1. Terms/Phrases to Investigate
Seismic Waves
Learning Intention: 8.ESS2.2 (Seismic Waves & Earth’s Structure)
Evaluate data collected from seismographs to create a model of Earth’s structure.
Terms/Phrases to Investigate
data, seismograph, model, and structure
Science and Engineering Practice(s)
Analyze and Interpret Data, Develop and Use Models
Crosscutting Concepts
Stability and Change, Energy and Matter, Cause and Effect
Success Criteria:
...I can create a model of Earth’s internal structure
using seismic data.

2. Seismic Waves
...are waves of energy caused by the sudden breaking of rock
within the Earth. Can also be generated by explosions or impacts.

3. Seismic Waves: Body Waves Link (4 sec): P-Wave Animation
...called body waves because they propagate (move) through the “body” of the Earth.
P-Waves
A.K.A. primary waves
are compression waves
move through solid and liquid rock
fastest kind of seismic wave
pushes/pulls as it moves through
Link (4 sec): P-Wave Animation

4. Seismic Waves: Body Waves Link (5 sec): S-Wave Animation
...called body waves because they propagate (move) through the “body” of the Earth.
S-Waves
A.K.A. secondary waves
are transverse waves
only move through solid rock
slower than P-Waves
up/down or side to side motion
second wave felt during earthquakes (after P-Waves)
Link (5 sec): S-Wave Animation

5. Link (1:04): How a Seismograph Works
Seismographs
What is a seismograph?
A.K.A. seismometer
an instrument that measures and records seismic waves
generally used for detecting and measuring earthquakes
also detects/measures volcanic events and explosions
Link (1:04): How a Seismograph Works

6. Seismogram from Alaska Seismogram from California
a seismogram is the graph output from a seismograph.
Seismogram from Alaska
Seismogram from California
Richter Scale: a 1 to 9 scale for measuring seismic waves.
Each level is ten times greater than the previous level.

7. After Nearpod Lesson on Seismic Waves

8. Locate anomalies in this seismic data.
Then draw a model of Earth’s structure from this data.
Crust
Slowed
Slowed
Mantle
Slowed
Slowed
Repeated
Repeated
Outer
Core
Question:
Why did the S-Waves
stop at 2900 km?
Inner
Core
Repeated

9. Draw a model of Earth’s structure from the data.
Crust
Depth: 0 to 50 km
Mantle
Depth: 50 to 2900 km
Outer Core
Depth: 2900 to 5200 km
Inner Core
Depth: 5200 to 6400 km

10. Earth’s Internal Structure
Link (5:49): How We Know About Earth's Interior?

11. Earth’s Internal Structure
Seismic waves change speed and refract (bend) as they move
through different rock layers. S-Waves stop at liquids.
Understanding this enabled us to analyze seismographic data which reveals Earth’s internal structure.

12. Review 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 7.5 km/s to 0 km/s. This occurred because P-Waves are unable to travel through liquid rock.
b) 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.

13. Review 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 5200 kilometers the P-Waves slowed from 11 km/s to 10 km/s. This occurred because P-Waves are unable to travel through solid rock.
b) After 5200 km, P-Wave speed was a constant 11 km/s all the way to Earth’s center. This occurred as the wave moved from the outer core through the inner core.

14. Review Question
Seismic waves refract 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 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.
b) At a depth of 2900 kilometers the P-Waves slowed from 7.5 km/s to 0 km/s. This occurred because P-Waves are unable to travel through liquid rock.

15. Review Question (A) (B)
Analyze the P-Wave and S-Wave speed patterns in Seismic Data Table 01 and 02.
Then select the model below which best matches the data.
(A)
(B)
(A) Model One
(B) Model Two