1. Ch 12-Earthquakes Objectives Elastic rebound
Compare body waves and surface waves
Explain how the structure of Earth’s interior affects seismic waves
Explain why earthquakes generally occur at plate boundaries
Describe the instrument used to measure and record earthquakes
Summarize the method scientists use to locate an eipcenter
Describe the scales used to measure the magnitude and intensity of earthquakes
Discuss the relationship between tsunamis and earthquakes
Describe possible effects of major earthquake on buildings
List safety techniques to prevent injury caused by earthquake activity
Identify methods scientists use to forecast earthquake risks

2. Earthquakes
Movement or trembling of the ground that is caused by sudden release of energy when rocks along a fault move
What happens?
Rocks under stress suddenly shift along a fault. What is a fault?
Break in body of rock along which one block slides relative to another
Why do earthquakes happen?

3. Concepts in Motion What do you think elastic rebound means?
Sudden return of elastically deformed rock to its undeformed shape
Anatomy of Earthquake
Focus-location w/in Earth along fault at which first motion of earthquake occurs
Epicenter-point on Earth’s surface directly above an earthquake’s starting pt
Earthquakes that have most damage=shallow foci
Seismic Waves
As rocks slip, rocks release energy in form of vibrations, travel in all directions
2 types-body and surface waves
Concepts in Motion

4. Seismic Waves Body Waves-travel through the body of a medium
P waves-travel fastest and 1st , causes particles to move back and forth parallel to direction that wave is traveling. Can travel through solids, liquids, and gases
S waves-shear waves, 2nd fastest, cause particles to move side to side, perpendicular to direction of wave. Only travel through solid material

5. Surface Waves
Form from motion along shallow fault or from the conversion of energy when P waves and S waves reach Earth’s surface
Slowest, most damage
2 types-Love and Rayleigh
Love-rock side to side and perpendicular to waves
Rayleigh-ground to move w/ elliptical, rolling motion

6. Seismic Waves and Earth’s Interior
What are Earth’s internal layers?
What are the mechanical layers?
Lithosphere, Asthenosphere, mesosphere, outer core, inner core
Composition of material determines the speed and direction of the waves
What are shadow zones?
Area on Earth’s surface where no direct seismic waves from particular earthquake can be detected. Why are there shadow zones?

7. Earthquakes and Plate Tectonics
What causes earthquakes?
Stresses in the Earth’s lithosphere
Earthquakes happen at 3 main tectonic environments
Convergent Oceanic Environment-plates move toward each other and collide
2 oceanic plates or oceanic and continental
Divergent Oceanic Environment-plates moving away from each other
Mid ocean ridges
Continental Environment-2 continental plates converge, diverge or move horizontally in opposite directions
Stress may cause frequent earthquakes or mts to form

8. Fault Zones
What is a fault zone? Region of numerous, closely spaced faults
Form at plate boundaries. Why?
Intense stress that results when plates separate
Not all earthquakes occur from movement along plate boundaries
New Madrid, Missouri
Mississippi River region

9. Sec 2-Studying Earthquakes
Seismology-study of earthquakes and seismic waves
What instrument is used to measure and record earthquakes?
Seismograph-instrument that records vibrations in ground, record motion by tracing wave shaped lines on paper or by translating the motion into electronic signals
What waves are recorded first?

10. Locating an Epicenter
Analyze arrival times of P waves and S waves Longer lag time between waves, the farther the earthquake is
Use computers- to perform triangulations based on data from seismograph stations
Earthquake measurement
Study magnitude and intensity and amount of damage
Magnitude-measure of strength of an earthquake
Measure the amount of ground motion caused by earthquakes
Richter scale
Moment magnitude-measurement of earthquake strength based on size of area of fault that moves
More accurate for large earthquakes

11. Intensity-amount of damage caused by an earthquake
Mercalli scale-provides description of effects of each earthquake
Intensity depends on earthquake’s magnitude, distance between epicenter and affected area, local geology, earthquake’s duration and human infrastructure

12. 1906-San Francisco

13. 1906-San Francisco

14. 1906-San Francisco

15. Sec 3-Earthquakes and Society
What is a tsunamis?
Giant ocean wave that forms after volcanic eruption, submarine earthquake, or landslide
Waves increase in height as they near shore
Destruction of earthquakes
Tall buildings, buildings build on loose soil and rock
How to prevent injury by earthquake activity
Be prepared, supply of food and water, flashlights, batteries, portable radio
Stay calm, move to safer position, stay away from windows and heavy furniture
Be cautious, check for fire or other hazards, wear shoes, avoid downed power lines

16. Earthquake Warnings and Forecasts
Study past earthquakes, nothing reliable to predict when and where
Studying Earth’s crust to detect changes
Seismic gaps-area along fault where relatively few earthquakes have occurred recently
Foreshocks-little earthquakes that precede actual earthquakes
Changes in rock
Use sensors to detect slight tilting of ground and to identify the strain and cracks in rocks caused by stress that builds up in fault zones