Download What is an earthquake?

What is an earthquake?
• An earthquake is the shaking of the ground due to the
movements of tectonic plates
• Earthquakes occur at different plate boundaries
What happens during an earthquake?
1. Foreshock: any of the usually minor
tremors commonly preceding the
principal shock of an earthquake
2. Earthquake!
3. Aftershock: smaller earthquakes
which are generated by the
continued movement of plates and
other materials after the main shock
Parts of an Earthquake
1. The focus of an earthquake is the point WITHIN
the Earth where the earthquake starts. It is the
place below the earth’s surface where the rocks
tear, come apart, or collide.
2. The epicenter is the
location on the EARTH’S
SURFACE directly above
the focus. Surface waves
move outward from the
epicenter.
3. The fault is the break in the
crust where the earthquake occurs,
between two blocks of rock that
have moved past each other.
Types of
Faults
Strike-Slip,
Reverse, Normal
Each fault occurs
at a different type
of boundary!
What is a reverse fault?
Convergent Boundary = Reverse
 Occur at convergent
boundaries, where two
plates are colliding
 A reverse fault happens
when two blocks of crust
are pushed up against
each other and they slide
vertically
 These types of
earthquakes are usually
strong and deep
What is a Normal Fault?
Divergent = Normal
• Occur at divergent
boundaries, where plates
move away from each
other
• A normal fault occurs
when two blocks of crust
are pulled away from each
other and slide vertically
• This type of earthquake is
usually weak and shallow
What is a strike-slip fault?
Transform = Strike-Slip
 If two plates have a
transform motion, they will
probably have a strike-slip
fault between them
 A strike-slip fault is when
two blocks of crust slide
past each other
horizontally
 These types of earthquakes
are moderate and shallow
What Causes Earthquakes?
• As tectonic plates push,
pull or scrape against
each other, stress
builds up along faults
until the rocks finally
move
• The elastic rebound
theory is the main
cause of earthquakes
Elastic Rebound Theory
• Definition: the gradual buildup, and release of stress
and strain, between tectonic plates which leads to
earthquakes
• http://www.iris.edu/hq/programs/education_and_outreach/animations/4
• What do scientists use to measure the strength of an
earthquake?
Magnitude
• What do scientists use to measure ground motion?
Seismogram
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Just the Basics!
P WAVES
• P waves (primary waves) are compression waves.
They push (compress) and pull (expand) in the
direction that the wave is traveling.
• These move really fast! They arrive first, but cause the
least damage.
S WAVES
S waves (secondary waves) move in right angles and
are slower than P waves.
They arrive second (hence the name), and cause a
moderate amount of damage.
SURFACE WAVES
• Travel along the earth’s surface. They do not travel
through the Earth. They move up and down, or side
to side.
• Although it is the slowest, this is the most
destructive type of wave!