Handout 1 Standard 2-1.a, b, and c Plate Tectonics 1

1. When Earth formed, its interior was heated by what two processes? Heat of formation Radioactive decay

2. Because Earth’s interior is warmer than its surface layers, hot materials move toward the surface in a process called __________. convection

3. When rocks along a fault slip into new positions, they release energy in the form of vibrations called seismic waves. The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is on the earth's surface directly above the focus.

4. Where do seismic waves travel? outward in all directions from the focus through the surrounding rock

5. How many types of waves do earthquakes produce? Two (3 if we count surface waves)

Matching 6-8 6. body wave a. the fastest seismic wave; causes particles of rock to move in a back-and forth direction parallel to the direction in which the wave is traveling; can travel through solids, liquids, and gases 7. p wave b. the second-fastest seismic wave; causes particles of rock to move in a side-to-side direction perpendicular to the direction in which the wave is traveling; can only travel through solids 8. s wave c. a seismic wave that travels through the body of a medium

P waves

S waves

P waves and S waves

Seismic Waves

Lag time in Arrival of P wave and S wave. Since P-waves travel faster than S-waves do, the seismograph will detect P-waves arriving first, and S-waves will follow. The time difference, as recorded on a clock, between when the P-waves and S-waves arrive is called the lag time.

9. The composition of the material through which P waves and S waves travel affects the speed and direction of the waves.

Huh?

10. What type of materials do P waves travel through fastest? materials that are very rigid and not easily compressed

11. What did Croation scientist Andrija Monorovicic discover in 1909? The speed of seismic waves increases abruptly at about 30 km beneath the surface of continents. This area is called the MOHO. Modern instruments have determined that seismic-wave velocity rapidly increases to more than 8 km per second (5 miles per second) at this boundary. Mohorovičić later discovered a technique for locating earthquake epicentres and calculated the travel time of seismic waves. He was an early advocate of earthquake-resistant construction.

12. Define shadow zone. An area on Earth’s surface where no direct seismic waves form a particular earthquake can be detected.

13. Why do shadow zones exist? Because the materials that make up Earth’s interior are not uniform in rigidity.

14. What happens to seismic waves as they travel through materials of differing rigidities? The speed of the waves changes and the waves will bend and change direction as they pass through different materials.

15. Why don’t S waves reach the S-wave shadow zone? Because S waves cannot pass through the liquid outer core.

16. How does a P-wave shadow zone form? The speed and direction of the waves change as they pass through each layer, and the waves bend in such a way that a P-wave shadow zone forms.

The End