1. Chapter 19 Notes
Earthquakes

2. Stress and Strain
Earthquakes occur when stress builds up and causes movement in the Earth’s crust
Compression: squeezing forces
Tension: pulling forces
Shear: opposing parallel forces/twisting
Elastic deformation: initial response to stress
plastic deformation occurs under high stress just before breaking

3. Faults Normal fault: produced by tension forces
Reverse fault: produced by compression forces
Strike-slip fault: produced by shear forces

4. Earthquake Waves Body Waves
Primary (P-waves): compression waves; move parallel to the direction of wave motion
Secondary (S-waves): transverse waves; move at right angles to the direction of wave motion
Surface waves: move sideways and up and down

5. Earthquake Waves P-waves move fastest
Surface waves are slowest, last the longest, and are the most destructive

6. Earthquake location Focus: the origin of the EQ waves
Epicenter: “above” the center

7. Earthquake Measurement
Seismometer: an instrument that records EQ waves
Seismogram: the record of EQ waves

8. Time travel curves
The difference in arrival time of the P-waves and S-waves can show how far the waves have travelled.

9. Clues to Earth’s Interior
EQ waves are reflected and refracted in different ways by the different materials inside the Earth

10. Measuring Earthquakes
Richter Scale:
measures magnitude
energy released
numeric scale (no true upper limit)
Modified Mercalli Scale:
measures intensity
based on the amount of damage
Roman numerals I to XII

11. Richter Scale

12. Mercalli Isoseismic Map

13. Locating an Earthquake
The P-wave and S-wave arrival times determine the distance a station is to an EQ
Three stations are required to locate the epicenter of an EQ

14. Seismic Belts
Circum-Pacific and Mediterranean-Asian belts

15. Earthquake Hazards “Earthquakes don’t kill people, buildings do.”
Structural failures
Brittle building materials cause more damage
Building height oscillations
Land and soil failure
Soil liquefaction
Tsunami
Ocean wave generated by sea floor movement

16. U.S. Earthquake Risk