# Chapter 2-Earthquakes

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```					                                 Chapter 2-Earthquakes

Section 1-Earth’s Crust in Motion

Stress in the Crust

An earthquake is the shaking and trembling that results from the movement of rock
beneath earth’s surface.

The movement of Earth’s plates create powerful forces that squeeze or pull the rock in
the crust- these are examples of stress.

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

Types of stress: Shearing, Tension, and Compression

Shearing: Stress that pushes a mass of rock in two opposite directions.

Tension: Stress that pulls on the crust, stretching rock so that it becomes thinner in the
middle.

Compression: Stress that squeezes rock until it folds or breaks.

Any change in the volume or shape of Earth’s crust is called deformation.
Kinds of Faults

A fault is a break in the Earth’s crust where slabs of crust slip past each other. Faults
usually occurs along plate boundaries, where the forces of plate motion compress, pull, or
shear the crust so much that the crust breaks.

Strike-Slip Faults- created by shearing. The rocks on either side of the fault slip past
each other side ways with little up or down motion. A strike slip fault that forms the
boundary between two plates is called a transform boundary.

Normal faults- tension forces in the crust cause normal faults. In a normal fault, the
fault is at an angle, so one block of rock lies above the fault while the other block lies
below the fault.

Hanging wall-

Footwall-

When movement occurs along a normal fault, the hanging wall slips downward.

Reverse Faults- Compression forces produce reverse faults. The fault has the same
structure as a normal fault, but the blocks move in opposite direction.

Skipping Friction Along Faults and Mountain Building
Chapter 2 Earthquakes

Section 2 - Measuring Earthquakes

An earthquake starts at one particular point. The focus is the point beneath Earth’s
surface where the rock that is under the stress breaks, triggering an earthquake. The point
on the surface directly

Seismic Waves are vibrations that travel through Earth carrying energy released during
an earthquake. The seismic waves move like ripples in a pond. Seismic waves carry the
energy of an earthquake away from the focus, through Earth’s interior, and across the
surface.

Three categories of seismic waves: P waves, S waves, Surface waves.

P waves-
*Primary waves.
*The first to arrive.
*Earthquake waves that compress and expand the ground like an accordion.
*Travels through solids and liquids

S waves-
*Secondary waves
* Earthquake waves that vibrate side to side as well as up and down
*When they reach the surface, they shake structures violently.
* Travels through solids not liquids
Surface Waves
*When P and S waves reach the surface, some are transformed into surface
waves.
*These move more slowly than P and S waves
*These produce severe ground movements.

Measuring Earthquakes

Three ways of measuring earthquakes: Mercalli scale, the Richer scale, the moment
magnitude scale.

Mercalli scale-developed in the early 20th century. Developed to rate earthquakes
according to their intensity. (see figure 14).

Richter scale-rating the size of seismic waves as measured by a seismograph. The
Richter scale provides an accurate measure for small, nearby earthquakes. But this scale
does not work well for large or distant earthquakes.

Moment Magnitude Scale-used today. The scale can be used to rate earthquakes of all
sizes, near or far. Earthquakes with a magnitude below 5.0 on the moment magnitude
scale are small and cause little damage. Earthquakes with a magnitude above 5.0 can
produce great destruction. Earthquakes with a magnitude of 6.0 release 32 times as much
energy as a magnitude 5.0 quake, and as nearly 1,000 times as much as a magnitude 4.0
quake.

Locating the Epicenter

Geologists use seismic waves to locate an earthquake’s epicenter. Seismic waves travel
at different speeds. P waves arrive first at a seismograph, with S waves following close
behind.

To tell how far the epicenter is from the seismograph, scientists measure the difference
between the P waves and the S waves. The farther away an earthquake is, the greater the
time difference between the arrival of the P waves and S waves.

Geologists draw at least three circles using data from different seismographs set up at
stations all over the world.
Chapter 2 Earthquakes

Section 3- Earthquake Hazards and Safety

How Earthquakes Cause Damage

When a major earthquake strikes, it can cause great damage. The severe shaking
produced by seismic waves can damage or destroy buildings and bridges, topple utility
poles, and fracture gas and water mains.

Local Soil Conditions- When seismic waves move from hard, dense rock to loosely
packed soil, they transmit their energy to the soil causing the soil to shake more violently
than its surroundings.

Liquefaction- Occurs when earthquake’s violent shaking suddenly turns loose, soft soil
into liquid mud. Liquefaction is likely to occur when an earthquake’s violent shaking
suddenly turns loose.

Aftershocks – an earthquake that occurs after a larger earthquake in the same area.
Aftershocks may strike hours, days, or even months later.

Tsunamis-When an earthquake jolts the ocean floor, plate movement causes the ocean
floor to rise slightly and push water out of its way. If the earthquake is strong enough,
the water displaced by the quake forms large waves, called Tsunamis.

Making Buildings Safer

To reduce damage, new buildings must be made stronger and more flexible. Older
buildings must be modified to withstand stronger quakes.

Choice of Location- The location of the building affects the type of damage it may suffer
during an earthquake.
*Steep slopes pose the danger of landslides
*Filled land can shake violently

Construction Methods- The way a building is constructed determines whether it can
withstand an earthquake. During an earthquake, brick buildings as well as some wood
frame buildings may collapse if their walls have not been reinforced.

