Transcript Earthquakes

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
.
*Focus: Point beneath the earth’s surface where
the earth moves
*Epicenter: The point on the surface directly
above the focus. It is where the strength of the
earthquake is strongest.
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 -
Types of Seismic Waves
Surface waves move more slowly than P waves and S waves,
but they produce the most severe ground movements.
Earthquakes - Earthquakes and Seismic Waves
Seismic Waves Activity
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Earthquakes - 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.
Earthquakes - Forces in Earth’s Crust
Types of Stress
The stress force called compression squeezes rock until it
folds or breaks.
Earthquakes - Forces in Earth’s Crust
Types of Stress
Stress that pushes a mass of rock in two opposite directions
is called shearing.
Earthquakes - Forces in Earth’s Crust
Kinds of Faults
Tension in Earth’s crust pulls rock apart, causing normal
faults.
Earthquakes - 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.
Earthquakes - 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.
Earthquakes - 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.
Earthquakes - 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.
Earthquakes - 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:
stress
hanging wall
tension
footwall
strike-slip fault
compression
anticline
shearing
syncline
normal fault
plateau
reverse fault
Examples:
Stress
is aofforce
on rocka to
change
itsisshape
The block
rock that
that acts
lies above
normal
fault
or
volume.
called
the hanging wall.
The
force
on the crust,
The stress
rock that
liescalled
belowtension
is calledpulls
the footwall.
stretching rock so that it becomes thinner in the
In
a strike-slip fault, the rocks on either side of the
middle.
fault slip past each other sideways, with little up or
The stress force called compression squeezes rock
down motion.
until it folds or breaks.
A
fold inthat
rock
that bends
upward
into
is an
Stress
pushes
a mass
of rock
in an
twoarch
opposite
anticline.
directions is called shearing.
A
fold in in
rock
that bends
downward
to form
a valley is
Tension
Earth’s
crust pulls
rock apart,
causing
a
syncline.
normal
faults.
A plateau
a large
of flatstructure
land elevated
high
reverse is
fault
has area
the same
as a normal
above
seathe
level.
fault, but
blocks move in the opposite direction.
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.
Earthquakes
Richter Scale
The Richter Scale for measures the 'size' or 'strength' of an
earthquake. This scale is quantitative and based on the
amount of energy released by an earthquake.
The energy of a quake is a function of both the amplitude
and the duration of a single wave.
The seismogram below shows waves with a wide range of
amplitude and duration.
This would be magnitude 8 quake!
Earthquakes - Earthquakes and Seismic Waves
Earthquakes - 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.
Earthquakes - Earthquakes and Seismic Waves
Seismic Wave Speeds
Reading Graphs:
What variable is shown on the
x-axis of the graph? The yaxis?
X-axis––distance from the
epicenter; y-axis––arrival
time.
Earthquakes - Earthquakes and Seismic Waves
Seismic Wave Speeds
Reading Graphs:
How long did it take the S
waves to travel 2,000 km?
7 minutes
Earthquakes - Earthquakes and Seismic Waves
Seismic Wave Speeds
Estimating:
How long did it take the P
waves to travel 2,000 km?
4 minutes
Earthquakes - Earthquakes and Seismic Waves
Seismic Wave Speeds
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?
2,000 = 3.5 minutes
4,000 = 4.5 minutes
Earthquakes - Earthquakes and Seismic Waves
Locating the Epicenter
Geologists use seismic waves to locate an earthquake’s
epicenter.
Earthquakes - 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.
Earthquakes - 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.
Earthquakes - 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.
Earthquakes - Earthquake Safety
Earthquake Risk
Geologists can determine earthquake risk by locating where
faults are active and where past earthquakes have occurred.
Earthquakes - Earthquake Safety
How Earthquakes Cause Damage
A tsunami spreads out from an earthquake's epicenter and
speeds across the ocean.
Earthquakes - Earthquake Safety
Designing Safer Buildings
To reduce
earthquake
damage, new
buildings must be
made stronger and
more flexible.
Earthquakes - 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.
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.
