Dictionary:Mudrock line

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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 line given by the mudrock equation (q.v.).

The equation reads:

Where and 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.




  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"
  3. Whaley, J., 2017, Oil in the Heart of South America, https://www.geoexpro.com/articles/2017/10/oil-in-the-heart-of-south-america], accessed November 15, 2021.
  4. Wiens, F., 1995, Phanerozoic Tectonics and Sedimentation of The Chaco Basin, Paraguay. Its Hydrocarbon Potential: Geoconsultores, 2-27, accessed November 15, 2021; https://www.researchgate.net/publication/281348744_Phanerozoic_tectonics_and_sedimentation_in_the_Chaco_Basin_of_Paraguay_with_comments_on_hydrocarbon_potential
  5. Alfredo, Carlos, and Clebsch Kuhn. “The Geological Evolution of the Paraguayan Chaco.” TTU DSpace Home. Texas Tech University, August 1, 1991. https://ttu-ir.tdl.org/handle/2346/9214?show=full.