Earth Structure An Introduction to Structural Geology and Tectonics

6. Brittle Deformation Processes

Drop a glass on a hard floor and watch as it smashes into dozens of pieces; you have just witnessed an example of brittle deformation! Because you've probably broken a glass (or a plate or a vase) or have seen cracked sidewalks and roads, you already have an intuitive feel for what brittle deformation is all about. In the upper crust of the Earth, rocks undergo brittle deformation, creating a myriad of geologic structures that resemble those in shattered glass or concrete. To understand why these structures exist and how they form in rocks of the crust, we must first learn why and how brittle deformation takes place in materials in general. Our purpose in this chapter is to introduce the basic terminology used to describe brittle deformation, to explain the processes by which brittle deformation takes place, and to describe the physical conditions that lead to brittle deformation. This chapter, therefore, provides a basis for the discussion of specific brittle structures that we present in Chapters 7 and 8.