1. ANALYZING SEISMIC WAVES

2. 3 Seismograms from Different Locations:
Note the P-Wave ALWAYS arrives first…(it’s faster!)

3. P and S wave Arrival Times
Station A: San Francisco, California
P-Wave arrival =
S-Wave arrival =
3:06:30
3:02:20
What is the time interval between P and S wave arrival times?
4min10sec

4. P and S wave Arrival Times
Station B: Denver, Colorado
P-Wave arrival =
S-Wave arrival =
3:05:00
3:01:40
What is the time interval between P and S wave arrival times?
3min20sec

5. P and S wave Arrival Times
Station C: Missoula, Montana
P-Wave arrival =
S-Wave arrival =
3:03:00
3:01:00
What is the time interval between P and S wave arrival times?
2min0sec

6. Difference in arrival times: Which place did the seismic waves hit first?
San Francisco, CA: :10´
Denver, CO: :20´
Missoula, MT: :00´
Missoula! The Time Interval is smallest which means it is closer to the earthquake!

7. Analyze the seismographs to find the P/S-wave time intervals
0:11m:50s – 0:10m20s=
1min 30 sec interval B
0:15m:30s – 0:10m 0s=
5min 30 sec interval C
0:14m:0s – 0:9m 50s=
4min 10 sec interval
Which station is closest to the earthquake?

8. ESRT to the RESCUE! (travel time graph)
We know “A” is closest, but what is the actual distance from “A” to the earthquake’s epicenter?? A
0:11m:50s – 0:10m20s=
1min 30 sec interval B
0:15m:30s – 0:10m 0s=
5min 30 sec interval C
0:14m:0s – 0:9m 50s=
4min 10 sec interval
ESRT to the RESCUE! (travel time graph)

9. How far is San Francisco away from the earthquake epicenter?
San Francisco, CA: 4m:10s interval
According to the ESRT, San Francisco is 2800km from the epicenter!
How is this figured out?

10. TAKE A PIECE OF PAPER, AND MARK OFF THE DIFFERENCE IN ARRIVAL TIME
4:10
2800Km

11. EPICENTER DISTANCES San Francisco, CA: 4:10 Denver, Co: 3:20
2,800 km
Denver, Co: 3:20
2,000 km
Missoula, MT :00
1,100 km

12. . . Where the 3 circles intersect is the Epicenter of the Earthquake.
1100 km .
2800 km
2000 km
You've found
The epicenter!
Does this seem
like a likely location
for an earthquake to occur?

13. Compare your answer to the historical record
Missoula
Syracuse X
San Francisco
Denver

14. 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

15. Recording Board Difference in arrival times:
San Francisco: 41:0
2,800 km
Line your compass up to the EXACT distance on the scale. Use the metric side (cm) beginning from zero.
1,000
2,000
3,000
4,000
5,000