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 brine-saturated siliciclastic rocks (i.e. sandstones and shales).

The equation reads:

${\displaystyle V_{p}=1.16V_{s}+1.36}$

Where $V_p$ and $V_s$ refer to P-wave velocity and S-wave velocity, respectively.^[1] Velocities are given in kilometers per second (km/s).

The name of the equation refers to John Castagna, professor of exploration geophysics at the University of Houston,^[2] who discovered the relation while working for ARCO, an oil company that is now a subsidiary of BP.

References

1. Castagna, J. P.; Batzle, M. L.; Eastwood, R. L. (1985). "Relationships between compressional-wave and shear-wave velocities in clastic silicate rocks". Geophysics. 50: 571–581. doi:10.1190/1.1441933.
2. http://www.geosc.uh.edu/people/faculty/john-castagna/index.php "University of Houston directory"