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Chapter 1
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Chapter 4
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Chapter 6
Chapter 7
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Chapter 9
Chapter 10
Chapter 11
Chapter 12

Chapter 6: Force, Traction, and Stress

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In this chapter we define the relationships among forces, tractions, and stresses. Structures develop as the rocks of the earth’s crust strain and flow, and the distribution of this deformation is related to the stresses acting within the rock mass and the tractions acting on its surfaces. In the context of a deformable solid the stress is associated with strain and in the context of a flowing fluid the stress is associated with the rate of deformation. In most natural examples the stress varies with position and time: it is a field quantity with spatial and temporal variations. For example, the frontispiece for this chapter is a photographic visualization of the distribution of shear stress in the grains of a model sandstone (Gallagher et al., 1974). An understanding of the possible variations of these fields in the earth is of fundamental importance to structural geologists.