Fractures strongly influence the permeability of geologic formations, and because most fractures in the subsurface are below the resolution of geophysical methods, predicting the spatial evolution of fracture networks is important for groundwater resources, oil and gas production, and geothermal energy. Previous researchers have established that variations in lithologic mechanical properties influence the propagation of joints and fractures in layered rocks under stable stress conditions, but few studies have addressed how instabilities in local stress fields, in conjunction with variations in rock mechanical properties, lead to fracture branching.

We investigate NE-striking fractures in the footwall of the west-dipping Sevier fault in Utah, USA, where canyons expose the sub-horizontal Jurassic Navajo Sandstone. We analyzed field data, petrographic data, and unmanned-aerial-vehicle (UAV) imagery to document the fracture network. We also used structure-from-motion (SfM) software to build a 3D virtual outcrop model, measuring 100 m high and 260 m wide, to aid our analysis of fracture network geometry, intensity, and spacing variations.

Data reveal an up-section increase in fracture intensity and decrease in spacing regularity partly accommodated by upward fracture branching. We suggest that branching was initiated by a combination of changes in mechanical behavior within cross-bed sets and twist hackle propagation associated with mixed mode fracture systems. These tree-like fracture geometries may be associated with high-velocity, earthquake-related fracture propagation events. Fracture branching strongly influences permeability and should be considered by researchers investigating fracture development in subsurface systems.

裂缝对地质地层的渗透率有很大影响，而且由于地下大部分裂缝都低于地球物理方法的分辨率，因此预测裂缝网络的空间演化对于地下水资源、油气生产和地热能具有重要意义。以前的研究人员已经确定，岩性力学性质的变化会影响稳定应力条件下层状岩石中节理和裂缝的扩展，但很少有研究解决局部应力场的不稳定性以及岩石力学性质的变化如何导致裂缝分支.

我们调查了美国犹他州西倾 Sevier 断层下盘的 NE 走向裂缝，那里的峡谷暴露了亚水平侏罗纪纳瓦霍砂岩。我们分析了现场数据、岩相数据和无人机 (UAV) 图像来记录裂缝网络。我们还使用 Structure-from-motion (SfM) 软件构建了一个 3D 虚拟露头模型，该模型高 100 m，宽 260 m，以帮助我们分析裂缝网络的几何形状、强度和间距变化。

数据显示，裂缝强度的上段增加和间距规则的减少部分是由向上的裂缝分支所调节的。我们建议分支是由交叉床组内机械行为的变化和与混合模式断裂系统相关的扭曲裂纹传播的组合引发的。这些树状裂缝几何形状可能与高速、地震相关的裂缝传播事件有关。裂缝分支对渗透率有很大影响，研究地下系统裂缝发育的研究人员应考虑这一点。