanic Ash Advisory Centre (VAAC). However, local monitoring systems are missing at many active volcanoes, but long range infrasound monitoring might provide useful information if able to detect and notify volcanic explosive events. Indeed, many studies have already highlighted the utility and the potential of long-range infrasound monitoring for this aim, but still open questions remain concerning its actual efficiency and reliability. In this study we investigate the potential of the IS06 array (Cocos Island, Australia) of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to remotely detect volcanic explosive eruptions in the Indonesian Arc between 2012 and 2019, when 11 volcanoes, positioned at a distance between 1000 and 2000 km from the array, erupted with an energy spanning from mild explosions to VEI (Volcanic Explosivity Index) 4 eruptions. For each volcano, using infrasonic data recorded at a single array and accounting for realistic infrasound propagation conditions, we calculate a range corrected Infrasound Parameter (IP) and propose two additional empirical thresholds on signal strength and persistency. The IP is used eventually to define an alert whenever an established threshold is exceeded and the corresponding reliability estimated. Results show that the range corrected IP is highly reliable for events VEI = 3 or greater under favorable propagation conditions, but smaller scale short-lasting explosive eruptions still remain usually undetected. Unresolved ambiguity remains due to short spacing among volcanoes with respect to the array. For regional scale monitoring purposes, this can be solved only considering volcanic sectors rather than single volcanic edifices that, despite preventing unambiguous notification of a given volcano, might allow to increase the attention of the VAAC over a specific area.

Megameter propagation and correlation of T-waves from Kermadec Trench and Islands

On 18 June 2020 and 4 March 2021, very energetic low-frequency underwater T-wave signals (2 to 25 Hz) were recorded at the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) hydrophone stations in the Pacific Ocean (Stations HA11 and HA03) and the South Atlantic Ocean (Station HA10). This work investigates the long-range (megameters) propagation of these T-waves. Their sources were three powerful submarine earthquakes in the Kermadec Trench and Islands, located at approximately 6000, 8800, and 15100 km from Stations HA11, HA03, and HA10, respectively. Arrival time and back azimuth of the recorded T-waves were estimated using the Progressive Multi-Channel Correlation algorithm installed on the CTBT Organization (CTBTO) virtual Data Exploitation Centre (vDEC). Different arrivals within the duration of the earthquake signals were identified, and their correlations were also analyzed. The data analysis at HA03 and HA10 revealed intriguing T-wave propagation paths reflecting, refracting, or even transmitting through continents, as well as T-wave excitation along a chain of seamounts. The analysis also showed much higher transmission loss (TL) in the propagation paths to HA11 than to HA03 and HA10. Moreover, strong discrepancies between expected and measured back azimuths were observed for HA11, and a three-dimensional (3D) parabolic equation model was utilized to identify the cause of these differences. Numerical results revealed the importance of 3D effects induced by the Kermadec Ridge, Fiji archipelago, and Marshall Islands on T-wave propagation to HA11. This analysis can guide future improvements in underwater event localization using the CTBT-IMS hydroacoustic sensor network.

Overview of temporary radioxenon background measurement campaigns conducted for the CTBTO between 2008 and 2018

