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Table of Contents. Forces in Earth’s Crust Earthquakes and Seismic Waves Monitoring Earthquakes Earthquake Safety. Plate Tectonic Boundaries. Forces in Earth’s Crust. How does stress in the crust change Earth’s surface? Where are faults usually found, & why do they form?

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table of contents
Table of Contents
  • Forces in Earth’s Crust
  • Earthquakes and Seismic Waves
  • Monitoring Earthquakes
  • Earthquake Safety
forces in earth s crust

Forces in Earth’s Crust

How does stress in the crust change Earth’s surface?

Where are faults usually found, & why do they form?

What land features result from the forces of plate movement?

stress
Stress
  • The movement of Earth’s plates create enormous forces that squeeze or pull the rock in the crust
  • A force that acts on rock to change its shape or volume is stress.
  • Stress adds energy to the rock
  • The energy is stored in the rock until it changes shape or breaks
3 kinds of stress in earth s crust
3 Kinds of Stress in Earth’s Crust
  • Tension- pulls on the crust, stretching rock so that becomes thinner in the middle.
  • 2. Compression-squeezes rock until it folds or breaks.
  • 3. Shearing-pushes a mass of rock in two opposite directions
types of stress

- Forces in Earth’s Crust

Types of Stress
  • The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.
types of stress1

- Forces in Earth’s Crust

Types of Stress
  • The stress force called compression squeezes rock until it folds or breaks.
types of stress2

- Forces in Earth’s Crust

Types of Stress
  • Stress that pushes a mass of rock in two opposite directions is called shearing.
faults
Faults
  • When enough stress builds up in rock, the rock breaks, creating a fault.
  • A fault is a break in the rock of the crust where rock surfaces slip past each other
  • Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks
  • There are three main types of faults: Normal faults, reverse faults, & strike-slip faults
kinds of faults

- Forces in Earth’s Crust

Kinds of Faults
  • Tension in Earth’s crust pulls rock apart, causing normal faults.
normal fault
Normal Fault
  • Tension causes a normal fault. In a normal fault, the fault is at an angle, & one block of rock lies above the fault while the other block lies below the fault.
  • The block of rock that lies above is called the hanging wall.
  • The rock that lies below is called the footwall.
kinds of faults1

- Forces in Earth’s Crust

Kinds of Faults
  • A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.
reverse faults
Reverse Faults
  • Compression causes reverse faults.
  • A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.
kinds of faults2

- Forces in Earth’s Crust

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.
strike slip fault
Strike-Slip Fault
  • Shearing creates strike-slip faults.
  • In a strike-slip fault, the rocks on either side of the fault slip past each sideways, with little up or down motion.
anticlines synclines
Anticlines & Synclines
  • Found on many parts of the Earth’s surface where compression forces have folded the crust
  • The collision of two plates can cause compression & folding of the crust over a wide area
  • Where two normal faults cut through a block of rock, fault movements may push up a fault-block mountain.
changing earth s surface

- Forces in Earth’s Crust

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.
landforms
Landforms
  • Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines & synclines, folded mountains, fault-block mountains, and plateaus.
anticline
Anticline
  • A fold in rock that bends upward into an arch is an anticline.
synclines
Synclines
  • A fold in rock that bends downward to form a valley is a syncline.
plateaus
Plateaus
  • The forces that raise mountains can also uplift, or raise plateaus.
  • A plateau is a large area of flat land elevated high above sea level.
changing earth s surface1

- Forces in Earth’s Crust

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.
building vocabulary

Key Terms:

Examples:

hanging wall

footwall

strike-slip fault

anticline

syncline

plateau

- Forces in Earth’s Crust

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:

stress

Stress is a force that acts on rock to change its shape or volume.

The block of rock that lies above a normal fault is called the hanging wall.

tension

The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

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.

compression

The stress force called compression squeezes rock until it folds or breaks.

A fold in rock that bends upward into an arch is an anticline.

shearing

Stress that pushes a mass of rock in two opposite directions is called shearing.

A fold in rock that bends downward to form a valley is a syncline.

normal fault

Tension in Earth’s crust pulls rock apart, causing normal faults.

A plateau is a large area of flat land elevated high above sea level.

reverse fault

A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

types of seismic waves

- Earthquakes and Seismic Waves

Types of Seismic Waves
  • Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.
types of seismic waves1

- Earthquakes and Seismic Waves

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.
types of seismic waves2

- Earthquakes and Seismic Waves

Types of Seismic Waves
  • Surface waves move more slowly than P waves and S waves, but they produce the most severe ground movements.
measuring earthquakes

- Earthquakes and Seismic Waves

Measuring Earthquakes
  • The Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place.
seismic wave speeds

- Earthquakes and Seismic Waves

Seismic Wave Speeds
  • Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data are shown in the graph.
seismic wave speeds1
X-axis––distance from the epicenter; y-axis––arrival time.

