Seismic tomography or imaging is a technique for imaging the Earth's subsurface with seismic waves generated by earthquakes or explosions. Velocity anomalies of seismic wave propagation in the Earth's interior are measured. The data are recorded by a seismometer and used to solve an inverse problem. In this way, the location, refraction, and reflection of the wave can be calculated based on the Radon principle.

Different wave types (pressure, shear, and surface waves) can be used for tomographic models with different resolutions.
Seismic imaging or tomography (tomo = slice and graph = picture) is a procedure for estimating the earth’s rock parameters from seismic data. These rock parameters can be represented by the spatial distribution of, e.g., P-wave velocity, S-wave velocity, porosity, density, or anisotropic parameters. The result of inversion is graphically presented as a 2-D or 3-D grid of pixels, where each pixel contains the value of the model parameter of interest. Such tomograms are used to estimate the geometry and lithology of geologic layers, and can help exploration geophysicists and earthquake seismologists understand the evolution of the earth’s interior.

Basically, three approaches are distinguished: local seismic tomography, teleseismic tomography, and attenuation tomography.

Used reference:

Schuster G.T. (2011) Seismic Imaging, Overview. In: Gupta H.K. (eds) Encyclopedia of Solid Earth Geophysics. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-8702-7_167