Laboratory Manual for Introductory Geology 4e

EXERCISE 11.4
Name:
Course:
Locating an Earthquake’s Epicenter and Determining When It Occurred (continued)
Section:
Date:
Locating an earthquake epicenter.
A second station in Caracas, Venezuela, calculated a
Compass
distance of 6,000 km to the epicenter— somewhere on a
circle with a radius of 6,000 km centered on Caracas. The
two circles cross in two places, one in the Rockies, the
other somewhere in the eastern Atlantic Ocean (outside
the figure). The epicenter must be at one of these
intersections, but both locations are equally possible.
A third station is needed to settle the question, in this
case pinpointing the epicenter in the Front Ranges of the
Station 3
Rocky Mountains. Data from at least three seismic stations
are needed to locate any epicenter, and the process is called
Epicenter
triangulation. The more stations used, the more accurate
the location.
To locate the approximate epicenter (at last!) from
your data, use an architect’s compass or piece of string
scaled to the appropriate distance for the map below.
Draw an arc representing the distance from the first
station and repeat the process for the other two stations.
0 1,000
km
Review your work. Because of the tools you are using, your three arcs might not intersect
perfectly, but they should be near one another. Draw a small circle with a 300-km diameter
showing the area where you would expect to find the epicenter.
Map and scale for locating the earthquake epicenter.
2,000 km
6,000 km
4,000 km
1,000 2,000 3,000 4,000
Station 1
km
Station 2
Seattle
Boston
Los
Angeles
(continued)
288 CHAPTER 11 EARTHQUAKES AND SEISMOLOGY