Do Now:

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Do Now
Compare and contrast the P and S seismic waves.
P
S
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How to Determine the Distance to the Epicenter of
an Earthquake
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Aim How do seismologists determine the distance
to an earthquake epicenter?
I. Determining the distance to an earthquake
epicenter
A. Read seismogram to determine the P-wave
arrival (PA) time and the S-wave arrival (SA)
time.
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(No Transcript)
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Look at seismogram hand-outs. How to read a
seismogram

• P-wave is the first to arrive (fastest). Look
  for first spike in seismogram. S wave is second
  to arrive. Look for next major spike usually
  larger in amplitude (height) than S wave.

• Observe how time is divided on the bottom of the
  seismogram (hours, minutes, seconds)

024730
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1. Record your P-wave arrival time to the nearest
second.
2. Record your S-wave arrival time to the nearest
second.
3. Find the difference in arrival times (S.A.
time subtract P.A. time)
4. Look at p. 11 of your ESRT (Earthquake
travel time graph)
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a. Vertical axis (Travel Time in minutes)
each minute is divided into three smaller boxes
20 seconds each.
b. Horizontal Axis Epicenter Distance (x103 Km)
distance is in thousands of kilometers and each
thousand is divided into 5 smaller boxes 200 km
each box.
c. P and S wave curves
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Sample Problems
1. How long does it take a P wave to travel 4000
km?

• Look at your E-quake Travel Graph
• Go to 4 on the x-axis (remember it is 4 x 103)
• Follow the 4 line up until it hits the P curve.
• Follow the Time line (y-axis) that the P curve
  intersects at this distance
• This is your P travel time
• 7 minutes

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1. How long does it take an S wave to travel
5400 km? 2. How far can a P wave travel in 5
minutes? 3. How far can an S wave travel in 4
minutes and 20 seconds?
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5. Using a piece of scrap paper, mark off your
arrival time difference.
6. Slide your scrap paper (Electric Slide)
until the top mark is on the S-wave line and the
bottom mark is on the P-wave line
simultaneously.
7. Follow that line down and note the distance.
This is your distance to the epicenter.
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Answer the problems in the first chart on your
travel Time Curve worksheet.
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How to Borrow Time!
S.A. 060300 P.A. 055820
1. Always start from the right (seconds)
2. If you cannot subtract the seconds, you need
to borrow a minute, which is 60 seconds
3. If you cannot subtract the minutes, you need
to borrow an hour, which is 60 minutes.
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Answer Part II of your Travel Time Worksheet.