1. CH 8 Earthquakes

2. What is an Earthquake?
- more than 30,000 earthquakes are measured each year, but only ~75 are major
- usually occur along a break in the Earth’s crust called a Fault.

3. Focus vs. Epicenter
Focus = point where the earthquake originates underground
- energy radiates outward in all directions from the focus

4. Focus vs. Epicenter
Epicenter = point on Earth’s surface that is directly above the focus. - point of most damage on surface

5. Elastic Rebound Hypothesis
= energy is built up slowly underground and rock bends
- eventually the energy gets too great and the rocks break at the focus
- after energy is released, rocks snap back to original shape but at a new location

6. How do we study Earthquakes?
Seismographs = instrument to measure energy of earthquake (ground shaking)
2. Seismogram = written record of ground movement
 Energy from Earthquakes travel through Earth as Seismic Waves

7. 2 Types of Seismic Waves
1. Surface Waves = travel only along Earth’s surface
- can move up & down or side to side
- most destructive wave to property
- slowest speed

8. 2 Types of Seismic Waves
2. Body Waves = travel through Earth’s interior P - Waves = primary waves - push/pull motion - fastest waves S - Waves = secondary waves - side to side motion - can’t travel through liquids

9.  Seismographs show all 3 specific waves for every earthquake

10. How strong are earthquakes?
Scientists have used 2 types of measurements to describe the size of an earthquake……

11. How strong are earthquakes?
Intensity = amount of shaking at a location
based on damage
Not really accurate
Based on personal estimates of damage

12. 2. Magnitude = measures size of seismic waves (amount of energy released) on seismograms
»Based on 2 scales

13. Richter Scale = based on largest seismic wave recorded on seismogram
- exponential scale
- outdated

14. EX: magnitude 5 is 10X stronger than magnitude 4 EX: magnitude 5 is 100X stronger than magnitude 3 Problems measuring larger quakes

15. more accurate than Richter
Moment Magnitude Scale
measures ground movement
- measures the energy
more accurate than Richter
more complicated
Not used outside of science

16. Dangers of Earthquakes
1. Property damage = depends on strength & length (time) of earthquake
- ground material = loose soil will shift during quake
- building material = rigid buildings (steel) don’t bend, so they break during a quake
- wood structures bend and sway

17. 2. Tsunamis = large wave created by an underwater earthquake
- very fast km/hr
- in open ocean tsunamis appear small but near land, can become m tall
- tsunami warning system (US) monitors Pacific Ocean earthquakes

18. 3. Landslides = shaking causes soil to slide downhill
4. Fire = gas & electrical lines can be cut during a quake causing a fire
- water lines are also broken so fires can’t be put out

19.  Most of our knowledge of the Earth’s interior comes from the study of earthquakes
As scientists studied seismic waves, they saw they do not travel straight through = curve, WHY???

20. - Because Earth’s interior is not the same throughout, it has layers with different properties

21. 4 Layers of the Earth CRUST- thin rocky outer layer of the Earth
- Oceanic Crust = ~7 km thick, dense, made of basalt, relatively young
- Continental Crust = ~40 km thick, made of granite & other light, very old

22. 2. Mantle = solid rocky layer that extends down to 2900 km deep, weakened because of increased temperature & pressure
3. Outer Core = made of liquid Fe & Ni, rotates to create Earth’s magnetic field, 2600 km thick

23. 4. Inner Core = made of solid Ni & Fe , 1220 km thick

24. 2 Special Zones
Lithosphere = crust and outer mantle, rigid shell, forms the continental plates

25. Asthenosphere = below lithosphere, about 150 km thick, very weak, partially melted, allows lithosphere above to move slowly

26. VERY IMPORTANT FOR PLATE TECTONICS
VERY IMPORTANT FOR PLATE TECTONICS