Transcript 7a earthquakes

Remember…
• Continental drift
• Plate tectonics
• Which movement causes earthquakes?
Earthquakes
• Shaking and trembling of the earth’s crust.
• About 8000 occur every day or one every 11
seconds
• Caused by plates sliding beside each other
(sliding/transform)
• Tsunami - earthquake on the ocean floor: causing
waves to become greater than 20 meters high
Faults
• Faults are weaknesses in the rock and
therefore earthquakes tend to happen over
and over along the same faults.
Most major faults in the United
States, particularly in California,
are what are known as strike-slip
faults.
A strike-slip fault is
formed where two
parts of the earth’s
crust (plates) slide
past each other.
Thrust Fault
A thrust fault occurs
when the plate moves
in an
upward motion.
Normal Fault
Normal plate
movement
is slipping in a
downward
motion.
Seismic Waves
• The three main types
of seismic waves are:
P waves, S waves,
and L waves
Seismic Waves
…are waves of energy that
travel through the Earth as a
result of an earthquake
P Waves
• Primary waves
• Fastest waves
• Arrive first at the
epicenter
S Waves
• Secondary waves
• Move in up-down
motion
• (think of holding
one end of a rope
and shaking it up
and down)
L Waves
• Slowest moving seismic waves
• Travel on top of Earth’s surface
Measuring Earthquakes
• Seismograph-measures
and detects seismic
waves
• Richter Scale- a scale
that allows scientists to
determine earthquake
strength
• 1-10 levels at which an
earthquake is measured.
Above a 6 is very
destructive
Measuring Earthquakes
• Epicentre: the point
on the Earth's surface
that is directly above
the centre of the
earthquake
• Most violent shaking
happens at the
epicenter
WHAT INFLUENCES THE AMOUNT OF
DAMAGE AN EARTHQUAKE CAUSES?
- Magnitude of the earthquake (how it is)
- Distance of location from epicentre of the earthquake
- Type of movement of the plates or along fault
- Soil conditions (loose, solid, flexible, stiff)
- Construction type and quality of buildings