Base-isolated buildings- a building designed to reduce the amount of energy that
reduces the amount of energy that reaches a building
Protecting Yourself during an Earthquake- The main danger is from falling objects
and flying glass.
         The best way to protect yourself is to drop, cover, and hold. (crouch
beneath a sturdy table or desk and hold on to it so it doesn’t jiggle away
during the shaking.
         If no desk is available, crouch against an inner wall, away from the
         If you are outdoors, move to an open area such as a playground. Avoid
power lines, trees, and buildings, especially ones with brick walls or
chimneys.
         Sit down to avid being thrown.
         After a major earthquake, water and power supplies may fail, food stores
may be closed, and travel may be difficult.
Chapter 2 Earthquakes

Section 4 Monitoring Faults

Story- In the early 1980’s, geologists predicted that a strong earthquake was going to
occur in Parkfield between 1985-1993. Geologists waited for the predicted earthquake,
but it never came. Finally, medium-sized earthquakes rumbled along the San Andreas
fault near Parkfield in 1993-1994.

What went wrong?

Geologists don’t know, but they continue to monitor the San Andreas fault. Someday
they may find a way to predict when and where an earthquake will occur.

Devices that Monitor Faults- To observe these changes in ground movement, geologists
put in place instruments that measure stress and deformation in the crust.

* Creep Meters-uses a wire stretched across a fault to measure horizontal
movement of the ground. Geologists can measure the amount that the fault
has by measuring how much the weight has moved against a measuring
scale.

* Laser-Ranging Devices- Uses a laser beam to detect even the tiny fault
movements. The device calculates any change in the time needed for the
laser beam to travel to a reflector and bounce back.

* Tiltmeters-measure the tilting of the ground. Consists of two bulbs that
are filled with a liquid and connected by a hollow stem.

* Satellite Monitors- Besides ground based instruments, geologists use
satellites equipped with radar to make images of faults. The satellite
bounces radio waves off the ground. As the waves echo back into space, the
satellite records them.

Monitoring Risk in the United States

Even with data from many sources, geologists can not predict when and where a quake
will start.

Geologists do know that earthquakes are likely wherever plate movement stores energy in
the rock along faults.

Geologists can determine earthquake risk by locating where faults are active and
where past earthquakes have occurred.
In the United States, the risk is highest along the Pacific coast where the Pacific and
North American plates meet - California, Washington, and Alaska.

Other regions of the United States also have some risk of earthquakes – rare east of the
Rockies.

Name__________________________________Date_______________Period______

Chapter 2 Earthquakes

Chapter 2, Section 1: Earth’s Crust in Motion

1. Checkpoint 1. How does deformation change Earth’s surface?

2. Figure 2 on page 54. Which type of deformation tends to shorten part of the crust?

3. Checkpoint 2. What are three types of faults? What force of deformation produces
each?

4. Which half of the reverse fault slid up and across to form this mountain, the hanging
wall or the foot wall? Explain.

5. What are the three main types of stress in rock?

6. Describe the movements that occur along each of the three types of faults.

7. How does Earth’s surface change as a result of movement among faults?

8. If plate motion compresses part of the crust, what landforms will form there in millions
of years? Explain.
Chapter 2, Section 2: Measuring Earthquakes

1. Figure 11 on page 65. What point is directly above the focus of the earthquake?

2. Checkpoint 1. What are the three types of seismic waves?

3. Figure 14 on page 67. How would you rate the damage to the Foligno city hall on the
Mercalli scale?

4. Checkpoint 2. What are the three scales for measuring earthquakes?

5. Figure 17 on page 69. Using the map scale to determine the distances from Savannah
and Houston to the epicenter. Which is closer?

6. How does the energy from the earthquake reach Earth’s surface?

7. Describe the three types of seismic waves.

8. What system do geologists use today for rating the magnitude of an earthquake?

9. Describe how energy released at an earthquake’s focus, deep inside the earth, can
cause damage on the surface many kilometers from the epicenter.
Chapter 2, Section 3: Earthquake Hazards and Safety

1. Figure 19 on page 73. What are some questions people might ask before building a
house in an area that is at risk for earthquakes?

2. Checkpoint 1. What are the major causes of earthquake damage?

3. Figure 22 on page 76. How does base isolation bearing absorb an earthquake’s
energy?

4. Explain how liquefaction occurs and how it causes damage during an earthquake.

5. What can residents do to reduce the risk of earth quake damage to their homes?

6. Describe safety measures you can take to protect yourself during and earthquake.

7. You are a builder planning a housing development where earthquakes are likely.
What types of land would you avoid for your development? Where would it be safe to
build?
Chapter 2, Section 4: Monitoring Faults

1. Figure 26 on page 78. How are a laser-ranging device and a creep meter similar?
How are they different?

2. Checkpoint 1. What do fault-monitoring instruments measure?

3. Figure 28 on page 81. Where are damaging earthquakes least likely to occur? Most
likely to occur?

4. What equipment do geologists use to monitor the movement of faults?

5. What two factors do geologists consider when determining earthquake risk for a
region?

6. Explain how satellites can be used to collect data on earthquake faults.

7. Why can’t scientists predict the exact time and place and earthquake is going to
occur?
Earthquakes Extra Credit (15 points)

Planning for an Earthquake: Create a Model of the City.

1.            Build a model of the city discussed in class (with the 5 sections)and
show (demonstrate to your class) what would happen if an earthquake
were to strike each of the areas.
2.            Present your proposal to the class on the highest priority areas

You may work in a group of 3 people or less to share the responsibilities.

Models should be creative, neat, clean, (not rushed).

Earthquake Extra Credit due date: Wednesday, March 3, 2010

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