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) specifies that an overall network of at least 40 International Monitoring System (IMS) stations should monitor the presence of radioxenon in the atmosphere upon its entry into force. The measurement of radioxenon concentrations in the air is one of the major techniques to detect underground nuclear explosions. It is, together with radionuclide particulate monitoring, the only component of the network able to confirm whether an event originates from a nuclear test, leaving the final proof to on-site inspection.Correct and accurate interpretation of radioxenon detections by State Signatories is a key parameter of the verification regime of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). In this context, the discrimination between the highly variable radioxenon background generated by normal operations of nuclear facilities and CTBT-relevant events is a challenging, but critical, task. To this end, the radioxenon background that can be expected at IMS noble gas systems must be sufficiently characterized and understood. All activities conducted to study the global radioxenon background are focused on the calibration and performance of the verification system as described in the Treaty.The unique CTBTO noble gas system network is designed to optimally covering the globe. By the end of 2019, 31 systems were put in operation, 25 of which being already certified. It took two decades from the first experimental setup of noble gas system in the field to reach this stage of maturity. In the meantime, it was an urgent need to gain empirical evidence of atmospheric radioxenon concentrations with the full spectrum of characteristics that IMS noble gas systems may be observing. This experience was significantly advanced through temporary measurement campaigns. Their objective was to gain the additional necessary knowledge for a correct understanding and categorization of radioxenon detections. The site selection for these campaigns put emphasis on regions with low coverage by the initially few experimental noble gas systems at IMS locations or where potential interferences with normal background might be observed.Short-term measurements were first initiated in 2008. Sites of potential interest were identified, and campaigns up to few weeks were performed. Based on the findings of these short campaigns, transportable systems were procured by the CTBTO. Longer temporary measurement campaigns were started afterwards and operated by local hosts in different regions of the globe. Site selections were based on purely scientific criteria. Objectives of the measurement campaigns were continually reassessed, and projects were designed to meet the scientific needs for radioxenon background understanding as required for nuclear explosion monitoring.As of today, several thousands of samples have been collected and measured. Spectra of temporary measurement campaigns were (and are still) analysed in the International Data Centre (IDC). As they are not part of the CTBT monitoring system, no IDC product is generated. Analysis results are stored in a non-operational database of the CTBTO and made available, together with raw data, to authorized users of States Signatories through a Secure Web Portal (SWP) and to scientific institutions for approved research projects through a virtual Data Exploitation Centre (vDEC) after signing a cost-free confidentiality agreement (https://www.ctbto.org/specials/vdec).This paper aims at providing an overview of the temporary measurement campaigns conducted by the CTBTO since the very first field measurements. It lays out scientific results in a systematic approach. This overview demonstrates the asset of radioxenon background measurement data that have been collected with a wide variety of characteristics that may be observed at IMS stations. It bears a tremendous opportunity for development, enhancement and validation of methodologies for CTBT monitoring.In 2018, a campaign started in Japan with transportable noble gas systems in the vicinity of the IMS station RN38 in Takasaki. It will be described separately once the measurements are completed.

Odhad detekční schopnosti stanice VRAC s ohledem na seismické jevy registrované v letech 2011 až 2021

Broadband seismic station VRAC (Vranov u Brna), operated by Institute of physics of the Earth (Masaryk University) is involved in various projects focused on monitoring of the seismic events. Above all, its involvement in the global seismic network of the International Monitoring System CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organization) is very important. The VRAC station is also one of the permanent broadband stations of the Czech Regional Seismic Network. Thus, the data of the VRAC station is routinely processed in respect to detection of the seismic events situated in various epicentral distances, from local, through regional to teleseismic. This article aims to briefly show a simple estimation of the detection capability of the VRAC station with respect to seismic events from various epicentral distances. Discussed estimation of the detection capability was based on study of the magnitude-frequency relations. For this purpose, the set of seismic events recorded by the VRAC station in the years 2011–2021 was used. This set included 52 246 seismic events, 33 161 being regional events situated up to epicentral distance of 2 000 km from the VRAC station. In the framework of the magnitude-frequency analysis, two parameters were determined for each subset containing events from the particular range of epicentral distances: the most frequent magnitude Ma and magnitude Mm in the minimum of the derived non-log magnitude-frequency function. The value of Mm shows well the point where the roll-off effect occurs on the classical magnitude-frequency graph. The graphs of both observed values (Ma and Mm) show steep increase at regional distances, followed by a flat part of the curve at epicentral distances of 20° to 80°. Low detection capability zones in the distances corresponding to seismic shadows zones connected both with the zone of decreased seismic velocities in the deep parts of the Earth (outer core) and in the asthenosphere are distinctly noticeable. Results of the study allow to estimate the detection threshold of the VRAC station between the magnitude value 4.5 to 4.9 in the case of epicentral distances from 20° to 80°.

Characterisation of Xe-133 background at the IMS stations in the East Asian region: Insights based on known sources and atmospheric transport modelling

