On the orientation and patterns of wing cracks and solution surfaces at the tips of a sliding flaw or fault

Abstract

Abstract. Sliding along a preexisting flaw can result in the formation of tensile cracks where stresses concentrate near the flaw tips. These tensile cracks are referred to as wing cracks and are generally oriented oblique to the preexisting flaw. Previous studies based on linear elastic fracture mechanics (LEFM) showed that the kink angle depends on the ratio of normal to shear loading on the flaw. We present analytical solutions for cohesive end zone (CEZ) flaw models and find that the relationship between kink angle and load differs significantly from that for LEFM flaws. Furthermore, the remote flaw-parallel normal stress may significantly reduce or increase the kink angle, especially for CEZ flaws with large end zones. These results suggest that multiple interpretations are possible for some measured kink angles. In some materials, solution surfaces may form at the tip of the sliding flaw. By considering the angle between wing cracks and solution surfaces it is possible to determine whether the LEFM or CEZ model is more appropriate and thus to provide a better constrained interpretation of the boundary conditions that accompanied sliding. For some CEZ flaws the stress state in the cohesive end zone is nearly homogeneous, possibly promoting formation of arrays of opening mode cracks and solution surfaces that together form a shear zone. The CEZ flaw model can explain some orientations and patterns of cracks and solution surfaces commonly observed along natural faults that cannot be accounted for with the LEFM model.

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

“…For more realistic fracture networks with finite-sized, non-planar discontinuities, the hydromechanical behaviour can be very different and (probably) more complex. Under in-situ stresses, finite-sized fractures aligned with the maximum principal stress direction may open and even propagate due to the high tensile stresses localised at their tips (Pollard and Segall 1987); furthermore, the sliding of pre-existing discontinuities can generate stress concentration at their ends and trigger the formation of wing/secondary cracks (Willemse and Pollard 1998). These new cracks may link pre-existing structures to form critical fluid pathways and result in an enhanced connectivity and permeability.…”

Effects of T-stresses on fracture initiation for a closed crack in compression with frictional crack faces

“…Failure of crystalline solids such as ice, rock, and silicate minerals, and the forming and expansion of a strike-slip fault in geology, are attributed to compressive loading, which is generated from the weight of the upper structure or confining pressure from the surrounding medium (Brace and Bombolakis 1963;Bobet 2000;Schulson et al 2006). Although great progress has been made in understanding the mechanisms of the shear fracture of a flaw or fault in compression (Nemat-Nasser and Horii 1982;Horii and Nemat-Nasser 1986;Ashby and Hallam 1986;Shen and Stephansson 1994;Willemse and Pollard 1998;Lauterbach and Gross 1998;Renshaw and Schulson 2001;Lee and Ravichandran 2003;Healy et al 2006), the dependence of crack growth, including the kink angle of wing crack initiation and apparent fracture toughness on remote loading, is poorly understood compared to tensile fracture, and further investigation is needed.…”

Geometric and Kinematic Characteristics of Fracture System in the Sancheong Anorthosite Complex, Korea

“…인장단열은 최대 주응력 σ1 과 중간 주응력 σ2가 이루는 σ1σ2면에 평행하게 형 성되고, 기존에 형성된 인장단열은 이후의 응력장 변 화로 새로운 인장단열의 형성과 함께 전단단열로 재 활동한다 (Petit, 1988;Pollard and Aydin, 1988;Reches and Lockner, 1994;Martel and Boger, 1998). 인장단열의 방향성 및 기하학적 특성은 다수 의 단열조가 발달하는 노두에서 인장단열들의 형성과 관련된 고응력장의 방향성을 복원하거나 인장단열들 의 상대적인 시간관계(선후관계 및 공존관계) 및 전 단단열의 운동성을 연구하는데 매우 유용한 도구로써 널리 이용되어 왔다 (Hancook et al, 1984;Martel et al, 1988;Dunne and North, 1990;Rawnsley et al, 1992;Renshaw and Pollard, 1995;Rawnsley et al, 1998;Willemse and Pollard, 1998;Wilkins et al, 2001).…”