- Volcanoes and Plate Tectonics
Earthquakes
Volcanoes and Plate Boundaries
Volcanic belts form along the boundaries of Earth’s plates.
- Volcanoes and Plate Tectonics
Earthquakes
Volcanoes and Plate Boundaries
Volcanoes often form where two oceanic plates collide or
where an oceanic plate collides with a continental plate. In
both situations, an oceanic plate sinks through a trench.
Rock above the plate melts to form magma, which then
erupts to the surface as lava.
- Volcanoes and Plate Tectonics
Earthquakes
Hot Spot Volcanoes
A volcano forms above a hot spot when magma erupts
through the crust and reaches the surface.
- Volcanoes and Plate Tectonics
Earthquakes
Properties of Magma
Magma’s viscosity depends on its physical and
chemical properties.
 Magma is made of elements and of
compounds, among them silica.
 Viscosity depends on silica content and
temperature.
- Properties of Magma
Earthquakes
Magma Composition
Magma varies in
composition and is
classified according
to the amount of
silica it contains.
The graphs show
the average
composition of the
two types of
magma.
- Properties of Magma
Earthquakes
Magma Composition
Reading Graphs:
Study both graphs. What
materials make up both types
of magma?
Silica, other oxides, and other
solids.
- Properties of Magma
Earthquakes
Magma Composition
Reading Graphs:
Which type of magma has
more silica? About how much
silica does this type of
magma contain?
Rhyolite-forming magma;
about 70 percent.
- Properties of Magma
Earthquakes
Magma Composition
Estimating:
A third type of magma has a
silica content that is halfway
between that of the other two
types. About how much silica
does this type of magma
contain?
About 60 percent
- Properties of Magma
Earthquakes
Magma Composition
Predicting:
What type of magma would
have a higher viscosity?
Explain.
Rhyolite-forming magma
would have higher viscosity
because it is higher in
silica.
- Volcanic Eruptions
Earthquakes
Magma Reaches Earth’s Surface
When a volcano erupts,
the force of the expanding
gases pushes magma from
the magma chamber
through the pipe until it
flows or explodes out of
the vent.
- Volcanic Eruptions
Earthquakes
Composite Volcano Eruption Activity
Click the Active Art button to open a browser window and
access Active Art about composite volcano eruption.
- Volcanic Eruptions
Earthquakes
Kinds of Volcanic Eruptions
Within the last 150 years, major volcanic eruptions have
greatly affected the land and people around them.
- Volcanic Landforms
Earthquakes
Landforms From Lava and Ash
Volcanic eruptions create landforms made of lava, ash, and
other materials. These landforms include composite
volcanoes, shield volcanoes, cinder cone volcanoes, and
lava plateaus.
- Volcanic Landforms
Earthquakes
Landforms From Lava and Ash
A caldera forms when an
volcano’s magma chamber
empties and the roof of the
chamber collapses. The
result is a large, bowlshaped caldera.
- Volcanic Landforms
Earthquakes
Landforms From Magma
Features formed by magma include volcanic necks, dikes,
and sills, as well as batholiths and dome mountains.
- Volcanic Landforms
Earthquakes
Batholiths
A batholith is a mass of rock formed
when a large body of magma cools
inside the crust. Several large batholiths
form the core of mountain ranges in
western North America. Half Dome in
Yosemite National Park, California, is
part of the Sierra Nevada batholith.
- Volcanic Landforms
Earthquakes
Outlining
As you read, make an outline
about volcanic landforms that
you can use for review. Use
the red headings for the main
topics and the blue headings
for the subtopics.
Volcanic Landforms
I. Landforms From Lava and Ash
A. Shield Volcanoes
B. Cinder Cone Volcanoes
C. Composite Volcanoes
D. Lava Plateaus
E. Calderas
F. Soils From Lava and Ash
II. Landforms From Magma
A. Volcanic Necks, Dikes and
Sills
B. Dikes and Sills
C. Batholiths
D. Dome Mountains
III. Geothermal Activity
A. Hot Springs
B. Geysers
C. Geothermic Energy