Of the 60 infrasound stations the Comprehensive Nuclear-Test-Ban Treaty (CTBT) foresees, 54 were certified by the end of 2025, or 90% of the network (54/60, CTBTO Annual Report 2025). Those arrays listen for pressure waves below the range of human hearing, and the same network recorded the 2022 Hunga Tonga eruption at every one of its 53 certified stations (Vergoz et al., EPSL 2022). It picked up the 2013 Chelyabinsk fireball at 20 of 42 operational stations (Pilger et al., EGU 2015), while the wider International Monitoring System detected all six nuclear tests North Korea declared between 2006 and 2017 (CTBTO International Monitoring System page). We aggregated data from the CTBTO Preparatory Commission’s annual report and technical pages, the Journal of Geophysical Research, Earth System Science Data, Science, Scientific Reports, Earth and Planetary Science Letters, and France’s CEA. If you came here from low-frequency noise near homes, our wind turbine infrasound statistics cover the same frequency band at a very different scale.
TL;DR
- 60 infrasound array stations are planned, spread over 35 countries (CTBTO Infrasound Monitoring page).
- 88% of the infrasound network was built and certified in approximately 25 years (Campus et al., CTBTO Infrasound Technology Workshop 2024).
- The full International Monitoring System will have 337 facilities: 321 stations plus 16 radionuclide laboratories (CTBTO International Monitoring System page).
- An explosion of about 500 t of TNT would be detected by at least two infrasound stations at any time of the year (Le Pichon et al., JGR Atmospheres 2025).
- The 2022 Hunga Tonga eruption was the first single event detected by all operational IMS infrasound stations, 53 of them (Vergoz et al., EPSL 2022).
- The 2013 Chelyabinsk fireball was detected by 20 out of 42 operational infrasound stations (Pilger et al., EGU 2015).
- The February 2013 North Korean test was the first time IMS infrasound stations IS30 and IS45 detected signals attributed to such an event (Statement of Japan, CTBTO Working Group A 2013).
- The 2020 Beirut port explosion produced detections at five IMS infrasound stations (Pilger et al., Scientific Reports 2021).
- The infrasound detection lists hold 81,267,602 entries for 2003 to 2020 (Hupe et al., ESSD 2022).
- 188 States Signatories and 179 ratifying States after Tonga’s ratification on 7 July 2026 (CTBTO press release, July 2026).
1. Network Build-Out: From 47 to 54 Certified Infrasound Stations
Certification, in CTBTO terms, is the formal confirmation that a station meets the treaty’s technical specifications and delivers data to Vienna; a station can be built and still not count. Measured that way, the infrasound network has crept forward: 54 of 60 stations certified at the end of 2025, up from 47 in 2015 (CTBTO Infrasound Technology Workshop 2015). That is 7 stations in 10 years, under one per year on average, so the final six stations are the slow part of the job.
The CTBTO Annual Report 2025 records one infrasound certification in 2025 (station IS16 in China) and the start of construction on another. Across all four technologies, 293 of the 321 planned stations were certified (293/321 = 91.3%), so infrasound is tracking the whole system almost exactly.
| Metric | Value | Source |
|---|---|---|
| Infrasound array stations planned under the treaty | 60, in 35 countries | CTBTO Infrasound Monitoring page |
| Infrasound stations at the end of 2025: certified / under construction / not started | 54 / 2 / 4 | CTBTO Annual Report 2025 |
| Share of the infrasound network built and certified after approximately 25 years (2024 status) | 88% | CTBTO Infrasound Technology Workshop 2024, Campus et al. |
| Certified infrasound stations sending continuous data to Vienna, 2015 | 47 | CTBTO Infrasound Technology Workshop 2015, Marty |
| Certified infrasound stations, end of 2020 | 53 | Hupe et al., Earth System Science Data 2022 |
| Certified IMS stations of all four technologies combined, February 2013 | 274 | Arms Control Association, February 2013 |
Context: the infrasound count stood at 53 certified stations at the end of 2020 and was still 53 in July 2025 according to the modelling study discussed in section 3, so the network spent close to five years at 53 before IS16 moved it to 54.
2. Inside the Arrays: Sensors, Sampling and 81 Million Detections
Each infrasound station is an array: four or more microbarometers (very sensitive barometers that record tiny, fast changes in air pressure) laid out in a geometric pattern, so that the time a wave takes to cross the array reveals its direction. The data stream is enormous because the sensors never stop. At full availability, 357 microbarometers deliver more than 615 million samples per day (Hupe et al., Earth System Science Data 2022), and very little of what they hear is an explosion.
