The classical Raymer-Hunt-Gardner functional form Vp=(1ϕ)2VpS+ϕVpF, where VpS and VpF denote the P -wave velocity in the solid and pore-fluid phases, respectively, and ϕ is the total porosity, can also be used to relate the S-wave velocity in dry rock to porosity and mineralogy as VsDry=(1ϕ)2VsS, where VsS is the S-wave velocity in the solid phase. Assuming that the shear modulus of rock does not depend on the pore fluid, Vs in wet rock is VsWet=VsDryρbDry/ρbWet, where ρbDry and ρbWet denote the bulk density of the dry and wet rock, respectively. This new functional form for Vs prediction reiterates Nur's critical porosity concept: The Vp/Vs ratio in dry rock equals that in the solid phase. It accurately predicts Vs in consolidated clastic and carbonate rock. Two motivations for using it are (1) it is simple, and (2) it predicts Vs not from Vp but directly from ϕ and mineralogy.

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