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CHAPTER 19
EARTHQUAKES
The following words are
on the quiz Friday 11/16/07
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fault
primary wave
secondary wave
surface wave
focus
epicenter
seismometer
magnitude
tsunami
seismogram
I. Forces Inside Earth
A. Causes of Earthquakes
1. stress of pressure is put on
rocks
2. The rock layers bend until they
reach their elastic limit
3. Once their limit is exceeded the
rocks break
a) fault: a break or crack in a
rock where movement occurs
4. This breaking produces
vibrations called earthquakes
B. Forces in the Earth
1. Compression: forces or stress that
squeezes or compresses
2. Tension: stress that causes
stretching & elongation
3. Shear: forces that causes slipping
a) causes rocks on either side of a
fault to move past each other
C. Types of Faults
1. Normal Fault
a) Tension pulls the rocks apart
b) Rock above the fault surface
moves downward in relation to
rock below the fault surface
NORMAL FAULT
2. Reverse Fault
a) Compression Pushes on Rocks
from opposite directions
b) Rocks above the fault surface are
forced up & over rocks below the fault
surface
REVERSE FAULT
3. Strike-Slip Fault
a) Shear forces cause rocks to slide
past each other
b) rocks on either side of the fault are
moving past each other without much
upward or downward movement
c) Ex. San Andreas Fault, CA
STRIKE-SLIP FAULT
4. Earthquakes occur as pressure builds up
in these faults and the rocks
finally break.
Use your notes to answer
the following
 1. List three forces inside the Earth
 2. What type of force causes a strike-slip
fault?
 3. What type of force causes a normal
fault?
 4. What type of force causes a reverse
fault?
II. Earthquake Information
A. Types of Seismic Waves
1. Seismic Wave
a) Energy waves generated by
an earthquake
2. Focus
a) point on the Earth’s surface
where seismic waves start
b) place where the energy is
released
c) Epicenter- point on the
Earth’s surface directly above
the focus
3. Primary Waves (P-waves)
a) cause particles & rocks to
compress & stretch apart in the same
direction of the wave.
b) can travel through solid, liquid, & air
c) the fastest wave 6km/sec or
21,600km/hr or 12,960mph
P-WAVES
4. Secondary Waves (S-waves)
a) cause rocks to move at right angles
to the direction of the wave.
b) can only travel through solids
c) second fastest wave 3.5km/sec or
12,600km/hr or 7560mph
S-WAVES
5. Surface Waves
a) surface waves start at the epicenter
b) the waves move up & down & side to
side
c) Ex. L-wave: move up and down
d) slowest wave 2.0km/sec or
7200km/hr or 4320 mph
SURFACE WAVES
Answer the following in
your notes
 1. List three types of seismic waves?
 2. Which seismic wave can only travel
through solids?
 3. What force causes a reverse fault?
 4. What force causes a strike-slip fault?
 5. What force causes a normal fault?
B. Locating an Epicenter
1. Seismograph Station
a) records the arrival of
earthquake waves
b) P-waves arrive 1st, S-waves
second
c) P-S wave graph pg 501
2. How to locate an epicenter
a) 3 stations are needed
b) the distance from the Earthquake is
used to find the epicenter
LOCATING AN EPICENTER
EARTH’S INTERIOR
C. Mapping Earth’s Interior
1. Inner Core
a) Solid Dense
b) composed of Iron and Nickel
2. Outer Core
a) Liquid
b) composed of Iron & Nickel
3. Mantle
a) Is directly above the outer core
b) the largest layer in the Earth
c) composed of silicon, oxygen,
magnesium, & iron
4. Crust
a) Outermost layer of the Earth
b) separated from the mantle by the Moho
Discontinuity
5. Moho Discontinuity
a) layer that lies between the crust and
the upper mantle
b) P & S wave slow down because this
layer is partially melted
c) was discovered by Andrija Mohorovicic
6. Shadow Zone
a) located 105o to 140o from the
focus
b) no earthquake waves are detected
there
c) liquid outer core prevents S-waves
from going through the Earth
d) P-waves slow down & are deflected
away from` the outer core
SHADOW ZONE
III. Destruction by Earthquakes
A. Measuring Earthquakes
1. Seismology
a) seismologist: scientist who
studies earthquakes
b) seismograph: records
primary, secondary, and
surface waves
SEISMOGRAPH
B. Earthquake Magnitude
1. Richter Scale
a) describes how much energy is
released by an Earthquake
b) Each degree of magnitude is 32
times greater than the one before
c) 5.5 – 6.5 = 32 times stronger
5.5 – 7.5 1025 times stronger (322)
2. Moment magnitude Scale
a) looks at fault size
b) measures how much movement
occurred
c) how stiff are the rocks?
d) the number is an average of several
seismic waves
3. Modified Mercalli Scale
a) Measures the amount of damage
b) I (little damage) XII (total destruction)
4. Depth of Focus
a) Ranked as shallow, intermediate
or deep
b) devastating earthquakes are
always shallow focus
C. Tsunamis (Tidal Wave)
1. Caused by an Earthquake under the
ocean
2. The quick movement pushes against
the water creating a powerful wave
3. These waves can be over 30m (80ft)
high when they reach the surface.
Use your notes to answer
the following
 1. How many seismometer stations are
needed to locate an earthquake
epicenter?
 2. Which type of earthquakes are more
devastating, shallow focus or deep focus
earthquakes?
 3. What causes a tsunami?
Use your notes to answer
the following
 1. When an area experiences an earthquake,
which waves arrive first, P, S, or surface
waves?
