1. Megaquake: Hour that Shook Japan (42:58min)
Earthquakes
Megaquake: Hour that Shook Japan
(42:58min)

2. What is an Earthquake?
A sudden release of stored potential energy that makes the Earth shake.
Happens within the lithosphere.
Most common along a transform boundary.

3. Parts of an Earthquake
Epicenter
Fault
Focus
Seismic Waves

4. Parts of an Earthquake Fault – the break in the Earth’s curst.
Focus – the point beneath the Earth’s surface where the rocks break and move.
Point of origin of an earthquake.
Epicenter – point directly above the focus on Earth’s surface.
Has the most violent shaking
Earthquake waves reach this location first.
Seismic Waves – vibrations created by the earthquake.

5. Seismic Waves There are three main types of seismic waves:
Primary Waves (P Waves)
“Push-Pull waves” or compression waves
they move only back and forth.
The fastest of the wave types
arrive at a given point first
Travel at 6.4km/sec
Travel through solids, liquids and gases

6. Seismic Waves Secondary Waves (S Waves)
Arrive at a given point second, after P Waves.
Travel at 3.2 km/sec
Travel through solids ONLY!
Cause rock particles to move from side to side and up and down.

7. Seismic Waves Surface Waves (L Waves) Arrive last
Cause the most damage for
they bend and twist Earth’s surface.

8. Detecting Earthquakes
To record and measure the vibration of seismic waves, geologists use an instrument called a seismograph.
The higher the peak on the seismogram the stronger the earthquake.
The shorter the peak on the seismogram the weaker the earthquake.
The time difference between the arrival of the P-wave and S-wave = S-P Interval.

9. Reading a Seismograph 9 min 19 min S-P Interval: 19 – 9 = 10 min (min)
9 min
19 min
S-P Interval: 19 – 9 = 10 min
(min)

10. Reading a Seismograph 9 min 19 min 19 – 9 = 10 min
How long did it take for the P Wave to arrive at the station?
How long did it take for the S Wave to arrive at the station?
What is the S-P Interval for this earthquake?
9 min
19 min
19 – 9 = 10 min

11. Measuring Earthquakes
The Moment Magnitude Scale - System used to rate the total energy released by an earthquake.
Rating criteria:
How strong the seismic waves were
How much movement occurred along the fault
The strength of the rocks that broke when the fault slipped

12. The Moment Magnitude Scale
2011 Earthquake off Japan
Haitian Earthquake of 2010

13. Locating the Epicenter
When an earthquake occurs, seismologists attempt to figure out where the exact point of the earthquake was located, epicenter.
To locate the epicenter of an earthquake, geologists use seismogram data at least three different seismograph stations.
P waves arrive first, followed by S Waves.
The closer the S-P Intervals the closer the seismograph station is to the epicenter.
The larger the S-P Interval, the farther the seismograph station is to the epicenter..

14. Locating the Epicenter
2.5 min
How long did it take the P wave to reach Station B?
How long did it take the S wave to reach Station B?
What is the S-P interval for Station B?
How far did the P wave travel before it reached Station C?
The closer to the epicenter a seismograph station is located, what happens to the S-P interval?
6 min
6 – 2.5 = 3.5 min
2000 km
It gets shorter, smaller

15. Locating the Epicenter
. B
Epicenter
. C
5cm = 1000km 10

16. Earthquake Damage
Other than just the shaking, twisting and breaking of the land earthquakes have other factors that cause damage as well:
Liquefaction
Aftershocks
Tsunamis

17. Liquefaction and Aftershocks
Liquefaction: When the Earth’s violent shaking suddenly turns loose, soft soil into liquid mud.
Occurs where soil is full of moisture.
Can trigger landslides.
Aftershocks: A smaller earthquake that occurs after a larger earthquake in the same area.
Can occur hours, days or even months later.

18. Tsunami
An earthquake occurring in the ocean floor causes the ocean floor to rise and push the water away from it, tsunami.
As the wave hit the coastline the water is then pushed up creating a mountain of water.