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Seismic Nuclear Detonation Detection
Forensic Seismology is one of several other methods used by the global community to determine compliance with the Comprehensive Nuclear Test-Ban Treaty (CTBT). A network of approximately 170 seismic stations, along with data generated from sources such as Infrasound, Hydroacoustics, and Radionucleotide detection, is used to identify and locate nuclear detonations. Forensic seismology is specifically used to locate nuclear detonations that may have occurred underneath the ground.

Seismic stations record underground pressure waves and transmit this data for processing via secure communication links. There are many challenges involved with trying to differentiate a nuclear explosion from other natural and man-made phenomena, such as earthquakes, mining explosions, and construction. Nuclear explosions exceeding 150 kilotons generate pressure waves that primarily travel through the Earth's core and mantle. These types of explosions are straightforward to identify because the mixture of rock the signals pass through is fairly homogeneous and the signals generated are free from noise. Smaller nuclear explosions are more difficult to identify because pressure waves primarily travel through the Earth's upper mantle and crust, leading to signal distortion due to the heterogeneity of rocks at this depth.

Nations may also conduct clandestine underground tests that are not easily identifiable. One method of hiding an underground nuclear detonation is called decoupling. This involves detonating a nuclear warhead in an underground cavity in order to significantly muffle the amplitude of the subsequent underground pressure waves. Another proposed method of hiding nuclear detonations is called mine masking. This technique uses a larger explosion to mask a smaller nuclear explosion. The feasibility of mine masking has been called into question because seismic events large enough to mask a nuclear explosion are exceedingly rare and would draw suspicion. Smaller nuclear detonation yields may also be hard to detect because they produce readings similar to small earthquakes or other natural events.

When seismic data is gathered, it has to be processed to produce meaningful information. Algorithms are used to isolate patterns, remove noise, and generate estimates. The development of efficient algorithms for nuclear detonation detection has led to many advancements in other fields such as kriging, an advanced method of interpolation used primarily in geostatistics. Algorithms are used to identify key characteristics of wave forms, such as peak-to-peak distance, amplitude, phase, P-wave amplitude, and S-wave amplitude. P-waves, or primary waves, are compression waves that propagate quickly through rock, and are generally the first waves to reach seismic stations. S-waves, or shear waves, arrive after P-waves. The ratio of P to S waves is one of several important values used to characterize seismic events.

Underwater Nuclear Detonation Detection via Hydroacoustics
There are several methods of detecting nuclear detonations. Hydroacoustics is the primary means of determining if a nuclear detonation has occurred underwater. Hydrophones are used to monitor the change in water pressure as sound waves propagate through the world's oceans. Sound travels through 20° C water at approximately 1482 meters per second, compared to the 332 m/s speed of sound through air. In the world's oceans, sound travels most efficiently at a depth of approximately 1000 meters. Sound waves that travel at this depth travel at minimum speed and are trapped in a layer known as the Sound Fixing and Ranging Channel (SOFAR). Sounds can be detected in the SOFAR from large distances, allowing for a limited number of monitoring stations required to detect oceanic activity. Hydroacoustics was originally developed in the early 20th century as a means of detecting objects like iceburgs and shoals to prevent accidents at sea.

Three hydroacoustic stations were built before the adoption of the Comprehensive Nuclear Test-Ban Treaty. Two hydrophone stations were built in the North Pacific Ocean and Mid-Atlantic Ocean, and a T-phase station was built off the west coast of Canada. When the CTBT was adopted, 8 more hydroacoustic stations were constructed to create a comprehensive network capable of identifying underwater nuclear detonations anywhere in the world. These 11 hydroacoustic stations, in addition to 326 monitoring stations and laboratories, comprise the International Monitoring System (IMS), which is monitored by the Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO).

There are two different types of hydroacoustic stations currently used in the IMS network; 6 hydrophone monitoring stations and 5 T-phase stations. These 11 stations are primarily located in the southern hemisphere, which is primarily comprised of oceans. Hydrophone monitoring stations consist of an array of three hydrophones suspended from cables tethered to the ocean floor. They are positioned at a depth located within the SOFAR in order to effectively gather readings. Each hydrophone records 250 samples per second, while the tethering cable supplies power and carries information to the shore. This information is converted to a usable form and transmitted via secure satellite link to other facilities for analysis. T-phase monitoring stations record seismic signals generate from sound waves that have coupled with the ocean floor or shoreline. T-phase stations are generally located on steep-sloped islands in order to gather the cleanest possible seismic readings. Like hydrophone stations, this information is sent to the shore and transmitted via satellite link for further analysis .Hydrophone stations have the benefit of gathering readings directly from the SOFAR, but are generally more expensive to implement than T-phase stations. Hydroacoustic stations monitor frequencies from 1 to 100 Hertz to determine if an underwater detonation has occurred. If a potential detonation has been identified by one or more stations, the gathered signals will contain a high bandwidth with the frequency spectrum indicating an underwater cavity at the source.

Infrasound for nuclear detonation detection
Infrasound is one of several techniques used to identify if a nuclear detonation has occurred. A network of 60 infrasound stations, in addition to seismic and hydroacoustic stations, comprise the International Monitoring System (IMS) that is tasked with monitoring compliance with the Comprehensive Nuclear Test-Ban Treaty (CTBT). IMS Infrasound stations consist of eight microbarometer sensors and space filters arranged in an array covering an area of approximately 1 to 9 km^2. The space filters used are radiating pipes with inlet ports along their length, designed to average out pressure variations like wind turbulence for more precise measurements. The microbarometers used are designed to monitor frequencies below approximately 20 hertz. Sound waves below 20 hertz have longer wavelengths and are not easily absorbed, allowing for detection across large distances.

Infrasound wavelengths can be generated artificially through detonations and other human activity, or naturally from earthquakes, severe weather, lighting, and other sources. Like forensic seismology, algorithms and other filter techniques are required to analyze gathered data and characterize events to determine if a nuclear detonation has actually occurred. Data is transmitted from each station via secure communication links for further analysis. A digital signature is also embedded in the data sent from each station to verify if the data is authentic.