Earthquakes

Quaking, Shaking, Earth

All about Earthquakes

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2

What is an earthquake?

• Simply put:

– An earthquake is the shaking of the earth.

Poll

Have you felt an earthquake?

• Yes

• No

• I don't think so

• Really not sure

Poll

In the last year, there have been 3 earthquakes of magnitude 2.5 or less in our region. One was about 79 miles away and the other two were about 45 miles away. One of these happened 7 months ago on April 8th in Sandy Hook, Ky at 8:01 am. Does this surprise you.

• Very much so

• Somewhat

• Kinda

• Not Really

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3

Many buildings in

Charleston,

South Carolina,
were damaged or
destroyed by the
large earthquake

that occurred

August 31, 1886.

Picture from the United States Geological Service www.usgs.gov

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San Francisco, California, Earthquake
April 18, 1906. East side of Howard
Street near Seventeenth Street. All
houses shifted toward the left. The
tall house dropped from its south
foundation wall and leaned against its
neighbor. 1906.

Picture from USGS.GOV

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5

San Fernando,
California,
Earthquake
February 1971.
Collapsed
overpass
connecting
Foothill
Boulevard and
the Golden State
Freeway. Feb 10,
1971.

Photo by R.E.
Wallace, USGS.

www.usgs.gov

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What causes an earthquake?

• Earthquakes are the Earth's

natural means of releasing
stress.

• Due to the constant motion of

the Earth’ plates, this put
stress on the edges of the
plates.

• To relieve this stress, the

rocks tend to bend, compress,
or stretch.

An aerial view of the San Andreas fault in the Carrizo
Plain, Central California. Picture from www.usgs.gov

Multiple Choice

What type of plate boundary does most earthquakes occur?

• Convergent

• Divergent

• Transform

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Locatin' the Shakin'

• Focus: the place on the Earth’s crust where

the pressure was released.

• Epicenter: the spot on the Earth’s surface

directly above the focus.

Hotspot

Identify the Epicenter.

Hotspot

Identify the focus.

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Faults

• If the force is great

enough, the rocks will
break.

• An earthquake is the

vibrations produced by the
breaking of rock.

• Most earthquakes occur

near plate boundaries.

The Hanshin expressway in Kobe,
Japan collapsed due to an
earthquake in 1995.

Picture from
http://www.ce.washington.edu/~liquefaction/html/quakes/kobe/kobe.html

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Normal Fault

• Rock above the fault

surface moves
downward in relation
to rock below the
fault surface.

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Reverse Fault

• Reverse faults result

from compression
forces that squeeze
rock.

• If rock breaks from

forces pushing from
opposite directions,
rock above a reverse
fault surface is forced
up and over the rock
below the fault surface.

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11

Strike-slip Fault

• At a strike-slip fault,

rocks on either side of
the fault are moving
past each other without
much upward or
downward movement.

• The San Andreas Fault

is the boundary between
two of Earth’s plates
that are moving
sideways past each
other.

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How does energy created by an

earthquake move through the Earth?

• Seismic waves are

energy waves that
travel outward from
the source of the
earthquake.

Multiple Choice

Seismic Waves are

• Energy

• Expandable

• Controlled

• Ellusive

Multiple Choice

What direction to seismic waves travel?

• North

• South

• Inward

• Outward

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Surfin the Waves

• When earthquakes

occur, three different
types of seismic
waves are produced.

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P Waves

• Primary waves (P-

waves) cause particles in
rocks to move back and
forth in the same
direction that the wave
is traveling.

• P-Waves are the fastest

waves and are felt first,
usually as a bang or a
thump.

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S Waves

• Secondary waves (S-

waves) move through
Earth by causing
particles in rocks to
move at right angles to
the direction of wave
travel.

• These waves are slower

than P-Waves.

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16

L Waves

• Surface waves cause

most of the destruction
resulting from
earthquakes.

• Surface waves (L-

Waves) or land
waves move rock
particles in a backward,
rolling motion and a
side-to-side, swaying
motion.

Multiple Choice

Which waves are felt first during an earthquake

• P

• S

• L

• D

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How are seismic waves

measured?

• Seismic waves from

earthquakes are
measured with an
instrument known as a
seismograph.

• Seismographs register

the waves and record
the time that each
arrived.

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Measuring Earthquake Magnitude

• Magnitude is a

measure of the
energy that is
released during
an earthquake.

Multiple Choice

Which type of wave has the most energy

• P

• S

• L

• D

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Richter Scale

• The Richter

magnitude scale is
used to describe the
strength of an
earthquake and is
based on the height
of the lines on the
seismogram.

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Richter Scale

• For each increase of 1.0

on the Richter scale,
the height of the line on
a seismogram is ten
times greater.

• However, about 32

times as much energy is
released for every
increase of 1.0 on the
scale.

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21

Earthquake Severity

•Richter Earthquake Magnitudes Effects

•

Less than 3.5 Generally not felt, but recorded.

•3.5-5.4 Often felt, but rarely causes damage.

•Under 6.0 At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings over
small regions.

•

6.1-6.9 Can be destructive in areas up to about 100
kilometers across where people live.

•7.0-7.9 Major earthquake. Can cause serious damage over
larger areas.

•8 or greater Great earthquake. Can cause serious damage in
areas several hundred kilometers across.