Impact of fluid pressure on failure mode in shear zones: Numerical simulation of en-echelon tensile fracturing and transition to shear
Impact of fluid pressure on failure mode in shear zones: Numerical simulation of en-echelon tensile fracturing and transition to shear
复制标题
流体压力对剪切区破坏模式的影响：梯形拉伸断裂和剪切过渡的数值模拟
DOI：
10.1016/j.tecto.2019.228277
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发表时间：
2020
期刊：
影响因子：
2.9
通讯作者：
Ito Takatoshi
中科院分区：
文献类型：
--
作者：
Okamoto Atsushi;Fuse Kazumasa;Shimizu Hiroyuki;Ito Takatoshi
雁列脉是在一定条件下剪切带形成过程中形成的一组张性裂缝，但控制裂缝形态的因素尚不清楚。在这项研究中，我们进行了数值模拟，使用二维离散元方法来了解在剪切变形过程中的有效正应力对裂缝的发展的影响。在低有效正应力（10 MPa）下，膨胀发生在与剪切边界成40° ~ 45 °的方向，张性裂缝呈雁列排列。在高有效正应力（150 MPa）下，雁列脉不发育，但形成明显的剪切面。中间有效正应力（~ 50 MPa）的瞬态行为特征：早期张裂纹产生，然后扩展形成较大的脆性断层。在这种情况下，在后期释放的较大应变能是由于较大的剪切强度。在地壳条件下，由于流体压力的变化，有效正应力会发生变化。我们的研究结果表明，雁列脉是高流体压力的指示，接近岩石静压力条件，即有效正应力接近于零，并且响应于流体压力的动态变化，破坏模式可能会从拉伸转变为剪切。在压裂过程中。
En-echelon veins are a set of tensile fractures that develop during the initiation of shear zones under certain conditions, but factors that control fracture patterns remain unclear. In this study, we performed numerical simulations using the two-dimensional distinct element method to understand the influence of effective normal stress on the development of fractures during shear deformation. At low effective normal stress (10 MPa), dilation takes place at an angle of ≈40°–45° to the shear boundary, and en-echelon arrays of tensile fractures develop. In contrast, at high effective normal stress (150 MPa), en-echelon veins are not developed, but a distinct shear plane forms. A transient behavior characterizes intermediate effective normal stress (≈50 MPa): early tensile cracks are generated and then propagate to form larger brittle faults. In this case, the larger strain energy released in the later stage is due to the greater shear strength. Under crustal conditions, effective normal stress varies, due to the change in fluid pressure. Our results suggest that en-echelon veins are indicators of high fluid pressure, close to lithostatic conditions, i.e. effective normal stress close to zero, and that a transition of the failure mode from tensile to shear could occur in response to a dynamic change of fluid pressure during fracturing.