1. Chapter 6 Earthquakes

2. 6.2 Pop Quiz What is the point on the surface directly
above the trigger of the earthquake called?
2) What is the point at which rock under stress breaks and triggers an earthquake called?
T/F – Seismic waves carry the energy of an earthquake away from the epicenter in all directions.
List the three types of waves in order for which the arrive.
What is a device that records the ground movements caused by earthquake waves called?

3. Earthquakes & Seismic Waves
– the shaking that results from the sudden
movement of part of the Earth’s crust
focus
– area beneath the Earth’s surface where the earthquake occurs
-this site triggers the earthquake
epicenter
– site of the earthquake on the surface of the Earth directly above the focus

8. Earthquakes & Seismic Waves
seismic waves – vibrations that travel through the Earth carrying the energy released during an earthquake
- move like ripples in a pond
-provide information about the Earth’s interior
Three types of seismic waves:
-P waves
-S waves
-Surface waves

9. Earthquakes & Seismic Waves
P waves (primary waves):
-arrive first
-compress and expand or “push, pull”
-travel through solids, liquids and gases
-can damage buildings, causes them to contract
and expand

11. Earthquakes & Seismic Waves
S waves (secondary waves):
-arrive second
-move “side to side” as well as “up and down”
-shake the ground back and forth
-shake structures “side to side”, can cause major damage
-can not move through liquids

13. Earthquakes & Seismic Waves
Surface waves:
-when P or S waves reach the surface
-move more slowly than P or S waves
-can produce severe ground movements
-can make the ground roll like ocean waves
-most destructive, shakes buildings violently

15. Measuring Earthquakes
seismograph
– instrument that records and measures seismic waves
magnitude
– the number geologists assign to an earthquake based on its size
-determined by measuring seismic waves and fault movement

16. Measuring Earthquakes
Richter scale
– a rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves
moment magnitude scale
–rating system that estimates the total energy released by an earthquake
-this is the number most quoted by news reports about the “size” of an earthquake
-looks at the type and strength of the seismic waves

17. Measuring Earthquakes
Richter scale no.
No. of earthquakes per year
Typical effects of this magnitude
< 3.4
800,000
Detected only by seismometers
30,000
Just about noticeable indoors
4,800
Most people notice them, windows rattle.
1,400
Everyone notices them, dishes may break, open doors swing.
500
Slight damage to buildings, plaster cracks, bricks fall.
6.2  6.9
100
Much damage to buildings: chimneys fall, houses move on foundations. 15
Serious damage: bridges twist, walls fracture, buildings may collapse. 4
Great damage, most buildings collapse.
> 8.0
One every 5 to 10 years
Total damage, surface waves seen, objects thrown in the air.
Measuring Earthquakes

18. Locating the Epicenter
-geologists use seismic waves to locate an earthquake’s epicenter
-geologists use data from at least three different seismographs