Transcript File

Chapter 8.1/8.2
https://www.youtube.com/watch?v=_YLjIvJ
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 Earthquake
– a vibration of the Earth
produced by a rapid release of energy.
 Most often caused by slippage along a
TRANSFORM FAULT boundary.
 https://www.youtube.com/watch?v=CtBX
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 When
the fault “snaps”. . . Energy travels out
from the focus in waves like ripples in water.
 Waves travel in ALL directions
 P waves, S waves, Surface waves
 Two
types – BODY waves and SURFACE
waves
• BODY WAVES – waves that travel through the
Earth’s interior.
• Two kinds: P-waves and S-waves.
 P-waves (push-pull waves)
 Move things forward and back
 S-waves (shake waves)
 Move things up and down
 Surface Waves
– waves that travel along
the Earth’s surface
• Surface waves travel up and down AND side to
side AT THE SAME TIME!
 Surface waves are the MOST DESTRUCTIVE of all
the seismic waves
Epicenter: point on surface above
earthquake focus
 Elastic
Rebound Hypothesis
• 1. As two plates are sliding past each other, they
get STUCK and stop moving.
• 2. The convection current below DOES NOT STOP,
so pressure builds up under the crust.
• 3. When TOO MUCH pressure has built up the
crust plates shift rapidly to release
the pressure.
This is an EARTHQUAKE!
 Foreshocks
– small earthquakes
that come days, weeks or even
years before the MAIN quake.
 Aftershocks
– small earthquakes
that follow a MAIN quake.
 Aftershocks
can cause MAJOR
damage (even though they are
smaller than the MAIN quake)
because the main quake has already
weakened all the structures.
 Seismology
– the study of earthquake waves
• Has been going on for almost 2000 years
 Seismograph
– the instrument used to
measure the strength of an earthquake
 The
machine is attached to the Earth
 The Earth moves during an earthquake –
moving the machine as well.
 The hanging weight DOES NOT MOVE!!
 Attached to the weight is a pen.
 As the paper moves back and forth with
the machine, the pen marks the paper,
recording the strength of the seismic
http://www.youtube.com/watch?v=83G
waves.
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http://www.youtube.com/watch?v=Gbd1FcuLJLQ
Seismograph
Used to measure Seismic Waves
 In
order from FASTEST to SLOWEST
• P-waves
• S-waves
• Surface waves
(PRIMARY – first)
(SECONDARY – second)
(last)
 The
difference in wave speeds give us
the information to determine two
important measurements:
• 1. How far away from the seismograph the
earthquake is
• 2. Where the epicenter of the earthquake is
 The
paper print out from the seismograph
 Shows the arrival times of P-waves, Swaves and Surface waves
 November
10, 2010
 How
to calculate distance
• 1. Read seismogram to determine the time
interval between 1st P-wave and 1st S-wave
• 5 minutes
 2.
Find on the time-travel graph where 5
minutes is the interval
 3.
Travel to the X-axis,
this is the earthquake
distance
You now know how far away
from the seismograph the
epicenter is.
But you DO NOT know the
DIRECTION
Could be North, South, East or West
How do you locate EXACT location of epicenter?
1. Determine the
distance from 3
different
seismographs
2. Draw circles that
have a radius of that
distance
3. The ONE PLACE
that all 3 circles
touch is the
epicenter