Finding an Epicenter

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Finding an Epicenter

• Finding the Distance to the Epicenter of an
  Earthquake!

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What is an Epicenter?

• A point on the surface of the Earth directly
  above the FOCUS of the earthquake.

• The point within the Earth from which earthquake
  waves originate.

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(No Transcript)
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Use the data from the recording stations

• Station A San Francisco, California
• P-Wave arrival 30220 S-Wave arrival 30630

What is the time difference between P and S wave
arrivals?
410
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Use the data from the recording stations

• Station B Denver, Colorado
• P-Wave arrival 30140 S-Wave arrival 30500

What is the time difference between P and S wave
arrivals?
320
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Use the data from the recording stations

• Station C Missoula, Montana
• P-Wave arrival 30100 S-Wave arrival 30300

What is the time difference between P and S wave
arrivals?
200
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Difference in arrival times
San Francisco 410
Denver, Colorado 320
Missoula, Montana 200
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TAKE A PIECE OF PAPER, AND MARK OFF THE
DIFFERENCE IN ARRIVAL TIME
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MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP
WITH THE P AND S CURVES
WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND
READ THE EPICENTER DISTANCE
EPICENTER DISTANCE OF 2800 KM
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EPICENTER DISTANCES
San Francisco 410
2,800km
Denver, Colorado 320
2,000km
Missoula, Montana 200
1100km
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Recording BoardDifference in arrival times
San Francisco 410
2,800km
Open your compass to the EXACT distance on the
scale.
3,000
4,000
5,000
1,000
2,000
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Use your carefully set compass to draw a circle
around each city.
.
.
.
You've found the epicenter!
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Finding the Earthquake Origin Time

• You take a distance to epicenter that you have
  already determined, or one given to you
• Lets say the epicenter distance is 4400km, and
  the arrival time is 32115 PM
• Well, use your ESRT and do some time math!!!
• Lets try it

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Do it!
P wave travel time 000740

• Find the distance on the horizontal axis.
• Go up to the point where you hit the P-wave
  travel line.
• Go over to the vertical axis and read off the
  travel time for the P-wave.

Epicenter dis 4400km
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Now, do the math!

• Take the arrival time, and subtract the travel
  time from it!
• 32115 000740
• 31335
• So, the origin time of the Earthquake is 31335
  PM.
• Now YOU try it for San Francisco!!