Radioxenon can be produced with a high fission yield during a nuclear explosion, making it an important tracer to demonstrate the nuclear origin of an explosion. For this reason, it is continuously monitored by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) as part of the verification regime. Radioxenon is emitted by civil nuclear facilities, like nuclear power plants (NPPs) or isotope production facilities (IPFs), providing significant but variable contribution to the noble gas background. The discrimination between CTBT-relevant radioxenon detections and the background is then a challenging task.This work aims at estimating the radioxenon background at 8 East Asian noble gas stations of the International Monitoring Systems (IMS) (out of 26 certified and 14 others foreseen) based on known sources and atmospheric transport modelling (ATM). For the purpose of this study, the transportable system in Mutsu, Japan, was also included. The results demonstrate a predominant contribution of NPPs to the radioxenon background at most of the East Asian IMS stations, especially during summertime. In autumn, as a result of large-scale atmospheric circulation, the contribution of remote IPFs starts to dominate. In the summertime, up to 80% of the Xe-133 detections at a station may be explained by contributions from NPPs. The detections even rise to 100% in some specific cases. At some stations under investigation in this study, a transition from NPP to IPF domination is observed in September and continues during the autumn season. It has also been shown that, for some stations, simulated concentrations above the detection limit may include observable contributions from up to 19 different sources per daily sample; at the same time the sample being sensitive to 80 or more possible sources of radioxenon. This indicates that the accumulation of many weak sources can lead to a measurable result in a single air sample. This might also explain observations at very remote stations. Another important conclusion is that, despite limited knowledge about release patterns of NPPs, the agreement between simulated and measured values was good in many cases.Availability of IMS measurements allowed for validation of simulations. This comparison revealed that approximately 76% of simulated values were underestimated. Based on the paired t-test, a 95% confidence interval for the true mean difference between measurements and simulations was constructed. It was estimated that for data dominated by NPPs contribution (i.e. NPPs contribution exceeds 70%), the overall uncertainty of simulated results lies between 0.07 and 0.10 mBq/m3. For data dominated by IPFs contribution (i.e. IPFs contribution exceeds 70%), the uncertainty for the simulations is in the range between 0.03 and 0.12 mBq/m3.

Impact of the noble gas system NEX48 in Niger on the radioxenon global network coverage for the International Monitoring System of the comprehensive nuclear-test-ban treaty

The radioxenon measurement components of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) play a significant role in uncovering clandestine nuclear weapons tests. The radioxenon network coverage is a critical component of the IMS capabilities. NEX48 is one of the still to-be-certified radioxenon stations and it will be the only IMS station with radioxenon measurement capabilities in the Sahara desert in Central Africa. Therefore, it may increase the radioxenon global coverage in a vast region. Seasonal contributions from NEX48 (in Niger) on the 133Xe global coverage of the IMS have been investigated in current and complete (39 stations) networks for a hypothetical one-kt subsurface nuclear explosion using atmospheric transport modelling. Adding NEX48 to the stations currently operating increased the daily global coverage by about 1.1 percent on average with most of the improvement between 15-45 N latitudes and 0–40 E longitudes. The improvements from adding NEX48 vary greatly by the seasons of the year. Removing NEX48 from the complete network leads to a daily coverage deterioration of about 0.2 percent, and the cumulative minimum coverage has a significant change.

A beta–gamma radioxenon detection system using PIPS and CZT-Array

Radioxenon monitoring is one of the important methods used by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect a clandestine nuclear weapon test. Many radioxenon detection systems have been developed in the past few decades. The disadvantages such as bad energy resolution, memory effect, and large size influence the performance of these systems. This work introduces a new detection system that utilizes a PIPSCell and two CZT-Arrays for radioxenon monitoring. Signals from ten detectors are processed and coincidence events are identified via the electronics based on time-stamped list mode. This compact system has good radiation detection resolution at room temperature and high detection sensitivity for both electron and gamma-ray. Preliminary 137Cs and 131mXe are used to calibrate the energy and efficiency of the system. Combined with the simulation results the minimum detection activity of four radioxenon were assessed.

Evaluation of the International Monitoring System and International Data Centre of the Comprehensive Nuclear-Test-Ban Treaty Organization

Abstract Evaluation and quality assurance activities of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) are reviewed with special emphasis on radionuclide technologies. The CTBTO carries out detailed evaluation in all fields of technical verification of the Treaty. The goal is to provide States Signatories with confidence in the quality of data from the International Monitoring System and data products of the International Data Centre. The largest technical evaluation effort has been the quality assessment of the operational software. About 1.3 million lines of source code and scripts were checked. Software characteristics, such as maintainability, were assessed using automated tool-based techniques and improvements were suggested. Specific to radionuclide technologies, several methods have been developed to cope with the large amounts of spectra produced each day by 80 radionuclide monitoring stations around the world. Some of the key evaluation results, such as the peak detection capability of the operational software are presented in detail.

