7-1 Forces in Earth’s Crust 7-3 Monitoring Earthquakes Earthquakes – Comp. Sci. 2.

7-1 Forces in Earth’s Crust

7-3 Monitoring Earthquakes

Earthquakes – Comp. Sci. 2

Vocabulary 7.1

Stress

Compression

Shearing

Normal Fault

Reverse Fault

Strike-slip Fault

Plateau

3 Kinds of Stress in Earth’s Crust pg. 223

As Earth’s plates move, they can bend or fold rock. Forces created by movement of the Earth’s plates are examples of stress. Stress adds energy to rock until the rock changes shape or breaks.

Three kinds of stress can occur in the Earth’s crust –

tension, compression, and shearing. All three work over millions of years to change the shape and

volume of rock.

Tension, compression, and shearing work over millions of years to change the shape and volume of rock

How Does Stress Change Earth’s Crust? Pg. 223

Tension-Tension is the stress force that pulls on the crust and thins the rock in the middle. It occurs where two plates pull apart.

1st kind of stress can occur in the crust.

How Does Stress Change Earth’s Crust? Pg. 223

Compression- Compression is the stress force that squeezes rock until it folds or breaks. It occurs where two plates come together and push against each other.

2nd kind of stress can occur in the crust.

How Does Stress Change Earth’s Crust? Pg. 223Stress can push, pull, or squeeze rock in Earth’s

crust.

Shearing-Shearing is the stress force that pushes rock in two opposite directions. It occurs where two plates slip past each other.

3rd kind of stress can occur in the crust.

Stress in Earth’s CrustStress can push, pull, or squeeze rock in Earth’s crust. Three kinds of stress can occur in the crust.

APPLY CONCEPTS

Look at the pair of arrows in the second diagram.

These arrows show how tension affects rock. Draw a pair of arrows on the third diagram to show how compression affects rock.

Then draw a pair of arrows on the bottom diagram to show how shearing acts on rock

Assess Your Understanding pg. 223I get it! Now I know that stress changes Earth’s crust by changing the ____________________________________

________________________________________________

How Do Faults Form? Pg. 224

When enough stress builds up in rock, the rock breaks and makes a fault.

The three main types of faults are:

normal faults

reverse faults

strike-slip faults

How Do Faults Form? Normal FaultsNormal faults form where rock is pulled apart by tension in Earth’s crust. The block above is angled fault called the hanging wall. The rock below the fault is called the footwall. The hanging wall slips downward when rock moves along the fault.

Reverse FaultsA reverse fault has the same structures as a normal fault, but the hanging wall moves up and the footwall moves down. Reverse faults form where compression pushes the rock of the crust together.

Strike-Slip FaultsShearing produces strike-slip faults. The rocks on either side of a strike-slip fault slip past each other and have little up or down motion. A strike-slip fault that forms the boundary between two plates is called a transform boundary.

Faults pgs. 224-225The three main types of faults are defined by the direction in which rock moves along the fault.

Apply It! Pg. 225The low angle of a thrust fault allows rock in the hanging wall to be pushed great distances. For example, over millions of years, rock along the Lewis thrust fault in Glacier National Park has moved 80 kilometers.

1.Identify- Based on the arrows showing fault movements in the diagram, a thrust fault is a type of (normal fault, reverse fault).

2. Challenge – Why might the type of rock in the hanging wall of the Lewis thrust fault be different from the type of rock in the footwall?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Assess Your Understanding pg. 2251a. Review – When enough stress builds up in brittle rock, the rock breaks causing a ____________________.

b. Infer- A geologist sees a fault along which blocks of rock in the footwall have moved higher relative to blocks of rock in the hanging wall. What type of fault is this?______________________________

I got it! Now I know that faults form when ____________________

___________________________________________________________________________________________________________________________________________________________

How Does Plate Movement Create New Landforms? Pg. 226

Over millions of years, the forces of plate movement can change a flat plain into features such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

Folding pgs. 226-227

Folding Earth’s Crust

Folds are bends in rock that form when Earth’s crust is compressed and gets shorter and thicker. A fold in rock that bends upward into an arch is an anticline. A fold that bends downward in a V shape is a syncline.

Anticlines and SynclinesCompression can cause folds in the crust. Two types of folding are anticlines, which arch up, and synclines, which dip down.

Fault Block MountainStretching Earth’s Crust

Tension forces create normal faults where two plates move away from each other. A fault-block mountain forms when the hanging walls of two normal faults drop down on either side of the footwall.

Tension and Normal FaultsAs tension forces pull the crust apart, two normal faults can form a fault-block mountain range.

