Types of Stress
The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.
- Forces in Earth’s Crust
Earthquakes
Types of Stress
The stress force called compression squeezes rock until it folds or breaks.
- Forces in Earth’s Crust
Earthquakes
Types of Stress
Stress that pushes a mass of rock in two opposite directions is called shearing.
- Forces in Earth’s Crust
Earthquakes
Kinds of Faults
Tension in Earth’s crust pulls rock apart, causing normal faults.
- Forces in Earth’s Crust
Earthquakes
Kinds of Faults
A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.
- Forces in Earth’s Crust
Earthquakes
Kinds of Faults
In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up and down motion.
- Forces in Earth’s Crust
Earthquakes
Changing Earth’s Surface
Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.
- Forces in Earth’s Crust
Earthquakes
Changing Earth’s Surface
Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.
- Forces in Earth’s Crust
Earthquakes
Building Vocabulary
A definition states the meaning of a word or phrase. As you read, write a definition of each Key Term in your own words.
Key Terms:
Examples:
- Forces in Earth’s Crust
stress
Stress is a force that acts on rock to change its shape or volume.
tension
The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.
compression
The stress force called compression squeezes rock until it folds or breaks.
shearing
Stress that pushes a mass of rock in two opposite directions is called shearing.
normal fault
Tension in Earth’s crust pulls rock apart, causing normal faults.
reverse fault
A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.
Key Terms:
Examples:
hanging wall
footwall
strike-slip fault
anticline
syncline
plateau
The block of rock that lies above a normal fault is called the hanging wall.
The rock that lies below is called the footwall.
In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up or down motion.
A fold in rock that bends upward into an arch is an anticline.
A fold in rock that bends downward to form a valley is a syncline.
A plateau is a large area of flat land elevated high above sea level.
Earthquakes
End of Section:�Forces in Earth’s Crust
Earthquakes
Types of Seismic Waves
Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.
- Earthquakes and Seismic Waves
Earthquakes
Types of Seismic Waves
P waves are seismic waves that compress and expand the ground like an accordion. S waves are seismic waves that vibrate from side to side as well as up and down.
- Earthquakes and Seismic Waves
Earthquakes
Types of Seismic Waves
Surface waves move more slowly than P waves and S waves, but they produce the most severe ground movements.
- Earthquakes and Seismic Waves
Earthquakes
Seismic Waves Activity
Click the Active Art button to open a browser window and access Active Art about seismic waves.
- Earthquakes and Seismic Waves
Earthquakes
Measuring Earthquakes
The Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place.
- Earthquakes and Seismic Waves
Earthquakes
Locating the Epicenter
Geologists use seismic waves to locate an earthquake’s epicenter.
- Earthquakes and Seismic Waves
Earthquakes
Identifying Main Ideas
As you read the section “Types of Seismic Waves,” write the main idea in a graphic organizer like the one below. Then write three supporting details. The supporting details further explain the main idea.
Main Idea
Detail
Detail
Detail
Seismic waves carry the energy of an earthquake.
P waves compress and expand the ground.
S waves vibrate from side to side as well as up and down.
Surface waves produce the most severe ground movements.
- Earthquakes and Seismic Waves
Earthquakes
End of Section:�Earthquakes and Seismic Waves
Earthquakes
The Modern Seismograph
Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.
- Monitoring Earthquakes
Earthquakes
Instruments That Monitor Faults
In trying to predict earthquakes, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movements along faults.
- Monitoring Earthquakes
Earthquakes
Using Seismographic Data
The map shows the probability of a strong earthquake along the San Andreas fault. A high percent probability means that a quake is more likely to occur.
- Monitoring Earthquakes
Earthquakes
Sequencing
As you read, make a flowchart like the one below that shows how a seismograph produces a seismogram. Write each step of the process in a separate box in the order in which it occurs.
How a Seismograph Works
Incoming seismic waves
Vibrate the rotating drum
The suspended pen remains motionless and records the drum’s vibration.
- Monitoring Earthquakes
Earthquakes
End of Section:�Monitoring Earthquakes
Earthquakes
Earthquake Risk
Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred.
- Earthquake Safety
Earthquakes
How Earthquakes Cause Damage
A tsunami spreads out from an earthquake's epicenter and speeds across the ocean.
- Earthquake Safety
Earthquakes
Designing Safer Buildings
To reduce earthquake damage, new buildings must be made stronger and more flexible.
- Earthquake Safety
Earthquakes
Asking Questions
Before you read, preview the red headings and ask a what, how, or where question for each heading. As you read, write answers to your questions.
Where is the quake risk highest?
Earthquake risk is the highest along faults and where past earthquakes have occurred.
How do earthquakes cause damage?
Earthquake damage occurs as a result of shaking, liquefaction, aftershocks, and tsunamis.
How can you stay safe during an earthquake?
The best way to stay safe during an earthquake is to drop, cover, and hold.
What makes buildings safe from earthquakes?
Buildings can be made safer by being built stronger and with greater flexibility.
- Earthquake Safety
Question
Answer
Earthquakes
End of Section:�Earthquake Safety
Earthquakes
Graphic Organizer
Reverse
Tension
Shearing
Strike-slip
Earthquakes
End of Section:�Graphic Organizer
Earthquakes