P-wave modulus

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There are two kinds of seismic body waves in solids, pressure waves (P-waves) and shear waves. In linear elasticity, the P-wave modulus , also known as the longitudinal modulus, or the constrained modulus, is one of the elastic moduli available to describe isotropic homogeneous materials.

It is defined as the ratio of axial stress to axial strain in a uniaxial strain state. This occurs when expansion in the transverse direction is prevented by the inertia of neighboring material, such as in an earthquake, or underwater seismic blast.

where all the other strains are zero.

This is equivalent to stating that

where VP is the velocity of a P-wave and ρ is the density of the material through which the wave is propagating.


References

  • G. Mavko, T. Mukerji, J. Dvorkin. The Rock Physics Handbook. Cambridge University Press 2003 (paperback). ISBN 0-521-54344-4
More information 3D Formulae, Knowns ...
Homogeneous isotropic linear elastic materials have their elastic properties uniquely determined by any two quantities among these; thus, given any two, any other of the elastic moduli can be calculated according to these formulas, provided both for 3D materials (first part of the table) and for 2D materials (second part).
3D Formulae
Knowns Bulk modulus (K) Young's modulus (E) Lamé's first parameter (λ) Shear modulus (G) Poisson's ratio (ν) P-wave modulus (M) Notes
(K, E) 3K(1 + 6K/E 9K) E/3 E/3K 1/2 E/6K 3K + E/3 E/3K
(K, λ) 9K(K λ)/3K λ 3(K λ)/2 λ/3K λ 3K
(K, G) 9KG/3K + G K 2G/3 3K 2G/6K + 2G K + 4G/3
(K, ν) 3K(1 2ν) 3/1 + ν 3K(1 2ν)/2(1 + ν) 3K(1 ν)/1 + ν
(K, M) 9K(M K)/3K + M 3K M/2 3(M K)/4 3K M/3K + M
(E, λ) E + 3λ + R/6 E + R/4 E + R/ 1/4 E λ + R/2 R = ±(E2 +2 + 2Eλ)1/2
(E, G) EG/3(3G E) G(E 2G)/3G E E/2G 1 G(4G E)/3G E
(E, ν) E/3 6ν /(1 + ν)(1 2ν) E/2(1 + ν) E(1 ν)/(1 + ν)(1 2ν)
(E, M) 3M E + S/6 M E + S/4 3M + E S/8 E + S/4M 1/4 S = ±(E2 + 9M2 10EM)1/2
(λ, G) λ + 2G/3 G(3λ + 2G)/λ + G λ/2(λ + G) λ + 2G
(λ, ν) λ/3(1 + 1/ν) λ(1/ν 2ν 1) λ(1/2ν 1) λ(1/ν 1)
(λ, M) M +/3 (M λ)(M+2λ)/M + λ M λ/2 λ/M + λ
(G, ν) 2G(1 + ν)/3 6ν 2G(1 + ν) 2 G ν/1 2ν 2G(1 ν)/1 2ν
(G, M) M 4G/3 G(3M 4G)/M G M 2G M 2G/2M 2G
(ν, M) M(1 + ν)/3(1 ν) M(1 + ν)(1 2ν)/1 ν M ν/1 ν M(1 2ν)/2(1 ν)
2D Formulae
Knowns (K) (E) (λ) (G) (ν) (M) Notes
(K2D, E2D) 2K2D(2K2D E2D)/4K2D E2D K2DE2D/4K2D E2D 2K2D E2D/2K2D 4K2D^2/4K2D E2D
(K2D, λ2D) 4K2D(K2D λ2D)/2K2D λ2D K2D λ2D λ2D/2K2D λ2D 2K2D λ2D
(K2D, G2D) 4K2DG2D/K2D + G2D K2D G2D K2D G2D/K2D + G2D K2D + G2D
(K2D, ν2D) 2K2D(1 ν2D) 2K2Dν2D/1 + ν2D K2D(1 ν2D)/1 + ν2D 2K2D/1 + ν2D
(E2D, G2D) E2DG2D/4G2D E2D 2G2D(E2D 2G2D)/4G2D E2D E2D/2G2D 1 4G2D^2/4G2D E2D
(E2D, ν2D) E2D/2(1 ν2D) E2Dν2D/(1 + ν2D)(1 ν2D) E2D/2(1 + ν2D) E2D/(1 + ν2D)(1 ν2D)
2D, G2D) λ2D + G2D 4G2D2D + G2D)/λ2D + 2G2D λ2D/λ2D + 2G2D λ2D + 2G2D
2D, ν2D) λ2D(1 + ν2D)/2ν2D λ2D(1 + ν2D)(1 ν2D)/ν2D λ2D(1 ν2D)/2ν2D λ2D/ν2D
(G2D, ν2D) G2D(1 + ν2D)/1 ν2D 2G2D(1 + ν2D) 2 G2D ν2D/1 ν2D 2G2D/1 ν2D
(G2D, M2D) M2D G2D 4G2D(M2D G2D)/M2D M2D 2G2D M2D 2G2D/M2D
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