Forces in Earth’s Crust – Figure 2

Tension and Normal FaultsAs tension forces pull the crust apart, two normal faults can form a fault-block mountain range, as you can see in the diagram.

PredictLabel the hanging wall and the two footwalls in diagram A.

in diagram B, draw the new position of the hanging wall after movement occurs. Describe what happens._____________________________________________________________________________________________________________________________________________________________________

PlateauUplifting Earth’s Crust

Forces can also raise plateaus. A plateau is a large area of flat land that was lifted up high above sea level.

The Kaibab PlateauLook at the sequence of drawings. In your own words, describe what happens in the last two diagrams.

Assess Your Understanding pg. 2292a. Review- Normal Faults often occur when two plates (come together / putt apart)

b. Interpret Diagrams – Look at the diagram that accompanies the photograph in Figure 5. Does the block of rock in the middle move up as a result of movement along the normal faults? Explain.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________

I get it! Now I know that plate movements create new features by

________________________________________________________________________________________________________________________________________________________________________________________________________________________________

7-2 Earthquakes and Seismic Waves

Vocabulary 7.2

1. Earthquake

2. Focus

3. Epicenter

4. P wave

5. S wave

6. Surface wave

7. Seismograph

8. Modified Mercalli scale

9. Magnitude

10.Richter Scale

11.Moment magnitude scale

Earthquakes and Seismic Waves

Earthquakes start below the surface of the Earth. An earthquake's seismic waves carry energy up toward the surface and down through the interior.

Seismic waves are vibrations that are similar to sound waves. They travel through Earth carrying energy released by an earthquake

1.Look at the drawing showing Earth’s interior. At which point(s) can seismic waves be detected?A onlyA and BA, B, and C

2. Infer – At which point do you think the seismic waves will have the most energy? Why?________________________________________________________________________________________________________________________

What Are Seismic Waves? Pg. 231

Plate movement increases the stress along a fault until the rock slips or breaks and an earthquake begins. An earthquake is the shaking and trembling that happens when rock under Earth’s surface moves. The focus is the place under Earth’s surface where rock starts to move. The point on the surface directly above the focus is called the epicenter.

Some of the energy released during

an earthquake travels through Earth

in the form of seismic waves. Seismic

waves travel out in every direction

from the focus.

Types of Seismic WavesP – Waves (A)The first waves to arrive, also known as primary waves. P waves compress and expand the ground like an accordion. P waves can damage buildings. P waves travel through solids and liquids.

S – Waves (B)After primary waves come secondary waves or S waves. S waves are seismic waves that can vibrate from side to side or up and down. Their vibrations are at an angle of 90 degrees to the direction that they travel. When S waves reach the surface, they shake structures violently. S waves cannot travel through liquids.

Surface Waves (C)When P and S waves reach the surface, they become surface waves. Surface waves move more slowly than P and S waves but they can produce severe ground movements. Surface waves can make the ground roll like water waves in an almost circular pattern or shake buildings from side to side.

Types of Seismic Waves pg. 233

P, S, and Surface Waves

Earthquakes release stored energy as seismic waves.

Identify – Draw a line from each type of seismic wave to the movement it causes.

How Are Earthquakes Measured? Pg. 234

Modified Mercalli Scale

The Modified Mercalli scale uses Roman numerals to rate the damage and

shaking at any given location, usually close to the earthquake.

How Are Earthquakes Measured? Pg. 234

Earthquake MagnitudeThe table gives the moment magnitudes of some recent

earthquakes.

Earthquakes and Seismic Waves pg. 236

Seismic Wave Speeds

Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data were used to draw the graph.

Earthquakes and Seismic Waves pg. 237 An Earthquake’s Epicenter

The map shows how to find the epicenter of an earthquake using data from three seismographic

stations.

Assess your Understanding

Monitoring Earthquakes

7.3

Vocabulary

Seismogram

Seismic Data From the USArray ProjectIn 2004, scientists in the USArray project placed 400 seismographs across the western United States. Every month, 18 seismographs are picked up and moved east, “leapfrogging” the other seismographs.

Monitoring Earthquakes

Monitoring Earthquakes

Recording Seismic WavesIn a simple seismograph, a pen attached to a suspended weight records an earthquake’s seismic waves.

Monitoring Earthquakes

SeismogramsWhen an earthquake’s seismic waves reach a simple seismograph, the seismograph’s drum vibrates. The vibrations are recorded by the seismograph’s pen,

producing a seismogram.

Monitoring EarthquakesEarthquake RiskThe map shows areas where serious earthquakes are likely to occur, based on the location of past earthquakes across the United States.

Monitoring EarthquakesEarthquakes Around the WorldEarthquakes are closely linked to plate tectonics. The map shows where past earthquakes have occurred in relation to plate boundaries.