Transcript What is an Earthquake

Today’s Objective:
What is an Earthquake?
Do Now:
Hand in Lab #17 – Seafloor
Earthquakes
– the vibration of Earth
produced by the rapid
release of energy.
- Often caused by slippage
along a break in the
Earth’s crust.
Vocabulary
Epicenter
The location on the
surface directly above
the focus
Focus
The point within
the Earth where
the earthquake
starts and energy
is released in all
directions.
Faults
- are fractures in Earth
where movement has
occurred.
(Earthquakes are usually associated
with large fractures in the Earth’s
crust and mantle.)
San Andreas Fault
California
Cause of Earthquakes
When there is
movement along a
fault stored energy
is released. The
vibrations of an
earthquake as the
rocks trying to
return to their
original state.
When the strength of the rock is
exceeded, it suddenly breaks,
causing the vibrations of an
earthquake.
How are Earthquakes
measured?
• Seismology – the study of earthquake
waves.
• Seismographs –
instruments that
record earthquake
waves.
Seismograph
Seismogram – a trace produced
recording ground motion.
Primary Waves
(P–Waves / Compression Waves)
• Are push-pull waves that push
(compress) and pull (expand) in the
direction that the waves travel.
• Travel through solids, liquids, and
gases.
• Have the greatest velocity of all
earthquake waves.
Secondary Waves
(S–Waves / Transverse Waves)
• Shake particles at right angles to
the direction that they travel.
• Travel only through solids.
• Slower velocity than P waves.
Surface Waves
(L- Waves)
• Seismic waves that travel along the
Earth’s outer layers
• These are the most destructive
earthquake waves
• The ground moves up and down and
back and forth
** A seismogram shows all three types
of seismic waves – first - P waves
then - S waves lastly - surface
waves.**
• P & S Wave Animation
Closure:
Why do most earthquakes cause little
damage and loss of life?
- Because most occur in
areas that are not
populated.
L.A. Earthquake
Earthquake Destruction