Tsunami

Causes:

• A tsunami can be generated when convergent or destructive plate boundaries abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent or constructive plate boundaries.. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis.
• Tsunamis caused by these mechanisms,unlike the trans-oceanic tsunami, may dissipate quickly and rarely affect distant coastlines due to the small sea area affected. These events can gives rise to much larger local shock waves, such as the landslides at the head of Lituya Bay 1958,which produced a wave with an initial surge estimated at 524 metres. However,an extremely large landslide might generate a megatsunami that can travel trans-oceanic distances, although there is no geological evidence to support this hypotesis.

Warning and prediction:

• A tsunami cannot be precisely predicted even if the right magnitude of an earthquake occurs in the right location. However, there are some warning signs of an impending tsunami and automated systems can provide warnings immediately after an earthquake in time to save lives. One of the most successful systems uses bottom pressure sensors that are attached to bouys. The sensors constantly monitor the pressure of the overlying water column.
• Regions with a high tsunami risk typically use tsunami warning systems to warn the population before the wave reaches land. On the west coast of the United States, which is prone to Pacific Ocean tsunami warning signs indicate evacuation routes.

Interference wave

In physics, interference is the addition (superposition) of two or more waves that results in a new wave pattern. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.

Two non-monochromatic waves are only fully coherent with each other if they both have exactly the same range of wavelengths and the same phase differences at each of the constituent wavelengths.

The total phase difference is derived from the sum of both the path difference and the initial phase difference (if the waves are generated from two or more different sources). It can then be concluded whether the waves reaching a point are in phase (constructive interference) or out of phase (destructive interference).

Theory

The principle of superposition of wave states that the resultant displacement at a point is equal to the vector sum of the displacements of different waves at that point. If a crest of a wave meets a crest of another wave at the same point then the crests interfere constructively and the resultant wave amplitude is greater. If a crest of a wave meets a trough of another wave then they interfere destructively, and the overall amplitude is decreased.

This form of interference can occur whenever a wave can propagate from a source to a destination by two or more paths of different length. Two or more sources can only be used to produce interference when there is a fixed phase relation between them, but in this case the interference generated is the same as with a single source; see Huygen's Principle.

Experiment

Thomas Young's double-slit experiment showed interference phenomena where two beams of light which are coherent interfere to produce a pattern.

The beams of light both have the same wavelength range and at the center of the interference pattern. They have the same phases at each wavelength, as they both come from the same source.

Transverse wave

A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer. If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the y-z plane.

If you anchor one end of a ribbon or string and hold the other end in your hand, you can create transverse waves by moving your hand up-and-down. Notice though, that you can also launch waves by moving your hand side-to-side. This is an important point. There are two independent directions in which wave motion can occur.

In this case, these are the y and z directions mentioned above.
Further, if you carefully move your hand in a clockwise circle, you will launch waves that describe a left-handed helix as they propagate away.
Similarly, if you move your hand in a counter-clockwise circle, a right-handed helix will form.

These phenomena of simultaneous motion in two directions go beyond the kinds of waves you can create on the surface of water; in general a wave on a string can be two-dimensional. Two-dimensional transverse waves exhibit a phenomenon called polarization

A wave produced by moving your hand in a line, up and down for instance, is a linearly polarized wave, a special case.
A wave produced by moving your hand in a circle is a circularly polarized wave, another special case.
If your motion is not strictly in a line or a circle your hand will describe an ellipse and the wave will be elliptically polarized.

The transverse plane wave animation shown is also an example of linear polarization. The wave shown could occur on a water surface.

Transverse waves are waves that are moving perpendicular to the direction of vibration.

Examples

Examples of transverse waves include seismic S (secondary) waves, and the motion of the electric (E) and magnetic (M) fields in an electromagnetic plane wave, which both oscillate perpendicularly to each other as well as to the direction of energy transfer. Therefore an electromagnetic wave consists of two transverse waves, visible light being an example of an electromagnetic wave. See electromagnetic spectrum for information on different types of electromagnetic wave.

An oscillating string is another example of a transverse wave; a more everyday example would be an audience wave.