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Physical Processes in Earth and Environmental Sciences Phần 6

Ảnh hưởng của áp suất chất lỏng lỗ chân lông trong sự hình thành vết nứt. (a) Với sự khác biệt giữa cao nhấn mạnh gãy xương Coulomb có thể được sản xuất khi các vòng tròn Mohr di chuyển sang bên trái do áp lực chất lỏng lỗ chân lông. | 156 Chapter 4 Fig. 4.91 Effect of pore fluid pressure in fracture formation. a With high differential stresses Coulomb fractures can be produced when the Mohr circle moves to the left by pore fluid pressure. b With low differential stresses even when the applied stress may be compressive and fully located in the field of stress stability fluid pore pressure can reduce the effective stress displacing the circle to the tensile field and producing joints if the condition E 3 To is satisfied. to a lower level while maintaining the differential stress Fig. 4.91 . With low differential stresses even when the applied stress may be compressive and fully located in the field of stress stability fluid pore pressure can reduce the effective stress displacing the circle to the tensile field and producing joints if the condition Eo-3 T0 is satisfied. 4.15 Faults are fracture surfaces or zones where several adjacent fractures form a narrow band along which a significant shear displacement has taken place Fig. 4.92a b . Although faults are often described as signifying brittle deformation there is a transition to ductile behavior where shear zones develop instead. As described in Section 4.14 shear zones show intense deformation along a narrow band where cohesive loss takes place on limited discontinuous surfaces Fig. 4.92c . Faults are commonly regarded as large shear fractures though the boundary between features properly regarded as shear fractures or joints is not sharply established. In any case although millimeter-scale shear fractures are called microfaults faults may range in length of order several decimeter to hundreds of kilometers they can be localized features or of lithospheric scale defining plate boundaries Section 5.2 . Displacements are generally conspicuous Fig. 4.93 and can vary from 10 3 m in hand specimens or outcrop scale to 105 m at regional or global scales. Faults can be recognized in several ways indicating shear displacement either by the presence of .