Mudrock line

In rock physics and petrophysics, the mudrock line, also called Castagna's equation or Castagna's relation, is an empirical linear relation between seismic P-wave velocity and S-wave velocity in siliciclastic rocks (i.e. sandstones and shales).

The equation reads:


 * $$V_\mathrm{P} = 1.16 V_\mathrm{S} + 1.36\ $$

Where $$V_\mathrm{P}$$ and $$V_\mathrm{P}$$ refer to P-wave velocity and S-wave velocity, respectively. Velocities are given in kilometers per second (km/s).

The name of the equation refers to John Castagna, a professor of exploration geophysics at the University of Houston, who discovered the relation while working with ARCO, an oil company that is now a subsidiary of BP.