International Monitoring System

The International Monitoring System is a worldwide network of monitoring stations and laboratories built to verify compliance with the Comprehensive Nuclear-Test-Ban Treaty by detecting evidence of nuclear explosions. When complete it will comprise 321 monitoring stations and 16 laboratories hosted by 89 countries, and around ninety percent of these facilities are already operating and supplying data in real time. It draws on four monitoring technologies: seismic stations that detect underground shockwaves, hydroacoustic stations that detect sound waves in the oceans, infrasound stations that listen for very low frequency atmospheric sound, and radionuclide stations that measure radioactive particles in the air. The system is operated under the Comprehensive Nuclear-Test-Ban Treaty Organization, and it detected all six of North Korea's declared nuclear tests between 2006 and 2017, as well as incidentally recording earthquakes, volcanic eruptions and large non-nuclear explosions.