 2. Which earthquake waves cause the most
damage at the epicenter?
 3. Explain the difference between an
earthquake focus and an earthquake epicenter.
 4. List three scales that describe earthquake
magnitude and/or damage.
Use your notes to answer
the following
 1. Which earthquake waves cause the
most damage at the epicenter?
 2. Explain the difference between an
earthquake focus and an earthquake
epicenter.
 3. List three scales that describe
earthquake magnitude and/or damage.
When the force on rocks is great enough,
they break, producing vibrations called
____.
a. faults
c. strains
b. earthquakes d. stresses
Once the elastic limit of rocks is passed, they
break and move along surfaces called ____.
a. faults
c. strains
b. earthquakes d. stresses
The height of the lines traced on paper is a
measure of the energy released or the ____
of the earthquake.
a. stress
c. magnitude
b. strain
d. intensity
Most earthquakes happen ____.
a. without warning
b. in areas where earthquakes have
occurred in the past
c. along plate boundaries
d. all of the above
Scientists discovered changes in Earth's
interior by studying ____.
a. tsunamis
c. changes in
seismic waves
b. tides
d. all of the above
____ is the force that squeezes rocks together.
a. Tension
c. Elastic limit
b. Shear
d. Compression
____ is the force that pulls rocks apart.
a. Tension
c. Elastic limit
b. Shear
d. Compression
____ is the force that causes plates to
move sideways past each other.
a. Tension
c. Elastic limit
b. Shear
d. Compression
____ faults are caused by tensional forces.
a. Normal
c. Reverse
b. Strike-slip
d. Elastic
____ faults are caused by compressional
forces.
a. Normal
c. Reverse
b. Strike-slip
d. Elastic
____ faults are caused by shear forces.
a. Normal
c. Reverse
b. Strike-slip
d. Elastic
Along a(n) ____ fault, rock above the fault
surface moves downward in relation to rock
below the fault surface.
a. normal
c. elastic
b. reverse
d. strike-slip
Along a(n) ____ fault, rock above the fault
surface moves upward in relation to rock
below the fault surface.
a. normal
c. elastic
b. reverse
d. strike-slip
At a(n) ____ fault, rocks on either side of
the fault surface move past each other.
a. normal
c. reverse
b. elastic
d. strike-slip
The most destructive seismic wave are
____.
a. primary waves
c. P-waves
b. secondary waves d. surface waves
The ____ waves are the first to reach a
seismograph after an earthquake.
a. surface
c. primary
b. secondary
d. tsunami
At least ____ seismographs are needed to
accurately locate an earthquake epicenter.
a. two
c. four
b. five
d. three
The point in Earth's interior where the
energy release of an earthquake occurs is
the ____.
a. focus
c. fault
b. epicenter
d. inner core
Seismic waves ____ when they reach the
bottom of the crust.
a. slow down
c. stop
b. stay the same
d. speed up
The magnitude of an earthquake is
measured by the ____.
a. Richter scale c. modified Mercalli scale
b. moho discontinuity d. elastic limit
Primary waves ____ when they hit the
liquid outer core.
a. slow down
c. stop
b. stay the same
d. speed up
Secondary waves ____ when they hit the
liquid outer core.
a. slow down
c. stop
b. stay the same
d. speed up
A ____ fault forms as a result of horizontal
compression.
a. blind
c. strike-slip
b. normal
d. reverse
The San Andreas Fault, a result of horizontal
shear, is a ____ fault.
a. blind
c. strike-slip
b. normal
d. reverse
The locations of seismic belts are
determined by plotting ____.
a.earthquake epicenters
b.seismic gaps
c.earthquake foci
d.epicentral
Deaths associated with earthquake deaths in
sloping areas can result from ____.
a. tsunamis
c. formation of fault scarps
b.
landslides
d.surface ruptures
Seismic waves generated by an earthquake at
point R are recorded at locations W and X.
Which pair of seismographs is more accurate?
A
B
C
D
Each dot on the above diagram marks the
origin of an earthquake. The area with the
highest concentration of earthquake origins
marks —
A a line of Earth’s magnetic field
B a seam of soft rock, such as limestone
C the path of the subducting tectonic plate
D the location of a developing igneous
intrusion
.
The diagram shown illustrates which
geological process?
A Faulting
B Folding
C Weathering
D Metamorphism
One part of California is on the Pacific
Plate, while the remainder of the state is on
the North American Plate. The two plates
are moving to the northwest at different
speeds, causing one plate to slide past the
other. This movement in plates creates a —
A normal fault
B reverse fault
C strike-slip fault
D thrust fault
What is usually responsible for an
earthquake?
A Pressure buildup within the mantle
B Slippage along faults within Earth’s crust
C Weathering along coastlines
D Force changes from the moon pulling on
Earth
The formations at X and Y in the picture
above were created by —
A tension
B shearing
C compression
D rifting
The edges of moving crustal plates are often
defined by —
A ocean basins
B frequent seismic activity
C intercontinental plains
D Earth’s largest rivers
An earthquake struck San
Diego, California. The above
map and table show that the
approximate difference in
arrival times between the Pwave and S-wave at Seattle
is —
A 2 minutes
B 3 minutes
C 4 minutes
D 5 minutes
The point from which an earthquake
originates is called the —
A focus
B epicenter
C fault line
D shock wave
What is the fewest number of seismographic
stations that must record the arrival time of P
and S waves in order for the epicenter of an
earthquake to be located?
A2
B3
C5
D 10