Activity 77: Our Fractured Earth: A Look at Fault Lines

Types of Faults

Directions: Draw an illustration showing each of the faults specified in Items

1 through 5. Then write answers to Items 6 and 7. Notice that the fault listed in

Item 5 has not been covered in this activity. You will need to conduct Internet

research to learn about it.

1. Right lateral fault

If the block on the far side moves to the right, the fault is called right-lateral. The fault motion of a strike-slip fault is caused by shearing forces.

2. Left lateral fault

In a strike-slip fault, the movement of blocks along a fault is horizontal. If the block on the far side of the fault moves to the left, as shown in this animation, the fault is called left-lateral.

3. Normal fault

In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by tensional forces and results in extension.

4. Reverse fault

In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of the fault plane is small.

5. Blind fault

An earthquake along a thrust fault that has not been mapped by standard surface geological mapping, hence the designation "blind" [1]. Although such earthquakes are not amongst the most violent, they sometimes constitute the most deadly, as conditions combine to form a classic urban earthquake which greatly affects urban seismic risk.

6. Normal faults and reverse faults are both called “dip-slip” faults. How do you suppose they got this name?

One side moves up or relative to the other side.

7. View a Web site that contains a map showing Earth’s tectonic plates. What is the name of the plate in your

part of the world? North American Plate

TechCONNECT © by the McGraw-Hill Companies, Inc.