Laboratory Manual for Introductory Geology 4e

EXERCISE 11.4
Name:
Course:
Locating an Earthquake’s Epicenter and Determining When It Occurred (continued)
Section:
Date:
Slide the station worksheet across the travel-time diagram until all four arrows coincide with the appropriate traveltime
curves (one possible worksheet position is shown in the figure below).
Using a travel-time diagram to determine distance to an earthquake epicenter and time the earthquake occurred.
35
R-wave
30
Seismic wave travel time (min)
25
20
15
R
L
S
S-wave
L-wave
10
P
P-wave
5
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000
Distance from epicenter (km)
Draw a vertical line from the edge of the station worksheet to the distance scale on the horizontal axis (as shown by the
dashed red arrow) and read the distance from the epicenter. Repeat for the other two stations and record the data.
Distance to epicenter from Seattle: km Boston: km Los Angeles: km
Step 4: Determining the Location of an Earthquake with Triangulation
It’s one thing to know how far an epicenter is from a seismic recording station, but quite a different thing to know exactly
where it is. Seismologists from Nova Scotia’s Cape Breton Island calculated that an earthquake occurred 4,000 km
from their station. Therefore, the epicenter must lie somewhere on a circle with a radius of 4,000 km centered on their
station—but that could be in the Atlantic Ocean, Hudson Bay, Mexico’s Yucatán Peninsula, or the Front Ranges of the
Rocky Mountains (see the map on the following page).
(continued)
11.3 LOCATING EARTHQUAKES
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