Coulomb subduction zone wedge mechanics
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摘要:
楔形体理论研究楔形体在底部摩擦力、重力和边界外力共同作用下内部的应力状态，有助于我们定量分析断层强度和岩石性质与楔形体稳定状态之间的关系.本文首先简要介绍基于不同楔形体材料而得出的应力解析解.然后介绍基于理想弹塑性材料的俯冲带库仑楔应力解析解.最后介绍基于该解析解而提出的动态库仑楔形体理论.俯冲带地震反射剖面数据表明，弧前靠近海沟部分地表坡度比较陡，其内部经历复杂永久塑性变形（称为外部楔形体，outer wedge）.而靠近内陆部分地表坡度比较平缓，反射剖面显示沉积层呈水平规则分布，常伴随沉积盆地（称为内部楔形体，inner wedge）.动态库仑楔形体理论认为弧前这种地表形态和内部构造特征的不同，可能反映了断层面摩擦性质的差异性.内部楔形体对应于断层面上的生震带，在地震周期可能主要经历弹性变形.而外部楔形体对应于断层面上的无震蠕滑部分，在地震发生时可能产生塑性破坏、永久变形.
Abstract:Wedge mechanics derives the stress status of a wedge due to the basal friction, gravitational force and boundary forces, and thus helps to quantitatively analyze the relationship between the fault strength and rock properties and the stability of the wedge. This paper summarizes analytical stress solutions in wedges with different rock materials. Then it introduces the dynamic Coulomb wedge theory based on an analytical solution of an elastic perfectly-plastic Coulomb subduction zone wedge. Seismic reflection profiles have indicated that the frontal forearc near the trench has a steeper surface slope and undergoes complicated permanent plastic deformation (outer wedge). The farther landward features flatter surface slope and smooth horizontal sedimentary layers and generally has sediment basins (inner wedge).The dynamic Coulomb wedge theory postulates that the contrasts of the geometry and deformation pattern between the outer and inner wedges may be due to the difference in the basal frictional property. The basal fault underlying the inner wedge is seismogenic, and the inner wedge may undergo mostly elastic deformation in earthquake cycles. However, the outer wedge overlies stable-sliding portion of the fault and may undergo plastic failure with permanent deformation.
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Key words:
- Wedge /
- Analytical stress solution /
- Fault frictional property /
- Forearc deformation
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图 1
楔形体应力解析解和海沟增生楔地震反射剖面[(a) 修改自Yin and Kelty(2000)图 3.(b)来自Hu and Wang (2006)图 1b.(c)来自Wang and Hu (2006)图 2a]
Figure 1.
Analytical stress solutions in the wedge and a seismic reflection profile in an accretionary prism [(a) Modified from Fig. 3 in Yin and Kelty (2000). (b) From Fig. 1b in Hu and Wang (2006). (c) From Fig. 2a in Wang and Hu (2006)]
图 3
楔形体内部应力状态随底部有效摩擦系数变化图[修改自Wang and Hu(2006)图 7]
Figure 3.
Stress status in a wedge with a varying basal effective frictional coefficient [Modified from Fig. 7 in Wang and Hu (2006)]
图 4
(a) 大坝和(b)三角形悬臂梁受力示意图
Figure 4.
Illustration of the stress status in (a) a dam and (b) a triangle-shaped hanging beam
图 5
外部和内部楔形体地震周期应力演化[(a)修改自Wang and Hu(2006)图 9a.(b)修改自Wang and Hu (2006)图 11a]
Figure 5.
Earthquake-cycle stress evolution in an outer wedge and an inner wedge [(a) Modified from Fig. 9a in Wang and Hu (2006). (b) Modified from Fig. 11a in Wang and Hu (2006)]
图 6
弧前外部和内部楔形体地震周期应力演化[修改自Wang and Hu (2006)图 12]
Figure 6.
The earthquake-cycle stress evolution of the outer and inner wedge in a forearc [Modified from Fig. 12 in Wang and Hu (2006)]
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