Slip on normal faults induced by surface processes after the cessation of regional extension—Insights from three-dimensional numerical modelling
Slip on normal faults induced by surface processes after the cessation of regional extension—Insights from three-dimensional numerical modelling
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区域伸展停止后地表过程引起的正断层上的滑动——三维数值模拟的见解
DOI：
10.1016/j.geomorph.2013.12.008
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发表时间：
2014
期刊：
影响因子：
3.9
通讯作者：
Hampel
中科院分区：
文献类型：
--
作者：
Turpeinen;Maniatis;Hampel
在活跃伸展的地区，正断层作用产生的地形不断受到侵蚀、沉积物搬运和沉积的影响。正如以前的数值模型与构造和地表过程之间的充分耦合所示，地球表面的质量重新分布通过影响地壳的应力状态来加速断层的速率。然而，如果作为断层活动主要驱动力的区域伸展停止，断层滑动如何作为持续的地表过程的结果而演变仍然是未知的。在这里，我们使用三维有限元建模表明，表面过程正常故障边界山脉可能会持续断层滑动数百万年，即使在区域扩张已经停止。该模型包括两个连续的阶段。在第一阶段，正断层积累位移由于拉伸边界条件，而侵蚀和沉积物沉积是活跃的模型表面上。在第二阶段开始时，停止模型的扩展，同时表面过程保持活跃。结果表明，在大多数模型中，正断层在第二阶段以~ 20 ~~ 70 m/Ma的速率持续1 Ma以上。在一些实验中，正常的滑动保持约3马，而在其他模型中，一个短阶段的正常断层其次是缓慢的反向滑动。在第二个模型阶段，在不同的实验中，最大的正常滑动量达到90米。如果通过将扩散常数增加5倍来加强侵蚀，则断层以更快的速率（即在更短的时间内）积累额外的正滑。相比之下，河流侵蚀常数的五倍变化不会显着影响断层滑动演化。断层倾角和长度的变化有一个类似的影响的持续时间的阶段与额外的正常滑动的扩散常数的变化。断层滑动演化与剥蚀速率和沉积速率的时间演化相关，在伸展结束后，剥蚀速率和沉积速率逐渐减小。最后，断层滑动行为是由差异应力的演变，这是随着时间的推移，由于在模型表面上的质量的重新分配，引起的侵蚀，泥沙运移和沉积的变化。我们的研究结果意味着，个别正断层可能仍然活跃，即使区域扩展停止，因为表面过程继续修改故障生成的地形。
In regions of active extension, normal faulting generates topography that is continuously modified by erosion, sediment transport and deposition. As shown by previous numerical models with full coupling between tectonics and surface processes, the redistribution of mass at the Earth's surface accelerates the rate of faulting by affecting the stress state of the crust. It remains unknown, however, how fault slip evolves as a result of ongoing surface processes if regional extension as the main driver of faulting ceases. Here we use three-dimensional finite-element modelling to show that surface processes acting on normal-fault bounded mountain ranges may sustain fault slip for millions of years even after regional extension has stopped. The models consist of two successive phases. During the first phase, the normal fault accumulates displacement owing to an extensional boundary condition, while erosion and sediment deposition are active on the model surface. At the beginning of the second phase, extension of the model is stopped while the surface processes remain active. The results show that in most models normal faulting continues during the second phase at rates of ~ 20 to ~ 70 m/Ma for more than 1 Ma. In some experiments, normal slip is maintained for ~ 3 Ma, whereas in other models, a short phase of normal faulting is followed by slow reverse slip. The maximum amount of normal slip in different experiments reaches up to 90 m during the second model phase. If erosion is intensified by increasing the diffusion constant by a factor of 5, the fault accumulates the additional normal slip at a faster rate, i.e. during a shorter time period. In contrast, a five-fold variation of the fluvial erosion constant does not significantly affect the fault slip evolution. Variations of the fault dip and length have a similar effect on the duration of the phase with additional normal slip as variations of the diffusion constant. The fault slip evolution is correlated with the temporal evolution of the erosion and sedimentation rates, which decrease more or less gradually after the end of extension. Ultimately, the fault slip behaviour is controlled by the evolution of the differential stress, which varies through time due to the redistribution of mass on the model surface that is induced by erosion, sediment transport and deposition. Our results imply that individual normal faults may remain active even if regional extension ceases because surface processes continue to modify the fault-generated topography.
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