1. Topic 5: Sudden Earth Events

2. Are the shaking of the Earth’s surface
Caused by the sudden release of energy in the curst
Movement of tectonic plates
Energy is released in 3 types of waves

3. Primary (P) Waves
Fastest moving waves
Cause a small vibration
“Warning waves”

4. Secondary (S) Waves
Travel more slowly
Shears the ground back & forth, up & down

5. Surface Waves Slowest waves
Move the ground sideways, roll in like ocean waves
Travel out in a “ripple effect” from focus

6. Aftershocks
Smaller earthquakes that occur after the main surface waves

7. Measuring Earthquakes
The earliest seismoscope was invented by the Chinese in 132 AD Large urn – on outside were 8 dragon heads facing the main directions of the compass; below each dragon head was a toad with its mouth open
When an earthquake occurred, one or more of the eight dragon mouths would release a ball into the open mouth of the toad sitting below
Direction of shaking determined which of the dragons released its ball
Reported to have detected an earthquake nearly 650km away

8. Seismograph
Device used to measure earthquakes
Attached to bedrock to feel vibrations
Marking pen positioned over a rotating drum covered in paper
Bedrock shakes causing the pen to move while the drum rotates

9. Richter scale Describes the magnitude (strength) of the earthquake
Starts at 0; can go as high as needed
As the number increases, the amount of energy released by the earthquake increases by 30X
Magnitude 3 is 30X stronger than a magnitude 2, and 900X stronger than a magnitude 1
How much stronger is a magnitude 10 than a magnitude 3?
The World’s largest earthquake with an instrumentally documented magnitude occurred on May 22, 1960 near Valdivia, in southern Chile. It was assigned a magnitude of 9.5

10. Magnitude 0-2.: not felt but is recorded
Magnitude : felt by a few
Magnitude : felt by some
Magnitude : felt by most
Magnitude : damaging shocks
Magnitude : destructive in populated regions
Magnitude : major earthquake, serious damage
Magnitude 8.0+: great earthquake, total destruction

11. Locating an Earthquake
Focus
Place deep in the earth where the earthquake begins
Epicenter
Surface location directly above the focus

12. Cause of Earthquakes Rock in Earth’s crust is under constant pressure
Pressure is too great = sudden break
Creates a FAULT – area where two larger rock surfaces move against each other
Fault zones are found where tectonic plates meet

13. Types of faults
1. Normal Fault
Diverging tectonic plates
Earthquakes are shallow – most happen on the sea floor and cause little damage

14. 2. Reverse Fault
Converging tectonic plates
Deepest quakes

15. 3. Slip-Strike / Transform Fault
Shearing tectonic plates
Surfaces get caught and the rock is twisted and strained