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FIGURE 19.15 (A) A seismometer for horizontal motion. Some
seismometers record Earth motion on moving strips of paper. The
mass is suspended by a wire from the column and swings as a
Revolving drum Wire
pendulum when the ground moves horizontally. A pen attached to
Heavy weight
the mass records the motion on a moving strip of paper. (B) A seis-
Column mogram of a 1967 earthquake in Taiwan, magnitude 6.2, recorded
in Berkeley, California, 6,300 miles away. First arrivals of P-, S-, and
surface waves are shown. Source: Courtesy of Berkeley Seismological Laboratory,
University of California Berkeley.
Pen

Ground
movement
A Rock

B First P-wave First S-wave First
surface wave

S-waves

Difference in
arrival times 200 km
P-waves X

150 km
Y
Time of Earthquake
first arrival

100 km Z
Distance from earthquake
A B

FIGURE 19.16 Use of seismic waves in locating earthquakes. (A) Difference in times of first arrival of P-waves and S-waves is a function
of the distance from the focus. (B) Triangulation using data from several seismograph stations enables location of the earthquake.

486 CHAPTER 19 Building Earth’s Surface 19-10