Researchers in Pakistan used seismic and acoustic monitoring data from the 2017 deployment of the GBU-43/B Massive Ordnance Air Blast in Afghanistan, calculating a 14-tonne TNT explosive yield through infrasound wave analysis.
The United States GBU-43/B Massive Ordnance Air Blast, widely known as the MOAB, returned to public attention after President Donald Trump raised the possibility of its use in the conflict with Iran. Originally developed in 2003 with a length of approximately 9.1 meters, the heavy-payload weapon is deployed from a C-130 transport aircraft and relies on GPS and inertial navigation systems to find its target.
Unlike munitions engineered to plunge deep into fortified underground structures, the MOAB detonates in the air before reaching the ground. This aerial trigger spreads the blast energy and pressure waves across the surrounding atmosphere, distributing the destructive force over a wider surface area instead of concentrating it at a single point of impact.
The 2017 Afghanistan Deployment and Infrasound Detection in Pakistan
The weapon has seen combat only once. The United States military dropped the device in the Achin district of Afghanistan on April 13, 2017, generating an extraordinary explosion that sent a low-frequency acoustic signature traveling nearly 249 kilometers. Researchers at the National Centre for Physics in Islamabad examined that acoustic footprint, using data recorded by a seismic and acoustic monitoring station inside Pakistan to reconstruct the power of the blast.
Explosions generate a wide spectrum of sound waves that travel at different frequencies. While some fall inside the human hearing range, others drop below 20 hertz into infrasound territory, which remains imperceptible to human ears under normal conditions but easily captured by specialized recording hardware.
Physics of Atmospheric Pressure Waves and the 0.1717 Pascal Reading
When a large bomb detonates, expanding hot gases shove the surrounding air outward, creating pressure shifts that travel far from the blast zone. These atmospheric waves can cross vast distances even when the original sound is too faint for human ears to register, allowing sensitive instruments to track events far beyond the horizon.
When the research team parsed the recordings from the Pakistani monitoring post, they isolated a mean pressure amplitude of 0.1717 pascals.
The idea is similar to dropping a stone in a pool of water, where strong ripples form near the point of impact, then spread in expanding circles and gradually weaken the further they get from their source. In a similar way, the infrasound waves resulting from the explosion spread through the atmosphere, reaching distant monitoring stations with a signal weaker than it was near its source.
Tawfik explained that the period or peak repetition time of an infrasound wave scales directly with the cube of the explosion’s yield. By combining this relationship with the measured wave amplitude and the distance from the detonation point, analysts can pinpoint both the location and the explosive power of the event.
There is a relationship connecting the infrasound wave period or its peak repetition time with the explosion force, which is directly proportional to the third power of the wave period (the cube of the wave period). Also, the measured wave amplitude and distance from the source can be linked with the explosion force, and by merging these two relations, we can determine the power and location of the explosion that caused the infrasound wave with high accuracy.
Calculations must account for several atmospheric factors that alter the wave during transit. The outlet reported that geometric wave expansion, atmospheric absorption, wind interference, and reflections or refractions across atmospheric layers all influence the final reading captured at a distance.
Measurement accuracy, and thus the calculation of force, depends on a set of factors including the geometric expansion of the wave, atmospheric absorption, wind effect, and reflections and refractions in the layers of the atmosphere.
Abdel Nasser Tawfik, professor of theoretical physics at the Canadian University in Cairo and visiting professor at the Islamic University in Madinah, via Aljazeera
Applying this methodology to the 2017 Afghan deployment yielded a calculated explosive output equivalent to approximately 14 tonnes of TNT. Researchers noted that the technique offers a reliable method for tracking explosions and weather events in remote areas where direct, on-the-ground measurements remain impossible.