A Model of Three Faults

Grades 7-12

Adapted from the USGS Learning Web Lesson Plans

Background

One of the most frightening and destructive phenomena of nature is a severe earthquake and its terrible aftereffects. An earthquake is a sudden movement of the Earth, caused by the abrupt release of strain that has accumulated over a long time. For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that form the Earth's surface slowly move over, under and past each other. Sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free. If the earthquake occurs in a populated area, it may cause many deaths and injuries and extensive property damage.

Today we are challenging the assumption that earthquakes must present an uncontrollable and unforecastable hazard to life and property. Scientists have begun to estimate the locations and likelihoods of future damaging earthquakes. Sites of greatest hazard are being identified, and designing structures that will withstand the effects of earthquakes.

Materials

Objective

Students will observe fault movements on a model of the earth's surface.

Time Needed

1 or 2 Class periods

Materials Needed (per group)

Instructions

  1. Have students work in pairs or small groups.
  2. Display the fault models in the classroom after the activity.
  3. An excellent world physiographic map, showing the ocean floor, can be obtained from the National Geographic Society.

Application Phase

  1. Explain that faults are often (but not always) found near plate boundaries and that each type of fault is frequently associated with specific types of plate movements. However, you can probably find all types of fault movement associated with each type of plate boundary.
  2. Ask the following questions:
  3. Explain that not all faults are associated with plate boundaries. Explain that there is a broad range of faults based on type, linear extension, displacement, age, current or historical activity and location on contintental or oceanic crust. Have students research examples of non-plate boundary faults.
  4. Explain to students that the stresses and strains in the earth's upper layers are induced by many causes: thermal expansion and contraction, gravitational forces, solid-earth tidal forces, specific volume changes because of mineral phase transitions, etc. Faulting is one of the various manners of mechanical adjustment or release of such stress and strain.
  5. Have students research and report on the types of faults found in your state.

Extension

  1. Have students Identify the fault movements in the recent Loma Prieta, California earthquake.
  2. Have students research the fault histories and recent theories concerning the Northridge, California Earthquake, the New Madrid, Missouri , and the Anchorage, Alaska fault zones.

Coloring Key


Part 1

Exploration Phase

  1. You may wish to introduce this activity by asking students:
  2. Illustrate compressive earth movements using a large sponge by squeezing from both sides, causing uplift. Using a piece of latex rubber with a wide mark drawn on it, illustrate earth tension, by pulling the ends of the latex to show stretching and thinning.
  3. Have students construct a fault model using the Fault Model Sheet. Instructions to students:
  4. Color the fault model that is included according to the color key provided.

    Note that an enlarged version of the fault block model can be made for classroom demonstrations.

  5. Have students develop a model of a normal fault.

Concept Development

  1. Ask the following questions:
  2. Explain that this type of fault is known as a normal fault.
  3. Have students label their drawing "normal fault".
  4. Many normal faults are found in Nevada. This is because Nevada is located in a region called the Basin and Range Province where the lithosphere is stretching.

Part 2

Exploration Phase

Have students develop a model of a thrust fault. Instructions to students:

Locate points C and D on your model. Move Point C next to point D. Observe the cross-section of your model.
Have students draw the thrust fault as represented by the model they have just constructed.

Concept Development

  1. Ask the following questions:
  2. Explain that this type of fault is known as a thrust fault.
  3. Have students label their drawing "thrust fault".
  4. An example of a thrust fault is the fault in which the Northridge earthquake occurred. The thrusting movement raised the mountatins in the area by as much as 70 cm.

Part 3

Exploration Phase

Have students develop a model of a strike-slip fault. Instructions to students:

Locate points F and G on your model. Move the pieces of the model so that point F is next to point G.
Have students draw an overhead view of the surface as it looks after movement along the fault.

Concept Development

  1. Ask the following questions:
  2. Explain that this type of fault is known as a strike-slip fault.
  3. Have students label their drawing "strike-slip fault".
  4. Explain to the students that a strike-slip fault can be described as having right or left-lateral movement. If you look directly across the fault, the direction that the opposite side moved defines whether the movement is left-lateral or right-lateral. The San Andreas fult in California is a right-lateral strike-slip fault.

Model