In previous chapters we have discussed how rock at the surface of the Earth is affected by the atmosphere, hydrosphere, and biosphere. We now shift our focus to processes in the solid Earth system or geosphere. In this chapter, we explain how rocks respond to these tectonic forces and how geologists study the resulting geologic structures, or architecture of Earth's crust.
The main purpose of this chapter is to help you recognize certain geologic structures, understand the forces that caused them, and thus determine the geologic history of an area.
Some principles discussed in chapter 8 should help you interpret the way structures develop in an area and their sequence of development. Recognition of unconformities as well as the principles of original horizontality, superposition, and cross-cutting relationships are as important to structural geology as they are to determining relative time.
Subsequent chapters will require an understanding and knowledge of structural geology as presented in this chapter. To understand earthquakes, for instance, one must know about faults. Appreciating how major mountain belts and the continents have evolved (chapter 5) calls for a comprehension of faulting and folding. Understanding plate tectonic theory as a whole (chapter 4) also requires a knowledge of structural geology. (Plate tectonic theory developed primarily to explain certain structural features.) In areas of active tectonics, the location of geologic structures is important in the selection of safe sites for schools, hospitals, dams, bridges, and nuclear power facilities.
Also, understanding structural geology can help us more fully appreciate the problem of finding more of Earth's dwindling natural resources. Chapter 21 discusses the association of certain geologic structures with petroleum deposits and other valuable resources.
