Why is seismic monitoring considered a critical component of the verification regime for the Comprehensive Nuclear-Test-Ban Treaty (CTBT)?

Seismic monitoring is a critical component of the verification regime for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) because it provides the most reliable means of detecting underground nuclear explosions, which are the most likely way a state might attempt to evade the treaty's ban on nuclear testing. The CTBT prohibits all nuclear weapon test explosions or any other nuclear explosion, and the verification regime is designed to ensure compliance. Underground nuclear explosions generate seismic waves that can be detected by a network of seismometers around the world. These seismic waves propagate through the Earth's crust and can be distinguished from naturally occurring earthquakes based on their characteristics, such as their depth, location, and the pattern of seismic waves they produce. The International Monitoring System (IMS), established under the CTBT, consists of a global network of seismic, hydroacoustic, infrasound, and radionuclide sensors designed to detect any violations of the treaty. Seismic monitoring stations are a crucial part of the IMS because they can detect even small underground explosions at significant distances. Without seismic monitoring, it would be extremely difficult to verify compliance with the CTBT, as states could potentially conduct clandestine underground nuclear tests without detection by other means. Therefore, seismic monitoring provides an essential deterrent against nuclear testing and is a cornerstone of the CTBT's verification regime.