Stnd 17: Seismic Waves and Earth’s
Structure.
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Use the
following data table to answer the next five questions
An earthquake occurred
at a plate boundary in California as huge blocks of the Earth’s crust slipped past one another.
The Pacific plate is moving northwest past the North America plate at this boundary at a rate of
about 50 millimeters (about 2 inches) each year. Seismographs at several locations detected and
measured the seismic waves from this earthquake, and the P-Wave data is shown below. Examine the
following table of seismic data.
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1.
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Examine the information in Seismic Data Table 01 to answer this
question. Layers of rock inside the Earth have been revealed by analyzing seismic data.
Geologists have observed that seismic waves change speed as they move downward toward Earth’s
center. What is one location where this is revealed in Seismic Data Table 01, and
what best explains this phenomenon?
a. | At a depth of 2900 kilometers the P-Waves slowed from 14 km/s to 8 km/s. This
occurred as the wave hit the boundary of the mantle and the outer core. | b. | At a depth of 1000
kilometers the P-Waves stopped. This occurred as the wave hit the boundary of the mantle and the
outer core. | c. | Don’t Select. | d. | At a depth of 3000 kilometers the P-Waves
decreased speed from 9 km/s to 8 km/s. This occurred as the wave hit the boundary of the crust
and the mantle. |
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2.
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Examine the information in Seismic Data Table 01 to answer this
question. What is the primary cause of seismic waves, and what pattern do you notice about the
P-Waves as they propagated downward towards the center of our planet?
a. | Seismic waves mainly result from tectonic plate movement. The P-Waves slow down as
they move through different rock layers within the Earth. | b. | The primary cause of
seismic waves are explosions from nuclear detonations. P-Waves are unable to travel through
liquids. So, they cannot be detected in oceans. | c. | Seismic waves mainly occur beneath the seas due
to the mass of the water. P-Waves speed up as they travel down towards the center of the
Earth. | d. | Don’t Select. |
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3.
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Examine the information in Seismic Data Table 01 to answer this
question. Seismic waves refact and change speed as they move through substances with different
densities. What is one location where this is revealed in Seismic Data Table
01, and what best explains this phenomenon?
a. | At a depth of 2900 kilometers the P-Waves stopped. This occurred as the wave hit
the boundary of the mantle and the outer core. | b. | Don’t Select. | c. | At a depth of 50
kilometers the P-Waves decreased speed from 9 km/s to 8 km/s. This occurred as the wave hit the
boundary of the crust and the mantle. | d. | At a depth of 5200 kilometers the P-Waves
slowed from 14 km/s to 8 km/s. This occurred as the wave hit the boundary of the crust and the
mantle. |
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4.
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Examine the information in Seismic Data Table 02 to answer this
question. Refraction and changes in speed have been observed in seismic wave data as the waves
travel towards the center of our planet. What is one location where this is revealed in Seismic
Data Table 02, and what best explains this phenomenon?
a. | Don’t Select. | b. | At a depth of 2900 kilometers the S-Waves
slowed from 5 km/s to 4 km/s. This occurred as the wave hit the boundary of the crust and the
mantle. | c. | At a depth of 50 kilometers the S-Waves increased speed from 4 km/s to 5 km/s. This
occurred as the wave hit the boundary of the inner core and the outer core. | d. | At a depth of 2900
kilometers the S-Waves slowed from 7.5 km/s to 0 km/s. This occurred because S-Waves are unable
to travel through liquid rock. |
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5.
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Examine the information in Seismic Data Table 02 to answer this
question. P-Waves can travel through both solid and liquid rock. S-Waves, on the other hand,
can only travel through solid rock. What is one location in Seismic Data Table 02 where liquid
rock is revealed by the S-Wave data?
a. | At a depth of 50 kilometers the S-Waves increased speed from 4 km/s to 5 km/s. This
occurred as the wave hit the boundary of the inner core and the outer core. | b. | Don’t
Select. | c. | At a depth of 5200 kilometers the S-Waves slowed from 14 km/s to 8 km/s. This
occurred as the wave hit the boundary of the crust and the mantle. | d. | At a depth of 2900
kilometers the S-Waves stopped. This occurred because after 2900 km there is a layer of
liquid rock. |
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