1. n. [Geophysics]

An equation used to calculate the interval velocity within a series of flat, parallel layers, named for American geophysicist C. Hewitt Dix (1905 to 1984). Sheriff (1991) cautions that the equation is misused in situations that do not match Dix's assumptions. The equation is as follows:

V_int = [(t₂ V_RMS2² − t₁ V_RMS1²) / (t₂ − t₁)]^1/2,

where
V_int = interval velocity
t₁ = traveltime to the first reflector
t₂ = traveltime to the second reflector
V_RMS1 = root-mean-square velocity to the first reflector
V_RMS2 = root-mean-square velocity to the second reflector.

Reference: Dix CH: "Seismic Velocities from Surface Measurements," Geophysics 20, no. 1 (January 1955): 68–86.

See: interval velocity,  reflector,  root-mean-square velocity,  traveltime