Earthquakes and Seismic Waves

**Seismic waves carry energy from an
earthquake away from the focus, through
Earth’s interior, and across the surface.

Parts of Earthquakes
**An earthquake is the
shaking that results
when rocks move inside
Earth. An earthquake is
caused by stress along
a fault. Stress increases
until the rocks break
and release stored
energy.

Focus
**Focus - The point
below the surface
where the rock breaks
and energy is
released. (This is
where the earthquake
occurred.)

Fault
**Fault - As soon as the rock breaks, there is
movement along the broken surface causing a
split in the surface.

Epicenter
**The seismic waves
from an earthquake
are usually strongest
at the epicenter. This
is the point on the
surface right above
the focus.

Earthquakes and Seismic Waves
**Earthquakes cause
waves, called seismic
waves, to travel through
Earth. Seismic waves
carry the energy
released by the rocks.
There are three kinds of
seismic waves: P waves,
S waves, and surface
waves.

Seismic Waves
**Primary (P) waves:
1. Move out from the earthquakes
focus, the point where energy is
released
2. Travel the fastest of the 3 waves.
3. Move through solid and liquid layers
of the Earth.
4. Push and pull rock creating a back-
and-forth (side to side) motion in the
direction the wave is moving
(longitudinal wave)

S Waves
S waves move rocks up and
down, like a wave passing
through a rope when you flick
it.
S waves travel more slowly
than P waves but do more
damage.
S waves can only go through
solid rock.

Surface Waves
Surface waves are
combined P and S waves
that travel along Earth’s
surface.
Surface waves are the
slowest seismic waves. They
also do the most damage
because they make the
ground roll like the ocean.

Review Questions
Label each drawing as S Waves or P Waves

Type of Wave Effect
____ P wave a. shakes buildings from
side to side
____ S wave b. shakes buildings violently
up and down.
____ Surface wave c. causes buildings to roll
like the ocean which makes
them break more easily.