seismic wave

Seismic wave

Seismic waves are waves of sound that travel through the core of the earth or other elastic bodies, for example as a result of an earthquake, explosion, or some other process that imparts light. Seismic waves are studied by seismologists, and measured by a seismograph, which records the output of a [[mmeter], or geophone. For seismic studies of oil reservoirs, hydrophones may give additional information.
The propagation velocity of the waves depends on density and elasticity of the medium which is penetrated. The velocities range from approximately 3–8 km/s in the Earth's crust up to 13 km/s in the deep mantle.
Earthquakes create various types of waves with different velocities; when reaching seismic observatories, their different travel time enables the scientists to locate the epicenter. In geophysics the refraction or reflection of seismic waves is used for research of the Earth's interior, and artificial vibrations to investigate subsurface structures.