Reading Graphs:

What variable is shown on the x-axis of the graph? The y-axis?

- Earthquakes and Seismic Waves

Seismic Wave Speeds
seismic wave speeds2
7 minutes

Reading Graphs:

How long did it take the S waves to travel 2,000 km?

- Earthquakes and Seismic Waves

Seismic Wave Speeds
seismic wave speeds3
4 minutes

Estimating:

How long did it take the P waves to travel 2,000 km?

- Earthquakes and Seismic Waves

Seismic Wave Speeds
seismic wave speeds4
2,000 = 3.5 minutes

4,000 = 4.5 minutes

Calculating:

What is the difference in the arrival times of the P waves and the S waves at 2,000 km? At 4,000 km?

- Earthquakes and Seismic Waves

Seismic Wave Speeds
locating the epicenter

- Earthquakes and Seismic Waves

Locating the Epicenter
  • Geologists use seismic waves to locate an earthquake’s epicenter.
identifying main ideas

Main Idea

Detail

Detail

Detail

- Earthquakes and Seismic Waves

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.

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.

the modern seismograph

- Monitoring 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.
the first seismograph
The First Seismograph?
  • Designed by the Chinese philosopher Chang Hêng in 132 A.D.
  • Said to be able to detect earthquakes 400 miles (644 km) away!
methods used for earthquake prediction
Methods Used For Earthquake Prediction
  • Increase in the rate of a seismic creep and the slow movement along the fault
  • Gradual tilting of the land near the fault zone
  • Drop or rise in the water level of a well
  • Decrease in the number of micro-quakes and foreshocks
  • Animal behavior
  • *None of these methods are 100% accurate!
instruments that monitor faults

- Monitoring 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 using GPS.
friction
Friction
  • Friction is the force that is exerted on two surfaces as they rub against one another.
  • The strength of the friction force depends on two things:
  • How hard the surfaces are pushed together
  • What material the surface is made of
types of friction
Types of Friction
  • Static friction acts on objects that are at rest.
  • Sliding friction occurs when two solid surfaces slide past one another.
  • Rolling friction occurs when an object rolls across a surface.
  • Fluid friction occurs when a solid object moves through a fluid.
gravity
Gravity
  • Gravity is a force that pulls objects toward one another.
  • Gravity keeps objects in place unless they are acted on by an outside force!
  • Sir Isaac Newton accurately described this in his law of universal gravitation.
  • Gravity acts on all objects regardless of their size and or location in the universe.
  • This means that all objects are attracted to one another but there are some rules involved in how much attraction occurs
  • This is mostly due to differences in mass
  • What is the difference between mass and weight?
  • Mass is the amount of matter in an object.
  • Weight is the measure of gravitational force on an object.
using seismographic data

- Monitoring 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.
sequencing

- Monitoring 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.

earthquake risk

- Earthquake Safety

Earthquake Risk
  • Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred.
how earthquakes cause damage
How Earthquakes Cause Damage
  • Shaking: the shaking caused by seismic waves can trigger movement of the soil at high elevations and destroy man made structures.
  • Liquefaction: is the result of shaking the soil particles often caused by increased water content and reduces the strength or stiffness of the soil.
  • Aftershocks: are caused by additional releases of energy in rocks after the larger earthquake occurred in the same area.
  • Tsunamis: “harbor waves” result from a large body of water displacement caused by a disturbance in the water.
how earthquakes cause damage1

- Earthquake Safety

How Earthquakes Cause Damage
  • A tsunami spreads out from an earthquake\'s epicenter and speeds across the ocean.
designing safer buildings

- Earthquake Safety

Designing Safer Buildings
  • To reduce earthquake damage, new buildings must be made stronger and more flexible.
asking questions

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

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.

Question

Answer

Where is the quake risk highest?

Earthquake risk is the highest along faults and where past earthquakes have occurred.

earthquake damage

- Earthquake Safety

Earthquake Damage
  • Click the Video button to watch a movieabout earthquake damage.
more on earthquake risk

- Earthquake Safety

More on Earthquake Risk
  • Click the PHSchool.com button for an activity about earthquake risk.
graphic organizer
Graphic Organizer

Reverse

Tension

Strike-slip

Shearing

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