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- sound
- L-wave
- secondary wave
- primary wave
infrasonics
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What is infrasonics?
Infrasonics refers to vibrational or stress waves traveling through elastic mediums, with frequencies below 20 hertz, which is the lower threshold of human hearing. Natural occurrences of these waves include earthquakes, ocean waves, and atmospheric phenomena like thunder. Monitoring infrasonic waves has many practical uses, such as identifying locations of oil and natural gas and detecting underground nuclear explosions.
Animals such as elephants, cattle, and birds are sensitive to infrasonic frequencies, which may help them with early warnings of earthquakes and weather disturbances, navigation, and migration. Exposure to high levels of infrasound can cause adverse reactions in humans, such as nausea, dizziness, and headaches.
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What are infrasound waves and how are they different from normal sound?
Infrasound waves are vibrational or stress waves in elastic media with frequencies below 20 hertz, which is below the range audible to the human ear. Normal sound waves have frequencies within the range of human hearing, typically between 20 hertz and 20,000 hertz.
Infrasonic waves occur naturally in events like earthquakes, volcanoes, ocean waves, and atmospheric phenomena. While humans can sometimes perceive infrasound as individual compression waves below 18 hertz, they lack the tonality of audible sound. Exposure to high intensities of infrasound can cause adverse effects such as nausea, headaches, and dizziness. Some animals, like elephants, are sensitive to infrasound, possibly using it for early warnings of weather disturbances or earthquakes.
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What is the frequency range of infrasound?
Infrasonics refers to vibrational or stress waves in elastic media with frequencies below 20 hertz, which is the lower limit of human hearing. The frequency range extends down to geologic vibrations completing a cycle in 100 seconds or longer.
Infrasonic waves occur naturally in phenomena such as earthquakes, volcanoes, ocean waves, waterfalls, and weather patterns. They can also be generated by human activities or technologies, such as sonic booms from supersonic aircraft and underground nuclear explosions.
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Where can infrasonic waves be found in nature?
Infrasonic waves, which have frequencies below 20 hertz, exist in nature in events such as earthquakes, waterfalls, ocean waves, and volcanoes. They also occur in various atmospheric phenomena like wind, thunder, and weather patterns. The great range of P-waves, a type of infrasonic wave, makes them useful in identifying earthquakes from observation points a great distance from the epicenter.
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How do scientists detect or measure infrasonic waves?
Scientists detect and measure infrasonic waves, which are vibrational or stress waves with frequencies below 20 hertz, using specialized instruments seismographs. These instruments record ground oscillations caused by seismic waves traveling through the Earth or along its surface.
P-waves, which are longitudinal waves similar to sound waves, have large ranges, making them useful for identifying earthquakes from observation points far from the epicenter. In many cases, smaller shocks precede the most severe shock of an earthquake, which seismographs can detect, providing advance warning.
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What are some applications or uses of infrasonics in science and technology?
Infrasonics involves vibrational or stress waves with frequencies below 20 hertz, beyond human hearing. These waves occur naturally in earthquakes, volcanoes, ocean waves, and weather patterns.
Uses and applications of infrasonics:
* Locating resources Man-made seismic shocks using infrasonic frequencies can help identify rock formations that are likely to have oil and natural gas deposits.
* Monitoring nuclear explosions Underground nuclear explosions produce P-waves, which are a type of infrasonic wave, that can be monitored to ensure compliance with nuclear test-ban treaties.
* Earthquake engineering Analyzing earthquake-generated infrasonic waves, such as P-waves and L-waves, is crucial for understanding and mitigating the impact of earthquakes on structures.
* Weather forecasting: High-speed computers can calculate the motion of infrasonic waves to predict weather patterns.
* Animal communication and navigation: Some animals, like elephants and birds, use infrasound for communication, early warning of weather disturbances, and navigation.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
infrasonics, vibrational or stress waves in elastic media, having a frequency below those of sound waves that can be detected by the human ear—i.e., below 20 hertz. The range of frequencies extends down to geologic vibrations that complete one cycle in 100 seconds or longer.
In nature such waves occur in earthquakes, waterfalls, ocean waves, volcanoes, and a variety of atmospheric phenomena such as wind, thunder, and weather patterns. Calculating the motion of these waves and predicting the weather using these calculations, among other information, is one of the great challenges for modern high-speed computers.
The reflection of man-made seismic shocks has helped to identify possible locations of oil and natural gas sources. Distinctive rock formations in which these minerals are likely to be found can be identified by sonic ranging, primarily at infrasonic frequencies. With an array of seismic detectors, a computational form of holography may be achieved.
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One of the most important examples of infrasonic waves in nature is in earthquakes. Three principal types of earthquake waves exist: the S-wave, a transverse body wave; the P-wave, a longitudinal body wave; and the L-wave, which propagates along the boundary of stratified mediums. L-waves, which are of great importance in earthquake engineering, propagate in a similar way to water waves, at low velocities that are dependent on frequency. S-waves are transverse body waves and thus can only be propagated within solid bodies such as rocks. P-waves are longitudinal waves similar to sound waves; they propagate at the speed of sound and have large ranges.
When P-waves propagating from the epicentre of an earthquake reach the surface of the Earth, they are converted into L-waves, which may then damage surface structures. The great range of P-waves makes them useful in identifying earthquakes from observation points a great distance from the epicentre. In many cases, the most severe shock from an earthquake is preceded by smaller shocks, which can be detected by seismographs and provide advance warning of the greater shock to come. Underground nuclear explosions also produce P-waves, allowing them to be monitored from any point in the world if they are of sufficient intensity. The development of extremely sensitive detectors to monitor such explosions has contributed to the maintenance of the Nuclear Test-Ban Treaty, which was signed in 1963 and banned all tests of nuclear weapons except those conducted underground so as to limit the amount of radioactive fallout in the atmosphere.
Infrasonic disturbances of the atmosphere that may extend to 50 km (30 miles) above Earth’s surface are often associated with severe earthquakes. These waves can travel considerable distances around the globe.
Human perception of low-frequency sound waves propagating in air does not have a well-defined cutoff point. Above about 18 hertz sound waves appear to have tonality; below this frequency the individual compression waves may be distinguished. Driving an automobile with an open window may generate an infrasonic resonance. The sonic boom of supersonic aircraft contains significant levels of infrasound. In certain circumstances occupational exposure to infrasound may be severe: transformer rooms, compressor plants, engine rooms, and air handlers and blowers in buildings may all produce levels that are extremely high and cause discomfort. Studies have shown that many people experience adverse reactions to large intensities of infrasonic frequencies, developing headaches, nausea, blurred vision, and dizziness. The mechanisms by which infrasonics may be perceived by humans and their physiological effects are incompletely understood.
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A number of animals are sensitive to infrasonic frequencies, as indicated in the table. It is believed by many zoologists that this sensitivity in animals such as elephants may be helpful in providing them with early warning of earthquakes and weather disturbances. It has been suggested that the sensitivity of birds to infrasound aids their navigation and even affects their migration.
| animal | frequency (hertz) | |
|---|---|---|
| low | high | |
| humans | 20 | 20,000 |
| cats | 100 | 32,000 |
| dogs | 40 | 46,000 |
| horses | 31 | 40,000 |
| elephants | 16 | 12,000 |
| cattle | 16 | 40,000 |
| bats | 1,000 | 150,000 |
| grasshoppers and locusts | 100 | 50,000 |
| rodents | 1,000 | 100,000 |
| whales and dolphins | 70 | 150,000 |
| seals and sea lions | 200 | 55,000 |