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).
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 Marathon Petroleum.
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