Forces in the Earth – Faults!

Physical Science Notes10/4/2012

Faults Fault

• Definition: a fault is a fracture in the Earth where rock movement occurs. This can happen either on the surface or deep beneath the Earth’s surface.

• Faults occur at tectonic plate boundaries

Faults Fault

• There are three types of plate boundaries:– Convergent: plates

pushed together by compression forces

– Divergent: plates pulled apart by tension forces

– Transform: plates sliding past each other with shearing forces

Faults Normal Fault • Definition: A normal

fault is a fault caused by tension forces at a divergent plate boundary. As a result, rock above the fault moves downward relative to rock below the fault surface.

Faults Reverse Fault • Definition: A reverse

fault is a fault caused by compression forces at a convergent plate boundary. As a result, rock above the fault moves upward relative to rock below the fault surface.

Faults Strike-Slip

Fault• Definition: A strike-slip

fault is a fault caused by shearing forces at a transform plate boundary.

Faults Elastic Limit • Definition: Elastic limit

measures the farthest something can bend or stretch and still return to its original shape without breaking

• Example: Stretching a rubber band. If it snaps, you are past the elastic limit.

Summarize!

• After you summarize, you may begin the homework assignment (summarizing and illustrating each type of plate boundary: convergent, divergent, and transform)

• In your notes, please answer the following question in complete sentences:

“How do yesterday’s activities with the Play-Doh, paperclips, and balloons relate to these two terms, fault & elastic limit?”

Faults

Compression & Transverse Waves

• What do you think a compression wave on a spring or slinky would look like? Use your prior knowledge of what compression is (including what you just learned about different forces making faults in the Earth).

Demo!

Which wave is faster?• Make a graph comparing the distance from the

earthquake focus and the time it took for each kind of wave to travel there.

• Set up your graph:– Title: “Compression and Transverse Waves”– X-axis: “Distance from focus (km)” – should go from

250 to 1000 km– Y-axis: “Time of Arrival (hr: min: sec)” – should go

from 4 hours to 4 hours: 22 minutes: 45 seconds– Key: which color will stand for compression and

which for transverse waves

Distance from focus (km)

Time of ArrivalHr: Min: Sec

COMPRESSION WAVE

Time of ArrivalHr: Min: SecTRANSVERSE

WAVE

250 4:01:00

500 4:03:00

1000 4:02:30

1750 4:04:00

2000 4:07:30

3000 4:10:15

4500 4:08:00

5000 4:15:00

6000 4:09:30

7250 4:18:00

8000 4:11:45

8250 4:21:25

9000 4:12:30

9500 4:22:45

Conclude & Apply:Answer questions under your graph

• Based on your graph, which is faster – a compression wave or a transverse wave?

• Do the waves remain the same distance apart as they travel?

• Do they grow closer together or farther apart over time?

• How could you use your graph to fill in the missing arrival times in the chart?

• Use your observations to tell why compression waves are called primary waves and transverse waves are called secondary waves.