velocitymodel

A velocity model is a spatial representation of how seismic wave speeds vary within a medium, typically used in geophysics and seismology. In its simplest form, a velocity model assigns P-wave and S-wave velocities (and often density) to points in space. Models may be isotropic, with speeds independent of direction, or anisotropic, where velocity depends on wave propagation direction. They can describe a one-dimensional profile with depth or a three-dimensional grid capturing lateral variations.

Velocity models are essential for interpreting seismic data and for imaging subsurface structure. They enable seismic tomography, which infers velocity variations from seismic travel times or waveforms; they support accurate travel-time and waveform modeling used in locating earthquakes and in predicting how waves propagate through the Earth or through engineered media. Velocity models also underlie seismic imaging techniques such as migration and full-waveform inversion, improving the resolution of subsurface images.

Common model types include global reference models, like the 1D Preliminary Reference Earth Model (PREM) and IASPEI 91, as well as regional and global 3D velocity models used in exploration geophysics and Earth science. Model construction typically relies on travel-time data from earthquakes or controlled sources, borehole logs, and sometimes geological or mineralogical information. Limitations arise from data coverage, nonuniqueness, and the need to account for anisotropy and attenuation, which can complicate interpretation.