Factors controlling normal fault offset in an ideal brittle layer
Factors controlling normal fault offset in an ideal brittle layer
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DOI：
10.1029/2000jb900108
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发表时间：
2000-10-10
影响因子：
3.9
通讯作者：
Poliakov, ANB
中科院分区：
文献类型：
--
作者：
Lavier, LL;Buck, WR;Poliakov, ANB
本文通过分析理想二维弹塑性（脆性）层在无粘流体中的伸展数值实验，研究了控制正断层发育演化的物理过程。层的屈服应力是层的粘聚力与层的摩擦应力之和。断层是由层中的一个小的塑性缺陷引起的。当断层内聚力随应变减小时，得到有限的断层错距。即使在这个高度理想化的系统中，我们也可以改变六个物理参数：层的初始内聚力、层的厚度、内聚力随塑性应变的减小率、摩擦系数、缺陷尺寸和断层宽度。我们得到了两种主要的断裂行为类型：（1）多个小偏移距的大断层和（2）单个大断层可以发展很大的偏移距。我们发现，只有两个参数控制这些不同类型的断层模式：（1）脆性层厚度为一个给定的凝聚力和（2）的凝聚力与应变减少率。对于一个大的脆性层厚度（> 22公里，44兆帕的凝聚力），拉伸总是导致多个断层分布在该层的宽度。对于一个较小的脆性层厚度的故障模式是依赖于故障弱化的速度：非常吹弱化率导致一个非常大的错断和快速的弱化率导致一个不对称的地堑，并最终到一个非常大的错断。当偏移量很大时，该模型产生了一些变质核杂岩中所见的地形和断层模式的主要特征。
We study the physical processes controlling the development and evolution of normal faults by analyzing numerical experiments of extension of an ideal two-dimensional elastic-plastic (brittle) layer floating on an inviscid fluid. The yield stress of the layer is the sum of the layer cohesion and its frictional stress. Faults are initiated by a small plastic flaw in the layer. We get finite fault offset when we make fault cohesion decrease with strain. Even in this highly idealized system we vary six physical parameters: the initial cohesion of the layer, the thickness of the layer, the rate of cohesion reduction with plastic strain, the friction coefficient, the flaw size and the fault width. We obtain two main types of faulting behavior: (1) multiple major faults with small offset and (2) single major fault that can develop very large offset. We show that only two parameters control these different types of faulting patterns: (1) the brittle layer thickness for a given cohesion and (2) the rate of cohesion reduction with strain. For a large brittle layer thickness (> 22 km with 44 MPa of cohesion), extension always leads to multiple faults distributed over the width of the layer. For a smaller brittle layer thickness the fault pattern is dependent on the rate of fault weakening: a very Blow rate of weakening leads to a very :large offset fault and a fast rate of weakening leads to an asymmetric graben and eventually to a very large offset fault. When the offset is very large, the model produces major features of the pattern of topography and faulting seen in some metamorphic core complexes.