Book contents
- Frontmatter
- Contents
- Preface
- Preface to the Second Edition
- ONE Plate Tectonics
- TWO Stress and Strain in Solids
- THREE Elasticity and Flexure
- FOUR Heat Transfer
- FIVE Gravity
- SIX Fluid Mechanics
- SEVEN Rock Rheology
- EIGHT Faulting
- NINE Flows in Porous Media
- TEN Chemical Geodynamics
- APPENDIX ONE Symbols and Units
- APPENDIX TWO Physical Constants and Properties
- Answers to Selected Problems
- Index
TWO - Stress and Strain in Solids
- Frontmatter
- Contents
- Preface
- Preface to the Second Edition
- ONE Plate Tectonics
- TWO Stress and Strain in Solids
- THREE Elasticity and Flexure
- FOUR Heat Transfer
- FIVE Gravity
- SIX Fluid Mechanics
- SEVEN Rock Rheology
- EIGHT Faulting
- NINE Flows in Porous Media
- TEN Chemical Geodynamics
- APPENDIX ONE Symbols and Units
- APPENDIX TWO Physical Constants and Properties
- Answers to Selected Problems
- Index
Summary
Introduction
Plate tectonics is a consequence of the gravitational body forces acting on the solid mantle and crust. Gravitational forces result in an increase of pressure with depth in the Earth; rocks must support the weight of the overburden that increases with depth. A static equilibrium with pressure increasing with depth is not possible, however, because there are horizontal variations in the gravitational body forces in the Earth's interior. These are caused by horizontal variations in density associated with horizontal differences in temperature. The horizontal thermal contrasts are in turn the inevitable consequence of the heat release by radioactivity in the rocks of the mantle and crust. The horizontal variations of the gravitational body force produce the differential stresses that drive the relative motions associated with plate tectonics.
One of the main purposes of this chapter is to introduce the fundamental concepts needed for a quantitative understanding of stresses in the solid Earth. Stresses are forces per unit area that are transmitted through a material by interatomic force fields. Stresses that are transmitted perpendicular to a surface are normal stresses; those that are transmitted parallel to a surface are shear stresses. The mean value of the normal stresses is the pressure. We will describe the techniques presently used to measure the state of stress in the Earth's crust and discuss the results of those measurements.
- Type
- Chapter
- Information
- Geodynamics , pp. 73 - 104Publisher: Cambridge University PressPrint publication year: 2002