# 9 Difference in Arrival Time of P and S Waves (min) 8 7 6 5 4 3 2 1

```Difference in Arrival Time of P and S Waves (min)
9
8
7
6
5
4
3
2
1
1000
2000
3000
4000
5000
6000
7000
Name
City
Denver, Co
Houston, Tx
Miami, Fl
1.
2.
3.
4.
5.
6.
1.
Period
Difference in P and S
Waves
2 min 10 sec
3 min 55 sec
5 min 40 sec
Distance To
Epicenter (km)
Date
Distance on map
(mm)
PROCEDURES
The graph shows how the difference in arrival time between P waves and S waves depends on the distance from
the epicenter of the earthquake. Find the difference in arrival time for Denver on the y-axis and follow this line
across to the point at which it crosses the curve. Follow this point down to find the distance to the epicenter.
Enter this data into the data table.
Repeat for Houston and Miami.
Measure the distance scale on your map and create a conversion in millimeters. Convert each of your distance
from km to mm. Write these conversions on your data table.
Using a ruler and a compass, find the correct distance to represent your epicenter distance.
Draw a circle with the compass from each city marking the possible epicenter location.
Where these 3 circles overlap (or at least are close to overlapping) is your epicenter. Mark your map with a star
to show where you believe the earthquake epicenter to be located.
ANALYSIS
Which city is closest to your epicenter?
2. How many kilometers away?
3. Which city, of the three in your data table, would sense the earthquake first? Last?
4. When you are trying to locate an earthquake why is it important to know distances from at least 3 cities?
5. What would the difference in time be for this earthquake for a recording station in San Francisco?
6. From what you know about this area, is this earthquake here a freak event or a normal occurrence?
7. Why?
8. What features of Earthâ€™s surface would you expect to find in this region? List 3
a.
b.
c.
```
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