Chapter 5 Section 1 What processes change Earth’s crust? Objective: Compare and contrast the processes of folding and faulting in Earth’s crust.

Key Terms anticline: upward fold syncline: downward fold fracture: break in a rock fault: break in Earth’s crust along which movement occurs

Folding Earth’s surface is always changing. Some changes occur very suddenly. Others take hundreds or thousands of years, or even longer. Over millions of years, pressure in Earth’s crust can cause rock layers to bend, curve, and wrinkle. This is called folding. Folding occurs when rock layers are squeezed from the sides. The rocks may crack under the pressure. However, the layers stay together.

Folding Folds in rock look like waves. An upward fold is called an anticline. A downward fold is called a syncline. Some folds are small enough to be seen in a single rock. Others are very large. You often see anticlines and synclines along roads cut through rock.

Anticline Syncline

DEFINE: What is a fold?

Faulting Pressure deep inside Earth can also break rocks. A break in a rock is called a fracture. When movement of rock takes place along a fracture, it is called a fault. Four common faults are shown in the figure.

Faulting Faulting causes rocks to move up and down or side to side a tiny distance. Each time movement occurs along a fault, the pressure between rock layers along the fault eases. Then, the pressure builds up again. Movement occurs again when this pressure is released.

2. DESCRIBE: What is a strike-slip fault?

San Andreas Fault There is a huge strike-slip fault that runs through a large part of California. This fault is called the San Andreas Fault. The San Andreas Fault extends from the Gulf of California through San Francisco Bay. The fault reaches more than 30 km down into Earth’s crust.

San Andreas Fault Movement along this fault caused the great San Francisco Earthquake of 1906. In 1989, another earthquake hit Santa Cruz and the Bay area. In 1994, an earthquake in the Northridge area put further stress on the San Andreas Fault and other faults nearby. Areas with networks of faults, such as southern California, have many earthquakes.

3. INFER: Why would a network of faults have many earthquakes?

Classwork CHECKING CONCEPTS What is a fracture? Which way does a syncline fold? What do rock layers that change shape but do not move form? What do rock layers that break but do not move form? What do rock layers that break and move form?

Classwork THINKING CRITICALLY 6. INFER: What slowly changes Earth’s crust? 7. INFER: What suddenly changes Earth’s crust?

Classwork INTERPRETING VISUALS Use the figure of the four common types of faults to answer the following questions. 8. IDENTIFY: Along which fault is the movement horizontal? 9. COMPARE/CONTRAST: How is the movement along a reverse fault similar to and different from that along the normal fault? 10. INFER: Why do you think the thrust fault was given its name?