Pore pressure

Pore pressure is the pressure exerted by fluid within the pores and fractures of rock. It affects how strongly the rock skeleton resists deformation and failure.

Effective stress: The stress carried by a porous material’s solid framework after fluid pressure is accounted for. Subtracting pore pressure from total stress estimates the load carried by the rock skeleton.
Hydrostatic pressure: The pressure in a fluid at rest caused by the weight of overlying fluid. It provides the baseline pore pressure expected when groundwater is in equilibrium.
Porosity: The fraction of a material’s volume occupied by pores. Pore volume provides the spaces in which pressurized fluid resides.
The 1960 Valdivia earthquake: A magnitude 9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake. Its rupture illustrates the role of fluid pressure in natural subduction-zone faulting.
Terzaghi's principle: A relation stating that effective stress equals total stress minus pore-fluid pressure in a saturated porous material. This principle formalizes how pore pressure reduces stress borne by rock.
Overpressure: Pore-fluid pressure greater than the local hydrostatic pressure. This abnormal condition can weaken rock and complicate drilling.
Permeability: A measure of how readily fluid flows through connected pores or fractures. It controls how quickly pressure disturbances propagate through rock.
The 2011 Prague earthquake sequence: A damaging sequence of earthquakes in Oklahoma, including a magnitude 5.7 event. The sequence has been linked to wastewater injection that altered subsurface pressure.
Mohr–Coulomb theory: A failure criterion relating a material’s shear strength to normal stress and friction. Rising pore pressure lowers effective normal stress and can bring a fault to failure.
Underpressure: Pore-fluid pressure below the local hydrostatic pressure. It is the converse of overpressure and can alter fluid movement and effective stress.

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