Much of the recorded energy is microbaroms, the continuous low-frequency hum radiated by interacting ocean waves, which the same paper places at between 0.2 and 0.3 Hz. That fits the finding that almost 55% of all detections fall between 0.1 and 0.5 Hz, and it is why the CTBTO’s scientists publish microbarom products for atmospheric research. The ocean side of this story, where the CTBTO’s hydroacoustic stations listen underwater, is covered in our marine bioacoustics and ocean noise statistics.
| Metric | Value | Source |
|---|---|---|
| Microbarometer elements per infrasound array | 4 or more | CTBTO Infrasound Monitoring page |
| Range of human hearing, which infrasound falls below | 20 to 20,000 Hz | CTBTO Infrasound Monitoring page |
| Microbarometer sampling rate | 20 Hz | Hupe et al., ESSD 2022 |
| Raw samples per day across the network at 100% availability | More than 615 million | Hupe et al., ESSD 2022 |
| Entries in the reprocessed detection lists, 2003 to 2020 (18 years) | 81,267,602 | Hupe et al., ESSD 2022 |
| Share of detections with frequencies between 0.1 and 0.5 Hz | Almost 55% | Hupe et al., ESSD 2022 |
Context: the same array-processing logic powers the beamforming covered in our acoustic camera and noise source localization statistics, only at wavelengths measured in kilometres rather than centimetres.
3. Detection Capability: 500 Tonnes, Two Stations, Any Season
The treaty network’s design goal is to detect and locate an atmospheric nuclear explosion with a minimum yield of 1 kiloton of TNT equivalent, and the 2025 modelling study suggests it beats that goal on paper: an explosion of about 500 t of TNT would be detected by at least two stations at any time of the year (Le Pichon et al., JGR Atmospheres 2025).
The catch is the atmosphere itself. Infrasound rides in wind-shaped channels between the ground and the stratosphere, and when those winds weaken around the equinoxes, the same explosion becomes harder to hear. A threshold that can swing by an order of magnitude is not a fixed line but closer to a weather forecast, and the authors call their own figures “optimistic detection limits” because they do not fully account for competing coherent signals or instrument malfunctions.
| Metric | Value | Source |
|---|---|---|
| Three-station detection threshold, best day vs worst day modelled | About 200 t (21 December 2023) vs about 1.3 kt (17 September 2022) | Le Pichon et al., JGR Atmospheres 2025 |
| Rise in thresholds near the equinoxes (March to May, September to November) | Factor of about 4 | Le Pichon et al., JGR Atmospheres 2025 |
| Range of threshold variation, from seasonal down to semi-diurnal (twice-daily) scales | Up to one order of magnitude | Le Pichon et al., JGR Atmospheres 2025 |
| Share of time a 1 kt explosion is covered by three stations in Southeast Asia | Decreases to 90% | Le Pichon et al., JGR Atmospheres 2025 |
| Station noise spectra computed for the model (53 stations, hourly, 2021 to 2024) | Approximately 19 million | Le Pichon et al., JGR Atmospheres 2025 |
Context: the thresholds are expressed at a 90% detection probability over 95% of Earth’s surface, and the attenuation model is built for distances up to 4,000 km. Regional gaps such as Southeast Asia are exactly where the six unfinished stations from section 1 matter.
4. Natural Giants: Chelyabinsk 2013 and Hunga Tonga 2022
The best calibration a monitoring network can get is an event nobody planned. The 15 January 2022 Hunga Tonga eruption was recorded by all 53 certified IMS infrasound stations, the first single event detected by every operational station (Vergoz et al., Earth and Planetary Science Letters 2022). Its estimated yield of 100 to 200 megatons exceeds the 50 megatons of the largest nuclear test ever detonated, a comparison the same paper draws.
