The distribution of crustal extension across the Gulf of Mexico was calculated from the present-day total sediment thickness and bathymetry. Estimates of 2.0-3.0 occur close to the hinge zone and become greater than 6 in regions that are supposedly floored by oceanic crust. In these profiles, the depth-coordinate is with respect to sea bottom, and thus to obtain the actual depth to an interface, the respective bathymetry or paleobathymetry must be added. Critical parameters in this analysis are the sediment specific storage, hydraulic conductivity and hydraulic diffusivity. Many of these parameters have equivalents in the equations describing the conductive-advective flow of heat.
Specific storage is the property of sediment to retain fluids during pore pressure variations.
It is formally defined as the amount of fluid expelled due to a unit increase of hydraulic head. Hydraulic conductivity defines the rate at which a fluid can pass through a porous medium. The hydraulic conductivity is directly proportional to the sediment permeability which can feasibly decrease 3 orders of magnitude within the upper sections of a sedimentary basin. Hydraulic diffusivity is defined as the ratio of hydraulic conductivity and specific storage. The generation of overpressure is caused mainly by the rapid deposition of sediment.