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Integrated Science
Unit 10, Chapter
28.3 Earthquakes

As tectonic plates move, friction
causes rock at plate boundaries to
stretch or compress, this causes
rocks to store energy.

When the rocks break, change
shape, or decrease in volume, the
stored energy is suddenly
converted to kinetic energy and an
earthquake occurs.
28.3 Earthquakes

A seismograph measures
earthquakes, and
seismologists use seismic
waves to study Earth’s
internal structure.

This is similar to how a
doctor uses X rays to look
at bone structure.
28.3 Earthquakes

The majority of
earthquakes occur at the
plate boundaries.

Earthquakes also occur at
a fault.

Fault - a place crack in
rocks along which
movement occurs.
Earthquake
Terms
–
point on earth’s
surface where
the EQ waves
touch surface
first.
Epicenter
Northridge,
California in
January 1994.
– point inside crust where the
EQ movement first occurred.
Focus
waves –
common name
given to all EQ
waves.
Seismic

Hawaii earthquake damage
Worldwide Earthquakes
Notice- most earthquakes occur on plate boundaries.
2 Categories of
Seismic Waves
Body & Surface
P waves

Short for Primary waves
 Fastest
and First body wave recorded by a
seismograph
 Travel
through solids and liquids (generate sound)
 Faster
through more rigid material
 They
—
are Compression waves
Cause rock particles to move
together and apart along the
direction of the waves
P-Wave movement
S waves
short for
Secondary Waves
 Second
body wave recorded
by a seismograph
 Only
travel through solids
 Can’t
be detected on the side of the
earth opposite the earthquake’s
epicenter.
 They
—
are Shear waves
Cause rock particles to move up & down
or side to side (right angle) to the
direction in which the waves are
traveling
S-Wave movement
Surface Waves
 Slowest
moving wave & last to be
recorded by seismograph
 Travel
similar to ocean waves
 Cause
the surface to rise, fall, turn
and twist
 Very
destructive: especially in loose
earth
2 Types of Surface waves
 Love
Waves
 Fastest
kind of surface wave is called a Love
wave , (named for A.E.H. Love, a British
mathematician)
 Love
worked out the mathematical model for
this kind of wave in 1911.
 It
moves the ground from side-to-side.
2 Types of Surface waves
 Rayleigh
Waves
 Slower
kind of surface wave (named for John
William Strutt, Lord of Rayleigh
 Rayleigh
predicted mathematically the
existence of this kind of wave in 1885.
 It
moves the ground up & down and side-toside rolling the ground like waves on water.
 Most
of the shaking felt from an earthquake is
due to the Rayleigh wave, which can be much
larger than the other waves
Surface Waves movements
28.3 Earthquakes in the U.S.
 The
west coast of U.S.
experiences most
earthquakes because
of the San Andreas
fault a boundary
between Pacific and
North American Plate,
and the 10,000 +
smaller faults.
 The
Midwest and
Eastern U.S. does
experience EQ but
they are more rare.
28.3 Earthquakes in the U.S.

Minor earthquakes release
stored energy in small, less
destructive amounts.

Rocks in areas that do not
experience frequent small
earthquakes may have a lot
of stored potential energy.

When this potential energy
is finally converted to kinetic
energy, the earthquake could
be big.
28.3 Earthquake Safety
 Get
outside to an open area (if possible), far
from buildings and objects that could fall. Sit
down to avoid falling.
 If
you are inside: Drop, cover, and hold.
28.3 Preparing for Earthquakes

A huge wave generated by an underwater earthquake
or landslide is called a tsunami.
 The speed at which this wave travels can be about 700
kilometers per hour. (435MPH)
28.3 Earthquakes
Key Question:
 What
mechanical factors affect earthquakes?
*Read text section 28.3 BEFORE Investigation 28.3