Chelyabinsk was a different kind of test: a single large fireball whose detection depended on each station’s direction relative to the trajectory and on local noise. Counts grew as analysts dug deeper, from 18 stations in France’s first bulletin to 20 in the later study, which shows how much careful reprocessing adds to first results.
| Metric | Value | Source |
|---|---|---|
| Chelyabinsk fireball: IMS infrasound stations detecting vs stations operational, 2013 | 20 of 42 | Pilger et al., EGU 2015 |
| Chelyabinsk fireball: equivalent yield | 500 kT TNT | Pilger et al., EGU 2015 |
| Chelyabinsk fireball: distance to the farthest station in the first bulletin (IS27, Antarctica) | 15,500 km | CEA DASE, February 2013 |
| Chelyabinsk fireball: altitude of disintegration | 23 km | CEA DASE, February 2013 |
| Hunga Tonga eruption: estimated equivalent TNT yield | 100 to 200 megatons | Vergoz et al., EPSL 2022 |
| Hunga Tonga eruption: Lamb wave amplitude at the nearest station (IS22, New Caledonia, 1,847 km away) | About 700 Pa | Vergoz et al., EPSL 2022 |
| Hunga Tonga eruption: Lamb wave passages around Earth | Four (plus three antipodal) over 6 days | Matoza et al., Science 2022 |
| Hunga Tonga eruption: distance at which audible sound was reported | About 10,000 km | Matoza et al., Science 2022 |
Context: a Lamb wave is a pressure pulse that hugs the Earth’s surface and travels around the whole planet. The precedent is 1883, when infrasonic waves from Krakatoa circled the globe at least seven times (CTBTO Infrasound Monitoring page), and Matoza et al. judge Hunga comparable in size to Krakatau as measured by Lamb wave amplitudes. For a human-made pressure wave on a far smaller scale, see our commercial supersonic low-boom statistics.
5. Explosions on the Ground: North Korea and Beirut
Underground tests are mainly a seismic problem, so infrasound plays a supporting role there. The IMS detected all six nuclear tests that North Korea declared between 2006 and 2017 (CTBTO International Monitoring System page), and the February 2013 test was the first time IMS infrasound stations, IS30 in Japan and IS45 in Russia, picked up signals attributed to such an event (Statement of Japan to CTBTO Working Group A, 2013). Japan credits that to routine infrasound analysis at the International Data Centre, which began in 2010.
Beirut shows the network’s civil value. The 2020 ammonium nitrate blast was not a weapons test, yet IMS arrays helped researchers bound its yield, combining infrasound with seismic, hydroacoustic and satellite radar data (Pilger et al., Scientific Reports 2021).
| Metric | Value | Source |
|---|---|---|
| North Korean declared nuclear tests detected by the IMS, 2006 to 2017 | All six | CTBTO International Monitoring System page |
| IMS stations detecting unusual seismic waveforms after the February 2013 test | 96 | Statement of Japan, CTBTO Working Group A, 2013 |
| Distance from the North Korean test site to IS45 (Russia) vs to IS30 (Japan) | Some 400 km vs nearly 1,200 km | Koch, BGR, CTBT Science and Technology 2017 |
| Distance from the 2017 test site to microbarometer array I45RU, where its infrasound was recorded | 401 km | Assink et al., Seismological Research Letters 2018 |
| Beirut 2020: IMS infrasound stations with detections | 5 | Pilger et al., Scientific Reports 2021 |
| Beirut 2020: yield range across all methods | 0.13 to 2 kt TNT | Pilger et al., Scientific Reports 2021 |
| Beirut 2020: ammonium nitrate reported in the harbour warehouse | Approximately 2.75 kt | Pilger et al., Scientific Reports 2021 |
| Beirut 2020: seismic moment magnitude | Mw 3.47 | Pilger et al., Scientific Reports 2021 |
Outlier note: BGR’s review of infrasound data for the North Korean tests since 2006 found that, except for the 2013 test and its signals at IS45, none of the detections could be identified in the waveform data (Koch, 2017). Underground tests couple only weakly into the air, so a quiet infrasound record is the norm, not a failure.
6. The Data Pipeline: International Data Centre Volumes and Speed
All of these signals converge on the International Data Centre (IDC) in Vienna, which turns raw recordings into event bulletins for the states. An average of 36 GB of data and products moved through the system per day in 2025 (CTBTO Annual Report 2025), and the archive now reaches back about three decades.
The more interesting trend is who uses the data beyond treaty verification. Streaming volumes through the SeedLink protocol (a standard way of delivering waveform data in near real time) tripled in a year, and the same data now feed tsunami warning centres, a sign that the network is becoming a scientific and civil-protection instrument as well as a treaty tool.
