EARTHQUAKES
&
SEISMIC WAVES
CHAPTER 6.2
WHAT IS AN EARTHQUAKE?
The
shaking and
trembling that results
from the movement of rock
beneath Earth’s surface
Caused by plate
movement
WHERE DOES AN EARTHQUAKE START?
 Focus:
area beneath Earth’s surface
where rock that is under stress
breaks, triggering an earthquake
 Epicenter:
point on the surface
directly above the focus
HOW DOES AN EARTHQUAKE MOVE?
Seismic
waves carry energy from
an earthquake away from the
focus, through Earth’s interior,
and across the surface.
ARE THERE DIFFERENT
TYPES OF SEISMIC
WAVES?
P WAVES
 First
waves to arrive
 Compress and expand the ground
like an accordion
 Crust vibrates forward and back
along the path of the wave
 Can damage buildings
 Travels through solids and liquids
S WAVES
Secondary
waves
Seismic waves that vibrate from
side to side as well as up and
down
Cannot travel through liquids
Shakes structures violently
Moves like an
accordion
Moves like ‘the wave’
at a football game
SURFACE
WAVES
Move
more slowly than P waves
and S waves, but can produce
severe ground movements
Can make the ground roll like
ocean waves or shake buildings
from side to side
HOW ARE SEISMIC WAVES MEASURED?
WHAT ARE THE 3 WAYS TO
MEASURE AN EARTHQUAKE?
1.
Mercalli scale: rates the
earthquakes according to level of
damage at a given place (pg 191)
MERCALLI SCALE XII IN LA PAZ, BOLIVIA
 2.
Richter Scale: rating of an
earthquake’s magnitude based on
the size of the earthquake’s seismic
waves
 Magnitude of an
Earthquake: a # that
geologist assign to
an earthquake based
on the earthquake’s size

. Moment Magnitude Scale:
rating system that estimates
the total energy released by
an earthquake
3
GEOLOGISTS USE THE
SEISMIC WAVES TO LOCATE
AN EARTHQUAKE….