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Earthquakes
Chapter 12 Section 1
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Earthquakes are
movements of the ground
caused by a sudden release
of energy when rocks
along a fault move.

Seismology – the study of
earthquakes and seismic
waves
Earthquakes can occur at plate
boundaries or along fault lines in
Earth’s crust.
 A fault is a break in a body of rock
along which one block slides relative to
one another.
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Earthquakes typically
occur along transform
boundaries when
tectonic plates slide past
one another.
However, the strongest
earthquakes occur at
convergent boundaries
due to the amount of
increased stress on the
rock.
Earthquakes can be felt over large areas
although they usually last less than one
minute.

FOCUS: the location within Earth along a
fault line where the first motion of an
earthquake occurs. (point of origin)

EPICENTER: the point on Earth’s surface
directly above the focus.
During an earthquake rocks release energy in
the form of vibrations called seismic waves
There are TWO categories of SEISMIC WAVES
Body waves – travel through the Earth
 primary and secondary waves
Surface waves- travel along the Earth’s surface
 Love and Rayleigh waves
 Primary Waves
(P waves)
 Fastest
 Travels through solids, liquids and gases
 First waves to be detected during an earthquake
 Moves rock back and forth, which stretches and
squeezes the rock.
 Longitudinal wave
 Secondary Waves (S waves)
 Slower than P waves
 Second waves to be detected during an earthquake
 Stretches rock moves rocks side to side
 Travels ONLY through solids (can not travel through
Earth’s outer core)
 Transverse wave
S waves can ONLY travel
through solids. They can
not travel through the
liquid outer core and will
change direction when
they reach that layer.
P waves can travel
through solid, liquids and
gasses. That means they
can travel through all of
Earth’s layers.
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Slowest moving waves
Can cause the most damage during an
earthquake
There are two types of Surface Waves
 Love Waves (L) – side to side motion
 Rayleigh Waves (R) – rolling elliptical motion
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Brain Pop: Earthquakes
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Discovery Education: Earthquakes