| Metric | Value | Source |
|---|---|---|
| SeedLink monthly data volume, 2024 average vs end of 2025 | 600 GB vs 1.8 TB | CTBTO Annual Report 2025 |
| Global Communications Infrastructure availability in 2025 vs target | 96.6% vs 99.5% (99.60% excluding affected sites) | CTBTO Annual Report 2025 |
| Timing of the automatic Standard Event Lists (SEL1, SEL2, SEL3) | 1, 4 and 6 hours after an event | CTBTO International Data Centre page |
| Deadline for the analyst-reviewed Reviewed Event Bulletin (REB) | Within 2 days of the event | CTBTO International Data Centre page |
| National Data Centres and national tsunami warning centres connected | More than 100 | CTBTO International Data Centre page |
| Communication links in the Global Communications Infrastructure | Over 600 | CTBTO International Data Centre page |
| Independent subnetwork links run by 10 State Signatories | Over 70 | CTBTO International Data Centre page |
| Tsunami warning centres receiving IMS data (as reported by Chile, June 2023) | 20, in 19 countries | CTBTO Measure (L) report, CTBT-Art.XIV/2025/4 |
Context: the CTBTO’s IDC web page still describes “over 30 gigabytes” per day; the 36 GB figure above is the dated 2025 average from the annual report (see Data watch).
7. Treaty Status: 179 Ratifications, Still Not in Force
The monitoring network runs ahead of the law that created it. The CTBT opened for signature on 24 September 1996 and is still not in force, because entry into force waits on a fixed list of states named in its Annex 2. Nine of those Annex 2 states had not ratified at the end of 2025, and three had not even signed (CTBTO Annual Report 2025), against 35 that had ratified.
Universalisation keeps moving at the edges: Tonga’s ratification on 7 July 2026 completed the treaty across the Pacific region and lifted the total to 179 (CTBTO press release, as published by PINA, July 2026). Tonga is not on the Annex 2 list, so its ratification widens support without changing the legal lock.
| Metric | Value | Source |
|---|---|---|
| States Signatories after Tonga’s ratification, July 2026 | 188 | CTBTO press release, July 2026 |
| Ratifying States after Tonga’s ratification, July 2026 | 179 | CTBTO press release, July 2026 |
| Tonga’s place in the ratification order | 179th State | CTBTO press release, July 2026 |
| Annex 2 states shown with no signature or ratification date | 3: North Korea, India, Pakistan | CTBTO Status of Signature and Ratification |
| Russian Federation’s entry in the CTBTO status table | Signed 24 September 1996, no ratification date listed | CTBTO Status of Signature and Ratification |
| Latin American and Caribbean States that have ratified | All, since June 2022 (Brazil’s statement) | CTBTO Measure (L) report, CTBT-Art.XIV/2025/4 |
| States associated with the CTBT Joint Ministerial Statement, as of 12 May 2025 | 86 States and 1 Observer | CTBTO Measure (L) report, CTBT-Art.XIV/2025/4 |
Context: the same Measure (L) report quotes Japan describing “the nine whose ratification is needed” for entry into force, which matches the annual report’s count.
Summary: CTBTO Infrasound Monitoring by the Numbers
| Metric | Value | Source |
|---|---|---|
| Infrasound array stations planned | 60, in 35 countries | CTBTO Infrasound Monitoring page |
| Infrasound stations certified, end of 2025 | 54 | CTBTO Annual Report 2025 |
| Certified infrasound stations, 2015 | 47 | CTBTO Infrasound Technology Workshop 2015 |
| Share of the infrasound network built and certified in approximately 25 years | 88% | CTBTO Infrasound Technology Workshop 2024 |
| IMS facilities when complete | 337 (321 stations, 16 laboratories) | CTBTO International Monitoring System page |
| IMS host countries | 89 | CTBTO International Monitoring System page |
| Explosion detected by at least two infrasound stations at any time of year | About 500 t TNT | Le Pichon et al., JGR Atmospheres 2025 |
| Detection-list entries, 2003 to 2020 | 81,267,602 | Hupe et al., ESSD 2022 |
| Hunga Tonga 2022: stations detecting | All 53 certified | Vergoz et al., EPSL 2022 |
| Hunga Tonga 2022: estimated equivalent yield | 100 to 200 megatons | Vergoz et al., EPSL 2022 |
| Hunga Tonga 2022: Lamb wave passages around Earth | Four (plus three antipodal) over 6 days | Matoza et al., Science 2022 |
| Chelyabinsk 2013: stations detecting vs stations operational | 20 of 42 | Pilger et al., EGU 2015 |
| Chelyabinsk 2013: distance to the farthest station in the first bulletin | 15,500 km | CEA DASE 2013 |
| North Korean declared tests detected by the IMS, 2006 to 2017 | All six | CTBTO International Monitoring System page |
| North Korea 2013: IMS stations detecting unusual seismic waveforms | 96 | Statement of Japan, CTBTO Working Group A 2013 |
| Beirut 2020: IMS infrasound stations with detections | 5 | Pilger et al., Scientific Reports 2021 |
| Beirut 2020: yield range | 0.13 to 2 kt TNT | Pilger et al., Scientific Reports 2021 |
| Standard Event Lists issued after an event | At 1, 4 and 6 hours | CTBTO International Data Centre page |
| Ratifying States, July 2026 | 179 | CTBTO press release, July 2026 |
| Annex 2 states still to ratify, end of 2025 | 9 | CTBTO Annual Report 2025 |
Methodology and Sources
- CTBTO Preparatory Commission, Annual Report 2025 (station status as of 31 December 2025, treaty status, IDC operations).
