Essential Questions How does a seismometer work How have seismic waves been used to determine the structure and composition of Earths interior Copyright McGrawHill Education Seismic Waves and Earths Interior ID: 398231
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Ch. 19.2 – Seismic Waves and Earth’s InteriorEssential QuestionsHow does a seismometer work?How have seismic waves been used to determine the structure and composition of Earth’s interior?
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Seismic Waves and Earth’s InteriorSlide2
Reviewmantle
New
seismometer
seismogram
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Vocabulary
Seismic Waves and Earth’s InteriorSlide3
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Seismometers and Seismograms
Most of the vibrations caused by seismic waves cannot be felt at great distances from an earthquake’s epicenter, but they can be detected by sensitive instruments called
seismometers
, which measure horizontal or vertical motion during an earthquake.Slide4
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Seismometers and Seismograms
The frame of a seismometer is anchored to the ground. When an earthquake occurs, the frame moves but the hanging mass and attached pen do not. The mass and pen record the relative movement as the recording device moves under them.Slide5
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Seismometers and Seismograms
The record produced by a seismometer that can provide individual tracking of each type of seismic wave is a
seismogram
.Slide6
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Travel-time
curves
Travel-time curves provide the average time it takes for P- and S-waves to reach seismic stations located at different distances from an earthquake’s epicenter.Slide7
Seismic Waves and Earth’s Interior
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Distance
from the epicenter
Waves recorded on seismograms from more distant stations are farther apart than waves recorded on seismograms at stations closer to the epicenter.Slide8
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Distance
from the epicenter
The separation of seismic waves on seismograms can be used to determine the distance from the epicenter of an earthquake to the seismic station that recorded the seismogram.Slide9
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Clues to Earth’s Interior
Earth’s internal structure
Seismic waves change speed and direction when at the boundaries between different materials.
As P-waves and S-waves initially travel through the mantle, they follow fairly direct paths. When P-waves strike the core, they are
refracted
, which means they bend.Slide10
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Earth’s
internal structure
Seismologists
first determined that the back-and-forth motion of
S-waves
does not travel through liquid. They then noticed that S-waves do not travel through Earth’s center. Slide11
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Earth’s
internal structure
The data collected for the paths and travel times of the waves inside Earth led to the current understanding that Earth has an outer core that is liquid and an inner core that is solid.Slide12
Seismic Waves and Earth’s Interior
Copyright © McGraw-Hill Education
Imaging
Earth’s interior
Because the speed of seismic waves depends on temperature and composition, it is possible to use seismic waves to create images of structures such as
slabs
and
plumes. In general, the speed of seismic waves decreases as temperature increases.Images like this one from Japan are generated by capturing the path of seismic waves through Earth’s interior. Slide13
Copyright © McGraw-Hill Education
ReviewEssential QuestionsHow does a seismometer work?How have seismic waves been used to determine the structure and composition of Earth’s interior?
Vocabulary
seismometer
seismogram
Seismic Waves and Earth’s Interior