Laboratory Manual for Introductory Geology 4e

FIGURE 11.4 Worldwide distribution of earthquake epicenters. Most earthquakes occur in distinct belts along plate
boundaries.
Alpine-Himalayan
collision
Atlantic
Ocean
Indian
Ocean
Pacific
Ocean
Shallow earthquakes
Intermediate earthquakes
Deep earthquakes
Exercise 11.2 illustrates the reasoning used to determine the distance from a
seismometer (the streetlight in questions c and d ) to an earthquake epicenter (the
starting line of each car). But, in this exercise, you have been given the velocity of
the cars. How do seismologists determine these measurements?
EXERCISE 11.2
The Logic of Locating Earthquake Epicenters
Name:
Course:
Section:
Date:
This exercise leads you through the reasoning used to calculate the distance from a seismic station to an earthquake
epicenter. But instead of two different seismic waves, let’s see first how this works with two cars that start along a road at
exactly the same time (see the figure on the next page). Both cars use cruise control set at 1 mile per minute (60 miles
per hour), but the controls are not exactly the same. Car 1 covers each mile in exactly 60 seconds and Car 2 in 61 seconds.
Because Car 1 arrives a second before Car 2 for each mile they travel, the delay between the arrival times of Car 1 and
Car 2 increases at each mile marker.
To see how this works, complete the illustration on the next page:
(a) In each of the boxes to the right of Car 1 and Car 2, note the travel time (in seconds) needed to arrive at that
milepost—the first one has been completed.
(b) In the boxes at the bottom of the figure, indicate the delay time between arrival of Car 1 and Car 2 at each
milepost.
(continued)
280 CHAPTER 11 EARTHQUAKES AND SEISMOLOGY