Seismic wave

Seismogram

Seismic velocity profile

Overview Seismic Waves

Seismic wave travel through Earth

Fundametal toroidal oscillation Earth

Fundamental spheroidal oscillation Earth

Seismic waves are energy waves that travel through the Earth's layers, primarily generated by earthquakes, volcanic activity, magma movement, large landslides, and large man-made explosions that give off low-frequency acoustic energy. These waves are recorded by a seismometer, hydrophone (in water), or accelerometer. The study of seismic waves and the propagation of these waves through the Earth or other planetary bodies is a crucial part of seismology, a branch of geophysics.

Types of Seismic Waves

Seismic waves are categorized into two main types: body waves and surface waves. Each type moves in different ways and travels at different speeds.

Body Waves

Body waves travel through the Earth's interior. They are further divided into:

• Primary Waves (P-waves): These are the fastest seismic waves and the first to be recorded by seismographs. P-waves are compressional waves that move material in the same direction as the wave is traveling. They can move through both solid and liquid layers of the Earth.
• Secondary Waves (S-waves): S-waves arrive after P-waves and can only move through solid materials. This property of S-waves is used to infer the presence of the liquid outer core of the Earth. S-waves move material perpendicular to the wave direction.

Surface Waves

Surface waves travel along the Earth's surface. They are slower than body waves but can be more destructive. Surface waves include:

• Love Waves: These waves cause horizontal shearing of the ground. They are named after A.E.H. Love, a British mathematician who first described them.
• Rayleigh Waves: Named after Lord Rayleigh, who mathematically predicted their existence, these waves roll along the ground like ocean waves, causing both vertical and horizontal ground movement.

Propagation and Speed

The speed of seismic waves depends on the type of wave and the material through which they are traveling. In general, seismic waves travel faster through denser and more elastic materials. For example, P-waves travel faster in solid rock than in molten rock or water.

Detection and Measurement

Seismic waves are detected, recorded, and analyzed by instruments called seismographs. The data collected by seismographs is crucial for understanding the Earth's interior structure and for locating the epicenter of earthquakes.

Applications

Beyond earthquake detection, the study of seismic waves has numerous applications, including:

• Exploring for oil and gas: Seismic waves are used in the exploration of oil and gas by providing detailed maps of the Earth's subsurface layers.
• Understanding Earth's interior: By analyzing how seismic waves travel through the Earth, scientists can infer the composition and state of the Earth's interior.
• Tsunami warning systems: Early detection of seismic waves can provide critical warnings for tsunamis generated by undersea earthquakes.

See Also

• Earthquake
• Geophysics
• Seismology
• Seismometer