Seismic blasting is a method of mapping what lies beneath the ocean floor by firing intense pulses of compressed air into the water. The sound waves travel downward, bounce off underground rock layers, and return to the surface, where sensors record them to build a picture of buried geological structures. It’s the primary tool used to locate oil, natural gas, and mineral deposits offshore, and it’s one of the loudest human-made sounds in the ocean.
How Seismic Airguns Work
The core device is a seismic airgun, a metal cylinder that stores air at extreme pressure, typically between 50 and 100 bar (roughly 725 to 1,450 psi). When the gun fires, air bursts through narrow ports in the cylinder wall into the surrounding water, creating a rapidly expanding bubble. That bubble produces a powerful shockwave that radiates outward and downward through the water column.
As the bubble expands, it eventually collapses under the surrounding water pressure, then re-expands and collapses again. Each collapse generates its own pressure pulse. A survey vessel typically tows not just one airgun but an array of them, sometimes dozens, firing in coordinated sequences every 10 to 15 seconds, around the clock, for weeks or months at a time. The combined output of a large array can reach a theoretical source level on the order of 260 decibels (referenced to 1 micropascal at 1 meter). For comparison, that’s far louder than a jet engine, though sound behaves differently in water than in air, so the numbers aren’t directly comparable.
Receivers called hydrophones, towed behind the vessel in long cables called streamers, pick up the reflected sound. Different rock layers and fluid-filled pockets reflect sound differently, letting geologists piece together detailed subsurface maps that reveal where petroleum reservoirs or mineral deposits might be hiding.
Why It’s Used
Seismic blasting exists almost entirely to serve offshore energy exploration. Before a company commits billions of dollars to drill in deep water, it needs a reliable picture of what’s below the seabed. Reflection and refraction surveys using airguns provide that picture, identifying the shape, depth, and composition of rock formations thousands of meters underground. The technique is also used for research purposes in geology and oceanography, but the vast majority of seismic surveys are tied to oil and gas development.
In recent years, federal approvals for seismic surveys in U.S. waters have expanded, particularly off the coast of Alaska, as part of broader pushes to increase domestic energy production.
How Loud and How Far
Although airguns concentrate most of their energy at low frequencies (below 100 Hz), the sound isn’t confined to that range. Measurements have detected airgun noise at frequencies up to 100 kHz, well above ambient ocean noise across the entire spectrum. This matters because different marine species hear at different frequencies. Low-frequency sound from airguns can travel hundreds of kilometers through the ocean, meaning a single survey can affect an enormous area.
At close range, the peak sound pressure levels recorded from airgun arrays have been measured above 190 dB. To put that in biological terms, a harbor seal exposed to a nearby airgun array experienced received levels approaching 195 dB peak-to-peak. These levels are high enough to cause physical harm to animals in the immediate vicinity and behavioral disruption at much greater distances.
Effects on Marine Mammals
Whales, dolphins, and seals rely on sound for communication, navigation, and finding food. Seismic blasting introduces a wall of noise that can mask their calls, alter their behavior, and potentially damage their hearing. Anatomical and behavioral studies suggest that whales and dolphins may have some natural resistance to temporary hearing loss compared to land mammals, but they are not immune. They experience the same age-related and disease-related hearing decline as other animals, and chronic exposure to human-generated noise is a reasonable candidate for accelerating those losses.
The honest reality is that existing data cannot precisely predict the full impact on marine mammals. Researchers lack enough information to describe how these animals respond physically and behaviorally to intense, repeated sound exposure over long periods. What is clear is that the effects extend beyond simple annoyance. Whales have been documented changing migration routes, abandoning feeding areas, and going silent during seismic surveys, all of which carry real costs to their survival and reproduction.
Damage to Fish and Plankton
The impacts don’t stop at marine mammals. A study examining commercial fish catches near seismic survey areas found that catch rates for whiting dropped by 99% and flathead by 75% immediately after a survey compared to control areas. For whiting, the negative effects persisted for at least 10 months, showing up clearly in commercial fishing logbook data. Fish don’t necessarily die from the blasts at typical distances. They flee, and they may not return for a long time.
At the base of the ocean food web, the picture is equally concerning. Experiments exposing tiny crustaceans called copepod larvae to airgun blasts at a depth of 6 meters found immediate mortality of about 14%, compared to less than 4% in control groups. The damage compounded over time: nearly all the exposed larvae were dead within four days, while more than half of the unexposed larvae survived past six days. These organisms are a critical food source for fish, seabirds, and whales, so even localized die-offs can ripple through the food chain.
Regulatory Safeguards
In U.S. federal waters, seismic surveys are overseen by the Bureau of Ocean Energy Management (BOEM) and subject to protections under the Endangered Species Act and the Marine Mammal Protection Act. The most recent federal protocols, updated in a May 2025 biological opinion from the National Marine Fisheries Service, require operators to follow mitigation measures during surveys in the Gulf of America.
Standard requirements typically include “soft starts,” where airguns are gradually ramped up to full power over a set period, giving nearby animals time to move away. Operators must also maintain exclusion zones around the airgun array, and trained marine mammal observers (either on-vessel or using passive acoustic monitoring) watch for protected species. If a whale or dolphin enters the exclusion zone, operations are supposed to shut down until the animal clears the area. Critics argue these measures are difficult to enforce in practice, especially at night or in poor weather, and that they do little to address impacts on species that can’t be easily spotted from a ship’s deck.
Quieter Alternatives in Development
The most promising alternative to conventional airguns is a technology called Marine Vibroseis, which generates continuous, controlled vibrations rather than explosive bursts. Modeling comparisons between a Marine Vibroseis array and a conventional airgun array with similar geological imaging capability found significant noise reductions. At 100 meters, the vibroseis system produced peak sound pressure levels 20 dB lower than the airgun array. At longer ranges, the difference narrowed but remained meaningful: at 100 kilometers, the vibroseis system produced broadband sound exposure levels about 8 dB lower, largely because it operates within a narrower frequency band and doesn’t generate the same high-frequency noise.
Several companies are actively working to bring Marine Vibroseis and other reduced-impact sources to commercial readiness. The goal is a tool that provides the same quality of subsurface data while generating substantially less underwater noise. Progress has been slow, partly because the oil and gas industry has relied on airgun technology for decades and the existing infrastructure is deeply established. But the combination of regulatory pressure, public opposition, and growing evidence of ecological harm is pushing development forward.