Complex, time‐dependent, and asymmetric rift geometries are observed throughout the East African Rift System (EARS) and are well documented, for instance, in the Kenya Rift. To unravel asymmetric rifting processes in this region, we conduct 2D geodynamic models. We use the finite element software ASPECT employing visco‐plastic rheologies, mesh‐refinement, distributed random noise seeding, and a free surface. In contrast to many previous numerical modeling studies that aimed at understanding final rifted margin symmetry, we explicitly focus on initial rifting stages to assess geodynamic controls on strain localization and fault evolution. We thereby link to geological and geophysical observations from the Southern and Central Kenya Rift. Our models suggest a three‐stage early rift evolution that dynamically bridges previously inferred fault‐configuration phases of the eastern EARS branch: (1) accommodation of initial strain localization by a single border fault and flexure of the hanging‐wall crust, (2) faulting in the hanging‐wall and increasing upper‐crustal faulting in the rift‐basin center, and (3) loss of pronounced early stage asymmetry prior to basinward localization of deformation. This evolution may provide a template for understanding early extensional faulting in other branches of the East African Rift and in asymmetric rifts worldwide. By modifying the initial random noise distribution that approximates small‐scale tectonic inheritance, we show that a spectrum of first‐order fault configurations with variable symmetry can be produced in models with an otherwise identical setup. This approach sheds new light on along‐strike rift variability controls in active asymmetric rifts and proximal rifted margins.

中文翻译：

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非对称裂谷动力学的控制：肯尼亚裂谷应变局部化和断层演化的数值模拟

在整个东非裂谷系统（EARS）中都观察到了复杂，随时间变化和不对称的裂谷几何形状，并且在肯尼亚裂谷等国家都有据可查。为了揭示该地区的非对称裂谷过程，我们进行了二维地球动力学模型。我们使用采用粘塑性流变，网格细化，分布随机噪声播种和自由表面的有限元软件ASPECT。与以前旨在理解最终裂谷边缘对称性的许多数值模拟研究相反，我们明确地专注于裂谷的初始阶段，以评估对应变局部化和断层演化的地球动力学控制。因此，我们将其与肯尼亚南部和中部裂谷的地质和地球物理观测联系起来。我们的模型提出了一个三阶段的早期裂谷演化，可以动态地桥接东部EARS分支的先前推断的断层构造阶段：（1）通过单个边界断层和悬挂壁地壳的挠曲来适应初始应变的位置，（2）裂壁的断层和裂谷盆地中心的上地壳断层的增加，以及（3）在盆地向形变局部化之前丧失明显的早期不对称性。这种演变可能为了解东非裂谷其他分支和全球不对称裂谷的早期伸展断裂提供了模板。通过修改近似小规模构造遗传的初始随机噪声分布，我们表明，在具有其他相同设置的模型中，可以产生具有可变对称性的一阶故障配置的频谱。这种方法为主动非对称裂谷和近缘裂谷边缘的走时裂谷变化控制提供了新的思路。