Chapter 7

Earthquakes

7.1 Stress in the Earth’s Crust.

Lesson Objectives

• List the different types of stresses that cause different types of deformation.


• Compare the different types of folds and the conditions under which they form.


• Compare fractures and faults and define how they are related to earthquakes.


• Compare how mountains form and at what types of plate boundaries.

Introduction

When you think about enormous plates of lithosphere traveling around on the planet’s
surface, you can probably imagine that the process is not smooth. Most geological activity
takes place where two plates meet, at plate boundaries. In the Earthquakes chapter, you will
learn that nearly all earthquakes, volcanic eruptions, and mountain building occur at plate
boundaries. In this chapter, you will learn more about the geological activity that occurs
because of plate tectonics, specifically mountain building and earthquakes.

When plates are pushed or pulled, the rock is subjected to stress. Stress can cause a rock
to change shape or to break. When a rock bends without breaking, it folds. When the rock
breaks, it fractures. Mountain building and earthquakes are some of the responses rocks
have to stress.