The difference between pore fluid pressure and normal pressure (q.v.). Normal pressure is the pressure produced by a column of formation water extending to the surface (hydrostatic pressure). Fluid pressure that is lower than normal pressure is called underpressure or subpressure and that greater than normal, overpressure (q.v.). The seismic effects of abnormal pressure are discussed in.
- Sheriff, R. E. and Geldart, L. P., 1995, Exploration Seismology, 2nd Ed., Cambridge Univ. Press, pgs 126-128.