Dix Equation for Interval Velocity
The Dix equation converts stacking velocities measured at the surface into the interval velocity of the layer between two reflectors.
The equation
Vint² = (V2²t2 – V1²t1) / (t2 – t1)
- V1, V2 are RMS velocities to the upper and lower reflectors
- t1, t2 are the corresponding zero offset two way times
- Vint is the interval velocity between them
Worked example
With V1 of 2000 meters per second at 1.0 seconds and V2 of 2200 at 1.4 seconds, the interval velocity is 2634 meters per second, notably faster than either RMS value, which is typical: RMS velocities smear the layers above.
When to use it
Reliable when reflectors are flat, times are well separated, and velocities are picked cleanly. Thin intervals amplify picking errors ferociously, so never Dix invert closely spaced picks without smoothing.
Related Calculators and Reference
- Seismic Wave Simulator: watch wavefronts obey these relations live.
- Seismic Velocity Converter: apply the Dix equation to your own picks.
- SEG Wiki: the standard reference for seismic methods.