- CTBTO, International Monitoring System page and Infrasound Monitoring page.
- CTBTO, International Data Centre page.
- CTBTO, Status of Signature and Ratification, and the Tonga ratification press release of 7 July 2026, read as republished by PINA.
- CTBTO, Activities under Measure (L), CTBT-Art.XIV/2025/4, September 2025.
- Campus et al., The IMS Infrasound Network: current status and existing challenges, Infrasound Technology Workshop 2024; Marty, Overview of IMS infrasound station and engineering projects, Infrasound Technology Workshop 2015.
- Le Pichon et al., Statistical Models for Infrasonic Propagation: Application to the Detection Capability of the Global IMS Network, JGR Atmospheres 130, 2025 (doi 10.1029/2025JD044937).
- Hupe et al., International Monitoring System infrasound data products for atmospheric studies and civilian applications, Earth System Science Data 14, 2022.
- Vergoz et al., IMS observations of infrasound and acoustic-gravity waves produced by the January 2022 volcanic eruption of Hunga, Tonga, Earth and Planetary Science Letters 591, 2022.
- Matoza et al., Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga, Science 2022.
- Pilger et al., Capability of the CTBT infrasound stations detecting the 2013 Russian fireball, EGU General Assembly 2015 abstract.
- CEA DASE, Chelyabinsk meteor bulletin, February 2013.
- Pilger et al., Yield estimation of the 2020 Beirut explosion using open access waveform and remote sensing data, Scientific Reports 11, 2021.
- Statement of Japan to the 44th session of CTBTO Working Group A, 2013; Koch (BGR), Detection Patterns for Two IMS Infrasound Stations in the Vicinity of the North Korean Test Site, 2017; Assink et al., A seismo-acoustic analysis of the 2017 North Korean nuclear test, Seismological Research Letters 2018.
- Arms Control Association, North Korean Nuclear Test and Meteorite over Siberia Demonstrate CTBTO Capabilities, February 2013 (historical station count and early Chelyabinsk count).
- Data watch: Event and history figures are older than three years by nature. Most recent available data: Chelyabinsk (Pilger et al., 2015), Beirut (Pilger et al., 2021), Hunga Tonga (Vergoz et al. and Matoza et al., 2022), North Korea (2013 to 2018 sources), and the detection-list totals (Hupe et al., 2022, covering 2003 to 2020). Sources disagree on several counts. Chelyabinsk detections were first reported as 17 of 45 infrasound stations (Arms Control Association, February 2013) and 18 stations (CEA, February 2013) before the 20 of 42 operational stations in Pilger et al.; CEA’s early energy estimate was 50 to 80 kt, against 500 kT in the later study. For Hunga Tonga, the Vergoz et al. abstract says infrasound circled Earth up to eight times while its body text describes one arrival travelling more than seven times around the globe, and Matoza et al. count four Lamb wave passages plus three antipodal ones. The CTBTO IDC page cites over 30 GB per day, while the Annual Report gives a 2025 average of 36 GB per day; we use the dated annual figure. Treaty counts changed in July 2026 (187 signatures and 178 ratifications at the end of 2025 in the Annual Report, 188 and 179 after Tonga). The Annual Report does not name the nine Annex 2 holdouts, so we only name the three that the CTBTO status table shows with no dates, plus Russia’s entry as it appears in that table. The 2025 detection thresholds are model results that the authors call optimistic. Station counts are expected to move again soon: the 2026 annual report should show whether either of the two infrasound stations under construction at the end of 2025 has been certified.
Last updated: October 24, 2026. We update this roundup quarterly, and the next refresh is expected when the CTBTO Preparatory Commission publishes its Annual Report 2026 with station status as of 31 December 2026.