Facets formed along the footwalls of active normal‐fault blocks display a variety of longitudinal profile forms, with variations in gradient, shape, degree of soil cover, and presence or absence of a slope break at the fault trace. We show that a two‐dimensional, process‐oriented cellular automaton model of facet profile evolution can account for the observed morphologic diversity. The model uses two dimensionless parameters to represent fault slip, progressive rock weathering, and downslope colluvial‐soil transport driven by gravity and stochastic disturbance events. The parameters represent rock weathering and soil disturbance rates, respectively, scaled by fault slip rate; both can be derived from field‐estimated rate coefficients. In the model's transport‐limited regime, slope gradient depends on the ratio of disturbance to slip rate, with a maximum that represents the angle of repose for colluvium. In this regime, facet evolution is consistent with nonlinear diffusion models of soil‐mantled hillslope evolution. Under the weathering‐limited regime, bedrock becomes partly exposed but microtopography helps trap some colluvium even when facet gradient exceeds the threshold angle. Whereas the model predicts a continuous gradient from footwall to colluvial wedge under transport‐limited behavior, fully weathering‐limited facets tend to develop a slope break between footwall and basal colluvium as a result of reduced transport efficiency on the rocky footwall slope. To the extent that the model provides a reasonable analogy for natural facets, its behavior suggests that facet profile morphology can provide useful constraints on relative potential rates of rock weathering, soil disturbance, and fault slip.

中文翻译：

---

模拟正断面的形状和演化

沿活动法向断层块的下盘壁形成的小面显示出各种纵向剖面形式，坡度，形状，土壤覆盖度以及断层迹线上是否存在斜坡折断的变化。我们表明，面向刻面轮廓演变的二维，面向过程的细胞自动机模型可以解释观察到的形态多样性。该模型使用两个无因次参数来表示断层滑动，渐进岩石风化和重力和随机扰动事件驱动的下坡冲积土壤输运。这些参数分别表示岩石的风化率和土壤扰动率，并由断层滑动率标定。两者都可以从现场估计的速率系数中得出。在模型的运输受限状态下，坡度取决于干扰与滑移率的比率，具有代表崩落休止角的最大值。在这种情况下，小面演化与土壤覆盖的山坡演化的非线性扩散模型是一致的。在受风化限制的条件下，基岩会部分暴露，但微地形可以帮助捕获一些坡度，即使小平面坡度超过阈值角也是如此。该模型预测，在运输受限的情况下，从下围墙到坡面楔形的坡度将是一个连续的梯度，而由于在岩石下围墙边坡上运输效率的降低，完全受天气影响的刻面往往会在下围墙和基底储层之间形成坡度折断。在一定程度上，该模型为自然面提供了合理的类比，其行为表明，面剖面形态可以为岩石风化的相对潜在速率提供有用的约束，