Figure F1. A. Overpressure results when sedimentation occurs more rapidly than fluids can be expelled by compaction. B. Overpressure (P*) is pressure that is greater than the hydrostatic pressure. Vertical effective stress (VES) is the difference between the lithostatic stress and the pore pressure. C. Overpressure causes low effective stresses, which are recorded by an "undercompacted" porosity profile. A suite of models describes how overpressure is generated during rapid deposition (Bethke, 1986; Bredehoeft and Hanshaw, 1968; Gibson, 1958; Koppula and Morgenstern, 1982; Osborne and Swarbrick, 1997; Swarbrick and Osborne, 1996).
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