SEISMIC WAVE BASICS

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SEISMIC WAVE BASICS
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Finding an Epicenter
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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
410
2800Km
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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
2,000
4,000
5,000
1,000
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Use your carefully set compass to draw a circle
around each seismic station.
.
.
.
You've found a possible epicenter! Does this
seem like a likely location for an earthquake
to occur?
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Compare your answer to the historical record
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Need a closer view to be sure? Go to
http//earthquake.usgs.gov/regional/states.php
and retrieve the seismicity map (like the one on
the left) for the state containing your possible
solution.
Based on this map, earthquakes have previously
occurred in the region where our epicenter fell.
Thus our answer seems likely
USGS
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What if our epicenter had fallen here instead?
Does this mean our solution is wrong or less
likely? What could help us find out?
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Credits This file was originally created by
Robert M. DeMarco of Marlboro Central High
SchoolEdits have been added by

• Chris Visco - Sachem High School
• Eric Cohen- Westhampton Beach High School
• Michael Hubenthal - IRIS Consortium