Birch's Law


Birch’s law establishes a linear relation of the compressional wave velocity of rocks and minerals of a constant average atomic weight with density as shown in this formula.

Birch’s Law was discovered by Francis Birch and allows for the seismic speed of a P-wave to be represented as a function of density with regard to the atomic weight of the substance the wave is moving through.

Applications of Birch’s Law

Birch’s law can be used in the discussion of geophysical data. The law is used in forming compositional and mineralogical models of the mantle by using the change in the velocity of the seismic wave and its relationship with a change in density of the material the wave is moving in. Birch’s law is used in determining chemical similarities in the mantle as well as the discontinuities of the transition zones. Birch’s Law can also be employed in the calculation of an increase of velocity due to an increase in the density of material.

Related formulas


upcompressional wave velocity rocks and minerals (dimensionless)
aMavgfunction of constant average atomic weight (dimensionless)
bdensity factor (dimensionless)
ρdensity (dimensionless)