Earthquake catalog improvements and their seismic hazard impacts for the Arabian Peninsula

The Reviewed Event Bulletin (REB) issued through the International Data Centre (IDC) using the International Monitoring System (IMS) network of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is a seismo-acoustic bulletin distributed to the Member States of the CTBTO for the purpose of verifying the Treaty. The REB is partially available within a few days on the public site of the International Seismological Center (ISC), where the REB events are labeled ‘IDC’. This study focuses on the seismicity of the Arabian Peninsula and its adjacent regions, but the conclusions would be similar for regions that include good quality seismic stations of the IMS auxiliary seismic network, which has no weight in the current Event Definition Criteria (EDC). It is indicated that the consideration of the confidence ellipse factors (semi-major a-axis, semi-minor b-axis, and the epicentral area (A) as alternative EDC would significantly improve the completeness of the REB for the Arabian Peninsula, which consequently enhance the quality of the ISC bulletin.The Arabian Peninsula has been chosen as a study region not only because it is surrounded by the IMS auxiliary seismic stations but also due to its increasing population, rapid urbanization, and strong economic growth in recent years. It has attracted many mega-projects (e.g., Multinational NEUM in Saudi Arabia, Expo 2020 in Dubai, the Special Economic Zone at Duqm in Oman, and the World Cup 2022 in Qatar). The earthquake hazards impact for the big cities in Saudi Arabia, such as Dammam in the east, and Jeddah, Tabuk, and Jizan in the west and the nearby cities are reviewed. The completeness catalog of the revised earthquakes may serve to improve the calculation of earthquake hazards threatening big cities in and around Saudi Arabia.

Classification of Infrasonic Atmospheric Events Using Electromagnetic Pulse Analysis

AbstractThe Comprehensive Nuclear‐Test‐Ban Treaty Organization (CTBTO) operates the international monitoring system (IMS), consisting of four complementary technologies: Seismic, hydroacoustic, infrasound, and radionuclide, to detect events that might indicate a treaty violation. Infrasound is the main technology aimed at detecting atmospheric nuclear explosions. However, there are many other sources of infrasound signals, which are low frequency inaudible sound‐waves in the atmosphere, that are detected. To deny that the source is of a nuclear nature, requires a lot of resources. As opposed to most other sources of infrasound, nuclear explosions also emit an electromagnetic pulse (EMP). Thus, if an infrasonically detected event is not accompanied by an EMP, it is certain that it has not originated from a nuclear explosion. In this research we use electromagnetic data recorded by a single antenna to examine coincidence of infrasonically detected events with detected EMPs. We show that a large fraction of infrasonically detected events are not accompanied by any EMP and thus the need to analyze them in the context of the IMS is eliminated. For those infrasonically detected events that do coincide with EMPs, we use machine learning techniques to classify the EMPs as either lightning or a potential explosion. We show that one can identify the lightning out of the EMPs. By filtering out all lightning signals one can almost always verify that there is no EMP other than lightning, which coincided with the infrasonically detected event. This way we can dramatically reduce the number of infrasound signals which require manual analysis.

Three-dimensional modeling of T-wave generation and propagation from a South Mid-Atlantic Ridge earthquake.

A three-dimensional (3D) hybrid modeling method is used to study the generation and propagation of T waves in the ocean triggered by a Southern Mid-Atlantic Ridge earthquake. First, a finite-element method model named SPECFEM3D is used to propagate seismic waves in the crust and acoustic waves in the ocean for the T-wave generation in a 200 × 50 km area near the epicenter. A 3D parabolic equation (PE) method is then used to propagate the T waves in the ocean for about 850 km further to the hydrophone stations deployed by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) near Ascension Island. All of the simulations considered the realistic bathymetry and water sound speed profile. The SPECFEM3D results suggest that T waves with clear modal features could be generated by the concentration of reflected head waves in two depressions 40 km away from the epicenter. To compare with the hybrid modeling method for calculating T-wave propagation losses and arrival azimuths at the CTBTO hydrophones, point source simulations using the 3D PE model from the T waves source locations, identified with SPECFEM3D, were also implemented. The advantages and limitations of each approach are discussed.

High-performance computing for long-range underwater acoustics

The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) has been recording underwater signals using seven hydrophone stations which cover the entire oceans and provides the data publicly available. One of the lessons learned during the data analysis, such as in the ARA San Juan submarine tragedy, is that underwater sound propagation paths become complex in a long-range propagation, and as such, computer modelling, particularly three-dimensional (3D), can play an important role in understanding sound source location. The biggest stumbling block toward long-range 3D modeling is obviously its huge computational resource demand. In this presentation, we will discuss the GPU implementation of the 3D Split Step Fourier Parabolic Equation (SSFPE) solver, and the domain decomposition parallelization of our newly developed 2D + 1D Finite-Difference Time-Domain (FDTD) solver. The obtained computational performances are: (1) 3D SSFPE on GPU performs approximately 20 times faster than the original Matlab code and (2) the parallel speedup of the FDTD solver with domain decomposition up to 4 nodes is 98%. Although the performances on a larger system are still of interest, those results already enable us to tackle realistic problems. Results highlight the importance of using high performance computing for realistic global scale underwater acoustic simulations.