NationMaster - Encyclopedia: Rayleigh waves

Rayleigh waves are a type of surface wave associated on the Earth with earthquakes and subterranean movement of magma. In physics, a surface wave is a wave that is guided along the interface between two different media for a mechanical wave, or by a refractive index gradient for an electromagnetic wave. ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ... Global earthquake epicenters, 1963–1998. ... This article is about the type of molten rock. ...

Contents

1 Characteristics

1.1 Dispersion

2 Earthquake shaking

3 Other manifestations

3.1 Animals
3.2 Non-destructive testing

4 See also

5 External links

6 Further reading

Characteristics

The existence of Rayleigh waves was predicted in 1885 by Lord Rayleigh, for whom they were named. They are distinct from other types of seismic waves, such as P-waves and S-waves, which are both body waves, or Love waves, another type of surface wave. Rayleigh waves are generated by the interaction of P- and S- waves at the surface of the earth. The Rayleigh wave travels with a velocity that is lower than the P-, S-, and Love wave velocities. Emanating outward from the epicenter of an earthquake, Rayleigh waves travel along the surface of the earth at about 10 times the speed of sound in air. See also Rayleigh fading Rayleigh scattering Rayleigh number Rayleigh waves Rayleigh-Jeans law External links Nobel website bio of Rayleigh About John William Strutt MacTutor biography of Lord Rayleigh Categories: People stubs | 1842 births | 1919 deaths | Nobel Prize in Physics winners | Peers | British physicists | Discoverer of a chemical element ... A seismic wave is a wave that travels through the Earth, often as the result of an earthquake or explosion. ... Surface waves that cause horizontal shifting of the earth during an earthquake. ... The speed of sound varies depending on the medium through which the sound waves pass. ...

Since Rayleigh waves are surface waves, the strength, or amplitude, of the waves decreases exponentially with the depth of the earthquake. However, since they are confined to the surface, their amplitude decays only as , where $r$ is the distance the wave has traveled from the earthquake. Surface waves therefore decay more slowly with distance than do body waves, which travel in three dimensions. Large earthquakes may generate Rayleigh waves that travel around the Earth several times before dissipating. Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation. ...

Dispersion

Rayleigh waves in the Earth are also dispersive: Rayleigh waves with a higher frequency travel more slowly than those with a lower frequency. This occurs because a Rayleigh wave of lower frequency has a relatively long wavelength. Long wavelength waves "see" more deeply into the Earth than waves with a short wavelength. Since the speed of waves in the Earth increases with increasing depth, the longer wavelength (low frequency) waves can travel faster than the shorter wavelength (high frequency) waves. Rayleigh waves thus often appear "spread out" on seismograms recorded at distant earthquake recording stations. Dispersion can mean any of several things: A phenomenon that causes the separation of a wave into components of varying frequency. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... The wavelength is the distance between repeating units of a wave pattern. ... A seismogram is a graph output by a seismograph. ...

Earthquake shaking

Due to their higher speed, the P- and S-waves generated by an earthquake arrive before the surface waves. However, the particle motion of surface waves is larger than that of body waves, so the surface waves tend to cause more damage. In the case of Rayleigh waves, the motion is of a rolling nature, similar to an ocean surface wave. The intensity of Rayleigh wave shaking at a particular location is dependent on several factors: Categories: Physics stubs | Physical oceanography | Waves ...

The size of the earthquake.
The distance to the earthquake.
The depth of the earthquake.
The geologic structure of the crust.

Local geologic structure can serve to focus or defocus Rayleigh waves, leading to significant differences in shaking over short distances.

Other manifestations

Animals

Rayleigh waves are inaudible, but yet can be detected by many mammals, birds, insects and spiders. Human beings should be able to detect Rayleigh waves through their Pacinian corpuscles, which are in the joints, although people do not seem to consciously respond to the signals. Some animals seem to use Rayleigh waves to communicate. In particular, elephants seem to use vocalizations to generate Rayleigh waves. Since Rayleigh waves decay slowly, they should be detectable over long distances.[1] (http://biox.stanford.edu/grant/klemperer_r2_iip.html) Note that these Rayleigh waves have a much higher frequency than Rayleigh waves generated by earthquakes. Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Orders Many - see section below. ... Orders Subclass Apterygota Symphypleona - globular springtails Subclass Archaeognatha (jumping bristletails) Subclass Dicondylia Monura - extinct Thysanura (common bristletails) Subclass Pterygota Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Blattodea (cockroaches) Mantodea (mantids) Isoptera (termites) Zoraptera Grylloblattodea Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, crickets... Families Suborder Mesothelae Liphistiidae (primitive burrowing spiders) Arthrolycosidae (primitive spiders) Arthromygalidae (primitive spiders) Suborder Mygalomorphae Antrodiaetidae (folding trapdoor spider) Atypidae (atypical tarantula) Ctenizidae (trapdoor spider) Cyrtaucheniidae (wafer trapdoor spider) Dipluridae (funnel-web tarantula) Hexathelidae (venomous funnel-web tarantula) Mecicobothriidae (dwarf tarantulas) Theraphosidae (tarantula) Suborder Araneomorphae Agelenidae (araneomorph funnel-web spider... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... A Pacinian corpuscle is a structure that functions as a mechanoreceptor. ... Genera and Species Loxodonta Loxodonta cyclotis Loxodonta africana Elephas Elephas maximus Stegodon (extinct) Deinotherium (extinct) Mammuthus (extinct) Elephantidae (the elephants) is the only extant family in the order Proboscidea. ...

After the 2004 Indian Ocean Earthquake, some people have speculated that Rayleigh waves served as warning to animals to seek higher ground, allowing them to escape the more slowly-traveling tsunami. At this time, evidence for this is mostly anecdotal. Another animal early warning system may rely on an ability to sense infrasonic waves. [2] (http://www.slate.com/id/2111608) The December 2004 Indian Ocean tsunami hits Thailand The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake, was an undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) on December 26, 2004. ... The tsunami that struck Malé in the Maldives on December 26, 2004. ... AS thunderous tones deepen, their power seemingly intensifies over frail barriers such as glass windows. ...

Non-destructive testing

Rayleigh waves in the ultrasonic frequency range are used in non-destructive testing applications to help find cracks and other imperfections in materials. Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ... In nondestructive testing, tests are carried out in such a way as to not disturb the specimen’s structural or surface integrity. ...

External links

Rayleigh wave page (http://www.uwm.edu/~bketter/Research/Surface_Theory/Rayleigh/rayleigh_index.html)