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, which is P velocity in Fig. 1g–h. 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.