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Titolo:
Influence of compression-induced fluid pressures on rock strength in the brittle crust
Autore:
Simpson, G;
Indirizzi:
Ecole Normale Super, Geol Lab, F-75231 Paris, France Ecole Normale Super Paris France F-75231 Geol Lab, F-75231 Paris, France
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
fascicolo: B9, volume: 106, anno: 2001,
pagine: 19465 - 19478
SICI:
0148-0227(20010910)106:B9<19465:IOCFPO>2.0.ZU;2-T
Fonte:
ISI
Lingua:
ENG
Soggetto:
SEDIMENTARY BASINS; REGIONAL METAMORPHISM; POROSITY REDUCTION; STRESS; FAULT; PERMEABILITY; FLOW; DEFORMATION; COMPACTION; WEAK;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
59
Recensione:
Indirizzi per estratti:
Indirizzo: Simpson, G ETH Zurich, Inst Geol, NO G 41, CH-8092 Zurich, Switzerland ETHZurich NO G 41 Zurich Switzerland CH-8092 ich, Switzerland
Citazione:
G. Simpson, "Influence of compression-induced fluid pressures on rock strength in the brittle crust", J GEO R-SOL, 106(B9), 2001, pp. 19465-19478

Abstract

Fluid pressures have an important influence on rock strength in the brittle crust. This study investigates the development of fluid overpressures andthe subsequent decrease in rock strength (differential stress at failure),induced by tectonic compression of a fluid-saturated poroelastic medium limited by a Mohr-Coulomb failure surface. It is shown that the pore pressureinduced by compression of a poroelastic medium is controlled by the rate of loading relative to the rate at which the fluid pressure can dissipate bydiffusion. Excess pore pressures may be generated by this loading mechanism if permeabilities are low, if the boundary deformation rate is fast, or if the distance between drained boundaries is large. The magnitude of the pore pressures developed, and the subsequent strength decrease, is controlledby Skempton's coefficient B, the undrained Poisson ratio v(u), and the friction angle phi. Numerical results for realistic parameter values indicate that in upper crustal settings characterized by rapid stress increases (5 x10(-10) MPa s(-1)), drainage length scales oil the order of a few kilometers, and moderate to low permeabilities (10(-18) to 10(-16) m(2)), the strength may be reduced to similar to 60% of the strength of rock containing a hydrostatic fluid pressure and to 40% of the strength of dry rock. Under undrained conditions, fluid pressures are generated in proportion to the magnitude of the differential stress. Even so, fluid pressures generated by compressive (plane strain) deformation under undrained conditions are unlikely to attain the lithostatic pressure (i.e., pf/(p(r)gz) < 1). Approximate analytic expressions are presented which enable a priori determination of compression-induced fluid pressures, and resulting rock strength modifications,in the brittle upper crust.

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Documento generato il 10/04/20 alle ore 02:43:14