Over three decades ago, Dix (1955) derived an approximate equation for the determination of interval velocity from observed reflection seismic data. Assuming a stack of m horizontal layers, with interval velocities Uj, layer thicknesses ΔZj, j = 1, m, and near-vertical raypaths, Dix (1955) showed that
where Tj+1 and Tj are the two-way vertical times and Vj+1 and Vj are the root-mean-square (rms) velocities to interfaces j + 1 and j, respectively.
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