1. 19.2 – Seismic Waves & Earth’s Interior

2. Measuring Seismic Waves
Seismometer = sensitive instruments that detect seismic waves
Rotating drum covered with paper
Pendulum with writing instrument attached
Mass on pendulum and pen are at rest due to inertia
When ground shakes, the pen registers it on paper
Seismogram = record produced by seismometer

3. Seismometer

4. Travel-Time Curve Seismic waves are recorded at various facilities
Seismologists construct graph showing arrival of waves

6. Distance from epicenter
Measure arrival of primary (P), secondary (S), and surface waves
As distance increases, separation between waves increase
Information is used to locate epicenter

7. Clues to Earth’s Interior
Seismic waves help give information about Earth’s interior
Seismic waves change speed and direction at boundaries between different materials
Through mantle P and S waves follow direct paths
When P waves strike Earth’s core they refract (bend)

8. By creating Travel-time curves and path of each wave, seismologist learn about difference in density and composition
S waves do not travel through liquid, which means they do not travel through core
Means Earth’s core is at least partially liquid

9. Earth’s composition Waves can also change speed
Earth’s composition
Waves can also change speed
Speed tells scientists thickness and composition of Earth’s different regions
Upper mantle = peridotite
Outer core = mostly liquid iron and nickel
Inner core = mostly solid iron and nickel

10. http://images. encarta. msn

11. In-Class Assignment/Homework