Seismic velocity

Seismic velocity is the speed at which a seismic wave travels through a material. It depends on the material’s elastic properties, density, and the wave type.

P-wave: A compressional seismic wave that travels through solids, liquids, and gases. Its speed is governed by bulk and shear moduli together with density.
Seismic tomography: A method that reconstructs Earth’s interior from seismic-wave travel times and paths. Its velocity images map variations in temperature, composition, and structure.
Seismic wave: A disturbance that propagates through Earth or along its surface, carrying seismic energy. Seismic velocity is the propagation speed of these waves through materials.
Mohorovičić discontinuity: The boundary between Earth’s crust and mantle, marked by a jump in seismic-wave speeds. The velocity increase across this boundary identifies a major compositional transition.
Group velocity: The speed at which a wave packet’s envelope and its carried energy propagate. It can differ from phase velocity in dispersive seismic waves.
S-wave: A shear seismic wave that propagates through solids but not fluids. Its speed depends on shear rigidity and density, unlike compressional-wave speed.
Travel-time curve: A graph or relation connecting seismic arrival time with source–receiver distance. Its slopes and bends encode seismic velocities and changes between layers.
Elasticity: The ability of a material to deform under stress and recover when the stress is removed. Elastic response supplies the stiffness that controls seismic-wave speeds.
Low-velocity zone: A region of the upper mantle where seismic waves travel more slowly than in surrounding material. Its reduced speeds indicate hot, weak mantle and partial melting in some regions.
Phase velocity: The speed at which a fixed phase of a wave travels through space. It describes individual wave phases, not necessarily the packet or energy speed.

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