Overburden pressure

In a stratigraphic layer that is in hydrostatic equilibrium; the overburden pressure at a depth z, assuming the magnitude of the gravity acceleration is approximately constant, is given by:

${\displaystyle P(z)=P_0+g{\int }_0^z\rho (z)dz}$

where:

• ${\displaystyle z}$ is the depth in meters.
• ${\displaystyle P(z)}$ is the overburden pressure at depth ${\displaystyle z}$.
• ${\displaystyle P_0}$ is the pressure at the surface.
• ${\displaystyle \rho (z)}$ is the density of the material above the depth ${\displaystyle z}$.
• ${\displaystyle g}$ is the gravity acceleration in ${\displaystyle m/s^2}$.

In deep-earth geophysics/geodynamics, gravitational acceleration varies significantly over depth and ${\displaystyle g}$ should not be assumed to be constant, and should be inside the integral.

Some sections of stratigraphic layers can be sealed or isolated. These changes create areas where there is not static equilibrium. A location in the layer is said to be in under pressure when the local pressure is less than the hydrostatic pressure, and in overpressure when the local pressure is greater than the hydrostatic pressure.